International Journal of Communication and Computer Technologies Volume 03 – No. 2 Issue: 06 June 2015 ISSN NUMBER : 2278-9723

DESIGN AND IMPLEMENTATION OF EFFICIENT MPPT FOR SOLAR POWER GENERATION WITH SEVEN LEVEL INVERTER 1

2

J.Karthika, ME (PED), PG Student, Department of EEE, PGP College of Engineering and Technology A.SenthamaraiKannan, Associate Professor, Department of EIE, PGP College of Engineering and Technology

ABSTRACT Designing and Implementation of a new solar power generation system, which is composed of a dc/dc power, MPPT controller using Incremental Conductance Algorithm and a seven-level inverter. The dc/dc power converter integrates a dc– dc boost converter and a transformer to convert the output voltage of the solar cell array into two independent voltage sources with multiple relationships. This new seven-level inverter is configured using a capacitor selection circuit and a full-bridge power converter, connected in cascade. Number of devices of the proposed seven-level inverter is fewer than that of the conventional multi-level inverters. The capacitor selection circuit converts the two output voltage sources of dc–dc power converter into a three-level dc voltage, and the full-bridge power converter further converts this three-level dc voltage into a seven-level ac voltage. In this way, the proposed solar power generation system generates a sinusoidal output current that is in phase with the utility voltage and is fed into the utility. The salient features of the proposed seven-level inverter are that only six power electronic switches are used, and only one power electronic switch is switched at high frequency at any time.

I. INTRODUCTION A cascade multilevel inverter is a power electronic device built to synthesize a desired AC voltage from several levels of DC voltages. Such inverters have been the subject of research in the last several years, where the DC levels were considered to be identical in that all of them were batteries, solar cells, etc. In, a multilevel converter was presented in which the two separate DC sources were the secondary‟s of two transformers coupled to the utility AC power. In contrast, in this paper, only one source is used without the use of transformers. The interest here is interfacing a single DC power source with a cascade multilevel inverter where the other DC sources are capacitors. Currently, each phase of a cascade multilevel inverter requires n DC sources for 2n+1 levels in applications that involve real power transfer In this work, a scheme is proposed that allows the use of a single DC power source (e.g., battery or fuel cell stack) with the remaining n - 1 DC sources being capacitors. It is shown that one can simultaneously maintain the DC voltage level of the

capacitors and choose a fundamental frequency switching pattern to produce a nearly sinusoidal output. II OPERATION AND DESIGN The concept of utilizing multiple small voltage levels to perform power conversion was patented by an MIT researcher over twenty years ago. Advantages of this multilevel approach include good power quality, good electromagnetic compatibility (EMC), low switching losses, and high voltage capability. The main disadvantages of this technique are that a larger number of switching semiconductors are required for lower-voltage systems and the small voltage steps must be supplied on the dc side either by a capacitor bank or isolated voltage sources. The first topology introduced was the series H-bridge design . This was followed by the diode clamped converter which utilized a bank of series capacitors. In this design, the semiconductors block the entire dc voltage, but share the load current. Several combinational designs have also emerged some involving cascading the fundamental topologies. These designs can create higher power quality for a given number of semiconductor devices than the fundamental topologies alone due to a multiplying effect of the number of levels. Recent advances in power electronics have made the multilevel concept practical. In fact, the concept is so advantageous that several major drives manufacturers have obtained recent patents on multilevel power converters and associated switching techniques. Furthermore, several IEEE conferences now hold entire sessions on multilevel power conversion. It is evident that the multilevel concept will be a prominent choice for power electronic systems in future years, especially for medium-voltage operation. III DC TO DC CONVERTER AND MPPT The switching converters convert one level of electrical voltage into another level by switching action. They are popular because of their smaller size and efficiency compared to the linear regulators. DC-DC converters have a very large application area. These are electronic devices to

