Control method for three-level neutral-point potential balance zone verification and correction based on zero sequence voltage injection

Abstract

The invention discloses a control method for three-level neutral-point potential balance zone verification and correction based on zero sequence voltage injection, and the method comprises the steps: measuring a voltage across two ends of an upper DC capacitor and a voltage across two ends of a lower DC capacitor in each control period, and calculating the voltage bias; calculating a mean neutral current according to the DC voltage bias of the upper and lower capacitors; pre-estimating a zero sequence voltage v0; carrying out the verification and correction of a pre-estimated calculation result: limiting an output result. The method adds a verification-correction link, carries out the analysis and verification according to a calculation result, and finally corrects a control instruction. The method reflects the essence of a problem of neutral point potential fluctuation, is suitable for a carrier modulation mode, and also suitable for an SVM method.

Description

Technical field: [0001] The invention belongs to the field of power electronics, and relates to a diode-clamped three-level inverter midpoint potential balance control method, a three-level midpoint potential balance control method based on zero-sequence voltage injection, and a method of estimation-verification-correction , to ensure real-time and accurate calculation results. This method is applicable to inverters whose main circuit structure adopts a diode-clamped three-level topology, such as frequency converters, PWM rectifiers, active power filters and other equipment. Background technique: [0002] In recent years, the application of multilevel converters has become more and more extensive, and the three-level neutral point clamped inverter is one of the most mature researched and applied multilevel inverter structures. The three-level converter needs Using the positive and negative current topology, the DC side midpoint potential balance control of this topology has...

AI Technical Summary

Problems solved by technology

However, due to the complexity of the space vector, the complexity of the control is greatly increased, and this method is only limited to the application in the SVM method

[0003] Patent CN 103138591 B proposes the idea of ​​analyzing the midpoint potential fluctuation problem from the perspective of zero sequence voltage in carrier modulation, and performs integral control processing on the deviation by detecting the direction of the output current and the voltage deviation on the midpoint of the three-level converter , generate the control amount, and fine-tune the three-level carrier signal. Since this method does not take into account the influence of the zero-sequence voltage on the reference voltage, it is only a qualitative and inaccurate adjustment control of the voltage deviation, and it lacks the essence of the midpoint potential fluctuation problem. cognition

[0004] Patent CN 101753044 B proposes a method of injecting zero-sequence components and taking the switching period as the control period to control the midpoint potential balance of the three-level diode-clamped inverter, because in actual situations, the midpoint shift of the DC side will not be very large , that is, the DC component of the midpoint current that needs to be injected or extracted will not be very large, so in this patent, the fundamental wave cycle is only divided into 6 sectors according to the zero-crossing points of the three-phase positive sequence output voltage, ignoring the injected zero sequence and only considering The interval division of the positive sequence component is defined, but after the zero-sequence component is injected into the command voltage, the division of the interval will be offset. If the injected zero-sequence component reaches a certain amount, the number of zero-crossing points will increase.

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