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

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 xycurrent 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.

Automated summary

This article presents a sensorless PTC algorithm for a five-phase IM drive, incorporating an adaptive full observer to estimate key parameters and eliminate CMV and xy current harmonics. The proposed algorithm outperforms the conventional PTC algorithm by using synthetic voltage vectors to reduce computational burden and implementing a hysteresis torque comparator to significantly reduce torque ripple.