University 2 Marks q & A

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

UNIT-I INTRODUCTION PART A 1)When the extraction of coal will not be cost effective? Extraction can only be achieved at greater energy and economic costs. When the energy input needed to power these methods approaches the amount of energy mined, extraction will no longer be energy costeffective (Hall et al. 1986). 2)Which are the major contributor for Global warming? Fossil fuel combustion, especially that based on oil and coal, is the major contributor to increasing carbon dioxide concentration in the atmosphere, thereby contributing to probable global warming. 3)Why Renewable energy is better than Coal burning? concerns about carbon dioxide emissions may discourage widespread dependence on coal use and encourage the development and use of renewable energy technologies. 4)How the life of Fossil fuel resources can be extended? Substantially reducing use of fossil fuels through the efficient use of energy and the adoption of solar energy technologies extends the life of fossil fuel resources and could provide the time needed to develop and improve renewable energy technologies. 5) What is land conflict introduced by renewable energy resources? With approximately 75% of the total US land area exploited for agriculture and forestry, there is relatively little land available for other uses, such as biomass production and solar technologies. Population growth is expected to further exacerbate the demands for land. Therefore, future land conflicts could be intense. 6)What are the drawbacks of renewable energy ? Although renewable energy technologies often cause fewer environmental problems than fossil energy systems, they require large amounts of land and therefore compete with agriculture, forestry, and other essential land-use systems. 7) What are the different renewable energy resources? Renewable energy technologies that have the potential to provide future energy supplies include: biomass systems, hydroelectric systems, hydrogen fuel, wind power, photovoltaic’s, solar thermal systems, and passive and active heating and cooling systems. 8)Why the net yield of Bio-Mass is lower? The net yield is, however, lower because approximately 33 liters of diesel fuel oil per hectare is expended for cutting and collecting wood and for transportation, assuming an 80 kilometer roundtrip between the forest and the plant. 9)When the economic benefits of Bio-Mass can be maximized? The economic benefits of biomass are maximized when biomass can be used close to where it is harvested. 10)What are the drawbacks of bio-mass? Several factors limit reliance on woody biomass. Certainly, culturing fast-growing trees in a plantation system located on prime land might increase yields of woody biomass. However, this practice is unrealistic because prime land is essential for food production. Furthermore, such intensely managed systems require additional fossil fuel inputs for heavy machinery, fertilizers, and pesticides, thereby diminishing the net energy available. In addition, Hall et al. (1986) point out that energy is not the highest priority use of trees. 11) What are the harmful effects of burning bio-mass ? The burning of biomass is environmentally more polluting than gas but less polluting than coal. Biomass combustion releases more than 100 different chemical pollutants into the atmosphere (Alfheim and Ramdahl 1986). Wood smoke is reported to contain pollutants known to cause bronchitis, emphysema, and other illnesses. These pollutants include up to 14 carcinogens, 4 cocarcinogens, 6 toxins that damage cilia, and additional mucus-coagulating agents. 12)What are the raw materials used for the production of Ethanol? A wide variety of starch and sugar crops, food processing wastes, and woody materials (Lynd et al. 1991) have been evaluated as raw materials for ethanol production. In the United States, corn appears to be the most feasible biomass feedstock in terms of availability and technology. 13) What are the drawbacks of ethanol production? Any benefits from ethanol production, including the corn by-products, are negated by the St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

environmental pollution costs incurred from ethanol production (Pimentel 1991). Intensive corn production in the United States causes serious soil erosion and also requires the further draw-down of groundwater resources. Another environmental problem is caused by the large quantity of stillage or effluent produced. During the fermentation process approximately 13 liters of sewage effluent is produced and placed in the sewage system for each liter of ethanol produced. 14) What are the raw materials used for the production of Methanol? Methanol is another potential fuel for internal combustion engines (Kohl 1990). Various raw materials can be used for methanol production, including natural gas, coal, wood, and municipal solid wastes. At present, the primary source of methanol is natural gas. 15) What are the limitations of using bio-mass for ethanol production? The major limitation in using biomass for methanol production is the enormous quantities needed for a plant with suitable economies of scale. A suitably large methanol plant would require at least 1250 tons of dry biomass per day for processing (ACTI 1983). More than 150,000 ha of forest would be needed to supply one plant. Biomass generally is not available in such enormous quantities from extensive forests and at acceptable prices (ACTI 1983). 16) What are the problems associated with the storage of Hydrogen? To consider hydrogen as a substitute for gasoline: 9.5 kg of hydrogen produces energy equivalent to that produced by 25 kg of gasoline. Storing 25 kg of gasoline requires a tank with a mass of 17 kg, whereas the storage of 9.5 kg of hydrogen requires 55 kg (Peschka 1987). Part of the reason for this difference is that the volume of hydrogen fuel is about four times greater than that for the same energy content of gasoline. 17) What are the merits of hydrogen fuel? Although the hydrogen storage vessel is large, hydrogen burns 1.33 times more efficiently than gasoline in automobiles (Bockris and Wass 1988). 18) What are the drawbacks associated with the setting up of hydro electric power plants? Reservoirs constructed for hydroelectric plants have the potential to cause major environmental problems. First, the impounded water frequently covers agriculturally productive, alluvial bottomland. This water cover represents a major loss of productive agricultural land. Dams may fail, resulting in loss of life and destruction of property. Further, dams alter the existing plant and animal species in the ecosystem (Flavin 1985). For example, cold water fishes may be replaced by warm water fishes, frequently blocking fish migration (Hall et al. 1986. 19) What are the drawbacks of wind farms to humans? Under certain circumstances shadow flicker has caused irritation, disorientation, and seizures in humans (Steele 1991). future widespread development may be constrained because local people feel that wind farms diminish the aesthetics of the area (Smith 1987a). Some communities have even passed legislation to prevent wind turbines from being installed in residential areas (Village of Cayuga Heights, New York, Ordinance 1989). 20) What are the environmental concerns of photo voltaic system? The major environmental problem associated with photovoltaic systems is the use of toxic chemicals such as cadmium sulfide and gallium arsenide, in their manufacture (Holdren et al. 1980). Because these chemicals are highly toxic and persist in the environment for centuries, disposal of inoperative cells could become a major environmental problem. 21) What are the types of fuel cell? Solid oxide fuel cell,Alkaline fuel cell,Molten-carbonate fuel cell,Phosporic acid fuel cell,Direct Methanol fuel cells, Polymer exchange membrane fuel cells 22) Write about fuel cell and mention its specifications. (Nov/Dec2014) A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Individual fuel cells produce relatively small electrical potentials, about 0.7 volts, so cells are "stacked", or placed in series, to increase the voltage and meet an application's requirements. The energy efficiency of a fuel cell is generally between 40–60%, or up to 85% efficient in cogeneration if waste heat is captured for use. 23) Mention about NOCT & STC of a solar cell. (Nov/Dec2014) Standard Test Conditions (STC). This means they put the solar panels in a flash tester in their factory that has been calibrated to deliver the equivalent of 1000 watts per square meter of sunlight intensity, hold a cell temperature of 25'C (77'F), and assume an airmass of 1.5. This flash test gives them their STC ratings. St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

