Switch Arrangement for Electric Motor Star Point Isolation
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Solution Overview
Problem
Inverter switch failures in electric motors or generators can lead to unwanted circulating currents due to short circuits, causing overheating, rapid deceleration, or directional deviations, especially in applications like electric vehicles and wind turbines, as existing solutions do not effectively manage these faults.
Innovation Solution
A single semiconductor switch is used to create and disconnect the star point connection of the coil windings, employing an n-phase bridge rectifier and a voltage clamping device to quickly interrupt currents and prevent torque production, utilizing a control system to activate the switch in case of faults or abnormal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single switch is used to disconnect the star point connection, then the response time for preventing circulating currents is improved, but the device complexity increases due to additional components
Solution Approach 1:
The patent combines the star point connection function with a single semiconductor switch that can simultaneously handle multiple phase connections. The switch integrates the functionality of multiple discrete switches into one component, achieving fast response time while managing complexity through functional integration rather than adding separate components for each phase.
Solution Approach 2:
The single semiconductor switch is designed to perform multiple functions: it serves as the star point connection for all three phases simultaneously, provides overcurrent protection, and enables rapid disconnection. This multi-functional design eliminates the need for separate switches per phase, improving response time without proportionally increasing device complexity.
2Device complexity
If inverter switches are used without additional protection, then the device complexity is reduced, but the reliability deteriorates due to circulating currents causing overheating and failure
Solution Approach 1:
The patent implements a preliminary protection mechanism where the single switch is positioned to disconnect the star point connection before circulating currents can cause damage. The control system monitors for fault conditions and activates the switch proactively to prevent overheating and failure, rather than reacting after damage occurs. This preliminary action ensures reliability while maintaining relatively simple device architecture.
Solution Approach 2:
The single semiconductor switch acts as an intermediary protective element between the inverter switches and the motor windings. It mediates the fault condition by providing a controlled disconnection path that prevents circulating currents from damaging the system, thereby improving reliability without requiring complex protection circuits for each inverter switch.
3Reliability
If multiple switches are used to protect each phase, then the reliability is improved, but the device complexity and cost increase significantly
Solution Approach 1:
The patent merges the protection function for all three phases into a single semiconductor switch located at the star point connection. This consolidated approach provides equivalent reliability to having multiple switches per phase while dramatically reducing device complexity. The single switch handles the collective protection need for all phases simultaneously.
Solution Approach 2:
The single switch is designed with universal protection capability that covers all three phases and multiple fault conditions. It provides overcurrent protection, short-circuit protection, and rapid disconnection functionality for the entire three-phase system, eliminating the need for separate protection mechanisms for each phase and reducing overall device complexity while maintaining high reliability.
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 prevents circulating currents and torque production, ensuring safe shutdown and preventing overheating or unintended braking torques by isolating the star point connection quickly, thereby enhancing operational safety and reliability.
Implementation Method 1
The switch is arranged in a closed circuit state in which the switch has low resistance to current flow therethrough, and in an open circuit state in which the switch provides electrical isolation across the switch
Implementation Method 2
a voltage clamping device, which limits a voltage across the switch, is connected in parallel with the switch
Implementation Method 3
an n phase bridge rectifier having n diode legs with two diodes incorporated within each leg to provide 2n diodes in total in the bridge rectifier
Implementation Method 4
the unwanted circulating currents being determined by the internally generated EMFs of the electric motor/generator
Data Source
Figure 1~2
Figure 3~4
Figure 5~6C
AI summary
A switch arrangement for an electric motor or generator having a plurality of coil windings that during operation of the electric motor or generator are electrically coupled to form a star point connection and that are arranged to have different voltage phases applied across the respective coil windings, the switch arrangement comprising a rectifier arranged to be coupled to the respective plurality of coil windings, wherein the rectifier is arranged to rectify an alternating current flowing in the respective coil windings and provide the rectified AC current to a DC output; and a switch coupled across the rectifier DC output, wherein the switch is operable to electrically isolate the plurality of coil windings.