split supply single phase uncontrolled full wave rectifier (ass pe)

3
Split supply single phase uncontrolled full wave rectifier. Fig 9.6 shows the circuit diagram and waveforms of a single phase split supply, uncontrolled full wave rectifier supplying an R L load. The split power supply can be thought of to have been obtained from the secondary of a center tapped ideal transformer (i.e. no internal impedance). When the switch is closed at the positive going zero crossing of v 1 the diode D1 is forward biased and the load is connected to v1. The currents i0 and ii1 start rising through D1. When v1 reaches its negative going zero crossing both i0 and ii1 are positive which keeps D1 in conduction. Therefore, the voltage across D2 is VCB = v2 - v1. Beyond the negative going zero crossing of vi ,D2 becomes forward biased and the current i 0 commutates to D2 from D1. The load voltage v0 becomes equal to v2 and D1 starts blocking the voltage VAB = v1 v 2. The current i0 however continues to increase through D2 till it

Upload: miz-aelyfha

Post on 31-Mar-2015

370 views

Category:

Documents


4 download

TRANSCRIPT

Page 1: Split supply single phase uncontrolled full wave rectifier (ass PE)

Split supply single phase uncontrolled full wave rectifier.

Fig 9.6 shows the circuit diagram and waveforms of a single phase split supply, uncontrolled full wave rectifier supplying an R – L load. The split power supply can be thought of to have been obtained from the secondary of a center tapped ideal transformer (i.e. no internal impedance).

When the switch is closed at the positive going zero crossing of v1 the diode D1 is forward biased and the load is connected to v1. The currents i0 and ii1 start rising through D1. When v1

reaches its negative going zero crossing both i0 and ii1 are positive which keeps D1 in conduction. Therefore, the voltage across D2 is VCB = v2 - v1. Beyond the negative going zero crossing of vi ,D2

becomes forward biased and the current i0 commutates to D2 from D1. The load voltage v0

becomes equal to v2 and D1 starts blocking the voltage VAB = v1 – v2. The current i0 however

Page 2: Split supply single phase uncontrolled full wave rectifier (ass PE)

continues to increase through D2 till it reaches the steady state level after several cycles. Steady state waveforms of the variables are shown in Fig 9.6 (b) from ωt = 0 onwards. It should be noted that the current i0, once started, always remains positive. This mode of operation of the rectifier is called the “Continuous conduction mode” of operation. This should be compared with the i0 waveform of Fig 9.3 (b) for the half wave rectifier where i0 remains zero for some duration of the input supply waveform. This mode is called the “ discontinuous conduction mode” of operation.

From the above discussion

For 0≤ ω t<

v0 = v1

i0 = ii1……………………………………....(9.45)

for π≤ωt<2π v0 = v2

i0 = ii2……………………………………........(9.46)

Since v0 is periodic over an interval π

Both the form factor and the ripple factor shows considerable improvement over their half wave counter parts.

Conclusion of uncontrolled rectifier

• A rectifier is a power electronic converter which converts ac voltage or current sources to dc voltage and current.

Page 3: Split supply single phase uncontrolled full wave rectifier (ass PE)

• In a rectifier, electrical power flows from the ac input to the dc output.

• In many rectifier circuits, power can also flow from the dc side to the ac side, where upon, the rectifier is said to be operating in the “inverter mode”.

• Rectifiers can be classified based on the type of device they use, the converter circuit topology, number of phases and the control mechanism.

• All rectifiers produce unwanted harmonies both at the out put and the input. Performance of a rectifier is judged by the relative magnitudes of these harmonies with respect to the desired output.

• For a given input voltage and load, the output voltage (current) of an uncontrolled rectifier can not be varied. However, the output voltage may vary considerably with load.

• Single phase uncontrolled half wave rectifier with resistive or inductive load have low average output voltage, high from factor and poor ripple factor of the output voltage waveform.

• Single phase uncontrolled full wave rectifier have higher average output voltage and improved ripple factor compared to a half wave rectifier with resistive and inductive load.

• With highly inductive load the output voltage waveform of a full wave rectifier may be independent of the load parameters.

• With a capacitive load the output voltage form factor approaches unity with increasing capacitance value for both the half wave and the full wave rectifiers. However, THD of the input current also increases.

• A full wave bridge rectifier generates higher average dc voltage compared to a split supply full wave rectifier. However it also uses more number of diodes.

Reference

1. Module First Edition Power Electronics, UTHM publisher, 2008.2. www.onlinefreeebook-power electronic, July 13,20083. Power Electronic Circuit, Devices and Applications, Third Edition, Muhammad H. Rashid,

Prentice Hall, 2004.4. First Course On Power Electronics & Drives, Ned Mohan, MNPERE, 2003.5. Power Converter Circuit, Wiliam Shepherd & Li Zhang, CRCnetBASE, 2009.