Normal Operating Cell Temperature (NOCT) - to calculate real available wattage on an average day and assumes the following: 800 watts per square meter of Sunlight Irradiance, an average of 20'C (68'F) Air Temperature, an average wind velocity of 1 meter per second (2.24 miles per hour), with the back side of the solar panel open to that breeze (as opposed to being on a roof where heats builds up under the panels). 24) How the tidal power is converted into electrical power? Power is generated by means of a generator capable of running in both directions achieved by tides coming in and out thereby giving power for the turbines to rotate thereby electricity is generated. 25) What are the types of solar cell? (i) Using Silicon semi conductor (ii) Using compound semi conductor 26) How Aluminum energy used in fuel cells? Composed of aluminum anode set in aqueous alkaline solution utilizes gas diffusion electrode/cathode. Oxidation of aluminum by oxygen from atmosphere provides an efficient power supply. 27) List the applications of fuel cells( MAY/JUNE 2015) i. ii. iii. iv.

fuel cells are also proposed as a power source for propulsion of electric vehicles. It can be used to power portable electronic devices ex. Mobile phones and other low power applications, for military communication devices also. It can be used as a moble power source in vehicles such as submarines and spacecrafts. It can be used for load leveling. During low demand excess energy of EB can be used to produce hydrogen by electrolysis of water. During peak demand the stored hydrogen can be used in fuel cell to produce electrical energy.

28) Mention some organic materials used in bio-mass plant. ( MAY/JUNE 2015) Scrap lumber,forest debris, certain crops manure, and some types of waste residues. Vegetable and fruits wastages, cow dung, goat dung, jatropha. 29) State the impact of wind power penetration in power grid? (NOV / DEC 2015) Induction generator used Wind mill consumes more amount of reactive power. When the power generation by wind mill is lower than minimum required level it has to be isolated from the grid otherwise it will acts motor by taking power from the grid. All wind mill generators using the static converters it causes reduction of grid power factor and introducing the harmonics also. 30) what are the limitations of solar power? (NOV / DEC 2015) Initial Cost: The initial cost of purchasing and installing solar panels always become the first disadvantage when the topic of solar energy comes up. The cost of installing solar panels is bit high. Although subsidy programs, tax initiatives and rebate incentives are given by government to promote the use of solar panels but we are still way behind in making full and efficient use of solar energy. Also, it might take up to 10 years to 15 years before you can break even with your initial investment. Its not about how much payback period is, anything that can reduce our dependence onfossil fuels is worth trying. As new technologies emerge, the cost of solar panels is likely to decrease and then we can see an increase in the use of solar cells to generate electricity. 2. Location and Availability of Sunlight: The location of solar panels is of major importance for generation of electricity. Houses which are covered by trees and landscapes and surrounded by huge buildings may not be suitable enough for installing a solar energy system. Areas which remains mostly cloudy and foggy will produce electricity but at a reduced rate and may require more panels to generate enough electricity for your home. In countries like UK, where it remains cloudy most of the day, cloudy skies reduce its effectiveness. During winters, solar collectors can not produce more energy than the home is using while during summers solar collectors can produce more energy than the home uses. St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

3. Pollution: Most of the photovoltaic panels are made up of silicon and other toxic metals like mercury, lead and cadmium. Pollution in the environment can also degrade the quality and efficiency of photovoltaic cells. New innovative technologies can overcome the worst of these effects. 4. Inefficiency: Since not all the light from the sun is absorbed by the solar panels therefore most solar panels have a 40% efficiency rate which means 60% of the sunlight gets wasted and is not harnessed. New emerging technologies however have increased the rate of efficiency of solar panels from 40 to 80% and on the downside have increased the cost of solar panels as well. 5. Reliability: Unlike other renewable energy sources which can also be operated during night, solar panels prove to be useless which means you have to depend on the local utility grid to draw power in the night or you can buy solar batteries to store excess power which you can later utilize in the night. Apart from that, storms or hurricanes also reduce your ability to draw power during those days.

PART – B 1)Discuss the environmental aspects of renewable energy resources? 2)Discuss the economic issues of renewable energy systems? 3)Explain how the Bio-mass energy is used as an alternate power and its limitations? 4)Discuss about the different types of liquid fuels how they are comparable with other fuels their advantages and their disadvantages? 5)Explain how the hydrogen can be used as a renewable gaseous and liquid fuel with its advantages and its disadvantages? 6)Explain in detail the environmental impacts of setting up of hydro electric power plant? 7)Explain how the power can be obtained by setting up wind farms and their environmental impacts? 8)Explain how the photo-voltaic system can be set up and how it is advantageous than other systems why? 9)Discuss about solar thermal conversion systems and their environmental impacts? 10)How does environment get affected by the use of the renewable energy? Also discuss the GHG emissions from the various energy sources? 11)What are the types of ocean thermal energy conversion power plants? Discuss in detail Anderson OTEC cycle? 12) (i)Brief about some of the renewable energy sources. (ii). Show how a dc-dc converter can be used as a part of an inverter designed to have a square wave output of 48V with a 12V dc input. The idea is to design the inverter without a transformer. Sketch a block diagram, showing design components to clearly express your design. (Nov/Dec 2014) 13) Two 36 cell PV modules are connected in series. One is shaded and one is fully illuminated, assume ideal IV characteristics for the module (i) If the output of the two series module is shorted, estimate the power dissipated in the shaded module. (ii) If the two modules are equipped with bypass diodes across each 12 series cells, estimate the power dissipated in the shaded module. (Nov/Dec 2014) 14) i) discuss the impacts of renewable energy generation on environment. ( MAY/JUNE 2015) ii) Explain the control strategy used for single stage grid connected PV system. ( MAY/JUNE 2015) 15)Explain the operating principle of any four types of renewable energy sources . ( MAY/JUNE 2015) 16)compare the environmental aspects of renewable and non-renewable energy conversion system. (NOV/DEC 2015) 17. describe the operation and contol strategy of solar power conversion system. (NOV/DEC 2015) St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

