What is an inverter, detailed structure of an inverter.

Inverter is a device that converts alternating current at one frequency into alternating current at another frequency that can be adjusted.

Image: Yaskawa inverter

In other words:

The inverter is a device that changes the frequency of the current applied to the coil inside the motor and through it can control the motor speed steplessly, without the use of mechanical gearboxes. The inverter uses semiconductor components to sequentially switch off the current applied to the windings of the motor to generate a rotating magnetic field that rotates the motor.

There are many types of inverters such as: AC inverter, DC inverter; 220V single-phase inverter, 220V 3-phase inverter, 380V 3-phase inverter, etc. Besides the multi-function inverter lines, the company also produces specialized inverter lines: specialized inverters for pumps, fans, transformers. specialized frequency for lifting and lowering, crane, inverter for elevator, inverter for HVAC system, matrix inverter…

Why is it necessary to use an inverter?

Image: Formula for AC motor speed

From the above formula, we see that there are 3 methods to change the engine speed:

1. Change the number of motor poles P
2. Change the coefficient of slip s
3. Change the frequency f of the input voltage

In which, the first two methods are difficult to implement and do not bring high efficiency. The method of changing the motor speed by changing the frequency is the most effective method. Inverter is a device used to change the frequency of the power supply applied to the motor, thereby changing the motor speed.

The inverter can change the frequency from 0Hz to 400Hz (some inverter models adjust to 590Hz or higher). Therefore, it is possible to make the motor run faster than usual compared to running at 50Hz.

Structure and working principle of inverter:

Inside the inverter are components that have the function of receiving fixed frequency input voltage to convert into variable frequency voltage to control motor speed. The main components of the inverter include rectifier, filter, IGBT inverter, control circuit. In addition, the inverter is integrated with a number of other parts such as: AC reactor, DC reactance unit, starting resistor, keyboard, display screen, communication module, etc.

Image: Circuit diagram of the inverter.

Operation principle of the inverter:

– First, a single-phase or three-phase power source is rectified and filtered into a flat DC power source. This stage is performed by a diode bridge rectifier and a capacitor. Power input can be single phase or 3 phase, but it will be at fixed voltage and frequency (eg 380V 50Hz)

– The DC voltage above will be converted (inversely) into a symmetrical 3-phase AC voltage. Initially, the generated DC voltage will be stored in the capacitor bank. Next, through proper self-triggering, the IGBT converter (short for an insulated gate bipolar transistor that acts like an ultrafast on and off switch to generate the inverter’s output waveform) will generate a 3-phase AC voltage by PWM pulse width modulation.

Image: Voltage/frequency variation through the inverter

Benefits of using an inverter:

• Easily change motor speed, reverse motor rotation.
• The inrush current is reduced compared to direct starting, star-delta starting, so there is no voltage drop or difficulty in starting.
• The process of starting through the low-speed magnetic inverter helps to prevent the motor carrying a large load from having to start suddenly, avoiding damage to the mechanical part, the bearing, and increasing the life of the motor.
• Significant energy savings compared to direct motor driving.
• Inverters usually have electronic systems for overcurrent, overvoltage and undervoltage protection, creating a safe system for operation.
• Thanks to the working principle of switching rectifiers through diodes and capacitors, the reactive power from the motor is very low, thus reducing the current significantly during operation, reducing costs in installing compensating capacitors, and minimizing waste. power loss on the line.
• The inverter is integrated with communication modules that make control and monitoring from the center very easy.

Inverter application:

Due to its outstanding advantages, inverters are widely used in industry and civil, especially in industry. Here are some common applications that cannot be without inverter: Water pump, suction/push fan, air compressor, conveyor, lifting equipment, rolling mill, injection molding machine, winding/unloading machine, elevator , HVAC systems, mixers, centrifuges, improve the controllability of the gearboxes, replacing the traditional stepless control mechanism in the working machine, etc.