Control and energy management of a large scale grid-connected PV system for power quality improvement

 ABSTRACT:

Power quality is highlighted as an important parameter in modern power systems. Moreover, grid-connected photovoltaic power plants are increasing significantly in size and capacity. Elsewhere, due to the progressive integration of nonlinear loads in the grid, the principal role of a Solar Energy Conversion System (SECS) is not only to capture the maximum power from solar but, also to ensure some ancillary services and improve the quality of power. This paper presents a novel strategy dedicated to improve the management of active power generation, reactive power compensation and power quality of a SECS, while guaranteeing the possibility of exploiting the full capacity of the Power Conditioning System (PCS) and the PhotoVoltaic System (PVS). The proposed control algorithm is applied to a large scale PVS connected to the grid through a cascade of a DC-DC converter and a PWM inverter. This control strategy manages the SECS function’s priorities, between main active power generation, reactive power compensation and active filtering in such a way to guarantee a smooth and stable DC voltage and ensure a sinusoidal grid current. Top priority is given to the active power production over power quality improvement. Then, priority is given to reactive power compensation over mitigation of current harmonics absorbed by the non-linear load connected to the Point of Common Coupling (PCC). Moreover, the whole system upper limits of active and reactive powers have been determined in the (PQ) power plane on the basis of PVS available power, converters rated power and DC bus voltage smoothness and stability. Finally, a control procedure dedicated to the calculation of the inverter current commands is proposed in order to exploit the full capacity of the SECS and respect the determined power limits. Simulation results confirm the effectiveness and the performance of this control strategy and prove that the SECS can operate at its full power whilst the power quality can be improved by reactive power compensation and active filtering.

KEYWORDS:

1.      Power decoupled control

2.      Harmonic currents

3.      Power quality

4.      Active filtering

5.      Reactive power compensation

6.      SECS full power exploitation

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

In this paper, a novel strategy has been proposed to manage and improve the power quality of a grid connected large scale PVS. More accurately, fuzzy logic controllers have been used to guarantee a decoupled control of active and reactive powers injected into the grid. The PWM inverter is controlled in such a way to manage between active power production and power quality improvement without exceeding the whole system power capacity. The proposed priority control block gives top priority to active power production, then reactive power compensation and finally active filtering. The power capability of the whole system has been delimited in the (PQ) power plane (on the basis of the PVS available power, the power electronics converters rated power and the DC bus voltage smoothness and stability) and fully exploited without over-rating, by the calculation of an appropriate portion of current commands in order to ensure a better active filtering quality and keep the inverter current under its limit value corresponding to the whole system power capacity. Simulation results show the effectiveness and the performance of the proposed approach in terms of power generation, reactive power compensation and active filtering.

REFERENCES:

Ahmad, Z., Singh, S.N., 2018. Improved modulation strategy for single phase grid connected transformerless PV inverter topologies with reactive power generation capability. Sol. Energy 153, 356–375.

Aboudrar, I., El Hani, S., Mediouni, H., Bennis, N., Echchaachouai, A., 2017. Hybrid algorithm and active filtering dedicated to the optimization and the improvement of photovoltaic system connected to grid energy quality. Int. J. Renw. Energy Res. 7 (2), 894–900.

Arul Murugan, S., Anbarasan, A., 2014. Harmonics elimination in grid connected single phase PV inverter. In: Int. Conference on Engineering Technology and Science, Tamilnadu, India, 10–11 February 2014, (3) 1, pp. 1474–1480.

Albarracin, R., Alonso, M., 2013. Photovoltaic reactive power limits. In: 2013 12th IEEE Int. Conference Environ. Electr. Eng. Wroclaw, Poland, 5–8 May 2013, pp. 13–18.

Bhole, N., Shah Dr, P.J., 2017. Enhancement of power quality in grid connected photovoltaic system using predictive current control technique. Int. J. Rece. Innova. Trends in Compu. Communi 5 (7), 549–553.

A Grid Connected Single Phase TransformerlessBuck-Boost Based Inverter Which Can Control TwoSolar PV Arrays Simultaneously

 ABSTRACT:

A new buck-boost based single phase transformerless grid connected photo voltaic (PV) inverter which is having the capability to operate two serially connected subarrays at their respective maximum power point is proposed in this paper. The series connection of the two subarrays and the buck-boost nature of the inverter reduces the number of serially connected modules in a subarray. Further, independent operation of the two subarrays enhances the overall power extraction from the subarrays while they are experiencing significant mismatch at their operating conditions, e.g. insolation level and/or operating temperature. The topological structure of the inverter and its control technique ensures negligible amount of high frequency components in its common mode voltage. As a consequence the overall leakage current associated with the subarrays are restricted well within the permissible limit specified in the standard, VDE 0126-1-1. The operating principle of the proposed scheme along with its rigorous analysis has been presented. The reference current generation for the buck-boost inductor and the controller configuration of the proposed inverter have been elaborated in detail. Detailed simulation study with a 1.3 kW PV system has been carried out to show the viability of the proposed scheme.

