A Circular Current Suppression Method for Modular Multilevel Converter

Abstract

The invention relates to a method for suppressing circulating current of a modular multilevel converter, comprising the following steps: S1, obtaining a PCHD model of MMC circulating current based on a single-phase equivalent circuit of MMC and based on a positive definite quadratic energy function; S2, Construct the MMC circulating current suppression passive controller based on the PCHD model; S3, input the double frequency actual value and reference value of the circulating current into the MMC circulating current suppressing passive controller to output the circulating current voltage compensation amount; S4, carry out the calculation of the circulating current voltage compensation amount Carrier phase-shift modulation controls the working state of the IGBTs in the sub-modules of the bridge arms of each phase of the MMC through modulation waves. Compared with the prior art, the present invention is based on the PCHD model and passive control theory, from the perspective of energy, through energy function shaping and control correction system performance, effectively ensuring the asymptotic stability of the MMC circulation system, and the control law form is simple and robust Strong resistance, obvious circulation suppression effect, easy to solve practical engineering problems.

Description

technical field [0001] The invention relates to the control field of modular multilevel converters, in particular to a method for suppressing circulation of modular multilevel converters. Background technique [0002] Modular multilevel converter (MMC) is widely used in large-scale renewable energy grid connection due to its advantages of low harmonic content, low switching loss, strong fault ride-through capability, easy modular expansion and industrial production. field. Taking the three-phase system as an example, such as figure 1 As shown, each phase of MMC includes two upper and lower bridge arms, each bridge arm is composed of N identical sub-modules sm cascaded, and each bridge arm is connected in series with a bridge arm inductance L m and arm resistance R m , the submodule sm includes two IGBTs (S 1 , S 2 ) and two antiparallel diodes (D 1 、D 2 ) and a capacitor C. By controlling the on and off of the two IGBTs through the pulse signal, the output voltage of...

AI Technical Summary

Problems solved by technology

Due to the cutting in and out of each sub-module, it is difficult to achieve a complete balance of the capacitor voltage of the sub-module, causing the voltage imbalance between the bridge arms, and then forming a circulating current between the three phases of the MMC. The existence of the circulating current will make the current peak value and effective value of the bridge arm increase, which will eventually affect the safe and stable operation of the system, so it is necessary to suppress the circulation of MMC

[0003] The traditional MMC circulation suppression method usually adopts the linear control method, which does not change the essence of the MMC nonlinear system, especially when there are internal and external disturbances in the MMC grid connection, the immunity and robustness of the linear control are not good; the existing circulation suppression Although the nonlinear control method can achieve better signal control effects, its calculation process is complicated, and it does not focus on solving the problem of excessive internal loss in the system. There are still deficiencies in energy optimization, which is not conducive to solving practical engineering problems.

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