Power Quality Improvement of Grid-Connected Photovoltaic Systems Using Trans-Z-Source Inverter Under Partial Shading Condition

ABSTRACT:

Voltage-source inverter has been used widely in traditional photovoltaic systems which have limitations. To overcome, Z-source inverter has been introduced. In spite of all the features introduced in Z-source inverter, its configuration has been improved over the years, like trans-Z-source inverter which has added advantages compared to traditional inverters, namely buck–boost feature, lesser passive elements, and higher voltage boost gain. In this paper, photovoltaic arrays are connected to the grid via the trans-Z-source inverter with the aim of improving its power quality. Moreover, the shoot through duty ratio is kept constant in the switching control method to add features like lower voltage stress (higher reliability), lower total harmonic distortion (lower maintenance cost), and higher voltage boost ratio. To evaluate the precision of the proposed system, the photovoltaic system is simulated on a standard grid and under partial shading condition which brings about voltage sag, and hence, a dynamic voltage restorer is used to mitigate voltage sag. Simulation results are presented to verify the validation of the proposed photovoltaic system in terms of voltage and current THD reducing 78.2% and 19.7%, respectively.

KEYWORDS:

1.      PV system

2.      Trans-Z-source inverter

3.      THD

4.      Partial shading

5.      Voltage sag

6.      DVR

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

In this paper, a PV system is connected to the IEEE 15-bus test network via trans-ZSI with the aim of power quality improvement, plus MCBC control is used to decrease voltage and current THD, and more importantly, to reduce voltage stress across the switches. The results indicate that applying the trans-ZSI and an appropriate switching method improve the power quality of the PV system to a considerable extent. Besides, the cost, volume, and weight of this inverter are low because of having no low-frequency ripples of the output voltage. What is more, as the shoot through does not damage the inverter, the reliability of the inverter is higher. In turn, not only is the reliability of this inverter higher, but also its maintenance cost is lower. The proposed PV system is also studied under partial shading conditions to validate its performance when there are some voltage sags. So, a DVR is employed to detect voltage sags and then mitigate them once partial shading happens. Two conclusions can be drawn from cases C and D: The voltage amplitude is roughly fallen back to its rated value, and the voltage THD is reduced when trans-ZSI is used. To summarize, the results illustrate that the PV system operates accurately with the trans-ZSI, as opposed to the PV systems with traditional VSI.

REFERENCES:

Abdulkadir M, Samosir AS, Yatim AHM, Yusuf ST (2013) A new approach of modelling, simulation of MPPT for photovoltaic system in simulink model. ARPN J Eng Appl Sci 8(7):488–494

Ajaykumar T, Manmadharao S, Kumar NG, Venkateswarlu G (2017) Compensation of unbalanced voltage sag/swell by multilevel inverter-based dynamic voltage restorer. Int J Pure Appl Math 114(7):11–20

Al Hosani K, Nguyen TH, Al Sayari N (2018) An improved control strategy of 3P4W DVR systems under unbalanced and distorted voltage conditions. Int J Electr Power Energy Syst 98:233–242

Bidram A, Davoudi A, Balog RS (2012) Control and circuit techniques to mitigate partial shading effects in photovoltaic arrays. IEEE J Photovolt 2:532–546

Boonchiam P, Mitholananthan N (2008) Understanding of dynamic voltage restorers through MATLAB simulation. Thammasat Int J Sci Technol 11(3):1–6 

Power Quality Improvement and PV Power Injection by DSTATCOM with Variable DC Link Voltage Control from RSC-MLC

ABSTRACT:

The study proposes a method to optimize dc-link voltage of Distribution Static Compensator (DSTATCOM) based on load compensation requirement using Reduced Switch Count Multi-Level Converter (RSC-MLC) integrated with Photo-Voltaic (PV) system. The proposed method is capable of compensating reactive power, unbalance and harmonics demanded by three phase unbalanced and non-linear loads connected to the distribution side, leading to improvement of power quality. It is also capable of providing real power support to the load and thus prevents source from getting over loaded whenever required. During off-peak loads, the dc-link voltage can be brought down to a lower value, which will reduce the voltage-stress across switches of inverter and minimizes the switching losses. The variation of dc-link voltage is provided using RSC-MLC which requires dc voltage supply. This method utilizes renewable resources of energy such as solar cells as the dc voltage source. The output voltage of PV panel is boosted to a higher value using High Gain Boost Converter (HGBC) and given to RSC-MLC. The maximum power point tracking (MPPT) of PV panels is achieved by using Perturb and Observe (P & O) algorithm. The results have been verified through simulation and experimental studies.

