A New Step-Up Switched-Capacitor Voltage Balancing Converter for NPC Multilevel Inverter-Based Solar PV System

 ABSTRACT:

This paper proposed a grid connected solar Photovoltaic (PV) Systems with a new voltage balancing converter suitable for Neutral-Point-Clamped (NPC) Multilevel Inverter (MLI). The switched capacitors used in the proposed converter is able to balance the DC link capacitor voltage effectively by using proper switching states. The proposed balancing converter can be extended to any higher levels and it can boost the DC input voltage to a higher voltage levels without using any magnetic components. This feature allows the converter to operate with the boosting capability of the input voltage to the desired output voltage while ensuring the self-balancing. In this paper the proposed converter is used for a grid connected solar PV system with NPC multilevel inverter, which is controlled using vector control scheme. The proposed grid connected solar PV system with associated controllers and maximum power point tracking (MPPT) is implemented in Matlab/SimPowerSystem and experimentally validated using dSPACE system and designed converters. The simulation and experimental results show that the proposed topology can effectively balance the DC link voltage, extract maximum power from PV module and inject power to the grid under varying solar irradiances with very good steady state and dynamic performances.

KEYWORDS:

1.      Solar photovoltaics

2.      NPC multilevel inverter

3.      Balancing circuit

4.      Dc-link voltage balancing

5.      Grid connected PV system

 

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A new step-up voltage balancing converter for solar photovoltaic system which is suitable for NPC-MLI has been proposed in this paper. The proposed converter not only can boost the input PV voltage at the desired output level, but also can remove the magnetic elements which reduces the weight and cost of the system. It also requires only one DC source or PV array output to produce multi-level output, which reduces the number of input voltage sources required in such systems. Capacitance calculation, voltage ripple of the capacitors, output power and normalized energy according to the number of output levels are also analyzed. A deep comparison with other DC-DC topologies has been done and showed the cost effectiveness of the proposed converter. The proposed converter is implemented for a grid connected solar PV system with a NPC multilevel inverter, which is controlled using vector control scheme. The proposed system with associated controllers is implemented in Matlab/SimPowerSystem and experimentally validated using dSPACE DSP (digital signal processor) system and designed converters. The simulation and experimental results confirms that the proposed topology can effectively balance the DC link voltage, extract maximum power from PV module and inject power to the grid under varying solar irradiances with very good steady state and dynamic performances.

REFERENCES:

[1] P. R. Bana, K. P. Panda, R. T. Naayagi, P. Siano, and G. Panda, ``Recently developed reduced switch multilevel inverter for renewable energy integration and drives application: Topologies, comprehensive analysis and comparative evaluation,'' IEEE Access, vol. 7, pp. 54888_54909, 2019.

[2] S. Shuvo, E. Hossain, T. Islam, A. Akib, S. Padmanaban, and M. Z. R. Khan, ``Design and hardware implementation considerations of modified multilevel cascaded H-Bridge inverter for photovoltaic system,'' IEEE Access, vol. 7, pp. 16504_16524, 2019.

[3] F. Z. Peng, ``A generalized multilevel inverter topology with self voltage balancing,'' IEEE Trans. Ind. Appl., vol. 37, no. 2, pp. 611_618, Mar./Apr. 2001.

[4] A. Taghvaie, J. Adabi, and M. Rezanejad, ``A self-balanced step-up multilevel inverter based on switched-capacitor structure,'' IEEE Trans. Power Electron., vol. 33, no. 1, pp. 199_209, Jan. 2018.

[5] V. Dargahi, A. K. Sadigh, M. Abarzadeh, S. Eskandari, and K. A. Corzine, ``A new family of modular multilevel converter based on modified flying-capacitor multicell converters,'' IEEE Trans. Power Electron., vol. 30, no. 1, pp. 138_147, Jan. 2015.

