Development of a control algorithm for the three-phase inverter of the two-phase electric drive for reducing the number of switching elements

Abstract

High overload capacity and ability to control speed in a wide range are important requirements for modern electric drives. Introduction of a low-power adjustable two-phase electric drive with these properties into me-chanical devices is limited by the frequency converter function to convert a three-phase network into a two-phase one when the unit power of such mechanisms increases. Previous studies have shown that it is possible to use a standard frequency converter with a three-phase bridge voltage inverter applying a new control algorithm based on space-vector PWM. When PWM is used, the switching frequency of the key inverter elements remains quite high, strictly specified, non-amenable to reduction without degrading the harmonic composition. The goal of this work is to develop an algorithm for two-phase electric drive control that would reduce the number of switching operations of the switch elements of a three-phase inverter with-out increasing the deviations of the instantaneous values of the phase currents from the reference sine curve. The study employed provisions of the theory of automatic control, the theory of electric drive and methods of mathematical modeling. The simulation object was the control system of a two-phase motor; the elements of the Matlab Simulink software package were used. An algorithm has been proposed for operating a three-phase inverter of a two-phase electric drive system. The difference of the algorithm from the well-known control system of a standard bridge inverter with space vector PWM consists in using phase current control relays and dividing the period of sinusoidal phase currents into four sections ensuring a decrease in the number of switching operations of the inverter switch elements when the maximum instantaneous deviations of current values from a sinusoidal reference are equal, the starting torque of the motor is stabilized and the speed control is smooth. The results show that with an equal maximum deviation of the instantaneous current values from a given sinusoidal value, the number of switching operations of the inverter switch elements in the proposed system is smaller than in the known analogues. The electric drive system ensures the start of a two-phase motor with stabilization of the starting torque under increased load. The considered system of variable frequency control with current control relays can be used for two-phase electric drives of mechanical devices and household electric appliances and is promising as a substitute for less cost-effective single-phase and capacitor motors.