AC Motor Rotor Position Estimation Using High-Frequency Signal Injection
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Solution Overview
Problem
Existing sensorless techniques for determining the initial rotor position of alternating current motors face challenges at standstill or low speed due to insufficient back electromotive force and interference between injected carrier signals and command voltage signals, leading to delayed and reduced initial start-up torque application.
Innovation Solution
A method involving a controller that generates a high-frequency reference signal to estimate the initial rotor position by transforming current components into rotating d-q coordinates, allowing for accurate positioning without physical sensors, and adjusts voltage signals based on stator current feedback to minimize interference and achieve rapid estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency reference signals are injected simultaneously with command voltage signals to determine rotor position, then rotor position information can be obtained, but interference between the injected carrier signal and command voltage signals occurs causing delayed and reduced initial start-up torque
Solution Approach 1:
The patent applies preliminary action by determining the initial rotor position using high frequency signal injection BEFORE applying the command voltage signals for motor operation. The controller first injects the high frequency reference signal into the stator windings while the motor is stationary, processes the resulting stator current to estimate the initial rotor position, stores this position information, and then applies the command voltage signals. This sequencing eliminates interference between the carrier signal and command voltage signals, allowing immediate application of full start-up torque without delay or reduction.
2Measurement precision
If physical position sensors are used to determine rotor position, then accurate position information is obtained, but the size, weight and complexity of the AC motor system increase
Solution Approach 1:
The patent replaces the mechanical position sensor system with an electrical field-based sensing method. Instead of using physical sensors, cabling, and connectors that increase system complexity, the controller determines rotor position by injecting high frequency reference signals into the stator windings and processing the resulting stator current feedback. This substitution eliminates the need for additional mechanical components while providing accurate initial rotor position information through signal processing of the electrical system's natural response.
3Measurement precision
If high frequency reference signals are injected to determine rotor position at standstill, then position information can be obtained, but the initial start-up torque is reduced due to misalignment between estimated and real rotor positions
Solution Approach 1:
The patent resolves the torque reduction issue by performing the high frequency signal injection and rotor position estimation as a preliminary action BEFORE applying command voltage signals for motor operation. The controller determines the initial rotor position while the motor is stationary, stores this accurate position information, and then uses it as the basis for applying command voltage signals. This ensures that the rotor position estimation is completed without any torque application interference, allowing full start-up torque to be applied immediately with correct phase alignment.
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 accurate and rapid determination of the initial rotor position without physical sensors, allowing for immediate application of full start-up torque with correct phase angles, reducing delays and misalignment issues.
Implementation Method 1
generates a high-frequency reference signal to estimate the initial rotor position by transforming current components into rotating d-q coordinates
Implementation Method 2
application of voltages corresponding to the high frequency reference signal vector in stationary coordinates to the stator windings of the motor
Data Source
AI summary
Determination of an estimated initial angular position of the rotor of an AC motor includes application of voltages corresponding to a high frequency reference signal vector to the stator windings of the motor and production of an estimated initial angular position of the rotor as a function of the resulting q-axis stator current component iq_HF, adjustment of transformation of signal vectors from stationary to rotating coordinates and vice versa using the estimated angular position and production of an adjusted estimated angular position of the rotor as a function of the q-axis stator current component as adjusted. Determination of an initial estimated angular position of the rotor and production of an adjusted initial estimated angular position of the rotor is performed with the rotor at standstill and before initially applying voltage corresponding to the drive signal vector to the stator windings, and production of an initial value of a drive signal vector command in stationary coordinates uses the adjusted estimated angular position. Determination of an estimated angular position of the rotor after application of stator current may use a different method, such as a physical relative position sensor.