Single-Phase PM Motor Control for High-Speed Back-EMF Limits
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Solution Overview
Problem
High-speed single-phase permanent-magnet electric machines face challenges in driving current and power due to increasing back emf, and high rotor losses, which are exacerbated by the need for additional phases that increase system cost.
Innovation Solution
A control system that drives a single-phase permanent-magnet electric machine with advanced timing of winding excitation and freewheeling to maintain constant output power and efficiency across a wide speed range, using a c-shaped stator with a high fill-factor winding and varying the advance and freewheel angles in response to speed and voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the speed of the electric machine increases, then the back emf in the phase winding increases, but it becomes increasingly difficult to drive current and thus power into the phase winding
Solution Approach 1:
The control system excites the winding in advance of zero-crossings of back emf by an advance angle, proactively driving current into the winding before the back emf rises to opposing levels, thereby overcoming the difficulty of driving power into the winding at high speeds
Solution Approach 2:
The control system dynamically varies the advance angle and freewheel angle in response to changes in speed and voltage, adapting the excitation timing to maintain optimal power transfer across the operating range despite varying back emf conditions
2Loss of energy
If additional phases are provided to achieve high-speed operation, then rotor losses are reduced, but the cost of the electric system increases
Solution Approach 1:
The invention changes the operating parameters of the single-phase machine by implementing controlled excitation with variable advance and freewheel angles, enabling the single-phase system to achieve high-speed operation with reduced rotor losses without requiring additional phases
Solution Approach 2:
The control system makes the single-phase winding perform multiple functions by strategically timing excitation and freewheeling periods, allowing the single-phase configuration to achieve performance characteristics typically requiring multi-phase systems
3Reliability
If the winding is excited during the region of falling back emf, then current spikes may be avoided, but less torque is achieved for a given level of current
Solution Approach 1:
The control system applies partial excitation by freewheeling the winding during part of the falling back emf region, avoiding current spikes while accepting reduced torque in that specific interval, compensated by optimized excitation during other portions of the cycle
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
Enables high-speed operation with efficiency exceeding 80% and constant output power over a broad range of speeds and voltages, reducing costs by eliminating the need for additional phases and minimizing copper losses.
Implementation Method 1
single-phase permanent-magnet electric machine
Implementation Method 2
c-shaped stator about which the winding is wound
Implementation Method 3
back emf in the phase winding increases
Data Source
AI summary
An electric system that includes a single-phase permanent-magnet electric machine and a control system for driving the electric machine under load at speeds in excess of 60 krpm. Additionally, a product that includes the electric system.