Compared with asynchronous motors, permanent magnet synchronous motors have obvious advantages. They have high efficiency, high power factor, good performance indicators, small size, light weight, low temperature rise, significant technical effects, and better improve the quality of the power grid. factors, fully utilizing the capacity of the existing power grid, saving investment in the power grid, and better solving the phenomenon of "big horse and small cart" in electrical equipment.
01.Efficiency and power factor
When the asynchronous motor is working, the rotor winding absorbs part of the electric energy from the power grid for excitation, which consumes the power of the power grid. This part of the electric energy is finally consumed in the rotor winding as heat. This loss accounts for about 20-30% of the total loss of the motor, which reduces the efficiency of the motor. The rotor excitation current is converted to the stator winding as an inductive current, which makes the current entering the stator winding lag behind the power grid voltage by an angle, resulting in a decrease in the power factor of the motor. In addition, from the efficiency and power factor curves of permanent magnet synchronous motors and asynchronous motors (Figure 1), it can be seen that when the load rate (=P2/Pn) is <50%, the operating efficiency and operating power factor of the asynchronous motor drop significantly, so it is generally required to operate within the economic zone, that is, the load rate is between 75%-100%.
After the permanent magnet is embedded in the rotor of the permanent magnet synchronous motor, the permanent magnet is used to establish the rotor magnetic field. During normal operation, the rotor and the stator magnetic field run synchronously, there is no induced current in the rotor, and there is no rotor resistance loss. This alone can increase the motor efficiency by 4%~50%. Since there is no induced current excitation in the hydromagnetic motor rotor, the stator winding may be a pure resistive load, making the motor power factor almost 1. From the efficiency and power factor curves of the permanent magnet synchronous motor and the asynchronous motor (Figure 1), it can be seen that when the load rate of the permanent magnet synchronous motor is >20%, its operating efficiency and operating power factor do not change much, and the operating efficiency is >80%.
02. Starting the cabinet
When the asynchronous motor is started, the motor is required to have a sufficiently large starting torque, but the starting current is not too large, so as to avoid excessive voltage drop in the power grid and affect the normal operation of other motors and electrical equipment connected to the power grid. In addition, when the starting current is too large, the motor itself will be impacted by excessive electric force. If it is started frequently, there is also the danger of overheating the winding. Therefore, the starting design of asynchronous motors often faces a dilemma.
Permanent magnet synchronous motors generally also use asynchronous starting. Since the rotor winding does not work when the permanent magnet synchronous motor is working normally, when designing the permanent magnet motor, the rotor winding can fully meet the requirements of high starting torque, for example, the starting torque multiple is increased from 1.8 times of the asynchronous motor to 2.5 times, or even larger, which better solves the phenomenon of "big horse pulling a small cart" in power equipment.
3. Working temperature rise
Since the rotor winding has current flowing when the asynchronous motor is working, and this current is completely consumed in the form of heat energy, a large amount of heat will be generated in the rotor winding, which will increase the motor's temperature and affect the service life of the motor. Due to the high efficiency of permanent magnet motors, there is no resistance loss in the rotor winding, and there is little or almost no reactive current in the stator winding, which makes the motor temperature rise low and extends the service life of the motor. 4. Impact on the operation of the power grid
Due to the low power factor of the asynchronous motor, the motor absorbs a large amount of reactive current from the power grid, resulting in a large amount of reactive current in the power grid, transformer equipment and power generation equipment, which in turn reduces the quality factor of the power grid and increases the load on the power grid, transformer equipment and power generation equipment. At the same time, the reactive current consumes part of the electric energy in the power grid, transformer equipment and power generation equipment, resulting in a lower efficiency of the power grid and affecting the effective use of electric energy. Also due to the low efficiency of the asynchronous motor, in order to meet the output power requirements, it is necessary to absorb more electric energy from the power grid, further increasing the loss of electric energy and increasing the load on the power grid.
There is no induction current excitation in the permanent magnet motor rotor, the motor has a high power factor, which improves the quality factor of the power grid and eliminates the need to install a compensator in the power grid. At the same time, due to the high efficiency of the permanent magnet motor, electric energy is also saved.