Carrier offset-based control method for mid-point voltage balance of multilevel inverter

Abstract

The invention discloses a carrier offset-based control method for the mid-point voltage balance of a multilevel inverter. The method comprises the following steps: detecting a capacitance transient voltage between the midpoint and the anode and a capacitance transient voltage between the midpoint and the cathode of a direct-current bus of the multilevel inverter by a sampling unit of a digital processing control module, and determining the bias of the two capacitance transient voltages; regulating the carrier offset of the current moment through a carrier offset control regulating unit; outputting a control regulating signal of the carrier offset control regulating unit to an SVPWM (space vector pulse width modulation) vector control unit; outputting a PWM signal through a drive circuit to control the working condition of the multilevel inverter, and meanwhile, controlling the mid-point voltage balance of a multilevel inverter. According to the carrier offset-based control method disclosed by the invention, on the basis that an original SVPWM control method is kept, the mid-point voltage balance is controlled only by changing the carrier offset without increasing the complexity of the control method, so that output voltage and current harmonics can be reduced, and the output waveform quality is increased. The carrier offset-based control method has the advantages that the real-time performance is good, the processing procedure is simple and realization is easy.

Description

technical field [0001] The invention belongs to the technical field of control in power electronic conversion technology, in particular to a carrier bias-based midpoint voltage balance control method of a multi-level inverter. Background technique [0002] Multi-level inverters have the advantages of low withstand voltage level of switching devices, high equivalent switching frequency and small output waveform harmonics, so they are widely used in medium-high voltage and high-power conversion occasions. Whether it is a neutral-point clamped inverter or a T-type inverter, there is a problem of unbalanced neutral point voltage, which is a common problem. The unbalanced midpoint voltage of the multilevel inverter will increase the harmonics of the output voltage of the system and affect the quality of the output waveform. At present, there are two main software control strategies for neutral point voltage balance. One is based on the carrier-based sinusoidal pulse width modula...

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When the synthetic space vector is in different sectors in the vector distribution diagram, and in different triangular areas, the formula for calculating the distribution factor is

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