基于输出侧双模块并联的电力电子变压器高电能质量控制策略

摘要

电力电子变压器(power electronic transformer,PET)在给不平衡或非线性负荷供电时,可能会出现PET装置输出侧电压幅值和频率不稳定的现象,甚至影响PET的供电可靠性.针对PET输出容量大、容量模块化可调、高电能质量供电等需求,避免单台逆变器输出模块在处理不对称或非线性负荷时的局限性,本文提出了PET输出侧(逆变级)双模块并联的高电能质量控制策略.主要思路为:输出侧中的一个逆变器模块采用电压电流双闭环控制策略,可视为电压源,负责提供稳定的PET输出侧电压,起到稳定其他输出侧逆变器模块的电压基准值的作用,既可以补偿所有负序、谐波及无功电流以降低对PET输出电压的不利影响,同时还按照既定的输出侧模块功率分配策略输出有功功率和无功功率.输出侧的其他逆变器模块则采用电流补偿控制策略,可视为电流源,用于增大输出电流,提升PET装置的容量.以两个输出侧逆变器模块并联输出为例进行理论分析,认为所提控制策略既可以提高PET装置的输出容量,又可以极大降低非对称负荷对PET输出电压稳定的不利影响,有效地提升了PET的负载适应性、容量扩展性及供电可靠性.仿真结果验证了本文所提出控制策略的有效性.%When power electronic transformer (PET) supplies power to the unbalanced or non-linear loads,the voltage amplitude and frequency of the output-side in PET may be unstable,and even affect the power supply reliability of the PET.Aiming at demands of large output capacity,adjustable capacity modules,and high-quality power supply of PET,and for avoiding the limitations of single inverter output module in handling asymmetric or non-linear loads,a dual-module control strategy with high power quality for parallel output sides (inverters) of PET is proposed.In which,one of the inverter modules in output side is regarded as a voltage source and adopts double closed-loop control strategy of voltage and current,it provides stable output voltage of PET and stabilizes the voltage reference values of the output sides for other inverter modules,which can not only compensate for negative sequence current,harmonics and reactive current to reduce the negative impacts on the output voltage of PET,but also provide active power and reactive power in accordance with established power distribution strategy for output side modules.Other output-side inverter modules treated as current sources adopt the current compensation control strategy.They are used to enlargc the output current and enhance the capacity of PET.Taking two parallel output-side inverter modules as an example,the proposed high power quality control strategy is analyzed theoretically.It is concluded that the proposed strategy can improve the output capacity of the PET,greatly reduce the adverse effects of asymmetric loads on the output voltage stability of PET and effectively enhance the adaptability,capacity expansion and power supply reliability of PET.The simulation results verify the effectiveness of the proposed control strategy.