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Title : SWITCHED COUPLED INDUCTOR BASED QUASI Z-SOURCE INVERTER FOR OBTAINING HIGH VOLTAGE GAIN Author (s) : SURENDHAR.A, BALAMANIKANDAN.M, RAGHURAMAN.V, Prof.B.M.PRABHU, Dr.S.PADMA

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International Journal of Inventions in Computer Science and Engineering, Volume 4 Issue 1 Jan 2017

25

SWITCHED COUPLED INDUCTOR BASED QUASI Z-SOURCE

INVERTER FOR OBTAINING HIGH VOLTAGE GAIN

1

SURENDHAR.A,

2

BALAMANIKANDAN.M,

3

RAGHURAMAN.V,

4

Prof.B.M.PRABHU,

5

Dr.S.PADMA

1,2,3

B.E. Electrical and Electronic Engineering, Angel College of Technology, Tamilnadu, India

4Assistant Professor, Department of Electrical and Electronic Engineering, Angel College of

Technology, India

5Professor, Department of Electrical and Electronic Engineering, Sona College of Technology,

India

ABSTRACT-Z-source inverters have become a research hotspot because of their single-stage buck-boost inversion ability, and better immunity to EMI noises. However, their boost gains are limited because of higher component-voltage stresses and poor output power quality, which results from the tradeoff between the shoot-through interval and the modulation index. To overcome these drawbacks, a new high-voltage boost impedance-source inverter called a switched-coupled-inductor quasi-Z-source inverter (SCL-qZSI) is proposed, which integrates a switched-capacitor (SC) and a three-winding switched- coupled-inductor (SCL) into a conventional qZSI. The proposed SCL-qZSI adds only one capacitor and two diodes to a classical qZSI, and even with a turns ratio of 1, it has a stronger voltage boost-inversion ability than existing high-voltage boost q-ZSI topologies. Therefore, compared with other (q)ZSIs for the same input and output voltages, the proposed SCL-qZSI utilizes higher modulation index with lower component-voltage stresses, has better spectral performance, and has a lower input inductor current ripple and flux density swing or, alternately, it can reduce the number of turns or size of the input inductor. The size of the coupled-inductor and the total number of turns required for three windings are comparable to those of a single inductor in (q)ZSIs. To validate its advantages, analytical, and experimental results are also presented.

INTRODUCTION:

Conventional voltage and current source inverters (VSIs and CSIs, respectively) despite their huge demand in industrial applications such as adjustable speed drives, distributed power systems, and hybrid electric vehicles (HEVs), suffer from some serious drawbacks, which make them less attractive. In particular, VSIs can perform only buck operations, while CSIs can perform only voltage boost inversions. Therefore, in applications that require both buck and boost operations, an additional dc-dc converter is needed, resulting in a two-stage power conversion with a higher system

cost and volume, low efficiency, and also complex control.

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surendhar.A et al.,

ISSN (Online): 2348 – 3539

(PWM)schemes,modeling and control applications, ac-ac and dc-dc converters and other ZSI topologies .In modified ZSIs referred to as quasi-Z-source inverters (q-ZSIs) were proposed, and they have advantages over ZSIs, such as continuous input current, lower component-voltage stresses, and common ground between the dc-voltage source and the inverter-bridge. One of the serious drawbacks of all the existing q-ZSIs is that despite having theoretically infinite gains, their practical boost ability is limited by higher component-voltage stresses and low output power quality due to their low modulation index M , which is caused by the tradeoff between the shoot-through duty-cycle D and M .This results in poor output power quality as the fundamental component of the ac output voltage decreases linearly with M and the magnitudes of higher-frequency harmonics (total harmonic distortion-THD) increase significantly.

