Comparative Analysis of Magnetically Coupled Z-Source Inverters

Comparative Analysis of Magnetically Coupled Z-Source Inverters

Reddy Prasad Reddivari, PG Student,

RGMCET/EEE Dept,

Nandyal, India.

1. Suresh Nandyal,

   India Asst. Prof ,RGMCET/EEE Dept Nandyal, India.

   Abstract– Z-source inverters are a new class of inverters proposed with output voltage or current buckboost ability. And also its having limitations as mainly two.one is not flexible to provide continuity to inductor current, and second was there is coupling effect between modulation index and duty ratio. Its effects property of inverter. To minimize these concerns, an motivating methodology is to use magnetically coupled transformers or inductors to raise the gain and modulation ratio simultaneously, with reduced components .in this paper I proposed the magnetically coupled type inverters by developing with help of genetic methodology.

   By comparing all magnetically coupled topologies the gamma source inverter shows matured characteristics.i.e the proposed topology use lesser turns ratio to produce same level of output. Other than gamma source inverter other topologies need infinite turns ratio to produce infinite gains. But proposed topology need 1:1 transformer enough to produce infinite gains.

   Index Termsz-source inverter, Trapped inductor ZSI, Cascaded ZSI,Trans z-source inverter,- SI,flipped SI

   1. INTRODUCTION

      THE application of power converters has grown rapidly, particularly with the recent proliferation of renewable energy, distributed generation, and more electric vehicles[9]. This trend is expected to continue and would therefore demand more challenging converters to be developed.now a days renewables plays vital role and that to PV Cells and Fuel Cells and MHDs in the case of thermal power stations to increase conversion efficiency. Solar cells and fuels still going to increase their generating capability. Output power of renewable not bat all constant because input available energy is unpredictable in nature.in order to meet grid requirements we need a powerful converter(shown in fig. to interface 1) renewables and grid system with boosting flexibilities. Prior to Z-source[2-6] the boost inverter, buckboost inverter,chuk[1] type topologies are very popular. Z_source[2-6] are inviting by F.Z.Feng at 2002,with voltage are current buck boost availability. And also those topologies have inherent

      short-circuits protection and also open-circuit protection which was drawbacks of VSI,CSI

      ,respectively.

      Figure1.alternatives for electrical energy generation The development impedance-source

      inverters says mainly two ways

      1. Primary revolution

      2. Secondary revolution

         The traditional Z-source inverter and its modifications.(quasi-ZSI, embedded ZSI, embedded dc bus ZSI )[11-12] & trapped inductor based models, hybrid models(cascaded types)[15] coming under primary revolution.

         The magnetically coupled ZSI[19-21] makes secondary revolution. And this type of topologies shows matured characteristics compared to primary stage ZSIs.is Cleary mentioned in fig.2.

         Figure2.impdence-source inverters

   2. PRIMARY STAGE IMPEDANCE MODELS

      TRADITIONAL

      1. Traditional Z-source inverters

         Active mode

         These types of topologies are primary models in

         impedance networks.by placing X-shaped LC components in between source and inverters

         Figure3.Z-source inverters

         Genetic derivation methodology

         The equation analysis is clearly discussed

         below

         -DT)+ iL(DT)

         Minimum at t=T

         Peak-peak ripple current

         )

         By volt-sec balance principle =

         Finally

         RMS value of ac voltage

         (In case of normal inverter)

         (In case of Z- Source inverter)

         Figure4.inductor current in ZSI

         Shoot through mode

         Major disadvantages of ZSI

         1. Not flexible to provide continuity to inductor currents

            • It effects on inductor size and max frequency limit

         2. Coupling effect between modulation index and shoot through duty ratio

         Boost factor

         gainG

         = M*B

         Peak at t=DT

         Peak-peak ripple current

         Where D= 1-M =

         1. Trapped inductor type ZSI

            The inductors going into modify such way that the high gain requirements. Here energy can transfer in both modes

            Figure5.trapped inductor Z-source inverters

            Its really show improvement to provide continuity to inductor currents so inductor size come down further by this topology. But the coupling effect still persists in network.

         2. Hybrid ZSI(cascaded ZSI)

         In this type of topologies we can increase boost factor and gain but still the drawbacks is following along this model.