UNIT – II ELECTRICAL MACHINES FOR RENEWABLE ENERGY CONVERSION PART A 1) What are wind turbine generators? Most wind turbines in the world use a so-called three phase asynchronous (cage wound) generator, also called an induction generator to generate alternating current. This type of generator is not widely used outside the wind turbine industry, and in small hydropower units. 2)Give reasons for using asynchronous generators for wind turbines? One reason for choosing this type of generator is that it is very reliable, and tends to be comparatively inexpensive. The generator also has some mechanical properties which are useful for wind turbines. 3)When the supply is given the turbine generator will run at synchronous speed? When the current is connected, the machine will start turning like a motor at a speed which is just slightly below the synchronous speed of the rotating magnetic field from the stator. 4) How the rotor rotates in a Induction motor? If we look at the rotor bars from above (in the picture to the right) we have a magnetic field which moves relative to the rotor. This induces a very strong current in the rotor bars which offer very little resistance to the current, since they are short circuited by the end rings. The rotor then develops its own magnetic poles, which in turn become dragged along by the electromagnetic force from the rotating magnetic field in the stator. 5) How the induction motor converts into generator operation? (April/May 2013) But what if we increase speed above 1500 rpm? In that case the rotor moves faster than the rotating magnetic field from the stator, which means that once again the stator induces a strong current in the rotor. The harder you crank the rotor, the more power will be transferred as an electromagnetic force to the stator, and in turn converted to electricity which is fed into the electrical grid. 6)Define generators slip? The speed of the asynchronous generator will vary with the turning force (moment, or torque) applied to it. In practice, the difference between the rotational speed at peak power and at idle is very small, about 1 per cent. This difference in per cent of the synchronous speed is called the generator's slip. 7)Give the reason for using synchronous generator for wind turbine? It is a very useful mechanical property that the generator will increase or decrease its speed slightly if the torque varies. This means that there will be less tear and wear on the gearbox. (Lower peak torque). This is one of the most important reasons for using an asynchronous generator rather than a synchronous generator on a wind turbine which is directly connected to the electrical grid. 8)What is automatic pole adjustment of rotor? (April/May 2013) the cage rotor is that it adapts itself to the number of poles in the stator automatically. The same rotor can therefore be used with a wide variety of pole numbers 9)What is the need of direct current conversion? AC current with a variable frequency cannot be handled by the public electrical grid. We therefore start by rectifying it, i.e. we convert it into direct current, DC. The conversion from variable frequency AC to DC can be done using thyristors or large power transistors. 10) What is the need of fixed frequency AC? We then convert the (fluctuating) direct current to an alternating current (using an inverter) with exactly the same frequency as the public electrical grid. This conversion to AC in the inverter can also be done using either thyristors or transistors. 11)Why filtering is Necessary? The kind of alternating current one gets out of an inverter looks quite ugly at first sight - nothing like the smooth sinusoidal curve we learned about when studying alternating current Instead, we get a series of sudden jumps in the voltage and current. 12)What are the advantages of Indirect Grid connection? The primary advantage is that gusts of wind can be allowed to make the rotor turn faster, thus storing part of the excess energy as rotational energy until the gust is over. The secondary advantage is that with power electronics one may control reactive power (i.e. the phase shifting of current relative to voltage in the AC grid), so as to improve the power quality in the electrical grid. This may be useful, particularly if a turbine is running on a weak electrical grid. 13)What are the disadvantages of indirect grid connection? St. Joseph’s College of Engineering ISO 9001:2008 5

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

The basic disadvantage of indirect grid connection is cost. As we just learned, the turbine will need a rectifier and two inverters, one to control the stator current, and another to generate the output current.. Other disadvantages are the energy lost in the AC-DC-AC conversion process, and the fact that power electronics may introduce harmonic distortion of the alternating current in the electrical grid, thus reducing power quality. 14)What are water cooled generators? Water cooled generators may be built more compactly, which also gives some electrical efficiency advantages, but they require a radiator in the nacelle to get rid of the heat from the liquid cooling system. 15)What is the difference between direct grid and indirect grid? Direct grid connection mean that the generator is connected directly to the (usually 3-phase) alternating current grid. Indirect grid connection means that the current from the turbine passes through a series of electric devices which adjust the current to match that of the grid. With an asynchronous generator this occurs automatically. 16)Why , permanent magnet synchronous generators are not used very much? One reason is that permanent magnets tend to become demagnetised by working in the powerful magnetic fields inside a generator. Another reason is that powerful magnets (made of rare earth metals, e.g. Neodynium) are quite expensive, even if prices have dropped lately. 17) What is the use of gear box? With a gearbox you convert between slowly rotating, high torque power which you get from the wind turbine rotor - and high speed, low torque power, which you use for the generator. 18) What is Danish concept? The easiest principle is to connect a squirrel cage induction machine with a gearbox directly to the grid. This is called the Danish concept. The gearbox is necessary to convert the low rotational speed of the wind rotor to a compatible frequency. 19) What are the disadvantages of fixed rotational speed? The blades are not in the optimal operating point for a wide wind speed range. The electrical power of the generator cannot be regulated quickly because the only possibility to influence is the pitchangle of the blades. Wind gusts and the back pressure of the tower result directly in power fluctuations. 20) What are the advantages of adjustable speed wind generator ? Mechanical stress of all parts of the turbine can be reduced because wind gusts can be absorbed by the inertia of the turbine._ Power fluctuations in the grid are reduced because the impacts of the wind are buffered in mechanical energy and are not passed onto the grid. Even the back pressure of the tower can be compensated .The system efficiency is improved by the adaption of the rotational speed as a function of the wind speed. The maximum output power can be achieved over a wide wind speed range. 21) What are the disadvantages of variable rotational speed? Output cannot be controlled 22) How the wind power control can be classified? The control of a wind power generator can be divided into two main parts, the machine control and the system control. The system control is for example responsible to align the nacelle into the wind. The machine control depends on the type of machine. 23) Name the switches used for fast disconnection from the grid? Ac switches based on back to back scr,gto. 24) How the turbine is rotated at variable speed? (Nov/Dec 2013) Most wind turbines run at almost constant speed with direct grid connection. With indirect grid connection, however, the wind turbine generator runs in its own, separate mini AC-grid, as illustrated in the graphic. This grid is controlled electronically (using an inverter), so that the frequency of the alternating current in the stator of the generator may be varied. In this way it is possible to run the turbine at variable rotational speed. 25) What is the need to conversion in DC? AC current with a variable frequency cannot be handled by the public electrical grid. We therefore start by rectifying it, i.e. we convert it into direct current, DC. The conversion from variable frequency AC to DC can be done using thyristors or large power transistors. 26) Why permanent magnets generators are not used widely? St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

