Self-Cascaded Electric Machine Torque Control
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Solution Overview
Problem
High-speed electric machines for hybrid-electric and electric vehicles face challenges due to high costs and complexity, primarily because of the need for expensive internal permanent magnet (IPM) machines that require high voltage inverters and intricate constructions, limiting their commercial viability.
Innovation Solution
A high-speed self-cascaded electric machine design with a stator having two sets of windings and a ferromagnetic rotor, where the controller determines an optimum phase shift angle based on detected currents and rotor position to generate high torque density and efficiency, reducing the need for expensive magnets and complex rotor-stator interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If internal permanent magnet (IPM) machines are used to achieve high power density and high efficiency, then the power density and efficiency are improved, but the manufacturing cost and system cost increase due to expensive magnets and high voltage inverter devices
Solution Approach 1:
The patent extracts and removes the expensive permanent magnets from the rotor construction, replacing them with a simpler ferromagnetic structure. This eliminates the need for costly sintered high energy-product magnets while maintaining the electric machine's ability to generate high power density through alternative magnetic field generation methods using stator windings only.
Solution Approach 2:
The patent replaces expensive permanent magnets with cheaper ferromagnetic materials that can be magnetized temporarily through electromagnetic induction. The ferromagnetic rotor acts as a temporary magnetic field carrier that is magnetized by the stator windings, eliminating the need for costly permanent magnet materials while achieving similar performance.
2Power
If IPM machines operate at high speed (e.g., 14,000 rpm) to obtain optimum power density, then the power density is improved, but the back electromagnetic field (EMF) increases, requiring high voltage inverter devices and increasing system cost
Solution Approach 1:
The patent changes the fundamental operating parameters by eliminating permanent magnets, which alters the back EMF characteristics. Without permanent magnets, the back EMF is reduced and can be better controlled through stator winding configuration and control strategies, allowing high-speed operation without requiring expensive high-voltage inverter devices.
3Power
If IPM machines use intricate rotor and stator constructions to achieve high power density, then the power density is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts the complex permanent magnet embedding structures from the rotor and replaces them with a simpler ferromagnetic core. The rotor construction is simplified to basic ferromagnetic material without the need for intricate magnet embedding, slotting, or bonding processes required for IPM machines.
Solution Approach 2:
Instead of using permanent magnets in the rotor to create magnetic fields, the patent inverts the approach by using electromagnetic induction from the stator windings to magnetize the ferromagnetic rotor temporarily. This reverses the traditional IPM machine architecture where magnets are passive and windings are active, making the windings the primary magnetic field source.
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 provides a high torque density, high efficiency, and low-cost electric machine capable of stable operation over a wide speed range, suitable for electric and hybrid-electric vehicle applications, with reduced volume and weight, and no need for brushes or slip rings, enhancing reliability and packaging efficiency.
Implementation Method 1
the controller is configured to detect an angular position of the rotor, detect the first current on the first set of windings, detect the second current on the second set of windings, and determine an optimum phase shift angle of the first current based on the angular position of the rotor, the detected first current, and the detected second current
Data Source
AI summary
An electric machine is disclosed comprising a first energy source, a second energy source, and a stator which comprises a first set of windings and a second set of windings. The electric machine has a rotor and a controller, the controller configured to control the first energy source to supply a first current to the first set of windings and control the second energy source to supply a second current to the second set of windings. The controller also detects an angular position of the rotor, detects the first current, detects the second current, and determines an optimum phase shift angle of the first current based on the angular position of the rotor, the first current, and the second current. The controller controls the first energy source based on the optimum phase shift angle to modify the first current supplied to the first set of windings.