The Feasibility of Permanent Magnet Synchronous Motor Applied to Fans and Pumps
1. BackgroundThe consumption in industrial production is mainly in electrical energy, while fan pumps are equipment that is used more in industrial production. Fans and pumps account for a large proportion of the load. According to the survey, the annual power consumption of fan and pump loads accounts for 50% to 60% of industrial power consumption; in modern tourist hotels, high-end hotels and office buildings with air-conditioning throughout the year , The electricity consumption of fans and pumps accounts for 30%-40% of the electricity consumption of the entire building, and about 40%-50% of the entire power consumption (that is, electricity consumption other than lighting);
Especially in the boiler room heating project, the power consumption of fans and pumps accounts for more than 80% of the total power consumption.
A large number of investigations have shown that asynchronous motors are generally used in operation of fans and pumps today, and there are the following problems with the use of asynchronous motor drive methods:
1. Low efficiency and power factor at rated load.
The air gap magnetic field of an asynchronous motor is generated by the stator current. This part of the current is about 20%-50% of the rated current of the asynchronous motor. Due to the existence of this part of the current, the efficiency and power factor of the asynchronous motor become low.
2. Narrow high efficiency zone.
The high-efficiency area of the asynchronous motor is narrow, and the efficiency and power factor deteriorate sharply at light load. Due to historical reasons, the existing mechanical equipment such as fans and pumps has a "big horse-drawn cart" phenomenon. In actual work, the average load rate is usually less than 70%. At this time, the efficiency of the asynchronous motor is very low, only the efficiency at the rated load. About 90% of the total, resulting in a great waste of energy.
3. The low power factor has a great impact on the factory's power distribution and increases the investment in power distribution equipment
Due to the low power factor of the asynchronous motor, the motor has to absorb a large amount of reactive current from the power grid, causing a large amount of reactive current in the power grid and power transmission and transformation equipment, which in turn reduces the quality factor of the power grid, and aggravates the power grid and power transmission and transformation equipment In order to improve the quality factor, factories often install reactive power compensation equipment for manual compensation, such as power capacitors, which increases equipment investment.
In summary, it is of great significance to develop high-efficiency and energy-saving permanent magnet synchronous motors for fan and pump loads. my country has huge reserves of rare earth permanent magnetic materials and has unique advantages. In the future, there is also a broad space for development in the international market.
Second, the characteristics of permanent magnet synchronous motors
1. High efficiency and power factor at rated load.
The air gap magnetic field of the permanent magnet synchronous motor is no longer established by the stator current, but is formed by high-efficiency permanent magnets. The power factor is high, which improves the quality factor of the power grid. The reactive power compensation part of the factory power distribution can be almost ignored, making the power grid It is no longer necessary to install a reactive power compensator.
Generally speaking, the efficiency of permanent magnet synchronous motor is 3%-5% higher than that of asynchronous motor at rated load. Under the condition of low load rate, the efficiency of permanent magnet synchronous motor is much higher than that of asynchronous motor. For example, the energy saving of permanent magnet motors is very considerable. For example, for a motor with a rated power of 15Kw, the efficiency of the permanent magnet motor is 94.5%, and the rated efficiency of the asynchronous motor is 90.6%, then the permanent magnet synchronous motor saves energy per hour than the asynchronous motor:
15/0.906-15/0.945=0.6833Kw, running for 320 days a year, running 24 hours a day, the annual energy saving is 0.6833*320*24=5247.7Kw, calculated at an average of 0.8 yuan per kilowatt-hour, the electricity cost will be saved by 5247.7 *0.8=4198 yuan.
2. Wide efficient area.
Permanent magnet synchronous motors can maintain high efficiency and power factor within the range of 20%-150% of the rated load. The change of the load factor has little effect on the efficiency of the permanent magnet synchronous motor, which is more suitable for the fan and pump loads whose load changes frequently.
3. Safe and durable, comparable to asynchronous motors.
Permanent magnet synchronous motors have been widely used in elevators, electric vehicles, oil fields, injection molding machines, machine tools and other industries. According to statistics from the Elevator Association, in 2018, the sales volume of permanent magnet synchronous motors used in elevators was more than 600,000 units, and the entire elevator market had more than 5 million units. As of 2018, there are 2.61 million electric vehicles in China, and the state plans that the ownership rate of electric vehicles in big cities will reach 5 million in 2020. The large number of applications of permanent magnet synchronous motors in many industries fully proves the reliability of permanent magnet synchronous motors.
4. Higher cost.
Higher cost is the disadvantage of permanent magnet synchronous motors. Because permanent magnet synchronous motors use high-performance neodymium iron boron permanent magnet materials, the price is 30%-50% higher than asynchronous motors. The increased cost can generally be 3- Recycle the saved electricity bills within 6 months. In addition, with the improvement of the manufacturing and processing technology of NdFeB materials, the price of the permanent magnet synchronous motor drive system will gradually fall.
Four, prospects
Permanent magnet synchronous motors have the characteristics of high efficiency, energy saving, reliable structure, and environmental protection. They have been widely used in elevators, electric vehicles, oil fields, injection molding machines, machine tools and other industries. It can be seen that permanent magnet synchronous motors are the future development trend.
