Online capacitance estimation of DC-link electrolytic capacitors for three-phase AC/DC/AC PWM converters using recursive least squares method

A novel online capacitance estimation method for a DC-link capacitor in a three-phase AC/DC/AC PWM converter is prepared. At no load, a controlled AC current with a lower frequency than the line frequency is injected into the input side, which then causes AC voltage ripples at the DC output side. By extracting the AC voltage and current components on the DC output side using digital filters, the capacitance can then be calculated using the recursive least squares method. The proposed method can be simply implemented with only software and no additional hardware. Experimental results confirm that the estimation error is less than 0.26%.