Sensorless AC Motor Start Using Active Short Rotor Alignment
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Solution Overview
Problem
Starting an AC electric motor without a rotor position sensor, particularly in applications like fans, is challenging due to rotor misalignment and resulting oscillations, especially when the rotor speed is below a certain threshold, leading to undesired rotation in the wrong direction and increased engagement time.
Innovation Solution
A method involving a sequence of active short profiles and open-loop control is applied to the motor, including a fixed magnetic field followed by active short circuits to stabilize the rotor position, allowing a smooth transition to closed-loop control once a reliable speed estimate is achievable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-frequency injection is applied to measure rotor position in sensorless synchronous motors, then rotor position can be estimated, but the rotor tends to turn in the wrong direction initially and oscillations occur due to mass inertia and undamped system
Solution Approach 1:
The patent applies a preliminary magnetic field alignment phase before the main acceleration phase. The magnetic field is applied at a reduced frequency initially to align the rotor with the stationary vector without causing excessive speed buildup that would lead to overshooting and oscillations. This preliminary action prepares the rotor in a stable position before full-speed operation begins.
Solution Approach 2:
The patent dynamically adjusts the frequency of the applied magnetic field during the start-up process. The frequency is reduced during the alignment phase to prevent rotor overshooting, and then increased afterward to achieve the desired operating speed. This dynamic adjustment of operational parameters allows the system to transition smoothly from a stable low-speed alignment state to a high-speed operational state without causing oscillations.
2Ease of operation
If the rotor is immobilized during start-up in fan applications, then sensorless operation below speed threshold is enabled, but oscillation effects are amplified
Solution Approach 1:
The patent employs periodic application of the magnetic field during the start-up phase rather than continuous application. The magnetic field is applied in cycles with specific durations, allowing the rotor to be gently accelerated and aligned without building up excessive momentum that would cause oscillations. This periodic action enables sensorless operation while maintaining rotor stability.
3Manufacturing precision
If a stationary magnetic field is applied to align the rotor, then rotor position can be controlled, but the rotor may overshoot the aligned position due to mass inertia leading to direction reversal
Solution Approach 1:
The patent applies a preliminary magnetic field alignment phase before the main acceleration phase. The magnetic field is applied at a reduced frequency initially to align the rotor with the stationary vector without causing excessive speed buildup that would lead to overshooting and oscillations. This preliminary action prepares the rotor in a stable position before full-speed operation begins.
Solution Approach 2:
The patent dynamically adjusts the frequency of the applied magnetic field during the start-up process. The frequency is reduced during the alignment phase to prevent rotor overshooting, and then increased afterward to achieve the desired operating speed. This dynamic adjustment of operational parameters allows the system to transition smoothly from a stable low-speed alignment state to a high-speed operational state without causing oscillations.
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 ensures a well-behaved motor start with reduced oscillations and eliminates the need for a rotor position sensor, reducing production costs and increasing reliability by avoiding sensor-related failures and system interferences.
Implementation Method 1
applying a first active short profile to the motor during a first period of time... applying a first current profile to the motor during a second period of time
Implementation Method 2
applying a first active short profile to the motor during a first period of time... stabilizing the rotor position
Data Source
Figure 1
Figure 2a~2c
Figure 3a
AI summary
The present disclosure relates to a method for starting an AC electric motor comprising: applying, in response to receiving a control signal for starting the motor, a first active short profile to the motor during a first period of time; applying, after the first period of time, a first current profile to the motor during a second period of time; applying, after the second period of time, a second active short profile to the motor during a third period of time; optionally, applying, after the third period of time, a second current profile to the motor during a fourth period of time; applying, after the third period of time and/or after the fourth period of time, open-loop control of the motor based on a crank-up profile wherein a speed of the rotor of the motor is increased from essentially zero to a speed threshold during a fifth period of time.