PMSM D-axis Current Control for Thermal Demagnetization Prevention
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Solution Overview
Problem
Conventional motor control devices for permanent magnet synchronous motors face challenges in maintaining stable torque generation due to thermal demagnetization caused by overheating, as they often concentrate iron and copper losses, leading to increased temperatures at the stator or rotor with permanent magnets.
Innovation Solution
A motor control device that includes a q-axis and d-axis current detection unit, a q-axis current command value generation unit, and a d-axis current command value generation unit, which sets the d-axis current command value to minimize temperature rise based on rotor speed, eddy-current loss, and copper loss, using functions approximated by straight lines or lookup tables to optimize d-axis current values for each rotation speed, thereby reducing thermal demagnetization risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a d-axis current command value is generated to minimize iron and copper loss, then energy efficiency is improved, but temperature rise of permanent magnets increases causing thermal demagnetization
Solution Approach 1:
The invention changes the control parameter from minimizing total loss (iron + copper) to specifically minimizing temperature rise of permanent magnets. This is achieved by generating a d-axis current command value based on a temperature rise model that considers eddy-current loss in permanent magnets, copper loss in windings, and thermal conduction, rather than simply minimizing the sum of iron and copper losses.
Solution Approach 2:
The invention introduces a temperature rise model as an intermediary between the loss minimization objective and the d-axis current command generation. This model acts as a mediator that translates the relationship between d-axis current and temperature rise into a controllable form, allowing the system to minimize temperature rise without directly measuring temperature.
2Reliability
If d-axis current is reduced to minimize temperature rise, then thermal demagnetization is prevented, but torque generation efficiency decreases
Solution Approach 1:
The invention changes the optimization target from total loss minimization to temperature rise minimization while maintaining torque requirements. By using a temperature rise model that incorporates eddy-current loss in permanent magnets and thermal conduction effects, the system can determine the optimal d-axis current command value that prevents thermal demagnetization while maintaining acceptable torque generation efficiency.
Solution Approach 2:
The invention makes the d-axis current command value dynamic by making it dependent on rotor speed through the temperature rise model. As rotor speed changes, the optimal d-axis current command value is adjusted accordingly, allowing the system to maintain reliability across different operating conditions while optimizing torque generation efficiency for each speed point.
3Loss of energy
If conventional loss minimization control is used, then energy efficiency is improved, but concentration of loss on stator or rotor with permanent magnets causes overheating
Solution Approach 1:
The invention applies local quality control by specifically addressing the temperature rise of permanent magnets rather than treating the motor as a uniform system. The temperature rise model separately considers eddy-current loss in permanent magnets, copper loss in windings, and thermal conduction to the case, allowing differential control that prevents heat concentration on the permanent magnets while maintaining overall energy efficiency.
Solution Approach 2:
The invention introduces a temperature rise model as an intermediary that distributes the loss management function across different components. This model mediates between the total loss minimization objective and the localized heat concentration problem by providing a structured approach to allocate losses appropriately between stator and rotor components based on their thermal characteristics.
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 solution effectively minimizes temperature rise in permanent magnets, preventing overheating and thermal demagnetization, allowing for efficient and stable torque generation without the need for magnetic force reduction or hardware modifications.
Implementation Method 1
the function of the amount of rise in the temperature of the permanent magnets that changes with the value of the d-axis current, and the function of the amount of rise in the temperature of the permanent magnets that changes with the value of the d-axis current is set for each speed of the rotor
Implementation Method 2
the function of the value of the d-axis current that changes with the speed of the rotor is set based on an eddy-current loss and a copper loss of the permanent magnet synchronous motor
Data Source
AI summary
A motor control device that performs vector control to control a q-axis current and a d-axis current of a permanent magnet synchronous motor independent from each other. The motor control device includes a q-axis current and d-axis current detection unit configured to detect a q-axis current and a d-axis current of a permanent magnet synchronous motor, a q-axis current command value generation unit configured to generate a q-axis current command value, a d-axis current command value generation unit configured to generate a d-axis current command value, in which an amount of rise in the temperature of permanent magnets in a steady state of the permanent magnet synchronous motor is a minimum, and a drive unit configured to drive the permanent magnet synchronous motor.