         Figure6.trapped inductor Z-source inverters

   3. SECONDARY STAGE IMPEDANCE MODELS

      This model is also called as magnetically coupled models.by eliminating all drawbacks in primary models eliminated by these models. See given table and fig.7 for further details.in that table we can observe that there is alternative for gain increment is turns ratio in magnetically coupled converters. Its eliminates coupling effect because doesnt vary the modulation inductor and so duty ratio

      D(constant)= 1-M(constant)

      TABLE I

      	Boost converter	Z-Source Inverter	Magnetically Coupled Z-Source Inverter
      Boost factor(B)
      Input to output gain(G)	No ac conversion

      Figure7.duty ratio relationship among impedance source inverters

      Figure8.alternatives to boost gains

      Above figure clearly explains how the magnetically coupled ZSI are going to eliminates the coupling effect called D=1-M by making M as constant.

   4. CONCEPT OF MAGNETICALLY COUPLED Z-SOURCE INVERTERS

      Fig 9.basic block diagram of developments of impedance networks TABLE -II DERIVATIVE EXPLORATION OF MAGNETICALLY COUPLED ZSI

      Feature	Traditional Z- source	Mutually coupled inductor type			comments
      		Trans Z-Source (TZ)	Source ()	Flipped Source (f)
      Turns ratio relationship	Not applicable	5.1(a)			-when5.1 (a)=1,response of traditional and mutually
      for gain					coupled inverters are same
      equalization
      Turns ratio trend & range	Not applicable	Increasing		Decreasing	Increasi ng 2	– and can becomes excessive at high gain – approaches 1 at high
      						gain
      						– demands the most
      						turns
      Range of modulation	0 1.15*(1- )				-Upper limit required can be made smaller than
      ratio M					0.5 by adjusting -upper limit of can be high even at high gain
      Range of shoot-through	0 <0.5
      duty ratio
      Capacitor voltage Vc			( )		( )	-same for all mutually coupled inverters if (a) satisfied
      DC link Voltage Vi			( )
      Peak output voltage Vac			( )
      Shoot -through	2*					-shoot-through currents generally high
      current
      Magnetizing current at low voltage	2* (2*current )					-value of TZ& f are the same if (a) satisfied -value for is smaller
      winding

      1. Trans Z-Source Inverters

         By replacing traditional inductors by coupled transformer and simplified such a way that two form trans z-source network. Generally the name trans Z- source called T- source is mainly due to the shape of impedance circuit is clearly showed in fig.9 (a).

         Fig10.circuit diagram of Trans Z-source inverter

         Circuit analysis

         Circuit analysis

         a) shoot trough: diode is OFF and two switches in same leg ON at the same time to form shoot trough

         Vw1=Vw2+Vc ; Vw2=Vc/(TZ-1) .

         c) non shoot trough: diode is ON and inverter acts they own work to form active state

         Vw 2 = Vdc VC ; Vw 1 = Z* Vw2

         Capacitor voltage:

         DC link voltage:

         AC RMS voltage:

         1. shoot trough: diode is OFF and two switches in same leg ON at the same time to form shoot

            trough

            Vw1=TZ* Vw2 ; Vw2=Vc.

         2. non shoot trough: diode is ON and inverter acts they own work to form active state

         Vw 2 = Vdc VC ; Vw 1 = Vdc

         Capacitor voltage:

         DC link voltage:

         AC RMS voltage:

      2. gamma() source inverters

         By replacing inductors by coupled parameters and is shown clearly in the fig.9(b).it was the best and matured topology among all magnetically coupled models and that discussed later.

         Fig11.circuit diagram of gamma-source inverter

      3. Flipped Gamma() source inverter

      By replacing inductors by coupled parameters and is showed clearly in the fig 9(c).this topology impedance source is flipped impedance of gamma source.

      Fig11.circuit diagram of flipped gamma-source inverter

      Circuit analysis

      1. shoot trough: diode is OFF and two switches in same leg ON at the same time to form shoot trough

         Vw1=TZ* Vw2 ; Vw2=Vc.

