Motor Overload Protection via Current Integral Calculation
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Solution Overview
Problem
Conventional methods for protecting electric motors from overload rely on hardware-based solutions that age or require precise time forecasting, which are ineffective in preventing motor damage from prolonged overheating.
Innovation Solution
A method that continuously detects real-time current values, calculates a current integral value, and adjusts an overload coefficient to reduce the input current, using a reference table to determine the coefficient and reset it when the motor is no longer overloaded, thereby preventing overheating without relying on hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical overload relay is used with a fixed current extremum value, then the motor can be stopped when overloaded, but the protection becomes invalid over time due to hardware ageing and chemical reactions
Solution Approach 1:
The patent replaces the mechanical overload relay system with a microprocessor-based control system that calculates current integral values and compares them against predetermined limits. This substitution eliminates hardware ageing issues by using electronic computation and software-based protection logic, where the motor control system continuously monitors current and automatically adjusts or stops motor operation based on calculated overload conditions.
Solution Approach 2:
The patent changes from using a fixed current extremum value to using a dynamic current integral value that accumulates current over time. The protection threshold is transformed from a static parameter to a time-integrated parameter, allowing the system to distinguish between temporary current spikes and sustained overload conditions that actually damage the motor.
2Reliability
If a current generating device forecasts time values to control the motor, then protection can be provided, but the motor cannot be controlled precisely due to inaccurate time forecasting
Solution Approach 1:
The patent replaces time-based forecasting methods with direct calculation of current integral values using numerical integration of real-time current measurements. Instead of predicting when overload will occur, the system directly computes the accumulated current effect and compares it against predetermined integral limits, providing precise control without relying on time prediction accuracy.
3Ease of operation
If the motor is protected by stopping power supply at fixed current values, then simple protection is achieved, but the motor cannot operate during temporary current fluctuations
Solution Approach 1:
The patent changes the protection parameter from instantaneous current value to time-integrated current value. By accumulating current over the integral period and comparing against an integral limit, the system allows temporary current fluctuations (where the integral remains below the limit) while still protecting against sustained overload conditions, thereby maintaining motor operation during non-damaging transient events.
Solution Approach 2:
The patent introduces dynamic adaptation by continuously updating the current integral value based on real-time measurements. The protection system dynamically adjusts its response based on the accumulated current history, allowing the motor to operate through temporary overloads that don't exceed the integral threshold while providing protection when the accumulated effect becomes dangerous.
Data Source
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AI summary
The present invention discloses a motor overload protecting method, comprising: (a) detecting the motor current real-timely, calculating the current integral value in every integral period and resetting the current integral value to be zero at the end of the integral period; (b) obtaining the overload coefficient according to the current integral value, which is bigger than or equal to zero and less than one when the current integral value is bigger than or equal to the current extremum and is equal to one when the current integral value is less than the current extremum, wherein the current extremum is the ultimate current integral value when the motor works normally; (c) obtaining a new input value by multiplying the input value relative to the motor operation by the overload coefficient and actuating the motor to operate under the new input value. The method according to the present invention can precisely control the motor and protects the motor from being burned when the motor is overloaded.