Double-Stator PM Machine Torque via 30° Shift and Harmonic Injection
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Solution Overview
Problem
Double-stator machines face limitations in achieving high torque without increasing the maximum amplitude of supply currents, which is essential for improving torque density and power efficiency.
Innovation Solution
A double-stator PM machine with an outer and inner stator, each with a three-phase winding, and a PM rotor, where a control arrangement allows for a relative mechanical shift of 30° between the stators and circulates a third-order current harmonic component between them, enabling increased torque without amplifying supply currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the maximum amplitude of supply currents is increased to achieve higher torque, then torque increases, but inverter losses and power electronic converter ratings increase
Solution Approach 1:
The patent changes the current waveform parameters by injecting a third-order harmonic component into the supply currents. This modifies the current shape from pure sinusoidal to a waveform with harmonic content, which increases the fundamental torque-producing component while maintaining the same maximum current amplitude, thereby avoiding increased inverter losses and converter ratings
Solution Approach 2:
The patent uses a composite current waveform consisting of fundamental frequency components and third-order harmonic components. This composite current structure allows the machine to produce higher torque for the same maximum current amplitude, effectively resolving the contradiction between torque and inverter losses
2Force
If the maximum amplitude of supply currents is increased to achieve higher torque, then torque increases, but the converter rating increases
Solution Approach 1:
The patent changes the current waveform parameters by injecting a third-order harmonic component into the supply currents. This modifies the current shape from pure sinusoidal to a waveform with harmonic content, which increases the fundamental torque-producing component while maintaining the same maximum current amplitude, thereby avoiding increased inverter losses and converter ratings
3Force
If a third order current harmonic component is circulated between the stators, then torque density increases, but the control complexity increases
Solution Approach 1:
The control of the double-stator machine is segmented into independent control of outer and inner stators. Each stator's supply current is controlled separately with its own harmonic injection, allowing the complex harmonic control to be managed in modular sections rather than as a single complex system
Solution Approach 2:
The control arrangement uses feedback mechanisms to regulate the supply currents to both stators, ensuring that the third-order harmonic components are properly injected and that the torque production remains stable and controllable despite the increased complexity of harmonic current control
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 configuration enhances torque density while reducing inverter losses and power electronic converter ratings, offering improved power density and efficiency in motor operations.
Implementation Method 1
an outer stator (2a) comprising an outer three-phase winding (4a) on an outer core (1a), for generating an outer electromagnetic field dependent on an outer three-phase supply current (Io) supplied to the outer stator
Implementation Method 2
a PM rotor (3) rotated by the outer and inner electromagnetic fields in a gap formed between the outer and inner stators
Data Source
AI summary
A double-stator PM machine having: an outer stator generating an outer electromagnetic field dependent on an outer three-phase supply current; an inner stator generating an inner electromagnetic field dependent on an inner three-phase supply current; a PM rotor rotated by the outer and inner electromagnetic fields between the outer and inner stators; and a control arrangement controlling the outer and inner supply currents. There is an electrical connection between neutral points of the outer and inner stators. The control arrangement is configured for controlling the outer and inner supply currents such that there is a relative angle shift of 30° between the outer and inner supply currents and such that a third order current harmonic component is circulated between the outer and inner stators.