Rotor Flux Control in Permanent Magnet Electric Machines
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Solution Overview
Problem
AC permanent magnet electric machines face efficiency issues at high speeds due to increased back electromotive force (EMF), leading to higher copper and iron losses, especially when operating below a critical temperature where magnetic flux density changes become irreversible.
Innovation Solution
A method for rotor flux control in permanent magnet electric machines involves controlling fluid flow through the rotor based on the operating point of the machine, reducing fluid flow when the operating point is below a predetermined threshold and increasing it when above, while inversely controlling fluid flow through the stator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If fluid flow through the rotor is increased to cool the permanent magnets, then magnet temperature is reduced and flux density is maintained, but copper losses and iron losses increase due to additional current required for field weakening operation at high speeds
Solution Approach 1:
The cooling system dynamically adjusts fluid flow rate through the rotor based on operating conditions (speed and torque). At high speeds below base speed, reduced fluid flow minimizes cooling requirements and associated losses. Above base speed, increased fluid flow maintains magnet temperature and flux density, reducing field weakening current and associated copper and iron losses.
Solution Approach 2:
The system changes the fluid flow parameter through the rotor based on operating point thresholds. By monitoring speed and torque, the controller adjusts cooling intensity to match thermal requirements, optimizing the balance between temperature control and energy losses across different operating regions.
2Loss of energy
If fluid flow through the rotor is reduced to decrease copper and iron losses, then machine efficiency improves at high speeds, but magnet temperature increases and may exceed critical temperature causing irreversible flux density reduction
Solution Approach 1:
The cooling control system uses feedback from operating point monitoring (speed and torque sensors) to continuously adjust fluid flow rate. This closed-loop control ensures that cooling intensity matches actual thermal demands, preventing both overheating and excessive cooling losses while maintaining reliable operation across the full operating range.
3Power
If larger magnetic flux density is used in permanent magnets, then machine performance is improved, but back electromotive force increases at high speeds requiring additional field weakening current that increases copper and iron losses
Solution Approach 1:
The system dynamically changes the effective flux density parameter by adjusting magnet temperature through controlled fluid flow. At high speeds, increased cooling maintains higher flux density, reducing the field weakening current required and thereby reducing copper and iron losses while preserving machine performance.
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 approach enhances machine efficiency by managing temperature and magnetic flux density, reducing copper and iron losses, and improving overall performance across various operating conditions.
Implementation Method 1
circulating oil through the rotor and stator
Implementation Method 2
permanent magnets having large magnetic flux density which affects machine performance
Implementation Method 3
a variable force solenoid valve receiving a pressurized fluid and controlling circulation of the pressurized fluid through the rotor in response to a control command
Data Source
AI summary
Rotor flux control in a permanent magnet (PM) electric machine involves controlling fluid flow through the rotor based on the torque versus speed operating point of the PM machine. When the torque at a given speed falls below a predetermined threshold, the rotor receives a reduced fluid flow compared to when the torque is above the threshold. Fluid flow through the stator is controlled in an inverse manner relative to the rotor's fluid flow such that when the rotor experiences reduced fluid flow, the stator receives an increased fluid flow. This approach enables efficient control of the rotor's magnetic flux, enhancing the performance and efficiency of the PM electric machine during various operating conditions.