Masterless Interleaving Scheme for Parallel-Connected Inverters Operating with Variable Frequency Hysteretic Current-Mode Control

This paper describes a new masterless interleaving scheme for parallel sub-inverters operating in variable frequency Hysteretic Current-Mode Control (HCMC). The proposed digital control scheme enables the development of fault-tolerant, modular, efficient, and power dense inverters. A feed-forward controller is used to instantaneously correct for phase error at each switching cycle, while a compensator corrects for the systematic difference in sub-inverter switching frequencies caused by inductor mismatch. The control is verified by simulation up to 2 kW in an inverter system consisting of three parallel sub-inverters. Experimental results are presented for the same system operating in Boundary Conduction Mode (BCM) at 895 W. Activation of the interleaving controller shows a reduction in peak current into the system EMI filter, while maintaining the soft-switching benefits of BCM operation. The proposed interleaving scheme reduces the magnitude of the lowest switching frequency harmonics by a peak of 35 dB and an average of approximately 10 dB, which is demonstrated by comparing the inverter system's current spectrum with and without interleaving.