KEYWORDS:

1.      Buck-boost inverter

2.      Maximum power point

3.      Single phase

4.      Transformerless

5.      Grid connected inverter

6.       Difference in operating condition

7.      Series connection

8.       Sub-arrays

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A new buck-boost based transformerless grid connected solar PV inverter which is capable of operating two serially connected subarrays at their respective maximum power points while significant amount of difference is present in their operating conditions, was proposed in this paper. The buckboost nature of the inverter along with its ability to operate two serially connected subarrays at their respective maximum power point enhances the overall power extraction from the subarrays while they are experiencing wide difference at their operating conditions. A simple inductor current control technique which is independent of modes of operation (CCM or DCM) was adopted to control ig. The topological structure of the inverter and its control technique restrict the overall leakage current associated with the subarrays within the permissible limit. The operating principle of the proposed inverter was mentioned. The reference current generation for the buck-boost inductor and the controller configuration of the proposed inverter was elaborated in detail. A 1.3 kW PV system with the proposed inverter was simulated, and the simulation results were presented to confirm the viability of the proposed inverter.

REFERENCES:

[1] M. Islam and S. Mekhilef, “Efficient Transformerless MOSFET Inverter for a Grid-Tied Photovoltaic System,” IEEE Transactions on Power Electronics, vol. 31, no. 9, pp. 6305-6316, 2016.

[2] H. Xiao and S. Xie, “Transformerless split-inductor neutral point clamped three-level PV grid-connected inverter,” IEEE Transactions on Power Electronics, vol. 27, no. 4, pp. 1799-1808, 2012.

[3] P. Sharma, and V. Agarwal, “Maximum power extraction from a partially shaded PV array using shunt-series compensation,” IEEE Journal of Photovoltics, vol. 4, no. 4, pp. 1128-1137, 2014.

[4] C. Olalla, C. Deline, D. Clement, Y. Levron, M. Rodriguez, and D. Maksimovic, “Performance of power-limited differential power processing architectures in mismatched PV systems,” IEEE Transactions on PowerElectronics, vol. 30, no. 2, pp. 618-630, 2015.

[5] V. Samavatian, and A. Radan, “A High Efficiency Input/Output Magnetically Coupled Interleaved BuckBoost Converter With Low Internal Oscillation for Fuel-Cell Applications: CCM Steady-State Analysis,” IEEE Transactions on Industrial Electronics, vol. 62, no. 9, pp. 5560- 5568, 2015.

Z-network Plus Switched-capacitor Boost DC-DC Converters

 ABSTRACT:

In this paper, two Z-network plus switched-capacitor based DC-DC boost converters (ZSCBC) are proposed. The integration of the Z-network with switched-capacitor is responsible for yielding a high voltage gain and that too at lower duty ratios compared to the conventional quasi Z-source DC-DC converter (QZSC). Since the proposed converters contains Z or impedance-network, the operating duty ratio is less than 0.5 like in QZSC and retains its advantages such as common ground and low voltage stress on Z-network capacitors. Unlike QZSC, the switch and all the diode voltage stresses in the proposed converters is low even at high voltage gains. A detailed steadystate analysis is presented to identify the salient features of the proposed Z- network based boost converter and thereafter compared with other Z-source based configurations. Small-signal analysis is established and a single-loop voltage mode controller is designed. A 48 to 250 V, 130 W prototype is built to demonstrate the effectiveness of the ZSCBC. The steady-state and closed-loop response measurements validate the theoretical studies.

