并联混合直流输电系统中传统直流和柔性直流暂态无功协调控制策略研究

Coordinated Reactive Power Control Approach for LCC-HVDC and VSC-HVDC in Hybrid Parallel HVDC System

针对电网换相换流器的高压直流输电系统(line commutated converter high voltage direct current,LCCHVDC)易于发生换相失败的缺点及柔性直流输电(voltage source converter based high voltage direct current,VSCHVDC)具有的有功无功快速独立控制的优点,为了充分发挥VSC-HVDC提高LCC-HVDC抵御换相失败能力的作用,提出了适用于并联混合直流输电系统的基于逆变器关断角γ的暂态无功协调控制策略。将故障时根据γ角得出的无功功率补偿值附加至柔性直流换流器外环无功控制环节,调节柔性直流换流器发出的无功功率,在故障时降低LCC-HVDC的直流电流增加量或调节换流母线电压,达到提高LCC-HVDC换相失败抵御能力的目的。在PSCAD/EMTDC仿真环境中搭建了并联混合双馈入直流输电系统模型,从换相失败免疫性指标(commutation failure immunity index,CFII)的角度研究了不同强度交流系统下基于γ角的暂态无功协调控制策略对LCC-HVDC抵御换相失败能力的影响。结果表明,基于γ角的暂态无功协调控制策略可以显著提高LCC-HVDC抵御换相失败的能力。

To reduce commutation failure risk of line commutated converter HVDC （LCC-HVDC） with flexible control of voltage source converter based HVDC （VSC-HVDC）, this paper proposes a coordinated reactive-power control strategy based on extinction angle γ for parallel hybrid HVDC system. Based on reactive power γ compensation, VSC-HVDC adjusts reactive power with outer control loop. Consequently, LCC-HVDC ability to resist commutation failure is enhanced by limiting DC current or adjusting busbar AC voltage. Based on hybrid parallel dual-infeed HVDC model in PSCAD/EMTDC, impacts of the proposed coordinated γ-based control approach on commutation failure immunity of LCC-HVDC are investigated based on commutation failure immunity index （CFII）. Simulation results indicate that the proposed strategy can effectively reduce LCC-HVDC commutation failure risk.