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DC distribution system has been considered as an effective solution to Internet Data Centers (IDC) where electronic loads which prefer dc-type power, account for most of the energy consumption and battery-applied Uninterruptible Power Supplies (UPS) are essential for system reliability. In dc-interfaced IDC, the system efficiency is improved streamlining the interfaces among the utility source, dc loads and battery storage device. While ac gridconnected PV systems are well known due to their wide application, the concept of the dc-interfaced PV systems would be unfamiliar to the public. EFFICIENCY provide DC voltages. The wide variety of circuit topology ranges from single transistor buck, boost and buck-boost converters to complex configurations comprising two or four devices and employing soft-switching or resonant techniques to control the switching losses. There are some different methods of classifying DCDC converters. One of them depends on the isolation property of the primary and secondary portion. The isolation is usually made by a transformer, which has a primary portion at input side and a secondary at output side. Feedback of the control loop is made by another smaller transformer or optically by opto coupler. Therefore, output is electrically isolated from input. However, in portable devices, since the area to implement the bulky transformer and other off-chip components is very big and costly, so non-isolation DC-DC converters are more preferred.



Buck converter (step down DC-DC converter),



Boost converter (step up DC-DC converter),

COST



Buck-Boost converter (step converter, opposite polarity),



Cuk converter (step up-down DC-DC converter).

The reduced number of power stages and components, and availability of simple structure and control would lead to cost reduction. In addition, maintenance cost can also be reduced due to the improved reliability.

up-down DC-DC

BOOST CONVERTER

Depicts a step-up or a PWM boost converter. It is comprised of DC input voltage source VS, boost inductor L, controlled switch S, diode D, filter capacitor C, and load resistance R. The converter waveforms in the CCM are presented. When the switch S is in the ON state, the current in the boost inductor increases linearly. The diode D is OFF at the time. When the switch S is turned off, the energy stored in the inductor is released through the diode to the input RC circuit. B.

RELIABILITY Electrolytic capacitors are employed to decouple ac side from PV side to guarantee high MPPT efficiency, but their short lifetime heavily affects the reliability of a PV generation system while the lifetime of PV panels continuously.

Non-isolated DC/DC converters can be classified as follows:

A.

In addition to the streamlined power flow without redundant stages, utilization of simple topologies and control methods would additionally improve the conversion efficiency. On the other hand, the ac counterpart requires complicated structure and control for injecting sinusoidal current. While the ac system requires PV power circuit be designed for the peak instantaneous power, which is double of average power, the dc PV system can be designed for the rated power, which would also improve its conversion efficiency. In addition, the elimination of ac fluctuation reduces line frequency voltage ripple on PV side which can contribute to achieving higher MPPT efficiency.

C.

CURRENT SENSOR-LESS BCM BOOST CONVERTER

Various topologies can be utilized as a PV interface. In this paper, a boost converter is selected for the interface circuit due to its simplicity and high efficiency considering the voltage and power rating of a BIPV module. However, conventional boost converters in Continuous Conduction Mode (CCM) suffer from high voltage stress on its active switch and reverse recovery problem of its diode.

DC DISTRIBUTION WITH PV GENERATIONS

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karthika and senthamaraikannan To overcome these drawbacks, BCM is employed in which Zero Voltage Switching (ZVS) can be achieved and the diode reverse recovery problem is avoided by letting it smoothly turn off at zero current.

analysis with the increasing attention to energy savings and battery life in mobile devices, microprocessors and chipsets integrate different functional blocks such as I/O, analog circuits, memory, and graphics on the same die.

D.

For power efficiency, each block may operate at a different DC supply voltage, resulting in multiple DC-DC power converters on the same printed circuit board, which occupy growing fraction of the board area. Integrated on-die DC-DC converters may provide a solution for the PCB resource issue, enabling a larger number of different on-chip voltage supplies. Power efficiency is one of the most critical parameters of on-chip DC-DC converters. These converters require inductors which cannot be efficiently implemented on die, but can be embedded inside the package. Typically, these inductors have an air-core (no ferromagnetic materials are used), and therefore exhibit a low inductance in the range of few nH. A buck converter needs to operate at high switching frequencies (hundreds of MHz) for the inductor to be sufficiently small.