In addition, it leads to the poor utilization of the dc-link voltage, resulting in higher voltage stresses on both the active switches and the passive components. With a larger D, the effect of the parasitic components becomes more prominent, and the voltage gain tends to decrease drastically .Many attempts have already been made to improve the boost capability of q-ZSIs. In modified PWM schemes, which are referred to as maximum boost control and constant boost control, were proposed with the attempt to increase the voltage boost ability. However, these SL-ZSI inverters have a higher component count and various other drawbacks such as discontinuous input current, large inrush current at start up, and the absence of a common ground between the dc-voltage source and the inverter-

bridge. An SL-qZSI is proposed and although it overcomes the above mentioned drawbacks associated with the SL-ZSI, but at the cost of reduced boost ability, which counters its other advantages. From the above discussions, it can be concluded that all of the existing high-boost q-ZSIs use either several additional components or coupled inductors with a high turn. In this paper, a combination of switched-capacitor (SC) and a three-winding switched-coupled-inductor (SCL) is applied to the q-ZSI, and the topology obtained is termed as SCL-qZSI. The proposed SCL-qZSI retains all of the advantages of the classical q-ZSI topology such as continuous input current and a common ground between the dc-voltage source and the inverter-bridge; it can also suppress the startup inrush current.

Fig(1).Proposed switched-coupled-inductor quasi-Z-source inverter (SCL-qZSI)

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ISSN (Online): 2348 – 3539

lower D and higher M , which results in lower component-voltage stresses, a better output power quality, and a lower input current ripple.

PROPOSED SCL-qZSI:

The circuit of the proposed SCL-qZSI, which is obtained by replacing inductor L2 in the classical qZSI with a combination of SC (C3 ) and a three-windings ( N1, N2 , and N3 ) SCL (obtained by adding winding N2 and diode D2 to the SC and the two-winding SCL cell in. The proposed inverter consists of three diodes ( Din, D1, and D2), three capacitors (C1 ,C2 ,and C3 ), an input inductor L1 , and an SCL with three windings ( N1 , N2 , and N3 ). Windings N1 and N2 have the same number of turns ( N1= N 2 ), and the turn ratio of windings N3 to N1 (or N2 ) is n( n=N3 / N1 =N3 / N2 ).

FEATURES:

The main features of the proposed SCL-qZSI are as follows: It has a continuous input current, and common ground between the dc-voltage source and the inverter-bridge. It also provides startup inrush current suppression. Compared to the T-source inverter and the trans-ZSI, where the energy stored in the leakage inductance of the coupled-inductor only causes switch voltage spikes, the leakage inductance of the SCL is effectively utilized in two ways: (1) it is in series with switched-capacitor C3 and

thus reduces the inrush current of C3; and (2) the energy stored in the leakage inductance is absorbed by capacitor C2 ,and is,therefore recycled without creating switch voltage spikes. It adds only one capacitor and two diodes to the qZSI, and even with a

turn ratio of 1, it boost factor of, which is higher than that of the other existing q-ZSIs and trans-ZSIs.

For the same input and output voltage conditions, compared to other (q)ZSIs, it uses a lower shoot-through duty-cycle D , and consequently, a higher modulation index M , which results in lower component-voltage stresses and better output power quality.

The total number of turns for the three windings and the size of the SCL are comparable to that of a single inductor in (q)ZSIs. In addition, for the same inductance value, the same core size and the same number of turns of input inductor L1, the input inductor current ripple, and the flux density swing are smaller than those of other (q)ZSIs. Alternately, for the same input inductor current ripple and flux density swing, the number of turns or core size of the input inductor L1 in the proposed SCL-qZSI can be reduced.

OPERATION PRINCIPLE:

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ISSN (Online): 2348 – 3539

L lk1 ,

L

lk2 , and L

lk3 of windings N1, N2 , and N3, respectively.

Fig. 2. Equivalent circuit of the proposed SCL-qZSI during (a) the shoot-through state, and (b) the non-shoot-through state.

Shoot-through state: Fig. 2(a) shows the equivalent circuit of the proposed inverter during the shoot-through state, which is obtained by simultaneously turning on both switches of a phase leg in the inverter-bridge. During this state, diode Din is off while diodes

D1 and D2 are on. Windings N1 and N2 are charged by C1 in parallel, while C3 obtains energy from C1 through winding N3 , which significantly enhances the boost factor. In addition, the charging current of Figs show the simplified equivalent circuits of the proposed

inverter during the shoot-through and non-shoot-through states,

C3is limited by the leakage inductance of the SCL.

