What is the inverter? and its operating principle?

Today’s article, I would like to mention some of the basic concepts of an inverter, an important component in automatic control devices.

Inverter is a device used to convert the voltage or alternating current at the input from one frequency into a voltage or current with a different frequency at the output.
Frequency converters are commonly used to control the speed of an AC motor by frequency control, whereby the frequency of the power grid changes to a variable frequency.

* Internal circuit diagram of an inverter:

* Principle of operation of inverter:
– First, the 1-phase or 3-phase AC power is rectified and filtered into a flat one-way source. This stage is done by rectifier bridge diode and capacitor. As a result, the cosphi power factor of the inverter system is independent of load and has a value of at least 0.96. This DC voltage is converted (inverted) into a symmetrical three-phase alternating voltage. This stage is now implemented through the IGBT (isolated gate insulated transistor) by pulse width modulation (PWM). Thanks to advances in microprocessor technology and current semiconductor technology, pulse-shift frequencies can reach the ultrasonic frequency range to reduce engine noise and reduce losses on the engine iron core.

Voltage waveform and inverter output current:

The three-phase AC system at the output can change the amplitude and frequency values ​​depending on the controller. In theory, between frequency and voltage there is a certain rule depending on the control mode. For constant load, the voltage-to-frequency ratio is constant. However, with pump and fan loads, this rule is a function of level 4. Voltage is a quadratic function of frequency. This creates the torque characteristic as a quadratic function of the speed that is suitable for the requirements of the pump / fan load since torque itself is also the second function of the voltage.
Power conversion efficiency of the inverter is very high because of the use of power semiconductor components manufactured by modern technology. Consequently, energy consumption is approximately equal to the energy required by the system.
In addition, today’s inverters have integrated a wide variety of control types suitable for most different types of load. Today, the inverter has a built-in PID and is suitable for a variety of communications standards, which are suitable for control and monitoring in SCADA systems.

* Benefits of using inverter:

The first benefit seen is the power savings: the power conversion efficiency of very high frequency inverters because of the use of modern semiconductor components. Consequently, energy consumption is approximately equal to the energy required by the system. Calculating with actual data, with actual costs, with a primary motor of about 100 kW, the return on investment for an inverter is about 3 months to 6 months. At present, in Vietnam, some enterprises use this frequency inverter and have got clear results.
With energy saving solutions in addition to improved system control, frequency inverters are now considered as a standard application for pump and fan drives.
Thanks to the high technology with the most advanced control technology (optimum power control), frequency converters are and will satisfy many investors in the country, in the region and in the world.
Types of load should use inverter to save power:
Modular loads (central air conditioning, water supply pump, fan pump, …).
+ The engine is always running under load but can not replace the engine, the additional inverter.
– The most special feature of the inverter drive system – the motor is that you can continuously adjust the speed of the engine. That is through adjusting the frequency you can adjust the motor speed to change as you wish in a wide range.
It also means that you have a lot of intelligent features, such as auto-recognition; Control features through the network; Can set up 16 speed levels; Control the engine start current for smooth soft start to improve the mechanical strength of the structure; Minimizing installation and maintenance costs; Space saving installation; Energy saving modes, …
– You will not have the worry of not mastering, controlling the power transmission process because you can control it now through the protection mode overload, overheat, overcurrent, Over voltage, low voltage, phase loss, phase difference, … of inverter.

* Some things to note when using inverter:
– Depending on the application you choose the inverter accordingly, in that way you will only pay a low cost but ensure reliability work.
Inside the inverter is electronic semiconductor components, so sensitive to environmental conditions, Vietnam has a hot and humid climate, so when choosing you must make sure that your inverter is tropical Suitable for the climate of Vietnam.
– You must ensure environmental conditions such as installation temperature, humidity, location.

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