Kinetic Energy Recovery System

Kinetic Energy Recovery System

CHAPTER 1 INTRODUCTION: Kinetic Energy Recovery Systems (KERS) were used for the motor sport Formula One's 2009 season, and under development for road vehicles. Its being mainly used by Ferrari, renault, BMW and Mc laren. It raises the car's center of gravity, and reduces the amount of ballast that is available to balance the car so that it is more predictable when turning. Physicist Richard Feynman postulated the theory of transferring the vehicles kinetic energy using the method of Flywheel energy storage. The F1 Kinetic Energy Recovery System or KERS was subsequently confirmed for introduction for the 2009 season, specifying a system that can recover, store and reapply 400 kJ of energy per lap to and from the vehicle at a maximum rate of 60 kW. In order to promote technical development, neither the type of system (be it electrical, mechanical, hydraulic, etc), the weight of the system nor the strategy for reapplication of the recovered energy have been defined. However, one suggestion is that the hybrid system should provide a “Push to Pass” boost system providing 60 kW of boost for 6.67 seconds per lap (= 400 kJ) with the obvious impact on overtaking potential. The 400 kJ / 60 kW specification can be viewed as a surprisingly low power and energy recovery requirement given the quantity of energy dissipated by an F1 car under braking. However, when one recognizes that the existing engine remains unchanged, delivering well in excess of 550 kW, then the safety implications of an additional power boost of greater than 60 kW are clear. The 400 kJ / 60 kW specification will remain for the 2010 F1 season and discussions regarding downsizing the engine and running a higher specification KERS of circa 200 kW is under discussion for subsequent seasons. In addition, the system is also being discussed in other areas of motorsport including Le Mans where the ACO are discussing KERS for the 2009 season.

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Kinetic Energy Recovery System

Keywords: Kinetic Energy Recovery System, Flywheel Energy Storage, Kinetic Storage, Flywheel, Reluctance Motor, Electric Generator / Motor, Regenerative /Recuperative Braking.

1.1INTRODUCTION TO REGENERATIVE BRAKING: A regenerative brake is a mechanism that reduces vehicle speed by converting some of its kinetic energy into another useful form of energy - electric current, compressed air. This captured energy is then stored for future use or fed back into a power system for use by other vehicles. For example, An Electrical regenerative brakes in electric railway vehicles feed the generated electricity back into the supply system In battery electric and hybrid electric vehicles, the energy is stored in a battery or bank of twin layer capacitors for later use. Other forms of energy storage which may be used include compressed air and flywheels. Regenerative braking utilizes the fact that an electric motor can also act as a generator. The vehicle's electric traction motor is operated as a generator during braking and its output is supplied to an electrical load [Fig. 1.1].It is the transfer of energy to the load which provides the braking effect.

Fig 1.1 Regenerative braking – kinetic energy stored in a battery

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Kinetic Energy Recovery System Regenerative braking should not be confused with dynamic braking, which dissipates the electrical energy as heat and thus is less energy efficient.

1.2INTRODUCTION TO FLYWHEEL ENERGY STORAGE: Kinetic storages, also known as Flywheel Energy Storages (FES), are used in many technical fields. While using this technical approach, inertial mass is accelerating to a very high rotational speed and maintaining the energy in the system as rotational energy. Then energy is converted back by slowing down the flywheel. Flywheel mass is either mechanically driven by CVT (Continuously Variable Transmission) gear unit [Fig. 1.2] or electrically driven via electric motor / generator unit [Fig.1.3.]

1.2 Mechanically driven composite flywheel

1.3 Electrically driven flywheels

Devices that directly use mechanical energy are being developed, but most FES systems use electricity to accelerate and decelerate the flywheel .In comparison with other conventional ways of storing electricity (batteries and capacitors), electric FES systems combined with innovative concept offer essential advantages. Especially considering full-cycle lifetime, operating temperature range and steady voltage and power level, which is independent of load, temperature and state of charge. Thus FES provides minimally much higher power output and energy efficiency. Dept of mechanical engineering

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Kinetic Energy Recovery System

CHAPTER 2 2.1SYSTEM COMPONENTS: [Fig2.1] refers to KERS components, respectively: Electric Propulsion Motor /Generator, Power Electronics – Inverter, and the Quad Flywheel Storage.

2.1KERS components

2.2 Motor / Generator

2.1.1Electric Propulsion Motor/Generator: Electric Propulsion Motor and Generator in one, also known as a MGU – Motor Generator Unit [Fig.2.2]

2.1.2System Control: System communication is provided via CAN interface (Controller–Area Network).

2.1.3Power Electronics: An inverter is an electrical or electro-mechanical device that reversely converts direct current DC- from flywheel, to alternating current AC - to MGU. The resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.