      2. non shoot trough: diode is ON and inverter acts they own work to form active state

      Vw 2 = Vdc VC-(-1)Vw1 ; Vw 1 = Vdc

      Capacitor voltage:

   5. TOPOLOGICAL COMPARISON OF MAGNETICALLY COUPLED INVERTERS

      1. GAIN EQUILISATION:

         Input to output gain

         ( )

         TABLE- III Turns ratio requirement to reach gain demands

         Fig12.gain variations in magnetically coupled

         topologies

         gain	Z- source	Trans Z- source		-source		Flipped – source
         G	D0	DTZ	1 TZ	D	2 > 1	D f	2
         2	0.3937	0.14	3.107	0.14	1.3218	0.14	4.107
         5	0.4575	0.14	4.92855	0.14	1.2029	0.14	5.928
         10	0.47875	0.14	5.535	0.14	1.1806	0.14	6.535
         20	0.4893	0.14	5.8392	0.14	1.171	0.14	6.839
         50	0.49575	0.14	6.0214	0.14	1.1661	0.14	7.0214

         The above table and figure.12 says that compare to other topologies the gamma source inverter needs lesser turns ratio transformer for producing higher gains. And not only single concern, the Trans Z-source and Flipped Gamma source needs almost turns ratio= infinity to produce infinity .i. e at high gains. But the gamma source inverter needs turns ratio .so the gamma source inverters going to produce higher gains at 1:1 transformer as placed there.it makes the size and weight low.

      2. COUPLED TRANSFORMER PERAMETERS

         fc =10 KHz

         fr =50 Hz

         M = 0.85*1.15(3rd harmonic)

         d =df =0.14 (boost) d =df =0 (buck)

         Whenever we are using coupled parameters we must analyze how the magnetizing inductance and flux going to varies and what was the flux strength, those parameters must help to design transformers according to requirements.

         By comparing all topologies we can says that gamma source inverter shows matured characteristics for voltage as a source.

         TABLE IV

         Components	Values
         Source	Vdc = 100 V
         		Winding turns(w1)=66
         		Winding turns(w2)=46
         Magnetically coupled		Turns ratio()=1.43 Coefficient of coupling(k)=0.999
         impedance		Mutual inductance(Lm)=0.4145mH
         parameters		Total transformer resistance=0.091
         		Z-source capacitance C=220F
         Inverter
         Filter	L=6.3mH/phase
         Load	Resistive: R=25/phase Motor: 4KW(5HP),400V,1450RPM

         DESIGN ASPECTS OF SIMULATION OF VOLTAGE TYPE GAMMA SOURCE INVERTER

         { }

         {

         } { }

         {

         } { }

         If we substitute the turns here means we got below equation.it says the gamma source and flipped gamma source must need higher magnetizing inductance to store energy

         { }

         { }

         { }

   6. RESULTS AND DISCUSSIONS

The gamma source inverters produces output voltages Vrms,Vc and fundamental components as given below

1. Capacitor voltage

=160.922 volts

2.D.C Link voltage

)

=187.11 volts

(

Fig8.maximum constant boost PWM techniques

3.A.C RMS voltage

( )

=79.52 volts

( )

The same output voltage can produce by using Trans Z-source[18-19] and Flipped Gamma source also but the only change is orientation of connection and turns ratio requirement. That can be explaining clearly by using given equation and table.

Where TZ= turns ratio in Trans Z-source

=turns ratio in gamma source

f =turns ratio in flipped gamma source

TABLE V TURNS RATIO REQUIREMENT

Fig.(9a) Simulink input, dc-link and output waveforms of -Z-source inverter when in voltage- boost mode in R-LOAD

.

Fig (9b).output current waveforms of -Z-source inverter when in voltage-boost mode in RL-LOAD

Fig.( 9c). Simulink dc-link and winding waveforms of -Z-source inverter when in voltage-boost mode.

Fig. (10). Simulink input, dc-link and output waveforms of -Z-source inverter when in voltage- buck mode.

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Authors Profile:

R.Reddy Prasad was born in chowdepalli,india in 1990. He received B.Tech (Electrical and Electronics Engineering) degree from JNT University, Ananthpur in 2011. And pursuing M.Tech (Power Electronics) in RGMCET, Nandyala. His area of interests are Power electronics converters, high frequency DC-DC converters, and

Z Source inverters, Embedded 8051 microcontroller interfacings. And hybrid electric vehicles.

K.Suresh was born in Kurnool, India in 1984. He received the B.Tech (Electrical and Electronics Engineering) degree from RGM college of engineering, India in 2005 and the M.Tech (Power Electronics) from RGM college of engineering in 2007. In 2007 he joined the Dept. Electrical and Electronics Engineering, R.G.M.

College of Engineering and Technology, Nandyal, as an Assistant Professor. he has published several National and International Journals/Conferences. His field of interest includes power electronics converters, power quality issues in DC-AC converters.