Online ESR Monitoring of DC-Link Capacitor in Voltage-Source-Converter Using Damping Characteristic of Switching Ringings

Online monitoring of dc-link capacitor's equivalent series resistance (ESR) could provide valuable and timely information for power converter failure prognosis and predictive maintenance. The conventional ESR estimation methods are mainly based on pulsewidth modulation (PWM) voltage and current ripples (ESR approximate to Delta u(c)/Delta i(c)), but the performance is affected by operating conditions (especially at light-load), quasi-resonance effect and sensor amplitude error. To overcome these difficulties, an online ESR monitoring method is proposed using the damping characteristic of dc capacitor switching ringings. The intrinsic high-frequency (HF) resonance incidents between the power device fast switching and converter parasitic parameters are utilized in this article. First, the mechanism of dc capacitor switching ringing is analyzed by the HF resonance equivalent circuit. The analytic relationship between the damping characteristic and the ESR is established. Then, the condition monitoring (CM) scheme, noncontact HF sensor, and half-power bandwidth algorithm for ESR estimation are presented. Finally, an experimental study is carried out to validate the feasibility and effectiveness. The damping of switching ringing is inherently sensitive to the ESR of dc capacitor under the condition of resonance. Both theoretical analysis and experimental results confirm that the proposed method can achieve m Omega-level accuracy and good robustness under different conditions.