How to choose a frequency converter? The difference between frequency converters and variable frequency power supplies

At the power level, everyone may know that frequency converters and variable frequency power supplies are auxiliary devices for charging electrical appliances, but many people do not know what a variable frequency power supply is and what a frequency converter is. With the continuous development of The New York Times, electrical appliances will also be continuously upgraded, and auxiliary equipment will also be constantly changing. Below, we will provide a detailed introduction to the differences between frequency converters and variable frequency power supplies, as well as how to choose a frequency converter.

Firstly, let's understand what a variable frequency power supply is? The variable frequency power supply converts the AC power of the main power supply from AC to DC and then to pure sine wave. The output frequency and voltage can be adjusted within a specific range. Unlike the variable frequency governor controlled by motor speed, it is also different from ordinary AC power sources. The ideal AC power has the characteristics of frequency stability, voltage stability, zero internal resistance, and pure sine wave voltage waveform (without frame loss). Variable frequency power sources are very close to ideal social communication power sources, so more and more variable frequency power sources are being used as standard power sources in advanced cultural development fields, bringing a good power grid environment for public utilities and facilitating objective evaluation of the characteristics of electrical equipment technology products. According to different structures, there are two types of variable frequency power supplies, namely linear amplification type and SPWM switching type.

What is a frequency converter? The standard name for AC frequency converters - DC-AC frequency converters is variable frequency governors. The derived voltage waveform consists of one waveform pulse and multiple high harmonic weights. The voltage and frequency are not independently adjusted, but vary proportionally, which cannot meet the requirements of AC power supply. Generally, it cannot be used as a power source and is limited to speed adjustment of three-phase asynchronous motors.

Due to the fact that the entire circuit of the variable frequency power supply consists of data exchange DC-AC - components such as filters, the voltage and current signal waves are derived as pure sine waves, making it an ideal AC electrical system in society. The power supply system is easy to approach the ideal communication of society.

The principle and basic functions of a frequency converter: A frequency converter is an electrical energy control system. It utilizes the switching operation of power semiconductor devices to convert the power of industrial power sources to another frequency. It can be divided into AC-AC frequency converters and AC-DC-AC frequency converters. The AC-AC frequency converter can directly convert AC power into variable voltage AC power. The AC-DC-AC frequency converter first rectifies AC power to DC power based on the rectifier, and then converts the DC power into AC power with variable frequency and voltage based on the inverter.

When selecting a frequency converter, the following points should be determined:

1) Select the frequency conversion effect; Constant voltage control or constant current control, etc.

2) The load type of the frequency converter; For example, for vane pumps or volumetric pumps, special attention should be paid to the load performance curve, as the characteristic curve determines the application method.

3) Matching between frequency converter and load;

I. Voltage pairing; The rated current of the frequency converter is consistent with the rated current of the load.

II Current pairing; The rated voltage of ordinary centrifugal pumps and frequency converters is consistent with the rated current of the motor. For special loads such as deep water pumps, the current and overload capacity of the frequency converter must be determined based on the performance parameters of the motor.

III. Pitch pairing; This situation may occur under constant torque loads or with a reduction device.

4) When using a frequency converter to drive a high-speed motor, due to the low resistance of the high-speed motor, the output current value increases and the output current value increases. Therefore, the selection volume of high-speed motor frequency converters is slightly larger than that of ordinary motors.

5) If the frequency converter wants to operate with long cables, measures should be taken to suppress the impact of long cables on the ground coupling capacitor to prevent insufficient output of the frequency converter. Therefore, on this premise, the volume of the frequency converter should be expanded or an output reactor should be installed at the output end of the frequency converter.

6) For some special applications, such as high temperature and altitude, it may cause the inverter to reduce its capacity, and the volume of the inverter should be increased by one gear.

Countermeasures for purchasing frequency converters:

1) Load purchase

The regulations for frequency converters vary depending on the load driven by the motor.

