Electrical Machine Control via Cross-Coupling Compensation
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Solution Overview
Problem
Existing methods for estimating the electric position of electrical machines, such as those described in EP1334552B1, fail to account for cross-coupling inductance/flux, resulting in poor precision.
Innovation Solution
A method involving the injection of voltage waveforms with specific fundamental frequencies into the electrical machine's rotor reference frame, determining current components, and adjusting voltage components to zero, allowing for the calculation of differential cross-coupling parameters, which are used to compensate for the electrical position and improve precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a first voltage waveform is injected into the d-axis to estimate electrical position, then sensorless control is achieved, but measurement precision deteriorates due to cross-coupling inductance/flux not being accounted for
Solution Approach 1:
The patent applies preliminary action by performing a calibration procedure before normal operation to determine cross-coupling parameters. During calibration, test voltage waveforms are injected and the resulting current responses are measured to calculate the cross-coupling inductance/flux values. These pre-determined parameters are then stored and used during normal sensorless control to compensate for cross-coupling effects, thereby improving electrical position estimation precision without adding complexity to the main control algorithm.
Solution Approach 2:
The patent applies parameter changes by introducing cross-coupling parameters (Ldq, Lqd) that characterize the magnetic coupling between d-axis and q-axis. These parameters are determined during calibration and then used to modify the electrical position estimation calculation. By changing the estimation algorithm to include these additional parameters, the system compensates for cross-coupling effects and achieves higher precision in electrical position estimation.
2Measurement precision
If cross-coupling parameters are determined through calibration to improve precision, then electrical position estimation accuracy is enhanced, but loss of time increases due to calibration requirements
Solution Approach 1:
The calibration procedure is performed as a preliminary action during machine installation or commissioning. Once the cross-coupling parameters are determined and stored, they remain valid for the lifetime of the machine under normal operating conditions. This one-time preliminary calibration eliminates the need for continuous calibration during operation, thereby minimizing time loss while achieving high precision electrical position estimation throughout the machine's operational life.
3Measurement precision
If voltage waveforms are injected to determine cross-coupling parameters, then control precision is improved, but use of energy increases during calibration
Solution Approach 1:
The calibration procedure uses partial action by injecting voltage waveforms at selected operating points rather than continuously across the entire operating range. Typically, calibration is performed at a few representative points (e.g., different current magnitudes or angles), and the determined parameters are interpolated or extrapolated for other operating conditions. This approach achieves sufficient control precision while minimizing energy consumption during calibration compared to exhaustive testing.
Data Source
Figure 1~2
AI summary
A method of controlling an electrical machine (9), wherein the method comprises: a) injecting a first voltage waveform (uhx) with a first fundamental frequency into the electrical machine (9) in a first axis of a rotor reference frame, combined with a voltage signal for controlling the electrical machine (9), b) determining a second axis current component iqhx of a second axis of the rotor reference frame, having the first fundamental frequency, generated in response to the injection of the first voltage waveform (uhx), c) controlling based on the second axis current component iqhx a second axis voltage component uqhx of the second axis, having the first fundamental frequency, to obtain an adjusted second axis voltage component for controlling the second axis current component iqhx towards zero, d) feeding back the adjusted second axis voltage component to combine the adjusted second axis voltage component with the voltage signal and the injected first voltage waveform (uhx), and repeating steps b)-d) until the second axis current component is smaller than a threshold value iqhx, e) determining a differential cross-coupling parameter of the electrical machine (9) based on the second axis voltage component uqhx and a first axis current component idhx having the first fundamental frequency, when the second axis current component is smaller than the threshold value iqhx, and g) controlling the electrical machine (9) based on the differential cross-coupling parameter.