Design of Step-Up/Step-Down DC-AC Converter without Transformer · 2018-03-15 · Design of Step-Up/Step-Down DC-AC Converter without Transformer T.Rajmohan1 and G.T. Sundar Rajan2

Design of Step-Up/Step-Down DC-ACConverter without Transformer

T.Rajmohan1 and G.T. Sundar Rajan2

1PG Scholar, Department of EEE, Sathyabama University,[email protected]

December 28, 2017

Abstract

Objectives: This paper presents a new DC-AC Con-verter to convert a continuous input voltage to an alternatedoutput voltage, whose instantaneous value in numerous sit-uations, may progress into higher than the input voltage,DCAC converters devices are developed.

Methods/Analysis: Per the Literature Survey, Thereare different approaches to this kind of application withthe feature that produces an instantaneous output voltagehigher or lower than the input dc voltage without an inter-mediate power stage or transformers.

Findings: This quality is provided by using one switch-ing cell including two switches, two diodes, one inductor,and one capacitor on individual inverter leg. No limita-tions on the source D.C. source. Inverter Circuit is basedon H-Structure Inductors was used to store the transientenergy. Inductive-capacitive filters were used for low fre-quency applications pure form of A.C. is given to Resistiveload. The controller unit compares output obtained fromthe circuit and feedback signals through sensor. Based onthe output, inverter can be switched (step-up or step-down)operation. As we aware, there are numerous modulationstrategies that can be applied to control the proposed con-verter; however, in this study, a Space Vector modulationscheme is employed.

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International Journal of Pure and Applied MathematicsVolume 118 No. 16 2018, 961-975ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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Applications: Uninterruptible power supplies, Electricmotor speed control, Induction heating, HVDC power trans-mission, Electroshock weapons, Portable consumer devices,Grid-tied inverters, Solar inverter.

Keywords : DC-AC converter, Inverter Circuit, H-Structure Inductor, Inductive-capacitive filters, Space Vec-tor modulation.

1 INTRODUCTION

For the adaptation of continuous input voltage to staggered out-put voltage, there are devices established as DC-AC converters innumerous circumstances, the input voltage is lower than the instan-taneous value. For these type of Application, There are differentmethodologies are presented as below. Debates with respect to theutilization of the step-up converter for various rationales can be es-tablished. Referring to [1], it is promising to add a step-up staticgain spending two DC-DC boost converters, linking the load in adifferential form and pertaining an 180o phase-shift modulation inevery converter. Alike analysis can be comprehensive to other dcdcconverters investigated in the literature. The Z-source structure isone more ancillary for inverters whose topology gives the step-upcharacteristic, since it is promising to coalesce the inductances andcapacitances in order to gain a single impedance between the in-put and output. Furthermore, it present a transitional power stageconnected in flow with the inverter stage, leading to a two-stagestructure. This paper suggests a new topology for voltage invert-ers, in an application where the instantaneous output voltage canbe higher or lower than the input dc voltage. From experimentalresults, some important aspects related to the proposed convertercan be highlighted:

1. The converter operates with the step-up/step-down.

2. The output inductor and output capacitor designs are notdependent on duty cycle.

3. The positive aspects have similarities with the buck inverter.

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2 MATERIALS AND METHODS

In this section, the basic principle of the previously modulatedstructure of the converter, its drawbacks and also presented theproposed modulation structure for reducing the harmonic in theoutput.

The projected dcac converter output power stage is shown inFig. 1. This planning consists of an input voltage source Vi,high frequency filter formed by Lf and Cf , load resistance R0,two switching cells, whose elements are S1, D1, C1, S2, D2 and L1

and S3, D3, C2, S4, D4 and L2, respectively. A number of modula-tion approaches can be applied to control the proposed converter,for example, space vector, unipolar, and bipolar modulations; nev-ertheless, here, a Space Vector modulation technique is employed.From the representative diagram in Fig. 2, the waveforms indicatedin Fig. 3 were obtained.

Fig 1 : Proposed Output

Fig 2 : Representative scheme applied to the proposed converter.

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Fig 3 : Waveforms obtained for SV modulation: (a) modulatorsignal and triangular carrier signal; (b) signals applied in switchesS1 and S4 ; (c) signals applied in switches S2 and S3 .

It is significant accentuate that the system waveforms at a highfrequency (from commutation) and a low frequency (from grid)component. In order to regularise the system mathematical andgraphical images, the variable time(t) will be involved to representthe system from the switching period point of assessment and thevariable angle(θ) will describe the system from grid period pointof view. In order to increase an accepting of the system operationstages, the switches shown in Fig. 1 will be swapped by their bidi-rectional models. In order to reveal the equivalent circuits of thesystem, two models were chosen: the first refers to inverter oper-ation with a duty cycle higher than 0.5, as shown in Fig. 4, andthe second the system operates with duty cycle less than 0.5, asdepicted in Fig. 5. Evaluating both, we can found that the equiv-alent Circuits for the two cases are similar, thus, for a prolongedanalysis, only the stages represented by Fig. 4 will be considered.

