Electric Machine Winding Control for Back-EMF Power Stability
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Solution Overview
Problem
As the permanent-magnet rotor of an electric machine rotates, it induces a back emf that increases with speed, making it difficult to drive current and control power effectively, leading to inefficiencies and current spikes.
Innovation Solution
The method involves sequentially exciting and freewheeling the winding, adjusting the advance and freewheel angles in response to speed and voltage changes to maintain constant power and efficiency, using tables to simplify control and prevent current spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rotor accelerates, then the back emf magnitude increases, but it becomes increasingly difficult to drive current and control power into the electric machine
Solution Approach 1:
The patent applies dynamics by making the excitation timing adjustable rather than fixed. The control system dynamically modifies the advance angle and freewheel angle based on real-time speed feedback, allowing the excitation strategy to adapt to changing back emf conditions. This enables effective power control across a wide speed range despite the increasing back emf opposition.
Solution Approach 2:
The patent changes key operational parameters (advance angle and freewheel angle) to compensate for increasing back emf. By varying these timing parameters with speed, the system maintains optimal current drive capability and power control effectiveness even as the rotor accelerates and back emf increases.
2Reliability
If the excitation voltage exceeds the falling back emf, then current spikes arise, but the electric machine loses efficiency in the region of falling back emf
Solution Approach 1:
The patent applies preliminary action by implementing freewheeling before the back emf falls to problematic levels. The control system proactively switches to freewheel mode in anticipation of falling back emf, preventing current spikes before they occur and maintaining smooth current waveforms while preserving efficiency.
Solution Approach 2:
The patent skips the problematic region of falling back emf by rapidly transitioning to freewheel mode when approaching this region. This quick transition avoids the efficiency loss and current spike issues associated with operating in the falling back emf region, allowing the system to rush through the problematic zone without sustained exposure.
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 and smooth current waveforms across a range of speeds and voltages, maintaining efficiency and power consistency, even at high speeds where back emf is significant.
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 sequentially exciting and freewheeling a winding of the electric machine. The winding is excited in advance of zero-crossings of back emf in the winding by an advance angle, and the winding is freewheeled over a freewheel angle. The method then includes varying the advance angle and the freewheel angle in response to changes in the speed of the electric machine. Additionally, a control system for an electric machine, and a product incorporating the control system and electric machine.