Power Conversion System for Reducing DC-Link Capacitor Stress

A power conversion system comprising:

• a first direct (DC)-current alternating current (AC) inverter;
• a second DC-AC inverter;
• an inverter controller coupled to the first DC-AC inverter and the second first DC-AC inverter and configured to provide a pulse-width modulation (PWM) signal to the first DC-AC inverter and the second DC-AC inverter;
• a DC-link circuit coupling the first DC-AC inverter and the second DC-AC inverter in parallel and comprising:
• a positive voltage line;
• a negative voltage line;
• a neutral voltage line;
• a high-frequency positive-line capacitor;
• a low-frequency positive-line capacitor, wherein each of the high-frequency positive-line capacitor and the low-frequency positive-line capacitor couples the neutral voltage line with the positive voltage line;
• a high-frequency negative-line capacitor;
• and
• a low-frequency negative-line capacitor, wherein each high-frequency negative-line capacitor and the low-frequency positive-line capacitor couples the neutral voltage line with the negative voltage line;
• a neutral-point balancer (NPB) circuit coupled to the DC-link circuit and configured to reduce low-frequency current oscillations in the DC-link circuit by switching between a first state for transferring charge from the positive voltage line to the neutral voltage line, and a second state for transferring charge from the neutral voltage line to the negative voltage line;
• and
• an NPB controller coupled to the NPB circuit, synchronized with the PWM signal, and configured to control the switching of the NPB circuit.