From June 1, 2021, the latest motor energy efficiency standard “GB18613-2020 Electric Motor Energy Efficiency Limits and Energy Efficiency Grades” officially implemented in my country. After the implementation of this standard, motors whose energy efficiency limit values of three-phase asynchronous motors cannot reach IE3 cannot be produced again. , sales and purchases.
At the end of last year, the Chinese Ministry of Industry and Information Technology and the State Administration for Market Regulation jointly issued the “Motor Energy Efficiency Improvement Plan (2021-2023)”. It is particularly emphasized in the document that by 2023, the annual output of high-efficiency and energy-saving motors will reach 170 million kilowatts, and the proportion of high-efficiency and energy-saving motors in service will reach more than 20%. tons, reducing carbon dioxide emissions by 28 million tons.Therefore, motor companies should make full preparations in terms of technology, equipment, craftsmanship, materials and sales.
So, what technical routes are available for high-efficiency motors? At present, there are mainly five technical routes:
Three-phase asynchronous motor
One is the three-phase asynchronous motor. It is an industrial electric machine with a power range from a few watts to tens of thousands of kilowatts and has a wide range of applications. Mainly used in fans, pumps, compressors, machine tools, light industry and mining machinery, threshers and pulverizes in agricultural production, processing machinery in agricultural and sideline products, etc.
Its advantages are simple structure, easy manufacture, low price, reliable operation, sturdy and durable, high operation efficiency, the rotor is cast aluminum, the design difficulty is small, the industrial chain is mature, and the specifications are complete. The disadvantage is that the power factor is poor, which is always less than 1; it is not yet economical to smoothly adjust the speed in a large range.
Therefore, the traditional application of three-phase asynchronous motors is in fixed-speed situations, but now more and more three-phase asynchronous motors are used with frequency converters (VFDs) or variable speed drives. The frequency converter can adjust the output voltage according to the frequency. If it is applied to centrifugal fans, pumps, or compressors, it can achieve energy-saving effects with induction motors.
At present, the three-phase asynchronous motors with high energy efficiency above IE4 are composed of YE4, YE5 series and so on. That is to say, it is necessary to develop YE4 and YE5 series three-phase asynchronous motors.
Cast copper rotor three-phase asynchronous motor
The second is a three-phase asynchronous motor with cast copper rotor. In fact, it is also a kind of three-phase asynchronous motor, but the rotor is changed to cast copper, because the resistivity of copper is lower than that of aluminum, so it will reduce the resistance of the rotor, thereby reducing the loss of the rotor and improving the efficiency of the motor. But it also brings a problem, that is, there are higher requirements for casting process and equipment. At present, the cast copper rotor three-phase asynchronous motors above the IE4 standard include the YZTE4 series.
Self-starting permanent magnet synchronous motor
The third is the self-starting permanent magnet synchronous motor. The characteristics of this series of motors are that the rotor is welded by cast aluminum or copper bars, which is difficult to design, the industry chain is relatively mature, the cost is high, and the specifications are complete. The disadvantage is that the starting impact is large and the speed cannot be adjusted.
At present, the IE4 standard motor of this series is TYE4 series self-starting permanent magnet synchronous motor.
Variable frequency speed regulation permanent magnet synchronous motor
The fourth is the frequency conversion speed regulation permanent magnet synchronous motor, which is also the BLDC motor we often say. Its characteristic is that the rotor has no guide bar but has permanent magnets. The biggest advantage is maintenance-free, high efficiency, general design difficulty, relatively mature industry chain and complete specifications, but because it needs to be equipped with a controller, the cost is relatively high and the economy is relatively low.
This kind of motor is also a hot spot in recent years, and many companies are doing it, especially semiconductor companies pay more attention to this. Because the control of permanent magnet synchronous motor requires a large number of chip products, such as microprocessors such as MCU and DSP, power devices such as MOSFET and IGBT, and sensors, etc.
Of course, in addition to advantages, permanent magnet synchronous motors, or BLDC motors, also have some development bottlenecks to face, such as power density, materials, and production processes.
Synchronous Reluctance Motor
The fifth is the synchronous reluctance motor. It uses the torque generated by the uneven reluctance of the rotor to work. The rotor is composed of ferromagnetic materials and non-ferromagnetic materials. There is no permanent magnet and no winding. It is one of the simplest motors. Synchronous reluctance motors can generate high power density at low cost, and combine the performance of permanent magnet synchronous motors with the ease of use and ease of maintenance of induction motors, making them attractive in many applications. In addition, the control strategy of synchronous reluctance motor is very similar to that of permanent magnet synchronous motor, and strategies such as vector control and direct torque control commonly used in permanent magnet synchronous motor can be used. Although synchronous reluctance motors are more difficult to design, they can meet IE4 and even IE5 standards relatively easily.
These are the five main technical routes of the current IE4 and above motor standards. Of course, in order to realize the design and production of higher-efficiency motors, it is also necessary to develop key upstream materials, such as insulating materials, cold-rolled silicon steel sheets; equipment (mainly punches), fans, pumps, compressors and other downstream products, etc. .
In other words, we need to optimize the motor industry structure in order to improve the development of high-efficiency motor products and ensure the supply capacity. As an industrial power, motor products are highly dependent on the country’s development speed and industrial policies. Therefore, how to seize market opportunities, adjust product structure in time, develop marketable products, choose differentiated energy-saving motor products, and keep up with the national industry Policy is the point. From a global perspective, the motor industry is developing towards high efficiency and energy saving, with huge development potential.
Energy-saving measures for a high-efficiency motor
Measures to improve the efficiency of electric motors. The energy saving of a motor is a systematic project, which involves the whole life cycle of the motor. From the design and manufacture of the motor to the selection, operation, adjustment, maintenance and scrapping of the motor, the effect of the energy saving measures should be considered from the whole life cycle of the motor. In this regard, domestic and foreign countries mainly consider improving the efficiency of the motor from the following aspects.
The design of energy-saving motor refers to the use of modern design methods such as optimization design technology, new material technology, control technology, integration technology, test and detection technology, etc., to reduce the power loss of the motor, improve the efficiency of the motor, and design an efficient motor.
While converting electrical energy into mechanical energy, the motor also loses a part of the energy itself. Typical AC motor losses can generally be divided into three parts: fixed loss, variable loss and stray loss. Variable losses are load-dependent and include stator resistance losses (copper losses), rotor resistance losses, and brush resistance losses; fixed losses are load-independent and include core losses and mechanical losses. The iron loss is composed of hysteresis loss and eddy current loss, which is proportional to the square of the voltage, and the hysteresis loss is also inversely proportional to the frequency; other stray losses are mechanical losses and other losses, including friction losses of bearings and fans, rotors and other winding losses due to rotation.
Features of high-efficiency motors
1. Save energy and reduce long-term operating costs. It is very suitable for textiles, fans, pumps, and compressors. The cost of motor purchase can be recovered by saving electricity for one year;
2. Direct start or speed regulation with frequency converter can fully replace the asynchronous motor;
3. The rare earth permanent magnet high-efficiency energy-saving motor itself can save more than 15℅ of electric energy than ordinary motors;
4. The power factor of the motor is close to 1, which improves the quality factor of the power grid without adding a power factor compensator;
5. The motor current is small, which saves the transmission and distribution capacity and prolongs the overall operating life of the system;
6. Power saving budget: Take a 55kw motor as an example, a high-efficiency motor saves 15℅ than a general motor, and the electricity fee is calculated at 0.5 yuan per kilowatt-hour. The cost of replacing the motor can be recovered by saving electricity within one year.
Advantages of high-efficiency motors
Direct start, the asynchronous motor can be completely replaced.
