Induction Motor Stopping Control via Smooth Current Transition
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Solution Overview
Problem
Existing methods for stopping an induction motor often result in drastic changes in output voltage and current, leading to poor stopping performance and potential reverse rotation, due to abrupt changes in control modes during the stopping process.
Innovation Solution
A device and method that set a final voltage output before stopping the motor and generate multiple current command patterns to gradually increase the final current command value, preventing drastic voltage and current changes by using a configuration including a frequency commanding unit, V/F pattern generating unit, selection unit, and d-q axis current command generating unit to manage the transition from V/F control mode to PI current control mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC current is applied to stators to stop the induction motor, then the motor can be stopped effectively, but a drastic change in output voltage and current occurs which deteriorates stopping performance
Solution Approach 1:
The patent applies preliminary action by generating multiple current command patterns before the actual stopping occurs. The system pre-calculates a series of current command values that gradually decrease from the operating current to zero, and applies these patterns in sequence during the stopping process. This prevents sudden current changes by ensuring the current transitions smoothly through predetermined intermediate states, thereby maintaining stopping performance without drastic voltage and current fluctuations.
Solution Approach 2:
The patent implements dynamics by making the current control adaptable during the stopping process. The system dynamically switches between different current command patterns based on the motor's current state and stopping progress. The current command values are adjusted in real-time according to the rotation speed and load conditions, allowing the control system to optimize the stopping trajectory dynamically rather than using a fixed control mode, thus avoiding harmful voltage and current spikes.
2Speed
If frequency is lowered applied from inverter to induction motor, then the motor slows down due to stopping torque, but kinetic energy returns to DC link condenser causing voltage to increase to dangerous level
Solution Approach 1:
The patent applies feedback by continuously monitoring the DC link voltage and rotation speed during the stopping process. The current command patterns are generated based on feedback from the motor's actual state, including the DC link voltage level. When the voltage approaches dangerous levels, the system adjusts the current command values to reduce the rate of deceleration, allowing the voltage to dissipate safely. This closed-loop feedback mechanism ensures that speed reduction does not cause hazardous voltage buildup.
3Reliability
If V/F driving control mode changes into PI current control mode during stopping, then DC current can be applied to stators, but stopping torque changes drastically causing poor stopping performance
Solution Approach 1:
The patent applies segmentation by dividing the stopping process into multiple discrete stages, each with its own current command pattern. Instead of a single abrupt mode transition from V/F control to PI current control, the system segments the deceleration into several phases with gradually changing current commands. Each segment corresponds to a specific rotation speed range or torque requirement, allowing smooth transition between control characteristics and preventing drastic changes in stopping torque that would degrade performance.
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
The solution allows for smooth stopping of the induction motor without pulsation or reverse rotation, by gradually adjusting current and voltage, thereby improving stopping performance and stability.
Implementation Method 1
when a conversion amount of a frequency applied to stators is less than a rotational speed of an induction motor in rotation, a slip of the induction motor becomes negative (-), and accordingly, the induction motor slows down due to stopping torque therein
Implementation Method 2
when DC current is applied to stators of the induction motor, spatially fixed flux occurs due to the DC current flowing in the stators. At this point, once the flux occurs, current induced in the rotator, and, due to the induced current, stopping torque occurs
Data Source
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AI summary
Provided are a device and method of stopping an induction motor. The includes: a frequency commanding unit for generating an operating frequency corresponding to a rotational speed command of the induction motor; a q-axis and d-axis V/F converter for outputting a first q-axis voltage (Vq1) proportional to the generated operating frequency and a first d-axis voltage (Vd1) proportional to a 0 frequency; a q-axis PI current controller for outputting a second q-axis voltage (Vq2) for stopping the induction motor when the operating frequency reaches a stopping frequency; a d-axis PI current controller for outputting a second d-axis voltage (Vd2) for stopping the induction motor when the operating frequency reaches the stopping frequency; and a selection unit for selecting and outputting the first q-axis and d-axis voltages (Vq1 and Vd1) or the second q-axis and d-axis voltages (Vq2 and Vd2) according to the operating frequency generated by the frequency commanding unit.