Sensorless AC Motor EMF Measurement via Winding Tap
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Solution Overview
Problem
Conventional electric vehicles rely on position sensors for motor control, which are prone to failure and expensive, and alternative methods like auxiliary windings for EMF measurement are complex and unclear about failure sources.
Innovation Solution
An electrical device with an alternating current electric motor and inverter that measures electromotive force directly by choosing a measurement point within the phase windings to divide them into out-of-phase parts, allowing EMF measurement even with non-zero current, without the need for position sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position sensors (encoders/Hall effect sensors) are used to control motor phases, then angular position can be detected, but the system becomes expensive and unreliable due to sensor failure
Solution Approach 1:
The invention extracts the EMF measurement function from the traditional position sensor system. By measuring the electromotive force directly from the motor windings through the inverter's existing voltage measurement capability, the system eliminates the need for separate position sensors (encoders/Hall sensors), thereby removing the reliability and cost issues associated with these sensors while maintaining angular position detection capability
Solution Approach 2:
The motor's own EMF generation is utilized to provide position information. The inverter measures the EMF induced in the motor windings during switching operations, and this self-generated signal is processed to determine angular position, making the system self-sufficient without external sensors
2Measurement precision
If auxiliary windings are added to measure EMF directly, then position information can be obtained without sensors, but the motor structure becomes complex and failure sources are unclear
Solution Approach 1:
The inverter's voltage measurement circuit, originally designed for general voltage monitoring, is made multi-functional by enabling it to measure EMF for position detection. This eliminates the need for separate auxiliary windings or dedicated EMF measurement circuits, maintaining simple motor structure while achieving sensorless position detection
Solution Approach 2:
The inverter acts as an intermediary that enables EMF measurement from existing motor windings without requiring additional windings. The inverter's switching operations and voltage measurement capability serve as the mediator to extract position information from the motor's natural EMF generation
3Measurement precision
If trapezoidal control is used to enable EMF measurement, then one phase can be measured during zero current period, but this control method is not suitable for sinusoidal motor controls
Solution Approach 1:
The invention implements a dynamic measurement strategy where the measurement timing and methodology adapt to the instantaneous motor state and control mode. During sinusoidal control, EMF is measured during freewheeling periods when current is naturally low, and the measurement is processed to account for the sinusoidal current profile, enabling compatibility with both trapezoidal and sinusoidal control methods
Solution Approach 2:
The measurement approach changes parameters based on control mode: during sinusoidal control, measurements are taken during freewheeling intervals and processed with knowledge of the sinusoidal current waveform, whereas trapezoidal control allows measurement during zero-current intervals. This parameter adaptation enables universal EMF measurement across different control strategies
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 direct and independent measurement of electromotive force for each phase, simplifying motor control and eliminating the need for position sensors, reducing costs and complexity while providing reliable operation.
Implementation Method 1
the measuring point being chosen so that it divides the winding into a first and a second part such that the induced electromotive forces of the two parts are out of phase with respect to each other
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The device (1) has a control inverter (5) for controlling phases (PA, PB, PC) of an alternating current (AC) electric motor (3). The motor includes measurement points (Ma, Mb, Mc) of the voltage with respect to a predefined potential, where one of the measurement points is provided on a winding of a phase. The point is chosen to divide the winding into impedance parts such that electromotive forces inducing the parts are out of phase with respect to each other. Measuring units (11A, 11B, 11C) measure the voltage between the measurement point and the predefined potential. The control inverter is a standard three phase inverter or an H shaped three-phase bridge inverter. The AC electric motor is a polyphase electric motor or an AC three phase electric motor. An independent claim is also included for a method for measuring the electromotive force of an electric device.