Electric Machine Excitation Timing for Back-EMF Speed Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As the permanent-magnet rotor of an electric machine rotates, the induced back emf increases, making it difficult to drive current and power into the machine, especially at higher speeds, complicating control over the electric machine.
Innovation Solution
The electric machine is controlled by exciting the winding in synchrony with zero-crossings at low speeds, advancing excitation by a fixed period at intermediate speeds, and varying the advance time with speed at high speeds, using a lookup table for speed-correction values and excitation voltage to maintain consistent power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the winding is excited in synchrony with zero-crossings of back emf, then the control is simple at low speeds, but the ability to drive current and power into the winding deteriorates as speed increases
Solution Approach 1:
The patent applies dynamics by making the excitation timing adaptive rather than fixed. The control system dynamically adjusts the excitation timing based on operating conditions: at low speeds, excitation occurs in synchrony with zero-crossings for simple control, while at higher speeds, excitation is advanced by a variable period that increases with speed to overcome back emf and maintain power delivery capability.
Solution Approach 2:
The patent changes the timing parameter of winding excitation based on speed conditions. The excitation advance period is varied as a function of rotor speed, allowing the system to optimize current drive capability at different operating points while maintaining simple synchronous control at low speeds.
2Power
If the winding is excited in advance of zero-crossings by a fixed period of time, then more power is driven into the winding at intermediate speeds, but the control complexity increases
Solution Approach 1:
The patent segments the speed range into three distinct ranges (low, intermediate, high) and applies different control strategies to each segment. This segmentation allows the system to use simple synchronous control at low speeds, fixed advance control at intermediate speeds, and variable advance control at high speeds, thereby managing complexity while optimizing performance across the full operating range.
3Power
If the winding is excited in advance of zero-crossings by a variable period of time, then power control is improved at high speeds, but the control algorithm complexity increases
Solution Approach 1:
The patent makes the excitation advance period a dynamic parameter that varies with rotor speed in the high-speed range. This dynamic adjustment allows the control system to maintain optimal power delivery and control precision at high speeds where back emf is significant, while the variation follows a defined relationship with speed to manage algorithm complexity.
4Power
If a three-stage speed range control method is implemented, then consistent power delivery is achieved across wide speed ranges, but the control system complexity increases
Solution Approach 1:
The patent divides the operating speed range into three segments and applies optimized control strategies to each: synchronous excitation for low speeds, fixed advance excitation for intermediate speeds, and variable advance excitation for high speeds. This segmentation enables consistent power delivery across the full range while managing control complexity through structured differentiation.
Solution Approach 2:
The control system is designed to perform multiple functions across different operating conditions using a single unified control framework. The same control system handles all three speed ranges, switching between different excitation timing strategies as needed, thereby achieving universal power delivery consistency without requiring separate control systems for each range.
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 method allows for efficient control of the electric machine across a wide speed range, ensuring consistent power delivery and reducing the complexity of control algorithms, thereby improving the machine's operational efficiency and stability.
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
AI summary
A method of controlling an electric machine that includes exciting a winding of the electric machine in synchrony with zero-crossings of back emf when operating over a first speed range. The method then includes exciting the winding in advance of the zero-crossings by a fixed period of time when operating over a second speed range, and exciting the winding in advance of the zero-crossings by a period of time that varies with speed when operating over a third speed range. Additionally, a control system for an electric machine, and a product incorporating the control system and electric machine.