FourQuadrant Control of Switched Reluctance Motors full report
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23032010, 11:16 PM
FourQuadrant Control of Switched Reluctance Motors.pdf (Size: 655.17 KB / Downloads: 845) FourQuadrant Control of Switched Reluctance Motors Presented By: Dr. Iqbal Husain Department of Electrical Engineering The University of Akron Akron, OH 443253904 Introduction Switched reluctance motor (SRM) drives are simpler in construction compared to induction and synchronous types of machine. Their combination with power electronic controllers may yield an economical solution. The switched reluctance motor with passive rotor has a simple construction, but the solution of its mathematical model is relatively difficult due to its dominant nonlinear behavior. OVERVIEW MAIN FEATURES OF SRM OPERATION AND CONTROL OF SRM 4QUADRANT CONTROL OF SRM RESULTS FROM OPTIMIZED 4Q CONTROL MODELING FOR SIMULATION AND CONTROLLER DEVELOPMENT 4QUADRANT SENSORLESS CONTROL SIMULATION RESULTS EXPERIMENTAL RESULTS CONCLUSIONS REFERENCES BASIC CONSTRUCTION OF AN SRM The SRM is a doublysalient, singlyexcited machine with independent windings of the stator. Hts stator structure is same as PM motor, but the rotor is simpler having no permanent magnet on it. Stator windings on diametrically opposite poles are connected in series or parallel to form one phase of the motor. Several combinations of stator and rotor poles are possible, such as 6/4 (6 stator poles and 4 rotor poles), 8/4, 10/6, 12/6 etc. 4/2, 2/2 configurations are also possible, but with these it is almost impossible to develop a starting torque when the stator and rotor poles are exactly aligned. The configurations with higher number of stator/rotor pole combinations have less torque ripple. The design objectives are to minimize the core losses, to have a good starting capability and to eliminate mutual coupling. Energy partitioning during one complete working stroke. (a) Linear case. (b) Typical practical case. W = energy converted into mechanical work. R = energy returned to the dc supply. The nonlinear saturating characteristics of real magnetic steel has a marked influence on the energy conversion process in an SRM. Only for very low values of saturation, the characteristics approximate the ideal linear case. The fluxcurrent characteristics in the unaligned position is approximately linear, because the magnetic path is dominated by large airgap and flux densities are small. In the aligned position the airgap reluctance is small and flux density is high, which causes high saturation at higher currents. The SRM is always driven into deep saturation to maximize the energy transfer in each stroke. SRM CHARACTERISTICS Rotor Position in degrees Torquecurrentangle characteristics of an SRM The phases in an SRM produce torque independent of each other. The total torque is the sum of the individual phase torques. The static torqueanglecurrent characteristics shows the overlap angles, which is useful is determining the commutation angle. The torque dip in the characteristics is an indirect measure of expected torque ripple. TORQUESPEED CHARACTERISTICS Rotor Speed (Per Unit) Region #1: Constant Torque Current, and hence torque, kept constant by PWM or chopping. At low speeds current rises instantaneously due to small backemf. At medium speeds, phase advancing is necessary. Phase turnoff is also advanced so that current decays to zero before rotor passes alignment. PWM or chopping is still possible. TORQUESPEED CHARACTERISTICS (Cont.) Region #2: Constant Power High backemf forces current to decrease once pole overlap begins. PWM or chopping no longer possible. Conduction angle is increased in proportion to speed, primarily through phase advancing. Maximum current can still be injected into the motor to sustain high enough torque. Core and windage losses increase rapidly. Constant power can generally be maintained upto 23 times the base speed. Region #3: Natural characteristics Upper limit of conduction angle is reached when equals half the rotor polepitch., i.e., half the electrical cycle at the onset of region #3. Conduction angle is fixed, but pulse position ca be advanced. Maintaining torque production is no longer rtrtcciktlo anrl it fa lie rtff inx/orcolw with cnooH2 POSITION FEEDBACK Conventional Method Inverter 0 H r Sensorless Method Control Inputs Inverter Control Strategies Appropriate positioning of the phase excitation pulses is the key in obtaining effective performance Control parameters: 0on, 0dwell and Iph Control parameters determine torque, efficiency and other performance parameters. Different Control Methods Voltage controlled drives. Current controlled drives. Advanced controllers: T/A or efficiency