A Microgrid Based on Wind Driven DFIG, DG andSolar PV Array for Optimal Fuel Consumption

ABSTRACT:

This paper presents a green energy solution to a microgrid for a location dependent on a diesel generator (DG) to meet its electricity requirement. The proposed microgrid is powered by two renewable energy sources such as wind energy conversion system (WECS) using doubly fed induction generator (DFIG) and solar photovoltaic (PV) system. The solar PV array is directly connected to common DC bus of back-back voltage source converters (VSCs), which are connected in the rotor side of DFIG. Moreover, a battery energy storage (BES) is connected at the same DC bus through a buck-boost DC-DC converter to provide path for excess stator power of DFIG. The extraction of maximum power both from wind and solar is achieved through rotor side converter (RSC) control and buck-boost DC-DC converter control, respectively. A modified perturb and observe (P&O) algorithm is presented to extract maximum power from the solar PV array. Moreover, the control of load side converter (LSC), is designed to optimize the fuel consumption of DG. A novel generalized concept is proposed to compute the reference DG power output for optimal fuel consumption. The microgrid is modelled and simulated using SimPowerSystems tool box of MATLAB, for various scenarios such as varying wind speeds, varying insolation, effect of load variation on bidirectional converter and unbalanced nonlinear load connected at point of common coupling (PCC). The DFIG stator currents and DG currents, are found balanced and sinusoidal. Finally, an experimental prototype is developed in the laboratory to validate the proposed scheme.

KEYWORDS:

1.      Wind Turbine

2.      Doubly fed induction generator (DFIG)

3.      Diesel generator

4.      Solar photovoltaic array

5.      Bidirectional buck boost converter

6.      Battery energy storage

7.      Power quality

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The proposed microgrid based on wind turbine driven DFIG, DG and solar PV array with BES, has been presented. The solar PV array is directly connected to DC link of back-back connected VSCs, whereas BES is connected through buck-boost converter. The system has been simulated for various scenarios such as variable wind speeds, variable insolation and unbalanced nonlinear load connected at PCC. Moreover, the performance of buckboost converter at change in load has been investigated. The simulated results have shown the satisfactory performance to achieve optimal fuel consumption. The DFIG stator voltages, currents and DG currents, are found balanced and sinusoidal, as per the IEEE 519 standard. A prototype has been developed in the laboratory to validate the performance of the microgrid. Test results have shown quite good performance under variable wind speeds, variable insolation and change in load.

REFERENCES:

 [1] J. Knudsen, J. D. Bendtsen, P. Andersen, K. K. Madsen, and C. H. Sterregaard, “Supervisory control implementation on diesel-driven generator sets,” IEEE Trans. Ind. Electron., vol. 65, no. 12, pp. 9698- 9705, Dec. 2018.

[2] J. Jo, H. An, and H. Cha, “Stability improvement of current control by voltage feedforward considering a large synchronous inductance of a diesel generator,” IEEE Trans. Ind. Applicat., vol. 54, no. 5, pp. 5134- 5142, Sept.-Oct. 2018.

[3] Y. Zhang, A. Melin, S. M. Djouadi, M. Olama, and K. Tomsovic, “Provision for guaranteed inertial response in diesel-wind systems via model reference control,” IEEE Trans. Power Systems, Early Access.

[4] N. Nguyen-Hong, H. Nguyen-Duc, and Y. Nakanishi, “Optimal sizing of energy storage devices in isolated wind-diesel systems considering load growth uncertainty,” IEEE Trans. Ind. Applicat., vol. 54, no. 3, pp. 1983-1991, May-June 2018.

[5] W. Li, P. Chao, X. Liang, J. Ma, D. Xu, and X. Jin, “A practical equivalent method for DFIG wind farms,” IEEE Trans. Sustain. Energy, vol. 9, no. 2, pp. 610-620, April 2018.