KEYWORDS:

1.      DC-link voltage

2.       DSTATCOM

3.      Power Quality

4.      PV system

5.      Reduced Switch Count Multi Level Converter (RSCMLC)

6.      Switching Losses

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A new method is proposed to regulate the dc-link voltage using RSC-MLC without affecting the performance of DSTATCOM. It also uses renewable energy resources for obtaining dc voltage source such as PV panels, Fuel cells. Using PV panels effectively enables it to deliver real power as well as compensation to the load during day time and work purely as DSTATCOM for power quality improvement at night. It can be observed from simulation and experimental results that compensation for reactive power and harmonics has been achieved effectively. The source current is balanced, sinusoidal, distortion-free and with improved power factor. The %THD has reduced significantly after compensation. Also, due to reduced dc-link voltage at lesser loads, voltage stress across the switches has reduced and switching losses are minimized to a great extent, increasing the life-time and efficiency of DSTATCOM. Hence, it can be a good alternative for power quality improvement and real power support to the load.

REFERENCES:

[1] J. Arrillaga, N. R. Watson, “Power system harmonics,” John Wiley and Sons, 2004.

[2] A. Ghosh A, G. Ledwich, “Power Quality Enhancement using Custom Power Devices,” Springer Science and Business Media, 2012.

[3] M. H. J. Bollen, “Understanding Power Quality Problems: Voltage Sags and Interruptions,” Wiley - IEEE press, Piscataway, NJ, USA, 2002 .

[4] B. Singh, S. R. Arya, C. Jain, S. Goel, “Implementation of Four-leg Distribution Static Compensator,” IET Gener. Transm. Distrib., vol. 8, no. 6, pp. 1127-1139, June 2014.

[5] R. P. Tondare, S. P. Gawande, M. R. Ramteke, “Modeling of Split Capacitor Based DSTATCOM and Voltage Balancing Scheme for Load Compensation,” International Conference on Emerging Trends in Communication, Control, Signal Processing and Computing Applications (C2SPCA), Bangalore, pp. 1-6, 2013.

 

Power optimisation scheme of induction motor using FLC for electric vehicle

ABSTRACT:

In electric vehicles (EVs) and hybrid EVs, energy efficiency is essential where the energy storage is limited. Adding to its high stability and low cost, the induction motor efficiency improves with loss minimisation. Also, it can consume more power than the actual need to perform its working when it is operating in less than full load condition. This study proposes a control strategy based on the fuzzy logic control (FLC) for EV applications. FLC controller can improve the starting current amplitude and saves more power. Through the MATLAB/SIMULINK software package, the performance of this control was verified through simulation. As compared with the conventional proportional integral derivative controller, the simulation schemes show good, high-performance results in time-domain response and rapid rejection of system-affected disturbance. Therefore, the core losses of the induction motor are greatly reduced, and in this way improves the efficiency of the driving system. Finally, the suggested control system is validated by the experimental results obtained in the authors’ laboratory, which are in good agreement with the simulation results.

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

When IM operates in less than full load condition, it can consume more power than needed. This excess power is in the form of heat. By using the FLC the starting current amplitude can be controlled and more power can be saved during this time. The inputs of the fuzzy controller are the error of speed and change of error which are used in the outer loop for producing an equivalent controller term. In this paper, a simulation study was conducted on a 50 hp IM-driven EV. Different performance indicators are tested such as peak overshoot, steady-state error, rise time, and settling time. The results showed that the phase current in the suggested system includes fewer loss components (less amplitude) with the same order components. The amplitudes of loss are reduced on the average for the actual torque in the steady state. It achieves a smooth torque and improves system performance. The simulation results of the suggested FLC scheme showed very good stability and better performance over the conventional PID controller in rising time, settling time, and peak overshoot. The proposed control system is validated by the experimental results which are in good agreement with the simulation results.

