Electric Machine Control Unit Low Temperature Heating
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Solution Overview
Problem
At low temperatures, the power output of the power output stage in electric machine control units for motor vehicles is reduced, leading to high voltage peaks that can damage the power output stage or driver unit due to increased internal series resistance of intermediate circuit capacitors, resulting in reduced performance and potential destruction.
Innovation Solution
The control unit incorporates a temperature signal input to actuate the power output stage with specific current application patterns that heat the intermediate circuit capacitor without generating effective torque, using stationary or alternating magnetic fields that the rotor cannot follow, thereby reducing voltage peaks and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the power output stage is operated at low temperatures, then the electric machine can function in cold environments, but the internal series resistance of the intermediate circuit capacitor increases causing high voltage peaks that can destroy the power output stage
Solution Approach 1:
The control unit performs a heating phase before normal operation at low temperatures. During this preliminary action, the processing unit actuates the power output stage with current application patterns that heat the intermediate circuit capacitor without generating effective torque, raising the capacitor temperature above the threshold (e.g., -10°C) before enabling full power operation.
Solution Approach 2:
The control unit uses periodic current application patterns during the heating phase, where the power output stage is actuated in cycles to generate heat in the intermediate circuit capacitor. This periodic actuation continues until the capacitor reaches the required temperature threshold.
2Reliability
If current is applied to heat the intermediate circuit capacitor, then the capacitor temperature increases improving power output stage reliability, but no effective torque is generated reducing productivity
Solution Approach 1:
The heating of the intermediate circuit capacitor is performed as a preliminary action before normal propulsion operation. The processing unit determines based on temperature signals whether the capacitor temperature is below the threshold, and if so, executes the heating current application pattern before enabling torque-generating operation.
Solution Approach 2:
The control unit converts the harmful effect of high voltage peaks (caused by high series resistance at low temperatures) into a beneficial heating effect. By deliberately applying current patterns that generate heat in the intermediate circuit capacitor, the system raises the capacitor temperature to reduce series resistance, thereby eliminating the original harmful effect.
3Reliability
If the power output stage is actuated with current application patterns that heat the intermediate circuit capacitor, then voltage peaks are reduced preventing damage, but the actuation complexity increases
Solution Approach 1:
The power output stage serves multiple functions: it can generate torque during normal operation and simultaneously heat the intermediate circuit capacitor during the preliminary heating phase. The same power output stage hardware is used for both propulsion and temperature management, avoiding the need for separate heating elements.
Solution Approach 2:
The intermediate circuit capacitor heats itself through the current application patterns generated by the power output stage. The capacitor's own internal series resistance converts electrical energy into heat, eliminating the need for external heating devices or complex thermal management systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively heats the intermediate circuit capacitor, maintaining it within a safe temperature range and preventing damage from high voltage transients, ensuring reliable operation even at low temperatures.
Implementation Method 1
the processing unit is designed to actuate the power output stage as a function of the temperature signal such that the energy store can be heated by a current application pattern generated by the power output stage
Implementation Method 2
The processing unit is preferably designed to actuate the power output stage as a function of the temperature signal such that the energy store can be heated by a current application pattern generated by the power output stage. The current application pattern preferably corresponds to a stator field, in particular a rotating magnetic field.
Data Source
AI summary
A control unit for an electric machine. The control unit has a processing unit and a power output stage connected to the processing unit. The power output stage is connected to outputs of the control unit for stator coils of a stator of the electric machine. The processing unit is designed to supply current to the power output stage for generating a stator field, in particular a rotating magnetic field. The control unit comprises an electrical energy store, in particular an intermediate circuit capacitor or accumulator, connected to the power output stage. The control unit includes an input for a control signal, for example a temperature signal. The processing unit is preferably designed to actuate the power output stage as a function of the temperature signal such that the energy store can be heated by a current application pattern generated by the power output stage. The current application pattern corresponds to a stator field which cannot generate an effective torque or a rotary motion, such as a full revolution of a rotor of the electric machine.