University of Jordan Faculty of Engineering and Technology Electrical Engineering Department Electric Drive EE 582 Project Supervisor: Prof. Mohammad Zeki Khedher By: Mostafa Walid Ali Alzahlan 0110486 Thabet Bassam Alalami 0095612 By: Mostafa W. Alzahlan Braking Systems 1 • Super capacitor regenerative braking system. • Regenerative braking systems in locomotives. • Regenerative braking systems in cars. • Regenerative braking systems in scooters. • KERS is used in F1 cars. • Electric motor braking. By: Mostafa W. Alzahlan Applications of regenerative braking 2 Super capacitor accept and release charge more quickly and can be discharged and recharged many times and with have longer life time than a battery. For example in MAZDA car the unit can accept a full charge in just 8-10 seconds. The capacitor may take up to about 113s for discharging when the load is at minimum at about 18A. By: Mostafa W. Alzahlan Super capacitor regenerative braking system 3 By: Mostafa W. Alzahlan Regenerative Braking with super capacitor unit in MAZDA A-6 4 Regenerative braking systems in locomotives By: Mostafa W. Alzahlan For example Jaipur Metro uses the Regenerative Braking System & saves 35% of Electricity. 5 Regenerative braking systems in cars Toyota Prius Honda Insight Ford Escape Hybrid Tesla Roadster Chevy Volt By: Mostafa W. Alzahlan For example the following cars contain regenerative braking systems 6 By: Mostafa W. Alzahlan 7 Circuit diagram of regenerative braking system in hybrid car Increase of overall energy efficiency of a vehicle. Improved Performance. Emission Reduction. Reduction in Engine Wear. Cuts down on pollution related to electricity generation. • Increases the lifespan of friction braking systems. • Smaller Accessories. • Less use of traditional mechanical brakes leads to less wear over time. • • • • • By: Mostafa W. Alzahlan Advantages of regenerative braking system 8 Added Weight-Extra components can increase weight. Complexity-depends on control necessary for operation of regenerative braking system. Cost of components, engineering, manufacturing and installation is high. Friction brakes are still necessary. Safety-Primary concern with any energy storage unit of high energy density. Added maintenance requirements dependent on the complexity of design. By: Mostafa W. Alzahlan Disadvantages of regenerative braking system 9 By: Mostafa W. Alzahlan Dynamic (Rheostatic) Braking system 10 • The energies involved in stopping high speed trains are so great that disc brakes alone are unsuitable because of their very high wear rates and consequent maintenance costs. Whenever possible, regenerative braking is used. In this case the drive motors convert the kinetic energy of the train into electricity, which is fed back into the power supply and used elsewhere on the network. Alternatively the same regenerated electricity may be dissipated as heat in on-board or trackside resistive (or rheostatic) brakes. • This is an effective and easy to control braking method. Rheostatic brakes are non-wearing and unlike regenerative braking systems are totally independent of the external network conditions. By: Mostafa W. Alzahlan Dynamic (Rheostatic) braking System 11 • The rheostatic (dynamic) braking system use the electric traction motors of a vehicle as generators when slowing. But instead of stored the generated electrical energy its dissipated as heat by a bank of onboard resistors or "braking grid". Large cooling fans are necessary to protect the resistors from damage. Modern systems have thermal monitoring and when the temperature of the bank becomes excessive, it is switched off and the system employs only friction braking. By: Mostafa W. Alzahlan Principle of operation of dynamic braking 12 • Why to use the rheostatic resistor? What are the benefits? • In order to dissipate the excess voltage as a heat. • To minimize the wear and tear of friction braking components. • Enable faster braking. • Eliminate the risk of a runaway due to overheating. By: Mostafa W. Alzahlan Rheostatic (Dynamic) resistor 13 • Braking resistors with smaller ohmic values will help motors stop faster but will also dissipate more heat. This will require the use of more mass in the resistor or a heat sink to keep its temperature within a safe limit. By: Mostafa W. Alzahlan Rheostatic (Dynamic) resistor 14 The two types of crowbar resistor, hard and soft, are both used in traction power supply circuits to deal with the effects of transient or longer lasting over-voltage conditions. The soft crowbar is pulsed to dissipate transient overvoltages; if these persist or worsen then the main breakers