Project 1

QUESTION-1

The three-phase diode rectifier is supplying approximately 2.2 kW load with VLL=208V at 60 Hz, Ls=1 mH and Cd=1100 μF, where Cd is the DC side capacitor. Design the circuit in one of the simulation platforms (MATLAB or Ltspice/Simetrix) and obtain the circuit waveforms. Based on their simulation studies find out the following:

Circuit diagram;-

In 3-phase power rectifiers, conduction always occurs in the most positive diode and the corresponding most negative diode. Thus as the three phases rotate across the rectifier terminals, conduction is passed from diode to diode.

Then each diode conducts for 120^o (one-third) in each supply cycle but as it takes two diodes to conduct in pairs, each pair of diodes will conduct for only 60^o (one-sixth) of a cycle at any one time as shown above.

Therefore we can correctly say that for a 3-phase rectifier being fed by “3” transformer secondaries, each phase will be separated by 360^o/3 thus requiring 2*3 diodes.

Note also that unlike the previous half-wave rectifier, there is no common connection between the rectifiers input and output terminals. Therefore it can be fed by a star connected or a delta connected transformer supply.

Calculations:-

Simulink model:-

Simulink model:-

3 phase ac source

load

Capacitor

Ls

Results:-

input voltage and current

output voltage and current

current

diode voltages

vd1,vd2,vd3

vd4,vd5,vd6

next we need to move on FFT ANALYSIS

FFT ANALYSIS

Input voltage

here

THD=0.03%

and fundamental 60hz=415.8

list for 60 hz

for 60hz it is 30 degree

output

input 1

it is 30 deg

input 2

here

THD =0.04%

list

for 60 hz

it is -90 degree

input 3

it showing 150 degree

showing THD=0.01%

fundamental=60hz

QUESTION-2

Circuit diagram:-

waveform

For a 3 - phase full wave controlled rectifier shown in Fig. 1, the output voltage is alwaysdifference between two phase voltages. At any instant of time two thyristors of differentlegs conduct. Let us consider the instant at which T1 and T6 conduct. Solving KVL, the output voltage Vout is equal to the difference between Va and Vb. Similarly this appliesfor every other combination of conduction of thyristors. The output waveform forcontinuous conduction is shown in Fig

Simulink model:-

Calculation:-

Ac source

R,L,Vdc

R,L,Vdc

Ls

Results:-

input voltage and current

output voltage and current

Thyristor voltages

t1,t2,t3

t4,t5,t6

FFT analysis

input analysis

input1

here ,

fundamental 60hz=22.84

and THD=169.80

LIST

LIST

60HZ= -69.5 DEGREE

INPUT2

for 60hz

232.0 degree

fundamental 60hz=10.7

and THD =45.63