Traction Motor Winding Reconfiguration to Prevent Back-EMF Braking
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Solution Overview
Problem
Existing electric vehicle traction systems face challenges in ensuring safety and reducing complexity and costs, particularly in preventing uncontrolled generator operations that can lead to sudden and dangerous braking.
Innovation Solution
The system includes an electric machine with variable configuration stator windings, a switching device that configures the stator between low-speed and high-speed configurations, and a control unit that manages the switching to prevent uncontrolled generator operations, eliminating the need for active safety strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active safety strategy (active short circuit) is adopted to prevent uncontrolled generator operations, then safety is improved, but device complexity and costs increase significantly
Solution Approach 1:
The control unit proactively manages the inverter switching states before uncontrolled generator operations can occur. By anticipating the risk condition (rotor voltages exceeding battery voltage) and preemptively controlling the switching device, the system prevents the dangerous braking condition without requiring complex active short circuit hardware.
Solution Approach 2:
The control unit acts as an intermediary between the inverter and the electric machine, mediating the power flow and switching operations. It coordinates the switching device to ensure safe operation during configuration changes, replacing the need for complex active safety strategies with intelligent control logic.
2Reliability
If active short circuit is generated to insulate the battery pack, then safety is improved, but manufacturing costs increase due to robust components and redundant branches
Solution Approach 1:
The control unit autonomously manages safety during configuration changes by coordinating the switching device and inverter states. The system serves its own safety needs through intelligent control logic rather than requiring externally redundant safety hardware, reducing manufacturing costs while maintaining reliability.
3Adaptability or versatility
If inverter is disconnected during configuration variation, then adaptability is improved, but risk of uncontrolled generator operations increases
Solution Approach 1:
The control unit prepares the inverter and switching device in advance before configuration changes occur. By pre-coordinating the switching states and ensuring safe operating conditions are established before disconnection, the system enables configuration variation while preventing uncontrolled generator operations.
Solution Approach 2:
The control unit continuously monitors the operating conditions and rotor voltages during configuration changes. This feedback mechanism allows real-time adjustment of the switching device and inverter states, ensuring that configuration variation proceeds safely without triggering uncontrolled generator operations.
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 approach simplifies the system structure, reduces costs, and ensures intrinsic safety and reliability by preventing uncontrolled generator operations, while maintaining high performance and a wide operating range.
Implementation Method 1
the voltages induced by the rotation of the rotor of the electric machine (back electromotive force-BEMF) tend to exceed the voltage level of the battery pack
Data Source
AI summary
An electric or hybrid electric-endothermic traction system, comprises an electric machine, an inverter, a battery, and a switching device configured to switch between a low-speed configuration, wherein the stator windings assume a first electric configuration, and a high-speed configuration, wherein the stator windings assume a second electric configuration, wherein the first electric configuration determines a voltage induced by the rotation of the rotor that, on reaching a pre-determined threshold value of the angular velocity of the rotor, exceeds a supply voltage of the battery pack, while the second electric configuration of the stator windings determines a voltage induced by the rotation of the rotor that is lower than the voltage of the battery for any angular velocity within a field of use of the machine. The switching device switches from the low-speed to the high-speed configuration when the rotor reaches a switching speed lower than or equal to the threshold value.