KEYWORDS:

1.      Boost converter

2.      Switched-capacitor

3.      Quasi-Z source DC-DC Converter

4.       Z-source Inverter

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

Two Z-network plus switched capacitor based DC-DC boost converters (ZSCBC) were proposed in this paper exhibiting voltage gain higher than QZSC while keeping the main advantages of QZSC intact such as low Z-network capacitor voltage stress, common ground and wider duty ratio range. The steady-state analysis of the ZSCBC and its comparison with other reported Topologies-1 to 7revealed that (i) the voltage stress of the switch and all the diodes is equal irrespective of their physical location, (ii) lower switch and diodes stress even at high voltage gain, and (iii) voltage gain enhancement through addition of a diode-capacitor network. Unlike the proposed converter, the Topologies-1 to 6 unable to incorporate the voltage gain enhancement feature. Detailed analysis was established and a single-loop voltage-mode controller was designed to ensure closed-loop stabilization of ZSCBC. Experimental measurements demonstrated the effectiveness of PID-type controller in terms of regulation against sudden changes in the load and source voltage. Furthermore, the controller designed was equally effective in rejecting low frequency disturbances present in the source.

 

REFERENCES:

[1] M. Forouzesh, Y. P. Siwakoti, S. A. Gorji, F. Blaabjerg and B. Lehman, "Step-Up DC–DC converters: A comprehensive review of voltageboosting techniques, topologies, and applications," in IEEE Trans. On Power Electron., vol. 32, no. 12, pp. 9143-9178, Dec. 2017.

[2] X. G. Feng, J. J. Liu and F. C. Lee: ‘Impedance specifications for stable dc distributed power systems’, in IEEE Trans. Power Electron., vol. 17, no. 2, pp. 157–162, Mar. 2002.

[3] F. Z. Peng, "Z-source inverter," in IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 504-510, Mar/Apr. 2003.

[4] J. Anderson and F. Z. Peng, "Four quasi-Z-Source inverters," in Proc. IEEE PESC, pp. 2743-2749, 2008.

[5] Y. P. Siwakoti, F. Z. Peng, F. Blaabjerg, P. C. Loh, and G. E. Town, “Impedance-source networks for electric power conversion part-I: A topological review”, in IEEE Trans. on Power Electron., vol. 30, no. 2,pp.699-716, Feb. 2015.

Symmetrical and Asymmetrical Reduced Device Multilevel Inverter Topology

 ABSTRACT:

This paper presents a single-phase symmetrical and asymmetrical multilevel inverter (MLI) topology. The presented topology can generate 9-level output voltage in a symmetrical configuration, 13-level and 17-level in asymmetrical configuration with a single cell. The number of output levels can be improved further by increasing either the number of cells or switches in a single cell. The presented topology contains the least number of DC sources, semiconductor switches, capacitors and diodes as compared to classical and recently proposed topologies. Reduction in component count decreases the size, complexity and cost of the overall converter. A detailed comparison has been done of the presented topology with recently proposed topologies in terms of DC sources, semiconductor switches, capacitor and total blocking voltage. Finally, to validate the presented concept, the prototype of the presented nine-level. Thirteen-level and seventeen-level MLI topologies have been tested in the laboratory for different switching frequencies, different modulation indexes, sudden load changes and nonlinear load.

KEYWORDS:

1.      Multilevel inverter topology

2.      Phase opposing disposition pulse width modulation

3.      Reduced device count

4.      Symmetrical and asymmetrical topology

5.      Total blocking voltage

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

This paper presented a symmetrical and asymmetrical MLI topology that can be used in high power/ high voltage applications with equal and unequal DC voltage sources. The presented topology generates nine-level output voltage in a symmetrical configuration, thirteen-level output voltage in asymmetrical binary (1:2) configuration and seventeen-level output voltage in asymmetrical trinary (1:3) configuration. The topology comprises the least number of power semiconductor switches, isolated DC sources, capacitors, diodes and low total blocking voltage on the switches as compared to classical and recently presented topologies. A detailed comparison of the presented topology with recently proposed topologies proves the superiority in aspects of component count and total blocking voltage which decreases the cost and increases the efficiency of the system. The performance of the presented topology has been tested through simulation and experimental validation shows the electrical feasibility of 9-/13-/17 level inverter.

REFERENCES:

[1] Morrison, J.,''Global Demand Projections for Renewable Energy Resources'', IEEE Canada Electrical Power Conference, Montreal, Que., pp. 537-542, Oct. 2007.

[2] Benner, J. P., Kazmerski, L.,''Photovoltaics gaining greater visibility'', IEEE spectrum, vol.36, no.9, pp. 34-42, Sep.1999.

[3] Zhao, Y.; Xiang, X.; Li, C.; Gu, Y.; Li, W.; He, X.,''Single-Phase High Step-up Converter with Improved Multiplier Cell Suitable for Half- Bridge-Based PV Inverter System'', in IEEE Transactions on Power Electronics, vol.29, no.6, pp. 2807-2816, Jul.2013.

