Rotary Electric Machine Position Estimation With Error Compensation
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Solution Overview
Problem
Current control methods for rotary electric machines without shaft position sensors face challenges in accurately estimating rotor position at low speeds due to cross-coupling effects between d and q axes, leading to increased computation time and costs, and reduced efficiency.
Innovation Solution
A control device with an error compensation unit that reduces the amount of signals required, using a current command unit, voltage conversion, signal demodulation, and position estimation to generate correction values for coordinate transformation, thereby simplifying processor operations and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional error compensation devices are used to minimize rotor position estimation error, then position estimation accuracy is improved, but computation time increases noticeably and processor work efficiency is reduced
Solution Approach 1:
The patent extracts and eliminates unnecessary signal collection and processing steps from the traditional error compensation device. Specifically, it removes the need to collect high-frequency flux current, high-frequency torque current, and measured rotor position signals, keeping only the essential d-axis and q-axis currents from the stationary coordinate system. This extraction of essential elements reduces computation time while preserving position estimation accuracy.
Solution Approach 2:
The patent inverts the traditional approach by using a simplified error compensation method that works backwards from the essential parameters. Instead of starting with multiple high-frequency signals and processing them through complex PI controllers, the invention directly uses the d-axis and q-axis currents from the stationary coordinate system to generate correction values, reversing the conventional signal processing flow to achieve faster computation.
2Measurement precision
If traditional error compensation devices with multiple signal collections are used, then position estimation accuracy is improved, but device complexity and system cost increase
Solution Approach 1:
The patent extracts only the necessary components from the complex traditional error compensation device. It removes the high-frequency signal injection hardware, multiple current sensors, and complex PI controller circuits, retaining only the essential d-axis and q-axis current collection from the stationary coordinate system. This extraction simplifies the device structure while maintaining position estimation accuracy.
Solution Approach 2:
The patent makes the error compensation device universal by using the same d-axis and q-axis currents from the stationary coordinate system for both control purposes and error compensation. This multi-functional use of the same signals eliminates the need for separate high-frequency signal injection systems and multiple sensor sets, reducing device complexity and cost while preserving accuracy.
3Speed
If high-frequency signal injection method is used for zero and low speed rotation, then position estimation is suitable for low speeds, but cross-coupling effect between d axis and q axis causes constant offset error and oscillation
Solution Approach 1:
The patent converts the harmful cross-coupling effect into a beneficial correction opportunity. Instead of trying to eliminate the cross-coupling effect between d-axis and q-axis at low speeds, the invention uses the d-axis and q-axis currents from the stationary coordinate system to calculate correction values that compensate for the position estimation errors caused by this cross-coupling. This transforms the harmful effect into a source of correction information, improving accuracy while maintaining low-speed operation capability.
Data Source
AI summary
A control device for controlling a rotary electric machine, the control device includes a current command unit, a voltage conversion device, a current conversion device, a signal demodulation device, an error compensation unit, an adding device and a position estimation device. The current command unit provides a d-axis current command and a q-axis current command. The current conversion device converts a current of the rotary electric machine to a synchronous reference coordinate current. The signal demodulation device computes a current variation of a high-frequency synchronous reference coordinate current. The error compensation device outputs a first correction value. The adding device adds the current variation of the high-frequency synchronous reference coordinate current and the first correction value to generate a second correction value. Based on the second correction value, the position estimation device adjusts a phase estimation value for the current conversion device and the voltage conversion device.