a single stage three phase inverter based …a single stage three phase inverter based on cuk...

A SINGLE STAGE THREE PHASEINVERTER BASED ON CUK

CONVERTER

S.Balakandhan1 and G.R.P.Lakshmi21P.G Scholar,

Sathyabama University Chennai 600119, [email protected]

2Associate Professor,Department of Electrical and Electronics Engineering,

Sathyabama University, Chennai 600 [email protected]

December 31, 2017

Abstract

In this paper the three phase voltage source inverterbased cuk converter with PID controller is proposed. In theproposed topology the passive elements such as inductorsand capacitors are reduced in order to improve the accu-racy and reduce the cost which in turn makes the systemcompact. The cuk converter is operated in buck and boostmode of operation which makes it feasible for standaloneand grid connected applications. In the proposed topologymore reliable non electrolytic capacitors are used for the fil-tering purpose which makes it suitable for PV applications.

Key Words : Three phase voltage source inverter (VSI),CUK converter, maximum power point tracker (MPPT),and photo-voltaic (PV) array.

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International Journal of Pure and Applied MathematicsVolume 118 No. 16 2018, 1179-1190ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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1 INTRODUCTION

An important attraction of PV systems is that they produce electricpower without polluting the environment, by directly transformingsolar irradiance into electricity. This fact, together with the contin-uously decreasing cost of PV arrays and the gain in their efficiency,makes the PV generation systems most popular in the immediatefuture. The ability of PV cells depends on many factors such astemperature, solar irradiance, spectral characteristics of sunlight,dirt environment, shadows, and many other factors [1-4]. Changesin irradiance on panels due to dynamic climatic changes such ascloudy weather and increase in ambient temperature can decreasethe PV array output power. Then, each PV cell produces energypertaining to its operational and environmental conditions. In ad-dressing poor efficiency of PV systems, few methods are proposedamong which a very new concept is called maximum power pointtracking (MPPT). Entire maximum power point tracking (MPPT)methods follow the same goal which is increasing the PV array out-put power by tracking the maximum power on whole operating con-dition. A switched-mode DC-DC converter is heart of MPPT con-troller. A DC to DC converter therefore implemented to maintaina constant voltage and deliver maximum power from solar panelto load. The output voltages of DC-DC converters are generallycontrolled by using a power semiconductor switching concept. Tra-ditionally choppers with silicon controlled rectifier (SCR) devicewere known as DC-DC converters [5-6]. But today for many in-dustrial application (Switched Mode Power Supply) SMPS basedDC-DC converters uses insulated Gate Bipolar Transistor (IGBT)and Metal Oxide Field Effect Transistor (MOSFET). For outputvoltage regulation Pulse width modulation (PWM) scheme is used.The inverters should be able to produce ac voltages of variable mag-nitude and variable frequencies. The affirmation of output voltagecan also be greatly enlarged, while compared with those of squarewave inverters. The PWM inverters are very universally used invariable speed ac motor drive loads where one needs to providethe motor with variable voltage, adjustable frequency supply [7-10]. For the wide variation in drive speed, the frequency of theapplied ac voltage needs to be adjusted over a wide range. Theapplied voltage also needs to vary completely linear with the fre-

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International Journal of Pure and Applied Mathematics Special Issue

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quency. PWM inverters are divided into two types namely singlephase and three phase inverters. In three phase inverters differenttypes of Pulse width modulation techniques are used. But in allthese techniques the goal is to generate an output voltage, withgood quality sinusoidal voltage waveform of desired fundamentalfrequency and magnitude. The inverter topology considered here,it may not be possible to decrease the overall voltage distortion dueto harmonics but by appropriate switching control, the magnitudesof lower order harmonic voltages can be reduced efficiently. Such asituation is widely acceptable in most cases as the harmonic volt-ages of high frequencies are satisfactorily filtered using smaller sizesfilter chokes and passive elements like capacitors [11-13].

2 CUK CONVERTER BASED THREE

PHASE INVERTER

The figure 1 shows the circuit diagram of the cuk converter basedthree phase inverter. It consists of PV array, CUK converter, Threephase voltage source inverter, peripheral interface controller (PIC),MOSFET driver, and ac load. The PV array converts light energyfrom sunlight into electrical energy using photo voltaic effect. CUKconverter is a buck-boost dc to dc converter. It maintains the out-put voltage greater or lesser or equal to the input voltage. Dutycycle of the transistor switch used in the CUK converter plays vitalrole in variation of output voltage. PIC controller generates gatepulses to the transistor switches used in the CUK converter. Thegate pulse depends on the feedback given by output voltage, cur-rent and solar panel voltage and current. Then three phase inverterconverts the dc power from cuk converter into three phase ac powerwhich is given to the ac load.

