BMW 3 Owners & Service Manuals

BMW 3: High-voltage power management

The power management for the high-voltage vehicle electrical system includes two subfunctions: one for driving and one for charging mode.

In driving mode, the energy flows from the high-voltage battery unit to the high-voltage consumers and the energy flows during energy recovery to the high-voltage battery unit are coordinated. The following steps are performed by the EME and are repeated constantly:

1. Query of the power available from the high-voltage battery unit (Signal source: SME).

2. Query of the power which the high-voltage battery unit can use (Signal source: SME).

3. Query of the requested drive or braking power from the electric drive (Signal source: DME).

4. Querying the requested power for climate control (electrical heating, electric A/C compressor, integrated automatic heating/air conditioning system).

5. Decision on the distribution of the electrical power and communication to the control units of the consumers.

In charging mode the high-voltage power management has another task: It controls the energy flow from outside the vehicle via the EME to the high-voltage battery unit and, if required, through the convenience charging electronics to the electrical heating or to the electric A/C compressor. The procedure is constantly repeated in the EME and consists of the following individual steps:

1. Query of the available power from outside (Signal source: KLE).

2. Query of the power which the high-voltage battery unit can use (SME).

3. Query of the power which is required for the climate control (IHKA).

4. Requesting the necessary power from the EME.

5. Communication of the available partial powers to the receivers, the high-voltage battery unit (SME control unit) and heating and air-conditioning system (IHKA control unit).

The externally available power cannot be at a high level; it is restricted by the power network and the EME. Therefore, the available power must be queried first before it can be distributed. Depending on its state of charge, for example, the high-voltage battery unit cannot absorb an arbitrary amount of power, which is why this value must also be queried first. Depending on the temperature of the high- voltage battery unit or on a heating or an air-conditioning request by the driver, the heating and air- conditioning system also needs electrical power. This value is the third important input signal for the high-voltage power management in charging mode. Using this information the externally requested power is controlled and distributed to the consumers.

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