A Management of power flow for DC Microgrid with Solar and Wind Energy Sources

 ABSTRACT:

Today there is a rapid proliferation of DC loads into the market and DC micro grid with renewable energy sources is emerging as a possible solution to meet growing energy demand. As different energy sources like solar, wind, fuel cell, and diesel generators can be integrated into the DC grid, Management of power flow among the sources is essential. In this paper, a control strategy for Management of power flow in DC micro grid with solar and wind energy sources is presented. As the regulation of voltage profile is important in a standalone system, a dedicated converter is to be employed for maintaining the DC link voltage. DC link voltage is regulated by the battery circuit while maximum power is extracted from Solar and Wind to feed the loads connected at the DC bus. A power flow algorithm is developed to control among three sources in the DC Microgrid. The algorithm is tested for various load conditions and for fluctuations in solar and wind power in MATLAB/SIMULINK environment.

KEYWORDS:

1.      DC microgrid

2.      Power flow administration

3.      Photovoltaics

4.      Wind conversion systems

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

A Management of power flow and control algorithm for DC microgrid with solar and wind energy sources is presented. As the system involves different intermitted energy sources and load whose demand can vary, it is necessary to develop a Management of power flow and control algorithm for the DC Microgrid. To provide ceaseless power supply to the loads and balance the power flow among the different sources at any time, a Management of power flow algorithm is developed. The feasibility of the algorithm has been tested for various load conditions and for changes in solar and wind power.

REFERENCES:

 

 [1] F. Katiraei, M. R. Iravani, A. L. Dimeas, and N. D. Hatziargyriou, "Microgrids management: control and operation aspects of microgrids," IEEE Power Energy Mag., vol. 6, no. 3, pp. 54-65, May/Jun. 2008.

[2] W. Jiang and B. Fahimi, “Active current sharing and source management in fuel cell-battery hybrid power system,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 752–761, Jan. 2010.

[3] L. Xu and D. Chen, "Control and operation of a DC microgrid with variable generation and energy storage," IEEE Trans. Power Del., vol. 26, no. 4, pp. 25 I 3-2522, Oct. 2011.

[4] Jin C, Wang P, Xiao J, "Implementation of hierarchical control in DC microgrids,"IEEE Transaction of Industrial Electronics, vol.61(8), pp.4032-4042,2014.

[5] L. Xiaonan, J. M. Guerrero, S. Kai, and J. C. Vasquez, "An Improved Droop Control Method for DC Microgrids Based on Low Bandwidth Communication With DC Bus Voltage Restoration and Enhanced Current Sharing Accuracy," Power Electronics, IEEE Transactionson,vol.29,pp.1800-1812,2014.

A low-voltage ride-through strategy using mixed potential function for three-phase grid-connected PV systems

 ABSTRACT:

This paper presents a new control strategy for low-voltage ride-through for 3-phase grid-connected photovoltaic systems. The proposed fault ride through control algorithm, which is designed based on mixed potential function, can protect the inverter from over current failure under both symmetric and asymmetric faults, reduce the double frequency oscillation and provides reactive power support by applying a voltage compensation unit. With the proposed method, the inverter can also inject sinusoidal current during asymmetric faults. The method does not require a hard switch to switch from the Maximum Power Point Tracking (MPPT) to a non-MPPT algorithm, which ensures a smooth transition.

KEYWORDS:

1.      Current control

2.      Fault-ride-through

3.      Photovoltaic

4.      Micro-grids

5.      Large-signal analysis

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This paper proposes a LVRT control strategy for low voltage distribution networks with PV system directly connected to the grid. The method is based on the classic cascaded voltage and current loops in dqframe, while the positive and negative sequence components are used to modify the reference DC-link voltage to limit the inverter current during the grid faults. The mixed-potential function is used to regulate the compensation term of the DC-link voltage. Through applying this regulation, the double grid frequency oscillation, which is appeared in inverter active power and DC-link voltage following an asymmetric fault, can be reduced. The method also generates sinusoidal inverter current during faults. The reactive power injection is used to supply the required reactive power to restore the voltage. In choosing the DC-link capacitor this should be taken into account that the proposed method increases the DC-link voltage during faults. However, since the protection systems must operate within a fracture of a second, this should not be a huge burden on an appropriate power capacitor. The proposed method is validated in MATLAB/SIMULINK. Simulation results show the proposed LVRT control strategy can be used for both symmetric and asymmetric faults. The simulation results also demonstrate that the proposed voltage compensation unit, derived from the mixed potential function, reduces the double grid frequency oscillation. The presented results show that for a severe voltage sag (3-phase fault), the proposed method could reduce the fault current to 1.5 pu to protect the inverter from overcurrent failure. For asymmetric voltage sags, the proposed method could limit the fault current to almost rated value. In addition, this method does not require a hard switch to switch from the MPPT to a non-MPPT algorithm, which ensures a smooth transition. It is noted that the proposed method does not affect the

