Voltage balance method between bridge arms of modular multilevel converter based on peak prediction

Abstract

The invention discloses a peak-prediction-based method for balancing voltage between modularization multi-level current converter bridge arms, and belongs to the technical field of power electronic device control. The method comprises the steps that the phase position of the equivalent voltage connected to a reactance valve side and the phase position of the bridge arm voltage are calculated when the equivalent voltage and the bridge arm voltage have the maximum value, the maximum value of the voltage fluctuation of each bridge arm is predicted, and the effective value of the interphase balance current and the effective values of the balance current of the upper and lower bridge arms of each phase are respectively calculated according to the predicted maximum value; according to the fundamental wave phase position of the equivalent voltage on the valve side and the proposed formula, coordinate transformation is conducted on the interphase balance current and the balance current of the upper and lower bridge arms in each phase, and a balance current instantaneous value instruction with the format being circular current inside a current converter is obtained. According to the peak-prediction-based method for balancing the voltage between the modularization multi-level current converter bridge arms, the response speed of a bridge arm voltage balance controller can be increased, the fluctuation peak can be directly controlled, capacitance overvoltage can be better avoided, and no influences on external characteristics of the current converter are produced.

Description

technical field [0001] The invention belongs to the technical field of power electronic device control, and in particular relates to a method for balancing voltage between bridge arms of a modular multilevel converter based on peak value prediction. Background technique [0002] Modular Multilevel Converter (MMC) has the characteristics of easy expansion, decoupling control of active and reactive power, excellent harmonic characteristics, and low loss of switching devices. It is the most widely used in the field of flexible direct current transmission. Potential Voltage Source Converter Topologies. [0003] The main circuit of the modular multilevel converter is as follows: figure 1 shown. This converter consists of six bridge arms, each of which contains a bridge arm inductance L arm And a set of submodules, as shown in the dotted box in the figure. Each sub-module in the bridge arm has a capacitor and several power electronic switches. This capacitor maintains a relati...

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Problems solved by technology

The main problem of the first type of method is that the dynamic process of rebalancing the bridge arm voltage is uncontrollable, and there is a possibility of overcurrent or overvoltage

However, most of the second-type methods currently proposed are based on cycle averaging and independent control of each phase. Cycle averaging (or other filtering methods) can eliminate the interference of the normal fundamental frequency fluctuation of the capacitor voltage on the calculation of the balance current, but it will lead to a balance The response speed of the controller slows down; at the same time, the independent control of each phase may cause the sum of the final balance current commands of the three phases to be non-zero, causing the current component used for balance to flow out of the converter, which affects the external characteristics of the converter. The effect of the balancing process

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