Single Phase Semi Controlled Converter R-L Load (Asymmetrical and Symmetrical)

Introduction to the Experiment

This experiment is aimed to study the operation of single phase semi-controlled (Asymmetrical and Symmetrical) converter using R-L load by observing the output waveforms. The circuit is implemented in simulation as well as hardware and the performance is studied.

Learning Outcomes:

• Understand the circuit diagram and working of symmetrical and asymmetrical semi-controlled converters.
• Simulate and analyze the converters with RL load using MATLAB Simulink.
• Implement the converters in hardware and observe the output waveforms.

Circuit Diagram:

Theory

In the period $0 < t \leq \frac{\pi}{\omega}$; the SCRs $T1$ and Diode $D1$ are forward biased and the SCR $T2$ and Diode $D2$ are reverse biased. Then current through the load and voltage drop across the load are zero. Let the SCR $T1$ be triggered at an angle of $\alpha$ $(0<\alpha<\frac{\pi}{\omega})$. As the Diode $D1$ is already conducting, the supply terminals are connected to the load through the SCR and Diode, and the current starts flowing through the load via SCR $T1$ and Diode $D1$. Therefore, the supply voltage appears across the load, the voltage drop across the SCR and the Diode is zero when they are conducting (SCR, Diode are assumed ideal).

Soon after $\frac{\pi}{\omega}$ load voltage tends to reverse, Free-wheeling Diode (FWD) gets forward biased and starts conducting. The load, or output current, is transferred from $T1, D1$ to FWD. As SCR $T1$ is reverse biased at $t = \frac{\pi}{\omega} +$ current flows through FWD and $T1$ is turned off. The load terminals are short-circuited through FWD, therefore load voltage is zero during $\left[\frac{\pi}{\omega} < t < \frac{\pi + \alpha}{\omega}\right]$. During the period $\left[\frac{\pi}{\omega} < t < \frac{2\pi}{\omega}\right]$; $T2$ and Diode $D2$ are forward biased. When $T2$ is triggered at an angle of $\frac{\pi + \alpha}{\omega}$, $\left[0 < \frac{\pi + \alpha}{\omega} < 2\pi/\omega\right]$, then the FWD is reverse biased and is turned off. During this period, supply terminals are connected to the load through the SCR and the Diode $D2$, the load current shifts from FWD to $T2$ and $D2$. Therefore, the supply voltage appears across the load. The voltage drop across the SCR and Diode is zero when they are conducting (SCR, Diode are assumed ideal). SCR $T2$ and Diode $D2$ continue to conduct up to $2\pi/\omega$. For the next half cycle, the load current is transferred from $T2$ and $D2$ to the FWD and SCR $T1$ and Diode $D1$ are forward biased. If we give triggering, SCR starts conducting and this cycle repeats.

Simulation of Single Phase Symmetrical Semi-Controlled Converter with RL Load

Aim

To simulate single phase symmetrical semi-controlled converter with RL load in MATLAB Simulink.

Implement the 1-phase Symmetrical semi-controlled converter with RL load of $R = 12.5 \Omega$ and $L = 6\text{mH}$ and observe the changes in the output voltage waveform at different firing angles. (Input voltage: $50V$ Peak = $35.35V$ RMS and $50Hz$).

Simulation of Single Phase Asymmetrical Semi-Controlled Converter with RL Load

Aim

To simulate single phase asymmetrical semi-controlled converter with RL load in MATLAB Simulink.

Implement the 1-phase Asymmetrical semi-controlled converter with RL load of $R = 12.5 \Omega$ and $L = 6\text{mH}$ and observe the changes in the output voltage waveform at different firing angles. (Input voltage: $50V$ Peak = $35.35V$ RMS and $50Hz$).

