Sensorless Three-Phase Motor Control Using Alias Signal Injection
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Solution Overview
Problem
Existing sensorless control methods for synchronous machines face challenges such as acoustic noise from high-frequency voltage injection and the need for significantly increased PWM frequencies, which lead to switching losses, electromagnetic compatibility issues, and reduced voltage precision.
Innovation Solution
The method involves disregarding the Nyquist-Shannon sampling theorem by applying a periodic injection voltage with a period shorter than double the cycle time of current measurement, allowing for the detection of alias signals instead of the complete injection response, thereby reducing noise and maintaining low PWM frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-frequency voltage injection is applied to enable sensorless control at standstill, then position detection capability is improved, but acoustic noise increases
Solution Approach 1:
The patent applies periodic voltage injection at frequencies above the human auditory threshold (≥20 kHz) to create noise-free operation. By using periodic injection patterns (square, triangular, or rotating patterns) at these high frequencies, the system achieves sensorless position detection without generating perceptible acoustic noise, thus resolving the contradiction between measurement capability and noise generation.
Solution Approach 2:
The patent changes the injection frequency parameter to be above the auditory threshold (≥20 kHz) while maintaining adequate signal detection through aliasing effects. This parameter change transforms the harmful acoustic noise into inaudible high-frequency signals, resolving the contradiction between position detection and noise generation.
2Object-generated harmful factors
If injection frequency is increased above auditory threshold to eliminate noise, then acoustic noise is reduced, but switching losses and electromagnetic compatibility issues increase
Solution Approach 1:
The patent introduces current measurement and alias signal detection as intermediaries to bridge the gap between high injection frequency and manageable processing requirements. By measuring current at a lower sampling frequency and detecting alias signals, the system can use high injection frequencies (≥20 kHz) for noise-free operation without requiring proportionally high switching frequencies, thus reducing switching losses while eliminating acoustic noise.
Solution Approach 2:
The patent replaces direct mechanical detection of injection response with electrical alias signal detection. Instead of requiring the mechanical system (power converter) to switch at the full injection frequency, the system uses electrical signal processing to detect position information from alias signals, reducing the burden on the mechanical switching system and thereby reducing switching losses.
3Measurement precision
If PWM frequency is increased to detect complete injection response, then measurement accuracy is improved, but switching losses and electromagnetic compatibility issues worsen
Solution Approach 1:
The patent uses current measurement and alias signal detection as intermediaries to extract position information without requiring the PWM frequency to match the injection frequency. The current measurement system acts as an intermediary that captures position information through aliasing effects, allowing the use of lower PWM frequencies while maintaining measurement accuracy, thus reducing switching losses and improving electromagnetic compatibility.
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 enables noise-free high-frequency injection without increasing the switching frequency, maintaining low PWM frequencies, and reducing switching losses and electromagnetic compatibility issues, thus enhancing the feasibility of sensorless control methods.
Implementation Method 1
high-frequency voltage signal components are superimposed on the fundamental voltage by the current controller, which is referred to as voltage injection, or injection for short. These high-frequency components, also in a standstill of the rotor, result in a high-frequency change in current, the so-called injection response, from which the inductance or the admittance of the machine may be calculated.
Implementation Method 2
Anisotropy methods evaluate the position dependency of the inductance of the machine. This requires no minimum rotational speed (the methods thus also function when the machine is at a standstill) but requires the additional application of high-frequency voltage signals, so-called injection.
Data Source
AI summary
A method for identifying magnetic anisotropy of an electric three-phase machine having a rotor and a stator is provided. The method includes actuating the machine with a periodic injection voltage via clocked clamping voltages according to a pulse width modulation (PWM) scheme having a switching frequency. An electric current of the machine responsive to the machine being actuated by the periodic injection voltage is cyclically measured at a sampling frequency. The periodic injection voltage has a period that is less than twice a period of the sampling frequency. An inductance and/or an admittance of the machine is determined based on the periodic injection voltage and the measured electric current. A position of the rotor is determined based on the inductance and/or the admittance of the machine. The machine is controlled according to the rotor position.