A bipolar cascaded modular current source converter and its control method

Abstract

The invention discloses a bipolar cascaded modular current source converter and a control method thereof, comprising a front-stage neutral point introduction circuit and a rear-stage modular cascade circuit, the front-stage neutral point introduction circuit The circuit includes two LCL circuits composed of inductors and capacitors, one side of the two LCL circuits is connected to the DC side power grid through the capacitor, and the other side is connected to the input end of the cascaded sub-module, and the two LCL circuits Capacitors are connected in series, and a neutral line is drawn from a neutral point between the two capacitors; the neutral line is connected to the midpoint of a rear-stage modular cascade circuit, thereby realizing bidirectional flow of power. The present invention adopts multiple current source type converter modules to be cascaded to meet the requirements of the withstand voltage level of the DC side. At the same time, a single converter module can be independently controlled, and the work loss can be reduced, and the bidirectional flow of power can be realized. The polarity cascaded modular current source converter can also work in the single-side fault operation state of the DC bus.

Description

technical field [0001] The invention relates to the technical field of converters, in particular to a bipolar cascaded modular current source converter and a control method thereof. Background technique [0002] Traditional converter types are mainly divided into two categories: voltage source converter (Voltage source converter, VSC) and current source converter (Current source converter, CSC). [0003] The traditional voltage source converter can control the active power and reactive power separately, but its power level is generally not high, and it is relatively difficult to suppress the fault current on the DC side. Therefore, the requirement for an additional DC circuit breaker is also Higher and more expensive. The current source converter allows the existence of a short-circuit state, and its operation stability and reliability are better, but its operation loss is also greater and the system efficiency is lower. Generally speaking, in order to improve the DC withs...

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Problems solved by technology

[0003] The traditional voltage source converter can control the active power and reactive power separately, but its power level is generally not high, and it is relatively difficult to suppress the fault current on the DC side. Therefore, the requirement for an additional DC circuit breaker is also Higher and more expensive

The current source converter allows the existence of a short-circuit state, and its operation stability and reliability are better, but its operation loss is also greater and the system efficiency is lower

Generally speaking, in order to improve the DC withstand voltage level of the converter, multiple current source converters are often cascaded. However, when the DC bus unilaterally fails, the cascaded modular current source converter will It will fail to operate, so that the application of current source converters is limited to a certain extent

[0004] In addition, the cascaded converter adopting the bipolar PWM control method, due to the different conduction voltage drop of each sub-module switching device, the delay of the driving signal is not synchronized, the transformation ratio of the transformer is different and the filter parameters (capacitance and inductance ) differences will cause differences in the divided voltage of each sub-module and the amplitude and phase of the output current, and the neutral point voltage of the cascaded converter will also shift accordingly, affecting the stability and reliability of the cascaded converter. The current traditional control algorithm for each sub-module of the cascaded converter can no longer solve the above problems

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