Speed Sensor-Less Predictive Torque Control for Five-Phase Induction Motor Drive Using Synthetic Voltage Vectors

Abstract

The predictive torque control (PTC) is researched extensively for control of electrical drives because of its fast-dynamic response and robust control. In multiphase motors, it is mandatory to design a multiobjective cost function with more than two terms for controlling xy-subspace current and common-mode voltage (CMV). However, selecting the weighting factor for multiple control variables is time penalizing and increases the computational burden. Using a noisy speed input from the speed sensor in the prediction model reduces the steady-state performance in terms of higher torque ripple, flux ripple, and phase current total harmonic distortion (THD), especially during low speeds. In this article, PTC for a five-phase induction motor (IM) drive without speed sensor [sensorless PTC (PTC-S)] is presented. The adaptive full observer is incorporated to estimate the stator flux, stator resistance, and rotor speed. The proposed algorithm is capable to eliminate CMV and xy-current harmonics having advantages over the conventional PTC (PTC-C) algorithm. The elimination of CMV is achieved by the selection of set of voltage vectors from available 243 voltage vectors. The proposed speed sensor-less control is implemented with a three-level neutral-point clamped (NPC) inverter using synthetic voltage vectors. The use of a synthetic voltage vector eliminates the xy-subspace current and reduces the computational burden. The PTC-S is implemented with a seven-level hysteresis torque comparator, which reduces the torque ripple significantly. To further improve the effectiveness of the control algorithm, two-step delay compensation is implemented. The discussed algorithms are tested on a laboratory prototype for experimental evaluation. The proposed study also highlights the effect of torque ripple reduction on the speed adaptive flux observer for sensor-less operation. The experimental results show the effectiveness and applicability by comparing the steady-state and dynamic performances of PTC.