Permanent-Magnet Motor Control with Fixed Back-EMF Advance Timing
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Solution Overview
Problem
As an electric machine accelerates, the increasing back emf makes it difficult to drive power into the machine, requiring complex on-the-fly calculations for optimal excitation timing, which is inefficient and prone to current spikes.
Innovation Solution
A method of controlling the electric machine by exciting the stator winding in advance of back emf zero-crossings with a fixed advance time that varies with excitation voltage, allowing for consistent power delivery across speed ranges without the need for on-the-fly calculations, and employing a freewheeling period to manage current spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the advance angle is increased with rotor speed to maintain optimal excitation timing, then power delivery efficiency is improved, but device complexity increases due to required on-the-fly calculations
Solution Approach 1:
The patent pre-calculates and stores excitation timing data in lookup tables during system initialization or manufacturing, rather than performing calculations in real-time during operation. The controller simply retrieves pre-computed advance angle values based on measured rotor speed, eliminating the need for complex on-the-fly trigonometric calculations while maintaining optimal excitation timing across the entire speed range
Solution Approach 2:
The patent creates a simplified model of the optimal control behavior by storing lookup tables that copy the results of complex calculations into easily accessible data structures. Instead of reproducing the full mathematical model during operation, the system uses pre-computed tables that approximate the optimal advance angle for each speed range, significantly reducing computational burden
2Measurement precision
If on-the-fly calculations are performed to determine advance angle for each rotor speed, then control precision is improved, but processing time increases
Solution Approach 1:
The patent performs all complex timing calculations in advance during system initialization or manufacturing, storing the results in lookup tables. During actual operation, the controller only needs to measure rotor speed and retrieve the corresponding pre-computed advance angle from memory, reducing processing time from milliseconds to microseconds while preserving timing precision
Solution Approach 2:
The patent implements a dynamic lookup table structure that can be efficiently queried based on real-time rotor speed measurements. The system interpolates between stored values when necessary to maintain precision for speeds between table entries, achieving both fast response and high accuracy
3Use of energy by moving object
If excitation voltage is reduced to manage power consumption, then energy efficiency is improved, but output power decreases
Solution Approach 1:
The patent pre-calculates optimal excitation strategies that account for varying voltage levels and rotor speeds, storing these strategies in lookup tables. When voltage is reduced, the controller retrieves pre-computed timing parameters optimized for lower voltage conditions, maintaining output power through precise timing control rather than relying solely on voltage magnitude
Solution Approach 2:
The patent changes the control parameter from voltage magnitude to excitation timing (advance angle). By precisely controlling when excitation is applied relative to rotor position, the system can maintain effective power transfer even at reduced voltage levels, as the optimized timing ensures maximum electromagnetic coupling between stator and rotor fields
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 ensures efficient power delivery into the electric machine as it accelerates, maintaining consistent output power and reducing current spikes, thereby enhancing the machine's performance and efficiency.
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 permantent- magnet electric machine, the method comprising exciting a winding of the electric machine in advance of zero-crossings of back emf in the winding by a fixed advance time over a range of speeds. Additionally, a control system for an electric machine, and a vacuum cleaner incorporating the control system and electric machine.