DC- Capacitance Estimation of DC-Link Capacitors using AC Voltage Injection in AC/DC/AC PWM Converters

In this paper, a novel online capacitance estimation method for a DC-link capacitor in a three-phase AC/DC/AC PWM converter is proposed. A controlled AC voltage with a lower frequency than the line frequency is injected into the DC-link voltage, which then causes AC power ripples at the DC output side. By extracting the AC voltage and power components on the DC output side using digital filters, the capacitance can then be calculated using the support vector regression (SVR) method. A continuous-valued function that plots the fundamental interrelation between a given input (capacitance power) and its corresponding output (capacitance value) can be estimated using SVR and based on the training data. This function then can be used to predict outputs for given inputs that are not included in the training set. The proposed method can be simply implemented with only software and no additional hardware. Experimental results confirm that the estimation error is less than 0.15%