REFERENCES:                                         

[1] Sato, E.: ‘Permanent magnet synchronous motor drives for hybrid electric vehicles’, IEEJ Trans. Electr. Electron. Eng., 2007, 2, (2), pp. 162–168

[2] Agency, I.E.: ‘Global EV outlook 2016: beyond one million electric cars’ (OECD Publishing)

[3] Sayed, K.: ‘Zero-voltage soft-switching DC-DC converter-based charger for LV battery in hybrid electric vehicles’, IET Power Electron., 2019, 12, (13), pp. 3389–3396

[4] Gomez, J.C., Morcos, M.M.: ‘Impact of EV battery chargers on the power quality of distribution systems’, IEEE Power Eng. Rev., 2002, 22, (10), pp. 63–63

[5] Stephan, C.H., Sullivan, J.: ‘Environmental and energy implications of plug in hybrid-electric vehicles’, Environ. Sci. Technol., 2008, 42, (4), pp. 1185– 1190 

Power Flow Control of Interconnected AC-DC Microgrids in Grid-Connected Hybrid Microgrids Using Modified UIPC

ABSTRACT:

  This paper introduces a new approach for power flow control of interconnected AC-DC microgrids in grid-connected hybrid microgrids based on implementing a modified unified interphase power controller (UIPC). A typical grid-connected hybrid microgrid including one AC microgrid and one DC microgrid is considered as studied system. Instead of using the parallel-connected power converters, these microgrids are interconnected using a modified UIPC. As the first contribution of this paper, the conventional structure of UIPC, which uses three power converters in each phase, is modified so that a reduced number of power converters is implemented for power exchange control between AC-DC microgrids. The modified structure includes one power converter in each phase, named as line power converter (LPC), and a power converter which regulates the DC bus voltage, named as bus power converter (BPC) here. The AC microgrid is connected to the main grid through the LPCs which their DC buses are linked and can operate in capacitance mode (CM) or inductance mode (IM). A fuzzy logic controller is used in the control structure of the LPCs. The fuzzy inference system is optimized based on H∞ filtering method to reduce the errors in membership functions design. Through the BPC, the DC voltage of LPCs is supplied by the DC microgrid. However, since the DC microgrid voltage is provided here by a PV system, the DC link voltage of the LPCs is fluctuating. Thus, as the second contribution, to stabilize the DC link fluctuations, a new nonlinear disturbance observer based robust multiple-surface sliding mode control (NDO-MS-SMC) strategy is presented for DC side control of the BPC. The simulation results confirm the effectiveness of the proposed power flow control strategy of the improved UIPC for hybrid microgrids.

KEYWORDS:

 

1.      Hybrid microgrid

2.      UIPC

3.      Power control

4.      Disturbance observer

5.      Multi-surface SMC

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The hybrid microgrid structure is the most probable option in the future smart grids to gather together the renewable resources as well as AC/DC loads. This is due to the fact that this structure has the merits of both AC and DC microgrids simultaneously. One conventional problem with this structure is the power exchange control between interconnected AC and DC microgrids. In this study, a UIPC based solution has been proposed as a superior alternative to the parallel-connected power converters which have brought many problems. A modified structure of the UIPC has firstly been proposed and then effective control strategies have been introduced for the modified UIPC. The simulation results validated the modified model as well as the power exchange control performance between AC and DC microgrids.

REFERENCES:

[1] Runfan Zhang, Branislav Hredzak, "Distributed Finite-Time Multi-Agent Control for DC Microgrids with Time Delays”, IEEE Transactions on Smart Grid, Early Access, 2018.

[2] Kumar Utkarsh, et al, "Distributed Model-predictive Real-time Optimal Operation of a Network of Smart Microgrids", IEEE Transactions on Smart Grid, Early Access, 2018.

[3] Haifeng Qiu, et al, " Bi-level Two-stage Robust Optimal Scheduling for AC/DC Hybrid Multi-microgrids", IEEE Transactions on Smart Grid, Early Access, 2018.

[4] Pengfeng Lin, et al, "A Distributed Control Architecture for Global System Economic Operation in Autonomous Hybrid AC/DC Microgrids", IEEE Transactions on Smart Grid, Early Access, 2018.

[5] Daniel E. Olivares, et al, "Trends in Microgrid Control", IEEE Transactions on Smart Grid Volume: 5, Issue: 4, pp. 1905 – 1919, 2014.  

