Single Phase Half Wave Controlled Rectifierpdf

SINGLE PHASE HALF-WAVE CONTROLLED RECTIFIER USING MATLAB Abstract-In this report, an effort is made to design Single Phase (1- ) Half Wave Rectifier with (i)R Load, (ii)RL Load, (iii)RL Load with Free Wheeling Diode using MATLAB simulation. Using simulation we can get the graph of the parameters (Output voltage and output current, thyristor voltage and thyristor current, source voltage and source current).

INTRODUCTION Single phase (1- ) half-wave controlled rectifiers are extensively used in number of power electronic based converters. In its simplest form, phase control can be described by considering the half-wave thyristor circuit. In half wave Single phase controlled rectifier only one SCR is employed in the circuit. It included in between the AC source and the load. The performance of the controlled rectifier very much depends upon the type and parameters of the output (load) circuit. They are used to provide an intermediate unregulated dc voltage source which is further processed to obtain a regulated dc or ac output. They have, in general, been proved to be efficient and robust power stages. The single phase half wave controlled rectifier consists of following: 1. AC supply 2. Thyristor 3. Load

SINGLE PHASE HALF-WAVE RECTIFIER

Depending upon the load requirements Single phase (1- ) rectifiers are divided into: i. ii. iii.

R Load RL Load RL Load with Freewheeling Diode

With R Load In this have wave rectifier, resistance is used as load. It is assumed that the peak supply voltage never exceeds the forward and reverse blocking rating of the thyristor. SCR is assumed to be ideal.

Modes of Operation MODE-1   

  

During positive half cycle, anode is connected to the positive terminal of the supply and the cathode is connected to negative terminal of supply and the thyristor is forward biased. When the thyristor is fired at a firing angle (α), full supply voltage (neglecting the thyristor drop) is applied to the load. Hence the load is directly connected to the AC supply. With a zero reactance source and a purely resistive load, the current waveform after the thyristor is triggered, will be identical to the applied voltage wave, and of magnitude dependent on the amplitude of the voltage and value of load resistance R. By varying the firing angle α, the output voltage can be controlled. The angle at during which the thyristor conducts is called the conduction angle (β). β = π-α

MODE-2 

(From 0 to π)

(From π to 2π)

During negative half cycle, anode is connected to the negative terminal of the supply and the cathode is connected to positive terminal of supply and the thyristor is reverse biased.

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a) Average output Voltage

The average output voltage can be derive as:

Vo(avg) =

m

sin t d(t)

where Vm is the peak value of the AC input voltage.

Vo(avg) =

Vm [-cos t]

Vo(avg) =

[1+cosα]

b) Average Output current

Io(avg)= Vo(avg)/R Io(avg)= =

[1+cosα]/R

c) RMS Output Voltage

Vo(rms) = Vo(rms) =

]1/2

[

m2 sin2 t d(t)

[

+

] 1/2

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With RL Load In this have wave rectifier, inductance is used as load. The load is assumed to be highly inductive.

Modes of Operation MODE-1    

During positive half cycle, anode is connected to the positive terminal of the supply and the cathode is connected to negative terminal of supply and the thyristor is forward biased. When the thyristor is fired at a firing angle (α), the load current will increase in a finite-time through the inductive load. The supply voltage from this instant appears across the load.. Due to inductive load, the increase in current is gradual. Energy is stored in inductor during time t01 to t1. At t1, the supply voltage reverses, but the thyristor is kept conducting because current through the inductance cannot be reduced to zero.

MODE-2     

(From 0 to π)

(From π to 2 π)

During negative half cycle, anode is connected to the negative terminal of the supply and the cathode is connected to positive terminal of supply and the thyristor is reverse biased. Current continues to flow till the energy stored in the inductance is dissipated in the loadresistor and a part of the energy is fed-back to the source. Hence due to energy stored in the inductor, current continues to flow up to instant t 11. At instant t11, the load-current is zero and due to negative supply voltage, thyristor turns-off. At instant t02, when again pulse is applied, the above cycle repeats. Hence the effect of inductive load is increased in the conduction period of SCR.

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a) Average output voltage

Vo(avg) =

m

sin t d(t)

where Vm is the peak value of the AC input voltage.

Vo(avg) =

[

Vo(avg) =

Vm ([-cos t] + [-cos t]

Vo(avg) =

m

sin t d(t)+

sin t d(t)+

m

m

sin t d(t)]

{ =β-π}

)

[cosα-cosβ]

b) Average Output current

Io(avg)= Vo(avg)/R Io(avg)= =

[cosα- cosβ]/R

c) RMS Output Voltage

Vo(rms) = Vo(rms) = t d(t)]

]1/2

[

m2 sin2 t d(t)

[

2 m

[

+

sin2 t d(t)+

2 m

sin2 t d(t)+

2 m

sin2

1/2

Vo(rms) =

] 1/2

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With RL Load using Freewheeling Diode In this have wave rectifier, freewheeling diode is connected in parallel with the load. This diode is described as a commutating diode, flywheel diode or by-pass diode .This diode is commonly described as a commutating diode as its function is to commutate or transfer load current away from the rectifier whenever the load-voltage goes into a reverse-state. This diode serves two main functions: i) ii)

It prevents reversal of load voltage except for small diode voltage-drop. It transfers the load current away from the main rectifier, thereby allowing all of its thyristors to regain their blocking state.

Operation  

    

With diode Df , thyristor will not be able to conduct beyond 180° Induced voltage in inductance will change its polarity as di/dt changes its sign and diode Df will start conducting as soon as the induced voltage is of sufficient magnitude, therby enabling the inductance to discharge its stored energy into the resistance. Here after 180°, the load current will freewheel through the diode and a reverse-voltage will appear across the thyristor. The power floe from the input takes place only when the thyristor is conducting. If there is no freewheeling diode, during the –ve portion of supply voltage, thyristor returns the enegy stored in the load inductance to the supply line. With diode Df the freewheeling action takes place and no power will be returned to the source. Hence the freewheeling diode improves the input power factor.

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CONCLUSION The proposed MATLAB/SIMULINK model for the Single Phase Half Wave controlled rectifier is able to simulate the phase thyristor rectifier, making it possible to study the voltage and current parameters across the source, thyristor, load and the freewheeling diode, at different load such as R load, RL load and RL load with Freewheeling diode.

RESULTS The following graphs are the results of the SIMULINK model for the Single Phase Half Wave controlled rectifier.

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REFRENCES 1. Analysis of Parallel Bridge Rectifier System, Conference Record of 1973 IEEE, AuthiorR.Ramakumar, July 1973 2. Analysis and Perform of Hybrid Thyristor Controlled Single Phase Resistive Loads, Conference Record Of 1989 IEEE, Author-Smiai, M.S. Haque, S.E. Malik, N.H. Shepherd, 1989 3. Analysis of Inductance Estimation for Half-Controlled Thyristor Converters, IEEE, AuthorPalanichamy, S. Subbiah, V. 4. Characteristics of Single and Three Phase Power Rectifiers with Active and Passive Loads, Electricals and Electronics Engineers Israel IEEE, 2012. 5. NEPTEL Phsae-2 Power electronics 6. Power Electronics by MD Singh and KB Khanchandani 7. Power Electronics by PS Bimbhra. 8. Power Electronics Converters applications and design by Ned Mohan. 9. Thyristorised Power Controllers by G.K Dubey, New Age, International Publishers, 2005.

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Single Phase Half Wave Controlled Rectifierpdf

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