First, the basic knowledge 1, an overview of the AC power supply countries, whether for home or in the factory, the voltage and frequency are 200v / 60hz (50hz) or 100v / 60hz (50hz), and so on. In general, a device that converts an alternating current of constant voltage and frequency to alternating voltage of variable voltage or frequency is called an "inverter." In order to produce a variable voltage and frequency, the device must first convert the power of the AC to DC (dc). The device that converts direct current (dc) to alternating current (ac) has the scientific term "inverter." As the main device in the inverter equipment to produce changes in voltage or frequency is called "inverter", so the product itself is named "inverter", that is: inverter, inverter can also be used for home appliances. Not only motor (such as air conditioners, etc.), but also fluorescent lamps and other products are used in household appliances that use frequency converters. Inverter for motor control, both to change the voltage, but also to change the frequency. However, the frequency converter for fluorescent lamps is mainly used to adjust the frequency of the power supply. Devices used in automobiles to generate alternating current from batteries (direct current) are also sold under the name "inverter." The working principle of the inverter is widely used in various fields. For example, the computer power supply, in this application, the inverter is used to suppress the reverse voltage, frequency fluctuations and power instantaneous power failure. 2. Why can the rotation speed of the motor be freely changed? For example: 4 pole motor 60hz 1,800 [r / min], 4 pole motor 50hz 1,500 [r / min], the motor's rotation speed is the same as the frequency proportion. The motors referred to in this article are inductive AC motors and most of the motors used in the industry are of this type. The rotational speed of an induction AC motor (hereinafter referred to simply as a motor) approximately depends on the number of poles and the frequency of the motor. The working principle of the motor determines the number of poles of the motor is fixed. Since the pole value is not a continuous value (a multiple of 2, for example, poles 2, 4, 6), adjust the motor speed by changing this value. In addition, the frequency is the electrical signal of the motor power supply, so the value can be adjusted to the motor outside the motor, so that the motor speed can be freely controlled. Therefore, to control the frequency of the purpose of the inverter, as a motor speed control equipment, the preferred equipment. n = 60f / p, n: synchronous speed, f: power frequency, p: number of motor poles, frequency and voltage change is the optimal motor control method. If only the frequency is changed, the motor will burn out. This problem is especially noticeable when the frequency decreases. In order to prevent the occurrence of motor burnout, the inverter must change the voltage at the same time to change the voltage, for example: in order to halve the motor rotation speed, the inverter output frequency must be changed from 60hz to 30hz, then the inverter output The voltage must be changed from 200v to about 100v. For example: In order to halve the rotation speed of the motor, the output frequency of the inverter must be changed from 60hz to 30hz, then the output voltage of the inverter must be changed from 200v to 100v. If you want to use the inverter correctly, you must carefully consider the issue of heat dissipation. The inverter failure rate increases exponentially with temperature. The service life decreases exponentially with temperature. Ambient temperature increased by 10 degrees, the inverter service life by half. Therefore, we must pay attention to the heat problem! When the inverter work, the current flowing through the inverter is very large, the heat generated by the inverter is also very large, can not ignore the impact of its heat. The frequency converter is usually installed in a control cabinet. We need to know about a drive's heat is about how much. Can be estimated using the following formula: The approximate value of heat = inverter capacity (kw) × 55 [w] Here, if the inverter capacity is constant torque load Quasi (Overcurrent 150% × 60s) If the drive has DC or AC reactors and is also inside the cabinet, the heat will be much greater. Reactor installed on the side of the inverter or measured above the better. At this time can be used to estimate: Inverter capacity (kw) × 60 [w] Because the inverter hardware manufacturers are similar, so the above can be for the brand of products. Note: If there is a braking resistor, because the braking resistor The heat dissipation is very large, it is best to install the best location and drive isolation, such as installed in the cabinet above or beside. So, how can we reduce the heat in the control cabinet? When the inverter is installed in the control cabinet, we must consider the issue of the heating value of the inverter. According to the heat generated in the cabinet to increase the value, it is necessary to increase the size of the cabinet. Therefore, to minimize the size of the control cabinet, the amount of heat generated in the cabinet must be minimized. If the heat sink part of the inverter is placed outside the control cabinet when the inverter is installed, 70% of the heat generated by the inverter will be released to the outside of the control cabinet. As large capacity inverter has a lot of heat, so the more efficient large-capacity inverter. You can also use the isolation plate to separate the body and the radiator so that the heat sink does not affect the cooling of the inverter body. This effect is also very good. Inverter cooling design are based on the vertical installation, horizontal heat will be worse! On the general power of the cooling fan slightly larger inverter, with cooling fan. At the same time, it is also recommended to install a cooling fan on the outlet of the control cabinet. Into the air inlet to filter to prevent dust from entering the control cabinet. Note that the control cabinet and inverter fan are necessary, who can not replace. Second, the other issues on the heat 1. At altitudes higher than 1000m place, because the air density decreases, it should increase the cabinet cooling air volume to improve the cooling effect. In theory, the inverter should also consider derating, 1000m per -5%. However, in fact, because of the design of the inverter load capacity and cooling capacity is generally larger than the actual use, so it depends on the specific application. For example, in 1500m, but the periodic load, such as elevators, it is not necessary derating. 