Modulation Design and Control for Bidirectional Converters in Energy Storage Applications

Power converters for energy storage applications employs bidirectional DC-DC converters to achieve high-efficiency power transfer with galvanic isolation. The high-frequency dual active bridge (DAB) DC-DC converter design is particularly sensitive to pulsewidth modulation (PWM) signal mismatches, layout issues, and modulator control asymmetries during dynamic operation. These issues can cause DC offsets in transformer currents, leading to transformer core saturation, distorted current waveforms, and converter premature activation of protection mechanisms. The design specifics of the modulator and control are analyzed, incorporating instantaneous balancing of on-time and off-time by adjusting the switching frequency. The modulator is designed to execute smooth phase adjustment using linear ramps while keeping the on-off balanced. Slope compensations are introduced independently between outer and inner phase-angles with ramp limiters. The performance of the proposed design is evaluated during bidirectional power flow transitions in both charge and discharge modes. The experimental results are performed using a 5 kW nominal power bidirectional DC-DC converter with silicon carbide devices.