light industry

一、Frequency converter Foundation
VVVF against against voltage and frequency change (Variable Voltage and Variable Frequency acronym). Against against
CVCF against against constant voltage and constant frequency (Constant Voltage and Constant Frequency acronym). Against against
Countries use the AC power supply, whether it is for the home or for the plant, its voltage and frequency are 200V/60Hz (50Hz) or 100V/60Hz (50Hz), etc.. In general, a device that converts the voltage and frequency of the alternating current into a voltage or frequency variable alternating current is called a transducer ". In order to produce a variable voltage and frequency, the device must first be converted to a DC power supply (DC). The direct current (DC) is transformed into alternating current (AC) and its scientific term is "inverter" (inverter). As the inverter equipment in the voltage or frequency of the main device is called "inverter", so the product itself is named "inverter", that is: frequency converter, frequency converter can also be used for home appliances. The use of inverter appliances in the home appliances not only have motor (such as air conditioning, etc.), as there are fluorescent lamps and other products. For motor control of the inverter, not only can change the voltage, but also can change the frequency. But the frequency converter used for fluorescent lamp is mainly used to adjust the frequency of power supply. The use of the car by the battery (DC) to produce alternating current equipment is also the name of "inverter" for sale. The principle of frequency converter is widely used in various fields. For example, the power supply of computer power supply, in this application, the inverter used to suppress the reverse voltage, frequency fluctuations and power of the instantaneous power

二、 Why the rotation speed of the motor can be changed freely?
R/min motor rotation speed unit: the number of rotations per minute, can also be expressed as rpm. For example: 4 pole motor 60Hz 1800 [r/min], 4 pole motor 50Hz 1500 [r/min], the speed of rotation of the motor is proportional to the frequency. In this paper, the motor is an induction motor, and most of the motors used in the industrial field are used for this type of motor. The rotational speed of induction motor (hereafter referred to as the motor) is approximately determined by the number and frequency of the motor. The motor's working principle is determined by the motor's working principle. Because the pole value is not a continuous value (for a multiple of 2, for example, the pole number is 2, 4, 6), the value is not appropriate and the value is changed to adjust the speed of the motor. In addition, frequency is the electrical signal of the motor power supply, so the value can be adjusted at the outside of the motor and then supply the motor, so that the rotation speed of the motor can be controlled freely. Therefore, to control the frequency of the frequency converter, is to be the preferred equipment for the motor speed control equipment.
N = 60f/p, n: synchronous speed, f: power frequency, p: motor pole number, change frequency and voltage is the best motor control method. If only changing the frequency of the motor will be burnt out. Especially when the frequency is reduced, the problem is very prominent. In order to prevent motor burned accident occurred, inverter in frequency change at the same time, we must want to also change voltage. For example: in order to make the motor rotation speed is halved, the output frequency of the inverter must change from 60 Hz to 30 Hz, then the output voltage of the inverter must from 200V change to about 100V. Against such as to make the motor rotate speed is halved, the output frequency of the inverter must change from 60 Hz to 30 Hz, then the output voltage of the inverter must change from 200V to about 100V. If you want to use the inverter correctly, it is necessary to consider the problem of heat dissipation. The failure rate of frequency converter rises exponentially with the increase of temperature. Service life decreases with the increase of temperature. Ambient temperature increased by 10 degrees, frequency converter service life halved. Therefore, we should pay attention to the heat problem ah! In the inverter, the current flow through the inverter is very large, the heat generated by the inverter is also very large, can not ignore the impact of its heat generation.
Against is usually installed in the control cabinet, frequency converter. We need to understand how much of a frequency converter. Can use the following formula estimation: the calorific value of the approximate value = converter capacity (kw) #215; 55 [w] here, if the capacity of the transducer is in constant torque load for quasi (flow capacity 150% * 60s) if the frequency converter with DC reactor or AC reactor, and also in the cupboard, then send the heat will be even greater. Reactor installed at the side of the inverter or measured at the top of the better. And this can be used to estimate the inverter capacity (kw) #215; 60 [w] because almost all the inverter manufacturers of hardware, so the formula can be for various brands of products. Note: if there is a brake resistor, because the brake resistance of a large amount of heat, it is best to install the best location and frequency converter to leave, such as installed in the cabinet above or next to, etc.. So, how to reduce the amount of heat in the control cabinet, when the transducer is installed in the control cabinet, to consider the issue of the inverter calorific value. According to the increase in the value of heat generated inside the cabinet, to properly 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 reduced as much as possible. If the transducer is installed, the transducer part of the inverter to control the outside of the cabinet, will make the inverter has 70% of the heat released to the outside of the control cabinet. Due to the large capacity inverter has a lot of heat, so the large capacity inverter is more effective. Can also use the isolation plate to separate the body and the radiator, so that the radiator heat does not affect the inverter body. This effect is also very good. Inverter heat dissipation design is to vertically installed for foundation, placed sideways heat will become poor. A cooling fan power slightly larger point of frequency converter with cooling fan. At the same time, it is recommended to install the cooling fan in the control cabinet. Inlet air inlet to prevent dust into the control cabinet to prevent dust. Note that the control cabinet and the inverter on the fan is to be, not who replace who.
Other issues about heat dissipation
(1) at an altitude higher than 1000m, because the air density is reduced, the cooling air volume of the cabinet should be increased to improve the cooling effect. Theoretically the inverter should also consider the drop volume, 1000m per -5%. But because in fact, the design of the inverter load capacity and heat capacity than the actual use of a large, so it is also to look at the specific application. For example, in the 1500m place, but the periodic load, such as the elevator, it is not necessary to reduce capacity.
(2) switching frequency: the frequency of the inverter is mainly from the IGBT, IGBT fever has concentrated in the opening and closing of the moment. Therefore, when the switch frequency is high, the heat capacity of the natural frequency converter becomes larger. Some manufacturers claim to reduce the switching frequency can be expanded, that is the reason.

