Power Semiconductor Drives. By S. Sivanagaraju. About this book · Shop for Books on Google Play. Browse the world's largest eBookstore and start reading. some pages are missing in this book. User Review Stator Voltage Control of Induction Motor Drives QR code for Power Semiconductor Drives . Power Semiconductor Drives book. Read 4 reviews from the world's largest community for readers. This textbook introduces students to the underlying princ.. .
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Power Semiconductor Drives [Shashi B. Dewan, G. R. Slemon, Alan Straughen] on azmibishara.info This comprehensive guide to the design of electric motor drives and speed and position control systems I'd like to read this book on Kindle. Power Semiconductor Drives [S.B. Dewan, Gordon R. Slemon, Alan Straughen] on azmibishara.info *FREE* I'd like to read this book on Kindle Don't have a. This book by a top researcher in the field of power devices, links the principles of semiconductor physics with the design and analysis of actual devices.
N-m When deciding about the torque requirements of the driving motor. W Rotor circuit copper loss. Inverters voltage souree or eurrent souree 5. To satisfy Kirchhoff's voltage law. Contents xiii O rpm.
Tata McGraw-Hill. Thyristor-Theory and Applications. Electric Machines. Affiliated East West Press. Bibliography Electromechanics and Electric Machines. Electrical Machines and Power Electronics. Principles of So lid State Power Conversion. Crosby Lockwood Staples. Silicon Controlled Rectifier Design Handbook. Va2 - 4e d. Answers to Selected Problems 2.
Few points on the characteristic are: N rpm O rpm. Devices conduct as follows: N is speed in rpm. Braking breakdown torques: Few points are f Hz 6 12 18 24 48 36 For Answers to Selected Problems 6.
N-m Above base speed: V and P m will be constant at Below base speed: For other parameters few points are: T and IF are held constant at 47 A. V and P m change linearly from their zero values at zero speed to V and 15 kW respectively at base speed. P m and V will increase linearly with speed from their zero values at zero speed to kW and O N-m. Three points on the speed-torque curves are: Index e A AC voltage controllers: Chopper control of de motors: R Rectifier see Controlled rectifiers Rectifier control of dc rnotors: Load torques: Kramer drive.
Ill pulse-width modulated rectifier. V Frequency. H Modulation index Speed. A kth harmonic in induction motor stator or synchronous motor armature current. A The ratio V IjX. A Pcr phase ac equivalent of lF for a. N-m also chopper period. Hz Base frequency. N'J lnstantaneous value of the de link current of a con verter. W Power recovered. A lnstantaneous value of ac source current. A Field current of a synchronous motor.
W Rotor circuit copper loss. A Fundamental component of induction motor stator or synchronous motor armature current. A Fundamental component of rotor current referrcd to stator.
A Rated value of l. E Voltage induced in the armature of a de motor or in the stator of an induction motor.
Power Semiconductor Drives - S. Sivanagaraju - Google книги
A Ripple in armature current. A Polar rnoment of inertia of motor-load system referred to the motor shaft. Kg-m" K. A Average value of the armature current at critical speed Wonc. Hz Average value of the armature current of a dc motor.
W Armature circuit resistance of a dc motor. W Air-gap power. S Torque developed. Braking resistance. A Average value of the dc link current of a con verter.
A Magnetising current. A lnstantaneous value of the armature current of a dc motor. W Develope mechanical power. A Fundamental component of rotor current. H DC link inductance. H Synchronous inductance of a synchronous motor. Hz Frequency of the carrier wave. V Injected voltage. V Peak value of an ac source voltage. V Average value of the dc motor armature voltage also rectitier output voltage. X lnstantaneous ac source voltage. V kth harrnonic component in a non-sinu.
V Excitation emf. V Fundamental component in a non-sinusoidal voltage. V Magnetising reactance. V lnstantaneous value of the de motor armature voltage. V Instantaneous inverter output voltage betwecn pha e A and the central point of the de ource.
