Dr. Unnikrishnan P.C. Professor, EEE EE305 Power Electronics Dr. Unnikrishnan P.C. Professor, EEE

Single Phase Half Controlled Bridge Rectifier with R-Load

Single Phase Half Controlled Bridge Rectifier with RL-Load This converter has a better power factor due to the freewheeling operation and is used for applications up to 15KW.

Voltage & Current Equations The average value of output voltage Therefore, Changing the firing angle from 0 to π, the output voltage varies from to 0. The rms value of output voltage

Single Phase Half Controlled Bridge Rectifier with RLE-Load For any load current to flow one device from the top group (T1 or T3) and one device from the bottom group must conduct. T1 T3 or D2 D4 cannot conduct simultaneously T1 D4 and T3 D2 conducts simultaneously whenever T1 or T3 are ON and the output voltage tends to go negative.  there are four operating modes of this converter when current flows through the load. Of course it is always possible that none of the four devices conduct. The load current during such periods will be zero.

Single Phase Half Controlled Bridge Rectifier with RLE-Load When T1 is fired in the positive half cycle of the input voltage, load current flows through T1 and D2. At the negative going zero crossing of the input voltage, load current is still positive it commutates from D2 to D4 and the load voltage becomes zero. If the load current further continuous till T3 is fired current commutates from T1 to T3. This mode of conduction when the load current always remains above zero is called the continuous conduction mode.

Single Phase Half Controlled Bridge Rectifier with RLE-Load

Single Phase Half Controlled Bridge Rectifier with RLE-Load

Variation of VDC as a function of firing angle 

Voltage & Current Equations The average value of output voltage Therefore, Changing the firing angle from 0 to π, the output voltage varies from to 0. The rms value of output voltage

Displacement Factor DPF If vi and ii are the input voltage and input current per phase of a rectifier respectively, then the Displacement Factor of a rectifier is defined as: DPF = cosφi where φi is the phase angle between the fundamental components of vi and ii. (Displacement Angle) or DPF = cosφ1

Distortion Factor Dff Let “f” be the instantaneous value of any voltage or current associated with a rectifier. Distortion factor by definition is Where F1 is the first harmonic component of f

Total Harmonic Distortion THD The amount of distortion in the waveform of f is quantified by means of the index Total Harmonic Distortion (THD). By definition

Power factor of a rectifier (PF) if the per phase input voltage and current of a rectifier are vi and ii respectively then If the rectifier is supplied from an ideal sinusoidal voltage source then

The Displacement Factor = cos(/2) Distortion Factor: Power Factor = DF x DPF

Single Phase Half Controlled Bridge Rectifier with RLE-Load DCM In DCM, two possibilities exist. In the first case the load current becomes zero before ωt = π. In the second case io continuous beyond ωt = π but becomes zero before ωt = π + α. In both cases however, io starts from zero at ωt = α