Maximization. Torque ripple minimization. Acoustic Noise Minimization. Sensorless controllers. CQref Outer Loop Controller PWM Controller Duty Cycle Electronic Commutator Gate Signal Converter Vph Voltage Controlled Drive In low performance drives, a fixed frequency PWM voltage control with variable duty cycle provides the simplest form of control. The angle controller generates the turnon and turnoff angles depending on the rotor speed. The duty ratio is changed according to the voltage command signal. A speed feedback loop can be added on the outside, if speed control is desired. The drive typically also incorporates a current sensor, placed in the lower leg of the dc bus, for overcurrent protection. Outer Loop Controller Torque Controller Current Controller! Gate Signal Converter + Sign(.) Angle eoff Electronic Calculator Commutator e Current Controlled Drive Used in torque controlled drives, where current is controlled in the inner loop. The controller needs current feedback information from each phase. The reference current is set by the torque command and the torqueanglecurrent characteristics of the motor. The method allows rapid resetting of the current level and has applications where fast motor response is required. POSITION HOLDING Effect of Position Holding The motor operation at a constant position will excite one phase for a prolonged period. This will lead to local overheating of any phases. Solution Â¢ When the position is held at a constant level, the oute loop must allow to dither the rotor around zero speed. Â¢ This effect results in some rotor movement on the order of one step angle. Therefore, the motor goes through more than one phase during position hold. 20 16 12 8 Phase Currents During Position Hold OPTIMIZATION RESULT COMPARISON Rise Time Comparison The response time (rise time) is considered as the time required for translational movement of 20% to 80% of the position command. Operating parameters Rise time (msec) Optimal turn on and turn off angles 48 Optimal turn on plus 10 and optimal turn off 58 Optimal turn on minus 10 and optimal turn off 51 Optimal turn on and optimal turn off plus 10 55 Optimal turn on and optimal turn off minus 10 52 The test results prove that the optimal turnon and turnoff angles give the fastest response. OBSERVER BASED 4Q SENSORLESS DRIVE SIMULATION AND EXPERIMENTS Â¢ The dynamics of the machine in statespace format is run in parallel with the real machine SOFTWARE  The model has the same inputs as the physic. machine. The difference between model outputs and measured outputs are used to force the estimated values to converge to the actual values. The function ef provides an indirect way of evaluating the sign of position error. CURRENT ESTIMATION The dynamics of the machine in statespace format is run in parallel with the real machine. The model has the same inputs as the physica machine. The difference between model outputs and measured outputs are used to force the estimated values to converge to the actual values. Estimated Current: The phase flux goes to zero in each, which helps impose the zero initial condition for the integrator repeatedly. ERROR DYNAMICS OF SMO Error Dynamics: ISSUES WITH 4Q SENSORLESS DRIVE > Effect of motor losses on model based flux calculation. > Integrator problem of flux estimator at low and zero speed operation. > Voltage measurement. >Zero speed sensorless operation. > Continuous existence of information. > Sensorless starting. EFFECT OF MOTOR LOSSES ON FLUX CALCULATION Rm is considered across the backemf to consider the effect of core losses. Therefore and X = XS (1  e  lff (6)) where f= 7 lph> and 7 is a core loss dependent parameter. MODIFIED FLUX ESTIMATOR Problems near zero speed At low speeds, the flux estimator output may exceed the saturation flux due to measurement noise. This makes the observer unstable. In the modified estimator, flux is reset to a lower value when saturation flux is reached. Results on Modified Flux Estimator: Time (sec) Â¢The capacitor voltage rise due to regeneration must be considered for accurate flux estimation. ZERO SPEED SENSORLESS OPERATION Measured and estimated position and speed during speed inversion and zero speed operation: A high frequency bipolar speed is commanded to dither the motor at a constant position. This allows extracting information from the response of the system. OTHER SENSORLESS ISSUE; > Reference Current Lower Limit: Â¢ SMO becomes unobservable due to nonexistence of information. Â¢ To receive the continuous information fo the SMO, the lower limit of the iref can be set to a small current level, say 0.5A. > Sensorless Starting: Â¢ The error may be large at startup, leadin to improper phase excitation, hesitation and possibly rotation