A Specific Harmonic Suppression Method for Current Source Converter at Very Low Switching Frequency

Abstract

The invention discloses a method for suppressing specific harmonics of a current source converter under extremely low switching frequency. The combined new hybrid modulation method actively controls the 5th and 7th harmonic components in the output PWM current, and actively compensates the 5th and 7th harmonic components in the line current. This control strategy enables the high-power current source converter to have the ability to actively compensate the 5th and 7th harmonics at the same time at extremely low switching frequency, and can effectively reduce the low-order harmonics of the line current in the case of grid voltage distortion. It greatly improves the line current power quality of the system and ensures the safe and stable operation of the system.

Description

technical field [0001] The invention relates to power quality control of a grid-connected converter, in particular to a method for suppressing specific harmonics of a current source converter at an extremely low switching frequency. Background technique [0002] In recent years, with the increasingly prominent energy problems and the increasing requirements of industrial production processes, medium-voltage high-power converters have become a common technical solution in many industries such as electric power, metallurgy, and transportation as a means of energy conservation and emission reduction. According to the difference in the energy storage link of the DC side, the converter is divided into a voltage source converter (VSC) and a current source converter (CSC). Although in the current medium-voltage high-power transmission system, VSC occupies a dominant position due to its high efficiency and the advantages of power switching devices, CSC, as one of the solutions for h...

AI Technical Summary

Problems solved by technology

However, since the switching angle of specific harmonic cancellation modulation needs to be calculated offline, although the switching angles with different harmonic content can be calculated in advance and stored in the controller, if you want to control multiple harmonic components at the same time, it will lead to Exponential increase in required memory

According to the memory size of the existing controller, the asymmetric specific harmonic elimination method can only control a specific harmonic component, and cannot control more than two harmonic components at the same time

However, since the cut-off frequency of the AC side filter of a high-power current source converter is generally 200-350 Hz, the 5th and 7th harmonics in the line current have the risk of being amplified, and it is still impossible to compensate only a specific harmonic component. Meet the requirements in the actual system

[0004] In addition, the proposal of the bypass pulse injection method also solves the inherent problem that the traditional specific harmonic cancellation modulation method has no adjustable degree of freedom from another perspective.

However, based on the current existing technology, the degree of freedom added by the bypass pulse injection method is only used for DC current control [2] or parallel current source current sharing control [3], and is not used to compensate specific harmonics

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