Webers tan -' wL. N-m Commutation overlap angle. Pha e of tator current with rcspect to the source voltage V. Torque developed. S Mechanical time constant. Cornrnutation lead angle of a load commutated inverter or the angle at which rhe de motor armature current drops to zero. N-m Torque required to do the useful mechanical work. N-m Load torque. The load is usually a machine designed to accomplish a certain task.
For example. Usually the requirements of the load can be specified in terms of speed and torque demands. A motor having speed-torque and speed-current characteristics that suit the load requirements is choseno A motor will have characteristics compatible to the load if it satisfies the speed and torque requirements of the load without exceeding the current limitation imposed either by the motor rating or the source capacity.
For examplevmachines like trains. As examples. The characteristic obtained when the supply is maintained at rated conditions is called the natural characteristic. An Introduction This chapter describes the common features of electrical drives controlled by power semiconductor converters.
The requirements of some specific loads are described in section 1. In the absence of isolation. Choice of various elements is also interrelated. Sensingof certgin parameters. The command signal. This function is perforrned by the sensing unit. The controls for the converter are built in a control unit which operates at much lower voltage and power levels. When sensing the power circuit's electrical parameters.
The complete drive system-c-consisting of the load. Converters generate a considerable amount of harmonics. Any such disturbance may produce changes which may affect the entire system. The control unit consists of linear and digital integrated circuits and transistors. Usually the converter is selected to make the motor characteristics suitable to the load.
Block diagrarn of an electric The power semiconductor convertor. The operating point of the motor may be disturbed due to a change in any of these elements of the drive. The low voltage control unit is electrically isolated from the power circuit or converter-motor circuit for two reasons: This may damage the control unit and may be detrimental to the safety of the operator who applies the command signal.
It may also consist of a microprocessor when sophisticated control is required.
The drive accelerates or decelerates depending on whether T is greater or less than TL. When the load has a high inertia. During the acceleration period. When the speed increases.
The following notation is adapted: N-m Any motor-load system can be described by the following fundamental torque equation: While the motor always rotates. Figure 1. In applications having a load with large inertia. Seco 1. The load speed may be different from that of the motor. During the deceleration period. It is convenient. The friction torque can be resolved into three components as shown in figure 1. This is known as the windage torque.
Friction at zero speed is called stiction or static friction. For the drive to start. The dynarnic torque and the motor torque together are able to produce the torque required for the pressing operation. A third component Ts accounts for the additional torque present at standstill.
Friction torque T F: The friction will be present at the motor shaft and also in the various parts of the loado The friction torque T F is the equivalent value of various friction torques referred to the motor shaft.
In the absence of the flywheel. The deceleration occurs. During the no-load period. Windage torque Tw: When a motor runs. Its value at standstill is much higher than its value at slightly above zero speed. The variation of friction torque with speed is shown in figure 1. The component Te which is independent of speed is known as coulomb friction. In some applications. When fast response is required. The component Tv which varies linearly with speed is called viscous friction and is given by the following equation: Torque required to do the useful mechanical work.
The nature of this torque depends on the type of loado It may be constant and independent of speed. A flywheel is mounted on the motor shaft to increase the equivalent inertia J. Since Ts is present only at standstill. During the pressing operation. The windage torque Tw. With this approximation. To resolve this anomaly. From the preceding discussion. When deciding about the torque requirements of the driving motor. It is comprised of the windage.
It is applicable to electric trains and road vehicles. The windage is also a predominant component at high speeds for trains.. The variation of the traction load torque with speed. In the case of centrifugal pumps. This is nothing but the windage torque given by equation One such example is a coiler drive which is used in steel strip. The foregoing equation suggests that for a given value of the coefficient of adhesion. If the torque drops by a large amount. In this case.
To get a high average speed. The wheels coupled to the motor are called driving wheels. Figure l. This is easily achieved when power semiconductor converters are used. This allows a much higher weight to come on the driving wheels. The acceleration and deceleration times form a major proportion of the total traveling time. Then the maximum weight on the driving wheels can be at the most equal to the weight of the locomotive.
