Permanent-Magnet Motor Control with Variable Freewheel Angle
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Solution Overview
Problem
Permanent-magnet electric machines face challenges in controlling power and efficiency due to increasing back emf as the rotor accelerates, making it difficult to drive current and maintain power delivery effectively.
Innovation Solution
A method involving sequential excitation and freewheeling of the stator winding, with a lookup table of control values for varying excitation voltages, allowing for adjustment of the freewheel angle to maintain constant power and efficiency across a range of voltages, and incorporating a speed-correction value to account for changes in speed and voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rotor accelerates, then the back emf increases, but it becomes increasingly difficult to drive current and power into the electric machine
Solution Approach 1:
The patent applies dynamics by making the freewheel angle variable rather than fixed. The control system dynamically adjusts the freewheel angle based on the excitation voltage level to compensate for changing back emf conditions during rotor acceleration, enabling maintained power delivery across varying speeds
Solution Approach 2:
The patent changes the parameter of freewheel angle in response to excitation voltage changes. By varying this angular parameter according to operating conditions (voltage and speed), the system compensates for increasing back emf and maintains effective current and power delivery to the winding
2Power
If the excitation voltage decreases, then power delivery may be reduced, but current can be driven into the winding for a shorter period
Solution Approach 1:
The patent changes the freewheel angle parameter in response to excitation voltage changes. When voltage decreases, the freewheel angle is decreased (extending the current drive period), and when voltage increases, the freewheel angle is increased (shortening the current drive period), thereby maintaining substantially constant power delivery
Solution Approach 2:
The control system uses feedback from the excitation voltage level to adjust the freewheel angle. This closed-loop approach ensures that power delivery remains substantially constant (within +/- 5% variance) despite variations in excitation voltage by compensating through angle adjustment
3Ease of operation
If the freewheel angle is fixed, then control is simpler, but power and efficiency cannot be maintained across varying voltages and speeds
Solution Approach 1:
The patent transitions from a static fixed freewheel angle to a dynamic variable freewheel angle controlled by a lookup table. This allows the system to adapt to different voltage and speed conditions while maintaining relatively simple control through pre-stored control values
Solution Approach 2:
The control system performs preliminary action by storing lookup tables of control values for different voltage levels before operation. During operation, the appropriate freewheel angle is quickly retrieved from the lookup table based on measured voltage and speed, avoiding complex real-time calculations while achieving adaptive 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 approach enables better control over power and efficiency, ensuring substantially constant power delivery with a variance of no more than +/- 5% and maintaining efficiency of at least 75% across a range of excitation voltages, suitable for battery-powered applications.
Implementation Method 1
As the permanent-magnet rotor of an electric machine rotates, it induces a back emf in a winding of the electric machine
Data Source
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AI summary
A method of controlling a single-phase permanent-magnet electric machine, the method comprising: sequentially exciting and freewheeling a winding of the electric machine, wherein the winding is excited by an excitation voltage and is free wheeled over a freewheel angle; and varying the freewheel angle in response to changes in the excitation voltage. Additionally, a control system for an electric machine, and a vacuum cleaner incorporating the control system and electric machine.