Essay: DESIGN DEVELOPMENT AND PHYSICAL PARAMETER ANALYSIS OF SWITCH RELUCTANCE MOTOR

Abstract:
Now a days switched reluctance motor (SRM) becomes more popular among the various electric drives available in the domestic and industrial application due to its simple and robust construction. The application of the machine, the operation of the switched reluctance motor can be categorized into the low and medium speed operation and high speed operation. The operation of the machine at high speed can exceed the speed of 20,000 rpm for the aerospace applications, which is beyond the speed encountered in wind energy system, which could be as low as 200 rpm. The potential of SRM is one of the prospects for variable speed applications. However, the available research generating operation mainly covers the high speed application. The SRM is one of the machine which can operates even under the faulty conditions with reduces the performance the reason behind this is that the rotor doesn’t have any excitation source even doesn’t generate power into the faulted phase. The control of SRM drive is developed by the converter circuit which controls excitation of the phase by SCS (switching converter switches). Thus the developed SRM circuit suffers from low power factor and high harmonic capacity which affects the performance of the SRM drive. In this present work is to design and develop a circuit which gives improved power factor and low torque ripples. From the various converter topologies, asymmetric bridge converter is used to analysis the performance of SRM and simulations as result carried out in MATLAB. Three phase asymmetrical power converter using the insulated-gate bipolar transistor (IGBT) which is a three-terminal power semiconductor device primarily used as an electronic switch which is developed to combine the high efficiency and fast switching and it used in the feedback of motor to control the power factor of motor. After simulating the model for much iteration and in each iteration new position of stator and rotor is assigned, an optimum position is reached where ripples are very less and depicts the reduction in torque ripples as result obtained.
Keywords: Switched Reluctance Motor (SRM), 3-Phase Power Converter, IGBT, Parameter Analysis of SRM.
1. Introduction
Electrical drive is one of the important equipment for any industries.60% of total energy is consumed by only electric motor. Rotor position of SRM is directly sensed by using sensor is called sensor type SRM. Sensor less SRM is indirect sensing the rotor position [4]. SRM is only considering for home appliance because it‘s simple construction and absence of permanent magnet and rotor windings. The torque ripples in the SRM are arises, due to the phase current commutation. If the converter has the ability to commutate the phase current faster, then the torque ripples can be reduced [7]. This Paper compared different techniques for the modelling of a SRM in view of its nonlinear magnetization characteristics due to the doubly salient structure. It proposes the nonlinear model of SRM`s from operating data. The simulated performance of SRM Drive system is presented to analyse the effect of switching angles on transient and steady state performance of the Drive in terms of speed, Current and torque response. A new analytical representation and simulation of the phase inductance of SRM using MATLAB/Mfile is presented [1]. Simulation method has many advantages:
• It is free from expression
• Can be applied widely
• Demonstrates inductance profile using motor parameters only
• Saves run time
Although the switched reluctance motor drive system has a simple structure, low cost, high reliability, superior performance, etc., making it one of the optimal scheme of the electric vehicles’ drive system. However, high torque ripple of switched reluctance motor is very harmful to motor itself and actuator of electrical vehicle. Therefore, in the electric vehicle drive system, to reduce the ripple of switched reluctance motor and increase the average torque are crucial to electric vehicle traction characteristics to obtain [10-12].
The operational principles of the SRM are quite simple and straightforward, but the proper control of the SRM is not sufficiently completed. The inherent nonlinearity of a SRM makes torque production highly dependent upon the geometry of the poles, which is characterized by the dependence on both stator current and rotor position.
2. Design Development of SRM Circuit
2.1 Switched Reluctance Motor
In Switched Reluctance Motor the torque is developed because of the tendency of the magnetic circuit to attain the minimum reluctance i.e. the rotor moves in line with then stator pole thus maximizing the inductance of the excited coil.. When a rotor pole is aligned with a stator pole, there is no torque because field lines are orthogonal to the surfaces (considering a small gap). If one displaces the rotor of its position, there will be torque production that will tend to bring back the rotor toward the aligned position. If current is injected in the phase when in the unaligned position there will not be torque production (or very little). If one displaces the rotor of the unaligned position, then a torque tends to displace the rotor toward the next aligned position. The magnetic behavior of SRM is highly nonlinear. But by assuming an idealistic linear magnetic model, the behavior pattern of the SRM can be easily studied without serious loss of integrity from the actual behavior pattern. SRM, when compared with the other ac and dc machines has some advantages and limitations [3].
2.2 Construction of SRM
This paper presents the torque optimization of a SRM by using a finite-element analysis. The effects of different rotor and stator shapes and sizes on the performance were investigated. Finite element method was used to simulate each shape of SRM, while various stator/rotor shapes are analyzed keeping the same ampere-turns for various SRM shapes. The investigation was performed on 3 phase, 6/4 poles and 4 phase 8/6 poles base designs SRM, with various configurations as follows:
• Changing the shape and size of the rotor and stator.