Power Flow Control of Hybrid Micro-Grids Using Modified UIPC

ABSTRACT:

This work introduces a replacement advent for power flow control of interconnected AC-DC micro-grids in hybrid micro-grids connected to grids. It also supports implementing an Adaptive Neuro Fuzzy Inference System (ANFIS) controlled modified Unified Inter-Phase Power Controller (UIPC). For study, a classic hybrid micro-grid connected to grid comprising of a AC micro-grid and a DC micro-grid is taken into account. These micro-grids are interconnected employing a modified UIPC, rather than using the power converters connected in parallel. As the first input of this paper is the standard structure of UIPC, which used three power converters in every phase. It was then modified such as number of power converters is used less and implemented for the control of the exchange of power between AC-DC microgrids. In every phase there is one power electronic converter in the improved structure. It is called as Line Power Converter (LPC). Also there is Bus Power Converter (BPC) to regulate the voltage of the DC bus. The Line Power Converters links the AC micro-grid to the main grid. The DC buses are also linked with them. It can be operated in Inductance Mode (IM) as well as Capacitance Mode (CM). The control structure of LPCs has an Adaptive Fuzzy Logic Controller in it. For hybrid micro-grids, the capability of the suggested power flow control strategy is confirmed by the MATLAB simulation results.

KEYWORDS:

1.      Ac micro-grid

2.      Dc micro-grid

3.      Grid control

4.      Hybrid micro-grid

5.      UIPC

6.      UPFC

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The hybrid micro-grid structure is the favorable option in the future smart grids to gather together the renewable resources for AC/DC loads. This is because of the fact that this structure holds the merits of AC as well as DC micro-grids simultaneously. There is one conventional problem with this structure. That is to efficiently control the exchange of power within interconnected micro-grids comprising of AC and DC system. In this particular work, an ANFIS controlled UIPC solution is suggested as a superior alternative to the power electronic converters connected in parallel which have brought many problems. An improved design of the UIPC was initially suggested and then effective strategies for control are presented for the modified UIPC. The results of simulation are used to validate the modified model along with performance of the control of power exchange between micro-grids having AC and DC system.

REFERENCES:

[1] H.a. Pan M. Ding R. Bi L. Sun Research on Cooperative Planning of Distributed Generation Access to AC/DC Distribution (Micro) Grids Based on Analytical Target Cascading Energies 12 10 2019 1847. (https://doi.org/10.3390/ en12101847)

[2] Du Yi, Jiang Daozhuo, Yin Rui, Pengfei Hu, Wang Yufen, ‘‘Modeling and simulation of DC distribution network based on distributed energy” 2013 2^nd International Symposium on Instrumentation & Measurement, Sensor Network and Automation (IMSNA)

[3] J.M. Guerrero J.C. Vasquez J. Matas L.G. de Vicuna M. Castilla Hierarchical Control of Droop-Controlled AC and DC Microgrids—A General Approach Toward Standardization IEEE Trans. Ind. Electron. 58 1 2011 158 172 10.1109/ TIE.2010.2066534 http://ieeexplore.ieee.org/document/5546958/

[4] JiaLihu, ‘‘Architecture Design for New AC-DC Hybrid Micro-grid”, DC Microgrids (ICDCM), IEEE First International Conference on, 2015.

[5] D. Riana Aryani and Hwachang Song, ‘‘Coordination Control Strategy for AC/DC Hybrid Microgrids in Stand-Alone Mode‘‘ Energies 9 6 2016 469. (https://doi.  org/10.3390/en9060469) 

Multifunctional Grid-Tied PV System Using Modified KLMS Control

 ABSTRACT:

This paper deals with the modified kernel least mean square (KLMS) control strategy in double-stage, solar photovoltaic (PV) grid tied system to enhance the power quality at common coupling point (CCP). This proposed control algorithm has less oscillations, fast convergence, fast dynamic response and good steady state performance. A control strategy is used to extract the fundamental active current component of load and generates reference grid current for a DC-AC converter. The proposed modified KLMS control mitigates multiple power quality concerns such as harmonics reduction, unity power factor and load balancing. The dynamic performance of proposed system is confirmed into the MATLAB\Simulink environment. Test results on hardware implementation are presented at varying solar irradiation levels and load unbalancing. Test results are found satisfactory and total harmonic distortion (THD) of the grid currents are observed well within the IEEE-519 standard.

KEYWORDS:

1.      Solar PV Generation

2.      Voltage Source Converter (VSC)

3.      Distributed Network

4.      Power Quality

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The proposed modified KLMS based control scheme for double stage solar PV system, has been simulated in MATLAB\Simulink environment and simulated results are validated through the experimental prototype. The MPPT has extricated the peak power point successfully (nearly 100%) from the solar PV array under varying insolation levels. The proposed control effectively provides harmonics compensation, grid currents balancing and unity power factor in the grid tied system. This proposed modified KLMS control scheme has extracted the fundamental current component efficiently. Under the load unbalancing condition, the fundamental current component has shown faster convergence and less oscillations than LMS and LMF controls. Moreover, it has good steady state and dynamic performances than LMS and LMF controls. Moreover, the THD of grid currents, is meeting the IEEE-519 standard[12].

