一种三相线电压级联单位功率因数整流器负载不均衡特性分析及电压均衡控制策略

Static Characteristics and Output Voltage Balance Control of a Novel Line-Voltage Cascaded Three-Phase Unity Power Factor Rectifier under Unbalanced Load

该文对一种由三个三相单开关整流器线电压级联构成的三相单位功率因数整流器的负载不均衡特性和输出电压均衡控制策略进行分析和研究,首先详细阐述此类整流器在三个直流侧负载不均衡时,交流输入端电流能自动保持均衡的独特特性及相应工作机理;然后研究系统整体分层控制策略。在传统的基于电压外环PI控制、电流内环PR控制的上层控制基础上,针对各整流模块参数不一致及负载功率不一致引起的各模块输出电压不均衡问题,通过加入偏差因子调制波补偿的底层控制,实现了对每个模块输出功率的独立调节,进而实现了各整流模块输出电压的均衡控制。仿真和实验结果验证了所研究拓扑结构的优越性和控制策略的可行性。

At present,the rectifier stage of high-power charging power supplies is based chiefly on three-phase Vienna circuit topology.Multiple Vienna modules achieve the output power increase in interleaving parallel connection or triple line-voltage cascade structure.Although such a method can effectively improve the overall power level of the system without increasing the voltage and current rating of the single-power device,it requires many active power electronic switches.This paper investigates a novel three-phase line-voltage cascaded unity power factor rectifier.The rectifier circuit is designed on a three-phase single-switch PFC rectifier as the basic cell,with three such basic cells connected to each other in a line-voltage cascade connection.The number of active power electronic switches and DC-link capacitors is greatly reduced compared to traditional rectifier structures.Moreover,the new rectifier circuit can operate under a unity power factor with sinusoidal input currents.In practical engineering applications,unbalanced DC-link load or inconsistent circuit parameters can lead to unbalanced DC-link capacitor voltage and asymmetric three-phase grid current.This paper provides a detailed analysis and discussion of the characteristics of three-phase line-voltage cascaded unity power factor rectifiers under unbalanced DC-link load conditions.Under the control goal of unity power factor,when the DC-link load is unbalanced,the input power of the three modules maintains automatically in uniform distribution.It is theoretically proven that the angular connection of the internal diode bridge in the input module allows for the automatic sharing of unbalanced DC-link loads among the three-phase input terminals.This paper then studies a DC-link voltage balancing control strategy.When the DC-link loads are unbalanced,the three-phase input power of the rectifier remains self-balanced.However,the active power output by each module may still be different,resulting in voltage imbalance among the three DC-links.Therefore,a hierarchical control strategy is designed based on the traditional voltage and current double closed loops,consisting of an outer voltage loop(PI controller)and an inner current loop(PR controller).The control system is divided into two layers:the upper layer and the lower layer.The upper layer focuses on controlling grid current and total transmission power,achieving stable output voltage and input current in phase with input voltage.The lower layer adjusts the DC-link voltage to the same value by injecting a modulation index increment to the upper system.Finally,simulation and prototype experiments verify the dynamic and static characteristics of the rectifier circuit.The correctness of the theoretical analysis and the feasibility of the proposed control strategy are also verified.