What is Inverter? All about the Inverter

What is Inverter?

An inverter is a device that converts alternating current at one frequency into an alternating current at another frequency that is adjustable.

In other words:

The inverter is a device that changes the frequency of the current placed on the coil inside the motor and thereby can control the engine speed steplessly, without using mechanical gearboxes. The inverter uses semiconductor components to "switch on and off" the current applied to the motor windings to produce a rotating magnetic field that rotates the motor.

There are many types of inverter such as: AC inverter, DC inverter; inverter 1 phase 220V, inverter 3 phase 220V, inverter 3 phase 380V, ... Besides the versatile inverter line, the company also produces specialized inverter lines: inverter for pumps, fans ; inverters specialized for lifting, hoisting cranes; inverters specialized for elevators; inverter used for air conditioning system, etc.

Inverter:

Structure and operating principle of the inverter

The principle of operation of inverter / inverter is also quite simple. The single-phase or three-phase alternating current source is rectified, then filtered into a flat dc power source by capacitor and diode bridge rectifier. As a result, Cos (p) - the inverter power factor has a value independent of the load and has Min = 0.96.

Next, the DC voltage is converted (inverted) into symmetrical three-phase AC voltage, through the IGBT system (bipolar transistor with isolating gate) by pulse width modulation (PWM).

Thanks to the highly developed microprocessor and semiconductor technology, pulse switching frequency can reach the ultrasonic frequency range to reduce engine noise and reduce engine iron core losses.

Detailed diagram of the circuit of the inverter:

Detailed diagram of the circuit of the inverter

Waveform of voltage and output current of inverter:

Waveform of voltage and output current of inverter

The output three-phase AC voltage may vary the amplitude and frequency values ​​depending on the controller.

In theory, between frequency and voltage there is a certain law depending on the control mode. For a constant torque load, the ratio of voltage to frequency is constant.

However, with pump and fan load, the rule is a fourth order function. The voltage is a fourth function of the frequency. This creates a torque characteristic that is a quadratic function of speed in accordance with the requirements of the pump-fan load as torque is also a second function of voltage.

Power conversion efficiency of the inverter is very high because of the use of power semiconductor components, manufactured by advanced technology, helping energy consumption approximates the energy required by the system.

In addition, the inverter incorporates many different control types to suit most different types of loads. The inverter also integrates PID, FOC, Vector (sensorless or encoder), Torque control (sensorless or encoder) and is suitable for many different communication standards (RS232 or RS485), suitable for control and monitoring. In SCADA systems or systems with integrated HMI displays, PLC programming

Benefits of using inverters

• Easily change the engine speed, reverse the motor rotation.
• Reduced starting current compared with direct-start method, star-triangular circuit start-up should not cause a drop in voltage or make it difficult to start.
• The process of starting through the inverter from low speed helps the motor carrying large loads do not have to start suddenly, avoid mechanical damage, bearings, increase engine life.
• Significant energy savings compared to the direct motor method.
• Inverters usually have an electronic system for overcurrent protection, overvoltage and undervoltage protection, creating a safety system when operating.
• Thanks to the principle of converting the inverter through the diode and the capacitor, the reactive power from the motor is very low, thereby reducing the current significantly during operation, reducing the cost of installing capacitor banks, minimizing power loss on the line.
• The inverter has integrated communication modules that make it easy to control and monitor from the center.

Changing motor speed thanks to The Inverter

Formula for 3-phase AC motor speed and frequency:

Formula for 3-phase AC motor speed and inverter

To change the engine speed we have 3 methods:

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

And the inverter is the device used to change the frequency of 3-phase alternating current placed on the motor. Thereby changing the engine speed according to the above formula.

The waveform of the inverter

Inverter generator sets function like ordinary generators, except that it uses Neodymium magnets in place of brushes and they can convert direct current into alternating current. Diverse forms use different types of mechanical power and transform it into electrical power. There are 3 different forms of inverters on hand; sine wave, square wave and customized or modified square wave inverters. The purchase of inverter generator you may desire depends on the plan of giving power to it.


Sine wave - this type of inverter generator delivers similar wave like the wave delivered from regular generator or Power Company. They make use of AC mechanism which obviously produces sine wave power. The most excellent thing regarding this generator is that almost all equipments in the market are designed to function on sine wave. Sine wave generators are more costly than other types but the worth of electric power and range of application it uses are more wanted.


Square wave inverters - are generators that are not seen as frequent as they could be. They are superior in giving power to universal motors, like those that can be seen in some power tools. These generators are hard to find but the cheapest among portable models.


Modified square wave generators - these inverter generators produce current with waveform more likely the square wave inverters rather than sine wave inverters. Pump motors, fans and refrigerators operate less effectively by means of these inverters than sine wave inverters.


Appliances having timers or digital watch will maintain accurate time, but generally will run more rapidly. Domestic devices with heat control can not function accurately and tools like multi-speed energy drills may work only in one rate with these generators. Other kinds of equipment may function normally through customized or modified square wave inverter generators.