适用于高压直流输电的组合型基频开关主动换相换流器功率因数控制策略研究

Power factor control method of combined actively commutated converter with switching frequency of 50 Hz for HVDC applications

采用可自关断功率的功率半导体器件主动换相换流器(ACC)相对于传统的电网换相换流器(LCC)能够抑制换相失败的风险,相对于电压源型的模块化多电平换流器(MMC)拓扑简单,无需大量的储能元件,体积小、重量轻,因此,ACC在高压直流输电场合有广泛的应用前景。本文针对由两台ACC直流侧串联、交流侧并联组成的组合型ACC,提出一种开关频率为50 Hz的基频开关高功率因数运行方法。与LCC不同,基频开关ACC的触发时刻不受外部电路条件约束,具备触发角超前和触发角滞后两种工作模式,使得组合型基频开关ACC具备调节有功功率和无功功率的能力,能够工作在高功率因数运行状态。此外,本文分析了基于电网电压定向时ACC的功率传输特性,在此基础上,为了进一步提高网侧功率因数,引入功率因数补偿角对基频开关ACC的触发角进行调整,使组合型基频开关ACC的网侧运行在单位功率因数附近。仿真和实验结果均验证了本文理论分析及所提出的功率因数控制方法的正确性和有效性。

Compared with the line commutated converter(LCC),the actively commutated converter(ACC)that adopts the self-turn-off power semiconductors can suppress the risk of commutation failure,and has the advantages such as simple circuit topology,does not need the large number of energy storage elements,small size,and light weight as compared with the voltage source modular multilevel converter(MMC).ACC has a wide application prospect in HVDC transmission.In this paper,a high-power factor operation method is proposed for the combined ACC with switching frequency of 50 Hz that is composed of two ACC’s DC side in series and AC side in parallel.Different from LCC,the trigger time of the ACC with switching frequency of 50 Hz is not constrained by external circuit conditions.It has two working modes:trigger angle lead and trigger angle lag,so that the combined ACC with switching frequency of 50 Hz has the ability to adjust active and reactive power and can work in high power factor operation state.In addition,this paper analyzes the power transmission characteristics of ACC based on grid voltage orientation.On this basis,the power factor compensation angle is introduced to adjust the trigger angle of the combined ACC with switching frequency of 50 Hz,so that it operates near the grid side unit power factor.The simulation and experimental results verify the correctness and effectiveness of the theoretical analysis and the proposed power factor control method.