MATHEMATICAL ANALYSIS OF BCM

Voltage and current waveforms of the BCM boost converter during a period are depicted in Fig. 5. It should be noted that the third subinterval exists during which inductor L and parasitic capacitor Cross of switch S resonate. This negative current interval TR from T0 to T1 should be considered for high reliability of current estimation especially in light load conditions because it is independent of power level. Considering this resonance interval, mathematical analysis of the three operation modes is carried out and it is utilized to estimate the PV current information in the proposed algorithm. E.

CONVERSION EFFICIENCY OPTIMIZATION

As the output power decreases, the converter operates in QRM using valley skipping and low frequency DCM to minimize the switching loss. As demonstrated in the efficiency optimizer determines the operation mode. In QRM, the ZCD signals are intentionally ignored and the pulse width modulation (PWM) controller turns on the switch at the next valley for high efficiency by achieving ZVS. In DCM, the switching loss is further reduced by lowering the switching frequency well below that of BCM. To determine when the efficiency optimizer changes the operation mode, loss analysis should be conducted for the target application. Results of the loss analysis for the target system specification and circuit parameters are well matched with the previous discussions. The analysis considers conduction, turn-on, and turn-off losses of the switch, conduction loss of the diode, and copper and core losses of the magnetic inductor. No reverse recovery loss of diode is included because soft turn-off of diode is achieved in the entire operation range. It is clear that BCM is the most efficient from medium to high power range, QRM is efficient from 20 to 40 W, and low frequency DCM is effective from 0 to 20 W due to the ZVS operation and the minimized switching loss. It is assumed that the converter operates at 20 kHz in DCM to prevent audible noise generation. The number of valley skipping operations affects the efficiency of QRM as shown in Fig. 8. However, it is fixed at 1 in the target system, as the power range where QRM with n = 2 has higher efficiency than that with n = 1, is covered by DCM according to the loss

IV. SOLAR PANEL A solar panel (photovoltaic module or photovoltaicpanel) is a packaged, interconnected assembly of solar cells,also known as photovoltaic cells. The solar panel can beused as a component of a larger photovoltaic system togenerate and supply electricity in commercial and residentialapplications.Because a single solar panel can produce only a limitedamount of power, many installations contain several panels.A photovoltaic system typically includes an array of solarpanels, an inverter, and sometimes a battery andinterconnection wiring. V. MPPT CONTROL TECHNIQUE The weather and load changes cause the operation of a PV system to vary almost all the times. Adynamic tracking technique is important to ensure maximum power is obtained from thephotovoltaic arrays. The following methods are the most fundamental MPPT Technique, andthey can be developed using micro controllers. The MPPT Technique operates based on the truth that the derivative of the output power (P) withrespect to the panel voltage (V) is equal to zero at the maximum power point. In the literature,various MPP algorithms are available in order to improve the performance of photovoltaic systemby effectively tracking the MPP. However, most widely used MPPT Techniqueare consideredhere, they are: 1. Perturb and Observe (P&O)

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Design and implementation of efficient MPPT for solar power generation with seven level inverter

2. Incremental Conductance (InCond) 3. Constant Voltage Method. A. Perturb and Observe (P&O) Method The most commonly used MPPT Technique is P&O method. This Technique uses simple feedbackarrangement and little measured parameters. In this approach, the module voltage is periodicallygiven a perturbation and the corresponding output power is compared with that at the previous perturbing cycle. In this algorithm a slight perturbation is introduce to the system. Thisperturbation causes the power of the solar module various. If the power increases due to theperturbation then the perturbation is continued in the same direction. After the peak power isreached the power at the MPP is zero and next instant decreases and hence after that theperturbation reverses as shown in Figure 3.1. When the stable condition is arrived the algorithm oscillates around the peak power point. Inorder to maintain the power variation small the perturbation size is remain very small. Thetechnique is advanced in such a style that it sets a reference voltage of the module correspondingto the peak voltage of the module. A PI controller then acts to transfer the operating point of themodule to that particular voltage level and this technique is very popular and simple.

