1. The vector control technology of permanent magnet synchronous motor has been developed by leaps and bounds after decades of tempering. Nowadays, the vector control system of permanent magnet synchronous motor has reached a certain level, and it has been further strengthened and improved in terms of system stability, fast response, and speed tracking accuracy. However, in industries requiring high-speed motor operation such as electric vehicles, ship power, and metal cutting, motor vector control speed regulation systems cannot meet the industry's demand for motor speed. Therefore, field weakening control speed regulation has been gradually researched and developed. The field weakening control not only inherits the excellent properties of the closed-loop control of the vector control but also has the characteristics of a certain width of speed regulation range and smooth field weakening transition. It is basically satisfied in dealing with the motor working conditions that require a high-speed operation. The research and development of field weakening control have become particularly important since the development of the times. The hot issue of tapping the potential of motors has been widely concerned by scholars at home and abroad, and the field weakening control strategy has developed rapidly. Figure 1 below is a comparison of torque and speed curves with and without field weakening control.
2. The three-phase current of the permanent magnet synchronous motor is output by the inverter, so to a certain extent the capacity of the inverter determines the output of the motor it controls, and this output is reflected in the load capacity and mechanical speed of the motor. However, in many applications, the use of permanent magnet synchronous motors is never satisfied with the speed of the rated speed. In other words, when the rated speed is satisfied, it is hoped that the motor can carry a load, that is, "drag" more loads. For example, the motor drives the main shaft of the machine tool and the electric drive hub of the electric vehicle. The emergence of field weakening control is precisely to meet the speed requirements under such special working conditions. Based on this demand, in order to make the motor work in the constant power range above the rated speed to obtain a wide range of speed regulation performance, it is necessary to resist the saturation problem of the current regulator. In fact, the field weakening idea of permanent magnet synchronous motor is derived from the traditional motor speed regulation principle of electric excitation. In the process of electric excitation motor speed regulation, the main magnetic flux can often be changed by adjusting the excitation current to satisfy the voltage balance of the motor. The premise makes the motor obtain a wide range of speed regulations. However, the excitation of the permanent magnet synchronous motor is to generate a natural magnetic field through the permanent magnet, which is the inherent property of the magnet. This method of adjusting the excitation current is obviously useless for permanent magnet synchronous motors. The "field weakening", as the name implies, is to weaken or relatively weaken this inherent property, that is, in the field weakening control, the current component of the stator current on the AC-DC axis can be changed so that the motor can obtain a wider speed range speed regulation and run at constant power zone.