What kind of motor is an AC variable frequency motor?

Characteristics of variable frequency motors 1. Electromagnetic design For ordinary asynchronous motors, the main performance parameters to consider when redesigning are overload capacity, starting performance, efficiency and power factor. As for the variable frequency motor, since the critical slip is inversely proportional to the power supply frequency, it can be started directly when the critical slip is close to 1. Therefore, overload capacity and starting performance no longer need to be considered too much. The key issue to be solved is how to improve the adaptability of the motor to non-sinusoidal power supplies. The method is generally as follows: 　　1) Reduce the stator and rotor resistance as much as possible. 　　Reducing the stator resistance can reduce the fundamental wave copper loss to compensate for the increase in copper loss caused by higher harmonics. 2) In order to suppress higher harmonics in the current, the inductance of the motor needs to be appropriately increased. However, the rotor slot leakage resistance is large, the skin effect is also large, and high-order harmonic copper losses also increase. Therefore, the size of the motor leakage reactance must take into account the rationality of impedance matching within the entire speed range. 　　3) The main magnetic circuit of the variable frequency motor is generally designed to be in an unsaturated state. First, it is considered that high-order harmonics will deepen the saturation of the magnetic circuit. Second, it is considered that at low frequencies, in order to increase the output torque, the output voltage of the frequency converter should be appropriately increased. 　　2. Structural design When designing the structure, the impact of non-sinusoidal power supply characteristics on the insulation structure, vibration, noise cooling method of the variable frequency motor is mainly considered. Generally, pay attention to the following issues: 　　1) Insulation level, generally Class F or higher, strengthens the ground insulation and wire turn insulation strength, especially the ability of the insulation to withstand impulse voltage. 　　2) Regarding the vibration and noise issues of the motor, we must fully consider the rigidity of the motor components and the entire body, and try our best to increase its natural frequency to avoid resonance with each force wave. 　　3) Cooling method: Forced ventilation cooling is generally used, that is, the main motor cooling fan is driven by an independent motor. 　　4) To prevent shaft current, bearing insulation measures should be adopted for motors with a capacity exceeding 160KW. Mainly, it is easy to produce magnetic circuit asymmetry, and also produce shaft current. When the current generated by other high-frequency components acts together, the shaft current will greatly increase, resulting in bearing damage, so insulation measures are generally required. 　　5) For constant power variable frequency motors, when the speed exceeds 3000/min, special high-temperature resistant grease should be used to compensate for the temperature increase of the bearings. Main features of variable frequency motors Special variable frequency motors have the following characteristics:: 　　Class B temperature rise design, Class F insulation manufacturing. The use of polymer insulating materials and vacuum pressure impregnation manufacturing processes as well as the use of special insulation structures greatly improve the insulation voltage and mechanical strength of the electrical windings, which is sufficient to handle the high-speed operation of the motor and resist the high-frequency current impact of the inverter and the damage to the insulation caused by voltage. The balance quality is high, the vibration level is R-level (vibration reduction level), the mechanical parts are processed with high precision, and special high-precision imported bearings are used, which can operate at high speed. The forced ventilation and heat dissipation system all adopts imported axial flow fans with ultra-quiet, long life and strong wind power. It ensures that the motor can effectively dissipate heat at any speed and can achieve long-term operation at high or low speed. The YP series motors designed by AMCAD software have a wider speed range and higher design quality than traditional variable frequency motors. The special magnetic field design further suppresses high-order harmonic magnetic fields to meet the design indicators of broadband, energy saving and low noise. It has wide range of constant torque and power speed regulation characteristics, smooth speed regulation and no torque pulsation. It has good parameter matching with various frequency converters, and with vector control, it can achieve zero-speed full torque, low-frequency high torque, high-precision speed control, position control and fast dynamic response control. YP series variable frequency special motors can be equipped with brakes and encoders, so that precise parking can be achieved and high-precision speed control can be achieved through speed closed-loop control. Using "micromotor + frequency conversion special motor + encoder + frequency converter" to achieve precise control of ultra-low speed stepless speed regulation. YP series variable frequency special motors have good versatility, their installation dimensions comply with IEC standards, and are interchangeable with general standard motors. Structural principles of variable frequency motors, speed regulation and control of motors, are one of the basic technologies for various types of industrial and agricultural machinery, as well as office and people's livelihood electrical equipment. With the amazing development of power electronics technology and microelectronics technology, the AC speed regulation method using "dedicated variable frequency induction motor + frequency converter" is leading an upgrading change in the field of speed regulation to replace the traditional speed regulation method with its excellent performance and economy. The good news it brings to all walks of life is that: It greatly improves the degree of mechanical automation and production efficiency, saves energy, improves product qualification rate and product quality, increases the capacity of the power system, miniaturizes equipment, and increases comfort. It is currently replacing traditional mechanical speed regulation and DC speed regulation solutions at a very fast speed. 　　