For the power conditioning, the conversion of electric power from one form to another is necessary and the switching characteristics of the power devices permit these conversions. The static power converters perform these functions of power conversions. A converter may be considered as a switching matrix. The power electronics circuits can be classified into six types:
Diode Rectifiers
AC-DC Converters (Controlled Rectifiers)
AC-AC Converters (AC Voltage Controllers)
DC-DC Converters (DC Choppers)
DC-AC Converters (Inverters)
Static Switches
The devices in the above mentioned converters are used to illustrate the basic working principles only. The switching action of a converter can be performed by more than one device. The choice of a particular device depends on the voltage, current, and speed required.
A diode rectifier circuit converts ac voltage into a fixed dc voltage. The input voltage to the rectifier Vi could be any of the single phase and three phase. Increasing the number of phases also increases the number of diodes that will be used for the design of diode rectifier circuits.
From the diagram it can be observed that in every single half of the input sinusoidal voltage waveform (positive half or negative half of sinusoidal voltage waveform), the current through the load is maintaining the same direction that is the potential difference across the load is having same polarity for both the halves of the input sinusoidal voltage waveform. So that the voltage waveform of the output will repeat its profile in every intervals with respect to t axis.
The average output voltage,
Vo = 10Vm Sin (t) d(t)
= Vm -Cos+Cos0
= 2Vm
AC-DC Converters
The average value of the output voltage can be controlled by varying the conduction time, that is, the turn-ON time of thyristors or in other words by varying the firing angle .
Average output voltage,
Vo = 1Vm Sin (t) d(t)
= Vm -Cos+Cos
= Vm(1+Cos)
Therefore, in this AC-DC Converters Vo become a function of firing angle . So, by varying , the control over output (average output voltage control) can be achieved.
AC-AC Converters
These converters are used to obtain a variable ac output voltage Vo from a fixed AC source and a single-phase converter with a TRIAC is shown in figure. The output voltage is controlled by varying the conduction time of a TRIAC or firing delay angle, . These types of converters are also known as AC Voltage Controllers.
DC-DC Converters
DC-AC Converters
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