What Is IGBT Based Power Inverters?

IGBTs or integrated gate bipolar transistors are the component of choice where high switching speeds and high voltage are required in a device such as a power inverter. Inverters convert direct current to alternating current at a specific voltage and frequency. Power converters can be of very small size – mobile phones have miniature power converters in their circuits – but may be of much larger size and deal with hundreds of mega watts of power. In a power converter, the voltage and current typically control the overall power rating, whereas in an electronic device, these two parameters carry the signal or information in the device.

Power inverters work with the help of a component such as an IGBT or a MOSFET or BJT. These are all switching devices that turn the power on or off at a specific speed and voltage range. In some applications, commutated thyristors are used rather than semiconductors.

The best type of power inverter should have a sinusoidal waveform, but in practice most are not sinusoidal and they tend to contain a specific set of harmonics.

Low and medium power inverters can use a non sinusoidal waveform, such as a square or semi- square waveform, and perform quite satisfactorily, but when the voltage increases, sinusoidal waveform inverters are to be preferred. Power inverters with adjustable alternating current frequency capacity can be designed by using control circuitry which varies the turn on and turn off ties of the IGBTs or other switching components in the circuitry. The switching method of these high speed power semiconductor devices can determine the harmonics of the resulting output voltage.

The input into the power inverter is typically a rectifier producing DC if the application is an industrial one, but the initial voltage may be coming from a variety of different sources, including fuel cells, solar cells or even a battery. The rectifier involves a DC link. The network frequency is at first rectified and then finally inverted back to AC at an adjustable frequency. This sort of rectification can be achieved by using thyristor converter circuits or standard diodes. The inversion itself is carried out by standard circuitry.

An example of a typical power inverter in which the switching components are IGBTs is a single phase Unipolar inverter. This type of inverter typically consists of a bridge form with four IGBTs which are bidirectional. In this example, the circuit’s input voltage is in the region of 220V which is being fed in by the rectifier unit. The AC output is achieved by triggering the four IGBTs in a prescribed sequence. Two of the IGBTs are at first switched on by triggering the IGBT gates. Current flows from the positive side of the IGBTs to the negative. The second half of the cycle reverses the direction of the current.