MMC电容电压开环预估及控制新方法

New Methods for Estimation and Control on MMC Capacitor Voltage Open-loop

对模块化多电平变换器(modular multilevel converter,MMC)的电容电压纹波进行了分析。针对开环调制中电容电压预估方法中含有积分环节,考虑估计所需电压电流信号中的谐波成分和干扰信号,直接积分运算受到影响,且存在积分初值选取和积分饱和等问题,提出两种改进的电容电压预估方法,即基于二阶广义积分的电容电压预估和基于双同步参考坐标系的电容电压预估方法。采用二阶广义积分器对输入的信号进行滤波,且不会对特定频率的信号幅值产生影响,可提高电容电压预估的准确性。在二倍频同步参考坐标系和基频同步参考坐标系上分别对上下桥臂电容电压之和与之差进行估计,避免了电容电压估计中的积分环节,适用于同步参考坐标系控制下的电压估计。最后,在PSCAD/EMTDC环境中搭建的MMC仿真模型验证了所提方法的正确性和有效性。

This paper analyzes ripple wave of capacitor voltage of modular multilevel converter （MMC）. In allusion to problems such as integration element in capacitor voltage estimate （CVE） in open-loop modulation, consideration of harmonic and interference signals in voltage current signals, direct integral operation being affected, selection for integration initial value and integral saturation, and so on, two kinds of improved estimation methods for capacitor voltage are presented, one is CVE based on the second order generalized integral （SOGI-CVE） and the other is based on double synchronous reference frame （DSRF-CVE）. It will not affect signal amplitude of specific frequency by using the second order integrator to filter input signals and can improve veracity of CVE. It can also avoid integration element in CVE by estimating sum or difference of capacitor voltage of the upper and lower bridge arms on the second harmonic frequency synchronous reference frame and fundamental frequency synchronous reference frame, which is suitable for voltage estimation under the control of synchronous reference frame. In PSCAD/EMTDC environment, a MMC simulation model is established to verify validity and effectiveness of proposed methods.