[4] Y, Liao.; and C, Lai.,''Newly-Constructed Simplified Single-Phase Multistring Multilevel Inverter Topology for Distributed Energy Resources'', in IEEE Transactions on Power Electronics, vol.26, no.9, pp. 2386-2392, May. 2011.

[5] Rodríguez, J.; Bernet, S.; Wu, B.; Pontt, J. O.; Kouro, S., ''Multilevel voltage-source-converter topologies for industrial medium-voltage drives''. IEEE Transactions on industrial electronics, vol. 54, no.6, pp.2930-2945, Oct.2007.

A New Multilevel Inverter Topology With Reduce Switch Count

 ABSTRACT:

Multilevel inverters are a new family of converters for dc_ac conversion for the medium and high voltage and power applications. In this paper, two new topologies for the staircase output voltage generations have been proposed with a lesser number of switch requirement. The first topology requires three dc voltage sources and ten switches to synthesize 15 levels across the load. The extension of the first topology has been proposed as the second topology, which consists of four dc voltage sources and 12 switches to achieve 25 levels at the output. Both topologies, apart from having lesser switch count, exhibit the merits in terms of reduced voltage stresses across the switches. In addition, a detailed comparative study of both topologies has been presented in this paper to demonstrate the features of the proposed topologies. Several experimental results have been included in this paper to validate the performances of the proposed topologies with different loading condition and dynamic changes in load and modulation indexes.

KEYWORDS:

1.      Asymmetric, hybrid inverter

2.      Inverter topology

3.      Multilevel inverter

4.      MLI

5.      Nearest level control

6.      Power electronics

7.      Single-phase inverter

8.      Reduce switch count

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This paper presents a new assembly of multilevel inverter topology with consideration of reduced switch count. The proposed topology has been discussed in details with the basic unit with 3S-15L configuration generating 15 levels, and the extension of the proposed topology with 4S-25L configuration to achieves 25 levels. Two generalized structure of the proposed topology has also been proposed. A detailed comparative study has been carried out with the proposed topology and recently reported topologies with three and four dc voltage sources. Finally, several experimental results proves the suitability and workability of the proposed topology with different type of loading combinations considering the change of modulation indexes.

REFERENCES:

[1] H. Akagi, ``Multilevel converters: Fundamental circuits and systems,'' Proc. IEEE, vol. 105, no. 11, pp. 2048_2065, Nov. 2017.

[2] J. I. Leon, S. Vazquez, and L. G. Franquelo, ``Multilevel converters: Control and modulation techniques for their operation and industrial applications,'' Proc. IEEE, vol. 105, no. 11, pp. 2066_2081, Nov. 2017.

[3] J. Rodríguez, J.-S. Lai, and F. Z. Peng, ``Multilevel inverters: A survey of topologies, controls, and applications,'' IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724_738, Aug. 2002.

[4] S. Kouro et al., ``Recent advances and industrial applications of multilevel converters,'' IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2553_2580, Aug. 2010.

[5] N. Prabaharan and K. Palanisamy, ``A comprehensive review on reduced switch multilevel inverter topologies, modulation techniques and applications,'' Renew. Sustain. Energy Rev., vol. 76, pp. 1248_1282, Sep. 2017.

 

Control of Solar Photovoltaic Integrated UniversalActive Filter Based on Discrete Adaptive Filter

ABSTRACT:

In this work, a novel technique based on adaptive filtering is proposed for the control of three phase universal active power filter with a solar photovoltaic array integrated at its DC bus. Two adaptive filters along with a zero crossing detection technique, are used to extract the magnitude of fundamental active component of distorted load currents, which is then used in estimation of reference signal for the shunt active filter. This technique enables extraction of active component of all three phases with reduced mathematical computation. The series active filter control is based on synchronous reference frame theory and it regulates load voltage and maintains it in-phase with voltage at point of common coupling under conditions of voltage sag and swell. The performance of the system is evaluated on an experimental prototype in the laboratory under various dynamic conditions such as sag and swell in voltage at point of common coupling, load unbalancing and change in solar irradiation intensity.

