Motor Controller Variable HF Injection for Low Acoustic Noise
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Solution Overview
Problem
Conventional high frequency injection techniques for brushless DC electric motors generate harsh acoustic noise, which is undesirable and needs to be reduced.
Innovation Solution
A motor controller employing a digital-based fixed-point random signal generation scheme with variable high frequency injection, utilizing direct voltage control and orthogonal coordinate system alignment to reduce acoustic noise, combined with random selection of injection signals to minimize noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency signal injection is used to improve sensorless control accuracy and eliminate rotor position ambiguity, then control precision is improved, but electromagnetic noise increases causing motor resonance and vibration
Solution Approach 1:
A low-pass filter is introduced as an intermediary component between the inverter and motor to attenuate high-frequency electromagnetic noise while allowing the control signal to pass through. The filter acts as a mediator that separates the useful control function from the harmful noise, enabling high-frequency signal injection for sensorless control while reducing electromagnetic interference and motor resonance.
2Object-generated harmful factors
If conventional low-pass filtering is applied to reduce electromagnetic noise, then noise is reduced, but phase shift between voltage and current occurs degrading control accuracy
Solution Approach 1:
The controller measures the actual voltage and current signals after filtering, detects the phase shift introduced by the low-pass filter, and applies phase compensation through feedback control. This feedback mechanism continuously adjusts the control signals to counteract the phase lag, maintaining accurate sensorless control despite the presence of the filter.
Solution Approach 2:
The system dynamically adjusts filtering parameters and compensation parameters based on operating conditions. By changing the cutoff frequency of the low-pass filter and adjusting phase compensation parameters according to motor speed and load conditions, the system optimizes the balance between noise reduction and control accuracy across different operating ranges.
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
The solution effectively reduces acoustic noise generated by electric motors, particularly in confined spaces with multiple motors, by using a digital-based fixed-point random signal generation scheme and direct voltage control, enhancing motor control efficiency and reducing harsh noise levels.
Implementation Method 1
a high frequency voltage signal is superimposed on the voltage commanded to the motor
Implementation Method 2
a current sensor measures phase currents
Data Source
Figure 1
Figure 2
Figure 3~3A
AI summary
Methods and apparatus for motor control having low noise variable-high frequency signal injection for an electric motor. Different injection signals have different signal characteristics. One of the first and second injection signals is selected on a cycle-by-cycle basis as part of a direct voltage signal input to control an electric motor. The first and second signal characteristics are configured to reduce acoustic noise generated by an electric motor.