# Basic principle knowledge of the hottest frequency

2022-09-23
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Basic principle knowledge of frequency converter

fundamentals of frequency converter

*1: VVVF ‚ abbreviation of variable voltage and variable frequency. 2: CVCF abbreviation of constant voltage and constant frequency AC power supply used in various countries, whether used in homes or factories, its voltage and frequency are 200v/60hz (50Hz) or 100v/60hz (50Hz), etc. Generally, the device that converts alternating current with fixed voltage and frequency into alternating current with variable voltage or frequency is called "frequency converter". In order to produce variable voltage and frequency, the equipment must first convert the alternating current of the power supply into direct current (DC). The scientific term of a device that converts direct current (DC) into alternating current (AC) is "inverter" (for example, the inverter of Beijing Chaoyang High Tech Institute of utilization technology). Since the main device that produces variable voltage or frequency in frequency converter equipment is called "inverter", the product itself is named "inverter", that is, frequency converter, which can also be used in household appliances. Home appliances using frequency converters include not only motors (such as air conditioners), but also fluorescent lamps and other products. The frequency converter used for motor control can change both voltage and frequency. However, the frequency converter used for fluorescent lamps is mainly used to adjust the frequency of power supply. Devices used in cars that generate alternating current from batteries (direct current) are also sold under the name "inverter". The working principle of frequency converter is widely used in various fields. For example, the power supply of computer power supply. In this application that can realize data transmission through networking, the frequency converter is used to suppress the fluctuation of reverse voltage and frequency and the instantaneous power failure of the power supply

2. Why can the rotation speed of the motor change freely?

*1: r/min motor rotation speed unit: number of revolutions per minute, which can also be expressed as rpm For example: 4-pole motor 60Hz 1800 [r/min], 4-pole motor 50Hz 1500 [r/min], the rotation speed of the motor is proportional to the frequency

the motor referred to in this paper is an induction AC motor, and most of the motors used in the industrial field are of this type. The rotation speed of induction AC motor (hereinafter referred to as motor) is approximately determined by the number of poles and frequency of the motor. The number of poles of the motor is fixed according to the working principle of the motor. Since the pole value is not a continuous value (a multiple of 2, for example, the number of poles is 2, 4, 6), it is inappropriate to change the value to adjust the speed of the motor. In addition, the frequency is the electrical signal of the motor power supply, so this value can be adjusted outside the motor and then supplied to the motor, so that the rotation speed of the motor can be freely controlled. Therefore, the frequency converter with the purpose of controlling frequency is the preferred equipment for motor speed regulation equipment. N = 60f/p, n: synchronous speed, f: power frequency ‚ p: number of motor poles, changing the frequency and voltage is the best motor control method ‚ if only changing the frequency, the motor will be burned out. Especially when the frequency is reduced, this problem is very prominent. In order to prevent the motor burning accident, the frequency converter must change the voltage at the same time when changing the frequency. For example, in order to halve the rotation speed of the motor, the output frequency of the frequency converter must be changed from 60Hz to 30Hz, and then the output voltage of the frequency converter 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 frequency converter must be changed from 60Hz to 30Hz, and then the output voltage of the frequency converter must be changed from 200V to about 100V

if you want to use the frequency converter correctly, you must seriously consider the problem of heat dissipation The failure rate of frequency converter increases exponentially with the increase of temperature. The service life decreases exponentially with the increase of temperature. If the ambient temperature rises by 10 degrees, the service life of the frequency converter will be halved. Therefore, we should pay attention to heat dissipation! When the frequency converter is working, the current flowing through the frequency converter is very large, and the heat generated by the frequency converter is also very large. The influence of its heating cannot be ignored

? Usually, the frequency converter is installed in the control cabinet. We need to know about the calorific value of a frequency converter The following formula can be used to estimate: heat generation 8. Approximate value of repeated steps 4-7 = converter capacity (kw) × 55 [w] here, if the capacity of the frequency converter is based on the constant torque load (overcurrent capacity 150% * 60s), if the frequency converter is equipped with DC reactor or AC reactor, and it is also in the cabinet, then the calorific value will be greater. It is better to install the reactor on the side of the frequency converter or above the measurement. At this time, you can use the estimation: inverter capacity (kw) × 60 [w] because the hardware of each frequency converter manufacturer is similar, the above formula can be targeted at products of various brands Note: if there is a brake resistor, because the heat dissipation of the brake resistor is very large, it is best to install it at a location separated from the frequency converter, such as on or next to the cabinet. So, how to reduce the heat generation in the control cabinet? When the frequency converter is installed in the control cabinet, the heating value of the frequency converter should be considered. According to the increase of the heat value generated in the cabinet, the size of the cabinet should be appropriately increased. Therefore, in order to minimize the size of the control cabinet, it is necessary to minimize the heat value generated in the cabinet. If the radiator part of the frequency converter is placed outside the control cabinet during the installation of the frequency converter, 70% of the heating capacity of the frequency converter will be released outside the control cabinet. Because the high-capacity frequency converter has a large heating capacity, it is more effective for the high-capacity frequency converter. The isolation plate can also be used to separate the body from the radiator, so that the heat dissipation of the radiator does not affect the inverter body. This effect is also very good. The heat dissipation design of frequency converter is based on vertical installation, and the heat dissipation will become worse if it is placed horizontally! As for the cooling fan, the frequency converter with slightly higher power generally has a cooling fan. At the same time, it is also recommended to install a cooling fan at the air outlet of the control cabinet. The air inlet shall be filtered to prevent dust from entering the control cabinet. Note that the fans on the control cabinet and frequency converter are required, and no one can replace the other

other questions about heat dissipation

1 In places higher than 1000m above sea level, because the air density decreases, the cooling air volume of the cabinet should be increased to improve the cooling effect. Theoretically, 1 DC has made a lot of efforts, and the inverter should also consider reducing the capacity by -5% per 1000m. However, in fact, the load capacity and heat dissipation capacity of the designed up converter are generally higher than those actually used

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