Permanent-Magnet Motor Freewheel Angle Control for Back-EMF
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Solution Overview
Problem
Permanent-magnet motors face challenges in controlling power and efficiency due to increasing back emf as the rotor accelerates, leading to difficulties in driving current and maintaining consistent power delivery across varying speeds and voltages.
Innovation Solution
A method involving the sequential excitation and freewheeling of the stator winding, with a lookup table of speed-control values to adjust the freewheel angle based on motor speed and voltage, ensuring constant power and high efficiency by optimizing current flow and preventing current spikes.
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 motor
Solution Approach 1:
The patent applies dynamics by making the freewheel angle variable rather than fixed. The controller dynamically adjusts the freewheel angle based on motor speed, increasing it as speed increases to compensate for rising back emf. This dynamic adjustment maintains effective current drive capability across the operating speed range, resolving the contradiction between speed increase and power delivery difficulty.
Solution Approach 2:
The patent changes the parameter of freewheel angle to resolve the contradiction. By varying the freewheel angle parameter in response to speed changes, the system compensates for the increasing back emf effect. This parameter change allows the motor to maintain power delivery capability despite the adverse effect of rising back emf at higher speeds.
2Power
If the freewheel angle is increased to maintain power at high speeds, then power delivery is improved, but the control complexity increases
Solution Approach 1:
The patent implements feedback control where the controller monitors motor speed and uses this information to adjust the freewheel angle accordingly. This closed-loop feedback mechanism automatically adapts the control parameters to maintain optimal power delivery across varying speeds, managing control complexity through systematic feedback rather than complex open-loop calculations.
Solution Approach 2:
The patent applies preliminary action by pre-determining the relationship between speed and optimal freewheel angle. The controller is programmed with the knowledge of how back emf varies with speed, allowing it to proactively adjust the freewheel angle before power delivery becomes problematic, rather than reacting after the fact.
3Loss of energy
If sequential excitation and freewheeling is used to improve efficiency, then efficiency increases, but current spikes may occur when back emf falls
Solution Approach 1:
The patent applies preliminary anti-action by proactively increasing the freewheel angle when back emf is falling. This preemptive measure prevents current spikes from occurring in the first place, rather than attempting to correct them after they arise. The controller anticipates the falling back emf condition and adjusts the freewheel angle to counteract the potential harmful effect.
Solution Approach 2:
The patent uses dynamic adjustment of the freewheel angle to simultaneously achieve efficiency improvement and current spike prevention. By making the freewheel angle variable and responsive to back emf conditions, the system can optimize for efficiency during normal operation while automatically preventing current spikes when back emf falls, without requiring separate control mechanisms.
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 allows for consistent power delivery and high efficiency (at least 75%) across a wide speed range (up to 10 krpm) by adjusting the freewheel angle in response to speed and voltage changes, preventing current spikes and maintaining efficiency despite increasing back emf.
Implementation Method 1
As the rotor of a permanent-magnet motor rotates, it induces a back emf in a winding of the motor
Data Source
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AI summary
A method of controlling a permanent-magnet motor, the method comprising: sequentially exciting and freewheeling a winding of the motor, wherein the winding is free wheeled over a freewheel angle; and varying the freewheel angle in response to changes in speed of the motor. Additionally, a control system for a permanent-magnet motor, and a product incorporating the control system and motor.