Dynamics Simulation of Permanent Magnet Wind Turbine Generator Based on MATLAB

Dynamics Simulation of Permanent Magnet Wind Turbine Generator Based on MATLAB

Abstract As the world’s fastest growing renewable energy source, wind energy has drawn worldwide attention. With the increase of wind turbine, it is becoming more and more important to do research on dynamic response of PMSG. This paper is under the project background of ‘3.2 MW PMSG system analyze”, and it aims at studying dynamic response of PMSG and its system in normal and special operation mode. It analyzes the effect of converter system and control strategy on generator and gives advice for optimization design of PMSG. Firstly, this paper analyzes variable speed and variable pitch control strategy on the foundation of discussing basic theory of permanent magnet turbine generator. Then it builds simulation model of permanent magnet wind turbine generator on MatLab/Simulink and analyzes performance of generator under maximum power tracking and variable pitch control. Secondly, generator-side and grid-side converter of double PWM converter system and its control strategy has been discussed. Model of generator-side controller with double PI regulator based on speed outer-loop and current inner-loop control has been built. Model of grid-side controller based on grid voltage-oriented control with voltage outer-loop and current inner-loop has also been built by MatLab/Simulink. Finally, simulation of dynamic response of PMSG during three phase short circuit and voltage dip of grid with different control, and three phase short circuit of generator terminal have been done. The result indicates: current change of grid converter and voltage change of direct current bus have an important influence on dynamic response of PMSG system. Dynamic response of PMSG system can be improved by maintaining inverter current and direct current bus voltage steady. Given generator design parameter satisfy the requirements of short circuit current. Impact of grid fault on generator can be reduced by using converter system. Key Words: Permanent Magnet Wind Turbine Generator; Special operation mode; MatLab; Dynamic simulation

1. Introduction 1.1. Background and significance With the rapid development of the global economy, human demand for energy is increasing at the same time, with the increase of human activities plays deteriorating natural environment. How to achieve sustainable development of energy, thus ensuring sustainable economic and social Sustainable development, the world has become a national issue that must be addressed. Based on consideration of conventional energy depletion and environmental protection projects former world countries have to develop new energy and renewable energy as the direction of future energy development [1]. Wind energy as a clean, renewable energy, from the mid-1970s began to receive attention of the world, wind power as a major form of wind energy use, other than as a result of renewable

energy sources (excluding hydro) use in the economy the more competitive, and therefore developing rapidly. In 1981 worldwide installed capacity of wind power is not more than 15,000 kilowatts, by the end of 1990 to $ 1.96 million kilowatts, to the end of 1998 had reached 9.56 million kilowatts. Currently, wind power in the global energy source consumption has accounted for the proportion of 1.5%, while in 1997, but accounted for a mere 0.1%. 1.1.1. Present situation of wind power development According to related statistics, in 2008 the global wind power capacity increased by 29%, new wind power capacity over 27 million kilowatts, of which the US wind power capacity jumped 50 percent to $ 2,517 million kilowatts, accounting for about 21% of the global total, surpassed Germany to become the first country in the world wind power. The world's total generating capacity of 12,000 kilowatts, the new installed capacity enough power for 2,700 homes. Europe's new wind power installed capacity of 8.877 million kilowatts, compared with the new Natural gas Power capacity 28% higher than coal-fired generating capacity added more than 10 times higher. Asia, China's new wind power installed capacity ranks second in the world, reaching 6.3 million kilowatts, the total wind power capacity of up to 1,220 kilowatts. As more countries are committed to the development and utilization of wind energy, which is expected to grow rapidly worldwide will continue. In order to accelerate the development of new energy industries, the National Energy Board is currently developing the new energy industry revitalization of Regulation Program. Among the many new energy industry sub-sectors, the wind will be the focus of future development. At present, China has emerged a number of large-scale wind farm, which is the single largest capacity on the prairie wind library Zhangbei full well the wind farm, wind power capacity has reached 200MW. There were more than five 100MW regulation Mold wind farm. By the end of 2007, China's installed capacity of wind power generation system has reached approximately 6GW. Figure 1.1 from 1990 to 2008 the development of China's wind power installed capacity. It shows that in recent years, China's wind power installed capacity is developing rapidly. As the share of wind power generation system in the whole power system as well as a growing proportion of large-scale centralized the emergence of wind farms, wind power systems and power relations are increasingly close. Therefore, wind power technology research study has important practical significance.

