A simple single phase step down cycloconverter with reduce numbers of Thyristors in P and N converter is described. A shunt capacitor connected with load is used to convert sinusoidal input at one frequency to non-sinusoidal output at another frequency.
Content
Section I: Introduction
Section II: Proposed diagram with reduce number of Thyristors
Section III: Theory
Section IV: Simulation in MATLAB Simulink:
Section V: Conclusion
Section VI: References
Section I: Introduction
Cycloconveters are the arrangement of power electronics which is used to convert Alternating Current (AC) at one frequency to AC at another frequency. The power circuit diagram of single phase bridge type cycloconverter is the basic circuit diagram to explain concept of cycloconverters. Fig. 1 shows the power circuit diagram [1] [2]. There are two, P and N, converters for carrying positive and negative half cycle output signals.
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Fig. 1 Power circuit diagram of single phase step down bridge type cycloconverter.
Section II: Proposed diagram with reduce number of Thyristors
Fig. 2 shows circuit diagram of modified circuit diagram of Fig. 1. In this circuit diagram there are two thyristor T1 and T2 for P converter and T3 and T4 for N converter. For the sake of clearness in operation, operating principle of modified diagram can be explained more specifically.
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Fig. 2 Proposed Diagram of Modified Cycloconverter with a Shunt Capacitor
A shunt capacitor is connected to resistive load (R). Suppose we want 220v(RMs) 50HZ(time period=20ms ) to 25HZ (time period=40ms ) cycloconverter. At first, T1 and T2 are ON at , which opens valve of T1 and T2 for the flow of the first half cycle of AC input. Upto capacitor is charged with maximum input voltage [illustration not visible in this excerpt] Now for 15ms (i.e remaining time period of first half of output waveform) capacitor discharges with suitable time for discharging (further clarification is done in Section III). After 20ms T3 and T4 are ON for negative half cycle of output. Same process of charging and discharging of capacitor takes place for negative cycle of output. Fig. 3 shows output waveform for this specified case.
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Fig. 3 Output of 50Hz to 25Hz Cycloconverter
Section III: Theory
A shunt capacitor is connected with R-load. In first half cycle of output, when Thyristors T1 and T2 are ON at 0ms, capacitor is charged upto time period [illustration not visible in this excerpt] . Now, we choose value of capacitor such that it discharges thorough load resistor for [illustration not visible in this excerpt] , until voltage across capacitor (Vc) becomes [illustration not visible in this excerpt] just before zero crossing of first half cycle of output voltage. We can also select a capacitor based on the value of Vc when it becomes say [illustration not visible in this excerpt](i.e.Vc at TD, discharging time constant of capacitor) at zero crossing of output voltage.
The voltage across capacitor when it discharges is given by [3]:
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We know capacitor discharging time, [illustration not visible in this excerpt]
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After mathematical reduction we get as,
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During negative half cycle when Thyristors T3 and T4 are ON at [illustration not visible in this excerpt], the charging and discharging of capacitor continues but with reversal appearance than that of positive half cycle. In this way desired frequency of output voltage with non-sinusoidal waveform is obtained.
Specified Case:
Let us take an instance that input frequency to be 50HZ for rms input voltage of 220V where maximum input voltage [illustration not visible in this excerpt]and resistive load is[illustration not visible in this excerpt]. A cycloconverter with output frequency, [illustration not visible in this excerpt], etc. can be obtain by choosing a suitable capacitor connected in shunt with the resistive load.
1. For [illustration not visible in this excerpt] is charged upto with maximum voltage[illustration not visible in this excerpt] Now we have to select a capacitor that discharges upto [illustration not visible in this excerpt]. Let, output voltage value just before zero crossing of first half cycle of output waveform (i.e. at [illustration not visible in this excerpt]) be [illustration not visible in this excerpt], which is output voltage at discharging time of capacitor, TD. Now, value of capacitor can be calculated as
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Simulation, with above input parameters, is done in Simulink Environment of MATLAB and output voltage waveform is shown in Fig. 4.[illustration not visible in this excerpt]
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Fig. 5 Block Diagram of Modified Single Phase Cycloconverter
Similarly, if just before zero crossing of output voltage we want output voltage across capacitor to be then for different values of , values of capacitor are calculated by using equation(1) and shown in Table I.
