Control Strategy Against Capacitance Degradation for BLDC Drives with Small DC-Link Capacitor in Series with IGBT

In brushless DC motor (BLDC) drives with a small DC-link film capacitor and a series-connected IGBT, capacitor degradation can significantly compromise system performance and reliability. To address this challenge, this paper proposes a control strategy specifically designed to mitigate capacitance degradation effects. The core of the strategy involves intentionally advancing the natural voltage separation point between the film capacitor and diode rectifier outputs, thus establishing an artificial voltage separation instant. This approach ensures that the capacitor voltage consistently remains above the peak AC voltage despite capacitor degradation, effectively compensating for reduced energy storage capability. Compared to the modulation strategy optimized for initial capacitor capacity, the proposed method only increases inverter switching actions during a limited portion of the control cycle in Zone I, without altering the switching frequency of the DC-link series IGBT. The proposed strategy does not require shutting down the system to replace the capacitor after degradation. Compared to the fault-tolerant topology of paralleling capacitors, the proposed strategy incurs no additional hardware cost. Experimental results confirm the effectiveness and reliability of the proposed control strategy.