# EE 423 POWER ELECTRONICS

```EE 423 POWER ELECTRONICS
EXPERIMENT #3
CONTROLLED RECTIFIERS
Rectifiers convert single phase or multiphase alternating current to direct current. To obtain
controlled output voltages, phase control thyristors are used instead of diodes. The output
voltage of thyristor rectifiers is varied by controlling the delay or firing angle of thyristors. A
phase-control thyristor is turned on by applying a short pulse to its gate and turned off due to
natural or line commutation; and in case of a highly inductive load, it is turned off by firing
another thyristor of the rectifier during the negative half-cycle of input voltage.
These phase-controlled rectifiers are simple and less expensive; and the efficiency of these
rectifiers is, in general, above 95%. Since these rectifiers convert from ac to dc, these
controlled rectifiers are also called ac-dc converters and are used extensively in industrial
applications, especially in variable-speed drives, ranging from fractional horsepower to
megawatt power level.
SINGLE PHASE CONTROLLED RECTIFIERS
PURPOSE
To analyze a single phase controlled rectifier with RL load.
EQUIPMENT
AC power supply (Function generator; max 10V, 100 mA),
Oscilloscope, board and other circuit elements (SCR, resistor,
capacitor, diode etc.)
PROCEDURE
Single Phase Half-Wave Controlled Rectifier
1- Set up the circuit shown in the figure (without FWD – Free wheeling diode)
2- By varying α between 0&lt; α &lt;180, Observe change in load current and voltage, and
relation with angle beta
3- For any value of α (α≠0) draw the waveforms of load current and voltage on the same
axes.
4- Indicate important points on your graphs.
5- Calculate average value of the load voltage you draw.
6- Repeat the items above with FWD connected.
Calculate the value of average DC load voltage which you draw as a function of α and record
BT169
CH1
L=200mH
1N4001
VS
CH2
220kΩ
10Ω
150nF
A
FWD
R=330Ω
1N4001
GND
Single phase half wave controlled rectifier circuit
VL
Vm
IL
α
π
2π
2π+ α
β
Waveforms for single phase half wave rectifier with RL load (FWD is not connected)
Single Phase Full-Wave Controlled Rectifier
Set up the following circuit and repeat the same procedure.
BT169
D1
VS
CH1
D3
L=200mH
1N4001
CH2
D2
D4
220kΩ
10Ω
150nF
1N4001
R=1.5kΩ
FWD
GND
D1,D2,D3,D4: 1N4001
```