A: Fan and water pump are very common loads: the regulation of frequency converter is the simplest, and only the volume of frequency converter is equal to the motor volume (air compressor, deep water pump, sedimentation pump, changing Musical fountain).

B: Crane load: This load has the characteristic of high operating impact, so the frequency converter needs to have a certain capacity. At the same time, when a heavy object is sent to the elbow, there will be energy feedback, so a braking unit or the same busbar method should be used.

C: Uneven load: Some loads are sometimes light and sometimes heavy, and then the volume of the frequency converter is selected based on the phenomenon of heavy load, such as rolling mill machinery, crushing machinery, mixer, etc.

D: High inertia loads: such as centrifuges, punches, and chemical rotary kilns, these loads have a high inertia and may experience impacts during operation, resulting in energy feedback when the motor slows down. A slightly larger frequency converter should be used to accelerate the start to prevent shock. Cooperate with the braking unit to clear feedback electrical energy.

2) Production purchase

Customers should purchase according to the specific situation of production machinery

If it is an excavator, a high-performance dedicated frequency converter with torque control function should be selected because the frequency converter has a large low-speed torque, large static mechanical characteristics, and high hardness, and is not afraid of load impact. The low-speed torque can be improved by increasing the capacity of the motor and frequency converter;

If operating a compressor, due to its complex distance characteristics, especially the high starting torque, a high-performance vector frequency converter with good distance characteristics and current limiting function should be selected. If used in papermaking and chemical fiber equipment, high-precision and highly responsive closed-loop vector frequency converters should be selected.

3) Purchase stability

The purpose of purchasing a frequency converter based on stability is to improve work efficiency. If the characteristics are good but the stability is poor, problems often arise, and the gains outweigh the losses. China has a vast territory, with long-term high temperatures and humidity in the south. Coastal cities are mainly affected by salt corrosion, which leads to a decrease in equipment insulation. The climate in the north is dry and prone to static electricity. The temperature difference between winter and summer is large, and the production environment of various enterprises is different. When purchasing frequency converters, various factors should be considered. Although some frequency converters have good characteristics, they have poor environmental adaptability and may often encounter faults that affect production.

4) Price purchase

Purchasing a frequency converter based on price is a key consideration when purchasing a frequency converter. However, one-sided emphasis on low prices often leads to a decrease in quality and reliability. Since the cost of power equipment and main circuit Electrolytic capacitor in frequency converter is about 70%, some manufacturers use compression resistant 1000 V module instead of 1200 V module, use current of 25A instead of 30A, and directly use low-frequency Electrolytic capacitor instead of special high-frequency Electrolytic capacitor for frequency converter. This kind of frequency converter will not find anything under normal conditions or in a short time, but because of the reduction of module power capacity, once the motor is blocked The power grid is easily damaged due to transient high voltage, high temperature weather, and other conditions.

5) Power purchase

According to the purchase of frequency converters based on power modules, common key equipment power modules for frequency converters are IGBT modules and IPM intelligent power modules, especially IPM modules. Although the cost is high, due to protection functions such as overcurrent, short circuit, undervoltage, export grounding, overheating, etc., once abnormalities occur, the module is immediately maintained independently. Then, secondary maintenance is carried out based on external protection circuits, greatly reducing the possibility of burning the module and significantly improving its stability. The use of GTR module products, due to the lack of protection function in GTR itself, the external protection circuit and propulsion circuit are very complex. Once maintenance cannot keep up, the module will immediately burn out. In order to reduce costs, some manufacturers still choose GTR modules, which also requires attention when purchasing frequency converters.

When using frequency converters, it should also be noted that the installation location must meet the requirements of the specified environment, otherwise it may easily cause faults or shorten the service life; The distance between the frequency converter and the drive motor generally does not exceed 50 meters. If a longer spacing is required, it is necessary to reduce the carrier frequency or increase the selection of output reactors in order to operate normally.

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