Sensorless AC Motor Position Estimation via Flux Axis Voltage
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Solution Overview
Problem
Existing methods for estimating the magnetic-pole position of AC rotating machines without sensors, such as those using high-frequency alternating voltages, face issues with accuracy under load conditions, leading to vibrations and noises due to magnetic saturation and axis deviations.
Innovation Solution
A control device that applies a high-frequency alternating voltage to an axis where no torque is generated, ensuring the estimated magnetic-pole position coincides with the axis on which no torque is produced, thereby suppressing errors and vibrations by maintaining the alternating current amplitude in alignment with the instruction amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-frequency alternating voltage is applied to estimate magnetic-pole position, then position estimation is achieved without sensors, but position estimation accuracy deteriorates under load conditions due to magnetic saturation
Solution Approach 1:
The patent dynamically adjusts the estimation method based on operating conditions. It switches between inductive voltage method (high-speed region) and saliency-based method (zero/low-speed region), and further refines the saliency method by applying high-frequency voltage along the flux axis rather than d-axis, adapting to magnetic saturation conditions under load
Solution Approach 2:
The patent changes the fundamental parameter of voltage application axis from d-axis to flux axis (ψ-axis). This parameter change ensures that high-frequency voltage is applied along the direction where inductance variation is minimal, thereby maintaining accurate position estimation even when magnetic saturation occurs under load conditions
2Measurement precision
If high-frequency voltage is applied to the d-axis to estimate position, then position estimation is obtained, but torque is generated causing vibrations and noises
Solution Approach 1:
The patent extracts the position estimation function from the torque-generating d-axis by applying high-frequency voltage along the flux axis instead. This separation allows position estimation to be performed independently without generating harmful torque components that cause vibrations and noises
Solution Approach 2:
The patent converts the potential harm of high-frequency voltage application into a benefit by carefully selecting the flux axis as the application direction. This ensures that while position estimation is achieved through current response measurement, no torque is generated because the voltage is applied perpendicular to the torque-producing direction
3Measurement precision
If sensors are attached to the rotating machine, then position detection accuracy is improved, but cost increases and wiring complexity deteriorates performance
Solution Approach 1:
The patent enables the motor to self-diagnose its own position by measuring its own current response to applied high-frequency voltage. The motor's inherent electrical characteristics (inductance variation with rotor position) are exploited to provide position information without external sensors, making the system self-sufficient
Solution Approach 2:
The patent replaces the mechanical sensor-based position detection system with an electrical field-based method. By applying high-frequency voltage and measuring current response, the system substitutes physical sensors and their associated mechanical wiring with an electrical measurement approach
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
This approach effectively estimates the magnetic-pole position without sensor errors, reducing vibrations and noises in AC rotating machines across various load conditions by ensuring the high-frequency voltage is consistently applied to the correct axis, thus enhancing fault tolerance and maintenance efficiency.
Implementation Method 1
there is a method using an inductive voltage and this method is chiefly advantageous in an operation in a high-speed region in which the inductive voltage is high
Implementation Method 2
when the inductance magnetically saturates while a load current is flowing, the estimated position deviates from the actual magnetic-pole position
Data Source
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AI summary
A control device of an AC rotating machine has control means (2) for receiving a current vector instruction and a detection current vector as inputs and outputs a voltage vector instruction to the AC rotating machine (1), alternating current amplitude computation means (5) for computing an alternating current amplitude of at least one of a parallel component and an orthogonal component with respect to the voltage vector instruction, alternating current amplitude instruction generation means (7) for generating an alternating current amplitude instruction from the current vector instruction, and magnetic-pole position computation means (6) for computing an estimated magnetic-pole position of the AC rotating machine (1). The magnetic-pole position computation means (6) computes the estimated magnetic-pole position so that the alternating current amplitude coincides with the alternating current amplitude instruction.