An investigation of minimum DC-link capacitance in PWM rectifier-inverter systems considering control methods

In this paper, minimum DC-link capacitance in PWM rectifier-inverter systems is investigated. Reduction of DC-link capacitor is one of the most effective issues to realize high power-density PWM rectifier-inverter systems. For the extreme reduction of the DC-link capacitor, the minimum required capacitance should be clarified theoretically, and the improved control method should be developed. Firstly, the calculation method of DC-link voltage variation of the PWM rectifier-inverter systems at a stepwise change in the output power is proposed. Next, based on the proposed calculation method of the DC-link voltage variation and the constraint conditions determined by parameters of the PWM rectifier, the calculation method of the minimum required DC link capacitance at a stepwise change in the output power is proposed. Then, a feed-forward controller based on the output power of the inverter is proposed and the least necessary capacitance is clarified.