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Figure 1: Circuit diagram of cuk converter based three phase in-verter

3 MODES OF OPERATION

Mode 1:

Figure 2: Inductor charging mode and switch S1 in ON state

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Figure 2 shows the mode 1 operation of cuk converter basedthree phase inverter. During this mode power semiconductor switchS1 in the Cuk converter turned ON. The inductor L1 current is in-creasing. Transistor switch S2 is turned OFF. Capacitor C1 is usedto transfer the energy between input and output by the commuta-tion of power semiconductor switches. Output capacitor C0 deliversthe dc power as input into the three phase voltage source inverter.This three phase inverter operated in 1800 mode. So three transis-tor switches are turned ON in each 600. The switching pattern oftransistor switches in this inverter for each cycle to generate threephase ac output is 834,345,456,567,678,783 then next cycle. Eachtransistor switches conduct for the period of 180 degree.

Mode 2:

Figure 3 shows the mode 2 operation. During this mode powersemiconductor switch S2 in the Cuk converter turned ON. Theinductor L1 current is decreasing. Transistor switch S1 is turnedOFF. Capacitor C1 is used to transfer the energy between inputand output by the commutation of power semiconductor switches.Inductors are used to maintain constant current.

Figure 3: Inductor discharging mode and switch S2 in ON state

Similar to mode 1 capacitor C0 provide dc power into input ofthree phase inverter. Operation of three phase inverter is similaras in mode1.

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4 SIMULATION

The simulation of cuk converter based three phase inverter wasdone using Matlab/Simulink. Switching frequency of the powersemiconductor switches used is 20 khz. The PV array is designedin the simulation using electrical characteristics of solar cell. Solarcells are connected in series and parallel to add the voltage andcurrent respectively [14-17]. The closed loop system is designedusing PID controller.

Figure 4: Simulation circuit of the cuk converter based three phaseinverter

Figure 4 shows the simulation circuit of the cuk converter basedthree phase inverter. Space vector pulse width modulation tech-nique (SVPWM) is used to generate gate pulses for three phasevoltage source inverter.

5 SIMULATION RESULTS AND DIS-

CUSSION

The results of the simulation of cuk converter based three phaseinverter are as shown below. Figure 5 shows the output dc voltageproduced from Cuk converter. The average voltage of the CUKconverter is 80V dc. Figure 6 shows switching current pulse for thetransistor switches.

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Figure 5: Output voltage ofcuk converter

Figure 6: Pulse signal for thetransistor switches

Figure 7 shows the phase to neutral voltage and figure 8 showsthe phase to phase voltage of the three phase inverter. Figure 9shows the output voltage of three phase inverter. The magnitudeof three voltage is 75V three phase ac.

Figure 7: Three phase P-Nvoltage

Figure 8: Three phase P-Pvoltage

Figure 9: Output voltage of three phase inverter

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Table 1 shows the comparison of the results of conventionalsystem and cuk converter based three phase inverter. The table 1indicates that the cuk converter based three phase inverter givesthe better results compared to the conventional system.

Table 1:

Sl. NoPERFORMANCE

DETAILSCONVENTIONAL

SYSTEM

CUK CONVERTERBASED THREE

PHASE INVERTER

1.INPUTVOLTAGE

50V 50V

2.OUTPUTRMS VOLTAGE

49.49V 84.84V

3.OUTPUT P-PVOLTAGE

70V 120V

4.OUTPUTFREQUENCY

50HZ 50HZ

6 CONCLUSION

This paper proposed cuk converter based three phase voltage sourceinverter to make the system suitable for standalone and grid con-nected applications if output voltage is greater or less than theinput dc side, the reliability of the system was improved accordingwith output results, and total cost and size of the system is reduced.The Proportional-Integral-Derivative controller helped to maintainthe desired output voltage and current, therefore efficiency of thesystem was improved.

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a single stage three phase inverter based …a single stage three phase inverter based on cuk...

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