Motor Driver Carrier Frequency Control for Magnet Temperature
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Solution Overview
Problem
Permanent magnet motors in hybrid and electric vehicles face demagnetization due to increased magnet temperature caused by eddy-current losses, leading to reduced operational efficiency and power generation efficiency, especially under low temperature conditions and high switching frequencies.
Innovation Solution
A motor driver system that includes a controller capable of detecting magnet temperature and adjusting the carrier frequency to reduce ripple currents and eddy-current losses, using a threshold-based approach to switch between normal and high-temperature carrier frequency maps to prevent demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching frequency is reduced to suppress electric power loss in the inverter, then the electric power loss is reduced, but the ripple current increases causing increased eddy-current loss and magnet temperature rise
Solution Approach 1:
The patent applies dynamics by making the carrier frequency adjustable rather than fixed. The control device dynamically changes the carrier frequency based on operating conditions (motor speed, temperature) to optimize the balance between inverter power loss and magnet temperature control. This resolves the contradiction by allowing the system to adapt the switching frequency in real-time rather than being constrained to a single fixed value.
Solution Approach 2:
The patent applies parameter changes by modifying the carrier frequency parameter according to operating conditions. The control device changes the carrier frequency based on motor speed and temperature feedback, adjusting this key parameter to prevent magnet temperature rise while managing inverter losses. This directly addresses the contradiction by using parameter adjustment to balance competing objectives.
2Temperature
If the carrier frequency is increased to reduce ripple current and eddy-current loss, then the magnet temperature is controlled, but the electric power loss in the inverter increases
Solution Approach 1:
The system uses dynamic carrier frequency adjustment based on real-time operating conditions. Rather than using a fixed high frequency to control temperature, the control device adapts the frequency according to motor speed and temperature feedback, achieving temperature control while minimizing inverter power loss at each operating point.
Solution Approach 2:
The control device changes the carrier frequency parameter dynamically based on operating conditions. By adjusting this parameter according to motor speed and temperature, the system achieves magnet temperature control without permanently increasing inverter power loss, resolving the contradiction through conditional parameter modification.
3Reliability
If high-frequency electric current is supplied to heat the permanent magnet and prevent low-temperature demagnetization, then low-temperature demagnetization is prevented, but the magnet temperature increases causing high-temperature demagnetization risk
Solution Approach 1:
The patent applies dynamics by making the carrier frequency adjustable based on temperature feedback. Rather than continuously applying high-frequency current to prevent low-temperature demagnetization, the system dynamically adjusts the frequency based on real-time temperature monitoring, preventing both low- and high-temperature demagnetization risks.
Solution Approach 2:
The patent implements feedback control by monitoring magnet temperature and adjusting the carrier frequency accordingly. The control device uses temperature feedback to determine when to increase or decrease the carrier frequency, preventing low-temperature demagnetization while avoiding excessive temperature rise that could cause high-temperature demagnetization.
Solution Approach 3:
The control device changes the carrier frequency parameter based on temperature conditions and operational requirements. By adjusting this parameter dynamically, the system prevents low-temperature demagnetization when needed while avoiding excessive heating that could lead to high-temperature demagnetization, resolving the contradiction through conditional parameter modification.
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
The system effectively suppresses demagnetization by reducing magnet temperature and maintaining operational efficiency by dynamically adjusting the carrier frequency based on detected magnet temperature and operational conditions.
Implementation Method 1
the driving force generated by electric energy is obtained by converting the direct current voltage supplied from a high-voltage power source into a three-phase alternating-current power with the use of an inverter and rotating the three-phase alternating-current motor with the use of the alternating-current power
Implementation Method 2
high-frequency magnetic field is generated by the high-frequency electric current that is supplied to the coils of the stator, whereby the permanent magnet is heated by the iron loss caused in the core portion as the high-frequency magnetic field is formed
Implementation Method 3
when a rare-earth permanent magnet is used, the electrical conductivity is relatively high and therefore, there is a possibility that eddy currents are generated in the permanent magnet and increase the loss
Data Source
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AI summary
A controller (30) controls switching of IGBT devices (Q3 to Q8) of an inverter (14) according to the desired output of the permanent magnet motor (M1). The controller (30) includes: a magnet temperature detection device that detects the magnet temperature of the permanent magnet motor (M1) based on the output of a temperature sensor (40, 42); a setting device that sets a threshold value of the magnet temperature corresponding to the desired output of the permanent magnet motor (M1), based on a predetermined relation between the output from the permanent magnet motor (M1) and a critical temperature, up to which demagnetization in the permanent magnet motor (M1) is not caused; and a carrier frequency control device that, when the magnet temperature detected by the magnet temperature detection device exceeds the threshold value, changes the carrier frequency, at which the IGBT devices (Q3 to Q8) are switched, such that a ripple current superimposed on a motor current that flows through the permanent magnet motor (M1) is reduced.