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Fig 4 : Equivalent circuits for duty cycle higher than 0.5 (inverteroperation) Stage related to the intervals

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Fig 5 : Equivalent circuits for duty cycle Lower than 0.5 (boostoperation) Stage related to the intervals

2.1 Space Vector modulation

Several modulation strategies can be used to control the proposedconverter, for example, space vector, unipolar, bipolar modulationsthough in this study, a Space Vector modulation scheme is em-ployed The main purposes of space vector pulse width modulationgenerated gate pulse are as follows:

• Wide linear modulation variety

• Less switching loss

• Less total harmonic falsification in spectrum of switching wave-form

• Easy implementation and less computational calculations

• Space vector pulse width modulation is applied to output volt-age and input current control

• This technique is an benefit because of increased elasticity inthe choice of switching vector for together input current andoutput voltage control

• It can yield useful benefit under unbalanced conditions

An inverter renovates a DC supply, via a series of switches, tothe three output legs which could be connected to a three-phase

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load. The switches must be restrained so that at no time are bothswitches in same leg turned ON or else the DC supply would beshorted. This state may be met by the balancing operation of theswitches within a leg. i.e. if A+ is on then A is off and vice versa.This leads to eight conceivable switching vectors for the inverter,V0 through V7 with 6 active switching vectors and 2 zero vectors.The purposes elaborate in each operation stage and their particularequations are obtained for a fixed duty cycle in view of one switchingperiod and steady-state analysis, since transient conditions and/orload variations were not considered. Table underneath shows theparameters and the mathematical functions for each variable of in-terest seeing all operational stages and a duty cycle higher than 0.5.These roles are satisfactory to evaluate the instantaneous averagevalues for capacitor voltages and inductor currents.

Note that looking down the columns for the active switchingvectors V1−6, the output voltages vary as a pulsed sinusoid, witheach leg offset by 120 degrees of phase angle.

Table 1: Parameters and the mathematical functions for each vari-able of interest considering all operational stages and a duty cyclehigher than 0.5.

Vector A+ B+ C+ A B C VAB VBC VCA

V0={000}OFF OFF OFF ON ON ON 0 0 0 zero vector

V1={100}ON OFF OFF OFF ON ON +Vdc 0 Vdc active vector

V2={110}ON ON OFF OFF OFF ON 0 +Vdc Vdc active vector

V3={010}OFF ON OFF ON OFF ON Vdc +Vdc 0 active vector

V4={011}OFF ON ON ON OFF OFF Vdc 0 +Vdc active vector

V5={001}OFF OFF ON ON ON OFF 0 Vdc +Vdc active vector

V6={101}ON OFF ON OFF ON OFF +Vdc Vdc 0 active vector

V7={111}ON ON ON OFF OFF OFF 0 0 0 zero vector

3 RESULTS AND DISCUSSION

Fig 6 shows the Open loop circuit diagram and Fig 6(a) showsthe Gate pulse Diagram and Fig 6(b) demonstrates the respectiveOutput.

Fig 7 shows the Open loop circuit diagram with SPWM and Fig7(a) shows the Output voltage in the Open loop model

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Fig 6 : Proposed Circuit Diagram (Open)

Fig 6(a) : Proposed Simulation Diagram (Open) Gate Pulse

Fig 6(b) : Gate Output

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Fig 7 : Proposed Simulation Diagram (Open) SPWM

Fig 7(a) : Output Voltage (Open)

Fig 8 shows the Close loop circuit diagram with and Fig 8(a)shows the Output voltage in the Open loop model

Fig 8 : PROPOSED CIRCUIT DIAGRAM (Close)

Fig. 8(b) shows the measured efficiency against the outputpower for the new proposed dcac converter. It can be observed

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Fig 8(a) : Output Voltage (Open)

that the maximum efficiency is 92.7%

Fig 8(b) : Output Efficiency

Comparison of the Performance details of Input and Outputvoltages of Existing and Proposed System is tabulated as shownbelow in Table 2.

4 CONCLUSION

This manuscript presented a new topology for DCAC converterswhose main feature is its capacity to provide an instantaneous out-put voltage higher or lower than the input voltage without an inter-mediate power stage or transformer. Based on experimental resultsthe following conclusion can be drawn as the maximum efficiencycalculated in the laboratory was 92.7%.

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Table 2: Performance comparison table of the Existing and Pro-posed System

Sl. NoPERFORMANCEDETAILS

EXISTINGSYSTEM

PROPOSEDSYSTEM

1. INPUT VOLTAGE 100 V 100 V2. OUTPUT RMS VOLTAGE 183 V 150 V3. OUTPUT P-P VOLTAGE 260 V 300V4. OUTPUT FREQUENCY 50 HZ 50 HZ

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Documents

Design of Step-Up/Step-Down DC-AC Converter without Transformer · 2018-03-15 · Design of Step-Up/Step-Down DC-AC Converter without Transformer T.Rajmohan1 and G.T. Sundar Rajan2