Table: I
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For several values of, simulation result shows various output voltage waveform:[illustration not visible in this excerpt]
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2. For [illustration not visible in this excerpt] to[illustration not visible in this excerpt], [illustration not visible in this excerpt]and[illustration not visible in this excerpt]. In this case capacitor charges upto [illustration not visible in this excerpt]and discharge for[illustration not visible in this excerpt]. Setting all parameter same, different values of capacitance of shunt capacitor can be calculated for different values of[illustration not visible in this excerpt] as shown in Table II.
Table II
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Section IV: Simulation in MATLAB Simulink:
Fig. 5 shows simulation block diagram made in MATLAB.
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Fig. 5 Block Diagram of Modified Single Phase Cycloconverter
The block diagram Modified Single Phase Cycloconverter in figure is a subsystem created using P and N converter which is shown in Fig. 6
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Fig. 6 P and N conveter of Modified Single Phase Cycloconverter
Simulation file for 50Hz to 25Hz, x=60 and C=0.0294, can be downloaded from link below:
https://drive.google.com/open?id=0By-me65CUlVyVkgydFJRaHJ2VlE
Various parameter like input voltage, value of capacitor C and gate pulses for thyristors can be changed to get the desired output frequency.
Section V: Conclusion
By reducing a number of thyristor in both P and N converters and choosing a suitable shunt capacitor at load terminal, a modified step down cycloconveter converts sinusoidal input at one frequency(Fm) to non-sinusoidal output another frequency (Fo), with [illustration not visible in this excerpt]=2,4,6
Section VI: References
[...]
[1] Rashid, Muhammad H. Power Electronics Handbook. San Diego: Academic, 2001. Print.
[2]Pelly, B. R. Thyristor Phase-controlled Converters and Cycloconverters: Operation, Control, and Performance. New York: Wiley-Interscience, 1971. Print
Frequently asked questions
What is the purpose of this document?
This document provides a comprehensive language preview, including the title, table of contents, objectives, key themes, chapter summaries, and key words related to a modified single-phase cycloconverter.
What is a cycloconverter?
Cycloconverters are power electronic arrangements used to convert alternating current (AC) at one frequency to AC at another frequency.
What is the basic circuit diagram for a cycloconverter?
The single-phase bridge-type cycloconverter is the basic circuit diagram used to explain the concept. It includes two converters, P and N, for carrying positive and negative half-cycle output signals.
What is the proposed modification to the cycloconverter circuit?
The proposed diagram reduces the number of thyristors and includes a shunt capacitor connected to a resistive load.
How does the modified cycloconverter circuit work?
Thyristors T1 and T2 are used for the P converter, and T3 and T4 are used for the N converter. During operation, the shunt capacitor charges and discharges during each half-cycle of the output waveform. The timing of the thyristor firing controls the output frequency.
What is the role of the shunt capacitor?
The shunt capacitor charges during a portion of each half-cycle and then discharges through the load resistor. The capacitor value determines the shape and frequency of the output waveform.
How is the value of the capacitor selected?
The capacitor value is chosen based on the desired discharge time and the voltage across the capacitor at specific points in the output cycle, like just before the zero-crossing. Equations are provided to calculate the appropriate capacitance value.
What is the relationship between the input and output frequencies in the modified cycloconverter?
The document suggests that the output frequency can be a fraction of the input frequency, specifically Fo=Fm/x, with x=2,4,6
What simulation software was used?
MATLAB Simulink was used to simulate the modified single-phase cycloconverter.
Where can I download the simulation file?
A simulation file for a 50Hz to 25Hz cycloconverter is available at https://drive.google.com/open?id=0By-me65CUlVyVkgydFJRaHJ2VlE
What is the conclusion of the study?
By reducing the number of thyristors and utilizing a suitable shunt capacitor, a modified step-down cycloconverter can convert sinusoidal input at one frequency to non-sinusoidal output at a lower frequency.
What are the references used in this document?
The document references the following resources: Power Electronics Handbook by Muhammad H. Rashid, Thyristor Phase-controlled Converters and Cycloconverters: Operation, Control, and Performance by B. R. Pelly, and a web article on Charging and Discharging a Capacitor.
- Quote paper
- Madhusudhan Pandey (Author), 2016, Single phase sinusoidal input to non-sinusoidal output Cycloconverter, Munich, GRIN Verlag, https://www.grin.com/document/351072
