An Online DC-Link Capacitance Estimation Method for Motor Drive Systems Based on an Intermittent Reverse-Charging Control Strategy

The dc-link capacitor in the three-phase ac-dc-ac motor drive system is a critical component. The degradation of dc-link electrolytic capacitors is a common failure that has a significant impact on system reliability, which can often lead to system breakdown or damage. It is significant to provide monitoring and prognostic techniques for dc-link capacitors to assist in preventive maintenance. To realize online estimation of the dc-link capacitance, a reverse-charging mode of dc-link capacitors is actively introduced during the normal operation, by actively altering the control of the power switches in the converter in an intermittent manner. During the proposed reverse-charging mode, the dc-link capacitor bank is charged by the motor, and the charging current exactly originates from the current in one particular phase, which can be designated and measurable in typical motor drive systems. Based on the reverse-charging mode, the capacitance can be calculated through the voltage rise and charging current. Simulation and experimental tests are implemented to verify the accuracy and feasibility of the proposed method. It is shown that this method is capable of providing online monitoring of dc-link capacitors with high accuracy.