配网三相不平衡调节的换相算法

针对低压配电网存在的三相不平衡问题，目前比较得到认可的解决方案是采用自动换相系统来实现。这种系统由智能换相终端和换相开关单元组成。在换相开关中，选用磁保持继电器与双向晶闸管并联的复合开关作为换相开关的执行机构，在投入和切除的瞬间由晶闸管承担过零投切，然后由磁保持继电器接通运行。双向晶闸管的触发一般采用硬件监测电网线电压过零点的方式，易受电网谐波影响，不能准确检测电网自然换相点，不能实现特定相位触发晶闸管。通过采用软件监测电网电压相位的方法，选用合理的换相算法来实现三相不平衡的调节，有效地防止了对负载和电网的冲击，提高了晶闸管触发的可靠性。实验结果的验证分析表明，所提出的算法在解决三相不平衡、提高电能质量方面具有可行性。

Commutation Algorithm for Three-Phase Unbalanced Load Regulation in Distribution Network

Automatic phase commutation system is widely used to deal with the load imbalance problem in low voltage distribution network. It consists of an intelligent commutation terminal and a number of phase commutation switches. In the commutation switch, the compound switch of paralleled magnetic latching relay and bidirectional thyristor is selected as commutation switch actuator, in which the thyristor is cut off by zero switching at the moment of commutation, and the magnetic latching relay is switched on without large current. The hardware devices are generally used to detect the zero crossing point on the line voltage. As high frequency harmonic waves exist on the line voltage, the zero crossing point is hard to be detected accurately, and dedicated phase trigging can not be implemented using this method. Therefore, the software method is used to calculate the line voltage phase, and a reliable commutation algorithm is adopted to realize the regulation of three-phase imbalance, which effectively prevents the impact impulse to load and power grid, consequently improving the reliability in triggering thyristor. Experimental results show that the proposed algorithm is feasible in solving three-phase unbalanced loads and improving power supply quality.