Fig. 1.1 National installed capacity in 1990-2008

The past two years, in the country to support the development of clean energy policy, China's wind power industry has shown rapid momentum. Authoritative statistics show that in 2007 new wind power capacity 3300 MW, over the past 20 years the cumulative installed capacity, new capacity is 2006 times more than 1340MW of wind power installed capacity reached 5900MW; 2008 new wind power installed capacity of 6300MW, the new volume ranked second in the world, the total installed wind power capacity reach 12210MW, accounted for 10% of total global installed capacity, ranked fourth in the world. Thus, the next few years, wind power equipment machine triumph has become a trend [2]. Just get wind power projects approved by the State, including, Rudong II expansion of wind power concession projects item currently, the total installed capacity of 100,500 kilowatts, the construction of 67 units 1500 kilowatts of wind turbines; Hebei Huadian Guyuan wind farm projects approved. Shanghai's first landfill built in the field of wind power projects in the upcoming year to start Xing built. The total investment of 200 million yuan, the Shanghai Environment Group Co., Ltd. and Shanghai Huadian Electric Power Development Co., Ltd. jointly established Shanghai China and Hong Kong Wind Power Co., Ltd. invested. 1.1.2.

Situation wind turbine research

Wind power generator system in the mechanical energy into electrical energy, is connected to the driving force of the output power pick a tool that not only directly affects the quality and efficiency of the output power, but also affects the nature of the entire wind energy conversion system structure can and apparatus. Therefore, the development and selection of suitable wind power converters, reliable operation, high efficiency, control, and power supply good performance of the generator system is an important part of the work of the wind power. Combining the characteristics of wind power generation system, requiring generators have the following properties: high quality wind energy is converted to frequency, constant voltage alternating current; to achieve high energy conversion efficiency, to reduce the cost per kWh; stable and reliable other power plant jointly run with the power grid, and provide stable power. In recent years, the use of new generators in order to speed constant frequency mode operation, increase the output power of the wind turbine wind power system has become a hot research. Wind Power Generating positive high reliability, low maintenance, less components, low cost, high efficiency, and high integration direction. Currently, the world's electrical energy conversion is upwind from the transition to a constant speed constant frequency VSCF system VSCF system optimization. One point: for maximum energy transfer in a variety of wind speeds, wind turbines prolong life. The constant speed constant frequency system, when the wind speed jumped huge wind passes through the turbine blades to the main shaft, gearbox and generator and other components, in this have a great mechanical stress these components, repeat the above procedure will cause fatigue damage to these components [2]. With advances in wind power technology for VSCF system and directly connected to the generator and wind turbine systems generators will become the mainstream in the development of wind power generator system. To improve the efficiency of wind power generation, to reduce costs, change good power quality, reduce noise, stable and reliable operation, the wind turbine will be toward the following directions: (1) Unit capacity of large-scale wind turbines Large wind turbines can reduce the area, and reduce network cost and unit cost of power, will help improve the wind efficiency, wind turbine technology is toward increasing the unit capacity, improve the conversion efficiency of direction. 1997 to before, the global market share of MW-level unit is less than 10% in 2001 and more than half of 2002 reached 62.1%, 2003 average unit capacity of wind turbines installed worldwide reach 1.2MW; China's wind turbine unit capacity from 600kW gradually Mw level. In addition, the construction of offshore wind farms also require larger unit capacity of the unit. Can foresee megawatt wind turbine offshore wind farm will be especially dominant in the wind power market.

(2) Direct-drive wind turbines Currently most of the wind power systems and wind turbine generators are not directly connected, but connected by transmission gears, this machine mechanical device not only reduces the efficiency of the system, increase the cost of the system, and prone to failure, acute wind power need to solve the bottleneck problem. Direct drive wind turbine can be directly connected to the wind turbine, eliminating the gearbox, reducing energy losses, costs and noise generation, not only increases the stability of the system, improve the efficiency and reliability of the system, reducing the into the wood of the system, and is particularly suitable for VSCF wind power control system, wind power generator system development mainstream. (3) Wind turbines brushless Brushless technology can improve system reliability, maintenance-free, to improve power generation efficiency. (4) Permanent magnet wind turbine technology Use of permanent magnet wind generator can not only improve the efficiency of the generator, and can simultaneously increase the capacity of the motor, reduce the volume, but also one of the development trend of wind power generators. Permanent magnet direct drive wind generator uses permanent magnets instead of ordinary excitation of the generator, eliminating slip ring brushes, multi-level permanent magnet synchronous generator directly coupled to the impeller, replacing the traditional gearbox parts, due to the gearbox is in megawatt wind turbines belong easy overload and premature failure rate higher components, therefore, there is no gearbox direct drive wind turbines, to improve the reliability and availability and reduce unit operation and maintenance costs, with low wind speed high efficiency, low noise, high life expectancy, reduce crew size, lower operation and maintenance cost and many other advantages. There is much room for development in the future development of the wind turbine [4].

