Power Converter Frequency Command Correction for Overcurrent Prevention
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Solution Overview
Problem
Existing power conversion devices face challenges in preventing overcurrent and overvoltage during motor acceleration and deceleration operations, especially when the inertia moment value of the attached machine is large, leading to instability and potential inoperability.
Innovation Solution
A power conversion device with a frequency command correction calculation unit that automatically adjusts the frequency command to limit output current and voltage, using proportional and integral control to maintain predetermined current and voltage values, thereby preventing overcurrent and overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the frequency command is increased to accelerate motor operation, then the productivity is improved, but the output current exceeds the current limit value causing overcurrent
Solution Approach 1:
The system performs preliminary action by calculating and storing the relationship between frequency command values and current limit values before actual motor operation. The frequency command correction calculation unit uses pre-stored data to determine appropriate frequency command values that prevent overcurrent, allowing the motor to accelerate without exceeding current limits.
Solution Approach 2:
The system implements feedback by continuously monitoring the actual current and comparing it with the current limit value. The frequency command correction calculation unit adjusts the frequency command based on the difference between actual current and current limit, ensuring the motor operation remains within safe current boundaries while maintaining optimal productivity.
2Productivity
If the frequency command is increased to improve motor operation speed, then the productivity is improved, but the DC voltage increases causing overvoltage
Solution Approach 1:
The system performs preliminary action by pre-calculating and storing the relationship between frequency command values and DC voltage levels. The frequency command correction calculation unit references this stored data to select frequency commands that achieve desired motor speed while keeping DC voltage within safe limits, preventing overvoltage conditions.
Solution Approach 2:
The system implements feedback by monitoring DC voltage levels and adjusting the frequency command accordingly. The frequency command correction calculation unit reduces the frequency command when DC voltage approaches the limit, preventing overvoltage while maintaining optimal motor operation speed and productivity.
3Device complexity
If a fixed frequency command is used for motor control, then the device complexity is reduced, but the motor cannot operate stably when inertia moment value is large
Solution Approach 1:
The system implements self-service by automatically measuring the inertia moment value of the motor and attached machine during the operation. The frequency command correction calculation unit uses this self-measured inertia information to adjust the frequency command, enabling stable motor operation without requiring complex external tuning or manual parameter setting.
Solution Approach 2:
The system applies parameter changes by dynamically adjusting the frequency command based on the measured inertia moment value. The frequency command correction calculation unit modifies the frequency command parameter according to the actual inertia characteristics of the motor load, ensuring stable operation across different inertia conditions while maintaining relatively simple control system architecture.
Data Source
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AI summary
In acceleration and deceleration operations of a motor, a problem has been posed in that a power converter gets into overcurrent or overvoltage when an inertia moment value of a machine mounted to the motor is large. In order to solve the above problem, provided is a power conversion device that controls a DC voltage, an output frequency, and an output current of a power converter that drives the motor. The power conversion device has a frequency command correction calculation unit that automatically adjusts a frequency command, and is configured to automatically adjust the frequency command such that the power converter does not get into overvoltage or overcurrent during acceleration and deceleration operations of the motor.