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

Engine 276 in model 222.057/157 

Engine 276 in model 222.163 

Engine 276 in model 222.173 

Engine 651.9 in model 222.004/104 

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

Information on 12 V energy management of the 12 V on-board electrical system and to request the 12 V alternator (for diesel engine only) has been documented in the associated functions.

Function requirements, general points 

• Activate the hybrid drive system using the "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, in terms of electrical figures, represents the interface between battery management system (N82/2) and power electronics (N129/1) control units and the electrical refrigerant compressor (A9/5) as well as the charger (N83/5) (model 222.163/173). 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 this process, all protective mechanisms (e. g. insulation measurement, monitoring the Interlock circuit, crash sensors) that prevent risks from electrical shock are monitored and taken into account.

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 capacitors 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
  • Voltage of high-voltage battery
  • 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
  • Status of internal DC/DC converter (except model 222.163)
• DC/DC converter control unit (N83/1) (model 222.163)
  • DC/DC converter control unit, status
• Charger (model 222.163/173)
  • Status of charger
• CDI or ME control unit (except model 222.163/173)
  • Status of alternator (G2)
• 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 (except model 222.163) 
• Function sequence for an energy exchange of the high voltage system and the 12 V on-board electrical system (model 222.163) 

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 on-board electrical system

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

The SOC value serves, for example, as the basis for the charge level display in the instrument cluster (A1) and generally to control all hybrid functions that depend 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 is fully responsible for monitoring the high-voltage battery in terms of temperature, voltage, and currents, specifies the safety limit for these values, and transfers the 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 

• 12-V on-board electrical system voltage above the minimum value (> 9 V)

Function sequence for controlling the contactor 

In the rear pre-fuse box (F33) terminal 30 is turned into terminal 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 pre-fuse 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.

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 assembly parts that can be removed or opened. To do this there is a electrical bridge in each removable high voltage plug connection which interrupts the interlock circuit upon disassembly of the high voltage plug 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.

Additional information on the Interlock circuit has been documented in the associated functions.

Engine 276 in model 222.057/157

Engine 276 in model 222.173

Engine 651.9 in model 222.004/104

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.

Engine 276 in model 222.163

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 exchange of the high voltage and 12 V on-board electrical system (except model 222.163) 

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 over the CDI control unit and ME-SFI [ME] control unit with the alternator.

A DC/DC converter has been integrated into the power electronics control unit to guarantee a permanent supply with electrical energy to convert the high-voltage DC (primary voltage) and the 12 V DC (secondary voltage) and transfer it between the high-voltage on-board electrical system and the 12 V on-board electrical system.

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

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) 

• an external onboard power supply is connected up
• Previously still no engine running in this ignition sequence
• Terminal 15 (> 2 min)

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 222.163) 

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 is a voltage converter that generates 12 V DC. 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-2067-97SEH
	Overview of system components, hybrid drive system		GF08.30-P-9999LFH