Thus a motor speed-torque characteristic with a low regulation of speed is preferred to prevent wheel slippage. The usual pattem is to use the motorized train car and trailer cars in a ratio of 1: Each motorized train car has its own driving motor. For a given value of the coefficient of adhesion.
An important factor known as the coefficient of adhesion is defined as follows: In the case of suburban trains. The mandrel is mounted on one side of the rolling stand s. In long distance trains. In a reversible cold rolling steel strip mill. When a wheel slips. The value of the coefficient of adhesion depends on the conditions of the rail and wheel surface. After rolling. Acceleration and deceleration times form only a very small proportion of the total time of travel between the two stations.
The coefficient of adhesion also depends on the speed-torque characteristic of the motor. A smooth change of torque is also desirable to prevent wheel slippage. Another mandrel is mounted on the other side of the rolling stands. The purpose of the rolling stand is to reduce the cross section and to improve the surface finish. Slipping is always to be avoided as it damages the track and reduces its life.
The characteristics shown in figure l. The part CD is obtained by imposing a limit on the maximum motor torque. Since the rolling stands receive and give out the strip at a fixed linear speed. As the rolling process progresses. A diesel electric loco motive employs a de motor fed by a dc generator driven by a diesel engine.
In a low speed hoist. The characteristics AB. This is achieved by the constant power characteristic Be. Instead of a dc generator. This explains why the portion Be has the nature shown in the figure. The crane-hoist characteristics are shown in figure 1. This is done for three reasons: The different speed and torque limits. The amount of power changes with the cross section and the material of the strip.
In high speed hoists. To maintain even. By interposing the de generator-rnotor set.
When the fuel injection is set at maxirnum. The purpose of the excavator is to dig earth. The diesel engine runs at full speed developing constant power.
Since the speed-torque curves of the diesel engine are not compatible with the traction requirements. The motor speed-torque requirements for excavators are shown in figure l. To make full use of the diesel engine power. In such a situation. The generator-rnotor system essentially acts as a torque converter.
Care is also taken to ensure that the diesel engine is not overloaded. For lower fuel injections. The motor will then simply stop.
A'B and C'D'. While digging. Load torques which have the potential to drive the motor under equilibrium conditions are called active load torques. The motor will stop only after the kinetic energy stored in its inertia is dissipated.
Torques due to friction. This confirms the features of the active load torque just stated. On the other hand. Let us consider the example of an electric train. Electric braking allows accurate steps without subjecting mechanical parts to unduly large stress. Passive load torques. There are applications where accurate stops are required. Load torques which always oppose the motion and change their sign on the reversal of motion are called passive load torques. Similarly in traetion.
The electric braking helps in achieving quick and smooth stops. Active load torques. If a motor running at some speed is disconnected from the supply. Torque due to the force of gravity and torques due to tension. When the train climbs up. When either the load torque is small or the inertia is large. Such load torques usually retain their sign when the direction of the drive rotation is changed. In certain applications involving active loads. In applications requiring frequent stops. The electric braking may be required due to the following reasons: The motor produces braking torque to limit the speed within the safe values.
When coupled to a passive load. For reversible drives the forward speed is chosen arbitrarily. The operation in quadrant II is called forward braking.
Then the rotation in the opposite direction gives the reverse speed which is assigned the negative signo The positive motor torque is defined as the torque which produces acceleration or a positive rate of change of speed in the forward direction. When selecting a drive. It is not as smooth as electric braking. The motor speed is considered positive when rotating in the forward direction. The reason for this convention is as follows.
In motoring. The speed. It tends to drive the motor in the forward direction. Hence the torque is regarded as the independent variable.
A motor operates in two modes-motoring and braking. For drives which operate only in one direction. According to equation 1. In quadrant ll. It tends to drive the motor in the reverse direction. The operation in quadrant 1 is called forward motoring. The same will happen when coupled to an active load torque with a positive signo However. In braking. For the proper use of equation 1. Operation in this quadrant will take place only under transients.
