柔性互联交流配电网的换流器并离网统一控制策略

提出一种并离网统一控制策略,在孤岛控制模式的基础上设计了主动功率调节功能,并网运行时按照有功-电压平方下垂的关系自动分配有功功率;离网运行时下垂功率控制自动切换成定交流电网频率和电压的孤岛模式。该方法适用于并网和离网2种不同的运行工况,并且省去了孤岛检测环节,大幅简化了控制系统结构。以四端柔性互联交流配电网系统为例,详细分析了并离网统一控制策略的参数设计方法,并建立电磁暂态仿真模型,针对并离网多种不同工况开展仿真。仿真结果表明,所提方法可以满足柔性互联系统的负荷均衡及转供的性能要求,同时也避免了并离网切换过程的过电流。

Connecting and islanding universal control strategy for VSC of AC distribution grids

A universal control strategy suitable for connecting and islanding VSC is proposed, which appends active power regulator to typical islanding control strategy. Under AC connecting condition, active power of VSC is regulated according to droop relation between power and square DC voltage. When disconnected from AC grid, droop control is seamlessly transferred to islanding control mode with fixed AC voltage and frequency. This method is suitable for two different operating conditions of grid connected and off grid, and eliminates the islanding detection link, greatly simplifies the control system structure. Based on four-terminal VSC connecting AC distribution grids, the parameter design method of the universal control strategy is analyzed, and an electromagnetic simulation model is built in which the control performance of proposed strategy is validated. The simulative results show that the regulation characteristic of load balance and load shift under contingency is satisfactory while the over current during shift from connecting to islanding mode is avoided.