Grid Connected Pv Inverter Matlab

International Journal on Science and Technology (IJSAT)

1Student, 2Professor

1,2NRI Institute of Research and Technology, Bhopal Abstract— In this article, a grid-connected photovoltaic system based on multilayer inverters (MLI) is modeled. The cascaded T-type inverter is responsible for developing the MLI topology. Connecting the PV sources in series raises the input voltage, making it challenging to connect other MLI circuits to the grid. Three-level buck-mode operation is produced by this cascaded T-type multilevel inverter (CT2MLI), which has the following benefits: a low peak inverse voltage (PIV), a low total harmonic distortion (THD), a low switching loss, and a minimal number of switches. The perturb and observe (P&O) MPPT technique is used to get the maximum power from a PV array. To simplify the gate pulse generation process, CT2MLI employs a hybrid level-shifted and phase-shifted pulse width modulation (PWM) approach. Low dv/dt stress across the switches, low peak inverse voltage (PIV), and low total harmonic distortion (THD).

The maximum power point tracking (MPPT) technique perturbs and watches the PV array to obtain the greatest power. To simplify the gate pulse generation process, CT2MLI employs a hybrid level-shifted and phase-shifted pulse width modulation (PWM) approach. The efficiency of the control strategy for the grid-connected PV system based on CT2MLI is shown by the MATLAB simulation results.

Keywords— CT2MLI, FFT Analysis, Photo Voltaic (PV) System, Pulse Width Modulation (PWM), T- Type Inverter.

I. Introduction

There is a significant shift in the energy system toward the widespread usage of green energy due to environmental concerns about CO2 emissions and global warming. Large-grid-dependent, centralized electric power systems will be supplemented with distributed, small-scale smart-grid-based energy generation systems in a sustainable future. Often, renewable energy sources like solar, tidal, and wind power are employed to achieve that objective. As solar energy is more available than any other fossil fuel substitute, the world is shifting toward solar solutions , .

Since photovoltaic sources provide DC power, which must be converted into AC via a DC to AC converter (inverter), power electronics are crucial for capturing solar energy. MLIs have garnered significant attention among various power converters for medium-voltage and high-power applications.

Due to the fact that it has the ability to handle large voltages, low harmonic distortion, and far less voltage stress on semiconductor switches than applied voltage to a circuit . Numerous topologies for MLI have been developed, including NPC-MLI, FC-MLI, MLDCL-MLI, T2MLI, and CHB-MLI. Because it raises the leveled AC output voltage, the cascaded H-bridge inverter topology is one of the most often utilized among them –. However, it necessitates an isolated DC-link input voltage for every cell.

2

The technique of varying a switch's ON and OFF duration at a fixed switching frequency is known as pulse width modulation. The literature has suggested a variety of modulation approaches for MLIs, including phase-shifted PWM, level-shifted PWM, discontinuous PWM, and others , . LS-PWM has an uneven power distribution across each module . D-PWM requires that the output waveform and switching time have a balanced relationship. Significant performance advantages of PS-PWM technology include high output waveform quality and balanced power distribution among modules. Conversely, low circuit efficiency and high frequency switching losses are some drawbacks of PS-PWM .

In order to address the challenges of directly connecting the higher PV output voltage of cascaded PV sources to the grid using traditional topologies and improve the power quality of PV systems, this study proposes a PV system that transmits electricity to the grid. There are two stages to this work: the first is a DC-DC boost converter using MPPT, and the second is a seven-level inverter. In order to reduce the number of switches and other factors, a CT2MLI is utilized in conjunction with hybrid LS-PWM and PS-PWM to generate a switching pulse that operates in buck-mode with a peak voltage of Vdc/2 . The leveled output then goes through a specially made LCL filter, producing high-quality AC output, and is linked to the grid. Representation of this work using block diagram is shown in Fig. 1.

Gate Driver

Fig. 1 block diagram of PV to grid connected system The work is arranged as follows: part II presents circuit topology with T-type inverter operation. Part III, includes hybrid modulation technique as LS-PWM and PS-PWM. In section IV, the results of a PV to grid connected CT2MLI based system are shown using MATLAB/Simulink. Finally, in part V, there are some closing observations.

A.

Design of Stage One DC-DC Boost Converter with MPPT To get the most power out of PV sources, the MPPT algorithm is employed. The point on a current- voltage (I-V) curve where the solar PV device generates the highest output is called the MPP. The P&O technique measures the power extracted from the PV array on a regular basis . To maintain a constant output voltage for grid-connected photovoltaic applications, a DC-to-DC boost converter is utilized. By lowering the ripples, the boost converter transforms a fluctuating PV voltage into a more steady DC voltage. To keep the output voltage constant, it uses feedback voltage.

