A Novel Two-Amplitude Control Strategy For Active-Clamped Resonant DC Link Inverter

The resonant DC link inverter (RDCLI) employs the resonance of the resonant inductance and the resonant capacitor to make the DC link voltage cross zero periodically, providing zero-voltage-switching condition for the switches. It is a potential candidate for ac power, UPS and AC adjustable speed systems.This thesis reviews the development of RDCLIs, and compares them in topologies and control strategies. The operation principle and control strategy for active-clamped RDCLI is analyzed and verified experimentally. The main reason why the DC link has high losses is explained.In order to reduce the loss of the resonant DC link, two-amplitude control strategy can be applied, i.e., once the inverter needs to change its switching modes, the resonant DC link will operate in big-amplitude mode, and the DC link voltage will resonates to zero, otherwise, the resonant DC link will operates in small-amplitude mode, just keeps the resonance. Based on the theoretical analysis above, this thesis proposes a novel two-amplitude control strategy. By shorting the bus voltage, the energy dissipated in the DC link can be supplied by input DC source. By regulating the big-amplitude turn-off-current, the balance of the clamping voltage can be realized. By the dual-loop control strategy, in which the current loop adopts HCPM, it can realize the approximate odd-polarity modulation for the output voltage, and reduce the output current ripples and output voltage harmonics.The losses in the DC link are analyzed and the parameter design of the main circuit is discussed. The simulation and experimental results are given to verify the feasibility of this novel control strategy for the active-clamped RDCLI.