1.1.3.

Research Overview three permanent magnet wind turbine systems

Permanent magnet synchronous generator with a simple structure, less without field winding, machining and assembly cost, reliable, efficient rate, etc., can be increased after the use of rare earth permanent magnet excitation flux density, reduce motor size, improve power quality ratio. Applications vast permanent magnet synchronous generator, power, such as aviation, aerospace main generator, large thermal power plants with auxiliary exciter, small power such as automobiles, tractors generators, wind turbines, small hydroelectric, small internal combustion generators and so extensive that enable a variety of permanent magnet synchronous generator. With high-performance permanent magnet material manufacturing processes mention high, high-capacity wind power generation systems also tend to use a permanent magnet synchronous generator. Permanent magnet wind turbine typically used to change speed constant-frequency wind power generation systems, wind turbine rotor drag directly from the wind turbine, so the speed is very low. Due to the out up gearbox, increasing the reliability and longevity of the unit, using a number of high-performance permanent magnets composed of poles unlike electrically excited synchronous motors that require complex, bulky field winding and improve the flux density and power density, at the same power level, reducing the motor size [5]. Direct drive (gearless) wind turbines began 20 years ago, due to technical and cost reasons, such as electrical, the development is slower. The world's first motor is a permanent magnet motor, but it was used in a very low performance permanent magnet materials, and soon to be electrically excited replaced by Magnets. In recent decades, as the aluminum-nickel-cobalt magnets, ferrite magnets, especially rare earth permanent succession ask world, has been greatly improved magnetic properties, and many have switched to another electric field of the permanent magnet motor excitation. Permanent magnet motors only can partial substitution of traditional electric motor excitation, and can achieve electrical excitation is difficult to achieve a highperformance motor. Permanent magnet electric current machine small mW-power level, ranging from

MW-class, was in industrial and agricultural production, aerospace, defense, and everyday life the widely used, a sharp increase in production. Germany, the US, Denmark are developed in the art more leading countries which Siemens has developed (direct drive) gearless synchronous generator installed in the world's largest wind Norway electric field, the maximum efficiency of 98%. Appeared in both gearless, variable speed pitch and other characteristics of the wind turbines on the wind turbine market in 1997, these high capacity, low-cost operation and maintenance of advanced models have E-33, E-48, E-70 and other models, the capacity from 330 kilowatts to 2 MW, manufactured by the German company Enercon, their development began in 1992. In 2000, a Swedish company ABB developed a new type of wind power generator, using a permanent magnet rotor permanent magnet generator, wind turbine and wind turbines turn sub coaxial gearbox no growth between the two, with a reliable technology, economic advantages. In recent years, direct drive wind turbine has also been a rapid development, direct drive wind turbine is in addition to the double-fed induction wind power generation system another major shift system outside the constant frequency generators. Currently, domestic enterprises have begun to enter the field of direct drive wind turbines. Xinjiang Goldwind Company, Limited division introduced the first 1.2MW direct-drive permanent magnet wind turbine, and in the national "863" project funding to complete the development of 1.5MW directdrive permanent magnet wind turbine, in 2007 to enter the market in volume, and the application of 2008 Beijing Guanting wind farm "Green Olympics" project, one of the projects on the early focus of attention. In the 2008 years, the direct-drive permanent magnet wind turbine in our country has made considerable progress, Harbin Electrical Equipment Co., Ltd. developed the 1.5MW direct-drive permanent magnet wind turbine installed in Shijiazhuang, Hebei Zhang North power plant: Dongfang Turbine Co. division also Repower technology digestion and absorption, developed a 1.5MW direct-drive permanent magnet wind turbine; Guangxi Yinhe Avantis Wind Power Co., the production of a 2.5MW direct-drive permanent magnet wind turbine [6]. Wind power generation system cancels growth organizations to adopt direct drive wind turbine generator mode, the advantage is obvious. MW-class wind turbines generally requires the use of three gears growth, the speed of the wind turbine by the dozens shares for every minute to thousands of rpm, the gear transmission not only reduces the wind power conversion efficiency and noise, and require lubrication due to mechanical wear regular maintenance and cleaning, the system tends to become an important source of mechanical failure. Cancel growth machine, using direct-drive wind turbine move the generator reliability is important for improving system efficiency and operation. With the change of fan speed, radio frequencies emitted by the permanent magnet wind turbine is constantly changing. Generator set stator winding through the full-power converter device connected to the grid, through the exchange means changing these frequencies for power change constant voltage and constant frequency alternating current, the input power. And can change according to wind speed rotor speed to maintain grid frequency change, to mention high wind energy utilization, you can achieve a smooth and network. Good adaptability with power fluctuations, net side power control more advantage of flexibility. Permanent magnet direct drive VSCF wind power system structure shown in Figure 1.2.

