Sensorless Motor Control via High-Frequency Voltage Injection
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Solution Overview
Problem
Conventional motor control systems face challenges in accurately detecting phase currents of two phases using a single shunt current detecting method, especially when voltage levels of phases become close, leading to instability in vector control, and there is a lack of techniques for combining this method with rotor position estimation without position sensors.
Innovation Solution
A motor control device that includes a current detecting portion for armature winding currents, a superposing portion for adding a predetermined frequency voltage, and an estimating portion to derive the rotor position, allowing for position sensorless vector control by converting phase currents into control currents and correcting drive voltages to maintain phase current detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single current sensor is used to detect bus current, then cost is reduced, but phase current detection accuracy deteriorates when voltage levels of phases become close
Solution Approach 1:
The patent applies periodic action by injecting a high-frequency voltage signal with a specific frequency (e.g., several kHz to several MHz) that is distinct from the fundamental power frequency. This periodic high-frequency signal enables the extraction of rotor position information through the motor's magnetic anisotropy, allowing sensorless control to function accurately without requiring continuous high-precision current detection during the injection period.
Solution Approach 2:
The patent changes the parameter of voltage frequency by superimposing a high-frequency voltage component on the drive voltage. This parameter change allows the system to exploit the motor's frequency-dependent magnetic characteristics, particularly the difference in inductance along different rotor axes, to estimate rotor position. The high-frequency current response contains information about the rotor's magnetic anisotropy that can be used for position estimation.
2Reliability
If voltage levels of phases are kept sufficiently separated, then phase current detection is stable, but control flexibility is reduced
Solution Approach 1:
The periodic injection of high-frequency voltage signals allows the system to periodically extract rotor position information without affecting the continuous vector control operation. This periodic measurement approach maintains detection stability while allowing flexible voltage control during the remaining time periods.
Solution Approach 2:
The high-frequency voltage signal acts as an intermediary that carries rotor position information without directly interfering with the fundamental power conversion operation. By using this intermediary signal, the system can estimate rotor position indirectly through the motor's magnetic characteristics, thereby maintaining both detection stability and control flexibility.
3Extent of automation
If high frequency voltage is applied for rotor position estimation, then position sensorless control is enabled, but voltage control precision is reduced due to interaction with single shunt current detecting method
Solution Approach 1:
The system uses periodic high-frequency voltage injection to extract rotor position information, while maintaining separate processing paths for the fundamental voltage control and the high-frequency position estimation. This periodic separation allows both functions to operate independently, preventing the high-frequency injection from degrading the precision of the fundamental voltage control.
Solution Approach 2:
The control system is segmented into separate functional blocks: one for fundamental voltage control and another for high-frequency position estimation. The voltage control portion processes the fundamental frequency components, while the position estimation portion processes the high-frequency components. This segmentation prevents interference between the two functions and maintains voltage control precision while enabling sensorless operation.
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 stable and cost-effective motor control by accurately detecting phase currents and estimating rotor position without sensors, improving system reliability and reducing costs by using a single current sensor.
Implementation Method 1
an estimating portion for deriving the estimated rotor position based on a superposed current that is extracted from the control current and flows in the motor in accordance with the superposed voltage
Data Source
AI summary
The motor control device includes a current detecting portion for detecting a phase current that flows in an armature winding of a stator of a three-phase motor based on current that flows between an inverter for driving the motor and a DC power supply. The motor control device performs a position sensorless vector control for the motor based on a control current that is obtained by a three-phase to two-phase conversion of the phase current based on an estimated rotor position of the motor. The motor control device farther includes a superposing portion for superposing a superposed voltage having a predetermined frequency on a drive voltage for driving the motor and an estimating portion for deriving the estimated rotor position based on the superposed current that is extracted from the control current and flows in the motor in accordance with the superposed voltage. A voltage vector locus of the superposed voltage from the superposing portion presents an ellipse.