reversal. Solution: Â¢ Drive the motor towards the desired direction using some preset phase voltages. Â¢ This allows starting the motor as an open loop fashion. This time is sufficient to reach at the sliding surface. Measured and estimated speed: 4Q Sensorless Control ^ SMO provides accurate position information in all quadrants at higher speeds. > Toggling through zero speed has been achieved. >The SMO may fail to estimate at zero speed operation (with extended stay at zero speed) due to dominating integrator problem. >SMO needs a finite convergence time. CONCLUSIONS SRM is suitable for servotype actuator applications. Fourquadrant control is necessary for dynamic actuator type loads. Appropriate turnon and turnoff angles based on certain optimization criterion, such as torque maximization,efficiency maximization, response time minimization etc. delivers high performance. Development of fourquadrant sensorless controller must consider practical limitations. 4Q sensorless operation demonstrated in laboratory prototype experiments. REFERENCES : S.A. Hossain, I. Husain, H. Klode, B.P. Lequesne and A.M. Omekanda, "Four Quadrant Control of a Switched Reluctance Motor for a Highly Dynamic Actuator Load," to appear in IEEEAPEC, Mar. 2002. : S.A. Hossain and I. Husain, Modeling of Switched Reluctance Motors for Practical Digital Implementation, submitted to IEEE Transactions on Power Electronics. A.V. Radun, "Design Considerations for the Switche Reluctance Motor," IEEE Trans. on Industry Applications, Vo 31, No. 5, pp. 10791087, Sept./Oct. 1995. : M.S. Islam, I. Husain, R.J. Veillette and C. Batur, "Design and Performance Analysis of SlidingMode Observers for Sensorles: Operation of Switched Reluctance Motors," accepted for publiation in IEEE Transactions on Circuits and Systems. : R. McCann, M.S. Islam and I. Husain, "Application of Sliding Mode Observer for Switched Reluctance Motor Drives," To appear in Jan./Feb. 01 issue of IEEE Trans. on Industry Applications. : S.A. Hossain, I. Husain, H. Klode, A.M. Omekanda and S. Gopalakrishnan, "Four Quadrant and Zero Speed Sensorless Control of a Switched Reluctance Motor," to be presented in IEEEIAS Annual Conference in Oct. 2002, Pittsburgh, PA. please read esat.kuleuven.be/electa/research/descriptions/SRMweb_page.pdf for more of FourQuadrant Control of Switched Reluctance Motors Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion



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SRM,prprstn.doc (Size: 125.5 KB / Downloads: 73) This article is presented by: L.Revathi K.Jaseema Banu Dept of Electrical & Electronics Engg NATIONAL COLLEGE OF ENGINEERING Maruthakulam Tirunelveli SPEED CONTROL OF THE SWITCHED RELUCTANCE MOTOR DRIVE ABSTRACT – This paper deals with the Speed Control of the Switched Reluctance Motor Drive. The SRM is a singly excited and doubly salient machine. This means that it has salient poles on both the stator and rotor but only stator is excited. The SRM can also be called Electronically Switched Motor. The position information is the essential one for the operation of the motor. The speed is sensed from the motor terminal and it is compared with the Ref speed and error signal is generated using the error detector. The error signal is processed using Speed Controller and it produces Current Reference. Current Reference is compared with the actual currents and error current is generated. The current error is processed using Hysteresis Current Controller. The Classical Converter switches current in to the windings. The simultaneous switching of currents in to the winding will provide continuous rotation. INTRODUCTION The SRM is a doublysalient, singlyexcited machine with independent windings of the stator. Its stator structure is same as PM motor, but the rotor is simpler having no permanent magnet on it. Stator windings on diametrically opposite poles are connected in series or parallel to form one phase of the motor. Several combinations of stator and rotor poles are possible, such as 6/4 (6 stator poles and 4 rotor poles), 8/6, 10/6, 12/6 etc. The configurations with higher number of stator/rotor pole combinations have less torque ripple. The torque is developed by the tendency of the magnetic circuit to adopt a configuration of minimum reluctance. The excitation currents are unidirectional and discontinuous in nature. The stator phases are sequentially excited to obtain continuous rotation. Besides, the SR motor operates well into saturation. The simplicity in both motor construction and power converter requirement made the switched reluctance motor (SRM) an attractive alternative to the induction motor and the PM motors in adjustable speed drive applications. 


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