International Journal of Research in Information Technology (IJRIT)
www.ijrit.com ISSN 2001-5569
Grid Interfacing Of PV/Battery Hybrid Energy Conversion System with Power Quality Improvement Features Based On
Interleaved Boost Converter
M.Veeranjaneyulu, K.Raghavaiah, P.A.Prasad
M.Tech Student, EEE, QISCET, Ongole, A.P, (India) Asst.Professor, EEE, QISCET, Ongole, A.P, (India) Associate Professor, EEE, K.L University, Guntur, A.P, (India)
Abstract----This Paper presents the Grid interfacing of PV/Battery Hybrid energy conversion system with power quality enrichment features based on interleaved boost converter. The commonly used renewable energy systems include photovoltaic cells and fuel cells. A proper DC-DC converter is proposed for highly efficient non conventional energy systems. Interleaved Boost Converter (IBC) topology is discussed in this paper for renewable energy applications. Grid integration of photo voltaic (PV)/Battery hybrid energy conversion system with (i) multi-functional features of micro grid-side bidirectional voltage source converter (µGVSC) (ii) tight voltage regulation capability of battery converter (iii) MPPT tracking performance of high gain integrated cascaded boost (HGICB) dc-dc Converter with quadratic gain and less current ripple are presented in this paper. The advantages of interleaved boost converter compared to the classical boost converter are low input current swell, More efficiency, quicker transient reaction, reduced electromagnetic emission and improved reliability The battery energy storage system (BESS) is regulated to balance the power between PV generation and utility grid The waveforms of input, inductor current ripple and output voltage ripple are obtained using MA TLAB/SlMULINK. The design equations for IBC have been presented.
Key Words---µGVSC, HGICB, Interleaved boost converter (IBC)
I. INTRODUCTION
Fossil fuels are energy sources such as coal, oil and natural gas. The world virtually depends on the Supply of fossil-fuel for energy. But the common issue is that fossil-fuels are running out. It would take millions of years to completely restore the fossil fuels that we have used in just a few decades.
This means fossil fuels are non-renewable sources of energy. Renewable energy comes in as a resolution for this global issue. Renewable energy is any natural source that can replenish itself naturally over a short amount of time. Renewable energy comes from many commonly known sources such as solar energy, wind energy, Hydal energy and geothermal energy. Renewable energy sources are wonderful options because they are limitless.
Also another great benefit from using renewable energy is that many of them do not pollute our air and water, the way burning fossil fuels does. Any such renewable energy system requires a suitable converter to make it efficient. Interleaved boost converter is one such converter that can be used for these applications.
Many DC-DC converter topologies are available to track the MPP in PV generating system. Cascade connection of conventional converters provides wider conversion ratios [1]. One of the major advantages of these converters is a high gain and low current ripple. However, this configuration has a drawback that the total
only when the required number of stages is not very large, else the efficiency will be reduced. However, this class of converters for PV applications is not reported in the technical literature.
Micro-grid power converters can be classified into (i) grid feeding, (ii) grid-supporting, and (iii) grid- forming power converters [2]. There are many control schemes reported in the literature
Such as synchronous reference theory, power balance theory, and direct current vector control [3], [4], for control of µG-VSC in micro grid application. These algorithms require complex coordinate transformations, which is cumbersome. Compared to the control strategies mentioned above, the Instantaneous symmetrical component based control proposed in this paper for micro-grid applications is simple in formulation, avoids interpretation of instantaneous reactive power and needs no complex transformations.
The Interleaved boost converter has high voltage step up, reduced voltage ripple at the output, low switching loss, reduced electromagnetic interference and faster transient response. Also, the steady-state voltage ripples at the output capacitors of mc are reduced. Though IBC topology has more inductors increasing the complexity of the converter compared to the conventional boost converter it is preferred because of the low ripple content in the input and output sides. In order to reduce this complexity, this paper investigates the benefits of coupled, uncoupled and inversely inductors for mc. Detailed analysis has been done to study the ripple content of all the three types of the converter. The suitable mc for fuel cell applications is proposed [5].
Gating pulses are generated using pulse generator. Simulations have been performed to validate the concepts.
This paper is structured as follows: In section 2, system description. In section 3, modeling’s of various components are presented. The proposed control strategies for HGICB DC-DC Converter, Interleaved Boost Converter (IBC) and µG-VSC are discussed in section 4. The simulation results are presented in section 5. With concluding remarks in section 6.
II. SYSTEM DESCRIPTION
The envisaged system consists of a PV/Battery hybrid system with the main grid connecting to non- linear and unbalanced loads at the PCC as shown in the Fig. 1. The photovoltaic system is modeled as nonlinear voltage sources [6]. The PV array is connected to HGICB dc-dc converter and interleaved boost converter are shown in Fig. 1, which are coupled at the dc side of a µG-VSC. The HGICB dc dc converter is connected to the PV array works as MPPT controller and battery converter is used to regulate the power flow between dc and ac side of the system.
Fig -1: Hybrid Energy Conversion System under consideration
III. MODELING AND CONTROL A. PV Array Model
The mathematical model of PV system referred in [6] is used in this work.
B. Operation of IBC
The two phases of the converter are driven 180 degrees out of phase, this is because the phase shift to be provided depends on the number of phases given by 360/n where n stands for the number of phases[7].