Design Of Stage Two T-Type Inverter

This project makes use of a T-type inverter (T2I), which may be connected to a photovoltaic array and send power to the grid. A four quadrant operating bipolar and bidirectional switch (S1 and S4) and two unipolar and bidirectional switches (S2 and S3) are part of this topology . Additionally, it features two capacitors (a dc-bus capacitor) that are linked after the DC-to-DC boost converter with MPPT, which is the first stage. In contrast to S1 and S4, which are rated for half of the DC-link voltage, S2 and S3 are rated for the whole DC-link voltage Vdc. Fig. 3 displays the three-level T2I topology.

Fig. 3 T-Type Inverter Topology

This inverter gives three output voltage levels as +Vdc/2, 0, and –Vdc/2. Different switching states are shown in Fig. 4-6. By connecting three modules in cascade can create seven-level voltage as leveled output of the inverter. This cascaded system provides a seven-leveled voltage as +1.5Vdc, +1Vdc, +0.5Vdc, 0, - 0.5Vdc, -1Vdc, -1.5Vdc. Table-1 shows the different switching states of inverter. During the positive and negative state only one device is conducting, that increase the efficiency of converter.

+Vdc/2 Level-

By turning ON switch S2 and keeping other switch OFF, capacitors C1 is connected in series through the load and C2 is by passed, it gives +0.5Vdc voltage at the output of inverter with positive load current Io. For negative load current, D2 gets turned ON.

0 Level-

By turning ON switch S1 and D4 and other switch OFF, capacitors C1 and C2 are by passed and zero voltage at the output of inverter with positive load current of Io occurs. For negative load current Io turned ON switch S4 and D1.

–Vdc/2 Level-

By turning ON switch S3 and other switch OFF, capacitors C2 is connected in series through the load and C1 is by passed and it gives –Vdc/2 voltage at the output of inverter with negative load current Io. For positive load current of Io, D3 gets turned ON.

Iii. Hybrid Modulation Technique

To provide a low and fixed switching frequency for high power and industrial applications, PWM should be used to provide sufficient switching pulses. Some switching techniques, such as hysteresis, have a variable switching frequency, resulting in annoying auditory disturbances. To modulate the measured reference signal, carriers are transferred vertically.

Fig. 4 Hybrid Modulation Technique

In this study, switching pulses are generated using a hybrid level-shifted and phase-shifted high frequency PWM method. As illustrated in Fig. 4, for ‘m’ level of output voltage including zero level

Deployment In Out-Of-Position Situations

D. Bendjaballah1, A. Bouchoucha1, M. L. Sahli1,2* and J-C. Gelin2

Abstract

Side-impact collisions represent the second greatest cause of fatality in motor vehicle accidents. Side-impact airbags have been installed in recent model year vehicle due to its effectiveness in reducing passengers’ injuries and fatality rates. In meeting these requirements, simulations of folding and deploying airbags are very useful and are widely used. The paper presents a simulation method for the deploying airbags using three materials in different working conditions. Finite element analysis is primarily used to evaluate this concept. In these simulations, the gas flow is described by the conservation laws of mass, momentum, and energy. The numerical results indicate that the FE method in this paper is capable of capturing airbag deploying process accurately.

Keywords: Airbag simulations, Out-of-position, Crash, Modeling, Out-of-position

Background

The passive safety of cars has become a very high prior- ity issue for the automotive industry. Today, there are not only one or two airbags in a car; certain models have ten times more than that. With the increasing usage of airbags, the number of accidents where the airbag itself can cause an injury to the occupant also increases

(Augenstein Et Al. 2003; Gabauer And Gabler 2010;

Audrey et al. 2011). As is well known, safety belts are also now devices designed to provide protection to the users of vehicles during crash events, minimizing the loads necessary to adapt their movement to the move- ment of the car (Freesmeier and Butler 1999; Schmitt et al. 1997). In general, the seat belt is designed to restrain the occupant in the vehicle and prevent the

Occupant From Having Harsh Contacts With Interior

surfaces of the vehicles. The airbag acts to cushion any impact with vehicle structure and has positive internal pressure, which can exert distributed restraining forces over the head and face. As a safety component of auto- mobile, an airbag decreases occupants’ injury likelihood effectively in case of an accident (Ruff et al. 2007). These safety elements can reduce the death rates on the roads, and its protection effects have been widely approved (Crandall et al. 2001; Teru and Ishikawa 2003). With computational tools such as finite element methods designed for dynamic contact problems, crashworthiness simulations can now be used with reliable accuracy to evaluate occupant protection in various collision condi- tions with safety metric/parameters such as acceleration, head injury criteria, intrusion distance, intrusion vel- ocity, and neck forces (neck injury risk or whiplash).