The motor can provide motoring and braking operations in both forward and reverse directions. The question of finding the drive speed arises only if the drive operates. In quadrant 1. Motor torque in the direction opposite to the positive motor torque will produce --deceleration or a positive rate of change of speed in the reverse direction. In drives. At a given equilibrium operating point. The stability of an equilibrium point can be readily investigated by using the concept of steady-state stability.
Multiquadrant operation of Reverse motoring Reverse braking librium speed in this quadrant.
Power Semiconductor Drives
Equilibrium speed will be viewed as the stable speed provided that the operation will be restored to this speed after any smaIl departure from it due. By the adjustment of the braking torque. Following the preceding arguments. This is the speed at which the drive will normally operate in steady-state provided it is a speed of stable equi. Then the drive will also operate in steady-state in this quadrant.
In this concept. This in effect means that the motor is assumed to be in electrical equilibrium for all operating points. The basis of this assumption is that the electrical time constant of a motor is usuaIly negligible compared to its mechanical time constant.
At a time t. Introduction Chap. Deceleration occurs and the operation is restored to point A. Acceleration occurs and the operation is restored to point A. A small increase in speed makes the load torque greater than the motor torque.
Let us next examine the stability of the equilibrium point B. A smalI increase in speed causes the motor torque to exceed the load. Let us examine the equilibrium points A and B. Let us first examine point A for the steady-state stability. Substituting from equations 1.
A is a stable equilibrium point. For this to happen. Now from equation 1. For small perturbations. The supply that is generally available is the fixed voltage and fixed frequency ac supply. The load T L2 has a characteristic similar to the fan load fig. Examination of point e shows that it is a stable equilibrium point. Note that points B and e lie on the same part of the motor speed-torque curve.
Sometimes a fixed voltage de supply may be available. Acceleration takes place and the operating point moves away from B. Such a motor characteristic gives unstable operation with most loads. For the control of de motors.
The variable voltage de supply is also used for the control of induction and synchronous motors. Thus B is an unstable equilibrium point. For the control of induction motors. Synchronous motors need a variable frequency supply with variable voltage or current. Let us now consider the equilibrium point e which is obtained when the motor drives the load-torque T L2. To satisfy the supply needs of various motors. Notice that the part of the motor characteristic on which points B and e are situated has a positive slope.
This shows that the stability of an equilibrium point depends not on either the motor characteristic alone or the load characteristic alone but on the relative nature of the two.
AC voltage eontrollers 4. Cycloeonverters Fixed voltage and frequeney ae to variable voltage and frequeney ae Applieations Control of de motors. A variable speed drive may use a single converter or more than one con verter. When fast response during transient operations is not necessary. The flow of current equal to the maximum permissible value allows full use of the motor torque capability both during motoring and braking. These circuits may not only differ in performance but also in terms of their capability for motor control in various quadrants.
Inverters voltage souree or eurrent souree 5. Choppers Fixed voltage de to variable voltage de Fixed voltage ae to variable voltage ae at same frequeney DC to fixed or variable voltage and frequeney ae. These converters along with their conversion functions and applications are listed in table 1. Some of the features cannot be explained at this. Converters use semiconductor elements which do not have any capacity for overload. Controlled reetifiers AC to variable de 2. The detailed explanations will be given in later chapters.
The available power increases linearly with speed and generally reaches maximum value-equal to the continuous power rating of the motor-at base speed.. Above base speed. This minimizes the cost of the con verter and the drive Motor operation at the rated current and rated volt- Maximum speed r -- -. The increase in the cost of the drive is well accepted as a price to be paid for the increase in the total work done by the drive.
Usually the motor is operated at a reduced voltage below base speed. Almost all converter drives are provided with some kind of current control.. When fast response is not necessary during transient operations..
The current control now provides protection against the sustained overloads as well.
Power Semiconductor Devices and Circuits | A.A. Jaecklin | Springer
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