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Power Harmonic Elimination Technique for Using Non-linear Ceramic Capacitors under Large Voltage Swings for Single-Phase Active Power Decoupling

To reduce the required capacitance for twice-line frequency power ripple buffering in single-phase conversion, active power decoupling methods in general increase the voltage swings on the main energy buffering capacitors to improve the energy utilization of the capacitor. For capacitor types with constant capacitance, the required capacitor voltage can be derived using the fundamental capacitor voltage/current differential equation. However, if non-linear ceramic capacitors are used in the same scenario to increase the power density of the buffer, the buffer power will contain strong high-order harmonic distortion due to the non-linear capacitance that depends on the voltage bias. In this work, a control technique is proposed to eliminate higher order harmonics in the power waveform when non-linear ceramic capacitors are used in active buffers. Ceramic capacitors with different voltage dependant characteristics are discussed. The proposed control technique is verified with a bipolar multilevel active buffer hardware at kilowatt level and 400 V dc-bus.