Electric Machine Converter With Switchable Windings and Torque Limits
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Solution Overview
Problem
Traditional electric machines face limitations in nominal rotation speed due to back EMF, leading to overvoltage situations and reduced torque capabilities, and existing converter designs struggle with current transients during winding configuration changes.
Innovation Solution
A converter system with a control mechanism that allows stator windings to switch between low-speed and high-speed configurations, limiting torque during transitions and deactivating the converter stage to manage current transients, enabling fast configuration changes resembling a mechanical gearbox.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the nominal rotation speed of a permanent magnet machine is increased to exceed the traditional 40% limit, then the speed capability is improved, but the back EMF increases linearly leading to overvoltage situations that may damage the machine and AC system
Solution Approach 1:
The patent applies dynamics by making the winding configuration changeable during operation. The stator windings can switch between low-speed configuration (more series connected turns) and high-speed configuration (fewer series connected turns), allowing the machine to adapt its electrical characteristics to different operating speeds. This dynamic reconfiguration enables safe operation above the traditional 40% speed limit by reducing the back EMF through fewer series turns at high speeds.
Solution Approach 2:
The patent changes the electrical parameter of the stator windings by altering the number of series connected turns through configuration switches. This parameter change allows the machine to operate at different speed ranges with appropriate back EMF levels, enabling both high-speed operation (with reduced series turns) and high-torque operation (with increased series turns) without damaging overvoltage conditions.
2Speed
If a permanent magnet machine with higher nominal rotation speed is selected to avoid overvoltage, then the speed capability is improved, but the maximum peak torque and steady-state torque that can be reached with given currents are decreased
Solution Approach 1:
The patent uses dynamic winding reconfiguration to switch between torque-optimized and speed-optimized states. During high-torque requirements, the system configures the windings in low-speed configuration with more series turns. When speed is the priority, it switches to high-speed configuration with fewer series turns. This dynamic adaptation allows the machine to achieve both high torque and high speed capabilities with the same physical machine.
Solution Approach 2:
The patent makes a single permanent magnet machine universal by enabling it to perform both high-torque and high-speed functions through configurable windings. The same machine can serve as a low-speed high-torque machine or a high-speed machine depending on the winding configuration, eliminating the need for separate machines for different applications.
3Force
If an AC system is designed for higher peak current and steady-state current to compensate for reduced torque capability, then the torque capability at given currents is improved, but the device complexity and cost increase
Solution Approach 1:
Instead of increasing the AC system's current capacity, the patent changes the machine's internal parameters by reconfiguring the stator windings. This approach maintains torque capability across different operating conditions by adjusting the winding configuration rather than oversizing the AC system components, thereby avoiding increased device complexity and cost.
4Adaptability or versatility
If configuration switches are used to change the winding configuration during operation, then the adaptability to different speeds is improved, but current transients may occur during the change of winding configuration
Solution Approach 1:
The patent applies preliminary action by controlling the converter stage to limit current transients before they can cause damage during winding configuration changes. The control system anticipates the configuration change and pre-adjusts the converter operation to suppress harmful current spikes, ensuring reliable operation during transitions between low-speed and high-speed configurations.
Data Source
AI summary
A converter (101) for driving an electric machine whose stator windings are changeable to be in a low-speed configuration or in a high-speed configuration includes a converter stage (102) for supplying stator voltages to the stator windings, and a control system (103) that controls the stator windings to be in the low-speed configuration or in the high-speed configuration. The control system deactivates the converter stage during a change between the low-speed configuration and high-speed configuration and limits torque of the electric machine so that a torque limit is higher when the stator windings are in the low-speed configuration than when the stator windings are in the high-speed configuration. As the torque limit is changed when the number of series connected turns of the stator windings is changed, unwanted current transients can be reduced.