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Three-Phase Semi Converter Simulation

The document describes a simulation of a three-phase semi converter. It discusses: 1. The circuit consists of three thyristors and three diodes, with one thyristor and diode conducting at a time in continuous mode. 2. The output voltage is controlled by varying the firing angles of the thyristors. Each diode conducts for 120 degrees starting from phase intersections. 3. Formulas are given for average and RMS output voltages based on the firing angle. 4. The simulation was done in MATLAB for resistive, inductive and RL loads, and observed the converter operates as 6-pulse for firing angles <60 degrees and 3-pulse for >60 degrees.

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Raj Kamal
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56 views15 pages

Three-Phase Semi Converter Simulation

The document describes a simulation of a three-phase semi converter. It discusses: 1. The circuit consists of three thyristors and three diodes, with one thyristor and diode conducting at a time in continuous mode. 2. The output voltage is controlled by varying the firing angles of the thyristors. Each diode conducts for 120 degrees starting from phase intersections. 3. Formulas are given for average and RMS output voltages based on the firing angle. 4. The simulation was done in MATLAB for resistive, inductive and RL loads, and observed the converter operates as 6-pulse for firing angles <60 degrees and 3-pulse for >60 degrees.

Uploaded by

Raj Kamal
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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NAME OF THE EXPERIMENT:

AIM: Simulation of a Three Phase Semi converter.

THEORY:
A three-phase semi converter consists of three thyristors T1, T2, T3 and three diodes D1, D2
and D3. In the continuous conduction mode only one thyristor and only one diode conduct at a time.
A Freewheeling Diode is connected in parallel across the RLE load. Three phase balanced supply is
given to phase A B C. The output voltage across the load is varied by controlling the firing angles of
thyristors T1 T2 T3. The diodes D1, D2 and D3 each conduct for 120 o starting from the instants
corresponding to the intersection of phase A-C, B-A, C-B. The instant the thyristor is fired with
firing angle 𝛼 < 60o, phase AB has the highest value compared to the other phases and hence T1 and
D2 conduct. After phase AB, AC has the highest value hence the conduction of diode D2 is
transferred to D3. But at 𝛼> 60o the output voltage becomes zero due to the freewheeling action of
the FD.
Formulae:
𝑉𝑚
i. Average output Voltage (V0 ) for 𝛼 <60o = 3 2π (1 + cos 𝛼)
𝑉𝑚
ii. Average output Voltage (V0 ) for 𝛼 >60o = 3 (1 + cos 𝛼)
2π
𝑉𝑚 1
iii. RMS Voltage (Vrms)= 3√𝜋 [(𝜋 − 𝛼) + 2 sin 2𝛼]

Circuit Diagram:
i. VS =326Vrms, 50 Hz
ii. R=25Ω, L=30mH, E=100V DC.
iii. Firing Angle =30O ,60O, 90O

Testing phase: compilation of code (error detection)


Fixing Angle = 30 (R LOAD)

Fixing Angle = 60
Fixing Angle = 90
RL LOAD
Fixing Angle = 30

Fixing Angle = 60

Output Current (oc)


Fixing Angle = 90
RLC LOAD
Fixing Angle = 30

Fixing Angle = 60
Fixing Angle = 90

s
CONCLUSION
The simulation of a three-phase semi converter was done using MATLAB and was observed that the
semi converter operates as a 6-pulse converter for α<60o and for α>60o it operates as a 3 pulse converter. Also
the freewheeling action takes place only for α>60o. Each periodic cycle of output voltage has a periodicity of
120o.
APPLICATIONS
Three phase fully controlled converters are very popular in many industrial applications particularly in
situations where power regeneration from the dc side is essential and can handle reasonably high power.
DISCUSSION
1. What is the conduction period of a thyristor and a diode in the three-phase semi converter?
Ans: The conduction period is 2π/3.
2. What is the periodicity of the output voltage waveform of a three-phase semi converter?
Ans: The output voltage waveform of a three-phase half-controlled converter is periodic over 1/3 of the input
voltage cycle.
How the applied and action learning encourages critical thinking problem solving,
idea generation and skill development etc.?

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