提高电力系统惯性水平的风电场和VSC-HVDC协同控制策略

Coordinated Control of Wind Farms and VSC-HVDC to Improve Inertia Level of Power System

针对海上风电场采用柔性直流输电(voltage source converter based high voltage DC,VSC-HVDC)接入陆上电网的技术方案,提出利用直流电容和风电机组转子动能去模拟同步发电机惯量的协同控制策略。通过网侧换流器直流电压滑差控制,在电网扰动下,直流电容能相应地吸收或释放能量。两端VSC交流系统频率通过风场侧换流器(wind farm VSC,WFVSC)的变频控制实现人工耦合,可以省去两端换流站之间的通信。为响应WFVSC的频率变化,风电机组功率控制器将调整功率指令值,使转子转速相应变化。通过一系列协同控制,海上风电场将参与电力系统频率控制。在允许的风电机组转速和直流电压变化范围内,该协同控制策略可提供大范围的惯量,增加系统稳定性。通过对负荷变化、风速变化和交流系统故障等工况的仿真,验证所提控制策略的有效性。

Based on the technical solution of large-scale offshore wind farm integrating into onshore grid by voltage source converter based HVDC （VSC-HVDC） transmission, this paper proposed a new coordinated control strategy. The strategy used electrical energy stored in HVDC capacitors and kinetic energy stored in wind turbine generator rotors to emulate the inertia of the synchronous generator （SG）. The HVDC link capacitors released or absorbed energy by the proposed droop DC voltage control of the grid side VSC （GSVSC）. No remote communication was needed since the artificial coupling of the frequency of the two-side AC systems was obtained through the variable frequency control of the wind farm VSC （WFVSC）. The rotor speed of the wind turbine generator changed with the power reference of its power controller in response to the frequency change of the WFVSC. As a result, the wind turbine generators were utilized to keep the grid frequency stable. Within the permissible variations of the wind turbine generator rotor speed and the DC voltage, the proposed coordinated control strategy can provide a wide range of inertia time constants, which improves the overall stability of the system. Simulation results of three operation conditions, i.e. sudden load changes, variations of wind speeds, and AC system faults, validate the effectiveness of the proposed control strategy.