A direct PWM technique for a single-phase full-bridge inverter through controlled capacitor charging

The controlled-capacitor-charging (CCC) technique is utilized in this paper to synthesize a sinusoidal voltage at the output from the unregulated dc at the input. The method is based on the controlled charging/discharging of a capacitor to realize the desired voltage waveform. A capacitor that is connected across the load is charged/discharged through an inductor by applying high-frequency pulses. The applied pulses could be of either positive or negative polarity, depending on the error signal in the controller. The controller senses the output voltage and current and operates to maintain zero-current switching at every turn-on while keeping the output voltage close to the reference waveform by a tracking-control algorithm, enforcing limits in maximum switching frequency and voltage ripples. This paper presents a direct method of implementing the pulsewidth modulation for the single-phase full-bridge inverter, using the CCC technique. A simple procedure to design such an inverter is also discussed. The proposed controller is simulated in a personal computer simulation program with integrated circuit emphasis. Supporting results from an experimental prototype confirm the usefulness of the proposed controller. The inverter may be used in uninterruptible power supply and many other applications.