The rare earth permanent magnet high-efficiency energy-saving motor itself can save more than 3℅ of electric energy than ordinary motors.
The power factor of the motor is generally higher than 0.90, which improves the quality factor of the power grid without adding a power factor compensator.
The motor current is small, which saves the transmission and distribution capacity and prolongs the overall operating life of the system.
Adding a driver can realize soft start, soft stop and stepless speed regulation, and the power saving effect is further improved.
The five major losses of the three motors
The main means to reduce the loss of the motor stator I^2R in practice are:
1. Increase the cross-sectional area of the stator slot. Under the same outer diameter of the stator, increasing the cross-sectional area of the stator slot will reduce the magnetic circuit area and increase the magnetic density of the teeth;
2. Increase the full slot ratio of the stator slots, which is better for low-voltage small motors. The application of the best winding and insulation size and large wire cross-sectional area can increase the full slot ratio of the stator;
3. Try to shorten the length of the stator winding end. The loss of the stator winding end accounts for 1/4 to 1/2 of the total winding loss. Reducing the length of the winding end can improve the efficiency of the motor. Experiments show that the end length is reduced by 20% and the loss is reduced by 10%.
The I^2R loss of the motor rotor is mainly related to the rotor current and rotor resistance. The corresponding energy-saving methods are as follows:
1. Reduce the rotor current, which can be considered from the aspects of increasing the voltage and the motor power factor;
2. Increase the cross-sectional area of the rotor slot;
3. Reduce the resistance of the rotor winding, such as using thick wires and materials with low resistance, which is more meaningful for small motors, because small motors are generally cast aluminum rotors, if cast copper rotors are used, the total loss of the motor can be reduced by 10% ～15%, but the manufacturing temperature of the current cast copper rotor is high and the technology is not yet popularized, and its cost is 15% to 20% higher than that of the cast aluminum rotor.
The iron loss of the motor can be reduced by the following measures:
1. Reduce the magnetic density and increase the length of the iron core to reduce the magnetic flux density, but the amount of iron used in the motor increases accordingly;
2. Reduce the thickness of the iron sheet to reduce the loss of the induced current. For example, replacing the hot-rolled silicon steel sheet with a cold-rolled silicon steel sheet can reduce the thickness of the silicon steel sheet, but the thin iron sheet will increase the number of iron sheets and the motor manufacturing cost;
3. Use cold-rolled silicon steel sheet with good magnetic permeability to reduce hysteresis loss;
4. Adopt high-performance iron chip insulation coating;
5. Heat treatment and manufacturing technology, the residual stress after processing the iron core will seriously affect the loss of the motor. When processing the silicon steel sheet, the cutting direction and punching shear stress have a greater impact on the core loss. Cutting along the rolling direction of the silicon steel sheet and heat treatment of the silicon steel punching sheet can reduce the loss by 10% to 20%.
Today, the understanding of motor stray losses is still in the research stage. Some of the main methods to reduce stray losses today are:
1. Heat treatment and finishing are used to reduce the short circuit on the rotor surface;
2. Insulation treatment on the inner surface of the rotor slot;
3. Reduce harmonics by improving stator winding design;
4. Improve the design of rotor slot coordination and reduce harmonics, increase stator and rotor cogging, design the rotor slot shape as inclined slots, and use series-connected sinusoidal windings, scattered windings and short-distance windings to greatly reduce high-order harmonics; Using magnetic slot mud or magnetic slot wedge to replace the traditional insulating slot wedge and filling the slot of the motor stator iron core with magnetic slot mud is an effective method to reduce additional stray losses.
Wind Friction Loss
To the attention it deserves, it accounts for about 25% of the total motor losses. Friction losses are mainly caused by bearings and seals, which can be reduced by the following measures:
1. Minimize the size of the shaft, but meet the requirements of output torque and rotor dynamics;
2. Use high-efficiency bearings;
3. Use efficient lubrication systems and lubricants;
4. Adopt advanced sealing technology.