DC-link Voltage Ripple Control of Regenerative CHB Drives for Capacitance Reduction

The diode-front-end (DFE) CHB inverters have prevailed in the non-regenerative industry drive domain for high-power medium-voltage applications. The regenerative version of the CHB drives is made possible by adding the extra active-front-end (AFE) rectifier in each power cell, such as a three-phase PWM rectifier. 

However, due to the instantaneous power unbalance, the dc-link capacitors of the regenerative power cell need to be overdesigned to maintain a stable low ripple dc-link voltage. To reduce the dc-link capacitance, this paper proposes a novel closed-loop voltage ripple controller for the regenerative CHB drive without adding extra sensors. 

In the proposed method, dc-link voltage ripple amplitude and phase angle are accurately detected with a high-performance adaptive filter. Moreover, a latent instability issue is discussed and is avoided in the proposed controller. The performance of the proposed control strategy is validated experimentally on a seven-level regenerative CHB drive.

Index Terms— Multilevel Drives, DC-Link Capacitor Reduction, Regenerative, Adaptive filtering, Stability