Sensorless Permanent Magnet Machine Using Rotating Transformer
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Solution Overview
Problem
Conventional methods for angular position and velocity estimation in permanent magnet synchronous machines, especially at zero and low speeds, lack accuracy and are complex, costly, and reduce power density, making them unsuitable for larger applications.
Innovation Solution
A sensorless electrical machine system utilizing a stator with a primary transformer coil and embedded permanent magnets, an inverter/active rectifier component, and a position and velocity decoder to estimate rotor position and velocity, eliminating the need for resolvers and improving power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensorless algorithms based on extended rotor flux are used at medium and high speed, then the negative effect of non-ideal resolver characteristics is reduced, but accuracy in rotor position estimation at zero and low speed deteriorates
Solution Approach 1:
An excitation coil is introduced as an intermediary component on the rotor that, when energized by a high-frequency signal from the primary transformer coil, creates an auxiliary magnetic field. This auxiliary field interacts with the stator windings to generate measurable voltages that serve as a mediator for position estimation, enabling accurate sensing at zero and low speeds without relying on resolver characteristics
Solution Approach 2:
The patent replaces the mechanical resolver system with an electrical field-based sensing mechanism. By substituting the mechanical/electromagnetic resolver with a high-frequency excitation coil and primary transformer coil arrangement, the system eliminates resolver-related issues (amplitude imbalance, imperfect quadrature, inductive harmonics) while achieving accurate position estimation across the full speed range
2Measurement precision
If a resolver is used for position sensing, then rotor position information is available, but system complexity and cost increase
Solution Approach 1:
The resolver component is completely extracted and removed from the system. Instead of using a separate mechanical position sensing device, the patent integrates position sensing functionality directly into the electrical machine structure through the excitation coil and primary transformer coil, eliminating the need for resolvers and their associated complexity
Solution Approach 2:
The primary transformer coil serves multiple functions: it acts as both the power transmission component for the high-frequency excitation signal and the sensing element for position detection. The excitation coil on the rotor similarly serves dual purposes, creating both the auxiliary magnetic field for sensing and interacting with stator windings for power conversion, thereby reducing overall system complexity
3Measurement precision
If sensor windings are added to each pole element, then accurate rotor position information is generated, but power density of the machine is considerably reduced
Solution Approach 1:
The sensing function is merged with the existing power winding structure. The primary transformer coil is integrated into the stator winding assembly, and the excitation coil is integrated into the rotor structure. This merging allows the same physical components to serve both power conversion and position sensing functions, avoiding the need for separate sensor windings that would reduce power density
Solution Approach 2:
The machine's own windings and magnetic field structure are used to provide position sensing information. The excitation coil and primary transformer coil utilize the machine's inherent electromagnetic structure to generate position signals, eliminating the need for external or additional sensing components that would compromise power density
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 system provides accurate rotor position and velocity estimation, enhancing reliability, complexity, and cost-effectiveness while maintaining power density, suitable for larger applications.
Implementation Method 1
An excitation coil is wound on the rotor and is operatively connected to form a rotating transformer with the primary transformer coil
Implementation Method 2
A rotor is operatively connected to rotate relative to the stator, wherein the rotor includes a plurality of embedded permanent magnets
Implementation Method 3
The inverter/active rectifier component is operatively connected to the stator winding and the primary transformer coil to control the stator winding based on excitation in the stator winding from the excitation coil and permanent magnets
Implementation Method 4
An RC damper is connected in parallel with the excitation coil
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A new and useful electrical machine (102) includes a stator including a stator winding (104) and a primary transformer coil (106). A rotor (108) is operatively connected to rotate relative to the stator, wherein the rotor includes a plurality of embedded permanent magnets (PM). An excitation coil (110) is wound on the rotor and is operatively connected to form a rotating transformer with a primary transformer coil (106). An inverter/active rectifier component (112) is operatively connected to the stator winding and the primary transformer coil to control the stator winding based on excitation in the stator winding from the excitation coil and permanent magnets. The inverter/active rectifier component can be configured to direct external power through the stator to drive the rotor in a motoring mode and to deliver power from the stator to an external DC load in a generate mode. An AC power source (114) can be operatively connected between the inverter/active rectifier component and the primary transformer coil to control power to the rotating transformer. An RC damper (116) can be connected in parallel with the excitation coil.