Diode Rectifiers EE

Transcription

1 Dioe Rectifiers EE

2 Half-Brige Rectifier Circuit: R an R-L Loa Current continues to flow for a while even after the input voltage has gone negative. 5-2

3 Half Brige Rectifier Circuit: Loa with c back-emf Current begins to flow when the input voltage excees the c back-emf. Current continues to flows for a while even after the input voltage has gone below the c back-emf. 5-3

4 Full-wave Rectifier with Center tap Transformer The DC currents of the two half- wave rectifiers are equal an opposite, Hence, there is no DC current for creating a transformer core saturation problem. Each ioe carries half of the loa average current, but the same peak loa current. Note that the V RRM rating of the ioes must be chosen to be higher than 2V m to avoi reverse breakown. The center-tap transformer is consiere bulky with aitional losses. 5-4

5 Full Brige Rectifier Simple R Loa Average value of output voltage: V ( 2 2 / ) V 0.9V (2/ ) V V o s s m m where V s an V m are the RMS an peak values of input voltage. Rectification Ratio = Pc/Pac = 0.81 or 81% Form Factor (FF) of DC sie voltage (or current) = Vrms/Vc = 1.11 Ripple Factor = rms value of AC component/dc component = (FF 2-1) 1/2 =

6 Filters Filters are employe in rectifier circuits for smoothing out the c output voltage of the loa. Ripple Reuction Factor at f r : 5-6

7 nuctor DC Filter Minimum value of inuctance require to maintain a continuous current is known as the critical inuctance L C : The choice of the input inuctance epens on the require ripple factor. Ripple voltage of a rectifier without filtering: Consiering only the lowest-orer harmonic (n = 2), the output ripple factor of a simple inuctor-input c filter is 5-7

8 Full Brige Rectifier with c-sie Voltage Average value of DC-sie current (obtaine numerically): Zero current correspons to c voltage equal to the peak of the input ac voltage 5-8

9 Full Brige Rectifier Simple Constant Loa Current RSM value of source current RMS value of funamental current RMS value of harmonic current s s1 sh (2 s1 2 / ) / h, h 0.9 3,5,7,... Current THD Displacement Power Factor Power Factor THD 100[ DPF 1 PF ( / 8) 1] 48.43% 5-9

10 Full Brige Rectifier Simple Constant Loa Current (AC-sie filtering) RMS value of harmonic source current THD of Source Current: 5-10

11 Dioe-Rectifier with a Capacitor Filter Approximate value of peak-to-peak ripple: Average output voltage: RMS value of output ripple voltage: Ripple Factor: nrush resistance R inrush is sometimes neee to limit the initial inrush current to a value below that of the ioes. t is usually place on the DC sie, then shorte out afterwars. n many cases, R inrush is not neee if the Equivalent Series Resistance of the capacitor an cable/transformer wire resistance are sufficiently large. 5-11

12 Dioe-Rectifier Brige with AC-Sie nuctance Commutation angle: Average of DC-sie voltage: cos 1 V 0.9V s 2L s 2V s 2Ls 5-12

13 Voltage Distortion at PCC PCC is the point of common coupling Distorte current flow results in istorte voltage 5-13

14 Dual Voltage Rectifier n 115-V position, one capacitor at-a-time is charge from the input. 5-14

15 Three-Phase, Four-Wire System A common neutral wire is assume The current in the neutral wire is compose mainly of the thir harmonic an can be higher than the phase currents 5-15

16 3-Phase Rectifier Circuit Star Connection: irect currents in the seconary winings cause transformer core saturation problem. The transformer core saturation problem in the three-phase star rectifier can be avoie by zig-zag (or interstar) connection. Three-phase Brige (or 6-pulse) Rectifier most commonly use in inustry applications. 5-16

17 Three-Phase Brige Rectifier with R Loa Average value of DC-sie voltage: 3 Vo 3V m V where V m is the peak value of the phase voltage. RMS value of DC-sie voltage: Vrms Vm V 2 4 m m 5-17

18 Six-Phase Brige Rectifier (12-Pulse) Average an RMS values of DC-sie voltage: V V V o rms where V m is the peak value of the phase voltage. m 5-18

19 Three-Phase Full-Brige Rectifier with DC Current 5-19

20 Three-Phase, Full-Brige Rectifier with DC Current RSM value of source current RMS value of funamental current RMS value of harmonic current Current THD Displacement Power Factor Power Factor s s1 sh ( 2 / 3 s1 6 / ) / h, THD 100[ DPF 1 3 PF h 3,5,7,... 2 ( / 9) 1] 31% 5-20

21 3-Phase, Full-Brige Rectifier with nuctance Commutation angle: Average of DC-sie voltage: cos 1 V 1.35V 2L LL s 2V LL 3L s 5-21

22 3-Phase Rectifier with DC Source 5-22

23 Three-Phase Rectifier with Capacitor Filter PSpice-base analysis 5-23