Synchronous Motor Magnet Temperature Estimation via Harmonic Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing magnet temperature estimation methods for synchronous electric motors, such as those described in Patent Literature 1 and 2, face challenges in achieving high estimation accuracy, especially at low revolution numbers where induced voltage measurements are small, leading to potential demagnetization issues due to temperature control limitations.
Innovation Solution
A magnet temperature estimating system that calculates the harmonic impedance's real part by superimposing a harmonic voltage on the stator coil and estimating the permanent magnet temperature based on this impedance, using a pulsating vector injection method to isolate the d-axis component, allowing for accurate temperature estimation across a wide operation range from zero speed to high revolutions without the need for temperature sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is provided on the permanent magnet to detect temperature, then temperature detection accuracy is improved, but the device complexity and size increase
Solution Approach 1:
The patent uses an intermediary parameter (induced voltage) to indirectly measure the permanent magnet temperature. Instead of directly measuring temperature with a sensor on the magnet, the system measures the induced voltage which varies with temperature, and then estimates the temperature from this voltage measurement. This intermediary approach avoids the need for direct temperature sensing while maintaining measurement capability.
Solution Approach 2:
The patent replaces the mechanical/physical temperature sensor system with an electrical measurement system. Instead of using a physical temperature sensor that contacts the permanent magnet, the system uses voltage measurements from the motor windings and electrical models to estimate temperature, substituting a simpler electrical measurement approach for a more complex thermal sensing approach.
2Device complexity
If induced voltage measurement is used to estimate permanent magnet temperature, then device complexity is reduced, but measurement precision deteriorates at low revolution numbers
Solution Approach 1:
The patent applies preliminary compensation for stator resistance effects before calculating the induced voltage. By measuring the stator current and knowing the stator resistance, the system pre-compensates for the voltage drop across the stator resistance, thereby obtaining a more accurate induced voltage value even at low speeds where the induced voltage signal is weak. This preliminary correction action improves the signal accuracy before temperature estimation.
Solution Approach 2:
The system uses feedback from stator current measurements to continuously monitor and compensate for resistance effects. By measuring the actual stator current and using it to calculate the resistance voltage drop, the system dynamically adjusts the induced voltage calculation to maintain accuracy across different operating conditions, particularly at low speeds where accuracy is most critical.
3Productivity
If the electric motor operates at high temperature, then productivity is maintained, but the permanent magnet suffers demagnetization
Solution Approach 1:
The patent implements a feedback control system that continuously estimates the permanent magnet temperature and uses this information to adjust motor operation. The estimated temperature feeds back to the control system, which then limits the motor output or adjusts operating parameters when the temperature approaches the demagnetization threshold, preventing magnet damage while maximizing productivity within safe temperature limits.
Solution Approach 2:
The system takes preliminary action by estimating temperature continuously and proactively limiting motor output before demagnetization occurs. Rather than waiting for temperature to reach critical levels, the control system uses the temperature estimation to preemptively adjust operating parameters and keep the magnet temperature within safe boundaries, preventing demagnetization before it happens.
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
This method provides improved temperature estimation accuracy for permanent magnets in synchronous electric motors, enabling effective temperature control and reducing demagnetization risks across a broad operational range, while minimizing motor losses and maintaining high estimation precision.
Implementation Method 1
a permanent magnet synchronous electric motor in which permanent magnets are disposed in a rotor and the rotor is rotated by an interaction between the permanent magnets and a rotating magnetic field generated by a stator
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A magnet temperature estimating system for a synchronous electric motor having a permanent magnet comprises: a superimposing unit (5) configured to superimpose a voltage or current of a frequency different from a frequency of a fundamental wave driving the synchronous electric motor on at least a d-axis of the synchronous electric motor; a calculator (18) configured to calculate an impedance of the synchronous electric motor from the superimposed voltage or current and a current or voltage obtained by the superimposing; and a magnet temperature estimating unit (19) configured to estimate a temperature of the permanent magnet on the basis of the calculated impedance.