考虑非计划孤岛的分布式电源无缝切换控制策略

A Seamless Transfer Control Strategy of Distributed Generation with Considering Unintentional Islands

为提高本地负载的供电安全,分布式发电(DG)并网逆变器需要工作在并网和离网两种状态,且能无缝切换。提出一种综合的DG无缝控制策略。针对非计划孤岛DG从并网切换离网状态存在失控区域,易引起本地负载电压和频率越限问题,提出采用P-σ、Q-v解耦的非线性控制,实现失控期间的直接电压限幅;提出结合锁频环和去除积分前向通道的锁相环,在不影响锁相环动态特性基础上,实现失控区域的频率限幅。另外,在该控制结构基础上提出一种虚拟并网的预同步方法,避免并网开关闭合时内外环失配,改善并网过渡过程。基于RT-LAB的硬件在环仿真验证了该策略的有效性。

In order to improve the power supply security of local load,gird-tied inverter of DG system need to work in both grid-tied and off-grid state,and need seamless switching between two states. This paper proposes a comprehensive seamless transfer control strategy. When unintentional island occur and DG need switch from gird-tied to off-grid state,it is easy to exist out of control area and cause the local load voltage and frequency outlimit. A decoupling P-σ,Q-v control strategy is adopted to realize direct limit voltage during out of control area.And an improved phase-locked loop（ PLL） algorithm is proposed to avoid frequency out of limited by combining the frequency lock loop（ FLL） and improved phase locked loop（ PLL）. Also,an improved pre-synchronization method based on virtual grid-connected is proposed to reduce transient process time when DG transfer form island to grid-connected mode. Hardware-in-the-loop（ HIL） simulation based on the RT-LAB is carried out to verify the effectiveness of the proposed strategy.