Power Factor Correction & Pfc Converters

POWER FACTOR CORRECTION & PFC CONVERTERS

Presented by

Sandeep Guha Niyogi M.Tech-Electrical Roll No.852010

CONTENTS

INTRODUCTION • power factor power factor =

average power Vs I s1 cos θ I s1 = = cos θ apparent power Vs I s Is

Reflects how effectively the given source power is utilized by the load. The ratio is the distortion factor; its value reflects the effect due to input current harmonics.

A non-corrected power supply with a typical PF equal to 0.65 will draw approximately 1.5 times greater input current than a PFC supply (PF = 0.99) for the same output loading

• PFC Techniques

Passive Power Factor Correction INDUCTIVE FILTER •

inserted between the output of the rectifier and the capacitor.

•

The inclusion of the inductor results in larger conduction angle of the current pulse and reduced peak and rms values. For low values of inductance the input current is discontinuous and pulsating.

•

Better power factor (PF) is achievable by using a larger value of the inductance and pushing the operation to continuous conduction mode (CCM).

Passive Power Factor Correction RESONANT INPUT FILTER •

The band pass filter is designed with a centre frequency equal to the supply frequency.

•

The quality factor "Q" determines the bandwidth and hence the harmonic content of the supply current. High "Q" (narrow bandwidth) will result in reduced harmonic content and close to unity power factor.

•

The high value parallel resistor is added to damp out circuit oscillations.

Active Power Factor Correction •

Lower harmonic content in the input current compared to the passive techniques.

•

Reduced rms current rating of the output filter capacitor.

•

Near unity power factor (0.99) is possible to achieve with the Total Harmonic Distortion (THD) as low as 3-5%.

•

For higher power levels active PFC techniques will result in size, weight and cost benefits over passive PFC techniques.

Conventional ACTIVE PFC topologies

The boost power factor correction converter The proposed converter switches operates at Soft switching condition by partial resonant condition by control of constant duty cycle. The turn on of the switches is done under zero current switching (ZCS) and turn off of the switches is worked under zero voltage switching (ZVS) by partial resonant method. Therefore the proposed converter is

PFC Boost Converter

Mode1 operation

The mode operates in the period t 0 ≤ t ≤ t1 Vcr = (Vr + Vdc ) cos ωr t − Vr i Lr

(V r+Vdc ) =− sin ωr t X

where, ωr =

Lr C r

when, Vcr = 0 the inductor current is given as I1 =

1 X

(Vdc 2 + 2VrVdc )

Mode2 operation

This mode operates in the period t 1 ≤ t ≤ t 2 i Lr =

Vr t + I1 Lr

This mode ends when both the switches turn off & the inductor current equation is given as V I 2 = I1 + r {TON − Lr C r cos −1 (v )} Lr

Mode3 operation

This mode operates in the period t 2 ≤ t ≤ t 3 The current flows through the path L r − d1 − C r − d 2 thus charging the capacitor The turning - off of the switches occur at ZCS condition The inductor value is assumed to be constant value I 2 , because of short period of this mode.

Mode4 operation

This mode operates in the period t 3 ≤ t ≤ t 4 Starts when diode d3 starts conducting The inductor current decreases linearly and is given by the equation : i Lr

Vr − Vdc = t + I2 Lr

This mode ends when the inductor current reaches ZERO value

Simulation Results Input to this simulation is given below • Input ac voltage =100 volt(rms) • Output dc voltage =300 volt • Switching frequency =50 kHz Soft switching of switches • Duty cycle=30%

S1 &S2

Simulation Results Input waveform of Discontinuous current mode

Input voltage & output voltage waveform

COMPARISON OF PASSIVE & ACTIVE PFC VERSUS NO PFC

APPLICATIONS  DC Power Supplies,  Telecommunication Power Supply,  Improved Power Factor ballast,  Power Supplies for equipments like computers, medical equipments, printers, scanners etc.  Drives Applications with Power Factor Improvement at AC side,  Electrical Welding,  Lighting such as ballasts, CFL etc.

CONCLUSION • The input current waveform got to be sinusoidal in proportion to supply voltage waveform with constant duty cycle i.e. 30% operation. • The DCM method reduces the complicacy of designing control circuit. The power factor & rms current is high. • The circuit switches operate under partial resonant soft switching method , thus it increases the efficiency of the circuit.