Power Conversion Apparatus Saliency Ratio Control for Sensorless Stability
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Solution Overview
Problem
Existing power conversion systems face challenges in achieving stable position sensorless control, particularly at higher torques, for both interior permanent magnet (IPM) and surface permanent magnet (SPM) motors due to the difficulty in maintaining a saliency ratio above 1, which leads to overcurrent issues and instability.
Innovation Solution
A power conversion apparatus that includes a current detection arithmetic unit, saliency ratio estimation unit, and saliency ratio control unit to adjust the current commands and inductance values, allowing for independent control of the d-axis and q-axis currents to increase the saliency ratio and stabilize position sensorless control even at higher torques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the total current including id current and iq current is lowered to prevent the estimated value of the saliency ratio from falling below a predetermined value, then the saliency ratio can be maintained, but it becomes difficult to enable position sensorless control for stably driving the motor even at a higher torque
Solution Approach 1:
The patent separates the control of d-axis current and q-axis current into independent channels with separate limit values. The d-axis current limit is determined based on maintaining the saliency ratio, while the q-axis current limit is determined based on torque requirements. This segmentation allows each axis to be optimized independently, resolving the contradiction between maintaining saliency ratio and achieving high torque output.
Solution Approach 2:
The patent dynamically adjusts the d-axis current command value based on the estimated saliency ratio to maintain it above a predetermined threshold. By changing the d-axis current parameter adaptively rather than using a fixed limit, the system can maintain reliable sensorless control while allowing the q-axis current to increase for higher torque applications.
2Power
If the d-axis current command value is increased to enable position sensorless control at higher torque, then the torque output can be increased, but the estimated value of the saliency ratio may fall below the predetermined value causing step-out
Solution Approach 1:
The patent employs feedback control where the estimated saliency ratio is continuously monitored and used to adjust the d-axis current command value. When the estimated saliency ratio approaches the predetermined threshold, the d-axis current is automatically adjusted to maintain stability, preventing step-out while allowing maximum torque output through q-axis current control.
3Reliability
If a limit value of the current command is set to prevent step-out when the saliency ratio approaches 1, then step-out can be prevented, but it becomes difficult to enable position sensorless control for stably driving the motor even at a higher torque
Solution Approach 1:
The patent applies different current limits to the d-axis and q-axis separately. The d-axis current limit is set to maintain the saliency ratio above 1 for step-out prevention, while the q-axis current limit is set independently to enable high torque output. This segmentation resolves the contradiction by allowing each axis to serve its specific function without restricting the other.
Data Source
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AI summary
A power conversion apparatus controls a load apparatus by position sensorless vector control. The power conversion apparatus includes: a current detection unit configured to detect a current passing through the load apparatus; a current detection arithmetic unit configured to calculate a harmonic current component on a dc-axis as a control axis and a harmonic current component on a qc-axis, based on the detected current; a saliency ratio estimation unit configured to output a saliency ratio estimated value based on the harmonic current component on the dc-axis and the harmonic current component on the qc-axis; and a saliency ratio control unit configured to output a current component that increases or decreases a current command value on a d-axis of a rotor coordinate system, based on a deviation between the saliency ratio estimated value and a predetermined saliency ratio.