Inverter Flying Start Control Using DC Ripple Current Estimation
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Solution Overview
Problem
Conventional methods for restarting a high-voltage inverter during a flying start, especially when the counter electromotive force is small, face challenges in accurately analyzing the motor's output current, leading to longer frequency estimation times and potential damage from excessive current noise.
Innovation Solution
The proposed solution involves estimating the motor's rotation speed by analyzing the ripple current resulting from injected DC currents, allowing for quick restarts even when the counter electromotive force is small, using a control device with a rectifying module, smoothing module, inverting module, and detection module, including a current transformer, to manage switching elements and estimate rotation speed based on output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional frequency estimation methods are used when counter electromotive force is small, then the inverter can be restarted, but the frequency estimation time becomes longer
Solution Approach 1:
The patent introduces DC current injection as an intermediary method to enable frequency estimation when conventional counter electromotive force analysis fails. By injecting DC current into the motor during free-running state and analyzing the resulting ripple current, the system can estimate rotation speed even when counter electromotive force is too small for conventional methods, thus resolving the time loss without sacrificing reliability
Solution Approach 2:
The patent changes the estimation parameter from analyzing counter electromotive force directly to analyzing ripple current generated by DC injection. This parameter change enables frequency estimation in conditions where the original parameter (counter electromotive force) is insufficient, thereby reducing estimation time while maintaining accurate speed detection for reliable flying start
2Loss of time
If DC current injection method is used to estimate rotation speed, then frequency estimation time is reduced, but device complexity increases
Solution Approach 1:
The control device is designed to perform multiple functions: normal V/f control during steady operation and DC injection-based frequency estimation during flying start. By integrating these functions into a single controller that can switch between operating modes, the patent reduces device complexity compared to having separate systems for each function
Solution Approach 2:
The system performs preliminary DC current injection before the main flying start operation to estimate rotation speed. This preliminary action provides the necessary speed information in advance, enabling the main restart operation to proceed quickly without complex real-time analysis during the critical restart phase
3Reliability
If conventional flying start method is employed when counter electromotive force magnitude is small, then the inverter can be restarted, but excessive current noise occurs
Solution Approach 1:
The patent uses feedback from ripple current analysis to estimate motor rotation speed during DC injection. This feedback mechanism allows the control system to accurately determine the motor's actual speed state and adjust the restart parameters accordingly, preventing excessive current noise while ensuring reliable inverter restart
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 significantly reduces the time required to estimate motor rotation speed, enabling faster inverter restarts and reducing the risk of damage from excessive current noise, with the flying start operation completed within about 10% of the conventional duration.
Implementation Method 1
An inverter is an inverting device that electrically converts DC to AC
Implementation Method 2
when a residual counter electromotive force exists in the motor, it is difficult to analyze an output current of the motor
Implementation Method 3
A direct current or a direct-current voltage is applied to the alternating-current motor in the free running state before it is restarted, and a secondary current, that flows across the rotor of the motor at this time, is employed to estimate the rotational direction and the velocity
Data Source
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AI summary
The present invention relates to an inverter-controlling device. The inverter-controlling device include a main controller configured to generate a predetermined command current; a comparison module configured to calculate a difference between the command current and an output current of an inverting module; a current controller configured to perform a proportional-integral (PI) control based on the difference; and a frequency estimation module configured to estimate a rotation speed of a motor based on a current response to the command current while the command current is injected to the current controller, wherein the main controller is further configured: when a flying start operation of the inverting module begins, to set an output frequency of the inverting module based on the rotation speed of the motor estimated by the frequency estimation module.