Field-Weakening Motor Control for High-Speed EPS Noise Suppression
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Solution Overview
Problem
Existing motor control devices using field-weakening control for three-phase brushless motors generate unpleasant sounds due to the superimposition of signals synchronized with the update cycle of the calculation cycle on the sine wave voltage during high-speed operation.
Innovation Solution
A motor control device that includes a voltage amplitude command limiter to restrict the voltage amplitude command when the motor state quantity, correlated with the time rate of change of the sine wave voltage, exceeds a predetermined limit, thereby suppressing the generation of noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field-weakening control is performed by vector control of a three-phase brushless motor, then the motor can operate at high speeds, but unpleasant sounds are generated due to superimposition of signals synchronized with the update cycle on the sine wave voltage
Solution Approach 1:
The invention applies preliminary action by predicting the motor state quantity (time rate of change of sine wave voltage) in advance and proactively limiting the voltage amplitude command before the noise problem occurs. The controller calculates the predicted motor state quantity based on current operating conditions and preemptively adjusts the voltage amplitude command to prevent superimposition of synchronization signals, thereby resolving the noise issue while maintaining high-speed operation capability.
2Object-generated harmful factors
If the voltage amplitude command is limited to suppress noise, then driving comfort is improved, but the motor output performance may be restricted
Solution Approach 1:
The invention applies dynamics by making the voltage amplitude command limit dynamic rather than fixed. The controller dynamically adjusts the voltage amplitude command limit value based on the predicted motor state quantity and current operating conditions. When the predicted motor state quantity indicates low noise risk, the voltage amplitude command is allowed to be higher, maintaining motor output performance. When the predicted motor state quantity indicates high noise risk, the voltage amplitude command is limited to suppress noise. This dynamic adjustment resolves the contradiction between noise suppression and power output.
Data Source
AI summary
A field-weakening controller determines a d-axis current command correction value in a field-weakening control according to a voltage of a DC power supply and a voltage amplitude of a voltage command. A d-axis current final value calculator outputs a d-axis current command final value calculated using a d-axis current command value and a d-axis current command correction value. A field-weakening controller has a voltage amplitude command limiter that limits a voltage amplitude command determined based on the power supply voltage. A voltage amplitude command limiter limits the voltage amplitude command to a voltage amplitude command limit value when the motor state quantity, which is correlated with a time rate of change when a sine wave center voltage of the voltage command crosses from negative to positive, is equal to or greater than a predetermined limit start value.