弱电网下电压源型逆变器多机系统交互影响及失稳机理研究

Study on Interaction and Instability Mechanism of Multi-VSC Parallel System in Weak Grid

在高比例可再生能源并网的背景下,新型电力系统的建设和安全高效运行与大规模并网逆变器的动态特性密切相关。目前针对电压源型逆变器并网系统的研究大多将多机系统视为单机系统展开分析,实际上,电压源型逆变器多机间存在着交互作用且不容忽视,因此该文对多机系统展开了研究。该文从外环控制的角度出发,建立了电压源型逆变器单、双机系统小信号模型,采用特征值分析、参与因子理论和电磁暂态仿真分析相结合的方式,对比分析了定功率因数控制、混合控制策略、交流侧恒定电压控制3种不同外环控制策略对双机系统的影响,揭示了定功率因数控制的失稳机理。研究的结果和结论表明:电压源型逆变器多机系统采用混合控制策略并网更有利于功率向外输送;交流侧恒定电压控制方式的响应速度主要受到有功控制环节积分增益的影响;定功率因数控制受限于无功调节能力不足和控制环节的延时,在弱电网下稳定性较差。

Under the background of high proportion of renewable energy,the construction and safe operation of novel power system are closely related to the dynamic characteristics of large-scale grid-connected inverters.At present,most of the researches on voltage source converter(VSC)grid connected system take the multi-VSCs system as a single machine system.In fact,there is interaction between multi-VSCs and it can not be ignored.Therefore,this paper studies the multi-VSCs system.From the point of view of VSC’s outer loop,this paper establishes the small signal model of VSC single machine and dual machine systems.By using the combination of eigenvalue analysis,participation factor theory and electromagnetic transient simulation analysis,the influence of three different outer loop control strategies,namely constant power factor control,hybrid control strategy and alternating current(AC)side constant voltage control,on dual machine systems is analyzed and compared,and the instability mechanism of constant power factor control is revealed.The results and conclusions show that the hybrid control strategy of multi-VSCs system is more conducive to power outward transmission.The response speed of AC-side constant voltage control mode is mainly affected by the integral gain of active power control loop;the constant power factor control is limited by the insufficient reactive power regulation ability and the delay of the control loop,and its stability is poor under the weak grid.