SPACE VECTOR PWM IN A MULTILEVEL VOLTAGE CONVERTER

Abstract

The present article considers the voltage forming by multilevel converters. Multilevel converters are widely used in industry applications with medium voltages up to 20 kV. An example is the oil industry, where multilevel converters are installed in electric drives of pumping units on pipeline systems. The location of the pipelines in isolated areas implies weak net connections for power system and expects increased requirements for the efficiency of the use of electricity. In this regard, for a multilevel voltage converter, an energy-efficient vector method of pulse-width modulation is proposed. With vector pulse-width modulation, the optimal number of voltage level switching occurs in the phases of the converter, which leads to the lowest harmonic distortion of the voltage, compared with other modulation methods. The features of vector pulse-width modulation in multilevel voltage converters caused by the increased number of basic voltage vectors of a static multilevel converter are analyzed. A step-by-step method of vector pulse-width modulation in a multilevel converter is proposed, including determining the base vectors of the converter closest to a reference voltage vector, calculating the time for each of the base vectors, maintaining the switching order between the base vectors. The method is considered in detail for a multilevel converter with five voltage levels in a phase. In conclusion, the results of modeling control system of this converter with the proposed method of vector pulse-width modulation are presented. According to the obtained time diagrams of voltage formation, a hodograph of the resulting vector of the output voltage of a multilevel static converter was constructed.