柔性直流输电系统自适应虚拟惯性调频控制策略

针对传统控制策略下柔性直流输电系统接入交流电网后无法为系统提供惯性以及参与调频的问题,提出了一种考虑频率稳定的自适应虚拟惯性调频控制策略。在直流侧保持下垂特性,自动分配直流功率的同时,使柔性直流输电系统能够参与二次调频,实现交流侧频率的无差调节。另外,通过虚拟惯性控制,进一步提高系统频率稳定性和惯性,改善二次调频控制所引起的暂态波动。针对惯性系数选取受直流电压偏差限制的问题,采用自适应惯性系数,在电压偏差较小时,可以增大惯性系数,得到更好的频率稳定效果,反之则减小惯性系数,防止直流电压越限。在PSCAD环境下搭建了五端柔性直流电网的仿真模型,仿真结果验证了所提控制策略的可行性和有效性。

Frequency Regulation Control Strategy for Flexible DC Transmission System Based on Adaptive Virtual Inertia

In order to solve the problem that the flexible DC transmission system cannot provide inertia for the AC power grid and participate in frequency regulation with the traditional control strategy, this paper proposes a frequency regulation control strategy based on adaptive virtual inertia with consideration of frequency stability. With the proposed control strategy, the flexible DC transmission system can participate in the secondary frequency regulation and realize the zero-error regulation of AC-side frequency, while keeping the droop characteristic of DC side and automatically distributing DC power. In addition, the frequency stability and inertia of the system are further improved through virtual inertia control, and the transient fluctuation caused by secondary frequency regulation control is improved. For the problem that the choice of inertia coefficient is limited by DC voltage deviation, the adaptive inertia coefficient is adopted. When the voltage deviation is small, the inertia coefficient can be increased for better frequency stability effect. On the contrary, the inertia coefficient is reduced to prevent DC voltage from exceeding the limit. The simulation model of a five-terminal flexible DC power grid is built in the PSCAD environment, and the simulation results verify the feasibility and effectiveness of the proposed control strategy.