One reason is that permanent magnets tend to become demagnetized by working in the powerful magnetic fields inside a generator. Another reason is that powerful magnets (made of rare earth metals, e.g. Neodynium) are quite expensive. 27) What are the problems associated with tapping solar energy? (Nov/Dec 2013) Not consistent, high capital investment, requirement of space 28) Enlist the wind turbine used for domestic applications. (Nov/Dec 2014) Horizontal-axis wind turbines (HAWTs) Vertical-axis wind turbines (VAWTs) 29) How to assess the wind energy pattern for a particular location? (Nov/Dec 2014) Meteorological towers equipped with anemometers, wind vanes, and sometimes temperature, pressure, and relative humidity sensors are installed. Data from these towers must be recorded for at least one year to calculate an annually representative wind speed frequency distribution. 30)What is the indirect vector control of a squirrel cage induction generator wind turbine? ( MAY/JUNE 2015) Indirect vector control is very popular in speed and torque control of squirrel cage induction generator wind turbine. In this method the ds – qs direct and quadrature axes are fixed on the stator, but the d r – qr axes, which are fixed on the rotor re moving at speed ω r. synchronousy rotating axes the d e-qe are rotating ahead of the dr-qr axes b the positive slip ange θ sl corresponding to slip frequency ω sl. Since the rotor pole is directed on the de axis and synchronously rotating axes speed. ωe= ωr+ ωsl 31) What is the need of active crowbar in DFIG? ( MAY/JUNE 2015) Wind turbines based on DFIG have the stator windings connected directly to the grid, making the rotor winding susceptible to high currents induced during grid faults. The rotor windings are connected to the grid via a back-to-back converter, which is very sensitive to over-currents. The most common way to avoid high induced currents in the rotor side converter (RSC) is the use of a crowbar system. The crowbar system makes the DFIG behave in the same way as a conventional Squirrel Cage Induction Generator (SCIG) with higher rotor resistance expanding the critical rotor speed during the disconnection of the RSC from the rotor winding. 32) state the significance of induction generator based wind power generatoion. (NOV / DEC 2015) i. Compact size ii. It does not need auxiliary DC power supply as in synchronous generators. iii. Four quadrant operation and many more methods available in speed torque control. iv. Highly rugged and needs less maintenance. 33) Distinguish between SCIG and DFIG? (NOV / DEC 2015) in the wind generation system with SCIG the active power reaches its nominal value faster than in the wind generation systems with DFIG where the active power reaches its nominal value later.

St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

PART B 1) Explain about wind turbine generators? 2) With neat diagram explain about the construction of cage rotor? 3) How the induction motor operate? 4) Explain the induction generator operation? 5) Explain how the generator is connected to grid? 6) What are the advantages of indirect grid connection? 7) What are the disadvantages of indirect grid connection? 8) Discuss about the cooling system adopted for generators? 9) Explain the synchronous generator operation? 10) Explain the operation of DFIG? 11) How does environment get affected by the use of renewable energy? Also discuss the GHG emissions from the various energy sources. 12) Explain machine capacity factor and capacity utilization factor. Explain the principle of operation of double output induction generator system with a neat diagram. 13) Describe the power conditioning schemes used in WECS. (Nov/Dec 2014) 14)i) Explain the working and operation of PMSG with neat diagram. (Nov/Dec 2014) ii) Draw and explain the characteristics of DFIG. 16)Explain the modeling and control of PMSG based variable speed wind turbine( MAY/JUNE 2015) 17) i) using the schematic explain the working of doubly- fed induction generator. ( MAY/JUNE 2015) ii) distinguish between induction generator and synchronous generator. ( MAY/JUNE 2015) 18) Explain the principle and control strategy of solar power conversion system. (NOV/DEC 2015) 19. explain DFIG based wind power generation. Illustrate the independent dq control strategy adopted for dq control. (NOV/DEC 2015)

St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

UNIT III POWER CONVERTERS PART A 1) What is the need for renewable energy systems? The Kyoto agreement on global reduction of greenhouse gas emissions has prompted renewed interest in renewable energy systems worldwide. Many renewable energy technologies today are well developed, reliable, and cost competitive with the conventional fuel generators 2) What are the advantages of renewable energy systems? One of the advantages offered by renewable energy sources is their potential to provide sustainable electricity in areas not served by the conventional power grid. 3)What are the types of inverters? There are two types of inverters: stand-alone and grid-connected. The two types have several similarities, but are different in terms of control. 4)What is the density of power radiated from sun? The density of power radiated from the sun (referred to as the ‘‘solar energy constant’’) at the outer atmosphere is1.373kW=m2. Part of this energy is absorbed and scattered by the earth’s atmosphere. 5)Which is the basic element of PV system? The basic element of a PV system is the solar cell. Solar cells can convert the energy of sunlight directly into electricity. 6)What are the different types of silicon cells? Monocrystalline Si cells Polycrystalline Si cells Amorphous Si cells 7)List the types of pv systems? Stand-alone, Hybrid, Grid connected 8)What are small systems? PV panels are connected to a grid through inverters without battery storage. These systems can be classified as small systems. 9)What are grid interactive inverters? The grid interactive inverters must be synchronized with the grid in terms of voltage and frequency. 10)List out some of the types of batteries? Lead-acid, nickel-cadmium, lithium, zinc bromide, zinc chloride, sodium–sulfur, nickel–hydrogen, redox and vanadium batteries. 11)What are factors are considered in the selection of batteries for PV application? Deep discharge (70–80% depth discharge) Low charging,discharging current,Long-duration charge (slow) and discharge (long duty cycle) Irregular and varying charge,discharge, Low self-discharge, Long lifetime, Less maintenance requirement, High energy storage efficiency,Low cost 12)What are the main factors affecting the battery life? Incomplete charging and prolonged operation at a low state-of-charge (SOC) 13)What are charge controllers?Charge controllers regulate the charge transfer and prevent the battery from being excessively charged and discharged. 14)What are the types of charge controllers? Series charge regulators Shunt charge regulators Dc–dc Converters 15) What are the types of Dc–dc Converter Type Charge Regulators.? Buck (step-down) converter Boost (step-up) converter Buck-boost (step-down=up) converter 16)What are the features of inverter in standalone photo voltaic system? (April/May 2013) Sinusoidal output voltage Voltage and frequency within the allowable limits St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

