Electric Machine Drive Method for Uniform Power Switch Load Distribution
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Solution Overview
Problem
In motor vehicle drive technology, electric machines face uneven loading of power switches during motor start-up, leading to thermal peak loads and reduced starting torque, especially when starting from standstill or low speeds, which can result in jerking sensations for the driver.
Innovation Solution
The method involves controlling power electronics with controllable switches to distribute the load evenly by step-wise changing the operating point of the power electronics, using field-oriented control and rotating current vectors along lines of constant or changing torque, ensuring the starting torque remains constant and efficient, thereby reducing thermal peak loads and maintaining smooth vehicle acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional field-oriented control is used to generate high starting torque, then the electric machine can deliver the required starting torque, but the power switches experience uneven loading and thermal peak loads
Solution Approach 1:
The patent applies periodic action by cyclically rotating the current vector among multiple switching positions in the dq coordinate system. Instead of maintaining a fixed switching position that causes concentrated thermal loading, the control method periodically changes the active switch configuration, distributing the thermal stress over time and across multiple power switches. This periodic rotation of the current vector ensures that no single power switch bears the full brunt of the starting torque generation continuously, thereby reducing peak thermal loads while maintaining the required starting torque.
2Device complexity
If a single power switch configuration is used for starting torque, then the control is simple, but the load on individual power switches becomes highly concentrated
Solution Approach 1:
The patent implements dynamics by transitioning from a static switching configuration to a dynamic one. The current vector is continuously rotated in the dq coordinate system, which dynamically changes which power switches are active at any given moment. This dynamic switching pattern ensures that the load is distributed across multiple power switches over time, improving loading uniformity and reliability. The dynamic nature of the control adds complexity compared to fixed switching, but this complexity is managed through the structured rotation of the current vector among predefined switching positions.
3Force
If high current is applied to generate starting torque from standstill, then the vehicle can be moved, but thermal peak loads occur on the power electronics
Solution Approach 1:
The patent applies periodic action by cyclically rotating the current vector among multiple switching positions in the dq coordinate system. Instead of maintaining a fixed switching position that causes concentrated thermal loading, the control method periodically changes the active switch configuration, distributing the thermal stress over time and across multiple power switches. This periodic rotation of the current vector ensures that no single power switch bears the full brunt of the starting torque generation continuously, thereby reducing peak thermal loads while maintaining the required starting torque.
Data Source
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AI summary
The invention relates to a method for driving an electric machine (14) in the motor runup mode by means of power electronics (18), in particular for use in a motor vehicle (10), wherein the power electronics (18) have a plurality of driveable power switches (26), which are connected for the purpose of supplying an electrical current (I) to the electric machine (14) in polyphase form, wherein the power electronics (18) are driven in such a way that the electric machine (14) emits a runup torque (t), and wherein the power electronics (18) are driven, for outputting the runup torque (t), in such a way that the switching position of at least two of the power switches (26) is changed, with the result that the power switches (26) are subjected to a more uniform load.