Power Electronics is the technology associated with efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form. Power electronic converters can be found wherever there is a need to modify the electrical energy form (i.e., modify its voltage, current or frequency). Therefore, their power ranges from some mill watts (as in a mobile phone) to hundreds of mega watts (e.g.in a HVDC transmission system).With “classical” electronics, electrical currents and voltage are used to carry information, whereas with power electronics, they carry power. Therefore the main metric of power electronics becomes the efficiency.
An inverter is a circuit which converts a DC power into an AC power at desired output voltage and frequency. The AC output voltage could be fixed or variable voltage and frequency. This conversion can be achieved either by controlled turn on and turnoff devices (e.g. BJT, MOSFET, IGBT, and MCT etc.) or by forced commutated thyristors, depending on application. The output voltage waveform of an ideal inverter should be sinusoidal. The voltage waveforms of practical inverter are however, non-sinusoidal and contain certain harmonics. Square wave or quasi-square wave voltage maybe acceptable for low and medium power application and for high power application low distorted, sinusoidal waveform are required. The output frequency of an inverter is determined by the rate at which the semiconductor devices are switched on and off by the inverter control circuitry and consequently, an adjustable frequency AC output is readily provided. The harmonics content of output voltage can be minimized or reduced significantly by switching technique of variable high speed power semiconductor devices.
The DC power input to the inverter maybe battery, fuel cell, solar cell or other DC source. But in most industrial applications, it is fed by a rectifier. This configuration of AC to DC converter and DC to AC inverter is called a DC link at network frequency is rectified and then filtered in the DC link before being inverter to AC at adjustable frequency. Rectification is achieved by standard diode or thyristors converter circuits and inversion is achieved by the circuit techniques.
The power circuit of Single Phase Unipolar inverter consists of four bidirectional IGBT arranged in bridge form. The circuit diagram of the power circuit is shown in figure 1
Figure 1 Power circuit
The circuit diagram consists of four distinct IGBTs such that they are connected as the bridge circuit. The input to the circuit is the 220v DC supply from the rectifier unit. The IGBTs are triggered accordingly such that the AC output voltage is obtained at the output. The operation of the circuit is as follows.
First the IGBT S1 and S4 are turned on by triggering the gate of the IGBT. During this time the input supply is 220v DC and at the output the 220v is applied across the load. The current starts from the supply positive, S1, S2, load and to the negative of the supply. The conduction path for the first cycle of operation is shown in figure 2.
Figure 2: Current conduction when S1 and S4 is ON
During the next phase or the cycle the IGBT S2 and S3 are turned on by giving trigger pulse to the gate of the IGBTs. During this period the input voltage is applied at the output but in the negative direction. The current conduction starts from the supply, S2, S3, load and to the negative of the supply. The current conduction is showed in the figure 3.
Figure 3: Current conduction during when S2 and S3 is ON
As the two cycles continue the positive and the negative voltage is applied at the load and the current direction changes in the two cycles. As the current direction changes the alternative voltage is obtained at the load thus converting Dc voltage to AC voltage.
we respect your privacy.