Sensorless Motor Control Using Variable-Frequency Signal Injection
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Solution Overview
Problem
High frequency signal injection for sensorless control of electric motors produces acoustic noise and vibration, and reducing the signal amplitude decreases the Signal-to-Noise Ratio, making it difficult to extract motor information effectively.
Innovation Solution
A method involving the injection of a high frequency signal with varying frequencies into the motor, where the current induced is demodulated using finite impulse response filters to separate the fundamental and disturbance currents, allowing for the determination of motor state information while spreading the acoustic noise spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high frequency signal is injected to the motor for sensorless control, then the rotor position can be accurately determined, but acoustic noise and vibration are produced
Solution Approach 1:
The patent applies parameter changes by varying the frequency of the injected high frequency signal over time. Instead of using a fixed frequency signal, the system modulates the signal frequency to adapt to different operating conditions, which improves rotor position determination accuracy across a wider range while managing acoustic noise and vibration through frequency variation.
2Object-generated harmful factors
If the amplitude of the high frequency signal is decreased to reduce acoustic noise, then the Signal-to-Noise Ratio deteriorates, making it difficult to extract motor information
Solution Approach 1:
The patent resolves this contradiction by dynamically changing the frequency parameter of the injected signal. By varying the frequency rather than reducing amplitude, the system maintains adequate signal strength for accurate measurement while spreading the acoustic noise energy across different frequencies, thereby reducing perceived noise levels.
Solution Approach 2:
The patent employs periodic action through frequency modulation of the injected signal. The signal frequency is varied periodically or in a controlled manner over time, which allows the system to maintain measurement accuracy while distributing acoustic noise energy across multiple frequency cycles, reducing the impact of noise at any single frequency.
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
This approach reduces acoustic noise and maintains a high Signal-to-Noise Ratio, enabling effective sensorless control of electric motors without external sensors, improving reliability and reducing manufacturing costs.
Implementation Method 1
injecting a high frequency signal to the motor superimposed on the voltages and extracting the rotor's position from a high frequency current induced by the injected signal
Implementation Method 2
applying a first finite impulse response filter to the current signal to extract the fundamental current, wherein a duration of a response from the first finite impulse response filter varies according to the one or more frequencies of the high frequency signal
Data Source
Figure 1~2
Figure 3~5
AI summary
There is proposed a method for sensorless control of an electric motor (14) implemented in a variable speed drive (12) comprising: determining a control voltage (u0) to be applied to the motor (14); injecting a high frequency signal (S0) to the control voltage (u0) to obtain an excitation voltage (u1), wherein one or more frequencies of the high frequency signal (S0) varies with time; applying the excitation voltage (u1) to the motor (14); measuring a current (y) induced in the motor by the excitation voltage (u1), wherein the current (y) comprises a fundamental current (ya), induced by the control voltage (u0), and a disturbance current (ybS1), induced by the high frequency signal (S0); and demodulating the current signal (y)