Direct instantaneous torque control of a four-phase switched reluctance motor

The paper presents an investigation on the direct instantaneous torque control (DITC) of a 1-hp four-phase 8/6 switched reluctance motor (SRM). In the proposed technique, the instantaneous phase torque was estimated in real-time using a pre-stored look-up table of measured static torque, T(i, ¿), where phase current and phase flux linkage were input parameters. Therefore, a high-resolution encoder can be avoided. The ripple-minimizing reference phase torques were generated from the torque distribution and commutation sequence controllers that use the knowledge of the reference total torque, rotor position information obtained from an inexpensive low-resolution encoder and the estimated phase torques. The fully digitalized closed-loop control consisted of effective and simplified PI controllers of phase torques, which straightaway gave the suitable PWM duty cycles to the IGBT-based asymmetric half-bridge converter. Obviously, the instantaneous torque of the SRM was directly controlled by continuously variable phase voltages without including any inner current control loop. Results obtained from computer simulations of the developed MATLAB/Simulink model and the DSP-based real-time control experiments have confirmed the validity and acceptable performance of the proposed scheme. Good step torque responses and good tracking abilities to various torque reference waveforms have been presented.