Cable to handle large variation in input voltage Output voltage regulation High efficiency at light loads. 17)Classify the grid connected systems? Rooftop application of grid-connected PV system Utility-scale large system 18)List out the types of inverters used in grid connected PV applications? Line-commutated inverter Self-commutated inverter PV inverter with high-frequency transformer 19)Based on the switching control classify the voltage source inverters? PWM (pulse width modulated) inverters Square-wave inverters Single-phase inverters with voltage cancellations Programmed harmonic elimination switching Current-controlled modulation. 20)List out the characteristics of grid compatible inverter characteristics? (April/May 2013) Response time,Power factor,Frequency control,Harmonic output,Synchronization,Fault current contribution, Dc current injection Protection 21)What is matrix converter? A cycloconverter or a cycloinverter converts an AC waveform, such as the mains supply, to another AC waveform of a lower frequency. It can synthesize the output waveform from segments of the AC supply without an intermediate directcurrent link. 22)How are the matrix converters classified? Direct matrix converters Indirect or sparse matrix converters 23)What is battery sizing? (Nov/Dec 2013) The battery type recommended for using in solar PV system is deep cycle battery. Deep cycle battery is specifically designed for to be discharged to low energy level and rapid recharged or cycle charged and discharged day after day for years. The battery should be large enough to store sufficient energy to operate the appliances at night and cloudy days. To find out the size of battery, calculate as follows: 24)What is inverter sizing? An inverter is used in the system where AC power output is needed. The input rating of the inverter should never be lower than the total watt of appliances. The inverter must have the same nominal voltage as your battery. For stand-alone systems, the inverter must be large enough to handle the total amount of Watts you will be using at one time. 25)What is solar charge controller sizing? The solar charge controller is typically rated against Amperage and Voltage capacities. Select the solar charge controller to match the voltage of PV array and batteries and then identify which type of solar charge controller is right for your application. Make sure that solar charge controller has enough capacity to handle the current from PV array. 26)What is the role of capacitor in boost converter? It provides the charge and for power factor improvement 27) Mention about SOC and its methods. (Nov/Dec 2014) State of charge (SOC) is the equivalent of a fuel gauge for the battery pack in a battery electric vehicle (BEV), hybrid vehicle (HV), or plug-in hybrid electric vehicle (PHEV). The units of SOC are percentage points (0% = empty; 100% = full). SOC is normally used when discussing the current state of a battery in use. In general there are five methods to determine SOC indirectly.1) chemical 2) voltage 3) current integration 4)Kalman filtering 5)pressure. 28) Specify about power conversion ratio. (Nov/Dec 2014)

St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

Power conversion ratio or Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat. Power conversion ratio = Pout/Pin 29) A battery rating at 0.2 C is 50Ah @ 25 0C what would happen to the battery if it is discharges at the rate of 0.10C under the ambient temperature of 100C? ( MAY/JUNE 2015) 30) Why loop compensation is used in Buck converter? ( MAY/JUNE 2015) The buck converter is a switch mode, DC-DC, power supply. It accepts a source voltage, Vg and produces a lower output voltage, V with high efficiency. An important component of a practical buck converter is control feedback which assures a constant output voltage and attenuates unwanted disturbances. 31) what are the limitations of AC voltage controller? (NOV / DEC 2015) 1. There has to be a load for a voltage controller to function: Since voltage controllers use thyristors for varying voltage, they need some kind of resistive load at the end to function. 2. The overall power is reduced by any inductive component of the resistive load. 3. The load has to be of increasing torque in nature: Voltage controllers can alter the speed of a motor by altering the incoming voltage, but the motor must have an increasing torque load (e.g. Industrial fans, winding machines). Voltage controllers are not suitable for a constant torque application. An example of an increasing torque application would be a wire winding machine: the initial load is almost zero as there is no wire wound at the beginning, with time the wire wound increases, thus increasing the torque (the force needed to turn the winding) proportionally. A voltage controller would be suitable here for increasing or decreasing the speed of the winding machine. 4. The starting torque must be low: The motor attached to the voltage controller is usually never started with high starting torque (or a loaded start); supplying a low voltage to a motor with a high load can heat up the motor and burn its windings (e.g. trying to start a motor which is attached to a stone crusher which is filled with stones) 32) write the various aspects of battery sizing. (NOV / DEC 2015) Materials of electrodes and electrolytes and its specific gravity, working temperature, area of plates determines the battery size. Back up time needed and Ah ( ampere hour capacity) also determines the battery sizing. Maximum load to be connected in the battery also determines the battery sizing. PART B 1) Explain the operation of line commutated converter under inversion mode with the help of neat circuit diagram and necessary waveforms? 2) Explain about grid interactive inverters? 3) Draw the block diagram of the solar PV system and explain the principle of operation in detail? 4) Draw the schematic of Buck-Boost converter and explain the operation in detail? 5) With neat diagram explain the operation of Ac voltage controller and voltage control in PWM inverters? 6) Explain using a power module and relevant sub circuits how a thyristorised three phase converter can operate as inverter? St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

