24-12-2012, 04:41 PM
Harmonics Analysis of Current and Voltage of Modified Sepic Converter
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Abstract:
This paper presents harmonics analysis of the
input current, inductor current and input voltage of
modified SEPIC dc-dc converter with low input voltage
and wide output voltage range. The operational analysis
and the design is done for the 380W power output of the
modified converter. The simulation results of modified
SEPIC converter are obtained with PI controller for the
output voltage. The results obtained with the modified
converter topology are shown in the table for the
fundamental values of the input current, inductor
current and input voltage. The harmonics tracking
curves are also shown for both topologies.
INTRODUCTION
Dc-dc converters are widely used in
regulated switched mode dc power supplies and in dc
motor drive applications. The input to these
converters is often an unregulated dc voltage, which
is obtained by rectifying the line voltage and it will
therefore fluctuate due to variations of the line
voltages. Switched mode dc-dc converters are used to
convert this unregulated dc input into a controlled dc
output at a desired voltage level. The recent growth
of battery powered applications and low voltage
storage elements are increasing the demand of
efficient step-up dc–dc converters. Typical
applications are in adjustable speed drives, switchmode
power supplies, uninterrupted power supplies,
and utility interface with nonconventional energy
sources, battery energy storage systems, battery
charging for electric vehicles, and power supplies for
telecommunication systems etc.. These applications
demand high step-up static gain, high efficiency and
reduced weight, volume and cost. The step-up stage
normally is the critical point for the design of high
efficiency converters due to the operation with high
input current and high output voltage[1].
OVERVIEW OF CIRCUIT AND
OPERATION
The modified SEPIC converter is
accomplished by including of the diode DM and the
capacitor CM in basic SEPIC converter. The voltage
multiplier technique is used to increase the static gain
of single-phase boost dc–dc converters. An
adaptation of the voltage multiplier technique with
the SEPIC converter is presented in Fig.1. Many
operational characteristics of the basic SEPIC
converter are changed with the proposed
modification.
Input Current Ripple and L1–L2 Inductances
As the basic sepic, boost, and the modified sepic converters present the same input stage, the equation for the determination of the input current ripple is the same for all converters. The input current ripple (ΔiL1) during the conduction of the power switch is defined by the following equation.
SIMULATION RESULTS
The designed parameters of the modified SEPIC system are given in table-1. The closed loop Simulink model for the modified SEPIC converter is shown in Fig.5: The single phase 115V, 50 Hz ac voltage is the input of the SEPIC. The input current is in phase with the input voltage waveform for the modified SEPIC converter. Fig.6 - Fig.9 are the input current and voltage waveforms with their harmonics waveforms of fundamental values respectively.
CONCLUSIONS
A modified SEPIC converter is analyzed and designed. The converter model is simulated on Simulink for closed loop. The PI controller is used to control the output voltage of the modified SEPIC which gives the controlled variation of output voltage with input voltage 115V. In Harmonics analysis, it has been observed that the fundamental value of the input voltage is 104.8V whereas 2.576A in input current. It is clear from the table-2 that the fundamental value for the inductor L1 and L2 current are 0.2635A and 0.03398A respectively.