Electric Vehicle Inverter Magnetic Force Estimation
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Solution Overview
Problem
Electric vehicles equipped with in-wheel motor drive systems face performance degradation and potential motor failure due to irreversible demagnetization of neodymium permanent magnets, which can lead to reduced driving performance or complete vehicle immobilization, as existing temperature-based monitoring systems are inadequate in addressing demagnetization-related issues.
Innovation Solution
Incorporating a magnetic force estimator within the inverter unit to estimate the magnetic force of the permanent magnet structure using detection signals from sensors, and a determiner to assess if the magnetic force falls within a defined acceptable range, triggering an abnormalities-responsive motor drive limiter to reduce or terminate output power and prevent further deterioration, thereby avoiding complete motor failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature-based monitoring is used to detect motor overload, then motor reliability is improved, but demagnetization of permanent magnets cannot be detected
Solution Approach 1:
The patent transitions from monitoring only temperature parameters to monitoring multiple parameters including current, voltage, and rotational frequency. By changing the monitored parameters from单一的temperature to a combination of electrical and mechanical parameters, the system can detect demagnetization through anomalies in the relationship between these parameters, thereby resolving the limitation of temperature-based monitoring.
2Measurement precision
If magnetic force estimation is implemented using multiple sensor signals, then demagnetization detection accuracy is improved, but system complexity increases
Solution Approach 1:
The patent establishes a feedback control loop where multiple sensors continuously monitor motor parameters, the ECU processes these signals to estimate magnetic force, and the system adjusts motor operation based on the estimation results. This feedback mechanism enables accurate demagnetization detection by continuously comparing actual parameter relationships against expected relationships, achieving high detection accuracy without requiring complex additional hardware.
Solution Approach 2:
The patent makes the existing motor control system multi-functional by enabling it to perform both its original control function and the additional function of demagnetization detection. The ECU uses the same sensor signals for both motor control and magnetic force estimation, making the system universal and avoiding the need for separate dedicated detection hardware, thus reducing overall system complexity.
3Reliability
If output power is reduced or terminated to prevent further demagnetization, then permanent magnet structure is protected, but vehicle mobility is reduced
Solution Approach 1:
The patent applies partial action by reducing output power rather than completely terminating it when demagnetization is detected. This allows the vehicle to maintain limited mobility for returning to a service location while still protecting the permanent magnet structure from further damage. The system adjusts the degree of power reduction based on the severity of demagnetization, achieving a balance between protection and mobility.
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 solution enables quick detection and mitigation of magnetic force reduction, preventing further demagnetization and maintaining vehicle operability by reducing output power or terminating it when the magnetic force exceeds safe limits, thus avoiding situations where the vehicle becomes impossible to drive.
Implementation Method 1
a synchronous motor unit 6 configured to drive a wheel 2... an IPM (e.g., Interior Permanent Magnet synchronous motor)... rotation of a permanent magnet structure 80 associated with a motor rotor 75 generates an electromotive force in coils 78 of a motor stator
Data Source
AI summary
An electric vehicle includes an inverter unit and an ECU. The inverter unit or the ECU includes a magnetic force estimator that estimates a magnetic force of a permanent magnet structure associated with a motor rotor of a motor unit. The inverter unit or the ECU may also include a determiner for the estimated magnetic force and an abnormalities-responsive motor drive limiter. The estimator is configured to estimate, according to a predefined rule, the magnetic force, based on at least two detection signals selected from a group consisting of a detection signal indicating a rotational frequency of the motor unit, a detection signal indicating a motor voltage of the motor unit and a detection signal indicating a motor current of the motor unit.