DC ripple analysis and influence suppression for transformer-less single-phase half-bridge UPQC
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.Ai-ming 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 in-fluence 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 re-duced the compensation voltage THD from 12.2%to 2.4%,and can reduce the DC-link capacitance de-mand by about 70%compared with the traditional control.
power qualityunified power quality conditionersub-capacitor voltage rippleripple influ-ence suppresscompensation voltage specific order harmonics control