Analysis of inverter control circuit schematic diagram

The first step in learning any technology is to thoroughly understand the schematic diagram. Only by thoroughly understanding the principle can you be at ease in your work. Today I will bring you an analysis of the inverter control circuit schematic diagram, and master the basic principle knowledge of the inverter!

Analysis of inverter control circuit schematic diagram

The figure below is a schematic diagram of the inverter control circuit.

The upper part is the main circuit and the lower part is the control circuit.

It is mainly composed of control core CPU, input signal, output signal and panel operation indication signal, memory and LSI circuit.

The analog signal of the external potentiometer is sent to the CPU through analog-to-digital conversion to achieve the purpose of speed regulation. The external switch signal is also sent to the control CPU through the NAND gate.

PART2 Basic knowledge of inverter

01. Frequency Converter Basics

(1) VVVF is the abbreviation of Variable Voltage and Variable Frequency, which means changing voltage and changing frequency, which is what people call variable voltage and variable frequency.

(2) CVCF is the abbreviation of Constant Voltage and Constant Frequency, which means constant voltage and constant frequency, or what people call constant voltage and constant frequency.

The power we use is divided into AC power and DC power. Most DC power is obtained by transforming AC power through a transformer, rectifying and filtering. AC power accounts for about 95% of the total power used by people.

Whether used in homes or factories, the voltage and frequency of single-phase and three-phase AC power supplies have certain standards according to the regulations of each country. For example, mainland my country stipulates that the single-phase AC power for direct users is 220V, and the three-phase AC line voltage is 380V and the frequency is 50Hz. The power supply voltage and frequency in other countries may be different from that in my country, such as single-phase 100V/60Hz, three-phase 200V/60Hz, etc. The AC power supply with standard voltage and frequency is called industrial frequency AC power.

Generally, a device that converts industrial frequency alternating current with fixed voltage and frequency into alternating current with variable voltage or frequency is called a "frequency converter".

To produce variable voltage and frequency, the device first converts the mains' alternating current into direct current (DC), a process called rectification.

The device that converts direct current (DC) into alternating current (AC) is scientifically called "inverter".

Generally speaking, an inverter is used to convert a DC power supply into an inverter power supply with a certain fixed frequency and a certain voltage. An inverter that converts the power supply into an adjustable frequency and voltage is called a frequency converter.

The waveform output by the frequency converter is a simulated sine wave, which is mainly used for speed regulation of three-phase asynchronous motors, and is also called a variable frequency speed regulator.

For variable frequency inverters that are mainly used in instrumentation and testing equipment and have high waveform requirements, the waveform needs to be tidied up so that a standard sine wave can be output, which is called a variable frequency power supply. Generally, the price of a variable frequency power supply is 15-20 times that of a frequency converter.

Since the main device that produces changing voltage or frequency in the inverter equipment is called "inverter", the product itself is named "inverter", that is, inverter.

Inverters can also be used in home appliances. Home appliances that use inverters include not only motors (such as air conditioners) but also fluorescent lamps.

The inverter used for motor control can change both voltage and frequency, but the inverter used for fluorescent lamps is mainly used to adjust the frequency of power supply.

Devices used in cars to 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, in the power supply of computer, frequency converter is used to suppress reverse voltage, frequency fluctuation and instantaneous power failure.

02. Why can the rotation speed of the motor be changed freely?

n = 60f/p(1-s)

n: motor speed f: power supply frequency p: number of motor pole pairs s: motor slip rate

Motor speed = 60 (seconds) * frequency (Hz) / number of motor pole pairs - motor slip rate

Motor rotation speed unit: rotations per minute, rpm/min can also be expressed as rpm

The rotation speed of the motor is proportional to the frequency. The torque difference of the synchronous motor is 0. The speed of the synchronous motor = 60 (seconds) * frequency (Hz) / number of magnetic pole pairs of the motor

The speed of asynchronous motor is lower than that of synchronous motor.

For example: 4-pole 3-phase stepper motor at 60Hz is less than 1,800 [r/min] 4-pole 3-phase asynchronous motor at 50Hz is less than 1,500 [r/min]

The motor referred to in this article is an induction AC motor, which is the type of motor used in most industrial fields. The rotation speed of an induction AC motor (hereinafter referred to as a motor) is approximately determined by the number of pole pairs and the frequency of the motor. The number of magnetic pole pairs of the motor is fixed according to the working principle of the motor. Since the number of magnetic pole pairs of the motor is 1, the number of poles of the motor is equal to 2, and the number of poles of the motor is not a continuous value (a multiple of 2, such as 2, 4, 6), it is not appropriate to change this value to adjust the speed of the motor.