A kind of three-level anpc converter neutral point voltage balance control method

Abstract

The invention relates to a method for controlling midpoint voltage balance of a three-level ANPC converter, comprising the following steps: (1), adopting a SVPWM pulse sequence to act on the three-level ANPC converter; (2), detecting the DC side capacitance of the converter in real time Voltage, get the midpoint voltage value, and compare it with the midpoint voltage reference value to determine whether the DC side capacitor needs to be charged or discharged; (3), real-time detection of the positive and negative of the three-phase load current of the converter; (4), comprehensive steps ( 2) and the detection value of step (3), dynamically adjust the duty ratio of the zero state of the switching sequence to the three-phase bridge arm in each switching cycle until the midpoint voltage is balanced, and repeat this process to maintain the midpoint voltage fluctuate within a small range. The invention can dynamically adjust the charging and discharging time of the capacitor according to the direction of the three-phase load current and the magnitude of the midpoint voltage, so that the midpoint voltage can quickly reach a balance and maintain a fluctuation within a small range.

Description

technical field [0001] The invention relates to a control strategy of a three-level converter, in particular to a midpoint voltage balance control method of a three-level ANPC converter. Background technique [0002] With the advancement of technology and the improvement of living standards, people's requirements for power quality are also constantly improving. The emergence of active neutral-point-clamped (ANPC) topology makes up for the diode-clamped topology and capacitor The shortcomings of the clamping topology are better suited for 6KV and 10kV high-voltage frequency conversion fields. ANPC multi-level converters are increasingly being used in fields such as industry and social life to provide better quality electric energy. At present, although it is common to use the SVPWM modulation method to act on the three-level ANPC converter at home and abroad, the method of controlling the midpoint voltage balance when using the SVPWM modulation method to act on the three-lev...

AI Technical Summary

Problems solved by technology

One of the prerequisites for the normal operation of three-level and above ANPC topologies is that the midpoint voltage must be balanced. During SVPWM control, if the key issue of midpoint voltage balance is not considered, the midpoint voltage will be relatively large during SVPWM control. The fluctuation of the output voltage will lead to the increase of the harmonics of the output voltage and the asymmetry of the three-phase output. In severe cases, the switching devices and filter capacitors will be damaged, which will lose practical significance.

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