REFERENCES:

[1] International Energy Agency, “Medium term renewable energy market report 2016,” [Online].Available http://www.iea.org

[2] P. Shukl and B. Singh, “Delta-Bar-Delta Neural Network (NN) Based Control Approach for Power Quality Improvement of Solar PV Interfaced Distribution System,” IEEE Trans. on Ind. Info.., early access 2019.

[3] S. M. Fatemi, M. S. Shadlu and A. Talebkhah, “Comparison of Three-Point P&O and Hill Climbing Methods for Maximum Power Point Tracking in PV Systems,” 10th Int. Power Elec., Drive Sys.and Tech. Conf.(PEDSTC), Shiraz, Iran, 2019, pp. 764-768.

[4] E. H. M. Ndiaye, A. Ndiaye, M. A. Tankari and G. Lefebvre, “Adaptive Neuro-Fuzzy Inference System Application for The Identification of a Photovoltaic System and The Forecasting of Its Maximum Power Point,” 7th Int. Conf. on Renew. Ene. Rese.and App.(ICRERA), Paris, 2018, pp. 1061-1067.

[5] N. Arab, B. Kedjar, A. Javadi and K. Al-Haddad, “A Multifunctional Single-Phase Grid-Integrated Residential Solar PV Systems Based on LQR Control,” IEEE Trans. on Ind. Appl., vol. 55, no. 2, pp. 2099-2109, March-April 2019.

 

Multifunctional Grid Connected Inverter Interfaced by Wind Energy Conversion System

ABSTRACT:

This study deals with a three-phase multifunctional grid-connected inverter interfaced with a wind energy conversion system (WECS) is described. The studied system consists of a permanent magnet synchronous generator (PMSG) based wind turbine, a rectifier and a three-phase voltage source inverter connected to the utility at the point of common coupling. To ensure the multifunctional feature, we propose a direct power control (DPC) which is applied to eliminate line current harmonics, compensate reactive power and feeding wind power into the utility. Simulation results are provided to demonstrate the effectiveness of the proposed system. The results show that the control algorithm of system is effective for eliminating harmonic currents, reactive power compensation and inject the active power available from the PMSG wind turbine into the load and/or grid, which allowed us to confirm the robustness of the proposed strategy.

KEYWORDS:

1.      Inverter

2.      Wind energy conversion system

3.      Permanent magnet synchronous generator

4.      Rectifier

5.      DPC

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This paper focused on applying direct power control to a three-phase multifunctional grid-connected inverter interfaced with a wind energy conversion system. The proposed control scheme is used in order to achieve harmonics elimination, reactive power compensation, and simultaneously inject the active power available from the PMSG wind turbine into the load and/or grid. The analysis of the simulation results obtained has attested the robustness, the effectiveness and the good performance of proposed system. The DPC method has very good performance in injection of active power produced by PMSG wind turbine to the distribution networks and simultaneously compensating harmonics and reactive power.

REFERENCES:

[1] H.G. Kim, D.C. Lee, J.K. Seok and G.M. Lee, “Stand-alone wind power generation system using vector-controlled cage-type induction generators,” in Proc. of Inter. Conference on Electrical Machines and systems, vol.1, pp.289-292, Nov.2003.

[2] B. Singh and G.K. Kasal, “Voltage and Frequency Controller for a threephase four wire autonomous wind energy conversion systems,” IEEE Trans. Energy Conversion, vol. 23, no.2, pp.509–518, June 2008.

[3] A.Krama, L.Zellouma and B. Rabhi “Improved Control of Shunt Active Power Filter Connected to a Photovoltaic System Using Technique of Direct Power Control,” 8th International Conference on Modelling, Identification and Control (ICMIC-2016).

[4] M.R. Bengourina, M. Rahli, S. Saadi,, L.Hassaine, “Optimization of direct power control of three-phase shunt active power filter by using PSO algorithm”, Leonardo Electronic Journal of Practices and Technologies, vol. 16, no.31, pp. 218-234, Dec 2017.

[5] A.Chaoui., J. Gaubert, F. Karim,, “Power quality improvement using DPC controlled three-phase shunt active filter”, Electric Power Systems Research, vol. 80, pp. 657–666, 2010.