I. Common Issues of Bidirectional DC/DC Converters (Typical Pitfalls)

1. Circulating Current Issue (Most Typical)

   Mismatched voltages between high-voltage and low-voltage sides during mode switching will generate large circulating currents.

   Consequences: MOSFET burnout, overcurrent protection, severe overheating.
2. Mode Switching Oscillation

   The control loop becomes unstable when switching between Boost (step-up) and Buck (step-down) modes, or between charging and discharging.

   Performance: Voltage ripple, current spikes, high noise.
3. Asymmetric Efficiency

   High efficiency in forward direction, but significantly lower efficiency in reverse direction.

   Cause: Topology, drive circuit, and MOSFET selection are optimized for unidirectional operation only.
4. Bus Voltage Out of Control

   Overvoltage occurs on the high-voltage bus during sudden load or battery voltage changes.

   Common especially in energy storage, PV, and automotive applications.
5. Poor Current Sharing in Parallel Operation

   Uneven current distribution when multiple bidirectional DC/DC converters are connected in parallel, leading to overload of individual units.
6. Large Startup Inrush Current

   Direct power-on causes high inrush current, which easily triggers protection mechanisms.
7. Difficult Thermal Design

   High power density in both directions makes thermal design much more challenging than for conventional DC/DC converters.

II. Correct Usage of Bidirectional DC/DC Converters (Key Points)

1. Determine Operating Direction First

• Low voltage → High voltage: Boost mode
  Battery discharging, energy storage output, motor driving.
• High voltage → Low voltage: Buck mode
  Battery charging, bus-to-battery power supplement, energy recovery.

1. Mandatory Soft Start

   Pre-charge before power-on to avoid inrush current.

   Ramp up voltage/current gradually.
2. Smooth Mode Switching

   Reduce current to near zero → Switch direction → Ramp up current slowly.

   Strictly prohibit abrupt full-power forward/reverse switching.
3. Voltage Matching

   Ensure before switching:

• Charging: High-voltage side ≥ Low-voltage side
• Discharging: Low-voltage side can be boosted to a reasonable range matching the high-voltage side
  Prevent backflow and circulating current.

1. Adequate Current Limiting Protection

   Overcurrent, overvoltage, undervoltage, over-temperature, reverse polarity protection.

   Bidirectional DC/DC converters rely more on protection than ordinary power supplies.
2. Thermal Design for Full Power in Both Directions

   Do not calculate power for one direction only.

III. Typical Applications of Bidirectional DC/DC Converters

1. New Energy Vehicles (Core Application)

   48V ? 12V bidirectional DC/DC

   Battery charging/discharging, regenerative braking energy recovery, 12V low-voltage power supply.
2. Battery Energy Storage Systems (BESS)

   Battery pack ? DC bus / Inverter

• Charging: Grid / PV → Battery
• Discharging: Battery → Grid / Load

1. PV & Energy Storage Integrated System

   PV + Battery + Bidirectional DC/DC

   Charging during daytime, discharging at night, for energy scheduling.
2. Elevator & Industrial Energy Saving

   Motor downward movement / braking → Energy recovered to battery or grid.

   Bidirectional DC/DC manages energy recovery and reuse.
3. Drones / AGVs / Robots

   Battery ? Power bus

   Supports regenerative braking and extends working range.
4. DC Microgrids

   Bidirectional energy interaction among distributed power sources, energy storage, and loads.
5. Backup Power / UPS

   Bidirectional energy exchange between battery and bus.