Soft Starter Torque Ripple Reduction via Transitional Control
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Solution Overview
Problem
Soft-starters for electric motors face challenges in smoothly transitioning between different operating modes, leading to significant torque and current fluctuations when switching between control methods optimized for low-speed and high-speed operations.
Innovation Solution
A system that controls the AC voltage supplied to an AC motor by determining the phase angle of the current and flux vectors to set the conduction interval of an electronically controlled switching device, reducing torque ripple during mode transitions by adjusting the connection time to the supply voltage based on torque pulsations and polarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple control methods are executed during a single motor operation to utilize improved operation at different operating points, then the performance at different speed ranges is improved, but significant levels of current and torque will result when switching between control methods
Solution Approach 1:
A transitional control mode is introduced as an intermediary between the first control mode (optimized for low speeds) and the second control mode (optimized for high speeds). This transitional mode acts as a mediator that smoothly bridges the two operating modes, preventing direct switching that would cause torque and current fluctuations. The transitional mode gradually transitions control parameters over a defined speed range, ensuring continuous and smooth operation without harmful transients.
Solution Approach 2:
The control system dynamically selects and transitions between different control modes based on the motor's operating speed. Rather than using a fixed control method, the system adapts its control strategy in real-time, switching from the first control mode to the transitional mode, and then to the second control mode as speed increases. This dynamic adaptation allows the system to optimize performance across the entire speed range while avoiding abrupt changes that would cause torque and current fluctuations.
2Adaptability or versatility
If switching between two control methods is performed to optimize operation at different speeds, then performance at low and high speeds is improved, but step or very quick changes in commanded voltage, current, or speed will result
Solution Approach 1:
The transitional control mode serves as a stabilizing intermediary that prevents direct switching between control modes with different characteristics. By introducing this intermediate stage, the system maintains continuity in commanded voltage, current, and speed parameters. The transitional mode gradually adjusts control parameters rather than making abrupt changes, ensuring stable and smooth transitions that preserve system stability throughout the mode change process.
3Use of energy by moving object
If a soft-starter provides a predefined speed profile for the motor during acceleration and deceleration, then the current drawn by the motor is limited, but the same level of control as variable frequency drive is not achieved
Solution Approach 1:
The soft-starter incorporates dynamic control that adapts to different operating conditions, transitioning between different control strategies based on motor speed. This dynamic approach enables the system to maintain current limiting benefits while achieving improved control precision across the entire operating range, including better low-speed control that was previously only available with more complex variable frequency drives.
Data Source
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AI summary
the subject matter disclosed herein describes a system for controlling torque in a soft starter. In particular, torque ripple is reduced when transitioning between two different operating modes of a soft starter. A soft starter may include a first operating mode, designed for improved performance during low-speed operation of a motor, and a second operating mode, designed for improved performance during high-speed operation of the motor. However, transitioning between two different operating modes may result in significant transient currents in the motor, which, in turn, produce torque in the motor. The system described herein reduces this transient torque production in the motor.