共直流母线开绕组变压器双逆变器的零序电流抑制策略

Zero Sequence Current Suppression Method for the Open-end Winding Transformer Based Dual Inverter With Common DC Bus

开绕组变压器双逆变器拓扑具有多电平输出、直流电压利用率高、调制自由度大、易容错的优点,在光伏并网发电系统中得到广泛的研究。当该拓扑共直流母线时,会存在零序电流的问题,而传统基于120°解耦调制的零序电流抑制策略会导致两逆变器的有功功率分配不均,影响系统性能。针对上述问题,提出一种基于新型零序电压消除空间矢量调制的零序电流抑制策略,所提调制策略仅选择零序电压为零的矢量进行调制,并通过合理配置开关时序使两逆变器的输出电压矢量幅值相等且相位互差180°,另外,两逆变器零矢量的作用时间可动态调节,用于抑制死区、管压降等非线性因素对系统零序电压的影响。所提方案可在有效抑制系统零序电流的同时,保证了两逆变器始终处于功率均分状态。最后,通过搭建实验平台,验证了所提策略的可行性和有效性。

Open-end winding transformer(OWT)dual-inverter topology has the advantages of multi-level output,high DC voltage utilization,high modulation freedom and easy fault tolerance.It has been widely studied in photovoltaic grid-tied system.When the topology has a common DC bus,there will be the problem of zero sequence current,and the traditional zero sequence current suppression strategy based on 120°decoupled modulation will cause the active power of the two inverters to be unevenly distributed.As a result,it will affect the system performance.Aiming at the above problems,a zero sequence current suppression strategy based on a novel zero sequence voltage elimination space vector modulation strategy was proposed.The proposed modulation strategy only selects the voltage vectors which generates no zero sequence voltage,and the voltage vectors were properly configured to make the output voltage vectors of the two inverters equal in amplitude and 180°out of phase with each other,in addition,the zero vectors’dwell time of the two inverters can be dynamically adjusted to suppress the influence of non-linear factors such as dead time and switches voltage drop.The proposed strategy can effectively suppress the zero sequence current of the system while ensuring that the two inverters are always in power sharing state.At last,the feasibility and effectiveness of the proposed strategy were verified by experiments.