REFERENCES:

[1] D.E. Olivares, A. Mehrizi-Sani, A.H. Etemadi, C.A. Canizares, R. Iravani, M. Kazerani, A.H. Hajimiragha, O. Gomis-Bellmunt, M. Saeedifard, R. Palma- Behnke, G.A. Jimenez-Estevez, N.D. Hatziargyriou, Trends in microgrid control, IEEE Trans. Smart Grid 5 (4) (2014) 1905–1919, https://doi.org/10.1109/TSG. 2013.2295514.

[2] B. Lasseter, Microgrids, Proc. IEEE Power Eng. Soc. Winter Meeting 1 (2002) 146–149.

[3] R. Meyer, A. Zlotnik, A. Mertens, Fault Ride Through Control of Medium-voltage Converters With LCL Filter in Distributed Generation Systems, (2013), pp. 1954–1961, https://doi.org/10.1109/ECCE.2013.6646947 edn..

[4] J. Hu, Y. He, L. Xu, B.W. Williams, Improved control of DFIG systems during network unbalance using PIR current regulators, IEEE Trans. Ind. Electron. 56 (2) (2009) 439–451, https://doi.org/10.1109/TIE.2008.2006952.

[5] A. Camacho, M. Castilla, J. Miret, J.C. Vasquez, E. Alarcon-Gallo, Flexible voltage support control for three-phase distributed generation inverters under grid fault, IEEE Trans. Ind. Electron. 60 (4) (2013) 1429–1441, https://doi.org/10.1109/TIE. 2012.2185016.

 

A High Efficiency Non-Isolated Buck-Boost Converter Based on ZETA Converter

ABSTRACT:

  In this paper, a new transformerless buck-boost converter based on ZETA converter is introduced. The proposed converter has the ZETA converter advantages such as, buck-boost capability, input to output DC insulation and continuous output current. The suggested converter voltage gain is higher than the classic ZETA converter. In the presented converter, only one main switch is utilized. The proposed converter offers low voltage stress of the switch; therefore, the low on-state resistance of the main switch can be selected to decrease losses of the switch. The presented converter topology is simple; hence, the control of the converter is simple. The converter has the continuous output current. The mathematical analyses of the presented converter are given. The experimental results confirm the correctness of the analysis.

KEYWORDS:

1.      Transformerless buck-boost converter

2.      Voltage gain

3.      Main switch

4.      Voltage stress

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

In this paper, a novel transformerless buck boost converter based on ZETA converter is presented. In this converter, only one main switch is used, which decreases the losses and improves efficiency. The active switch voltage stress is low and switch with low on-state resistance can be utilized. The voltage gain of the converter is higher than that of the classic boost, buck-boost, ZETA, CUK and SEPIC converters. The presented converter structure is simple; hence, the converter control is simple. The buck-boost converters are used in some applications such as fuel-cell, car electronic devices, and LED drivers. Finally, the experimental results are given to verify the proposed converter.

REFERENCES:

 [1] W. Li and X. He, “Review of nonisolated high-step-up DC/DC converters in photovoltaic grid-connected applications,” IEEE Trans. Ind. Electron., vol. 58, no. 4, pp. 1239-1250, Apr. 2011.