7) Discuss how a buck boost converter can be used to charge a battery? 8) Describe using a diagram the working of a Matrix converter as an inverter. 9) Describe working of Ac-Dc-Ac converter with circuit and waveform for wind energy conversion? 10) Describe principle of operation of PWM inverter and describe how it is used for wind energy conversion? 11) Explain with neat diagram the theory of self excited capacitance used in SEIG. (Nov/Dec 2014) 12) Explain and classify the working of MPPT in a solar PV system. (Nov/Dec 2014) 13) i) draw and explin the equivalent circuit of PV module. ( MAY/JUNE 2015) ii) discuss the application of matrix converter in wind energy conversion system employing synchronous generator. ( MAY/JUNE 2015) 19) The relationship between the output voltage and curret for PV array is defined by the data given in table. The PV array is connected to resistive load RL of 30Ω through a buck boost type second order converter operating in continuous mode. Determine the duty cycle of the interfacing converter required to operate the Pv array at a voltage of 28.08V. ( MAY/JUNE 2015) Vpv (V) Ipv(A)

27.86

27.91

27.97

28.02

28.08

28.13

28.18

28.24

28.29

28.35

1.76

1.73

1.71

1.69

1.67

1.64

1.62

1.59

1.57

1.54

20.draw and explain the converter topologies used for solar power generation. (NOV / DEC 2015) 21. explain about various aspects of grid interactive inverters. (NOV / DEC 2015) . UNIT IV ANALYSIS OF WIND AND PV SYSTEMS PART A 1) What are the factors that contribute to the importance of wind power? High-strength fiber composites for manufacturing large, low-cost blades Variable-speed operation of wind generators to capture maximum energy Advances in power electronics and decreased associated cost Improved plant operation and efficiency. 2) What are the types of wind turbines. Horizontal-axis wind turbines (HAWTs) Vertical-axis wind turbines (VAWTs) 2) What are the types of wind generators? Dc generators Synchronous generators or permanent-magnet synchronous generators Asynchronous generators 3) How are wind power systems classified? Stand alone, Hybrid and grid connected 4) What is the purpose of standalone wind energy systems? Battery charging , House hold power supply 5) What are the basic elements of wind energy systems? Wind generator, Tower, Charge control system, Battery storage, Distribution network 6) What are the drawbacks of diesel systems without batteries? Diesel systems without batteries in a remote area are characterized by poor efficiency and high maintenance and fuel costs. The diesel generators must be operated above a certain minimum load level to reduce cylinder wear and tear due to incomplete combustion. 7) What are the limitations in wind research process? High wind penetration also poses significant technical problems for the system designer in terms of control and transient stability With the continual research in this area, there is now software available to assist in this process. 8) What are the major problems related to grid interconnection? Remote-area power supplies are characterized by low inertia, low damping, and poor reactive power support. Such weak power systems are more susceptible to sudden changes in network operating conditions . In this weak-grid situation, the significant power fluctuations in the grid would lead to St. Joseph’s College of Engineering ISO 9001:2008 12

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

reduced quality of supply to users. This may manifest itself as voltage and frequency variations or spikes in the power supply. 9) What are the advantages of adding an inverter? The addition of inverter control would further reduce the fluctuations and increase the total output power. Thus the total output of the wind energy system can be stabilized or smoothed to track the average wind speed. 10) What is the purpose of system controller? The system controller should track the peak power to keep the output of the wind energy system constant. It should monitor the stator output and adjust the inverter to smooth the total output. The amount of smoothing would depend on the state of charge of the battery. 11)What is the function of Dc-Dc Converter? The function of the dc–dc converter will be to adjust the torque on the machine and hence ensure by measurement of wind speed and shaft speed that the turbine blades are operating so as to extract optimum power. 12) What is the purpose of using soft starters? When an induction generator is connected to a load, a large inrush current flows. This is something similar to the direct on-line starting problem of induction machines . It has been observed that the initial time constants of an induction machine are higher when it tries to stabilize initially at the normal operating conditions. There is a need to use some type of soft-starting equipment to start the large induction generators. 13) What is soft starting? Two thyristors are connected in each phase, back to back.Initially, when the induction generator is connected, the thyristors are used to control the voltage applied to the stator and to limit the large inrush current. As soon as the generator is fully connected, the bypass switch is used to bypass the soft-starter unit. 14) What is a cyclo converter? A cycloconverter is a converter that converts ac voltage of one frequency to another frequency without an intermediate dc link. 15) What are the possible methods of accessing the rotor in wound round motor? The possible methods of accessing the rotor can have the following configurations: Slip power recovery, Use of cycloconverter, Rotor resistance chopper control . 16) What is slip power recovery scheme? The slip power recovery configuration behaves similarly to a conventional induction generator with very large slip, but in addition energy is recovered from the rotor. 17) What is static Kramers system? The rotor power is first carried out through slip rings, then rectified and passed through a dc link to a linecommutated inverter and into the grid. The rest of the power comes directly from the stator as it normally does. 18) What is the disadvantage of Kramer system? A disadvantage with this system is that it can only allow super synchronous variable-speed operation. 19) How are multiple generators used? This configuration is based on the use of a multiple generator design. In one case, there may simply be two separate generators (as used on many European wind turbines). Another possibility is to have two generators on the same shaft, only one of which is electrically connected at a time. 20) What are dual stator winding two speed induction generators? These machines have two separate stator windings, only one of which is active at a time. Thus, a variety of speed ranges can be obtained depending on the number of poles in each winding. As in the consequent pole machines, only two speeds may be obtained. 21) What is the disadvantage of two speed induction generators? These machines are significantly heavier than single-speed machines and their efficiency is less, since one winding is always unused, which leads to increased losses. These machines are commercially available. Their cost is approximately twice that of single-speed machines. 22) What are the types of control available for variable systems? Mechanical control ,Combination of electrical & mechanical, power electronics control 23) What is tandem induction generator? St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