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Kinetic Energy Recovery System

2.3Liquid cooled Inverter

2.2CONTROL ELECTRONICS:

2.4 Design of bonding pad provides direct connection of control unit, which works similar to ECU - Engine Control Unit.

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Kinetic Energy Recovery System

CHAPTER 3 3.1FLYWHEEL ENERGY STORAGE:

Fig 3.1Flywheel energy storage

Devices employing the concept of kinetic energy storage date back to ancient times. Pottery wheels and spinning wheels are early examples of systems employing kinetic energy storage in a rotating mass. With the advent of modern machinery, flywheels became commonplace as steam engines and internal combustion engines require smoothing of the fluctuating torque that is produced by the reciprocating motion of the pistons of such machines. More recently, flywheel systems were developed as true energy storage devices, which are also known as mechanical or electromechanical batteries. A remarkable example of such a system was the sole power source of the ’Gyro bus’ - a city bus that was developed by the Maschinenfabrik Oerlikon in Switzerland in the 1930’s, see Motor Trend (1952). This vehicle contained a rotating flywheel that was connected to an electrical machine. At regular bus stops, power from electrified charging stations was used to accelerate the flywheel, thus converting electrical energy to mechanical energy stored in the flywheel. When traveling between bus stops, the electrical machine gradually decelerated the flywheel and thus converted mechanical energy back to electricity, which was used to power the electrical motor driving the bus. The diskDept of mechanical engineering

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Kinetic Energy Recovery System shaped flywheel rotor was made of steel, had a mass of about 1.5 metric tons and reached a maximum angular velocity of 314 rad/s or 3000 rounds per minute (rpm). In regular operation, deceleration of the flywheel was limited to about half of the maximum disk speed. The amount of energy thus made available allowed the Gyro bus to travel for a distance of up to 6 km in regular traffic. Contemporary flywheel energy storage systems, or FES systems, are frequently found in high-technology applications. Such systems rely on advanced high-strength materials as flywheels usually operate at speeds exceeding 10,000 rpm. Vacuum enclosures and magnetic bearing systems are frequently employed to minimize energy losses due to friction. Only through the use of advanced technology have FES systems become commercially viable for a range of applications, causing FES research and development to be an active and rapidly evolving field.

3.2Flywheel Rotor - Reluctance Motor: Rotor flywheel mass works as reluctance motor in contrast to common mechanical flywheel. [Fig3.2] refers to cross-section through storage subunit as reluctance motor.

Fig 3.2 FES - Reluctance motor

fig 3.3 Hybrid-Bearing

Flywheel energy storage subunit consists of stator, incl. stator windings and channel for coolant backflow. Further we could see flywheel rotor equipped with Hybrid-Bearing [Fig3.3] Hybrid-Bearing is combination of hydrodynamic and ball bearing, works in dependence on RPM. Ball bearing acts during starting acceleration from low speed. Hydrodynamic bearing starts working contactless at high revolutions

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Kinetic Energy Recovery System

CHAPTER 4 KERS TRANSMISSION SYSTEM: To control and fully optimize the flywheel operation, a torque controlled variable drive system is required to transfer energy to and from the flywheel storage medium irrespective of the speeds of the driveline of the flywheel. In addition, the transmission system needs to be robust, lightweight and in a small package. The Torotrak full-toroidal traction drive system satisfies these requirements with the familiar twin cavity Variation design utilizing the previously described “compact lever” roller control system.

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Kinetic Energy Recovery System

CHAPTER 5 BASIC PRINCIPLES: Basic principle of kinetic energy storage is made by rotational energy. While using this technical approach, inertial mass is accelerating to a very high rotational speed and maintaining the energy in the system as rotational energy. Stored energy is proportional to inertia of rotor and is a quadratic function of revolution speed.

5.1REGENERATIVE BRAKING - CHARGE MODE: Car is decelerating during recuperative charge mode.

Fig 5.1 Electric motor works as generator and sending energy to flywheel storage .

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Kinetic Energy Recovery System

5.2BOOST ACCELERATION - DISCHARGE MODE: Car is accelerating during boost discharge mode

Fig 5.2The Flywheel rotor is decelerated during boost discharge mode and the energy is converted back

Fig 5.3 Flywheel acts as a generator and sending energy back to electric motor, which works as propulsion motor.

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Kinetic Energy Recovery System

CHAPTER 6 KERS BY MEANS OF FES ARE CURRENTLY UNDER DEVELOPMENT BOTH FOR F1 MOTOR SPORT AND ROAD HYBRID VEHICLES. KERS by means of FES are currently under development both for F1 motor sport and road hybrid vehicles. F1 Teams have said they must respond in a responsible way to the world's environmental challenges. The FIA allowed the use of 60 kW KERS in the regulations for the 2009 Formula One season. Energy can either be stored as mechanical energy, as in a flywheel [Fig6.1], or can be stored as electrical energy, as in a battery or super capacitor.

