The power in a single-phase system is shown in figure. In the figure current (I) lags voltage (V ) by an angle ?. The current has two components – the energy component and the watt less component. Only the energy component has a power value. Hence, the power in a single-phase circuit is given by the following equation:
V×I×cos?
Where
P = power (watts)
V = voltage (rms)
I = current (rms)
cos? = power factor.
A power diode is a semiconductor power on/off switch that allows flow of current in one direction, depending upon its connection. It is a two-terminal semiconductor device.
The two terminals of a diode are called the anode (A) and the cathode (K). These names are derived from the days when valves were commonly used.
Construction-wise, it has a single P–N junction. It consists of a two-layer silicon wafer attached to a substantial copper base. The base acts as a heat sink, a support for the enclosure and one of the electrical terminals of the diode. The other surface of the wafer is connected to the other electrical terminal. The enclosure seals the silicon wafer from the atmosphere and provides adequate insulation between the two terminals of the diode.
Power electronic components are semiconductor devices, such as diodes, thyristors, transistors, etc. that are used in the power circuit of a converter. In power electronics, they are used in the non-linear switching mode (on/off mode) and not as linear amplifiers. In other words, these devices behave like an electronic switch.
An electronic switch electronically connects or disconnects an AC or DC circuit and can usually be switched ON and/or OFF. Conduction is usually permitted in one direction only.
The following components are devices that are commonly used as electronic switches in power electronic converters.
• Power diodes
• Power thyristors
• GTO
• MOS-controlled thyristors (MCT)
• Power bipolar junction transistors (BJT)
• Field effect transistors (FET, MOSFET)
• Insulated gate bipolar transistor (IGBT)
• Resistors (provide resistance)
• Reactors or chokes (provide inductance)
• Capacitors (provide capacitance).
