Compared with asynchronous motors, permanent magnet synchronous motors have obvious advantages. It has high efficiency, high power factor, good capacity index, small size, light weight, low temperature rise, and remarkable technical effect, which can better improve the quality factor of the power grid. , give full play to the capacity of the existing power grid, save the investment of the power grid, and it better solves the phenomenon of "big horses and small carts" in electrical equipment.1. Efficiency and power factor When the asynchronous motor is working, the rotor winding has to absorb 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 by current in the rotor winding. This loss accounts for about 20~30% of the total loss of the motor. It makes The efficiency of the motor is reduced. The rotor excitation current is converted to the stator winding and becomes an inductive current, so that the current entering the stator winding lags behind the 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) of the asynchronous motor is <50%, its operating efficiency and operating power factor drop significantly , so it is generally required to operate in the economic zone, that is, the load rate is between 75% and 100%. The picture shows the efficiency and power factor of permanent magnet synchronous motor and asynchronous motora. Asynchronous start permanent magnet synchronous motor b. Asynchronous motorAfter permanent magnets are embedded in the rotor of permanent magnet synchronous motors, the rotor magnetic field is established by the permanent magnets. During normal operation, the rotor and the stator magnetic field operate synchronously. There is no induced current in the rotor, and there is no rotor resistance loss. Only this item can improve Motor efficiency 4%~50%. Since there is no induction current excitation in the rotor of the hydromagnetic motor, the stator winding may be a purely resistive load, so that the power factor of the motor is almost 1. From the efficiency and power factor curves (Figure 1) of Yonghui synchronous motor and asynchronous motor, it can be seen It is shown that when the load rate of the permanent magnet synchronous motor is >20%, its operating efficiency and operating power factor will not change much, and the operating efficiency is >80%.2. Starting torqueWhen starting an asynchronous motor, the motor is required to have a sufficiently large starting torque, but it is also hoped that the starting current should not be too large, so as to avoid excessive voltage drop in the grid and affect the normal operation of other motors and electrical equipment connected to the 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 a danger of overheating the winding. Therefore, the starting design of asynchronous motors often faces a dilemma.The permanent magnet synchronous motor generally adopts the asynchronous starting method. 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, such as making the starting torque The multiple increases from 1.8 times that of asynchronous motors to 2.5 times, or even larger, which better solves the phenomenon of "big horses and small carts" in power equipment.3. Working temperature riseWhen the asynchronous motor is working, the rotor winding has current flowing, and this current is completely consumed in the form of heat energy, so a large amount of heat will be generated in the rotor winding, which will increase the temperature of the motor and affect the service life of the motor.Due to the high efficiency of the permanent magnet motor, 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 temperature rise of the motor low and prolongs the service life of the motor.4. Impact on grid operationDue to the low power factor of the asynchronous motor, the motor has to absorb a large amount of reactive current from the grid, resulting in a large amount of reactive current in the grid, substation equipment and power generation equipment, which in turn reduces the quality factor of the grid and aggravates the load on the grid and the power grid. The load of substation equipment and power generation equipment, while the reactive current consumes part of the electric energy in the power grid, substation equipment and power generation equipment, resulting in low efficiency of the power grid and affecting the effective use of electric energy. Also due to the low efficiency of the asynchronous motor, to meet the output power requirements, it is necessary to absorb more electric energy from the grid, which further increases the loss of electrical energy and increases the load on the grid. There is no induction current excitation in the rotor of the permanent magnet motor, and the power factor of the motor is high, which improves the quality factor of the power grid and makes it unnecessary 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.
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