Fig.1.2 Variable speed constant frequency permanent magnet synchronous generator system

Use direct drive variable speed permanent magnet synchronous generator constitute constant frequency wind power generation system, the use of direct drive wind turbine low speed permanent magnet synchronous generator to produce electricity between the wind turbine and the generator does not need to install the gearbox, to improve the system's efficiency and reliability, but also reduces system maintenance costs and direct costs. Permanent magnet generator and the grid is not directly connected, but the converter is connected to the grid through full power, because between the wind turbines to the grid by full-power converter provides isolation, compared with double-fed wind power generation systems, direct-drive wind power generation system is running in a non-working condition has more ability big advantage, while the direct-drive wind power system also has the flexibility of reactive power control. With the current growing direct-drive wind power generation system market share, expand the permanent magnet wind power system dynamic properties has a certain practical significance. This paper focuses on permanent magnet synchronous generator suddenly shorted, permanent magnet wind power machine and network systems grid voltage drop, short circuit dynamic process simulation study, so as to optimize the design of the motor to provide reference.

1.2. Research Status grid voltage drop With the social development and technological progress, modern production of power quality made increasingly stringent requirements. In many National grid voltage drop has risen to the most important impact of power quality problems safe and stable operation of electrical equipment, because this grid voltage drop has become a hot topic. Connected in electrical power-line voltage source converter for grid disturbances quite sensitive, it is susceptible to the grid voltage disturbances, such as voltage sags, voltage step up the voltage transient in off and so on. Grid voltage drop which accounted for most of the various voltage fault. Therefore, countries in recent years, scholars have begun to electricity analysis and research net voltage drop problems [7]. Conventional wind power generation system, when the grid voltage is reduced to a certain value, the wind turbines will be automatically off the network. The new rules require some power: when the grid fails if the pressure drops, the wind power system needs to stay connected to the grid, only serious fault is permitted off-grid, so wind power system must have a strong low voltage ride through (Lower voltage ride through, LVRT) capability. Direct drive wind power systems and power isolation by the power converter, voltage drop, you can take steps to the side of the power converter, so that the wind turbine and generator to run the basic shadow from power failures ring, resulting in elimination of the fault, the rapid return to normal work, so direct drive wind power system with respect to the doublefed wind power system, has strong fault ride-through capability. To improve the direct-drive wind power system fault ride-through capability, usually by the DC side during plus overvoltage (crowbar) circuit, fault by crowbar absorb excess energy, and through the grid side converter cooperation, maintain the power balance DC side, so direct drive wind power system security and network can continue to run [8]. In order to maintain the security of the power grid, the new rules require power still in the case of wind turbines grid voltage sag and connected to the grid, many grid operators have asked the wind power system voltage sag ride-through capability. Right now the rapid development of wind power countries such as Germany, Denmark and the United States, have recognized this problem, the introduction of wind power the relevant requirements, and short-term grid voltage drop case and made off-grid wind turbine limit [9]. With a permanent magnet wind power generators increasing grid capacity, the grid of parallel operation of permanent magnet wind generators have become increasingly demanding high. Especially during grid faults, from the perspective of power system stability starting grid requires permanent magnet wind turbine do not run off the net. For example: the northern German power company (E.On Netz company) can require wind farms shown in Figure 1.3 within the voltage range (i.e., shaded area) does not run off the network [10]. Herein refers to a voltage the

voltage of the wind farm connection point. And as part of the UK's National Grid electricity Supply company is required when above 200kV transmission line failure when all the parallel operation of power plants or wind farms must remain within 140ms not off-grid operation. Also known Scottish Power Division (Scottish Hydro Electric Company) on the grid failure or power plant off-grid wind farms do not have similar requirements to run [11].

