Online Capacitance Estimation for the DC Link Capacitor of PWM Inverter

In the inverter for driving an electric vehicle, a DC link capacitor is an important component. To ensure the reliability and stability of the inverter, research on a method capable of predicting the capacitor lifespan is becoming important. Therefore, research on methods capable of predicting the durability, heat generation management, and lifespan of capacitors is actively being conducted. The capacitance decreases according to the accumulated usage time of the inverter. Therefore, if the capacitance decrease amount can be estimated based on the initial capacitance of the capacitor in real time, then the remaining lifespan of the DC link capacitor may be predicted, and a failure may be diagnosed. The existing capacitance estimation method requires an additional circuit for relatively simple implementation and has the limitation that the real-time motor control is affected by additional signal injection into the capacitor. This paper proposes a method for estimating the capacitance of an additional circuit and a DC link capacitor online and offline without additional signal injection by analyzing the voltage and current characteristics of the capacitor during space vector pulse width modulation (SVPWM)-based control of a real-time motor. A capacitor current analysis equation considering the voltage sampling time of the capacitor and the dead time (DT) of the inverter is newly established to improve the capacitance estimation performance for the capacitor. The reliability of the capacitance estimation algorithm is confirmed by comparing the proposed capacitance estimation method and the manual measurement method under various motor driving and constraint conditions.