International Journal of Electrical Electronics Computers & Mechanical Engineering (IJEECM)

ISSN: XXXX-XXXX www.ijeecm.org Volume 1 Issue1 ǁ Nov. 2015

IJEECM journal of Electrical Engineering (ijeecm-jee)

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Grid Interconnection of Multiple Hybrid Sources Input of DC-to-DC Converters

Guggulothu Gopalanaik1, D Sunder Singh2

1,2 Electrical & Electronics Department, 1,2 Gudlavalleru Engineering College, Gudlavalleru, Krishna Dist., A.P(India)

Abstract— This paper suggests a four-port dc-to-dc power conversion circuit for hybrid input sources are interconnected with the grid system. With the four-port converter, the load can be powered from four different dc sources, which can be a combination of four from a solar-cell panel, a fuel-cell set, a battery bank, etc.. The power conversion circuit consists of three active power switches by commonly using an inductor and an output filter capacitor. By adjusting the duty-ratio of the active power switch, the voltage regulation at the output as well as the power coordination between four input sources can be made. The circuit operation is described in detail with the extension of MATLAB/simulink results. Keywords— Four port DC-DC Converter, Power coordination, Hybrid sources, Grid interconnection.

I. INTRODUCTION

THE increasing tension on the global energy supply has resulted in greater interest in renewable energy resources. This presents a significant opportunity for distributed power generation (DG) systems using renewable energy resources, including wind turbines, photovoltaic (PV) generators, small hydro systems, and fuel cells. However, these DG units produce a wide range of voltages due to the fluctuation of energy resources and impose stringent requirements for the inverter topologies and controls. Usually, a boost-type dc–dc converter is added in the DG units to step up the dc voltage. This kind of topology, although simple may not be able to provide enough dc voltage gain when the input is very low, even with an extreme duty cycle. Also, large duty cycle operation may result in serious reverse-recovery problems and increase the ratings of switching devices. Furthermore, the added converter may deteriorate system efficiency and increase system size, weight, and cost.

A conventional power electronic converter is supplied from a single input source, but may provide

multiple outputs. In the case that three or more voltage or current levels are required by the loads, a transformer with multiple output windings is employed [1], [2]. On the other hand, however, for some applications, the loads may not be powered from a single source but from three or more input sources specified by different voltage, current, and power ratings [3-13]. For example, a solar power based street lamp is mainly supplied from solar cells, but needs a subordinate battery power. Such a prerequisite can be found more and more frequently in applications with renewable power generation, especially in a hybrid system with different kinds of power sources.

Conventionally, multiple power converters are needed to convert power from manifold power sources. Such a simple solution is obviously of high cost and inefficient. To cope with this prerequisite, this paper proposes a four-port dc-to-dc converter, which is capable of converting power from three inputs sources to the load. The hybrid power sources deliver energy to the load alternatively by switching active power switches on and off, respectively. The power converter can be utilized for the applications with three different dc power sources, such as solar cells, fuel cells, batteries, or a dc power grid.

II. CIRCUIT CONFIGURATION The power conversion circuit of the proposed

hybrid input dc-to-dc converter is shown in Fig. 1, which is essentially an integration of a boost converter and a buck-boost converter. The integrated power converter consists of three active power switches, S1, S2 and S3 for boost conversion and buck-boost conversion, respectively, by commonly using a diode, D, an inductor, L, and a filter capacitor, C. The three dc sources, Vin1,Vin2 and Vin3, are treated as the primary and secondary, tertiary sources, depending on the capacity and the dependability of the power sources. The primary source has a capability of providing more energy to the load and is more durable than the secondary and tertiary source is. Three active power switches are turned on and off periodically at a same frequency but are activated alternately in a period. The

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powers delivered by three sources are coordinated by controlling their duty-ratios.

Fig.1.Triple source four port DC to DC Converter

III. CIRCUIT OPERATION The power conversion circuit can be operated at

the continuous conduction mode (CCM) or the discontinuous conduction mode (DCM), depending on the continuity of the inductor current. According to the status of four power switches, S1, S2,S3 and D, this circuit operation can be divided into five stages, as shown in Fig. 2. In which, the duty-ratios of three active power switches are d1, d2 and d3 respectively. At the CCM, the power conversion circuit is operated through Stages I, II, III and IV sequentially in a switching period, TS . Stage V occurs only at the DCM when the inductor current falls down to zero. The steady state operation is described in the followings.

Stage I [t0~t1]: As the active power switch S3 is turned on, the diode D will be reversely biased and turned off. The inductor is charged by the tertiary voltage source, V3, and the inductor current, iL, increases linearly.

In this stage, the filter capacitor delivers the stored energy to the load. Stage II [t1~t2]: As S3 is turned off, the active power switch, S2 is turned on, and the diode D is now still turned off. The secondary dc power source is providing electromotive force for charging the inductor in this stage. At the same time, iL increases linearly after preceding stage.

The filter capacitor is still providing energy to the load in

this stage. Stage III [t2~t3]: As S2 is turned off, the active power switch, S1 is turned on, and the diode D is now still turned off. The primary dc power source is providing electromotive force for charging the inductor in this stage. At the same time, iL increases linearly after preceding stage.

The filter capacitor is still providing energy to the load in

this stage. Stage IV [t3~t4]: When the power switch S2 is turned off, the diode D is forced to be turned on to conduct the inductor current. In this stage, the load draws energy from the primary source and the inductor.