Due to the particularity of the variable frequency power supply and the system's requirements for high-speed or low-speed operation and dynamic response of rotation speed, stringent requirements have been put forward for the motor as the main power source, which has brought new issues to the motor in terms of electromagnetism, structure, and insulation. Application of variable frequency motors Variable frequency speed regulation has now become a mainstream speed regulation solution and can be widely used in continuously variable speed transmission in various industries. 　　Especially with the increasingly widespread application of frequency converters in the field of industrial control, the use of variable frequency motors has also become increasingly widespread. It can be said that due to the superiority of variable frequency motors over ordinary motors in terms of frequency control, it is not difficult to see variable frequency motors wherever frequency converters are used. 　　 Frequency conversion energy saving 1. What is a frequency converter? 　　Frequency converter is a power control device that uses the on-off function of power semiconductor devices to convert industrial frequency power into another frequency. 　　2. What is the difference between PWM and PAM? 　　PWM is the abbreviation of Pulse Width Modulation in English. It is a value adjustment method that changes the pulse width of the pulse train according to certain rules to adjust the output volume and waveform. 　　PAM is the abbreviation of Pulse Amplitude Modulation in English. It is a modulation method that changes the pulse amplitude of the pulse train according to certain rules to adjust the output value and waveform. 　　3. What is the difference between voltage type and current type? 　　The main circuit of the frequency converter can be roughly divided into two categories:: The voltage type is an inverter that converts DC from a voltage source into AC. The DC circuit filter is a capacitor. ； The current type is an inverter that converts DC from a current source into AC, and its DC circuit is filtered by a stone inductor. 　　4. Why does the voltage and current of the frequency converter change in proportion? 　　The torque is generated by the interaction between the magnetic flux of the motor and the current flowing in the rotor. At the rated frequency, if the voltage is constant and the frequency is only reduced, the magnetic flux will be too large and the magnetic circuit will be saturated. In severe cases, the motor will be burned. Therefore, the frequency and voltage should be changed in proportion, that is, while changing the frequency, the output voltage of the inverter should be controlled to keep the magnetic flux of the motor constant and avoid the occurrence of field weakening and magnetic saturation. This control method is mostly used in energy-saving frequency converters for fans and pumps. 　　5. When the motor is driven by industrial frequency power supply, the current increases when the voltage drops. ； For an inverter drive, if the voltage decreases when the frequency decreases, does the current increase? 　　When the frequency decreases (low speed), if the same power is output, the current will increase, but under the condition of constant torque, the current will almost remain unchanged. 　　6. When running with a frequency converter, what are the starting current and starting torque of the motor? 　　Using a frequency converter to operate, the frequency and voltage increase accordingly as the motor accelerates, and the starting current is limited to less than 150% of the rated current (125% to 200% depending on the model). When starting directly with industrial frequency power supply, the starting current is 6~7 times, so there will be mechanical and electrical impact. Using frequency converter drive can start smoothly (starting time becomes longer). The starting current is 1.2~1.5 times the rated current, and the starting torque is 70%~120% of the rated torque. ； For inverters with automatic torque enhancement function, the starting torque is above 100% and can be started with full load. 　　7. What does V/f mode mean? 　　When the frequency decreases, the voltage V also decreases proportionally. This question has been explained in answer 4. The proportional relationship between V and f is predetermined taking into account the characteristics of the motor. There are usually several characteristics stored in the controller's storage device (ROM), which can be selected with a switch or dial. 8. How does the motor's torque change when V and f are changed proportionally? 　　When the frequency decreases, the voltage is completely reduced in proportion. Then, since the AC impedance becomes smaller and the DC resistance remains unchanged, the torque generated at low speed will tend to decrease. Therefore, when V/f is given at low frequency, the output voltage should be increased in order to obtain a certain starting torque. This compensation is called enhanced starting. Various methods can be used to achieve this, including automatic methods, selecting V/f mode or adjusting the potentiometer. 9. The manual states that the speed range is 60~6Hz, which is 10: 1. So there is no output power below 6Hz? 　　Power can still be output below 6Hz, but depending on conditions such as motor temperature rise and starting torque, the minimum operating frequency is around 6Hz. At this time, the motor can output rated torque without causing serious heating problems. The actual output frequency (starting frequency) of the inverter is 0.5~3Hz depending on the model. 10. For general motor combinations above 60Hz, a certain torque is also required. Is this okay? 　　Normally this is not possible. Above 60Hz (there is also a mode above 50Hz) the voltage does not change and it is generally a constant power characteristic. When the same torque is required at high speed, attention must be paid to the selection of motor and inverter capacity. 　　11. What does open loop mean? 　　If a speed detector (PG) is provided for the motor device used and the actual speed is fed back to the control device for control, it is called "closed loop". If it does not operate with a PG, it is called "open loop". Most general-purpose inverters are open-loop, and some models can use options to provide PG feedback. 12. What should I do when the actual speed deviates from the given speed? 　　In open loop, even if the inverter outputs a given frequency, when the motor is running with load, the motor's speed will fluctuate within the rated slip range (1%~5%). For occasions that require relatively high speed regulation accuracy and require operation close to a given speed even if the load changes, an inverter with PG feedback function (optional) can be used. 　　13. If a motor with PG is used, can the speed accuracy be improved after feedback? 　　The frequency converter with PG feedback function has improved accuracy. However, the speed accuracy depends on the accuracy of the PG itself and the resolution of the inverter output frequency. 　　14. What does the stall prevention function mean? 　　If the given acceleration time is too short and the change in the output frequency of the inverter far exceeds the change in the rotational speed (electrical angular frequency), the inverter will trip due to the flow of overcurrent and stop running, which is called stalling. In order to prevent stalling and allow the motor to continue running, it is necessary to detect the magnitude of the current and perform frequency control. When the acceleration current is too large, slow down the acceleration rate appropriately. The same goes for slowing down. The combination of the two is the stall function. 　　15. There are models where the acceleration time and deceleration time can be given separately, and there are models where the acceleration and deceleration time can be given together. What is the significance of this? 　　Models whose acceleration and deceleration can be set separately are suitable for short-term acceleration and slow deceleration situations, or for small machine tools that require strict production cycle times. However, for fan transmission and other situations where the acceleration and deceleration times are long, the acceleration time and deceleration time can be set together. 　　16. What is regenerative braking? 　　If the command frequency of the motor is reduced during operation, the motor will become an asynchronous generator and work as a brake. This is called regenerative (electrical) braking. 　　17. Can I get greater braking force? 　　The energy regenerated from the motor is stored in the filter capacitor of the frequency converter. Due to the relationship between the capacity and withstand voltage of the capacitor, the regenerative braking force of a general frequency converter is approximately 10% to 20% of the rated torque. If the optional braking unit is used, it can reach 50%~100%. 　　18. Please explain the protection function of the frequency converter? The protection function can be divided into the following two categories:: 　　(1) Automatically perform corrective actions after detecting abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention. 　　(2) After detecting the abnormality, block the PWM control signal of the power semiconductor device to cause the motor to automatically stop. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power outage protection, etc. 　　19. Why does the protection function of the inverter activate when the clutch is used for continuous load? 　　When a clutch is used to connect a load, at the moment of connection, the motor changes sharply from the no-load state to an area with a large slip, and the large current flowing causes the inverter to trip over current and become unable to operate. 　　20. In the same factory, as soon as a large motor is started, the inverter stops during operation. Why is this? 　　When the motor starts, a starting current corresponding to the capacity will flow through the motor. The transformer on the stator side of the motor will produce a voltage drop. When the motor capacity is large, the voltage drop will have a greater impact. The inverter connected to the same transformer will make a judgment of undervoltage or instantaneous power failure, so sometimes the protection function (IPE) will operate, causing the motor to stop running. 　　21. What is frequency conversion resolution? What's the point? 　　For digitally controlled inverters, even if the frequency command is an analog signal, the output frequency is given in steps. The smallest unit of this step difference is called the frequency conversion resolution. 　　Frequency conversion resolution usually takes a value of 0.015~0.5Hz. For example, if the resolution is 0.5Hz, then the upper part of 23Hz can be changed to 23.5 or 24.0 Hz, so the movement of the motor is also followed in steps. This causes problems for applications such as continuous coil control. In this case, if the resolution is about 0.015Hz, it can be fully adapted to a 4-stage motor with a step difference of less than 1 r/min. In addition, the given resolution and output resolution of some models are different. 　　