Hardware Implementation of Single Phase Symmetrical Semi-Controlled Converter with RL Load

Procedure

1. Connect the circuit as shown in the figure (with RL load $R = 12.5 \Omega$, $L = 6\text{mH}$).
2. Switch ON the MCB of 3Ø supply on the left-hand side of your Experimental Table.
3. Switch ON the MCB on the POWER MODULE kit.
4. Switch ON the MCB on the SCR-Diode Power module and slowly increase the voltage to reach up to $35.35V$ RMS using + symbol Push Button in the Power Module kit.
5. Switch on the driver power switch.
6. Connect CRO probes across the RL load to measure the output voltage.
7. Vary the firing angle as mentioned and note down the results.
8. Observe the Output voltage waveforms in the DSO.

Hardware Implementation of Single Phase Asymmetrical Semi-Controlled Converter with RL Load

Procedure

1. Connect the circuit as shown in the figure (with RL load $R = 12.5 \Omega$, $L = 6\text{mH}$).
2. Switch ON the MCB of 3Ø supply on the left-hand side of your Experimental Table.
3. Switch ON the MCB on the POWER MODULE kit.
4. Switch ON the MCB on the SCR-Diode Power module and slowly increase the voltage to reach up to $35.35V$ RMS using + symbol Push Button in the Power Module kit.
5. Switch on the driver power switch.
6. Connect CRO probes across the RL load to measure the output voltage.
7. Vary the firing angle as mentioned in the “Exp6_Part B.doc” file.
8. Observe the Output voltage waveforms in the DSO.

Results

I) Symmetrical Semi-converter with RL load

1. Attach the circuit diagram of Single phase Symmetrical Semi-converter with RL load in MATLAB Simulink.
2. Attach the waveforms of:
   • Input voltage
   • Input Current
   • Output Voltage
   • Output Current in Simulink (at firing angle 45°)
3. Attach the waveforms of:
   • Thyristor Voltage
   • Thyristor current
   • Diode Voltage
   • Diode current in Simulink (at firing angle 45°)
4. Attach the waveforms of Output Voltage (at firing angle 45°) (experimentally from the DSO).
5. Calculate Performance parameters with RL-Load (in Simulink).

S. no	Firing angle (measured in time) msec	Firing angle (measured in time converted into angle) degrees	Average Output voltage	RMS Output Voltage	Average Diode current	Average Thyristor current
1.	0 msec	0°
2.	2.5 msec	(2.5/10*180) = 45°
3.	5 msec	90°
4.	6.66 msec	120°



6. Calculate Performance parameters for RL-Load (Experimentally).

S. no	Firing angle (measured in time) msec	Firing angle (measured in time converted into angle) degrees	Average Output voltage	RMS Output Voltage
1.	0 msec	0°
2.	2.5 msec	(2.5/10*180) = 45°
3.	5 msec	90°
4.	6.66 msec	120°

II) Asymmetrical Semi-converter with RL load

1. Attach the circuit diagram of Single phase Asymmetrical Semi-converter with RL load in MATLAB Simulink.
2. Attach the waveforms of:
   • Input voltage
   • Input Current
   • Output Voltage
   • Output Current in Simulink (at firing angle 45°)
3. Attach the waveforms of:
   • Thyristor Voltage
   • Thyristor current
   • Diode Voltage
   • Diode current in Simulink (at firing angle 45°)
4. Attach the waveforms of Output Voltage (at firing angle 45°) (experimentally from the DSO).
5. Calculate Performance parameters with RL-Load (in Simulink).

S. no	Firing angle (measured in time) msec	Firing angle (measured in time converted into angle) degrees	Average Output voltage	RMS Output Voltage	Average Diode current	Average Thyristor current
1.	0 msec	0°
2.	2.5 msec	(2.5/10*180) = 45°
3.	5 msec	90°
4.	6.66 msec	120°



6. Calculate Performance parameters for RL-Load (Experimentally).

S. no	Firing angle (measured in time) msec	Firing angle (measured in time converted into angle) degrees	Average Output voltage	RMS Output Voltage
1.	0 msec	0°
2.	2.5 msec	(2.5/10*180) = 45°
3.	5 msec	90°
4.	6.66 msec	120°