To address these issues, researchers at Arizona State University have developed novel control schemes for bidirectional dc-dc dual active bridge converters. The proposed control schemes combine the traditional method of phase shift control with Pulse Width Modulation (PWM) of one single H-bridge and two converter bridges simultaneously in a composite control scheme that depends on the input to output voltage ratio and the load condition. One key element is that the scheme automatically transitions between dual PWM, single PWM, and only phase shift control by utilizing directly measured input and output voltages, and using the load information implicit in the required phase shift.
- Uninterruptible Power Supplies (UPS)
- Grid Tie Renewable Resources (Photovoltaic Energy)
- Fuel Cells
Benefits and Advantages
- Extends the soft-switching range down to zero load condition
- Reduces rms and peak currents
- Results in significant size reduction of the transformer
- Lower magnetic core losses
- As an example, the efficiency at 3% load and half nominal output voltage is increased from 25% with phase shift control alone to 77% with the proposed scheme. The transformer size is also reduced by 33%.