When talking about Inverter, you may be familiar with it. In our daily life or in the laboratory, we can see Inverter. It is mainly used to transform the DC and AC current in the current to achieve high current applications. Moreover, the types of electrical appliances we use today are also very complex. So for us, if we master the principle of Inverter, it will be a very important thing, Today, I will give you a detailed introduction to the principle and application of Inverter, hoping to help you.
Principle and application of Inverter
Working principle of Inverter
The main circuit is the power conversion part that provides voltage regulation and frequency modulation power supply for asynchronous motor. The main circuit of Inverter can be divided into two types [1]: voltage type is the converter that converts the DC of voltage source to AC, and the filter of DC circuit is capacitor. Current mode is a Inverter that converts the DC of current source into AC, and its DC circuit filter is inductance. It is composed of three parts: a "rectifier" that converts power frequency power into DC power, a "smoothing circuit" that absorbs voltage fluctuations generated by converters and inverters, and a "inverter" that converts DC power into AC power.
(1) Rectifier: diode converter is widely used recently, which converts power frequency power supply into DC power supply. Two sets of transistor converters can also be used to form a reversible converter. Because of its reversible power direction, it can be used for regenerative operation.
(2) Smoothing circuit: the DC voltage after rectifier rectification contains a pulsating voltage of 6 times the frequency of the power supply. In addition, the pulsating current generated by the inverter also changes the DC voltage. In order to suppress voltage fluctuation, inductors and capacitors are used to absorb fluctuating voltage (current). When the capacity of the device is small, if the power supply and main circuit components have a margin, the inductance can be omitted and a simple smoothing circuit can be used.
(3) Inverters: Contrary to rectifiers, inverters convert DC power into AC power at the required frequency, and make 6 switching devices turn on and off at the determined time to obtain 3-phase AC output. Taking the voltage source pwm inverter as an example, the switching time and voltage waveform are shown.
The control circuit is the circuit that provides control signals to the main circuit of the asynchronous motor power supply (voltage and frequency are adjustable). It consists of the "operation circuit" of frequency and voltage, the "voltage and current detection circuit" of the main circuit, the "speed detection circuit" of the motor, the "drive circuit" that amplifies the control signal of the operation circuit, and the "protection circuit" of the inverter and motor.
(1) Operation circuit: compare the external speed, torque and other instructions with the current and voltage signals of the detection circuit to determine the output voltage and frequency of the inverter.
(2) Voltage and current detection circuit: isolate the voltage and current from the main circuit potential.
(3) Drive circuit: the circuit that drives the main circuit components. It is isolated from the control circuit to make the main circuit device on and off. (4) Speed detection circuit: take the signal of speed detector (tg, plg, etc.) installed on the asynchronous motor shaft machine as the speed signal, send it into the calculation circuit, and make the motor run at the command speed according to the command and calculation.
(5) Protection circuit: detect the voltage and current of the main circuit. In case of overload or overvoltage and other abnormalities, in order to prevent the inverter and asynchronous motor from being damaged, make the inverter stop working or suppress the voltage and current values.
Function of Inverter
The converter integrates high-voltage high-power transistor technology and electronic control technology, and is widely used. The function of Inverter is to change the frequency and amplitude of AC motor power supply, thus changing the period of its moving magnetic field, and achieving the purpose of smooth control of motor speed. The emergence of Inverter simplifies the complex speed control. The combination of Inverter+AC squirrel-cage induction motor replaces most of the work that can only be completed by DC motor, reduces the volume, reduces the maintenance rate, and advances the transmission technology to a new stage.
Transport pump applications:
It replaces the slip motor speed control system with high failure rate caused by the environment and various valve control modes with poor control accuracy. It can save 20~40% energy, reduce equipment wear, reduce investment in spare parts, improve control accuracy and extend the service life of equipment.
Application of fans:
It can replace the wind deflector to adjust the air volume, reduce the fan vibration, eliminate the current impact of large motor starting, avoid mechanical vibration, greatly reduce the equipment failure rate, reduce the equipment maintenance workload, and easily realize the closed loop automatic adjustment of computer or air volume pressure.
Application on machine tools:
Reduce the number of variable speed transmission gears, reduce noise, improve spindle accuracy, and have strong adaptability to the spindle speed distribution required for various products and different materials processing. It is convenient to realize numerical control, and its cost is much lower than that of similar numerical control systems composed of DC speed regulation. The audio frequency quenching machine bed drive system of Kunming Milling Machine Factory, the numerical control milling machine of Power Company, the main drive system of 450 vertical mill of Liangting Steel Rolling Plant of Kunming Iron and Steel Company, the grinding machine of Yunnan Bearing Factory, and the missile shell polishing machine of Beijing Aerospace Department Factory have achieved good results. At present, VLT converter has been used for a long time in the products of professional manufacturers such as engraving machines, extruders, wire drawing machines, CNC lathes, etc.
Cigarette machine application:
Eliminate the high failure rate caused by the original old cigarette machine, such as (MK8R) speed regulation in different gears, improve the utilization rate of the equipment, extend the service life of the equipment, save electricity by 20%, and realize the localization and standardization of the main motor. It has saved foreign exchange, expanded the source of spare parts and improved the working environment.
Through Jimmy's introduction to the principle of Inverter, do you have a deeper understanding of the principle and function of Inverter? If you master the working principle of the Inverter, it is a great progress and breakthrough for the high-voltage high-power transistor technology and the cushion control technology. The working principle of the Inverter is divided into two parts, the main circuit and the auxiliary circuit, and it uses the current of DC and AC power, which is very high-tech. Well, Jimmy's introduction ends here.
