Device and method for operating an electrical machine for a motor vehicle

A method for open-loop or closed-loop control of an electrical system and a propulsion system of a motor vehicle, with the propulsion system having an internal combustion engine and a transmission with a variable step-up and/or step-down ratio, the electrical system having a vehicle power supply system and at least one battery connected to the vehicle power system, and at least one electrical machine being provided which is operable during a normal charging mode as a generator for supplying current to the battery and to the vehicle power supply system from the propulsion system, and is also drivable by the propulsion system as a generator in a recuperation mode to produce a braking torque and to supply the at least one battery and the vehicle power supply system with current and the electrical machine is also operable as an electric motor for emitting torque to the propulsion system, the method comprising the acts of:

• controlling the at least one electrical machine in different operating states by different signals, in which case a charging voltage for the normal charging mode is produced automatically as a voltage reference variable for controlling the electrical machine from signals from a vehicle management as a function of the respective electrical power requirements from the vehicle power supply system and from the battery at any given time,
• automatically providing the respective torque demand at any given time as a torque reference variable for controlling the electrical machine as a function of respective torque requirements, at that time, for a positive or negative torque for the propulsion system, in which case changes in the voltage reference variable downwards and upwards are limited by predetermined torque limit values for the electrical machine which define a torque tolerance band, in which further case, changes in the torque reference variable upwards and downwards are limited by predetermined voltage limit values for the electrical machine, which form a voltage tolerance band,
• automatically cyclically checking the reference variables,
• controlling the electrical machine automatically by the voltage reference variable, wherein a change takes place to the torque reference variable for controlling the electrical machine, provided that the torque tolerance band and the voltage tolerance band are complied with, when and for as long as the torque reference variable demands from the electrical machine a positive or negative torque which is not the same as the predetermined torque on the electrical machine in order to produce the charging voltage.

A method for operating at least one electrical machine for a motor vehicle equipped with a propulsion system, a vehicle power supply system, and at least one battery, the method comprising the acts of:

• coordinating torque requirements for the propulsion system and voltage requirements for the vehicle power supply system and the at least one battery for the vehicle power supply system, by forming a voltage reference variable for the voltage requirements of the vehicle power supply system and a torque reference variable for the torque requirements of the propulsion system;
• limiting the voltage reference variable by upper and lower torque limit values which must not be overshot or undershot in an event of changes to the voltage reference variable;
• and
• limiting the torque reference variable by voltage limit values which must not be overshot or undershot in an event of torque changes;
• and
• utilizing the voltage reference variable and torque reference variable to control the electrical machine in different operating states.