非隔离单相半桥UPQC直流纹波分析及其影响抑制

DC ripple analysis and influence suppression for transformer-lesssingle-phase half-bridge UPQC

非隔离单相半桥统一电能质量调节器(UPQC)两侧变换器的脉动功率差将在直流电容及分电容上产生复杂的多倍频电压纹波,各次电压纹波会对串联侧变换器的补偿电压有不同的影响,降低串联侧变换器的补偿效果。为了抑制直流电压纹波影响,利用等效电容电流模型计算直流电容电压表达式,分析直流纹波及非线性负载对补偿电压的影响路径,并仿真验证其正确性。针对分电容电压纹波和非线性负载对电压补偿效果的影响,提出一种抑制多倍频纹波影响的补偿电压特定次谐波控制策略。最后,基于SiC器件建立了非隔离单相半桥UPQC实验平台进行实验验证,实验结果表明在非线性工况下,所提控制策略将补偿电压THD从12.2%降低至2.4%,相比于传统控制可以减少约70%的直流电容需求。

The pulsating power difference between the series and parallel converter of the transformer-less single-phase half-bridge unified power quality conditioner(UPQC)generates multiple frequency voltage ripples on the DC-link capacitor and sub-capacitor.Different frequency voltage ripples generate different effects on the compensation voltage,and reduce the compensation effect of the series converter.In order to suppress the influence of the DC-link voltage ripple,the expression of DC-link voltage was calculated by using the equivalent capacitance current model,the influence path of DC-link ripple and nonlinear load on the compensation voltage was analyzed,and the ripple analysis was verified by simulation.Aiming at the influence of harmonic load and sub-capacitor voltage ripple on the voltage compensation effect,a compensation voltage specific order harmonics control strategy was proposed to suppress the influence of multiple frequency ripple.Finally,a UPQC experimental platform based on SiC devices was established.Experimental results show that under nonlinear conditions,the proposed control strategy reduced the compensation voltage THD from 12.2%to 2.4%,and can reduce the DC-link capacitance demand by about 70%compared with the traditional control.