三、Vector control is how to make the motor with a large torque?
1, torque enhancement: this function increases the frequency converter output voltage, so that the output torque of the motor and the voltage of the Ping Fangcheng direct ratio increase, thereby improving the output torque of the motor. To improve low speed output torque shortage of technology, using the vector control, the motor at low speed, such as (without speed sensor) 1 Hz (on a four pole motor, the speed about 30R) output torque can reach the motor in 50Hz power supply output torque (up to a maximum of about 150% of rated torque). For the conventional V/F control, the voltage drop along with the motor speed decreases and the relative increase, which leads to the lack of excitation, and the motor can not get enough rotation force. In order to compensate for this problem, the inverter needs to improve the voltage to compensate for the voltage drop caused by the motor speed. This function of the transducer is called "torque boost" (*1). Torque lifting function is to improve the output voltage of the inverter. However, even if the output voltage is increased, the torque of the motor can not be improved. Because the motor current contains the torque component and other components (such as the excitation component) generated by the motor. Vector control to assign the current value of the motor, so as to determine the current component of the motor torque and other current components (such as the excitation component) of the numerical value. Vector control can be through the voltage drop of the motor terminal response, to optimize the compensation, in the case of no increase in current, allowing the motor to produce a large torque. This function is effective for improving the temperature rise of the motor at low speed.
2, Inverter Brake situation
The concept of braking: refers to the power from the motor side flow to the inverter side (or the power supply side), then the motor speed is higher than the synchronous speed. The load energy is divided into kinetic energy and potential energy. The kinetic energy (determined by the speed and weight of its size) with the movement of the object. When the kinetic energy is reduced to zero, the thing is stopped. Method of mechanical brake device is the brake device for the object can be consumed for the energy transfer and friction. For the frequency converter, if the output frequency is reduced, the motor speed will follow the same frequency. At this time, the braking process will be generated. The power generated by the brake will return to the inverter side. These power can be consumed by resistance heating. Energy (potential energy) is also going to return to the inverter (or power) side, when used for lifting the load. This kind of operation method is called "regenerative brake", and this method can be applied to the frequency converter brake. During the deceleration, the power generated if not consumed by the heat consumption, but the energy return to the inverter power side of the method is called power return regeneration method". In practice, the application of "energy feedback unit".
3, how to improve the braking ability?
In order to use against heat regenerative power consumption, need to install the brake resistor in the inverter side. In order to improve the braking ability, can not expect to rely on the capacity of the inverter to solve the problem. Please use the brake resistor and braking unit "or" renewable power converter "option to improve the braking capacity of inverters.
4, when the rotation speed of the motor changes, the output torque will be how?
(1) power frequency power supply by power supply (commercial power supply)
Starting current when the motor begins to run, the inverter output current transducer drive starting torque and maximum torque is less than the direct use of power frequency power supply.
2) we often hear the following statement: "when the motor power supply in the power supply (*1), the motor start and accelerate the impact of a large, and when the use of inverter power supply, the impact will be weak". If you use a large voltage and frequency of starting motor, such as the use of power grid direct power supply, it will generate a large starting shock (a large starting current (*2)). And when the inverter is used, the output voltage and frequency of the inverter is gradually added to the motor, so the torque generated by the motor is less than the power supply of the power grid. So inverter driven motor starting current to be smaller. Usually, the torque generated by the motor to decreases with increasing frequency (slow down) and reducing the actual data by reducing some in some inverter manual will description is given. By using the flux vector control inverter, it will improve the low speed torque of the motor at low speed, even in the low speed area of the motor can also be output enough torque. When the frequency converter is more than 60Hz, the output torque of the motor will be reduced. The usual motor is designed and manufactured according to 50Hz (60Hz) voltage, and the rated torque is also given in this voltage range. Therefore, under the rated frequency speed is called the constant torque speed (T=Te, P<=Pe) frequency inverter output frequency is greater than the 50Hz frequency, the torque generated by the motor and the frequency is inversely proportional to the linear relationship. When the motor runs at a speed greater than 60Hz, the magnitude of the load of the motor must be considered, in order to prevent the output torque of the motor. For example, the torque generated by the motor at 100Hz is about to be reduced to 1/2 when the torque generated by 50Hz. So the speed on the rated frequency is called the constant power speed regulation (P=Ue*Ie).