22. Is there any restriction on the installation direction when installing the inverter? 　　The structure inside and on the back of the inverter considers the cooling effect, and the up-down relationship is also important for ventilation. Therefore, the unit type should be installed in the longitudinal position in the panel or hung on the wall, and should be installed as vertically as possible. 　　23. Is it possible to directly put the motor into a fixed frequency inverter without using soft start? 　　It is possible at a very low frequency, but if the given frequency is high, it will be similar to the conditions for direct starting of the power frequency power supply. A large starting current (6 to 7 times the rated current) will flow, and the motor cannot start because the inverter cuts off the overcurrent. 　　24. What should we pay attention to when the motor runs above 60Hz? When operating above 60Hz, the following matters should be noted: (1) The machinery and equipment must be fully capable of operating at this speed (mechanical strength, noise, vibration, etc.). 　　(2) When the motor enters the constant power output range, its output torque must be able to maintain operation (the output power of shafts such as fans and pumps increases in proportion to the cube of the speed, so pay attention when the speed increases slightly). 　　(3) The issue of bearing life must be fully considered. 　　(4) For motors with medium capacity or above, especially 2-pole motors, please discuss carefully with the manufacturer when operating above 60Hz. 　　25. Can the inverter drive a gear motor? 　　Depending on the structure and lubrication method of the reducer, several issues need to be paid attention to. In terms of gear structure, 70~80Hz can usually be considered as the maximum limit. When oil lubrication is used, continuous operation at low speed may cause damage to the gear. 　　26. Can the frequency converter be used to drive a single-phase motor? Can single phase power be used? 　　The machine is basically unusable. For single-phase motors with speed regulator switch starting, the auxiliary winding will be burned in the speed regulation range below the operating point. ； For capacitor starting or capacitor operation, the capacitor will explode. The power supply of the inverter is usually 3-phase, but for small capacity, there are also models that operate on single-phase power. 　　27. How much power does the inverter itself consume? 　　It is related to the inverter model, operating status, frequency of use, etc., but it is difficult to answer. However, the efficiency of the inverter below 60Hz is about 94% to 96%, and the loss can be calculated based on this. However, since there is a built-in regenerative braking (FR-K) inverter, if the loss during braking is also taken into account, the power consumption will become larger, so attention must be paid to the design of the operating panel. 　　28. Why can’t it be used continuously in the whole range of 6~60Hz? 　　Generally, the motor uses an external fan mounted on the shaft or blades on the rotor end ring for cooling. If the speed is reduced, the cooling effect decreases, so it cannot withstand the same heat as high-speed operation. The load torque at low speed must be reduced, or a large-capacity inverter and motor combination should be used, or a special motor should be used. 　　29. What should you pay attention to when using a motor with brake? 　　The brake excitation circuit power supply should be taken from the input side of the frequency converter. If the brake operates when the inverter is outputting power, overcurrent will be cut off. Therefore, the brake must be activated after the inverter stops output. 　　30. If you want to use an inverter to drive a motor with a capacitor for improving the power factor, but the motor does not move, explain the reason. The current of the inverter flows into the capacitor for improving the power factor. The charging current causes the inverter to overcurrent (OCT), so it cannot start. As a countermeasure, please remove the capacitor and run it, or even improve the power factor. It is effective to connect an AC reactor to the input side of the inverter. 　　31. How long is the service life of the inverter? 　　Although the inverter is a static device, it also has consumable components such as filter capacitors and cooling fans. If they are maintained regularly, they are expected to have a lifespan of more than 10 years. 　　32. There is a cooling fan built into the inverter. What is the direction of the wind? What happens if the fan breaks? 　　For small capacities, there are also models without cooling fans. For models with fans, the direction of the wind is from bottom to top, so where the inverter is installed, do not place any mechanical equipment above or below that would hinder the suction and exhaust. Also, do not place parts that are sensitive to heat above the inverter. When the fan fails, it is protected by the fan stop detection or the overheat detection on the cooling fan. 33. The filter capacitor is a consumable, so how to judge its lifespan? 　　The capacitance of capacitors used as filter capacitors gradually decreases with the passage of time. The capacitance is measured regularly and the life is judged based on reaching 85% of the product's rated capacity. 　　34. Is there any restriction on the installation direction when installing the inverter? 　　It should be basically stored in the disk. The problem is that the disk with a fully enclosed structure has a large external size, takes up a lot of space, and has a relatively high cost. Its measures include: 　　(1) The design of the disk should be based on the heat dissipation required by the actual device. ； 　　(2) Use aluminum heat sinks, fin coolants, etc. to increase the cooling area ； 　　(3) Use heat pipes. 　　