Fig -2: Circuit diagram of a two phase uncoupled IBC
Since two phases are used the ripple frequency is doubled and results in reduction of voltage ripple at the output side. The input current ripple is also reduced by this arrangement.
When gate pulse is given to the first phase for a time t1, the current across the inductor rises and energy is stored in the inductor. When the device in the first phase is turned OFF, the energy stored is transferred to the load through the output diode D. The inductor and the capacitor serve as voltage sources to extend the voltage gain and to reduce the voltage stress on the switch. The increasing current rate across the output diode is controlled by inductances in the phases. Gate pulse is given to the second phase during the time t1 to t2 when the device in the first phase is OFF. When the device in the phase two is ON the inductor charges for the same time and transfers energy to the load in a similar manner as the first phase. Therefore the two phases feed the load continuously.
IV. DESIGN METHODOLOGY OF IBC
The design methodology for all types of IBC's require a selection of proper values of inductor, capacitor and proper choice of the power semiconductor devices to reduce the switching losses[8]. The steps involved in designing IBC are as follows [9]:
• Decision of duty ratio and number of phases
• Selection of Inductor values
• Selection of power semiconductor switches
• Design of output filter
1) Selection of duty ratio and number of phases two phase IBC is chosen since the ripple content reduces with increase in the number of phases. If the number of the phases is increased further, without much decrease in the ripple content, the complexity of the circuit increases very much, thereby increasing the cost of implementation.
Fig –3: Switching pattern for two phase IBC
The input current ripple can be zero at specific duty ratios which are multiples of l/N, where N stands for the no of phases. Here the number of phases is two therefore the duty ration is taken as 0.5. The switching pattern is shown in Figure 3.
A. Generation of reference currents for µG-VSC
The main aim of the µG-VSC control is to cancel the effects of unbalanced and harmonic components of the local load, while supplying pre-specified amount of real and reactive powers to the load. Upon successfully meeting this objective, the grid current ig will then be balanced and so will be the PCC voltage vp provided, grid voltage vg is balanced. Let us denote the three phases by the subscripts a, b and c. Since ig is balanced, we can write:
iga + igb + igc = 0 (2)
From the Fig. 1, Kirchhoff’s current law (KCL) at PCC gives ig,abc + iinv,abc = iL,abc . (3)
Therefore, from (2) and (3), we can write as:
iinv,a + iinv,b + iinv,c = iL,a + iL,b + iL,c . (4)
Since ig is balanced due to the action of the compensator, the voltage vp will also become balanced. Hence, the instantaneous real powers Pg will be equal to its average component. Therefore, we can write
Pg = vpa iga + vpb igb + vpc igc (5) TABLE I
SYSTEM PARAMETERS
Solving above equations, the µG-VSC reference currents are obtained as follows:
(6)
and Qs = Ql − Qµs, and by substituting β Ps = √Qs 3 into the equation (9), the modified G-VSC reference current equations in terms of active and reactive components are obtained as:
(7)
In equations (6) and (7), Pµs, Plavg, and Ql are the available micro source power, average load power, and load reactive power respectively. Ploss denotes the switching losses and ohmic losses in actual compensator. The term Plavg is obtained using a moving average filter of one cycle window of time T in seconds.
V. SIMULATION RESULTS
The proposed control strategies for PV hybrid generating system are developed and simulated using Matlab/SIMULINK under different solar insolation levels with IBC.
Irradiance(kw/m^2)
Load Currents (A)
Grid Currents (A)
Fig -5: Simulation results using proposed control approach for Micro-grid side VSC: (a) Insolation Changes (b) Load currents (c) Grid currents (d) µG-VSC currents.
VI. CONCLUSIONS
Interleaved boost converter has so many advantages and is a suitable converter for renewable energy applications. The performance of PV/Battery hybrid energy conversion system has been demonstrated with the application of modified instantaneous symmetrical components theory to µG-VSC proposed in this paper, an efficient control strategy is also proposed for battery interleaved boost converter to regulate the dc bus voltage tightly, under varying solar insolation and dc load conditions. HGICB converter topology is used to track the MPPT with high gain and less current ripple. The µG-VSC is able to inject the generated power into the grid along with harmonic and reactive power compensation for unbalanced non-linear load at the PCC simultaneously. The system works satisfactorily under dynamic conditions. The simulation results under an unbalanced non-linear load with current THD of 12% confirm that the µGVSC can effectively inject the generated active
Power along with power quality improvement features and thus, it maintains a sinusoidal and UPF current at the grid side with THD of 1.61%.
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BIBLIOGRAPHY
Mr. M.Veeranjaneyulu was born in Andhra Pradesh, India. He is pursuing his M.Tech (Power systems control & Automation) degree in Electrical and Electronics Engineering from QIS College of engineering & Technology, ONGOLE, Jawaharlal Nehru Technological University, Kakinada. His area of interest includes Power Electronics, power systems, and machines.
E-mail: [email protected]
Mr. Katuri.Raghavaiah was born in Andhra Pradesh,India.He is working as assistant professor in Electrical and Electronics Engineering from QIS College of engineering &Technology, ONGOLE, Jawaharlal Nehru Technological University, Kakinada. His area of interest includes Power Electronics, power systems, and machines.
E-mail: [email protected]