6.1Williams Hybrid Power F1 KERS

6.2Kinetic storage for hybrid car

Same technology can be applied to road hybrid cars to improve fuel efficiency, especially in city traffic. [Fig6.2].Road vehicles with electric or hybrid drive utilizing regenerative braking. Vision for stock car is in convenient hybrid system with high energetic efficiency and dynamics. Flywheel storage technology provides boost acceleration and braking force. FES supports starting and guarantees light, silent and emission free starts of combustion engine. KERS also supplies all electric appliances, stabilizes on-board power supply and offers stable air-condition.

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Kinetic Energy Recovery System

6.1ROAD CAR APPLICATIONS: The some benefits of the mechanical hybrid system over the electric hybrid system as identified in the Formula 1 application apply to road car applications namely 

efficiency



package



cost and



lack of performance degradation

Starting with efficiency, to store recovered energy a battery based electric hybrid system converts mechanical energy into electrical energy, may undertake a DC to AC conversion and then converts the electrical energy to chemical energy in a battery. To reapply the energy to the driveline, the above energy conversions are repeated. The result is a circa 31% to 34% round trip efficiency. The mechanical hybrid system stores the energy mechanically in a rotating flywheel so eliminating the various energy conversions and providing a far more efficient system with measured overall round trip efficiencies of >70% measured – twice as efficient as an electric system. The further advantage of eliminating the various energy conversions, together with the high energy density of the flywheel energy storage medium and the full toroidal variable drive system, is a significant reduction in the system packaging requirements. Overall, the mechanical hybrid provides twice the efficiency of an electric hybrid with half the weight, half the volume and an estimated quarter of the system costs. Regarding energy efficiency and fuel economy, starting with the F1 specification of 400kJ at a rate of 60kW, even allowing for a zero initial “state of charge” of the flywheel (due to the current requirements to “soak” the vehicle for 24 hours before testing), the mechanical hybrid system provides a significant energy saving over a range of test cycles with over 30% reduction in energy usage from the engine resulting in certain applications. Open items for determining the fuel economy benefit for a specific application include the “state of charge”, the required energy storage, power rating and flywheel drag and efficiency, etc.

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Kinetic Energy Recovery System

CHAPTER 7 ADVANTAGES AND DISADVANTAGES OF FES SYSTEMS:  Most commonly cited are the superior power and excellent energy capacity per system mass of FES units.  Compared to lead-acid battery systems, higher energy stored can be expected for FES systems  FES systems is offset by their significant longer life, which may exceed that of electrochemical batteries by the same factor.  In this context it is often emphasized that FES units can sustain a practically unlimited number of charge/discharge cycles without reductions in energy storage capacity, whereas for electrochemical batteries the number of charge/discharge cycles is limited due to decreasing battery performance  Modern FES units are 90 to 95% efficient whereas corresponding values for electrochemical batteries are typically much lower, i.e. 60 to 70% for lead-acid batteries.  Other advantages of FES technology are a lesser environmental impact due to the absence of harmful chemicals that are usually part of electrochemical batteries, and  The ability of FES units to operate effectively over a wide temperature range; electrochemical batteries perform effectively only within a relatively narrow temperature band.

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Kinetic Energy Recovery System

CHAPTER 8 FES APPLICATIONS:  FES systems offer superior energy discharge rates which are considerably higher than in comparable electrochemical battery systems.  The installation of clusters of FES units provides for power capacity in the megawattlevel.  More recently, emerging segments in the automotive field, such as highly energy efficient and hybrid vehicles have become another area of applications.

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Kinetic Energy Recovery System

CONCLUSION In comparison with other battery storage technologies, KERS offers, Cycle durability 90% efficiency of flywheel (including power electronics) in both directions during KERS reference duty cycle. Extensive operating temperature range. Steady voltage and power level which is independent of load, temperature and state of charge. High efficiency at whole working speed range. No chemistry included, thus no environmental pollution and great recycling capability.

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Kinetic Energy Recovery System

REFERENCE  H. J. & Sander, M. (1997)- flywheel energy storage plant for power utility applications  D. R. & Chavla, W. D. (2005). Flywheel energy storage: An alternative to batteries  for UPS systems  Genta, G. (1985). Kinetic energy storage: theory and practice of advanced flywheel systems,  Butterworth and Co. Ltd, London.  Theory of machines, Rattan SS Tata McGraw hill publication, new delhi,2nd edition 2006.  http://en.wikipedia.org/wiki/kinetic_energy system

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