Multiphase Winding Turns Adjustment for Electric Machine Speed Control
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Solution Overview
Problem
Traditional electric machines, such as permanent magnet and induction machines, face limitations in nominal rotation speed due to linearly increasing back electromotive force (EMF), leading to overvoltage issues and reduced torque capabilities when exceeding recommended speeds, necessitating higher peak and steady-state currents in AC systems.
Innovation Solution
An electric machine element with multiphase windings, comprising two portions with different cross-sectional conductor areas and slot allocations, allowing adjustable number of turns by selecting a star-point at the second ends of phase-windings, enabling flexible nominal rotation speed adjustment without compromising torque generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the nominal rotation speed of a permanent magnet machine is increased beyond the recommended limit, then the machine can operate at higher speeds, but the back electromotive force (EMF) increases linearly leading to overvoltage situations that may damage the machine and connected AC system
Solution Approach 1:
The multiphase winding is divided into multiple winding portions (first winding portion, second winding portion, etc.) with different conductor cross-sectional areas. Each portion contributes differently to the total number of turns, allowing the back EMF to be controlled within acceptable limits while maintaining the desired nominal rotation speed.
Solution Approach 2:
Different portions of the winding have different local properties - specifically, different conductor cross-sectional areas. The first winding portion has a larger conductor cross-sectional area compared to the second winding portion, creating local quality variations that enable flexible control of the total number of turns and back EMF.
2Object-affected harmful factors
If a permanent magnet machine with a higher nominal rotation speed is chosen to avoid overvoltage, then overvoltage issues are prevented, but the maximum peak torque that can be reached with a given peak current is reduced
Solution Approach 1:
The winding configuration is made dynamically adjustable by providing multiple winding portions that can be selectively connected to form the complete multiphase winding. Switches are provided to connect or disconnect different winding portions, allowing the total number of turns to be adjusted based on operating conditions. This enables the system to optimize between back EMF control and torque generation capabilities.
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 allows for increased flexibility in nominal rotation speed without exceeding maximum allowable back EMF, reducing the need for higher peak and steady-state currents, thereby enhancing torque production and system stability.
Implementation Method 1
This limit is due to a linearly increasing back electromotive force 'EMF' of a permanent magnet machine as a function of the rotation speed of the permanent magnet machine.
Implementation Method 2
at least one multiphase winding connected to the electric terminals and comprising at least two multiphase winding portions each comprising phase-windings
Data Source
Figure 1a
Figure 1b~1c
Figure 1d
AI summary
An electric machine element comprises electric terminals (101) for connecting to an external AC system and a multiphase winding (102) comprising at least two multiphase winding portions (103, 104). Each multiphase winding portion comprises phase-windings (106a-106c, 107a-107c) each having a first end (109) and a second end (110). The multiphase winding portions are successively connected to constitute chains (113a-113c) of the phase-windings so that the first ends of the phase-windings of a first one (103) of the multiphase winding portions are connected to the electric terminals. Each multiphase winding portion comprises switches (114a, 114b, 115a, 115b) for connecting the second ends of the phase-windings of the multiphase winding portion to each other. Thus, the number of turns of the multiphase winding is changeable by selecting which one of the multiphase winding portions has a star-point at the second ends of its phase-windings.