Non-shoot-through state:This consists of

six active states and two zero states of the main circuit, and the equivalent circuit during this state is shown in Fig. 2(b). During this state, diode Din is on while D1 and D2 are off. Capacitors C 1 and C2 are charged, whereas the windings ( N1, N2 , and N3 ) and capacitor C3 are in series and transfer energy to the main circuit. During this state, the energy stored in the leakage inductance of the SCL is absorbed by C2 , and it is, therefore, recycled without creating switch voltage spikes.

BOOST ABILITY: The boost factorBofthe SCL-impedance network is the ratio of the dc-link voltage of the inverter-bridge VPN to the input dc-voltage Vin. The leakage inductance of the SCL is very small because of the trifilar windings and similar to the derivation of the boost factor for trans-ZSIs; the leakage inductance is ignored in order to

derive the boost factor of the SCL-qZSI.

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respectively. We observed that the voltage gain g increases with a decrease in the modulation index, and for the same

modulation index m , the proposed inverter has a higher voltage conversion ratio than the other topologies. Therefore, for the same

COMPARISION OF THE SWITCH VOLTAGE

STRESSES: In order to compare the stresses

of the proposed SCL-qZSI, SL-qZSI, and qZSI, all the three topologies are represented by their simplified equivalent circuits, as shown in Fig. A inductive load impedance ( Zl = Rl ) is connected in parallel with an

active switch S . In vl and il denote the instantaneous load voltage and current, respectively, whereas Vl and Il denote the average load voltage and current, respectively, during a switching cycle in steady-state. Applying the steady-state analysis method, the current and voltage stresses of the components in the main power circuit are obtained. The performance illustrates the governing equations of the three inverters under the conditions of the same input voltage Vin and the same shoot-through duty ratio D . From the table, we see that the voltage and current stresses of the proposed SCL-qZSI are higher than those of the other two inverters because of its higher voltage boost ability B. In this case, the conventional qZSI has lower current and voltage stresses owing to its lower boost ability. In the equations given in Tables I and II, SD is the shoot-through switching function, having a value of 1 during the shoot-through state and 0 during the non-shoot-through state.

However, when these three inverters are used in a particular application, the input dc-voltage Vin and the output peak phase voltage vˆph are fixed, and the voltage gain G is therefore fixed. In this case, the

voltage conversion ratio, the proposed SCL-qZSI makes use of the larger modulation index.

voltage and current stresses in terms of the voltage gain G , are given in Table II for the three inverters.this behaviour shows that for the same input voltage Vin and voltage gain G , the proposed SCL-qZSI has lower voltage stress across active switches, capacitors, and diode Din . The current stress of the main power circuit in the proposed inverter during shoot-through interval has a rise for the same load impedance Rl which shows that it has a stronger power processing capability at higher modulation index.

EXPERIMENTAL RESULTS:

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surendhar.A et al.,

ISSN (Online): 2348 – 3539

CONCLUSIONS: This paper presented a

new high-voltage boost impedance-source inverter called a switched-coupled-inductor quasi-Z-source inverter (SCL-qZSI), which can overcome the boost limitations of (q)ZSIs caused by higher component-voltage stresses and poor output power quality, which are attributed to the use of a lower modulation index. The proposed topology is obtained by combining the switched-capacitor SC and a three-winding SCL into the classical qZSI. The charging of the SC through the SCL significantly enhances the boost ability of the proposed inverter, without increasing the turn ratio of the SCL. The proposed inverter also retains all the advantages of the qZSI over the ZSI topology, such as a continuous input current, common ground between the dc-voltage source and the inverter-bridge, lower voltage stress on capacitors, and startup inrush current suppression. The proposed SCL-qZSI adds only one capacitor and two diodes into the classical qZSI, and even with a turn ratio of 1, compared to the other (q)ZSI and SL-(q)ZSI topologies for the same input and output voltage conditions, it has a lower voltage stress on active switches and passive components, better output power quality, and reduced current ripple and flux density swing in the input inductor. The size of the coupled-inductor and the total number of turns for the three windings are also comparable to those of a single inductor in the qZSI and SL-qZSI topologies. The proposed inverter is best suited for applications that require a single-stage high step-up boost inversion of low dc-voltage sources such as fuel cells and PV systems. A comprehensive theoretical analysis of the proposed inverter was performed, and we successfully verified its

performance through simulations and experimental results.