2. Switching Frequency: Inverter fever comes mainly from igbt, igbt fever focused on the moment of opening and closing. Therefore, when the switching frequency is high natural heat of the inverter becomes larger. Some manufacturers claim that reducing the switching frequency can be expanded, is the truth. 3. Vector control is how to make the motor has a large torque? Torque boost function is to increase the output voltage of the inverter. However, even with much higher output voltage, the motor torque does not increase corresponding to its current. Because the motor current contains the torque components and other components (such as excitation components) generated by the motor. The "vector control" distributes the motor current values ​​to determine the values ​​of the motor current components and other current components (such as excitation components) that produce the torque. "Vector Control" optimizes compensation by responding to the voltage drop across the motor end, allowing the motor to generate large torques without increasing current. This function is also effective to improve temperature rise of the motor at low speed. Third, the case of braking the brake Braking concept: refers to the flow of electricity from the motor side to the inverter side (or power supply side), then the motor speed is higher than the synchronous speed The load energy is divided into kinetic energy and potential energy. (Size determined by speed and weight) accumulates as the object moves. When kinetic energy is reduced to zero, the thing is stopped. Mechanical brake device approach is to use the braking device to convert the kinetic energy of friction and can be consumed. For frequency converters, the motor speed will also decrease following the frequency if the output frequency decreases. Braking occurs at this time, and the power generated by braking is returned to the inverter side. These power can be consumed by resistance heating. When used for lifting the load, the energy (potential energy) should also be returned to the inverter (or power) side for braking when descending, which is called "regenerative braking", and this method can be applied to Inverter braking. During deceleration, if the generated power is not consumed by the heat consumption method, the method of returning the energy to the power supply side of the inverter is called "power return regeneration method". In practice, this application requires the "energy feedback unit" option. Fourth, how to improve the braking capacity? In order to dissipate regenerative power with heat dissipation, a braking resistor needs to be installed on the inverter side. In order to improve the braking capacity, can not expect to increase the capacity of the inverter to solve the problem. Please use "brake resistor", "brake unit" or "power regeneration converter" and other options to improve the inverter's braking capacity. When the motor rotation speed changes, the output torque will happen? We often hear the following statement: "The motor starts and accelerates greatly when the motor is powered by commercial power (* 2), and the impact is weaker when using the inverter." If the motor is started with a large voltage and frequency, for example using a commercial power grid, a large starting shock (large starting current (* 3)) is generated. When using the inverter, the output voltage and frequency of the inverter are gradually added to the motor, so the torque generated by the motor is less than the torque value of the power supply of the power frequency network. Therefore, the inverter drive motor starting current to be smaller. Normally, the torque generated by the motor is reduced as the frequency decreases (the speed decreases). Actual data reduced is given in some drives manuals. By using a flux-vector-controlled inverter, the motor torque will be reduced at low speed and the motor will output enough torque even in the low-speed range. When the inverter speed control to more than 60hz frequency, the motor output torque will be reduced. The usual motor is 50hz (60hz) voltage design and manufacturing, the rated torque is also given in this voltage range. Therefore, the speed regulation under the rated frequency is called constant torque speed regulation (t = te, p Reference: * 1: Torque boost: This function increases the inverter output voltage so that the motor output torque and voltage Of the square of the increase in relation to improve the motor output torque to improve the motor low-speed output torque shortage of technology, the use of "vector control", you can make the motor at low speed, such as (without speed sensor) 1hz Motor with a speed of approximately 30 r / min) can reach the torque output of the motor at 50 hz (up to approx. 150% of the rated torque). For normal v / f control, the voltage drop of the motor The motor speed is reduced and relatively increased, which leads to the lack of excitation, which makes the motor can not get enough rotational force.To compensate for this deficiency, the inverter needs to increase the voltage to compensate for the voltage drop caused by the motor speed reduction. This function of the inverter is called "torque boost" (* 1). * 2: Commercial power supply Power supply from commercial power supply (commercial power supply) * 3: Starting current When the motor starts running, Starting torque and the maximum torque is less than the drive frequency power driver directly employment.