Thus, new types of airbag products are being developed to handle different collision scenarios.

Become Standard Equipment On Most New Passenger

vehicles (Braver and Kyrychenko 2004; Teng et al. 2007; Yoganandan et al. 2007). The airbag cushion is com- posed of a woven fabric which is rapidly inflated during a car crash. The airbag dissipates the passenger’s kinetic energy thereby reducing injury through biaxial stretching of the fabric bag and escaping gas through vents. There- fore, the performance of the airbag is greatly influenced by the mechanical properties of the fabric. Generally, air bags are designed to deploy in a crash that is equivalent to a vehicle crashing into a solid wall at 8 to 14 mph.

Air bags most often deploy when a vehicle collides with another vehicle or with a solid object like a tree. There are various types of airbags: frontal, side-impact, and curtain airbags. In general, the passenger side airbags are usually larger than the driver airbags (see Fig. 1).

Besançon, France

© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Bendjaballah et al. International Journal of Mechanical

Doi 10.1186/S40712-016-0070-2

Extensive studies have shown that the airbag deploy- ment in load cases consists of two occupant loading phases: a punch-out effect where the airbag bursts out of its container with the airbag and airbag module cover accelerating towards the occupant and a second loading phase during which the airbag is taking on its deployed shape and volume (membrane-loading effect). Bankdak et al. (2002) developed an experimental airbag test system to study airbag-occupant interactions during close proximity deployment. The results provided insight for simulating the effect of inflation energy and mass flow on target response. Bedard et al. (2002) found that while left-side (driver-side) impacts accounted for only 13.5% of all crashes, the fatality rate among these

Crashes Was 68.3% In Comparison To Front Impact

(48.3%), right-side impact (31.3%), and rear impact (38.4%). These studies underscore the importance of oc- cupant safety during side-impact collisions. In the last years, the current market requested to reduce the time and cost airbag development. In order to achieve this result, virtual simulations play an important role since they allow to minimize the number of experimental tests (Pei et al. 2013; Cao et al. 2014). Several simulation models of airbag were established (Wang et al. 2007). It is feasible to optimize the parameters of airbag deploy- ment using simulation technology. Experimental and numerical studies have quantified injury risks to close- proximity occupants from deploying side airbags. These studies have focused on the prevention of the most ad- verse effects of airbag deployment (Duma et al. 2003).

Other studies have proposed airbag characteristics to minimize particular biomechanical responses (Haland and Pipkorn 1996). In a more recent study, Marklund and Nilsson (2003) compared deformation patterns with experimental data as well as the computational costs associated with three different airbag deployment simu- lation methods; they concluded that the SPH method is relatively inexpensive and produces incremental deform- ation patterns that compare most closely to the experi- mental results. The process of inflation of an airbag is one of the determining factors in saving lives. The duration from the initial impact of the crash to the full inflation of an airbag is about 40 ms, and during this time, the airbag goes from being in a folded state to a fully inflated state, with a high internal pressure. After achieving this state, the airbag begins to deflate, thus providing a nice cushion for the body impacting it.

Ideally, the person in the crash should come into contact with the airbag at this time. In the present study, a large volume passenger side airbag model is developed to handle different collision scenarios. The main aim is evaluate the performance of deploying of passenger side airbag using finite element methods (FEM).

Materials

The tensile specimens were made in different airbags (P: Peugeot, R: Renault, and VW: Volkswagen) with a length of 200 mm long and a width of 40 mm. Table 1 shows the mechanical properties of the airbag.

Tensile Tests

To determine the mechanical properties of the material of airbag used in the test pieces, tensile tests were performed on Lloyd EZ20 universal testing machine in Constantine. These tests were conducted using rect- angular samples. The axial force and axial displacement acquired during a test are converted into stress and the strain in order to be used for the fabric material model.

The continuous recording of the stress-strain data was performed during both the load and unload phases. A minimum of five samples were made in order to check the repeatability of the measurements. All the data was collected by using a PC-based data acquisition system and analyzed by commercial software. The picture frame test device that is made for this study is shown in Fig. 2.

