Motor Control Device Prevents Circulating Current Demagnetization
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Solution Overview
Problem
Existing motor control devices fail to properly manage the timing of switching off motors connected in parallel, leading to circulating currents and potential demagnetization of permanent magnets due to mistiming.
Innovation Solution
A motor control device with a power converter, a switching unit, and a current detector, controlled by a controller that deactivates the power converter upon abnormality detection and switches the switching unit off to prevent circulating currents and demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching unit is turned off before the power converter comes to a complete stop, then the motors can be disconnected from the power converter, but circulating current flows between the motors causing demagnetization of permanent magnets
Solution Approach 1:
The patent applies preliminary action by turning off the switching unit AFTER the power converter stops, rather than before. The controller monitors the output voltage of the power converter and only turns off the switching unit when the voltage falls below a predetermined threshold, ensuring that circulating current is prevented while avoiding demagnetization of permanent magnets.
2Object-generated harmful factors
If the switching unit is turned off after the power converter stops, then circulating current is prevented, but the switching unit remains exposed to potential damage during the stop period
Solution Approach 1:
The patent uses the output voltage of the power converter as an intermediary parameter to control the switching unit. The controller monitors the output voltage and uses it as a trigger condition - only when the voltage drops below a predetermined threshold does the controller turn off the switching unit. This intermediary voltage signal ensures that the switching unit is protected from circulating current while being turned off at the optimal moment.
3Device complexity
If multiple motors are connected in parallel to a single power converter, then the system structure is simplified, but mistiming of switch-off can cause demagnetization of permanent magnets in the motors
Solution Approach 1:
The patent applies feedback control by continuously monitoring the output voltage of the power converter and using this information to control the switching unit. The controller receives feedback about the power converter's output voltage and adjusts the switching unit's state accordingly - keeping it on during operation and turning it off only when the voltage drops below a predetermined threshold after stopping, thus preventing demagnetization while maintaining simplified parallel motor connection.
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
Effectively reduces circulating currents and prevents demagnetization of motors by ensuring precise control of the power converter and switching unit, extending the lifespan of the switching unit and maintaining motor performance.
Implementation Method 1
a power converter to which a first motor and a second motor are connected in parallel, the power converter being configured to convert a direct-current voltage into an alternating-current voltage and supply the alternating-current voltage to the first motor and the second motor
Data Source
AI summary
A motor control device includes: a power converter to which a first motor and a second motor are connected in parallel, the power converter being configured to convert a direct-current voltage into an alternating-current voltage and supply the alternating-current voltage to the first motor and the second motor; a switching unit provided between the second motor and the power converter; a current detector configured to detect an electric current flowing through the first motor and the second motor; and a controller configured to control the power converter based on at least a current value detected by the current detector. The controller deactivates the power converter upon receiving from outside an abnormal step signal, attributed to the occurrence of an abnormality, that excludes a normal stop signal representing a stop command and switches the switching unit from an on state to an off state upon deactivation of the power converter.