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Energy Management For Hybrid Drive System, Function - GF08.30-P-1005RFH

Engine 274.920 in model 205.047/147/247, 253.954 

Engine 274.920 in model 205.053/253 

Engine 274.920 in model 253.354 

Engine 651.921 in model 205.012/212 

Engine 654.920 in model 205.013/213 

IMPORTANT The subfunction "hybrid drive system energy management function" is considered and described from the point of view of the hybrid drive system.

Function requirements, general 

Hybrid drive system energy management, general points 

The energy management module in the powertrain control unit (N127) coordinates the energy flow of the hybrid drive system and, based on the electrical factors, creates the interface to the battery management system control unit (N82/2), power electronics (N129/1) and electric refrigerant compressor (A9/5). To do this is exchanges information with all relevant control units via the CAN network. The powertrain control unit also communicates with the CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine) via the CAN network using the torque interface for coordination of energy recuperation and use of energy.

The energy management activates and deactivates the high voltage on-board electrical system by controlling the contactor (A100s1) in the high-voltage battery (A100g1) and all other voltage sources in the high voltage on-board electrical system. In doing so, all protective mechanisms (e.g. insulation measurement, interlock circuit monitoring, crash sensors) that avoid danger due to electric shocks are monitored and taken into consideration.

The energy management module is also responsible for the following tasks:

The powertrain control unit reads in the following signals via the CAN network as part of the energy management:

IMPORTANT DC/DC converter

A DC/DC converter is integrated in the power electronics control unit, which converts the high voltage direct voltage (primary voltage) into 12 V direct voltage (secondary voltage) and vice versa and transfers these between the high voltage on-board electrical system and the 12 V on-board electrical system.

IMPORTANT DC/DC converter control unit

The DC/DC converter control unit is installed in the vehicle as a separate component. The DC/DC converter control converts high-voltage direct voltage (primary voltage) into 12-V direct voltage (secondary voltage) and transfers these between the high voltage on-board electrical system and the 12-V on-board electrical system.

Function sequence for energy management for a hybrid drive system 

The following tasks of the energy management are explained in more detail:

Function sequence for computation of the SOC value for high-voltage battery charge level 

The computation of the charge level of the high-voltage battery as a SOC (State of Charge) value takes place on the basis of the data transmitted by the battery management system control unit and power electronics control unit via the CAN network. These data are:

The powertrain control unit uses this as a basis to calculate the SOC value and provides the result in the form of a percentage (0 to 100 %) to other control units that are integrated into the CAN network.

The SOC value serves, for example, as the basis for the charge level indicator in the IC (A1) and generally for control of all hybrid functions, dependent on the high-voltage battery charge level.

In order to calculate the SOC value the powertrain control unit evaluates the open circuit voltage of the high-voltage battery measured by the battery management control unit and the power electronics control unit and sent via the CAN network, as well as all currents flowing from and to the high-voltage battery as well the current flows of the attached consumers of the high voltage on-board electrical system.

Function sequence for battery management 

The battery management system control unit takes on complete monitoring of the high-voltage battery regarding temperature, voltage and currents, establishes safety limits for these values and transmits values and safety limits to the powertrain control unit.

These further functions are explained in more detail below:

Additional function requirements for controlling the contactor 

Function sequence for controlling the contactor 

IMPORTANT In the pyrofuse (F63), circuit 30 becomes circuit 30c. This serves the battery management system control unit and power electronics control unit as a signal line to recognize a crash event as well as the contactor as a power supply. If the supplemental restraint system control unit (N2/10) triggers the detonation fuse in the rear prefuse box or the high-voltage disconnect device (S7) is opened as a result of a crash, the circuit 30c signal line is interrupted and the contactor in the high-voltage battery disconnects the high-voltage battery from the high-voltage on-board electrical system.

IMPORTANT The interlock circuit is used as contact protection to protect people against inadvertent contact with high-voltage components. In order to do this, a 12 V/88 Hz interlock signal is looped through all assembly parts of the high voltage on-board electrical system that can be removed or opened. To do this there is an electrical bridge in each removable high-voltage connection which interrupts the interlock circuit during removal of the high-voltage connection. The interlock circuit is also led switched in a series over the 12 V control units plug connection of the high-voltage components.

The interlock alternator is located in the battery management system control unit. In every active high-voltage component (e.g. high-voltage battery and power electronics control unit) there is an interlock evaluation logistic, which executes its own evaluation. In the event of interlock circuit discontinuity, the battery management system control unit actuates the contactor for opening it. The high-voltage battery is disconnected in this way from the high voltage on-board electrical system.

Furthermore the battery management system control unit executes all of the switchings of the contactor requested by the powertrain control unit via the CAN network or for a CAN failure over a direct line.

Function sequence for an energy exchange of the high-voltage system and the 12 V on-board electrical system (model 205.012/212) 

The energy management module in the powertrain control unit regulates the energy flows in the high voltage on-board electrical system along with the voltage conversion and energy exchange from and to the 12 V on-board electrical system. To do this, the powertrain control unit communicates via the CAN network with the power electronics control unit and with the alternator via the CDI control unit.

One differentiates between the following modes of the DC/DC converter dependent on operating state:

Function sequence for charging the 12 V on-board electrical system (buck mode) 

In buck mode supply of the 12 V on-board electrical system with energy takes over the power electronics control unit from the high-voltage battery.

Additional function requirements for supporting the high voltage on-board electrical system (boost effect mode) 

Function sequence for supporting the high voltage on-board electrical system (boost effect mode) 

If the battery output of the high-voltage battery is very low when the hybrid drive system is started (below SOC (State of Charge)) but the charge level of the on-board electrical system battery (G1) is extremely good or an external power supply is connected, starting capability can be ensured by transferring power from the 12 V on-board electrical system to the high-voltage on-board electrical system.

If an external charger is attached and the power electronics control unit measures an on-board electrical system voltage of more than 13 V in the 12 V on-board electrical system with the engine hood open, the 12-V on-board electrical system is loaded with a max. of 500 W. In this way energy is transferred over the on-board electrical system battery and the power electronics control unit into the high voltage system and the high-voltage battery.

Function sequence for energy exchange of the high-voltage and 12-V on-board electrical system (model 205.047/147/247) 

In order to ensure a permanent supply of electrical energy, a DC/DC converter is integrated in the power electronics control unit, which converts the high voltage direct voltage (primary voltage) into 12 V direct voltage (secondary voltage) and vice versa and transfers these between the high voltage on-board electrical system and the 12 V on-board electrical system.

Function sequence for an energy exchange of the high-voltage system and the 12 V on-board electrical system (model 253) 

The energy management module in the powertrain control unit regulates the energy flows in the high voltage on-board electrical system along with the voltage conversion and energy exchange from and to the 12 V on-board electrical system. To do this the powertrain control unit communicates via the CAN network with the DC/DC converter control unit. The DC/DC converter control unit enables energy to be exchanged between the high voltage on-board electrical system and the 12 V on-board electrical system, by transforming the high voltage direct voltage (primary voltage) into 12 V direct voltage (secondary voltage). This means that the DC/DC converter control unit could also be regarded as an electrical alternator which takes over the task of the conventional mechanically driven alternator.

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