|
The rise of permanent magnet synchronous motor in the new energy automobile industry seems to be inevitable, and some problems have been exposed in this process. This paper will introduce some problems to be solved in the process of improving the performance of permanent magnet synchronous motor.
.
1. cost problem
Compared with asynchronous motor, the maximum cost of PMSM increases from permanent magnet material or rare-earth permanent magnet material, and its cost accounts for nearly 1/4 of the whole motor material cost. Taking NdFeB material as an example, the news of Tesla Model3 will use the permanent magnet synchronous motor to become the most important catalytic factor of NdFeB, and the price will continue to rise. Neodymium and iron boron industry began to stop production because of the purchase of raw materials, and the lower price of NdFeB in the lower reaches began to rise rapidly. The relevant institutions believe that the magnetic materials will be the third important upstream raw materials of new energy vehicles after lithium and cobalt.
At the time of design, it is necessary to make trade-offs between performance and price according to the specific occasions and requirements, and also to innovate and optimize the structural process, so as to reduce the cost.
2. weak magnetic speed control problem
With the rapid development of motor speed control theory, the rapid development of power electronics and microelectronics, and the continuous improvement of the performance and price ratio of permanent magnet materials, the frequency conversion speed regulation of permanent magnet synchronous motor has entered a stage of further research and extensive application. At the same time, the speed control performance of permanent magnet synchronous motor is also put forward higher request. High performance permanent magnet synchronous motor speed control system should not only have good torque control performance, but also have a wide speed range. With the increasing speed of permanent magnet synchronous motor, the stator winding of the motor back emf will increase when the rated voltage of back EMF to motor or DC voltage of the inverter when the input current of the motor will not output given current tracking controller, current regulator in saturated state. At this time, the anti electromotive force of the permanent magnet synchronous motor should be reduced, that is, using the weak magnetic control to achieve the purpose of expanding the speed.
Theoretically, flux weakening control can achieve constant torque at low speed, and output constant power at high speed and wide speed range. The strong weak magnetic performance can improve the system performance under the condition that the inverter capacity is constant. Or, if the system performance is unchanged, the maximum power of the motor will be reduced, and the capacity of the inverter will be reduced. At present, the weak magnetic speed control with high speed still have much room for improvement.
3. demagnetization problem
NdFeB permanent magnetic materials have been widely used in permanent magnet motors because of their high magnetic energy product, remanence and coercivity. However, the most outstanding deficiency of NdFeB permanent magnet is poor thermal stability, and the Curie temperature is generally about 310~410 degrees C. The following figure is the demagnetization curve of NdFeB permanent magnetic materials at different temperatures.
This thermal stability defect increases the complexity of the design of the permanent magnet motor and reduces the reliability of the motor. If the design or improper use of permanent magnet synchronous motor in high (NdFeB permanent magnet) or low (ferrite permanent magnet) temperature, armature reaction in impact current, or in mechanical vibration when it is possible to produce irreversible demagnetization, or loss of excitation, the motor performance decline can't even use.
Therefore, it is necessary to research and develop the methods and devices for checking the thermal stability of permanent magnet materials for motor manufacturers, and analyze the anti degaussing capability of various structural types. In order to design and manufacture, the corresponding measures should be adopted to ensure the permanent magnet synchronous motor is not demagnetizing.
4. control problems
Permanent magnet synchronous motor can maintain its magnetic field without external energy, but it also makes it very difficult to adjust and control the magnetic field from outside. With the development of MOSFET, IGBT and other power electronic devices and control technologies, most of the permanent magnet synchronous motors can be controlled without magnetic field and only by armature control. The design of permanent magnetic materials, power electronic devices and microcomputer controlled three new technologies should be combined to make the permanent magnet synchronous motor run in a new working condition.
In addition, the permanent magnet synchronous motor is nonlinear, strong coupling and time-varying, and the permanent magnet synchronous motor as the actuator of the permanent magnet AC servo system, the servo object has strong uncertainty and nonlinear, coupled with the operation of the system is vulnerable to interference in different degree. These reasons make it permanent control magnet synchronous motor.
80%
One
|