When the optimum operating point in the P-V plane is to the right of the MPP, we have (dIPv/dvPv)+(IPV/VPV)0. The MPP can thus be tracked by comparing the instantaneous conductance Ipv/Vpvto the incremental conductance dIpv/dVpv. Therefore the sign of the quantity (dIpv/dVpv)+(Ipv/Vpv) indicates the correct direction of perturbation leading to the MPP. Once MPP has been reached, the operation of PV array is maintained at this point and the perturbation stopped unless a change in dIpvis noted. In this case, the algorithm decrements or increments Vrefto track the new MPP. The increment size determines how fast the Maximum power point is tracked. Through the IC algorithm it is therefore theoretically possible to know when the MPP has been reached, and thus when the perturbation can be stopped. The IC method offers good performance under rapidly changing atmospheric conditions. There are two main different IC methods available in the literature. The classic IC algorithm (ICa) requires the same measurements shown in Fig.10, in order to determine the perturbation direction a measurement of the voltage Vpvand a measurement of the current Ipv. The Two-Model MPPT Control (ICb) algorithm combines the CV and the ICa methods: if the irradiation is lower than 30% of the nominal irradiance level the CV method is used, other way the ICa method is adopted. Therefore this method requires the additional measurement of solar irradiation S as shown in Fig.3.2

Figure 3.2.Block Diagram of Incremental Conductance Algorithm Figure 3.1. Graph Power versus Voltage for Perturb and Observe Algorithm B. Incremental Conductance Method The Incremental Conductance (IC) algorithm is based on the observation that the following equation holds at the MPP. [dIPV/dVPV] + [IPV/VPV]=0(1) VI. BLOCK DIAGRAM OF PROPOSED SYSTEM whereIPVand VPVare the PV array current and voltage, respectively.

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theproposed solar power generation system generates a sinusoidaloutput current that is in phase with the utility voltage and is fedinto the utility, which produces a unity power factor. As canbe seen, this new seven-level inverter contains only six powerelectronic switches, so the power circuit is simplified. A. OUTPUT CHARACTERISTICS

Figure.6.1 Proposed Block diagram of the seven level

H-Bridge S.No

Output Voltage

ON switches

OFFswithces

Levels

1 2 3 4 5

S1,S2 S1,S2 S1,S2 S1,S2 S3,S4

S3,S4 S3,S4 S3,S4 S3,S4 S1,S2

+3Vdc +2Vdc +1Vdc 0 -1Vdc

6

S3,S4

S1,S2

-2Vdc

7

S3,S4

S1,S2

-3Vdc

Seven level inverter with new MPPT Technique Figure.6.1shows the configuration of the proposed solar power generation system. The proposed solar power generation system is composed of a solar cell array, a dc–dc power converter, anda new seven-level inverter. The solar cell array is connected to the dc–dc power converter, and the dc–dc power converter is a boost converter that incorporates a transformer with a turn ratioof 2:1. The dc–dc power converter converts the output power of the solar cell array into two independent voltage sources with multiple relationships, which are supplied to the seven-level inverter. This new seven-level inverter is composed of a capacitor selection circuit and a full-bridge power converter, connected in a cascade. The power electronic switches of capacitor selection circuit determine the discharge of the two capacitors whilethe two capacitors are being discharged individually or in series.Because of the multiple relationships between the voltagesof the dc capacitors, the capacitor selection circuit outputs athree-level dc voltage. The full-bridge power converter furtherconverts this three-level dc voltage to a seven-level ac voltagethat is synchronized with the utility voltage. In this way,

Figure 6.4 Seven-level output phase voltage and each HbridgeOutput voltage. B.

