Motor Control Device for Preventing Step-Out via Voltage Shortage Detection
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Solution Overview
Problem
Conventional motor control systems fail to detect supply voltage shortages promptly, leading to motor step-outs, as they rely on input voltage monitoring which is insufficient due to dependencies on rotation speed and torque, and existing detection methods only react after the step-out occurs, failing to prevent it.
Innovation Solution
A motor control device that vector-controls permanent magnet synchronous motors by deriving an excitation current command value based on rotation speed and using a determination unit to assess supply voltage shortages, allowing for instantaneous detection and prevention of step-outs through speed command adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If input voltage monitoring is used to detect supply voltage shortages, then the monitoring system is simple, but the detection accuracy is insufficient because voltage requirements depend on rotation speed and torque
Solution Approach 1:
The patent changes the detection parameter from input voltage to excitation current command value. The excitation current command value is derived based on rotation speed and reflects the actual voltage requirements of the motor under different operating conditions. This parameter change enables accurate detection of supply voltage shortages without requiring complex monitoring systems that account for speed and torque variations.
2Device complexity
If conventional detection methods are used, then the detection mechanism is simple, but the detection timing is too late causing step-outs to occur before prevention
Solution Approach 1:
The patent performs preliminary detection of supply voltage shortages by continuously monitoring the excitation current command value before the motor actually steps out. By deriving the excitation current command value from the rotation speed and comparing it against threshold values, the system detects potential voltage shortages in advance, allowing preventive action to be taken before the step-out occurs.
Solution Approach 2:
The patent implements a feedback mechanism where the excitation current command value is continuously derived from the rotation speed, compared against threshold values, and used to generate determination results that trigger speed command adjustments. This closed-loop feedback enables real-time detection and prevention of supply voltage shortages, preventing step-outs by adjusting the rotation speed before they occur.
3Reliability
If weak magnetic flux control is applied to prevent step-outs, then the supply voltage shortage is suppressed, but the control response is too slow due to control delay
Solution Approach 1:
The patent performs preliminary detection of supply voltage shortages using the excitation current command value before the motor actually steps out. By continuously monitoring this derived parameter and comparing it against threshold values, the system identifies potential voltage shortages in advance, allowing preventive speed adjustments to be made before the step-out occurs, thus eliminating the need for reactive weak magnetic flux control.
Solution Approach 2:
The patent enables the motor control system to self-detect and self-correct supply voltage shortages by monitoring the excitation current command value and automatically adjusting the rotation speed when shortages are detected. This self-service mechanism eliminates the need for external intervention or complex weak magnetic flux control algorithms, providing rapid response without control delay.
Data Source
AI summary
To prevent a step-out of a permanent magnet synchronous type motor (1), a motor control device (3a) is provided to include a flux control unit (16) for deriving an excitation current command value (iγ*) according to the rotation speed (ωe) of the motor, and a voltage shortage determination unit (30) for determining whether or not the supply voltage to the motor is running short based on the excitation current command value (iγ*). When a negative excitation current command value (iγ*) is smaller than a negative determination threshold value, the motor control device determines that the supply voltage is running short and prohibits an increase of the rotation speed or decreases the rotation speed.