are opened and the system is short-circuited through the hard crowbar to absorb the stored energy By: Mostafa W. Alzahlan Crow bar (Rheostatic) resistors 15 Dynamic Braking Resistor Crow bar resistors By: Mostafa W. Alzahlan Dynamic Braking Resistor inside a NEMA 1 enclosure 16 • Rheostatic Braking (Hitachi train). • Rheostatic Brake (Comeng train). • DC motor braking using rheostatic braking. • Dynamic (Rheostatic) braking of induction motor. By: Mostafa W. Alzahlan Applications of dynamic (rheostatic) braking system 17 By: Mostafa W. Alzahlan Rheostatic Braking (Hitachi train) 18 Simple wiring diagram for traction motor By: Mostafa W. Alzahlan Traction motor under rheostatic braking mode. (Hitachi train) 19 By: Mostafa W. Alzahlan Rheostatic Brake (Comeng train) 20 Direct-current motors are extensively used in variablespeed drives and position-control systems where good dynamic response and steady-state performance are required. For example in application of robotic drives, printers, machine tools, process rolling mills, paper and textile industries, and many others. Control of a dc motor, especially of the separately excited type, is very straightforward, mainly because of the incorporation of the commutator within the motor. The commutator brush allows the motor-developed torque to be proportional to the armature current if the field current is held constant. Classical control theories are then easily applied to the design of the torque and other control loops of a drive system. By: Mostafa W. Alzahlan DC motor braking using rheostatic braking 21 By: Mostafa W. Alzahlan DC motor braking using rheostatic braking Dynamic braking in separately excited DC motor 22 By: Mostafa W. Alzahlan DC motor braking using rheostatic braking Dynamic Braking Speed-Torque characteristics of separately excited DC motor with variable RD 23 By: Mostafa W. Alzahlan DC motor braking using rheostatic braking 24 Dynamic Braking of DC Motor 25 By: Mostafa W. Alzahlan extensively increasing because of their high robustness, reliability, low cost, high efficiency and good self-starting capability. For the use of industrial applications one of the most important control parameter in the motor drive system is braking. There is a need to bring a drive system quickly to rest to hold a drive at standstill after some operation has been completed, or under the condition of faulty operation to save the machinery parts or operating personal. Basically, the braking system for electric motor fundamental is one mechanism to create retarding torque to stop the motor rotation with sudden or slow stop depending on application in the system. In other word, braking is essentially the removal of stored kinetic energy from a mechanical part of the system. One of the most effective way to brake the induction motor is to use the dynamic (rheostatic) braking. By: Mostafa W. Alzahlan Dynamic (Rheostatic) braking of induction motor In many industrial applications the use of induction motor is 26 Four types of dynamic (rheostatic) braking could be applied on the induction motor to be braked: • AC dynamic braking. • Self-Excited braking using capacitor. • DC dynamic braking. • Zero-Sequence braking. By: Mostafa W. Alzahlan Dynamic (Rheostatic) braking of induction motor 27 By: Mostafa W. Alzahlan Capacitor Self-excitation braking Capacitor braking 28 By: Mostafa W. Alzahlan DC injection braking DC injection braking 29 By: Mostafa W. Alzahlan Magnetic braking Magnetic braking 30 By: Mostafa W. Alzahlan Zero-Sequence Dynamic Braking Zero-sequence braking 31 By: Mostafa W. Alzahlan Countercurrent Braking System 32 Countercurrent (reverse current) braking system is an electric braking achieved by switching the power supplied to the windings of an actuating motor in such a way that the direction of the tractive force is reversed. This reversal can be obtained either by changing the polarity of the voltage connected to the winding of the rotating armature of the motor or by switching two phases of the stator winding. The magnitude of the braking torque can be regulated by adjusting a resistance in the armature circuit. When reverse-current braking is applied, the power feed must be immediately disconnected from the power supply network after every shutoff of the electric drive in order to prevent the actuating motor from reversing its motion. By: Mostafa W. Alzahlan Countercurrent (Reverse current) breaking 33 • Hoisting • Conveying machines. • Rolling machine. • Roller conveyers. • Braking of DC motors • Braking of induction motors By: Mostafa W. Alzahlan Applications of countercurrent braking system 34 By: Mostafa W. Alzahlan Braking of DC motor 35 By: Mostafa W. Alzahlan Braking of DC motor 36 Plugging of DC motor 37 By: Mostafa W. Alzahlan Plugging is one of the electrical braking methods applicable in induction motor. The principle of traditional plug braking, is that changing the direction of revolving magnetic field to oppose the direction of former magnetic field by changing the phase sequence of three-phase voltages supply to the stator windings, and then the motor will be brought to a halt by opposing torque in a short time. As the rotor always tries to catch up with the rotating field, it can be reversed rapidly simply by interchanging any two of the supply leads. If the leads on the stator windings are reversed suddenly, the direction of rotation of the stator field is reversed. The resulting slip is larger than one. The motor will come to an abrupt stop. Very rapid reversal is possible using plugging but large cage motors can only be plugged if the supply can withstand the very high currents involved, which are even larger than when starting from rest. Frequent plugging will also cause serious overheating, because each reversal involves the “dumping” of four times the stored kinetic energy as heat in the windings. Moreover, there is a possibility of reversing the rotation of motor if it fails to remove the braking as soon as the motor speed reached to zero rpm. By: Mostafa W. Alzahlan Countercurrent braking of induction motor 38 By: Mostafa W. Alzahlan Countercurrent braking of induction motor Plugging Braking of induction motor 39 By: Mostafa W. Alzahlan Countercurrent braking of induction motor 40 Plugging speed –torque curves of induction motor Dynamic brakes ("rheostatic brakes" in the UK), unlike regenerative brakes, dissipate the electric energy as heat by passing the current through large banks of variable resistors. Vehicles that use dynamic brakes include forklifts, Diesel-electric locomotives, and streetcars. This heat can be used to warm the vehicle interior, or dissipated externally by large radiator-like cowls to house the resistor banks. The main disadvantage of regenerative brakes when compared with dynamic brakes is the need to closely match the generated current with the supply characteristics and increased maintenance cost of the lines. With DC supplies, this requires that the voltage be closely controlled. By: Mostafa W. Alzahlan Dynamic vs. Regenerative 41 Only with the development of power electronics has this been possible with AC supplies, where the supply frequency must also be matched (this mainly applies to locomotives where an AC supply is rectified for DC motors). A small number of mountain railways have used 3phase power supplies and 3- phase induction motors. This results in a near constant speed for all trains as the motors rotate with the supply frequency both when motoring and braking. By: Mostafa W. Alzahlan Dynamic vs. Regenerative 42 • The regenerative braking effect drops off at lower speeds; therefore the friction brake is still required in order to bring the vehicle to a complete halt. Physical locking of the rotor is also required to prevent vehicles from rolling down hills. • The friction brake is a necessary back-up in the event of failure of the regenerative brake. • Most road vehicles with regenerative braking only have power on some wheels (as in a two-wheel drive car) and regenerative braking power only applies to such wheels, so in order to provide controlled braking under difficult conditions (such as in wet roads) friction based braking is necessary on the other wheels. • The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. By: Mostafa W. Alzahlan Assisting regenerative braking with frictional braking why?? 43 • No regenerative braking effect can occur if another electrical component on the same supply system is not currently drawing power and if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy. • Under emergency braking it is desirable that the braking force exerted be the maximum allowed by the friction between the wheels and the surface without slipping, over the entire speed range from the vehicle's maximum speed down to zero. The maximum force available for acceleration is typically much less than this except in the case of extreme high-performance vehicles. Therefore, the power required to be dissipated by the braking system under emergency braking conditions may be many times the maximum power which is delivered under acceleration. By: Mostafa W. Alzahlan Assisting regenerative braking with frictional braking why?? 44 Any Questions ?? By: Mostafa W. Alzahlan Thank You For Listening 45