PERFORMANCE COMPARISON

Table 6.1 Performance comparison of Proposed system with Existing system VII. CONCLUSION Design of an efficient solar power generation system which converts the dc energy generated by a solar cell array efficiently into ac energy that is fed into the utility is obtained. The proposed solar power generation system is composed of a dc–dc power converter and a seven level inverter with Incremental Conductance MPPT. For nonvarying conditions, the two algorithms performed similarly, Converters Efficiency

Existing

Proposed

Input

Output

Input

output

Power in Watts 30.199

24.583

30.199

25.5424

230

201.5

230

208.8

0.1313

0.1120

0.1313

0.1228

Voltage in Volts Current in Amps Efficiency

81.15 %

84.58%

and both oscillated around the MPP. The incremental conductance method has a slight advantage, and could potentially oscillate lightly less due to turning around quicker once passing the MPP. This reduces the switching power loss and improves the power efficiency. The voltages of the two

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karthika and senthamaraikannan dc capacitors in the proposed seven-level inverter are balanced automatically, so the control circuit is simplified. And concluding that the Incremental conductance method has high power generation compare to perturb and observer method which result in higher efficiency.

VIII. FUTURE ENHANCEMENT The system can be extended for more voltage range by increasing the step level. Increase in more voltage range will increases the voltage gain and efficiency of the Proposed system. When voltage and Current range increases automatically Efficiency of the circuit also increases. REFERENCES 1) E. Miller, “Smart grids – a smart idea?,” Renewable Energy Focus Magazine, vol. 10, pp. 62-67, Sep.-Oct. 2009. H. Yang, Z. Wei, and L. Chengzh, “Optimal design and technoeconomic analysis of a hybrid solar-wind power generation system,” Applied Energy, vol. 86, pp. 163-169, Feb. 2009. 3) S. Dihrab, and K. Sopian, “Electricity generation of hybrid PV/wind systems in Iraq,” Renewable Energy, vol. 35, pp. 13031307, Jun. 2010. 4) J.P. Reichling, and F.A. Kulacki, “Utility scale hybrid wind-solar thermal electrical generation: a case study for Minnesota,” Energy, vol. 33, pp.626-638, Apr. 2008. 5) O. Ekren, B.Y. Ekren, and B. Ozerdem, “Break-even analysis and size optimization of a PV/wind hybrid energy conversion system with battery storage – A case study” Applied Energy, vol.86, pp. 1043-1054, July-August 2009. 6) M.I.M. Ridzuan, M. Imran Hamid And MakbulAnwari „Modeling and Simulation of Synchronizing System for GridConnected PV/Wind Hybrid Generation‟. 7) SweekaMeshram, Ganga Agnihotri and Sushma Gupta‟ Modeling of Grid Connected DC Linked PV/Hydro Hybrid System‟ Electrical and Electronics Engineering: An International Journal (ELELIJ) Vol 2, No 3, August 2013. 8) E. M. Natsheh, Member, IEEE, A. Albarbar, Member, IEEE, and J. Yazdani, Member, IEEE „Modeling and Control for Smart Grid Integration of Solar/Wind Energy Conversion System‟. 9) YannRiffonneau, SeddikBacha, Member, IEEE, Franck Barruel, and StephanePloix‟ Optimal Power Flow Management for Grid Connected PV Systems With Batteries‟ IEEE Transactions on Sustainable Energy, Vol. 2, No. 3, July 2011. 10) V.Srikanth, A. Naveen kumar „Power Quality Improvement Techniques In Hybrid Systems – A Review‟ International Journal Of Engineering And Computer Science ISSN:2319-7242 Volume 3 Issue 4 April, 2014 Page No. 5495-5498. 2)

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