Adjustable-Field Electric Motor With Excitation Ring for Wide Speed Range
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Solution Overview
Problem
Permanent magnet electric motors have a constant air gap magnetic field, limiting their ability to achieve high torque at low speeds, high efficiency at high speeds, and wide constant power operation, which restricts their application in various fields.
Innovation Solution
An electric motor design with an adjustable magnetic field, featuring a housing, stator, permanent magnet rotor, excitation rotor, and excitation ring assembly, where the excitation rotor and ring assembly generate an auxiliary magnetic field through an excitation winding, allowing for adjustment and control of the main magnetic field by varying the current, thereby enhancing torque, efficiency, and operational range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a permanent magnet electric motor uses a constant air gap magnetic field, then the structure is simple and reliable, but the motor cannot achieve high torque at low speeds, high efficiency at high speeds, and wide constant power operation
Solution Approach 1:
The motor is divided into two independent rotor systems: a permanent magnet rotor and an excitation rotor. Each rotor can be controlled independently, allowing the permanent magnet rotor to provide constant power operation while the excitation rotor adjusts the magnetic field strength to achieve high torque at low speeds and high efficiency at high speeds without complicating the overall structure
Solution Approach 2:
The excitation rotor enables dynamic adjustment of the air gap magnetic field strength through controlled current in its windings. This dynamic magnetic field adjustment allows the motor to adapt to different operational requirements (high torque at low speed, high efficiency at high speed) while maintaining a relatively simple permanent magnet rotor structure
2Force
If the air gap magnetic field is increased to provide high torque at low speed, then torque output improves, but efficiency at high speed deteriorates due to excessive magnetic field strength
Solution Approach 1:
The excitation rotor provides dynamic control of magnetic field strength. At low speeds, the excitation winding generates a strong magnetic field to produce high torque. At high speeds, the excitation current is reduced or reversed to weaken or eliminate the magnetic field, preventing energy losses and maintaining high efficiency
Solution Approach 2:
The magnetic field strength parameter is dynamically changed based on operating conditions. By adjusting the excitation current magnitude and direction, the system optimizes the magnetic field parameter to achieve high torque at low speeds and high efficiency at high speeds, avoiding the trade-off present in constant field motors
3Ease of operation
If a constant magnetic field is used in permanent magnet motors, then the control is simple, but the constant power operation range is limited
Solution Approach 1:
The control system is segmented into two independent control channels: one for the permanent magnet rotor and another for the excitation rotor. This segmentation allows simple control of the permanent magnet rotor for constant power operation while the excitation rotor is controlled to extend the operational range, achieving both simplicity and versatility
Solution Approach 2:
The excitation rotor serves multiple functions: it extends the constant power operation range, enables high torque at low speeds, and maintains high efficiency at high speeds. This multi-functionality allows the motor to operate across a wide speed range with constant power while keeping the control system relatively simple through unified dual-rotor 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
The design achieves high torque at low speeds, high efficiency at high speeds, and a wide range of constant power operation, making it suitable for applications in aerospace, wind power, and electric vehicles.
Implementation Method 1
the excitation rotor and ring assembly generate an auxiliary magnetic field through an excitation winding, allowing for adjustment and control of the main magnetic field by varying the current
Implementation Method 2
an air gap magnetic field (i.e., a magnetic field at a first air gap between a rotor and a stator) of the permanent magnet electric motor is provided by a permanent magnet steel
Data Source
AI summary
Provided are an electric motor having an adjustable magnetic field, and a vehicle. An excitation ring assembly of the electric motor includes an excitation ring having an outer ring wall and an inner ring wall and an excitation winding. An excitation rotor of the electric motor includes first permanent magnets and a rotor core provided with first and second magnetic pole forming sections that are circumferentially arranged alternately, a first magnetic pole cooperating portion corresponding to the first magnetic pole forming section, and a second magnetic pole cooperating portion corresponding to the second magnetic pole forming section. The first permanent magnets correspond to the first and second magnetic pole forming sections. A second air gap is defined by the outer ring wall and the first magnetic pole cooperating portion and a third air gap is defined by the inner ring wall and the second magnetic pole cooperating portion.