Development of a control strategy for variable frequency operation of a three phase buck-boost inverter

Abstract

The thesis proposes and analyzes a control strategy for three different scheme of Buck-Boost Inverter. Three different single-phase inverters based on two-quadrant Buck-Boost DC-DC Converter topology were proposed and analyzed for differentially connected load with modified delta modulation control strategy. The proposed single-phase inverter schemes were adopted for three phase operation by connecting the two-quadrant DC-DC Buck-Boost Converter with differentially connected load in delta or Y arrangement which were controlled by three individual modified delta modulators for each of the phases. A modified voltage controlled quadrature oscillator circuit was introduced and developed in order to generate and control the reference signal of the individual delta modulator for three-phase inverter operation. The three control signal were generated by converting the two 900 phase shifted output of the voltage controlled quadrature oscillator into three individual 1200 phase shifted outputs by vector addition. Delta Modulation output pulse train variation was investigated by changing different parameters of the proposed delta modulation scheme. Three-phase Buck-Boost Inverters were also investigated with the proposed control strategy for variable operating condition for three different schemes with load connected in delta and Y arrangement. Received output wave-shapes were nearly sinusoidal for a certain range of operation.