Power Electronics

Power ElectronicsPhase Control Rectifier

Kumar goswami M.TECH(Power electronics) B.E.(electrical engg.) Rcet bhilaiPrinciple of Phase ControlSingle phase Half wave Control with R load

Waveforms

Performance ParametersAverage O/P Voltage

The maximum value of output voltage occurs at = 0 ,Vom = (Vm/2).2 = Vm/Continued.Average Load Current ,

RMS value of load voltage (For electric heating and incandescent lamps)

Continued.Power delivered to Resistive Load = (RMS load voltage x RMS load current) Input Volt Amperes = (rms source voltage x total rms line current) = Vs . IorInput power factor = Power delivered to load/Input VA = (Vor.Ior)/(Vs.Ior) = (Vor/Vs)Input displacement factor (DF) or fundamental power factor = cos (angle between supply voltage and current)Input current distortion factor (CDF) Ratio of rms value of fundamental component Is1 of the input current to rms value of input = Is1/Is

Continued.Rectification ratio : ratio of DC output power to AC output power

Also known as rectification efficiency or figure of merit . In case forward resistance Rd then

Continued.Form Factor (FF) Ratio of rms value Vor of output voltage to the dc value of Vo

FF is a measure of shape of output voltage.Close to unity, better dc output voltage waveform

Continued.Voltage Ripple Factor (VRF) : Ratio of ripple voltage to the average output voltage.

Effective or, Ripple value of the ac component of output voltage is given by

Continued.Transformer Utilization Factor (TUF) :

Rms secondary voltage and current or, transformer VA rating

Single phase Half wave Control with R-L load

Continued.

Continued.

Single phase Half wave Control with R-L load & Free Wheeling Diode

Continued.

Continued.Freewheeling diode, by pass or commutating diodeTwo modes are :Conduction modeFree wheeling modeContinued.Input pf is improved (power delivered to load in both modes / Input KVA)Load current waveform is improvedFrom above, load performance is betterAs energy stored in L transferred to R during the freewheeling period, overall converter efficiency increases.Supply current is unidirectional in both cases (dc pulses) introduces dc component to supply line. This is undesirable as as it leads to saturation of supply transformer and harmonics etcContinued.

Single phase Half wave Control with R-L-E load

Continued.

Continued.Firing angle lies :

Full wave Controlled ConvertersSCR controlled converters (or rectifiers) Classification:According to No of supply phases to inputAccording to No of load current pulses during one cycle of source voltageContinued.

Continued.

Single Phase Full wave ConvertersSingle Phase Full wave mid point converter (M-2 connection)Single Phase Full wave Bridge converter (B-2 connection)

Single Phase Full wave mid point converter (M-2 connection)

Waveforms

Single Phase Full wave Bridge Converter (B-2 connection)

Waveforms

29