KEYWORDS:

1.      Power quality

2.      Universal active power filter

3.      Adaptive filtering

4.      Photovoltaic system

5.      Maximum power point tracking

6.      Quadrature signal generation

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

The performance of adaptive filter based PV-UAPF system under both steady state and dynamic conditions, have been analyzed in detail. The method of sampling the fundamental component of load current obtained through adaptive filter enables fast extraction of fundamental active component of nonlinear load currents for all phases in one sampling. Only two adaptive filters are required to extract magnitude of active component of three phase load currents. This technique requires reduced computational resources while achieving good dynamic and steady state performance in extraction of fundamental active component of nonlinear load current. The system performance has been found to be satisfactory under various disturbances in load current, PCC voltage and solar irradiation. The series active filter is able to regulate load voltage at 220 V under variations of PCC voltage from 170 V to 270 V. The grid current THD is maintained at approximately 3% even though the THD of load current is 28% thus meeting requirement of IEEE-519 standard. The PV-UAPF system has been able to maintain the grid currents balanced under unbalanced loading condition.

The proposed topology and algorithm are suited for employing in conditions where PCC voltage sags/swells and load current harmonics are major power quality issues. Certain power quality issues not addressed include voltage distortions, flicker, neutral current compensation etc. This power quality issues can be addressed by modification of topology and control algorithm according to the requirements in the distribution system. The PV-UAPF system provides dual benefit of distributed generation as well as improving power quality of the distribution system.

REFERENCES:

 [1] N. R. Tummuru,M. K. Mishra, and S. Srinivas, “Dynamic energy management of hybrid energy storage system with high-gain pv converter,” IEEE Transactions on Energy Conversion, vol. 30, no. 1, pp. 150–160, March 2015.

[2] B. Singh, A. Chandra, K. A. Haddad, Power Quality: Problems and Mitigation Techniques. London: Wiley, 2015.

[3] S. Devassy and B. Singh, “Control of solar photovoltaic integrated upqc operating in polluted utility conditions,” IET Power Electronics, vol. 10, no. 12, pp. 1413–1421, Oct 2017.

[4] S. Devassy and B. Singh, “Performance analysis of proportional resonant and adaline-based solar photovoltaic-integrated unified active power filter,” IET Renewable Power Generation, vol. 11, no. 11, pp. 1382– 1391, 2017.

[5] L. Ramya and J. Pratheebha, “A novel control technique of solar farm inverter as pv-upfc for the enhancement of transient stability in power grid,” in 2016 International Conference on Emerging Trends in Engineering, Technology and Science (ICETETS), Feb 2016, pp. 1–7.                                         

A New Circuit of Modular Multilevel Inverter for Grid-Connected Photovoltaic Conversion Plants

ABSTRACT:

This study presents a new circuit topology of the Modular Multilevel Converter (MMC) which is deployed for photovoltaic grid applications. In the conventional MMC, two arm inductors are placed in each phase to limit the circulating current. In the proposed topology, the inductors are replaced by a transformer. The proposed circuit gives a 50% reduction of the voltage rating of the power devices and the capacitors in comparison with the conventional MMC. The required dc-link voltage which is fed directly by PV panels is also reduced by half. The paper presents a PWM method to control the solar inverter output voltage. The proposed concept is confirmed through simulation and experimental results.

KEYWORDS:

1.      Photovoltaic (PV) conversion

2.      Modular multilevel converter

3.      Pulse width modulation

4.      Parameter

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

In this paper, the feasibility of a new circuit topology for the MMC has been outlined, where it is deployed as an interface between the grid and PV modules. With this arrangement, the voltage rating of capacitors and the power semiconductor devices are effectively reduced by half. The dc bus magnitude which is formed by the dc output from PV array is also reduced by half. A method to suppress the 2nd harmonic current in the inverter has been discussed. The concept of level-shifted PWM, where the modulating waveform is shifted and scaled to bring inside one carrier, has been used to reduce the switching frequency. With this, there is no need to calculate the duty cycle of individual cells. The proposed idea has been verified by simulation and experimental results under disturbance in the system caused by solar irradiance changes.

REFERENCES:

[1] Q.-C. Zhong and T. Hornik, Control of Power Inverters in Renewable Energy and Smart Grid Integration, Hoboken, NJ: Wiley, 2013.

[2] A. G. Golnas, “PV system reliability: An operator’s perspective,” IEEE J. Photovolt., Vol. 3, No. 1, pp. 416-421, Jan. 2013.

[3] International Energy Agency. (2010, May). Technology Roadmap, Solar Photovoltaic Energy [Online].

[4] E. Romero-Cadaval, G. Spagnuolo, L. G. Franquelo, et al., “Grid-Connected Photovoltaic Generation Plants,” IEEE Ind. Electron. Mag., Vol. 7, No. 3, pp. 6-20, Sept. 2013.

[5] M. G. Villalva, J. R. Gazoli and E. R. Filho, “Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays,” IEEE Trans. Power Electron, Vol. 24, No. 5, pp. 1198-1208, May 2009.