Split Stator Winding Switching for Three-Phase Machine Speed Control
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Solution Overview
Problem
Existing three-phase permanent magnet AC electric machines face challenges in reducing back EMF and increasing torque and power at higher speeds due to the increase in induced voltage, which limits machine speed, and existing solutions complicate the stator winding configuration with additional switches and potential circulating currents.
Innovation Solution
A method for switching between full winding control mode and half winding control mode in a three-phase PM electric machine with split stator windings, using inverter switches and switch assemblies to adjust the winding configuration based on motor speed and torque command signals, reducing the number of required switches and leads while minimizing circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If split windings are electrically coupled in series for low machine speeds, then torque/ampere ratio is maximized, but back EMF increases as speed increases until it reaches DC bus voltage, limiting machine speed
Solution Approach 1:
The patent implements dynamic reconfiguration of the split windings from series to parallel connection based on machine speed. At low speeds, windings are connected in series to maximize torque/ampere ratio. When back EMF approaches DC bus voltage at higher speeds, the system dynamically switches to parallel connection to reduce back EMF and maintain speed capability, thus adapting the electrical configuration to operating conditions.
Solution Approach 2:
The patent changes the electrical parameters of the stator windings by altering their connection configuration. By switching from series to parallel connection, the effective winding turns ratio changes, which directly affects the back EMF constant and allows the machine to operate at higher speeds without exceeding the DC bus voltage limit.
2Power
If switches are provided to control split windings configuration, then back EMF is reduced at high speed, but the number of required AC switches increases to nine and total machine leads to ten
Solution Approach 1:
The patent merges the function of additional switching devices with the existing inverter switches. By utilizing the existing inverter switches in combination with simpler switch assemblies containing only two AC switches per phase, the system achieves winding reconfiguration without requiring nine AC switches and ten leads as in conventional solutions, thus reducing overall device complexity.
Solution Approach 2:
The inverter switches are designed to perform multiple functions: they control both the standard inverter operation and the winding reconfiguration between series and parallel connections. This multi-functionality eliminates the need for dedicated switching devices solely for reconfiguration, reducing the total number of switches and leads required.
3Adaptability or versatility
If coils are required to be in the same stator slot for parallel operation, then winding reconfiguration is achieved, but lower coil inductance in parallel operation may need higher switching frequencies to reduce current ripple
Solution Approach 1:
The patent places coils in the same stator slot during the design phase to enable parallel operation capability. This preliminary arrangement of coils facilitates easy reconfiguration between series and parallel connections, though it results in lower coil inductance that requires higher switching frequencies to maintain acceptable current ripple levels during parallel operation.
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 method effectively reduces back EMF and increases torque and power at higher speeds by optimizing the winding configuration, reducing the number of switches and leads, and minimizing circulating currents, thereby enhancing the machine's performance and efficiency.
Implementation Method 1
Switches are provided and are controlled so that the split windings for each phase are electrically coupled in series for low machine speeds and are electrically coupled in parallel when the speed of the machine reaches the point where the back EMF reduces the machine torque
Implementation Method 2
because the induced voltage is proportional, especially as the speed of the machine increases, the back electro-motive force (EMF) generated by the machine also increases as the machine speed increases
Implementation Method 3
separate the stator windings for each phase of an electric machine into two split windings to reduce machine back EMF at high machine speed
Data Source
AI summary
A method for controlling switching between a full winding control mode and a half winding control mode for a multi-phase electric machine. The machine includes a stator and a rotor, split stator windings for each phase of the machine, where each stator winding includes a first winding section and a second winding section, an inverter circuit including a pair of inverter switches for each phase of the machine, where the pair of inverter switches for each phase is electrically coupled to the first and second winding sections for that phase, and a plurality of switch assemblies for switching between the full winding mode and the half winding mode, where each switch assembly is electrically coupled to the pair of inverter switches and the first and second winding sections for a particular phase, and where each switch assembly includes a first AC switching device and a second AC switching device.