Fig 1.3 The voltage region requirements of wind farm during the grid fault defined by E. On Netz Because of variable speed wind power generation system is usually located in remote places, to go through the long-distance air wired to the grid connection, therefore, are susceptible to line faults. Even if the power system fault distance wind turbine farther, but grid disturbance will cause a short time, a phenomenon known as voltage sags [12]. Usually this condition causes wind turbine to be forced off the network downtime, especially momentary drop in voltage, the AC current flow occurs over a short time. For a grid contains a lot of wind, this situation is not allowed, because it will affect the stability of the grid. In addition unbalanced voltage drop when the DC voltage oscillation occurs, it will affect the normal operation of the wind turbines.

Fig. 1.4 Fault in wind power generation system 1.3. The purpose of this study and the main work The issue with "3.2MW wind turbine permanent magnet systems analysis" for the engineering background to study 3.2MW permanent magnet wind turbines in a variety of normal and abnormal conditions of dynamic performance, provide a reference for the optimal design of the motor. Contents of this paper include the following aspects: (1) According to the basic theory of permanent magnet wind generator build a mathematical model and PMSG wind turbine, according to the change speed pitch control strategy, based

on MatLab/Simulink to establish a variable speed variable pitch wind turbine simulation model to power. Speed characteristics, and analyzed the response performance permanent magnet wind generators. (2) About double PWM flow system on the motor side converter and grid-side converter control method to conduct research base In MatLab/Simulink to build a motor speed based on the outer side of the controller model, current inner dual PI regulator outer loop voltage and voltage-oriented, network-side controller model based on current inner loop control for permanent magnet wind turbine systems provide the basis for dynamic simulation. (3) Based on MatLab/Simulink are established permanent magnet three-phase short circuit and power grid voltage drop under fault wind turbines and grid system simulation model and a permanent magnet wind generator-side three-phase short circuit simulation model; separately for each fault into the network-side converter to take measures limiting applied, DC capacitor voltage does not take measures to limit pressure and the grid-side converter limiting measures are not taken, the DC side capacitor voltage pick take limit permanent magnet wind turbine performance under pressure and its system measures three control modes were simulated; permanent magnet wind motor dynamic performance of normal and abnormal conditions were simulated, analyzed the converter system and method for controlling the motor performance.

2. Permanent magnet wind turbine machine model and pitch control 2.1. Wind turbine model Wind turbine to capture wind energy, the wind vane portion of the air sweeping swept area within the kinetic energy is converted to useful machine mechanical energy, which determines the device's effective power output of the entire wind power generation system. According to the principle of wind energy capture, wind turbine wind swept surface is:

Where

–air density, 1.225 [kg/m3];

R –wind turbine blade radius, [m]; V –wind speed [m/s] Machinery and mechanical torque wind turbine wind speed obtained are constantly change, according to Betz theory, wind turbine wind energy capture is [13]:

Wind turbine output mechanical torque:

Where,

for wind energy utilization coefficient;

is the tip speed ratio; for blade pitch angle. From the above equation, wind energy utilization factor is a function of the tip speed ratio and blade pitch angle , the tip speed ratio into tip line for rotation speed and wind speed ratio:

Where,

is for wind turbine speed, [rad/s].

Maximum power coefficient ideal wind turbine for 0.593, greater the higher the efficiency of the wind turbine. For a given tip speed ratio and blade pitch angle , can be calculated power coefficient :

Where, , With a coefficient value of c1 to c6 respectively: c1 = 0.5176, c2 = 116, c3=0.4, c4=5, c5=21, c6=0.0068. According to the above equation in MatLab/Simulink modeling and simulation to get different and evening curve corresponding to the value as shown below:

Fig 2.1 The mathematical model of rotor power coefficient

Fig 2.2 Curve of wind energy efficiency coefficient corresponding to various and Analysis of the graph can be obtained the following two points: (1) For any of the tip speed ratio , the pitch angle evening for , wind energy utilization factor value the most, along with value increases, value is significantly reduced; (2) On the eve of a fixed value, the presence of only one optimum tip speed ratio opt, maximum corresponding cylinder. Also (2.4) known by the formula, under certain wind speed, the existence and uniqueness - wind speed wheel which corresponds to opt, making the wind maximum utilization, capture the largest wind power. If you can guarantee there is a change in wind speed at any wind speed wheel corresponds making the tip speed ratio is always optimal tip speed ratio opt knock, wind machines are running goblet point, you can get the maximum output power busy, and the maximum output torque .