REFERENCES:

[1] R. R. Errabelli, and P. Mutschler, “Fault- tolerant voltage source inverter for permanent magnet drives,” IEEE Trans. Power Electron., vol. 27, no. 2, pp.500-508, Feb. 2012.

[2] B. Sahan, S. V. Araujo, C. Noding, and P. Zacharias, “Comparative evaluation of three-phase current source inverters for grid interfacing of distributed and renewable energy systems,” IEEE Trans. Power Electron., vol. 26, no. 8, pp. 2304-2318, Aug. 2011.

[3] M. Shen, A. Joseph, J. Wang, F. Z. Peng, and D. J. Adams, “Comparison of traditional inverters and Z-source inverter for fuel cell vehicles,” IEEE Trans. Power Electron., vol. 22, no. 4, pp.1453–1463, Jul. 2007.

[4] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 504–510, Mar./Apr. 2003.

[5] F. Z. Peng, M. Shen, and Z. Qian, “Maximum boost control of the Z-source inverter,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 833–838, Jul. 2005.

[6] M. Shen, J. Wang, A. Joseph, F. Z. Peng, L. M. Tolbert, and D. J. Adams, “Constant boost control of the Z-source inverter to minimize current ripple and voltage stress,” IEEE Trans. Ind. Appl., vol. 42, no. 3, pp. 770–778, May/Jun . 2006.

[7] J. Liu, J. Hu, and L. Xu, “Dynamic modeling and analysis of Z source converter-Derivation of ac small signal model and design-oriented analysis,” IEEE Trans. Power Electron., vol. 22, no. 5, pp. 1786–1796, Sep. 2007.

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IEEE Trans. Energy Convers., vol. 22, no. 2, pp. 467–476, Jun. 2007.

[9] F. Z. Peng, X. Yuan, X. Fang, and Z. Qian, “Z-source inverter for adjustable speed drives,” IEEE Power Elec. Lett., vol. 1, no. 2, pp. 33–35, Jun. 2003.

[10] F. Z. Peng, A. Joseph, J. Wang, M. Shen, L. Chen, Z. Pan, E. O.-Rivera and Y. Huang “Z-source inverter for motor drives,” IEEE Trans. Power Electorn., vol. 20, no. 4, pp. 857–863, Jul. 2005.

[11] Y. Huang, M. Shen, F. Z. Peng, and J. Wang, “Z-source inverter for residential photovoltaic systems,” IEEE Trans.

Power Electron., vol. 21, no. 6, pp. 1776– 1782, Nov. 2006.

[12] F. Guo, L. Fu, C.-H. Lin, C. Li, W. Choi, and J. Wang, “Development of an 85-kW bidirectional quasi-Z-source inverter with dc-link feed-forward compensation for electric vehicle applications,” IEEE Trans. Power

Electron., vol. 28, no. 12, pp. 5477– 5488, Dec. 2013.

[13] X. P. Fang, Z. M. Qian, and F. Z. Peng, “Single phase Z-source PWM ac-ac converters,” IEEE Power Electron. Lett., vol. 3, no. 4, pp. 121–124, Dec. 2005.

[14] M.-K. Nguyen, Y.-G. Jung, and Y.-C. Lim, “Single-phase ac-ac converter based on quasi-Z-source topology,”

Figure

Fig. 3. Simplified equivalent circuit of the proposed inverter during, (a) shoot-through state, and (b) non-shoot-through state

References

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