含无功电流注入的光伏低电压穿越策略研究

Low voltage ride through strategy with reactive current injection for grid connected photovoltaic system

针对光伏系统低电压穿越问题,为保证光伏在一定时间内不脱网连续运行且向电网提供无功电流,对光伏并网逆变器控制策略进行了研究。在考虑逆变器电流限制的情况下,提出了一种根据电压跌落情况向电网注入无功电流的低电压穿越策略。该策略在电压跌落不严重情况下,保持光伏有功功率输出不变,尽量提供无功功率;在电压跌落较严重情况下,光伏不输出有功功率,全部输出无功功率。同时在电网不对称故障下,引入了负序控制消除由负序分量引起的有功功率波动,并推导出了最大无功功率设定值计算公式。在PSCAD仿真环境下,验证了控制策略的合理性和有效性。研究结果表明,该控制策略能根据电压跌落情况充分利用光伏对有功功率和无功功率的控制能力,在一定情况下保证有功功率输出又能最大限度地提供无功功率,有助于并网点电压的恢复。

Aiming at solving voltage ride through problem of photovoltaic system,ensuring grid-connected operation within a certain time as well as providing reactive current,the control strategy of the inverter for Grid Connected Photovoltaic System was studied. Considering the limitation for electric current of inverter,a low voltage ride-through strategy injected with reactive current in accordance with voltage dropping condition was put forward. On condition of slight voltage sag,this strategy maintains the output of photovoltaic active power to supply reactive power as much as possible. On condition of severe voltage sag,the output was completely reactive power instead of active power. If the power grid was in asymmetrical faults,negative sequence control was adopted to eliminate the fluctuation of active power so as to deduce the setting value of maximum reactive power. It was verified that the controlling strategy was rational and effective by PSACD. The results indicate that this controlling strategy can fully utilize photovoltaic inverter to ensure the output of active power and to provide reactive power support in certain cases,which can help the restoration of voltage in power network.