AC/DC Rectification Lecture 4 PDF

Rectification Definition of rectification: this is the conversion of alternating voltage (AC) to direct voltage (DC) Uncontrolled rectifiers, Single-Phase single-Diode Single phase-Bridge Rectifiers, Three-Phase Full-Bridge Rectifiers controlled rectifiers, Single-Phase single-Diode Singl...

Rectification Definition of rectification: this is the conversion of alternating voltage (AC) to direct voltage (DC) Uncontrolled rectifiers, Single-Phase single-Diode Single phase-Bridge Rectifiers, Three-Phase Full-Bridge Rectifiers controlled rectifiers, Single-Phase single-Diode Single phase-Bridge Rectifiers, Three-Phase Full-Bridge Rectifiers  Classification Rectifiers may be classified as uncontrolled and controlled rectifiers. Controlled rectifiers can be further divided into semi-controlled and fully-controlled rectifiers. Uncontrolled rectifier circuits are built with diodes, and fully-controlled rectifier circuits are built with SCRs. Both diodes and SCRs are used in semi-controlled rectifier circuits. Single-Phase Half-Wave Rectifier with R load  Performance Parameters Average value of the output voltage, Vdc Average value of the output current, Idc Output dc power, Pdc P dc = VdcIdc rms value of the output voltage, Vrms Output ac power, Pac Pac = VrmsIrms  Performance Parameters (continued) Efficiency, η η = Pdc/Pac Effective (rms) value of the ac component of the output voltage, Vac Vac = Vrms2 – Vdc2 Form factor, FF FF = Vrms/Vdc Ripple factor, RF RF = Vac/Vdc  Performance Parameters (continued) Alternate form for ripple factor V R F = ( ) − 1 = FF − 1 rms 2 2 V dc Transformer utilization factor, TUF TUF = Pdc/VsIs Vs, Is are rms voltage and current of the transformer secondary  Example Determine η, FF, RF, TUF.  Determine the Average Voltage, Vdc 1 V = T dc v L (t )dt T 0 T 1 V = sin tdt 2 dc V m T 0 V T V =− (cos m − 1) dc T 2  1 f = T  = 2 f V V = m = 0.318V dc  m V 0.318V I = dc = dc m R R  Determine the rms Voltage, Vrms 1 V =  1 T  v (t )dt 2  2 rms T 0 L  1   T 1 2 V =  (V sin t ) dt 2 2 T rms 0 m V V = rms = 0.5V m m 2 V 0.5V I = rms = rms m R R  Determine Pdc, Pac, and η (0.318V ) 2 P = dc m R (0.5V ) 2 P = ac m R (0.318V ) 2  = = 40.5% m (0.5V ) m 2  Determine FF and RF V 0.5V FF = rms = m V dc 0.318V m FF = 1.57 = 157% R F = FF − 12 R F = 1.57 − 1 = 1.21 = 121% 2  Determine the TUF 1 V =  1   (V sin t ) dt = T V = 0.707V 2 2 m s T 0  m 2 m 0.5V I =I = s load m R (0.318V ) m 2 P R T UF = = dc VI 0.5V (0.707V )( s s ) m m R T UF = 0.286  Summary – Half-Wave Rectifier RF=121% High Efficiency = 40.5 Low TUF = 0.286 Low – 1/TUF = 3.496 – transformer must be 3.496 times larger than when using a pure ac voltage source SINGLE-PHASE UNCONTROLLED HALF- WAVE RECTIFIERS WITH R-L LOADS  It is important to note the following facts: 1. The diode remains forward biased longer than π. 2. The point when the diode turns off is when the current i(t) reaches zero. The first positive value of ωt that results in zero current is called the extinction angle,β. 3. The inductor voltage is negative when the current is decreasing (VL(t)=Ldi(t)/dt) Single-Phase Full-Wave Rectifier Center-Tapped Transformer Waveforms for the Full-Wave Rectifier T 2 2 Vdc =  Vm sin t T 0 2Vm Vdc =  Vdc = 0.636Vm Single-Phase Full-Wave Rectifier PIV = 2Vm Full-Wave Bridge Rectifier Waveforms for the Full-Wave Bridge  Full-Wave Bridge with Waveforms Conduction pattern D1 – D2 D3 – D4 PIV = Vm  Efficiency Efficiency, η is the ratio of dc output power to ac input power The maximum efficiency of a Full Wave Rectifier is 81.2%.  Transformer Utilization Factor Transformer Utilization Factor, TUF can be used to determine the rating of a transformer secondary. It is determined by considering the primary and the secondary winding separately and it gives a value of 0.693.  Form Factor Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage.  Peak Factor Peak factor is defined as the ratio of the peak value of the output voltage to the rms value of the output voltage. Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode.