Explain the principle of different types of power electronic circuits

Introduction:

In this script, we will confer on Power Electronics, In this blog, we will discuss types of power electronic circuits.

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Types of power electronic circuits:

The static power converters perform these functions of power conversions. A converter may be considered as a switching matrix, in which one or more switches are turned on and connected to the supply source in order to obtain the desired voltage or current. 

The power electronics circuits can be classified into six types:

1. Diode Rectifiers
2. AC-DC Converters (Controlled Rectifiers)
3. AC-AC Converters (AC Voltage Controllers)
4. DC-DC Converters (DC Choppers)
5. DC-AC Converters (Inverters)
6. Static Switches        

1. Diode Rectifier

Rectifier circuit converters ac input voltage into a fixed dc voltage. These are uncontrolled rectifiers. Used in battery charging, electroplating, and power supply.

A diode conducts when its anode voltage is higher than the cathode voltage, and it offers a very small voltage drop, ideally zero voltage, but typically 0.7V, A diode behaves as an open circuit when its cathode voltage is higher than the anode voltage, and it offers Ωvery high resistance, ideally infinite resistance, but typically 10kΩ. The output voltage is a pulsating dc, but it is distorted and contains harmonics. The average value of the output voltage can be controlled by varying the conduction time of thyristors and calculated from vo(AVC)= 2Vm/ℿ

2. AC-DC Converters (Controlled Rectifiers)

 A diode rectifier circuit converts fixed ac voltage to a variable dc output voltage. These are controlled rectifiers. Used in DC drives, and chemical industries.

A single-phase converter with two natural commutated thyristors is shown. The average value of the output voltage can be controlled by varying the conduction time of thyristors. These converters are also known as controlled rectifiers

 

3. AC-AC Converters (AC Voltage Controllers)

These converters convert fixed ac voltage directly to a variable ac voltage at the same frequency using line commutation.

• Used to obtain variable AC output voltage from a fixed AC source
• a single-phase converter with a TRIAC is shown below.

Working Principle:

A TRIAC allows a current flow in both directions. It can be turned on by applying gate voltages at  wt= ⍺ for a current flow in the positive direction, and also at wt = π + ⍺  for a current flow in the negative direction. The output voltage is controlled by varying the conduction time of a TRIAC or firing delay angle ⍺ .

4. DC-DC Converters (DC Choppers)

A chopper converts fixed dc input voltage to a variable dc output voltage. Used in DC Drives, and battery vehicles.

It is called a Chopper or Switching Regulator. The average output voltage is controlled by varying the conduction of the transistor, t1$t_1$. If T$T$ is the chopping period, then t1=δT$t_1=\delta \mathrm{T. }$$\delta$ is called the duty cycle of the chopper.

5. Inverters (DC to AC converters) 

An inverter converts a fixed dc voltage to a voltage of variable frequency and of fixed or variable magnitude.

• A dc-ac converter is also known as an Inverter. 
• When Q1 and Q2 are turned on by applying gate, voltage, the dc supply voltage Vs appears across the load and the instantaneous output voltage is vo = + Vs.
• Similarly, When Q3 and Q4 are turned on by applying gate, voltage, the dc supply voltage Vs appears across the load in the opposite direction and the instantaneous output voltage is vo = - Vs
• If transistor 
  Q1
  $Q_1$ and Q2
  $Q_2$ conduct for the one-half period and Q3
  $Q_3$ and Q4
  $Q_4$ conduct the other half, the output voltage is of alternating form.
• V0(rms) = Vs
• The output voltage contains harmonics that could be filtered out before supplying to the load.

5. Static Switches 

These circuits convert input power at one frequency to output power at a different frequency. Used in lighting control, and speed control of fans. Power devices can be operated as static switches or contactors, the supply to these switches could be either AC or DC, and the switches are called AC static switches or DC switches.