Torque control in SRM by Neuro-Fuzzy SMC

A conventional SRM drive produces very high level of harmonics content and poor power factor at ac mains. The proposed converter with midpoint converter fed SRM drive improves the power factor at ac mains with low current harmonics. So many researchers also turned towards that for torque ripple minimization and also gain success. But this method suffers from chattering problem and the solution of this problem has been selected as our objective for this dissertation. Chattering problem in SMC will be controlled by neuro-fuzzy controller and robustness will be checked against load disturbance and nonlinearities. The switched reluctance motor (SRM) represents one of the earliest electric machines which was introduced two centuries back in the history. It was not widely spread in industrial applications such as the induction and dc motors due to the fact that at the time when this machine was invented, there was no simultaneous progress in the field of power electronics and semiconductor switches which are necessary to drive this kind of electrical machines properly. The problems associated with the induction and dc machines together with the revolution of power electronics and semiconductors in the late sixties of the last century led to the reinvention of this motor and redirected the researchers to pay attention to its attractive features and advantages which helped in overcoming a lot of problems associated with other kinds of electrical machines such as brushes and commutators in dc machines and slip rings in wound rotor induction machines besides the speed limitation in both these motors. The simple design and robustness of the switched reluctance machine made it an attractive alternative for these kinds of electrical machines for many applications recently specially that most of its disadvantages which are mentioned in the following chapter could be eliminated or minimized by use of high speed and high power semiconductor switches such as the power thyristors, power GTOs, power transistors, power IGBTs and the power MOSFETs. The availability and the inexpensive cost of these power switches nowadays besides the presence of microprocessors and microcontrollers, PIC controllers and DSP chips makes it a strong opponent to other types of electrical machines. In industry, there is a very wide variety of design of the switched reluctance machines which are used as motors or generators, these designs vary with number of phases, number of poles for both stator and rotor, number of teeth per pole, the shape of poles or whether a permanent magnet is included or not. These options together with the converter topology used to drive the machine led to an enormous number of designs and types of switched reluctance machine systems, which mean both the switched reluctance machine with its drive circuit, can suit varied applications with different requirements. It is well known to those who are interested in this kind of electrical machines that the drive circuit and the machine is an integrated system, one part of such a system cannot be separately designed without considering the other part. A switched reluctance machine is a rotating electric machine where both stator and rotor have salient poles. The stator winding is comprised of a set of coils, each of which is wound on one pole. Switched reluctance motors differ in the number of phases wound on the stator. Each of them has a certain number of suitable combinations of stator and rotor poles. When operated as a motor, the machine is excited by a sequence of current pulses applied to each phase. The individual phases are consequently excited, forcing the motor to rotate. The current pulses need to be applied to the respective phase at the exact rotor position relative to the excited phase. The inductance profile of switched reluctance motors is triangular shaped, with maximum inductance when it is in an aligned position and minimum inductance when unaligned. When the voltage is applied to the stator phase, the motor creates torque in the direction of increasing inductance. When the phase is energized in its minimum inductance position the rotor moves to the forthcoming