Electric Motor Over-Temperature Protection Using Harmonic Loss Estimation
Solution Overview
Problem
Conventional electric motor over-temperature protection methods inaccurately estimate motor losses due to harmonic waves, leading to underestimation of motor temperature, especially when using motor current alone for calculations.
Innovation Solution
A control device that calculates stator and rotor losses, including fundamental and harmonic losses, using DC voltage, output voltage, and motor frequency to improve temperature estimation and provide accurate over-temperature protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If motor current alone is used for loss calculation, then device complexity is reduced, but measurement precision of motor temperature deteriorates
Solution Approach 1:
The patent introduces an intermediary calculation method that uses readily available electrical parameters (voltage, current, frequency) to estimate motor losses and temperature. Instead of directly measuring temperature or using complex thermal models, the system calculates copper losses and iron losses as intermediate steps to infer temperature, thereby avoiding complex hardware while improving accuracy over current-only methods
Solution Approach 2:
The patent changes the parameters used for temperature estimation from solely motor current to a combination of voltage, current, and frequency parameters. By incorporating voltage and frequency information alongside current, the system captures harmonic effects and iron losses that current alone cannot represent, thereby improving measurement precision without significantly increasing device complexity
2Measurement precision
If harmonic losses are included in loss calculation, then measurement precision of motor temperature is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical or hardware-based temperature measurement systems with an electrical calculation-based approach. By substituting physical temperature sensors and complex thermal modeling with electrical parameter measurements and loss calculations, the system achieves improved temperature estimation accuracy while avoiding the complexity of additional sensing hardware and thermal models
Solution Approach 2:
The system uses the inverter's existing control parameters (voltage, current, frequency) that are already being measured for motor control purposes. By leveraging these self-generated data streams, the system calculates harmonic losses and temperature estimation without requiring external sensors or additional measurement infrastructure, thereby limiting the increase in device complexity
3Reliability
If temperature sensor is added for over-temperature protection, then reliability of motor protection is improved, but manufacturing cost increases
Solution Approach 1:
The patent creates a virtual copy of temperature sensing functionality through calculation rather than physical sensing. By computing temperature estimation from electrical parameters, the system replicates the protective function of physical temperature sensors without the associated cost, complexity, and installation challenges of actual temperature sensors in the motor
Solution Approach 2:
The patent uses inexpensive electrical parameter measurements (voltage, current, frequency) that are already part of the control system to replace expensive physical temperature sensors. The calculation-based approach uses readily available data streams that cost nothing additional to measure, thereby achieving reliable over-temperature protection without increasing manufacturing cost
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
Enhances the accuracy of electric motor over-temperature protection by considering harmonic losses, preventing motor burnout through precise control of inverter operations.
Implementation Method 1
These iron and copper losses become thermal energy and cause a rise of temperature of the electric motor
Implementation Method 2
The inverter main circuit converts inputted DC electric power into variable voltage-variable frequency AC electric power and drives the induction electric motor
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
Object of the present disclosure is to improve accuracy of over-temperature protection of an electric motor (1). A control device (7) controls an inverter main circuit (2) for driving the electric motor (1). An electric power conversion circuit controller (4) acquires DC voltage input to the inverter main circuit (2), output voltage of the inverter main circuit (2), motor amperage of current flowing through the electric motor (1), and motor frequencies indicating rotation rate of the electric motor (1). Based on at least one of the DC voltage, output voltage, motor amperage and motor frequencies, a motor loss estimator (5) calculates a stator loss and rotor loss, each including fundamental and harmonic losses of the electric motor (1). Based on the inverter output voltage, stator loss and rotor loss, the electric power conversion circuit controller (4) outputs an actual control value for control of the inverter main circuit (2).