Online Monitoring Research Of Output Capacitance And Input Current Harmonics Of PFC Converter Based On Ripple Voltage Analysis

In the power factor correction(PFC)converter,input power is pulsating but output power is constant.So capacitor is needed to balance the input and output power.Aluminum electrolytic capacitor is used as the output capacitor of power factor correction converter due to its advantages of low cost and wide range of capacity and voltage.However,aluminum electrolytic capacitor is the most easily failed device in the whole converter,so it is very meaningful to monitor the state of aluminum electrolytic capacitor in the converter.In this paper,the basic structure and main electrical parameters of aluminum electrolytic capacitor are introduced.The factors leading to the degradation of aluminum electrolytic capacitor are studied.The change of capacitance after degradation of aluminum electrolytic capacitor is analyzed by establishing the equivalent model of aluminum electrolytic capacitor.The failure extent can be evaluated by monitoring the capacitance of aluminum electrolytic capacitor online.The input current of PFC converter may inevitably contain some harmonics,which can be expressed in the output voltage ripple.By analyzing the output voltage ripple,a method of on-line monitoring the output capacitance and input current harmonic contents is proposed.This method does not need to change the main circuit structure or add sensors.In light of the change of output voltage ripple amplitude caused by different output power or input current harmonics,a voltage ripple sampling circuit with adaptive amplification factor is proposed.Finally,taking DCM boost PFC as the monitoring target converter,the proposed online monitoring method is verified.The calculated results are uploaded to the PC and compared with the actual values to verify the proposed online monitoring method.