In addition, a type in which the back of the inverter can be exposed has been developed. 　　35. If you want to increase the speed of the original conveyor belt and run it at 80Hz, how should you choose the capacity of the inverter? 　　Assume the reference speed is 50Hz, and above 50Hz is the constant power output characteristic. When a load with constant torque characteristics such as a conveyor belt increases in speed, the capacity needs to be increased to 80/50≈1.6 times. The motor capacity also increases like the frequency converter. Energy-saving principle of frequency conversion speed regulation energy-saving device 1. Frequency conversion energy-saving can be known from fluid mechanics, P (power) = Q (flow) ╳ H (pressure), the flow rate Q is proportional to the square of the rotational speed N, the pressure H is proportional to the square of the rotational speed N, and the power P is proportional to the cube of the rotational speed N. If the efficiency of the water pump is certain, when the flow rate is required to decrease, the rotational speed N can decrease proportionally, and at this time the shaft output power P decreases in a cubic relationship. That is, the relationship between the power consumption of the water pump motor and the rotation speed is approximately a cubic ratio. For example: The power of a water pump motor is 55KW. When the speed drops to 4/5 of the original speed, the power consumption is 28.16KW, saving 48.8%. When the speed drops to 1/2 of the original speed, the power consumption is 6.875KW, saving 87.5% of power. 2. Power factor compensation energy-saving reactive power not only increases line losses and equipment heating, but more importantly, the reduction in power factor leads to a reduction in the active power of the grid. A large amount of reactive power is consumed in the lines, the equipment usage efficiency is low, and the waste is serious. According to the formula P=S╳COSФ, Q=S╳SINФ, where S-apparent power, P-has Active power, Q - reactive power, COSФ - power factor. It can be seen that the greater the COSФ, the greater the active power P. The power factor of an ordinary water pump motor is between 0.6-0.7. After using the frequency conversion speed regulating device, due to the effect of the filter capacitor inside the frequency converter, COSФ≈1, thus reducing the reactive power loss and increasing the active power of the power grid. 　　3. Soft start energy saving. Since the motor is started directly or Y/D, the starting current is equal to (4-7) times the rated current. This will have a serious impact on the electromechanical equipment and the power supply grid, and will also require too high grid capacity. The large current and vibration generated during startup will cause great damage to the baffles and valves, and are extremely detrimental to the service life of the equipment and pipelines. After using the frequency conversion energy-saving device, the soft start function of the frequency converter will make the starting current start from zero, and the maximum value will not exceed the rated current, which reduces the impact on the power grid and the requirements for power supply capacity, and extends the service life of the equipment and valves. Saves equipment maintenance costs. 　　It is an indelible fact that the frequency converter can save electricity. In some cases, it can save more than 40% of electricity, but in some cases it will be more wasteful than not connecting the frequency converter! 　　The inverter achieves energy saving by reducing voltage at light loads. Since the speed of the drag torque load does not change much, even if the voltage is reduced, it will not be much, so the energy saving is very weak. However, it is different when used in a fan environment. When a smaller air volume is required, the motor will reduce its speed. We know that the energy consumption of the fan is proportional to the 1.7th power of the speed, so the motor's torque will drop sharply, and the energy saving effect is obvious. If we use it on an oil well, a lot of electric energy will be wasted by using the braking resistor on the return journey, which will result in even more waste electricity. 　　Of course, if the environment requires speed regulation, the energy-saving effect of the inverter is still relatively obvious. When the speed is not adjusted, the inverter will not save power and can only improve the power factor. 　　1. If two identical motors both work at a power frequency of 50HZ, one uses an inverter and the other does not, and both the speed and torque are at the motor's rated condition, can the inverter still save power? How much can you save? 　　answer: In this case, the frequency converter can only improve the power factor but cannot save power. 　　2. If the torque of the two motors does not reach the rated torque of the motor (the frequency and speed are still the same 50HZ), how much power can the one with an inverter save? 　　answer: If automatic energy-saving operation is used, the inverter can run at reduced voltage at this moment, which can save some power, but the power saving is not obvious. 　　3. Under the same conditions, how much can be saved in the no-load state? Which of the three states saves more? 　　answer: The no-load state of the drag type load cannot save much electric energy.

The variable frequency motor is a special motor for frequency converters. It has forced air cooling and does not change with the shaft speed to ensure heat dissipation at low frequencies. In addition, the structure also changes accordingly. You can consult a professional motor factory. Explosion-proof variable frequency motors are also mature products and are optional. .

Thanks for the answer, I will reply too* one time

What we here are based on ordinary explosion-proof motors, adding a frequency converter to the motor power supply, and it becomes a portable frequency motor.