Air Core Brushless Motor with Variable DC Link Drive
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Solution Overview
Problem
Conventional electric motors, particularly induction motors and brushless permanent magnet motors, face efficiency limitations and high operating costs, especially in smaller sizes and high-duty cycle applications, which restrict their practical size for efficiency improvements.
Innovation Solution
A brushless electronically commutated motor with an air core construction and unique electronic drive configuration that maximizes efficiency by minimizing magnetic losses and eliminating the need for additional inductors, using a variable DC link topology and resonant switch mode converters to regulate power and control commutation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional slotwound motors with ferromagnetic stators are used, then magnetic flux can be effectively conducted, but magnetic induced losses and eddy current losses increase significantly
Solution Approach 1:
The patent extracts and removes the ferromagnetic stator core from the motor structure, replacing it with an air-core design. This eliminates the magnetic induced losses and eddy current losses that occur in conventional ferromagnetic stators, while the magnetic flux is instead conducted through the rotor portions and air gap. The stator windings are positioned in the air gap without a ferromagnetic core, directly reducing magnetic losses.
Solution Approach 2:
The patent changes the magnetic circuit parameters by transitioning from a ferromagnetic stator core to an air-core structure. This fundamental parameter change alters the magnetic flux path, requiring the flux to travel through air rather than high-permeability ferromagnetic material, thereby eliminating hysteresis and eddy current losses in the stator.
2Loss of energy
If surface mounted magnet air core motors are designed, then higher efficiency can be achieved, but winding inductance becomes very low and commutation synchronization is lost
Solution Approach 1:
The patent implements a feedback control system using Hall effect sensors to detect rotor position and provide real-time feedback to the electronic commutator. This feedback mechanism allows the commutation timing to be precisely adjusted based on actual rotor position, maintaining synchronization even with very low winding inductance. The system continuously monitors and adjusts commutation timing to compensate for the low inductance characteristics.
Solution Approach 2:
The patent replaces traditional mechanical commutation methods with an electronic commutation system that uses Hall effect sensors and electronic switching. This substitution allows for precise electronic control of commutation timing based on actual rotor position feedback, overcoming the limitations of low winding inductance that would prevent reliable mechanical commutation.
3Productivity
If conventional flux vector sine wave drives are used, then all three phase windings are powered simultaneously, but sensorless position determination becomes difficult and commutation accuracy decreases
Solution Approach 1:
The patent employs a six-step trapezoidal commutation method where only two of the three phase windings are energized simultaneously at any given time, creating distinct periodic commutation steps. During each 60-degree electrical interval, specific phase combinations are activated, creating clear periodic patterns in the back-emf signals. This periodic action with distinct commutation steps makes sensorless position determination feasible by detecting the zero-crossing points of the non-energized phase winding back-emf.
Solution Approach 2:
Instead of using all three phase windings simultaneously as in conventional flux vector drives, the patent inverts the approach by deliberately leaving one phase winding non-energized at any given time. This inversion strategy creates a clear, detectable back-emf signal in the non-energized phase that directly indicates rotor position, making sensorless commutation accurate and reliable.
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
The solution achieves significantly higher efficiency, reduced weight, and smaller size, leading to substantial energy cost savings and lower manufacturing costs, while maintaining reliability and simplicity in operation.
Implementation Method 1
The rotor is constructed of two ferromagnetic spaced apart co-rotating rotor portions having a circumferential array of alternating polarity permanent magnet poles that drive magnetic flux back and forth across an armature air gap created between the spaced apart rotor portions, and circumferentially through each of the rotor portions
Implementation Method 2
The air core armature has three phase windings that magnetically exert torque upon the rotor when the windings are electrically energized by the electronic drive
Implementation Method 3
The electronic drive is configured to convert electrical supply power into power that is synchronous with the rotor rotation by regulating power through a switch mode converter that varies voltage to a variable DC link
Implementation Method 4
The switch mode converter comprises a resonant converter. Resonant switch mode conversion is more efficient that PWM switching because the resonance causes the voltage and current to naturally pass through zero passively
Data Source
AI summary
An electronically commutated electric motor includes a rotor, a stator and an electronic drive. The rotor is journaled to rotate about an axis of rotation, the stator is stationary relative to the rotor, and the electronic drive provides synchronous power to the stator and drives the rotor. The rotor has two ferromagnetic radially spaced apart co-rotating rotor portions having a circumferential array of alternating polarity permanent magnet poles that drive magnetic flux back and forth across an armature air gap between said spaced apart rotor portions, and circumferentially through each of said rotor portions. The stator includes an air core armature supported in the armature airgap, and has a non-ferromagnetic structure where located in the magnetic flux in the armature air gap. Three phase windings wound on the armature magnetically exert torque upon the rotor when the windings are electrically energized by the electronic drive. The phase windings are wound from wire that is formed from bundled together multiple individually insulated conductor strands, wherein said strands are electrically connected in parallel and are electrically insulated between each other along their lengths where they lie in the magnetic flux in the armature airgap. The electronic drive is configured to convert electrical supply power into power that is synchronous with the rotor rotation by regulating power through a switch mode converter that varies voltage to a variable DC link supplying a transistor output H-bridge for commutating the phase windings. The electronic drive electrically energizes only two of the three phase windings simultaneously to provide trapezoidal excitation to the phase windings, leaving one of the three phase windings instantaneously electrically non-energized. The electronic drive monitors the instantaneous non-energized phase winding back-emf zero crossing events for controlling triggering of advances in the commutation.