Real-Time Estimation of ESR and Capacitance in the DC-Link Capacitors of AC Machine Drives

This paper presents method to estimated ESR (Equivalent Series Resistance) and capacitance in three phase inverters for motor drives. The dc-link voltage and output current of the inverter are measured in online condition while motor in running state. The recursive least squares (RLS) algorithm is applied to the ac-ripple signal on the voltage and the current to estimate process. A simulation model in MATLAB/Simulink software package and an experiment with DSP-controlled, 1$/_{2}$ Hp of induction motor drives based on SVPWM inverter system are used to verify the proposed method. Analytical, simulated, and experimental results agree well with each other. Experimental waveforms confirm the effectiveness of the presented algorithm to estimate both capacitance and ESR of the electrolytic capacitor on the common dc-link. The results show that the error between the actual value and estimated value of ESR and capacitance, which are quite acceptable value for capacitor conditioning monitoring in online during the motor operation to predict the lifetime of the capacitor by using the simple technique without additional sensors.