补偿不平衡负载的HC-SVG相间电压平衡控制与直流电压取值分析

HC-SVG phase-to-phase voltage balance control and DC voltage value analysis to compensate for unbalanced loads

针对由中点钳位型(neutral-point clamped,NPC)功率单元和H桥级联型(cascade H-bridge,CHB)功率单元构成的混合级联型静止无功发生器(hybrid cascade static var generator,HC-SVG)在补偿不平衡负载时产生的CHB功率单元相间电压失衡问题,提出一种基于零序电压前馈的CHB功率单元相间电压平衡控制方法,并对零序电压注入后HC-SVG直流侧电压取值进行分析。首先,分析CHB功率单元承担基波电压分量与HC-SVG输出基波电压的关系。推导HC-SVG补偿不平衡负载时CHB功率单元相间电压平衡所需的零序电压,建立零序电压前馈控制。其次,基于零序电压与补偿电流的解析关系,讨论补偿电流不平衡度与HC-SVG直流侧电压取值之间的约束关系。以6 kV/3 Mvar装置为算例,进行直流侧电压的取值分析。并与星接CHB-SVG进行对比,揭示补偿不平衡负载时HC-SVG所需直流电压低的特点。仿真验证了相间电压平衡控制与直流电压取值分析的有效性。

A hybrid cascade static var generator(HC-SVG)composed of neutral-point clamped(NPC)and cascade H-bridge(CHB)power units produces phase-to-phase voltage imbalance when compensating for unbalanced loads.To address this,a phase-to-phase voltage balance control method for the CHB power unit is established based on zero sequence voltage feedforward.The DC side voltage value of HC-SVG after zero sequence voltage injection is analyzed.First,the relationship between the fundamental voltage component of the CHB power unit and the output fundamental voltage of the HC-SVG is analyzed.The zero-sequence voltage required by the phase-to-phase voltage balance of the CHB power unit when the HC-SVG compensates for unbalanced loads is deduced and zero sequence voltage feedforward control is established.Secondly,the constraint relationship between the degree of compensation current imbalance and the HC-SVG DC side voltage is discussed based on the analytical relationship between zero sequence voltage and compensation current.Taking a 6 kV/3 Mvar device as an example,the value of the DC side voltage is analyzed and compared with the star CHB-SVG.It reveals the characteristics of low DC voltage required by the HC-SVG when compensating unbalanced loads.Simulation results show the effectiveness of clustered voltage balance control and DC side voltage value analysis.