兼顾功率协调控制的两级式光伏逆变器低电压穿越控制策略

Control Strategy Considering Power Coordinated Control for Low-Voltage Ride Through Two-Stage PV Inverter

为提高基于Boost电路的两级式光伏逆变器的低电压穿越(LVRT)能力,设计了以基于Boost的直流母线电压控制环为核心的兼顾有功、无功电流协调控制的LVRT策略.首先分析了两级式光伏逆变器的常规Boost电压控制模式和输出电流控制策略;在电网电压跌落时,通过引入基于故障前光伏阵列最大功率点电压前馈的母线电压控制外环改变Boost电压控制模式来快速调节光伏阵列的输出功率,以稳定直流母线电压和防止逆变器过流;同时,根据电压跌落深度,按比例减小有功电流id,在保证逆变器不过流的前提下输出无功电流iq,为电网提供无功支撑,以帮助电网故障恢复.最后,利用PSCAD/EMTDC仿真软件搭建100 k W两级式光伏逆变器模型进行控制策略验证,结果表明该策略不仅在电压发生深度跌落时仍能快速、有效地抑制直流母线电压升高,使光伏逆变器安全地实现低电压穿越,而且提高了其在电网故障期间的无功支撑能力.

In order to enhance the low-voltage ride capability of the two-stage grid-connected system PV inverter based on Boost circuit,a control strategy with the DC bus voltage control loop based on Boost for LVRT is designed in this paper.Firstly,the conventional Boost voltage control mode and output current control strategy of the two-stage PV inverter are analyzed.A DC bus voltage control outer loop based on PV array maximum power point vol-tage feed forward is introduced to change the Boost voltage control mode.In this way,the purposes of making the DC bus voltage stable and preventing over current of the inverter are to be achieved.At the same time,the refe-rence value of the active current is adjusted according to the voltage drop depth.On the premise that the inverter is not over current,the maximum reactive current is provided to help the power grid recovery.Finally,a 100 kW PV inverter PSCAD simulation model is built to verify the proposed control strategy.The result shows that the method not only can suppress the DC bus voltage rise rapidly and effectively,but also can make the inverter provide more dynamic reactive power support for the grid even when the voltage drops.