State switching digital control technique for switched reluctance motor drives

It has been anticipated that switched reluctance motor (SRM) drives will become the future drives of choice due to the simplicity of the motor construction, high speed capability, and relatively high power density. The motor has windings on the stator and a passive rotor made of ferromagnetic material such as iron. However, the control of the motor is quite complex due to the nonlinearities in the magnetic flux linkage seen on the stator as the rotor spins, as well as the saturation of the magnetic material. Numerous memory and/or processor intensive solutions have been proposed to deal with the control problem. The focus of this paper is to develop a simple controller for the SRM based on state switching (digital) control concept. The concept of digital control is that the motor can be brought to and kept in any state by switching the motor mode of control between two predefined states (the two "digital" states), which are above and below the desired steady state of the motor. This controller can be implemented in low-complexity analogue circuitry. In the current work it was shown that the optimal method of controlling the motor is to switch between two states which differ by reference current at low speeds (below pulse mode), and conduction angles at very high speeds. Control design equations are derived, and disturbance rejection capability is calculated. Simulation results for various operating modes are presented.