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

ENGINE 276.821 in MODEL 166 

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

No further discussion of information about the 12 V energy management of the 12 V on-board electrical system will be entered into here.

Function requirements, general 

• Hybrid drive system activated over "Wake Up" function

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 ME-SFI [ME] control unit (N3/10) via the CAN network with the torque interface to coordinate energy recovery and usage.

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:

• Calculation and calibration of SOC value (State of Charge) for charge level of high-voltage battery
• Implementation of the charging/discharging strategy while taking into account the boundary conditions of the high-voltage battery, the internal combustion engine and the electrical machine (A79/1)
• Prognosis for energy reserves and maximum available high-voltage battery output
• Controlling the energy exchange between the high voltage on-board electrical system and the 12 V on-board electrical system

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

• Battery management system control unit
  • High-voltage battery voltage
  • Temperature of high-voltage battery
• Power electronics control unit
  • Charging voltage/current
  • Status of electrical machine
  • Rotational speed of electrical machine
  • Available torque from electrical machine
  • Torque of electrical machine
• DC/DC converter control unit (N83/1)
  • DC/DC converter control unit, status
• Charger (N83/5)
  • Status of charger
• Electric refrigerant compressor
  • Status of electric refrigerant compressor

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 
• Function sequence for battery management 
• Function sequence for energy exchange of the high voltage and 12 V on-board electrical system 

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

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

• Voltage of high-voltage battery
• Current flows from and to the high-voltage battery
• Temperature of high-voltage battery
• Current flows of the attached consumers of the high voltage onboard electrical system

  The powertrain control unit uses them to calculate the SOC value and then presents this value as 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:

• Function sequence for controlling the contactor Additional function requirements for controlling the contactor 
• V on-board electrical system voltage above the minimum value (>9 V)

Function sequence for controlling the contactor 

A circuit 30c is generated from circuit 30 in the battery compartment prefuse box (F33). 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 battery compartment prefuse box or the high-voltage disconnect device is opened as a result of a crash, the circuit 30c signal line is interrupted and the contactor in the high-voltage battery (S7) disconnects the connection of the high-voltage battery to the high voltage on-board electrical system.

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 high voltage on-board electrical system components 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 energy exchange of the high voltage and 12 V on-board electrical system 

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.

	Electrical function schematic, maximum performance and torque prognosis		PE08.30-P-2067-97NAH
	Overview of system components, hybrid drive system		GF08.30-P-9999GRH