[2] H. S. Lee, H. J. Choe, S. H. Ham and B. Kang, “High-efficiency asymmetric forward-flyback converter for wide output power range,” IEEE Trans. Power Electron., vol. 32, no. 1, pp. 433-440, Jan. 2017.

[3] N. Mohan, T. M. Underland, W. P. Robbins, “Power Electronics Converters,Applications and Design” Wiley, New York, USA, 2nd Edition, 1995.

[4] H. Tao, J. L. Duarte, M. A. M. Hendrix, “Line-interactive UPS using a fuel cell as the primary source,” IEEE Trans. Ind. Electron., vol. 55, no. 8, pp. 3012-3021, Aug. 2008.

[5] P. James, A. Forsyth, G. Calderon-Lopez, V. Pickert “DC-DC converter for hybrid and all electric vehicles,” EVS24 Stavanger, Norway, May 13-16, 2009.

 

A frequency response strategy for variable speed wind turbine based on a dynamic inertial response and tip-speed ratio control

 ABSTRACT:

Participation of the wind turbine generators (WTGs) in the frequency regulation service is an appealing issue in order to consider the safe increasing of the wind power generation. The droop and virtual inertia control are the most popular approaches that facilitate the WTGs to provide frequency regulation. However, the intermittent nature of the wind complicates the implementation of these methods and has impacts on the wind turbine stability and may cause violation of the allowed power reserve and minimum turbine rotor speed. Therefore, in this paper, a control approach based on the dynamic de-loading technique is proposed, where the wind turbine operating curve is dynamically adjusted in the response of the frequency deviation throughout controlling the turbine tip-speed ratio which helps the turbine provide steady-state power sharing within the reserved power as well as the transient response within its stability criteria. In addition, the inertial response based on a dynamic gain is suggested. The inertial weighting gain has been formulated where it is continuously regulated in the response of rotor speed and reflects the amount of available kinetic energy in the rotating mass. The effectiveness of the proposed control approaches is verified throughout the comparisons of the results with the fixed inertial gain control and the droop control. The simulation results confirm that the combined control of the proposed tip-speed ratio and dynamic inertia control improve the overall system dynamic behavior in terms of frequency response and turbine stability.

KEYWORDS:

1.      Variable speed wind turbine

2.       Frequency regulation

3.      De-loading

4.      Inertia response

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This study focused on the frequency regulation capability of VSWTs. A tip-speed ratio control is presented, where the wind turbine operating curve is dynamically adjusted in the response of frequency deviation. Furthermore, inertial response based on a dynamic gain is suggested, where the inertial weighting gain is continuously regulated in the response of the rotor speed and reflects the amount of available kinetic energy. According to the proposed control strategy, the wind turbine can provide frequency regulation effectively up to rated wind speed (over-speed control zone).However, above rated wind speed, the wind turbine will be operated at rated power and cannot provide frequency regulation supports. The proposed control strategy has been analyzed at different load step disturbances at up- and down-frequency events along the over-speed control zone. Also, the proposed control methods are compared with the two different implementations of the droop control and the inertial control. The results proved that the proposed dynamic tip-speed ratio control has the ability to improve frequency nadir and steady state frequency while ensuring stable operation of the wind turbine. Moreover, the proposed control approaches ensure stable operations of the wind turbine even at low wind speed at 7.5 m/s and high step disturbances of 0.15 pu. The proposed control strategy can be extended in the future to be valid for all wind speed ranges and also can be extended to help the WTGs to participate in the load frequency control.

