基于ACC的海上风电场高压直流输电系统控制策略

Control Strategy of Offshore Wind Farm HVDC Transmission System Based on Actively Commutated Converter

高压直流(high voltage direct current,HVDC)输电技术相对于高压交流(high voltage alternating current,HVAC)输电技术具有线路损耗低、输电走廊占地少、不存在交流电网同步问题等突出优势,特别适用于大容量、长距离、高效率的电能输送场合.相较于传统的电网换相换流器(line commutated converter,LCC)和以模块化多电平换流器(modular multi-level converter,MMC)为典型代表的电压源型换流器(voltage source converter,VSC),主动换相换流器(actively commutated converter,ACC)具有电路拓扑简单、功率因数可控、不存在换相失败风险、具备黑启动的能力、直流侧无需配置储能电容等优点,在高压直流输电领域尤其是海上风电汇集等场合有广泛的应用前景.本文提出了一种大陆端和离岸端换流站均选用ACC作为换流器的海上风电场背靠背高压直流输电系统,大陆端换流站采用开关频率为50 Hz的高功率因数运行的工作模式,离岸端换流器选取脉冲宽度调制(pulse width module,PWM)的工作模式,并分别建立了大陆端换流站和离岸端换流站的数学模型,分析了基于ACC的海上风电场高压直流输电系统的黑启动方法和稳态功率传输特性,并提出了一种大陆端换流站采用直流电流控制、离岸端换流站选取交流侧电压控制的控制策略.在PSCAD/EMTDC中搭建了500 kV/1000MW的基于ACC的海上风电场背靠背高压直流输电系统仿真模型,仿真结果验证了本文理论分析以及所提出控制策略的正确性和有效性.

Different from high voltage alternating current transmission,high voltage direct current(HVDC)technology has advantages such as low line loss,reduced transmission corridor floor space,and no AC grid synchronization problem.It is especially suitable for large capacity,long distance,and high efficiency power transmission systems.Compared with the traditional line commutated converter and the voltage source converter represented by the modular multilevel converter,the actively commutated converter(ACC)has advantages,including simple circuit topology,a controllable power factor,no risk of commutation failure,black start capability,and no need to configure the energy storage capacitor on the DC side.It has wide applicability in the field of HVDC transmission,especially in offshore wind power gathering and other applications.In this paper,a back-to-back HVDC transmission system for offshore wind farm is proposed,in which ACC is selected as the converter in both the mainland and offshore converter stations.The mainland converter station adopts the high power factor operation mode with the switching frequency of 50 Hz,and the offshore converter adopts the pulse width module mode.The mathematical models of the mainland converter station and the offshore end are established,and the black start method and steady-state power transmission characteristics are analyzed.A control strategy for DC current control of the converter station at the land end and AC voltage control of the converter station at the offshore end is proposed.A 500 kV/1000MW simulation model based on ACC offshore wind farm back-to-back HVDC transmission system is built in PSCAD/EMTDC.The simulation results verify the correctness and effectiveness of the theoretical analysis and the proposed control strategy.