Sensorless Motor Start Control via Adaptive Frequency Ramp
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Solution Overview
Problem
Sensorless synchronous electric motors face difficulties in starting due to the lack of generated electromotive force when the rotor is stationary, leading to trial-and-error methods and inefficiencies, especially under unknown load or inertia conditions, causing incorrect commutation speeds or frequencies.
Innovation Solution
A method and system for starting a sensorless motor using a start signal with increasing frequency, adjusting the rate of change based on previous start attempts, iterating until a successful start is determined, and activating sensorless driving once started, utilizing a detector and signal generator to manage the frequency ramp-up and motor state assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed frequency ramp-up rate is used for starting the motor, then the starting process is simple, but the motor fails to start reliably under variable load or inertia conditions
Solution Approach 1:
The patent applies dynamics by making the frequency ramp-up rate adjustable rather than fixed. The controller dynamically adapts the ramp-up rate based on whether the motor successfully starts or not, switching between a first ramp-up rate for successful starts and a second ramp-up rate for failed starts. This dynamic adjustment resolves the contradiction by enabling reliable starting under variable conditions without requiring complex predictive algorithms.
Solution Approach 2:
The patent changes the frequency ramp-up rate parameter based on start success or failure. When a start attempt fails, the controller modifies the ramp-up rate parameter for the next attempt, thereby adapting to unknown load or inertia conditions. This parameter change approach allows the system to maintain simplicity while improving starting reliability under varying conditions.
2Productivity
If trial and error method is used to start the motor, then the motor can eventually start, but the starting process becomes complex and time-consuming
Solution Approach 1:
The patent implements feedback by monitoring whether the motor successfully starts during each start attempt. Based on this feedback, the controller adjusts the frequency ramp-up rate for subsequent attempts. This feedback mechanism eliminates the need for complex trial-and-error sequences with multiple phase skips, thereby improving starting efficiency while maintaining simple control logic.
Solution Approach 2:
The patent applies preliminary action by pre-defining two frequency ramp-up rates (first and second rates) before starting attempts begin. The appropriate rate is selected based on start success or failure, avoiding the need for complex real-time calculations or multiple trial phases. This preliminary preparation simplifies the starting sequence while improving productivity.
3Ease of operation
If an arbitrary phase is used for motor starting, then the starting attempt can be initiated, but the motor may run backwards adding complexity to the startup sequence
Solution Approach 1:
The patent uses dynamics by adaptively adjusting the frequency ramp-up rate based on rotation direction correctness. When the motor runs backwards (incorrect direction), the system detects the failure and modifies the ramp-up rate for the next attempt. This dynamic adaptation ensures that subsequent starting attempts use the correct phase sequence, thereby maintaining ease of operation while improving rotation direction reliability.
Data Source
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AI summary
A method and system is provided for starting a motor which is useful, among other things, for motors under unknown or variable load/inertia conditions. If a first attempt to start the motor using a first frequency ramp-up rate fails, a subsequent start attempt may be performed at a decreased frequency ramp-up rate. Iteration may be performed until starting of the motor is successfully achieved.