REFERENCES:

1. Dong J, Xue G, Dong M, Xu X (2015) Energy-saving power generation dispatching in China: regulations, pilot projects and policy recommendations-A review. Renew Sustain Energy Rev 43:1285–1300. https://doi.org/10.1016/j.rser.2014.11.037

2. Amano RS (2017) Review of wind turbine research in 21st century. J Energy Resour Technol 139:050801–050801–050801–050808. https://doi.org/10.1115/1.4037757

3. Sawin JL, Seyboth K, Sverrisson F (2016) Renewables 2016: Global Status Report. In: REN21. http://www.ren21.net/wpcontent/ uploads/2016/05/GSR_2016_Full_Report_lowres.pdf

4. Magdy G, Mohamed EA, Shabib G et al (2018) SMES based a new PID controller for frequency stability of a real hybrid power system considering highwind power penetration. IET RenewPowerGener 12:1304–1313. https://doi.org/10.1049/iet-rpg.2018.5096

5. Choi JW, Heo SY, Kim MK (2016) Hybrid operation strategy of wind energy storage system for power grid frequency regulation. IETGenerTransm Distrib 10:736–749. https://doi.org/10.1049/ietgtd. 2015.0149

A Comprehensive Strategy for Power QualityImprovement of Multi-Inverter-Based MicrogridWith Mixed Loads

 

ABSTRACT:

In order to solve the influence of nonlinear and unbalanced mixed loads on output voltage of micro source inverters in microgrid, this paper proposes a comprehensive strategy which can be used to accurate power distribution, harmonic suppression, negative-sequence voltage component suppression, and stability improvement. On one hand, a fundamental control strategy is proposed upon the conventional droop control; the problem of accurate reactive power distribution is solved by introducing virtual impedance to inverters, while considering the aggravating problem of stability because of introducing virtual impedance, a secondary power balance controller is added to improve the stability of voltage and frequency. On the other hand, the fractional frequency harmonic control strategy and negative-sequence voltage control strategy are proposed to solve the influence of mixed loads, which focus on eliminating specific harmonics caused by the nonlinear loads and the negative sequence component of the voltage. The power quality of microgrid can be improved effectively. Finally, small signal analysis is used to analyze the stability of the multi converter parallel system after introducing the whole control strategy. The simulation results show that the strategy proposed in this paper has a great performance on distributing reactive power, regulating and eliminating harmonic components, eliminating negative-sequence components and stabilizing output voltage of inverters and frequency, and improving the power quality of multi inverter-based microgrid.

KEYWORDS:

1.      Microgrid

2.      Mixed loads

3.      Power quality

4.       Harmonic suppression

5.      Negative sequence voltage

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This paper proposes a comprehensive strategy for accurate power distribution, harmonic suppression, voltage negative sequence component suppression, and stability improvement of multi-inverter-based microgrid, with the combination of virtual impedance droop control and secondary power balance control, the active and reactive can be distributed accurately, meanwhile the stability of voltage and frequency are obviously improved, next a harmonic suppression control strategy is introduced to suppress harmonic components in microgrid. Furthermore, small signal analysis is used to analyze the stability of the proposed multi-converter parallel system after introducing the comprehensive theory. The simulation and experimental of results certify that proposed the strategy has great performance on accurate reactive power distribution, harmonic suppression, voltage negative sequence component suppression, stability improvement.

REFERENCES:

[1] Y. Li, B. Feng, G. Li, J. Qi, D. Zhao, and Y. Mu, ``Optimal distributed generation planning in active distribution networks considering integration of energy storage,'' Appl. Energy, vol. 210, pp. 1073_1081, Jan. 2018.

[2] G. Benysek and M. Pasko, Power Theory and Power Quality Management, 1st ed. Beijing, China: China Machine Press, Oct. 2013.

[3] Z. Jianhua and H. Wei, Microgrid Operation Control and Protection Technology, 1st ed. Beijing, China: China Electric Power Press, Jul. 2010.

[4] Y. Li, Y. Li, G. Li, D. Zhao, and C. Chen, ``Two-stage multi-objective OPF for AC/DC grids with VSC-HVDC: Incorporating decisions analysis into optimization process,'' Energy, vol. 147, pp. 286_296, Mar. 2018.

[5] W. Jibiao, C. Qihong, and L. Li, ``Grid connected inverter control of three phase voltage unbalance compensation in micro grid,'' Autom. Electr. Power Syst., vol. 41, no. 8, pp. 38_44, 2017.