Charging energy storage units of a vehicle at weak energy supply systems

An onboard power subsystem for a vehicle, the onboard power subsystem comprising:

• an energy storage unit;
• a closed-loop control device for charging the energy storage unit of the vehicle;
• an onboard power connection for connecting electrical components of the vehicle to the onboard power subsystem;
• an energy subsystem;
• a switching device arranged between the onboard power connection and the energy subsystem;
• a DC voltage connection electrically conductively connected to the energy subsystem and configured to connect the onboard power subsystem to a land-based charging station;
• a charger arranged between the energy storage unit and the energy subsystem;
• and
• a power converter operable as both as an AC/DC converter and as a DC/DC converter, and connected on an AC voltage side to the energy subsystem, wherein the power converter is configured, by way of the closed-loop control device, to operate the energy subsystem as a DC voltage system during a charging process and as an AC voltage system during an independent operation of the vehicle.