Stage V [t4~t5]: This stage only happened when the inductor current declines to zero, both S and D are turned off. The filter capacitor supplies a current to the load, and voltage on the capacitor declines.

Fig. 3 depicts the theoretical waveforms on the key components of the power converter for CCM and DCM operations, respectively.

IV. CIRCUIT ANALYSIS WITHOUT GRID INTEGRATION

A. Continuous Conduction Mode

The relationship between the four input voltages,

V1, V2 and V3, and the output voltage, Vo, can be obtained by the voltage second balance.

(a)stage-I

(b)stage-II

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(C)stage-III

(d)stage-IV

(e)stage-V

Fig.2.Operation Stages

Fig.3.Grid integrated system

The output voltage of the power converter is the sum of V1

and the buck-boost conversion output voltage from V1, V2

and V3. This equation indicates the output voltage is always higher than the input voltage. In practice, the sum of d1, d2

and d3 in one cycle is limited to be less than 0.9.

(a)CCM

(b)DCM

(C)Voltage at PCC

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(d)Current at PCC

Fig.4.Simulation Results

Theoretically, the output power is the sum from four inputs.

In (6), I'1 is the input current of the primary source at stage II while I1 is the sum of I'1 and the output current IO.

Then, the output current can be obtained as

Fig. 4 shows the relationship between the voltage step-up ratio with respect to the duty-ratios of the four active power switches under different input voltages. In which, the ratio between d1 and d2 is denoted by α1 and d1 and d3 is denoted by α2.

And, the ratio between the four input voltages is denoted by β1 & β2

It is noted that d2 & d3 are the dominant parameters that affects the variation of the output voltage rather than d1. In the figure, the red curve represents the characteristic of boost conversion when V2 & V3 are zero. B. Discontinuous Conduction Mode

With a smaller inductance, the inductor current may decrease to zero when both active power switches have been turned off. The boundary inductance can be calculated as

By substituting (5) into (12), the boundary inductance can be rewritten as

The duty-ratio for decreasing the inductor current is denoted by d4, Then the relation between three input voltage and the output voltage can be obtained as

The output current of the converter is

TABLE I. CIRCUIT PARAMETERS

PRIMARY INPUT VOLTAGE, VIN1 10V

SECOND INPUT VOLTAGE, VIN2 5 V - 30 V

THERED INPUT VOLTAGE, VIN2 5 V - 30 V

CONSTANT LOAD CURRENT, ILOAD 0.3 A

INDUCTANCE, L 237 UH

FILTER CAPACITANCE, C 330 UF

IGBT, S1 , S2 AND S3 IXGR35N120B

DIODE, D PSR10C40

V. CONCLUSION

This paper proposed a four-port dc-to-dc power conversion circuit which can be powered from three input sources to interconnection of grid. The power coordination between three input sources and the voltage regulation can be made by adjusting the duty-ratios of three active power switches. As compared with the conventional multiple-input power converter, the proposed conversion circuit has less component count. The power conversion circuit can be used in a small-scale distributed generation system with three different dc power sources.

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VI. REFERENCES

[1]Chin-Sien Moo, Yao-Ching Hsieh, “DC-to-DC Converter with Hybrid Input Sources” 3rd IEEE International Symposium on Power Electronics for Distributed Generation Systems (PEDG) 2012. [2] B. G. Dobbs, P. L. Chapman, “A Multiple-Input DC-DC Converter Topology,” IEEE Power Electronics Letters, vol.1, no.1, pp. 6-9, March 2003. [3] K. P. Yalamanchili and M. Ferdowsi, “Review of Multiple Input DC-DC Converters for Electric and Hybrid Vehicles,” in Proc. IEEE VPPC Conf., September 2005, pp. 160-163. [4] Y. M. Chen, Y. C. Liu, and S. H. Lin, "Double-input PWM DC/DC converter for high/low voltage sources," in Telecommunications Energy Conference, 2003. INTELEC '03. The 25th International, 2003, pp. 27-32. [5] D. Liu and H. Li, “A Novel Multiple-Input ZVS Bidirectional DC-DC Converter,” in Proc. IEEE IECON Conf., Nov.r 2005, pp. 579-584. [6] H. Tao, A. Kotsopoulos, J. L. Duarte, and M. A. M. Hendrix, “Family of Multiport Bidirectional DC–DC

Converters,” IEE Proceedings-Electric Power Applications, vol. 153, no. 3, pp. 451-458, May 2006. [7] N. Vazquez, A. Hernandez, C. Hernandez, E. Rodriguez, R. Orosco, and J. Arau, “A Double Input DC/DC Converter for Photovoltaic/Wind Systems,” in Proc. IEEE PESC Conf., Jun. 2008, pp. 2460-2464. [8] A. Khaligh, “A Multiple-Input Dc-Dc Positive Buck-Boost Converter Topology,” in Proc. IEEE APEC, Feb. 2008, pp. 1522-1526. [9] S. H. Choung and A. Kwasinski, “Multiple-Input DC-DC Converter Topologies Comparison,” in Proc. IEEE IECON Conf., Nov. 2008, pp.2359-2364. [10] K. Gummi and M. Ferdowsi, “Derivation of New Double-Input DC-DC Converters Using H-Bridge Cells as Building Blocks,” in Proc. IEEE IECON Conf., November 2008, pp. 2806-2811. [11] R. C. Zhao and A. Kwansinski, “Multiple-Input Single Ended Primary Inductor Converter (SEPIC) Converter for Distributed Generation Applications,” in Proc. IEEE ECCE Conf., Sep. 2009, pp. 1847-1854.