Usually, a device that converts alternating current with constant voltage and frequency into alternating current with variable voltage or frequency is called a frequency converter. In order to produce variable voltage and frequency, the device first converts three-phase or single-phase alternating current into direct current (DC). Then the direct current (DC) is converted into three-phase or single-phase alternating current (AC). We call this converter "inverter".
(1) according to the different types of flow links,
1. The AC-DC-AC frequency converter first converts AC with fixed frequency into DC, and then converts DC into three-phase AC with arbitrarily adjustable frequency.
2. The AC-AC converter converts the AC with fixed frequency into the AC with arbitrary adjustable frequency (the same number of phases before and after conversion).
(2) according to the energy storage link (filtering method) of DC circuit,
1. voltage type frequency converter its energy storage element is capacitor. The middle and small capacity inverters are mainly voltage type converters.
2. the current type frequency converter\'s energy storage element is inductor coil.
(3) according to the modulation mode of voltage:
The voltage of the 1. pulse width modulation (SPWM) converter is achieved by adjusting the duty cycle of the pulse. Almost all the general and small capacity inverters use this kind of frequency converter.
The voltage of the 2. pulse amplitude modulation (PAM) converter is achieved by adjusting the magnitude of the DC voltage.
(4) according to the number of phases of input power,
1. the input and output sides of the three input and three output inverter are three phase alternating current. Most frequency converters belong to this category.
2. the single input and three output frequency converter\'s input side is single-phase alternating current, and the output side is three-phase alternating current. Inverters in household appliances are all of this type, usually with a smaller capacity.
It is widely used in home cinema, electric grinding wheel, electric tools, DVD, VCD, computer, TV, washing machine, fan, lighting and so on.