125kW Bidirectional DC/DC Converter Design

Research funded in part by Army Research Labs (ARL)

This project involved many phases to develop the new technology required for a bidirectional (step-up and step-down) DC-to-DC voltage converter with a regulated output.

• Conducted an initial simulation study.
• Tested IGBT device under many supply and load conditions, monitoring: IGBT voltage and current, conduction and switching energy, and switching time (turn-on and turn-off)
• Tested 2 inductors of approximately 29µH, examining core saturation and device desaturation point
• Open loop buck converter test, up to 5kW output power per leg, to measure efficiency and monitor temperature. Efficiency increases as power increases because device ringing decreases, and within the 15 minute test time heat sink has a relatively high temperature (rising steady).
• Open loop buck interleaved converter test, up to 5kW output power, to ensure interleaved operation is functional correctly and to measure efficiency. Interleaved buck operation was tested successfully with substantial ripple reduction. Compared with non-interleaved converter at the same output power level, efficiency seems to be lower, but the temperatures are also lower. Measurements need substantial calibration effort. Within test time of 16min, inductor and heat sink indicate a steadily linear increasing temperature.
• Open loop boost interleaved converter test, up to 6kW output power, to ensure boost mode interleaved operation is funcional correctly and to measure efficiency. Open-loop interleaved boost mode operation was tested successfully. Input current ripple is significantly reduced. Although the individual inductor current is discontinuous, the input current becomes continuous. Significant ripple current reduction also occurs at light load and low duty condition.
• Closed-loop tests to verify control responses and stability under large signal step load output current disturbance. The �Average Current Mode� control loops are stable under both buck and boost modes.

Proposal for next phase

• Expand to three phase
• Implement soft switching
• Design integrated closed loop current sensor
• Integrate with ARL liquid cooled heatsink