A Direct Control Method of Bridge Arm Instantaneous Current in Modular Multilevel Converter

Abstract

The invention relates to a bridge arm instantaneous current direct control method of a modular multilevel converter and belongs to the field of a power electronic equipment control technology. The method comprises the following steps: data required by control is acquired and obtained; a bridge arm current reference value is calculated by the use of each obtained current reference value; a bridge arm induction voltage reference value is calculated by the use of a bridge arm inductance value, a control cycle, the calculated bridge arm current reference value and a measured bridge arm current value; a bridge arm output voltage reference value is calculated by the use of an obtained AC port voltage reference value, a DC port voltage reference value and the obtained bridge arm induction voltage reference value; each bridge arm modulation reference wave is calculated by the use of the calculated bridge arm output voltage reference value and measured bridge arm total capacitor voltage; and the generated modulation reference wave is sent to a valve trigger pulse modulator so as to directly control bridge arm instantaneous current. The method has fast control response speed and is not influenced by the transient process. By the method, it is guaranteed that bridge arm overcurrent will not happen to a converter and capacitor overvoltage also will not happen.

Description

technical field [0001] The invention belongs to the technical field of power electronic device control, and in particular relates to a method for directly controlling instantaneous current of a bridge arm of a modularized multilevel converter. 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 one of the most potential applications in the field of flexible DC transmission. Voltage source converter topology. [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 relatively stable ...

AI Technical Summary

Problems solved by technology

In the steady state, the quantities in the dq coordinate system are all DC quantities, and it is easy to obtain a better control effect; but in the transient process or the three-phase asymmetry, the quantities in the dq coordinate system will also appear AC components, resulting in a decline in the control effect

In addition, the dq decoupling control of the internal circulating current can usually only suppress the circulating current of a specific sequence component of a specific frequency (usually choose to suppress the negative sequence component of double frequency), but cannot achieve complete control of the circulating current, so that in transient or non-current Under symmetrical conditions, the dynamic process of the total capacitor voltage of each bridge arm is in an uncontrolled state, which may easily lead to the limitation of the power output capability of the converter or even stop the operation due to overvoltage / overcurrent

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