Surface PM Motor Rotor Structure for Q-Axis Flux Blocking
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Solution Overview
Problem
Surface mounted permanent magnet motors face issues with cogging torque and stator winding faults, particularly short-circuited phases leading to excessive heat and reduced motor performance, due to limitations in d-axis and q-axis inductance.
Innovation Solution
The motor design incorporates magnetically conductive magnet carriers with curved outer faces and central flux barrier regions of varying permeability, which block undesirable q-axis flux while allowing beneficial d-axis flux, thereby achieving high inductance and reducing cogging torque, and uses separate stator windings to manage faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the q-axis inductance is increased to reduce short-circuit drag torque, then the motor can operate safely with shorted phases, but the motor runs out of voltage at lower speeds
Solution Approach 1:
The magnet carrier employs different magnetic permeability regions: a central barrier region of relatively low permeability to block q-axis flux, surrounded by regions of relatively high permeability to conduct d-axis flux. This local differentiation of magnetic properties allows independent control of d-axis and q-axis inductance, enabling high q-axis inductance for fault tolerance without proportionally increasing d-axis inductance that would limit speed range
2Power
If the d-axis inductance is increased by adding more stator winding turns, then the motor can generate more torque, but the q-axis inductance increases proportionately which limits maximum speed
Solution Approach 1:
The magnet carrier structure creates spatially differentiated magnetic pathways: d-axis flux flows through high permeability regions enabling strong torque, while q-axis flux is blocked by the low permeability central barrier. This allows the motor to achieve high d-axis inductance for torque generation without proportionate increase in q-axis inductance, thus maintaining wide speed range
3Adaptability or versatility
If the motor operates with a shorted phase winding, then the motor can continue rotating, but excessive heat builds up causing potential damage
Solution Approach 1:
The magnet carrier's central barrier region of low magnetic permeability proactively blocks q-axis flux paths that would otherwise create excessive current in shorted phases. By preventing the harmful flux linkage before it can cause excessive heating, the motor can safely operate with shorted phase windings without requiring complex protection systems
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 design effectively limits short-circuit drag torque, maintains high power levels across a wide range of speeds, and reduces the risk of demagnetization and cogging torque, while allowing for continuous operation even with faults in one phase.
Implementation Method 1
each of the magnet carriers comprises a central flux barrier region of relatively low magnetic permeability that blocks q-axis flux flowing from the stator radially towards the rotor axis
Implementation Method 2
a first one of those high permeability regions defining a continuous flux path that extends on the side of the barrier region closest to the rotor axis and links a central region of each of the two magnets carried by the magnet carriers
Data Source
AI summary
A surface mounted permanent magnet motor includes a stator having poles and windings. A rotor includes magnets fixed to an outer surface of a support assembly. The stator poles face the outer surface of the rotor. The support assembly has magnetically conductive magnet carriers spaced from each other and supporting two magnets of opposing polarity. The magnet carriers have a central region of low permeability that blocks q-axis flux flowing from the stator radially towards the rotor axis surrounded by regions of high permeability. A first high permeability region defines a continuous flux path on the side of the barrier region closest to the rotor axis and links central regions of the two magnets carried by the magnet carriers. A second high permeability region is located on the side of the barrier nearest the stator that defines a flux path linking the end regions of the magnets.