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What is an inverter? How is it different from a converter?
Even if you have never seen an inverter, you must be familiar with home appliances equipped with inverters. Some people may not understand what kind of inverter is essential in our life.


Of course, the inverter is not a compelling electronic component. Also, some parts are easily confused with converters and difficult to understand.
1. What is an inverter?


Inverter is written as inverter in English, which is literally translated as "inverter". Then, it is current and voltage that are reversed. Specifically, it refers to the circuit or device itself that converts direct current to alternating current.


Inverters are typical components in power electronics and have been used in a wide range of scenarios from industrial to consumer applications. Also, there is a similar term called a converter, but this is the etymology of convert, which means "something to be converted" and refers to a device that converts alternating current to direct current, also known as a forward converter or rectifier. Inverters do the opposite, so they are sometimes called inverse converters.
Second, it may be difficult to understand even if it is "converting direct current to alternating current", and it may be difficult to come up with a purpose. In order to know this, unless you know what currents and voltages DC and AC are, it's hard to get an image, so here's a quick review.


"DC" always provides constant voltage. On the other hand, "alternating current" is in a state where the positive and negative voltages are switched and reversed periodically. The number of rotations of this reversal in one second is called the frequency. This "frequency" is the point, an inverter can generate AC power of any frequency from a DC source and provide the current and voltage suitable for the electronics used.


The device most often used for this inverter is the motor. Usually, commercial power is provided by alternating current, but generally electronic circuits are driven by stable direct current. However, there are DC-driven and AC-driven motors, each with their own advantages, but inverters play an active role in AC-driven motors. AC drive motors are commonly used in household appliances because of their simple structure and durability. However, the number of revolutions cannot be controlled by the motor alone. Therefore, by using an inverter to generate an arbitrary frequency, the motor can be operated at a desired rotational speed.


In addition to motors, there are many scenarios for converting direct current to alternating current. For example, DC electricity stored in sunlight will be converted into AC electricity for home use. The question may also arise here: "Why bother to use alternating current when electronic components are often driven by direct current?" This is because the disadvantage of direct current is that it is more expensive to convert voltage than alternating current. Directly delivering DC voltage to electronic equipment that has more energy than required results in energy loss and increased equipment burden. So by converting it to any AC voltage using an inverter, the proper amount of energy can be dissipated.


On the other hand, the disadvantage of an inverter is that it is prone to noise due to its working principle. If noise is introduced, it may be difficult to connect the device or may cause malfunction. Therefore, the inverter will take noise countermeasures such as separation of wiring and installation of noise filters.


2. Inverter principle/mechanism


Inverters work on the principle of "switching". Currently, inverters are equipped with high-speed switching elements such as MOSFETs. The ideal form of alternating current is a beautifully arranged waveform called a "sinusoid".


The inverter performs a voltage control called PWM control (pulse width modulation) to generate this waveform. PWM control is the most common voltage control method today. It means that the switch opens and closes according to the direction of the alternating current, but by adjusting the time, the desired frequency (pulse of desired width) is extracted.


By the way, it's not just about changing the frequency. In an inverter, frequency and voltage are proportional, and as frequency increases, so does the voltage. As mentioned above, when we say inverter, we may be referring to the device itself or the circuit.


However, when an inverter is referred to as a device, it usually includes not only the inverter but also the converter and the capacitor. As a mechanism, the AC current supplied from the commercial power source (outlet, etc.) is first rectified to DC by the converter, then smoothed by the capacitor, and then subjected to the above PWM control by the inverter, and then any AC voltage is taken out.