A tandem induction generator consists of an induction machine fitted with two magnetically independent stators, one fixed in position and the other able to be rotated, and a single squirrel-cage rotor whose bars extend the length of both stators. 24) What is a high slip induction generator? This is the simplest variable speed system, which is accomplished by having a relatively large amount of resistance in the rotor of an induction machine. 25) Write about opti slip concept used in wind energy conversion system. (Nov/Dec 2014) It deals with that, avoiding the problem of introducing slip rings, brushes, external resistors, and maintenance altogether. By mounting the external resistors on the rotor itself, and mounting the electronic control system on the rotor as well, the amount of slip need to the rotor has to be communicated. OptiSpeed feature is the possibility to exploit even more of the energy in the rotor and transfer it to the grid, not forgetting the high quality of the power delivered to the grid. 26) Mention some of the standards used for grid integration. (Nov/Dec 2014) Grid interconnection standards: 1) IEC 61400 series on wind turbines developed by IEC TC 88 2) IEC 60904 series on PV devices developed by IEC TC 82.IEEE 1547.1 3) IEEE 1547.2 Application Guide for IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems (Approved 2008) 4) IEEE 1547.3 Guide For Monitoring, Information Exchange, and Control of Distributed Resources Interconnected with Electric Power Systems (Approved 2007). 27) What is meant by pitch control? ( MAY/JUNE 2015) Pitch control gearboxes serve the essential purpose of setting wind turbine blades at the best angle to the wind to turn the rotor. 28) Define solar insolation. ( MAY/JUNE 2015) Solar insolation is a measure of solar radiationenergy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m2) or kilowatt-hours per square meter per day. 29) what are the limitations of fixed speed induction generator based wind power conversion. (NOV / DEC 2015) The reactive power and, therefore, the grid voltage level cannot be controlled Owing to its fixed-speed operation, all fluctuations in the wind speed are further transmitted as fluctuations in the mechanical torque and then as fluctuations in the electrical power on the grid. Less efficiency. 30) list few grid connection requirement of renewable power system. (NOV / DEC 2015) i. ii. iii.

Power conditioning equipment Safety equipment Meters and instrumentation.

PART B 1) Explain with diagram the standalone fixed speed and variable speed operation of WECS. State the advantages of fixed speed system over variable speed system. 2) Discuss in detail the grid system characteristics and explain with a neat diagram the standalone and grid integrated solar system. 3) Explain the block diagram of SCIG based wind energy conversion system. 4) Explain the operation of grid integrated PMSG system with a neat block diagram. St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

5) Explain the torque speed characteristics of a wind energy conversion system and there from reason out as how energy extraction can be maximized. 6) Develop a control scheme for regulating the speed of a wind energy conversion system. 7) Explain the process of power generation using a photo voltaic system. 8) Discuss how a photovoltaic system is integrated with the utility grid. 9) Develop a mechanism that facilitates a wind energy conversion system to limit the turbine output at above the rated wind system and illustrate its implementation using a schematic. 10) Explain with a block diagram the theory of operation of a grid integrated SCIG based wind energy conversion system and discuss its relative merits and demerits 11) Design Solar PV pump and clearly explain the accessories required. Also justify the importance of implementing MPT for the pump system. (Nov/Dec 2014) 12) Explain the grid related problems in wind farms and refer the performance improvements of generator controls. (Nov/Dec 2014) 13) i) Derive an xpression for power extracted from the wind 20)ii) explain rixed speed grid connected wind energy conversion system with a squirrel cage induction generator. ( MAY/JUNE 2015) 14) The Cp- λ characteristic of a fixed-pitch wind turbine is given by Cp = Cp , opt λ / λopt (2 – λ / λopt) in the normal working region. The wind turbine drives a grid connected squirrel cage IM which has a full-load slip of 5% and breakdown slip of 10%. If the breakdown torque of the machine is 1.5 times the full-load torque, find i) Furling speed of the turbine as a percentage of the rated wind speed ii) The electrical power output of the machine at the furling wind speed in terms of the rated output power. Assume that the gear ratio between the turbine and the machine is chosen such that the machine operates at the rated slip and rated wind velocity with λ = λopt. neglect all mechanical and electrical losses in the machine stator. (MAY / JUNE 2015) 15 describe about stand alone operation of wind energy conversion systems. (NOV / DEC 2015) 16. explain about grid integrated PMSG based WECS(NOV / DEC 2015) UNIT V HYBRID RENEWABLE ENERGY SYSTEMS PART A 1) What is Photovoltaic–diesel hybrid energy systems Photovoltaic–diesel hybrid energy systems generate ac electricity by combining a photovoltaic array with an inverter, which can operate alternately or in parallel with a conventional engine-driven generator. 2) Write some of the hybrid systems used in industry. (Nov/Dec2014) Series hybrid energy systems, Switched hybrid energy systems, Parallel hybrid energy systems. 3) What are series hybrid systems? Ac power delivered to the load is converted from dc to regulated ac by an inverter or a motor generator unit. The power generated by the diesel generator is first rectified and subsequently converted back to ac before being supplied to the load, which leads to significant conversion losses. 4) What are the factors to ensure reliable operation of series hybrid energy systems? Both the diesel generator and the inverter have to be sized to meet peak loads. This results in a typical system operation where a large fraction of the generated energy is passed through the battery bank, resulting in increased cycling of the battery bank and reduced system efficiency. 5) What are the benefits of series hybrid systems? The engine-driven generator can be sized to be optimally loaded while supplying the load and charging the battery bank, until a battery state-of-charge (SOC) of 70–80% is reached. No switching of ac power between the different energy sources is required, which simplifies the electrical output interface. 6) What is the need for sizing the inverter? The inverter cannot operate in parallel with the engine driven generator; therefore, the inverter must be sized to supply the peak load of the system. 7) What is the impact of inverter failure? St. Joseph’s College of Engineering ISO 9001:2008 15