• Dimensional variations for stator and rotor poles.
Rotor poles for the 3 phase, 6/4 poles SRM. After gathering the results of the highest developed torque for the stator, and the rotor poles, a new SRM optimized design is obtained. The base design and the optimized design for 3 phase, 6/4 poles SRM. The stator pole arc/pole pitch ratio (β) for the optimized SRM is 0.5; the rotor pole arc/pole pitch ratio γ for optimized SRM is 0.38. Figure 1 shows the flux density through the stator pole, air-gap, and rotor for 3 phase, 6/4 poles base and optimized cross-section design SRM. Figure 2 shows the graphical results for developed torque for the 3 phase, 6/4 poles reference base and optimized SRM designs. Developed torque is analyzed when rotating the rotor from 0º to 45º for the optimized and base designs [15].
Figure 1 : Flux density for 3 phase, 6/4 poles; a) base design SRM, b) optimized design SRM
Figure 2 : Position Sensor Circuit model in MATLAB/Simulink
Figure 3 : SRM Circuit model in MATLAB/Simulink
3. Physical Parameters Analysis
Experimental investigation based on a DC supply voltage of 240 V is used. The converter turn-on and turn-off angles are kept constant at 45deg and 75deg, respectively over the speed range. The reference current is 200 A and the hysteresis band is chosen as + 10 A. The SRM is started by applying the step reference to the regulator input. The acceleration rate depends on the load characteristics. Following are the various physical parameters used in SRM Drive:
a) Stator Voltage, V (in Volt)
b) Flux Linkage, flux (in V.s)
c) Stator Current, I (in Amp)
d) Torque, Te (N.m)
e) Rotor Speed,  (in rad/sec)
f) Rotor Position,  (in rad)
The output characteristics for the following are obtained from the simulation using MATLAB/Simulink model.
Graph 1: Stator Voltage, V (in V) v/s time, t (in Sec)
Graph 2: Flux linkage, flux (in V.s) v/s time, t (in Sec)
Graph 3: Stator Current, I (in Amp) v/s time, t (in Sec)
Graph 4: Developed Torque, Te (in N.m) v/s time, t (in Sec)
Graph 5: Rotor Speed,  (in rad/sec) when Angle is OFF v/s time, t (in Sec)
Graph 6: Rotor Position,  (in rad) when Angle is ON v/s time, t (in Sec) at Torque Settling
4. Result & Discussion
SRM circuit model simulate in MATLAB/Simulink the following parameter analysis results were obtained for the many iteration, in each iteration new position of stator and rotor is assigned.
1. Voltage versus time graph shows the stator voltage of SRM, where voltage shown vertically and time shown horizontally. In the resultant graph (Graph – 1) three colours (Pink, Light Blue and Yellow) shows the output of three different DC voltages. No delay time is observed thus the waveform starts just near to the zero value and small delay in trigging ON of the power switch. Observed magnitude of the voltage is 240 Volt.
2. Flux versus time graph shows the Flux linkage of SRM, where Flux shown vertically and time shown horizontally. In the resultant graph (Graph – 2) three colours (Pink, Light Blue and Yellow) shows the waveform of three different phases between stator and rotor pole of SRM. No delay time is observed thus the output is stable initially. Observed flux linkage is depends on alignment of the stator and rotor pole.
3. Current versus time graph shows the Stator current of SRM, where current shown vertically and time shown horizontally. In the resultant graph (Graph – 3) three colours (Pink, Light Blue and Yellow) shows the waveform of three different phases currents. No delay time in switching of the devices is observed. The maximum value of current reaches 200 Amp and after a steady value of 0.17 second it’s finally become lower and lower.
4. Torque versus time graph shows the Developed torque of SRM, where torque shown vertically and time shown horizontally. It is clearly seen in Graph — 4 (yellow colour waveform) the maximum value of torque reach 155 N.m and after a steady value of 0.14 second it’s finally become constant at 90 N.m. It’s also observed that the starting torque of SRM drive is very high.
5. Rotor Speed versus time graph shows the rotor speed of SRM, where speed shown vertically and time shown horizontally. It is clearly seen in Graph — 5 the maximum value of rotor speed reach 4600 rad/sec and after a gradually increment the rotor speed becomes constant.
6. Rotor positions versus time graph shows the rotor position of SRM, where rotor position shown vertically and time shown horizontally. It is clearly seen in Graph — 6 the maximum value of rotor position reach 40 rad and after a gradually increment the rotor position becomes constant at 0.20 seconds.
Conclusion made on performance of SRM drive is the torque ripples induce due to changing of position of rotor and stator which sets into optimal position then torque ripples are reduced.
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