LCC-MMC混合多端直流输电系统的潮流计算和机电暂态建模方法

Methods for Power Flow Calculation and Electro-mechanical Transient Modeling of LCC-MMC Hybrid Multi-terminal HVDC System

为实现含混合直流输电系统的大规模交直流电力系统暂态稳定计算,提出了电网换相换流器–模块化多电平换流器(LCC-MMC)型混合多端直流输电系统的潮流计算和机电暂态建模方法。首先分析了混合直流输电系统机电建模的总体思路,然后分别建立了LCC/MMC的交直流侧等效电路模型;与MMC直流侧的传统等效电路模型不同,采用了二阶微分方程描述的MMC直流侧等效电路来构建混合直流系统的机电暂态模型。此外,提出了一种考虑LCC触发角约束条件的混合多端直流输电系统交替迭代潮流计算方法。最后在机电暂态仿真平台PSS/E里实现了LCC-MMC型混合多端直流输电系统的潮流计算和机电暂态仿真,并将模型应用到南方电网的算例中。仿真计算表明:所提出的混合直流系统交替迭代潮流计算方法确保了系统模型初始化的可靠性;所建立的混合直流系统机电暂态模型和详细电磁暂态模型的阶跃响应特性基本一致;含乌东德三端混合直流系统的南方电网算例表明,在相对严重的受端换流母线三相短路故障下,送端系统在故障清除后能够恢复稳定运行。因此,所提出的混合多端直流输电系统潮流计算和机电暂态建模方法能够满足大规模交直流电力系统的暂态稳定计算。

To realize the transient stability calculation of large-scale AC/DC power systems including hybrid HVDC transmission systems,we proposed methods for power flow calculation and electro-mechanical transient modeling of line commutated converter-modular multilevel converter(LCC-MMC)based hybrid multi-terminal HVDC system.Firstly,the general idea of modeling the LCC-MMC hybrid multi-terminal HVDC system was analyzed,then the AC-side and DC-side equivalent circuits of the LCC/MMC were established.Different from the traditional DC-side equivalent circuit of MMC,the second-order differential equations describing the MMC DC-side circuit was used to construct the electro-mechanical transient model of the hybrid HVDC system.Besides,taking the firing angle limit of the LCC into account,we proposed a sequential power flow algorithm for a hybrid multi-terminal HVDC system.Finally,the power flow calculation and electro-mechanical simulation of the LCC-MMC hybrid HVDC system were implemented in electro-mechanical simulation platform PSS/E,and the model was applied to the case of China Southen Power Grid.The simulation and calculation results show that the proposed method can be used to ensure the reliability of system model initialization;and the step response characteristics of the electro-mechanical model and the detailed electromagnetic model are basically the same;the simulation in China Southen Power Grid embedded with Wudongde three-terminal hybrid HVDC system shows that,under the relatively serious three-phase short-circuit fault on the converter bus of the receiving-end system,the sending-end system can resume stable operation after the fault is cleared.Therefore,the power flow calculation and electro-mechanical transient modeling methods proposed in this paper can satisfy the transient stability calculation of large-scale AC/DC power systems.