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

Inverter failure results in complete loss of power to the load, unless the load can be supplied directly from the diesel generator for emergency purposes. 8) What is the impact of battery cycling? The battery bank is cycled frequently, which shortens its lifetime. The cycling profile requires a large battery bank to limit the depth-of-discharge. 9) Why the overall system efficiency is low in series configuration? The overall system efficiency is low, since the diesel cannot supply power directly to the load. 10) What is switched configuration? It allows operation with either the engine driven generator or the inverter as the ac source, yet no parallel operation of the main generation sources is possible. 11)What is the advantage of switched configuration compared to series configuration? The main advantage compared with the series system is that the load can be supplied directly by the engine-driven generator, which results in a higher overall conversion efficiency. 12) What are the advantage of switched configuration? The inverter can generate a sine-wave, modified square wave, or square wave, depending on the particular application. The diesel generator can supply the load directly, therefore improving the system efficiency and reducing the fuel consumption. 13) What are the disadvantages of switched configuration? Power to the load is interrupted momentarily when the ac power sources are transferred. The engine-driven alternator and inverter are typically designed to supply the peak load, which reduces their efficiency at part-load operation. 14) What are parallel configuration hybrid systems? The parallel configuration allows all energy sources to supply the load separately at low or medium load demand, as well as supplying peak loads from combined sources by synchronizing the inverter with the alternator output waveform. 15) What is bi-directional inverter? The bidirectional inverter can charge the battery bank (rectifier operation) when excess energy is available from the engine-driven generator, as well as act as a dc–ac converter (inverter operation). 16) What is use of bi-directional inverter? The bidirectional inverter may provide ‘‘peak sharing’’ as part of the control strategy when the enginedriven generator is overloaded. 17) What is doubling of the system capacity? The inverter plus the diesel generator capacity rather than their individual component ratings limit the maximum load that can be supplied. Typically, this will lead to a doubling of the system capacity. 18) What is the purpose of synchronizing the inverter with diesel generator? The capability to synchronize the inverter with the diesel generator allows greater flexibility to optimize the operation of the system. 19) What are the advantages of parallel hybrid systems? The system load can be met in an optimal way. Diesel generator efficiency can be maximized. Diesel generator maintenance can be minimized. A reduction in the rated capacities of the diesel generator, battery bank, inverter, and renewable resources is feasible, while also meeting the peak loads. 20) What are the disadvantages of parallel hybrid systems? Automatic control is essential for the reliable operation of the system. The inverter has to be a true sine-wave inverter with the ability to synchronize with a secondary ac source. System operation is less transparent to the untrained user of the system. 21) What is the need for wind diesel systems? Diesel systems without batteries in a remote area are characterized by poor efficiency and high maintenance and fuel costs. The diesel generators must be operated above a certain minimum load level to reduce cylinder wear and tear due to incomplete combustion. It is a common practice to install dump loads to dissipate extra energy. More efficient systems can be devised by combining the diesel generator with a battery inverter subsystem and incorporating renewable energy sources, such as wind or solar where appropriate. St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

22) What is maximum power point locus and MPPT? The points of maximum power form a curve termed as the maximum-power-point locus. A controller that tracks the maximum power point locus of the PV array is termed as a MPPT. 23) What is the need to operate the system in max power point locus? Because of the high cost of PV array, it is necessary to operate the system at its maximum-power-point locus. For overall optimal operation of the system, the load line must match the PV array’s maximumpower-point locus. 24) What are the possibilities to operate PV arrays at the maximum power point? There are two possibilities to operate PV arrays at the maximum power point: Open-loop control, Closed-loop control. 25) What is hill climbing algorithm? It involves in varying the input voltage around the optimal value by giving it a slightly increment or decrement alternately. As the consequences, the output power is then assessed and a small correction is made to both input voltage and input current. This method is called as “hill-climbing algorithm”. 26) Define charge controller used for wind energy conversion system. (Nov/Dec 2014) Charge controllers regulate the charge transfer and prevent the battery from being excessively charged and discharged. 27)List the different types of hybrid system. ( MAY/JUNE 2015) Solar and wind power hybrid, Solar and fuel cell hybrid, Solar with conventional power plants such as thermal, hydro, DG sets etc. Hybrid energysystems generate AC electricity by combining RES such as PV array with an inverter which can operate alternatively or in parallel with a conventional engine driven generator. Different classifications are Series hybrid energy systems, Switched hybrid energy systems, Parallel hybrid energy systems. 28) How is electrical maximum power tracking different from a mechancical power tracking? ( MAY/JUNE 2015) The open ciruit voltage of PV panel is depends on solar insolation. While maximum loading the PV panel terminal voltage becomes zero due to short circuit mode. A buck converter duty cycle is adjusted using PAO (perturb and observation and ICT (incremental conductance technique) based on available solar insolation. It is used to trap the time based maximum power available in solar panel by operating it in between open circuit mode and short circuit mode. 29) state the need for hybrid renewable energy systems? (NOV / DEC 2015) i. ii. iii. iv.

Wonderful standalone systems for remote areas. Reiliability can be increased due to hybridization. Overall Per unit Energy cost can be reduced Effectiveness and other performance parameters improved.

30) what are the significances of MPPT? (NOV / DEC 2015) It operates the solar panel between open circuit mode and short circuit mode. Hence maximum power is traped from the solar panel. In mechanical type MPPT solar panel is tilted using a motor, based on sun direction to get the maximum power. PART B 1) Is wind energy an excellent supplement to the PV? If so justify with a suitable case study. 2) What is MPPT? Discuss the types of MPPT with its merits and demerits? Explain the incremental – conductance algorithm with a neat example. 3) Explain the need of Hybrid systems for renewable energy power generation? St. Joseph’s College of Engineering

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ISO 9001:2008

PX7301 Power Electronics for Renewable Energy Systems

Dept OF EEE

2015-2016

4) Explain the method to integrate hybrid solar PV and wind energy conversion system to the grid with neat block diagram. (Nov/Dec 2014) 5) Describe using the diagram the operation of wind assisted gas turbine generating unit? 6) Explain using a schematic the working of an interconnected solar wind system with a storage battery. 7) Explain the operating principle of PV Maximum power point tracking in energy conversion. 8) Explain with case study how to get maximum power generation in wind energy conversion system. 9) Describe with the aid of schematic the working of a wind energy conversion with battery storage and explain how the storage of wind energy permits peak sharing and capacity saving. 10) Develop a scheme for converting and storing wind energy with hydrogen storage and there from explain its salient features using a diagram. 11)Explain with an example how to control the harmonics and improve the power quality when solar pv is connected to the grid. (Nov/Dec 2014) 12) Design a hybrid PV system which should be able to supply the power to the load of your college for 24 hours. It should be using solar, diesel and wind as the source of energy. Explain with neat block diagram. ( MAY/JUNE 2015) 13) What are the commonly used algorithms for MPPT? Explain PAO MPPT algorithm with a neat flow chart. ( MAY/JUNE 2015) 14) . explain the design aspects of hybrid renewable energy systems. (NOV / DEC 2015) 15) . explain MPPT for solar power generation system. (NOV / DEC 2015)

St. Joseph’s College of Engineering

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ISO 9001:2008