Fig. 1 a Frontal and side airbags. b Oblique view of facet occupant model in sitting posture following airbag deployment (Lim et al. 2014)

0.150

Bendjaballah et al. International Journal of Mechanical and Materials Engineering (2017) 12:12

Page 2 Of 9

Figure 3 shows the stress-strain relationship of the airbag sample under axial tensile loads. The results are showing a linear increase in extension with the increas- ing stresses. This is an expected output and it confirms with the theoretical behavior of a sample subjected to tensile stress. The rupture strain values for different airbags (R/P/VW) were 0.322, 0.441, and 0.472, respect- ively. The measured elastic parameters (i.e., Young’s modulus E and initial yield strength) and Poisson’s ratio are summarized in Table 2. The tensile tests of the woven fabrics can show differences on mechanical prop- erties because woven fabrics can resist in-plane shear loads once the yarn lock-up angle has been reached. The differences of material property on material direction can affect the shape of fully deployed bag (see Fig. 3b).

Theoretical Background

Numerical simulations of airbags use very complex and techniques such as an orthotropic model to identify the mechanical behaviors during the airbag inflation and the fluid mechanics (gas flow) to describe the inflator gas flow (pressure gradient) and improve the representation of the pressures within the airbag. To model the airbag as an orthotropic model, three material constants have to be provided. Assuming a plane stress condition, the

Ð1Þ

where σ is the normal stress and τ is the shear stress, the subscript refers to the principal material directions, i.e., the fill and warp directions. Also, ε and γ are the strain components. The material elastic constants Qij are

Ð2Þ

where E1 and E2 are the Young’s modulus in the fill and wrap directions and G12 is the shear modulus of the fabric material. νij is the Poisson ratio of the material.

The gas exerts a pressure load on the airbag causing it to expand. This expansion puts the airbag under tensile stress lowering the expansion rate. In this study, heat conduction and heat transfer is not taken into account.

Fig. 2 A photograph of Lloyd EZ20 universal testing Fig. 3 Stress versus strain using Lloyd EZ20 machine for a three different airbags at 0° and 90° and b VW airbag test specimens at

Different Angles

Table 2 Physical and mechanical properties of the airbag

Page 3 Of 9

In the deployment of an airbag, an inflator supplies high velocity gas into an airbag causing it to expand rapidly. The gas inside the airbag is assumed to be ideal, to be of constant entropy, and to satisfy the equation of state:

Ð3Þ

Here p, ρ, and e are respectively the pressure, density, and specific internal energy, and γ is the ratio of the heat capacities of the gas. The gas flow is described by the conservation laws for mass, momentum, and energy that

Ð4Þ

here, V is a volume, A is the boundary of this volume,

N Is The Normal Vector Along The Surface A, And U

denotes the velocity vector in the volume. Applying Bernoulli’s equation in the case of an ideal gas with

Ð5Þ

Here, the subscript ex denotes quantities at the throat of the tube. Furthermore u, p, and ρ denote the quan- tities inside that part of the tube that is supplying mass.

Materials And Boundary Conditions

The airbag system mainly consists of three parts: the airbag itself, the inflator unit, and the crash sensor or diagnostic unit. Thus, to study the behavior of the airbag using FE simulations, we need to have an FE model of the airbag in the folded position. A FE model of the airbag was used to simulate the test condition as shown in Fig. 5. LS-DYNA® material model FABRIC (MAT_34) is used to simulate the airbag material. It is a variation of the layered orthotropic material model. Additionally, in the LS-DYNA® material model, fabric leakage can be accounted for. However, for this CAB material, the leak- age is almost negligible and therefore no leakage is specified. The mechanical properties can be determined from the physical test. Typical material properties for airbag fabrics are taken as given in Chawla et al. (2004a) (Table 3). These properties are used to simulate inflation process of airbag (see Table 1). The car dashboard is modeled as the rectangular thin plate using a MAT_RI-

Gid Material, And The Degrees Of Freedom Are Con-

strained in all the directions. The similar properties of thermoplastic polymer are assigned for contact purposes. The porosity of the fabric is assumed zero. The nitro- gen gas is taken for inflating the airbag. Properties of nitrogen gas and initial bag conditions are shown in Table 4. The example on which we perform the study is a typical passenger side airbag. The geometric de- tails have been measured from a commercially avail- able airbag. The initial state of the airbag is a closed rectangular whose sides are to be finished to 482 × 635 mm2 and is shown in Fig. 4.

Table 3 Material properties of airbag and rigid plate used in FE

–

Table 4 Initial values used for FE simulation of the swelling of

3.33 × 10−4

Fig. 4 The initial airbag geometry in the form of a rectangular Bendjaballah et al. International Journal of Mechanical and Materials Engineering (2017) 12:12

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