Increasing the Utilization Factor of an Autonomous Inverter under Space Vector Control

Abstract

Control systems for ac electric drive frequency converters are based on pulse width modulation (PWM) algorithms. Their use leads to problems: significant output voltage and current distortion, the appearance of shaft torque pulsation and its rotation frequency, and, as a result, an increase in vibrations and noise of the drive motor. Semiconductor PMW converters are also characterized by underutilized voltage. The solution to these problems is possible through applying space vector modulation (SVM) algorithms, however the voltage efficiency remains at the PWM level. To solve these problems, it is reasonable to use modified SVM algorithms that will provide semiconductor converter operation in the overmodulation mode. This article considers the development of overmodulation algorithms, the application of which will solve these problems. The following developed algorithms for the overmodulation of spatial vector control systems are presented: an alternating active overmodulation algorithm, adaptive overmodulation algorithm, and synchronous overmodulation algorithm. Their mathematical formulation is given. It is shown that overmodulation algorithms provide an increased voltage utilization factor of the autonomous inverter. When using the developed overmodulation algorithms, the output current of the autonomous inverter has a quasi-sinusoidal shape. The minimum autonomous inverter output current distortion coefficient is provided when using the synchronous overmodulation algorithm at a level of no more than 10%. The switching frequency of the autonomous inverter becomes lower, which leads to reduced switching losses. It is shown that the use of overmodulation algorithms is feasible and provides higher values of such indicators of electric energy conversion efficiency as: output current and voltage distortion coefficients, voltage utilization factor of the autonomous inverter, amplitude of the fundamental harmonic at the same value of the space vector modulation period and switching frequency.