负载不对称H桥级联APF直流电压平衡控制

H桥级联型有源电力滤波器(APF)在高压场合的谐波处理方面具有广阔的应用前景。三相三线制系统下负载不对称时,APF输出的基波电压和电流产生不同的有功分量分配至三相,再加上H桥各个模块的差异等原因,导致直流侧电压不均衡,影响APF的正常运行。通过对级联APF功率模型的推导,控制APF输出基波正序有功电流稳定全局电压、输出基波负序电流实现三相之间电压均衡。在全局稳压和相间均压条件下,控制各H桥交流侧输出补偿有功电压矢量实现相内电压均衡,最终将每个H桥直流电压维持在给定值附近,同时APF补偿谐波电流,降低网侧电流THD。在低压条件下的仿真和实验结果验证了所用方法的可行性,为级联APF向更高电压等级场合的应用提供了基础。

DC voltage balance control for cascaded H bridge APF with unbalanced loads

The cascaded H-bridge APF (active power filter)has wide application prospect in the field of high voltage harmonic processing.When the load is unbalanced in the three-phase three-wire system,the fundamental wave voltage and current outputted from APF generate different active components and they are assigned to each phase.With the differences between H-bridge modules,the DC side voltages will be unbalanced.It can affect the normal operation of APF.By derivation of the power model of cascaded H-bridge APF,the global voltage stabilization is achieved by controlling the fundamental positive sequence active current and the three-phase voltage balance is achieved by controlling the fundamental negative sequence current outputted from APF.Under these two conditions,the voltage balance in one phase is achieved by controlling the active voltage vector of AC side in each H-Bridge.They control each DC side voltage at a given value eventually.At the same time,the cascaded APF compensates harmonic current and reduces THD of the grid current.The feasibility of the method is verified by simulation and experimental results under low voltage conditions,and it provides the basis for application of the APF to a higher voltage level.