Droop Control of Distributed Electric Springs for Stabilizing Future Power Grid

ABSTRACT:

This paper describes the droop control method for parallel operation of distributed electric springs for stabilizing ac power grid. It provides a methodology that has the potential of allowing reactive power controllers to work in different locations of the distribution lines of an ac power supply and for these reactive power controllers to support and stabilize the ac mains voltage levels at their respective locations on the distribution lines. The control scheme allows these reactive power controllers to have automatically adjustable voltage references according to the mains voltage levels at the locations of the distribution network. The control method can be applied to reactive power controllers embedded in smart electric loads distributed across the power grid for stabilizing and supporting the ac power supply along the distribution network. The proposed distributed deployment of electric springs is envisaged to become an emerging technology potentially useful for stabilizing power grids with substantial penetration of distributed and intermittent renewable power sources or weakly regulated ac power grid.

KEYWORDS:

1.      Droop control

2.      Electric springs

3.      Smart gird

4.      Voltage regulation

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

 Fig. 1. Single phase diagram of the experimental setup of the power grid and loads (with 3 distributed electric springs working as a group).

EXPECTED SIMULATION RESULTS:

Fig. 2. (a) Measured root-mean-square values of the mains voltage V_S1,V_S2 and V_S3 (b) Measured root-mean-square values of the mains voltage V_S1,V_S2 and V_S3 from 1800 to 1440 sec (ES activated without the proposed droop control) (c) Measured root-mean-square values of the mains voltage V_S1,V_S2 and V_S3 from 1800 to 2160 sec (ES activated with the proposed droop control).

Fig. 3. Measured average value of reactive power generated by the 3 electric springs (Q_a1 ,Q_a2 and Q_a3 ).

Fig. 4. Measured modulation indexes of the electric springs M₁,M₂ and M₃ .

Fig. 5. Measured average value of the critical load power P_R1,P_R2 and P_R3 .

Fig. 6. Measured root-mean-square values of the non-critical load voltage V_o1 ,V_o2 and V_o3 .

Fig. 7. Measured average value of the non-critical load power P_o1,P_o2 and P_o3

.

CONCLUSION:

A control scheme has been successfully developed and implemented for a group of electric springs. It enables individual electric springs to generate their mains voltage reference values according to their installation locations in the distribution lines and to work in co-operative manner, instead of fighting against one another, therefore allowing the electric springs to work in group to maximize their reactive power compensation effects for voltage regulation. The control method also leads to more evenly distribution of load power shedding among the non-critical loads. The attractive features of the control scheme have been successfully verified in an experimental smart grid setup.

With the droop control scheme,many electric springs of small VA ratings could be embedded into non-critical loads such as electric water heaters and refrigerators to form a new generation of smart loads that are adaptive to power grid with substantial penetration of renewable energy sources of distributed and intermittent nature. If many small electric springs are deployed in the power grid in a distributed manner, their collective voltage stabilizing efforts can be added together. Because the electric springs allow these smart loads to consume power following the varying profile of intermittent renewable energy sources, they have the potential to solve the stability problems arising from the intermittent nature of renewable energy sources and ensure that the load demand will follow power generation, which is the new control paradigm for future smart grid. Since the electric appliances embedded with the electric springs can share load shedding automatically, this approach should be more consumer-friendly when compared with the on-off control of electric appliances. For example, shutting down refrigerators is intrusive and inconvenient to the consumers (and may involve consumers’ rights issues) and requires some forms of central control. Allowing many smart refrigerators to shed some load without being noticed and central control is more consumer- friendly.

The individual operations of the electric springs have previously been evaluated. The successful implementation of the droop control for 3 electric springs working as a group in a small distributed network in this study is a just a step forward to confirm that multiple electric springs can work together without ICT technology. The collective effects of electric springs and their capacity are new topics that deserve further investigations. Extensive simulation studies are needed to confirm the effectiveness of many such electric springs working together in a large-scale power system model.

REFERENCES:

[1] P. P. Varaiya, F. F. Wu, and J. W. Bialek, “Smart operation of smart grid: Risk-limiting dispatch,” Proc. IEEE, vol. 99, no. 1, pp. 40–57, 2011.

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[3] P. Palensky and D. Dietrich, “Demand side management: Demand response, intelligent energy systems, and smart loads,” IEEE Trans. Ind. Informatics, vol. 7, no. 3, pp. 381–388, 2011.

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[5] M. Parvania and M. Fotuhi-Firuzabad, “Demand response scheduling by stochastic SCUC,” IEEE Trans. Smart Grid, vol. 1, no. 1, pp. 89–98,2010.

Cascaded Multilevel Inverter Based Electric Spring for Smart Grid Applications

ABSTRACT:

This paper proposes “Electric Spring” (ES) based on Single Phase three-level Cascaded H-Bridge Inverter to achieve effective demand side management for stabilizing smart grid fed by substantial intermittent renewable energy sources (RES). Considering the most attractive features of multilevel inverter (MLI), an effective structure of Electric Spring is proposed for suppressing voltage fluctuation in power distribution network arising due to RES and maintaining the critical load voltage. Also, the operation of ES in capacitive as well as inductive mode is discussed. Further, the paper describes droop control method for parallel operation of distributed electric spring for stabilization the power grid. An exclusive dynamic performance of the system using electric spring has been tested and demonstrated through detailed MATLAB simulation.

KEYWORDS:

1.      Critical load

2.      Cascaded H-Bridge Inverter

3.       Droop control

4.       Electric Spring

5.       MLI

6.       RES

7.       Smart load

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1. Schematic of Electric Spring.

EXPECTED SIMULATION RESULTS:

Fig. 2. Observed RMS value of (a) Source voltage (V_s), (b) Non–critical voltage (V_nc), (c) Electric spring voltage (V_a) & current (I_a), (d) Critical voltage (V_c) in capacitive mode.

Fig. 3. Observed Instantaneous value of (a) Source voltage (V_s), (b) Non–critical voltage (V_nc), (c) Electric spring voltage (V_a) & current (I_a), (d) Critical voltage (V_c) in capacitive mode.

Fig. 4. Observed RMS value of (a) Source voltage (V_s), (b) Non–critical voltage (V_nc), (c) Electric spring voltage (V_a) & current (I_a), (d) Critical voltage (V_c) in inductive mode.

Fig. 5. Observed Instantaneous value of (a) Source voltage (V_s), (b) Non– critical voltage (V_nc), (c) Electric spring voltage (V_a) & current (I_a), (d) Critical voltage (V_c) in inductive mode.

Fig. 6. THD analysis of (a) Two-level and (b) Three-level CHMLI based ES.

CONCLUSION:

The paper proposes new approach for regulating the mains voltage using MLI based ES for smart grid applications. The implemented Three-level CHMLI based ES for smart grid application effectively regulates the ac mains voltage and reduces the THD content as compared with Two-level VSI based ES. The effectiveness of ES is validated through digital simulation in terms of THD. Lastly simulation results of droop control for Four Electric springs have been implemented in a large-scale distributed pattern in order to make multiple ES act in coordinating manner so as to have robust stabilizing effect.

REFERENCES:

[1] Edward J.Coster, Johanna M.A.Myrzik, BAS Kruimer, “Integration Issues of Distributed Generation Distribution Grids,” Proceedings of the IEEE, vol.99, no.1, pp.28-39, January, 2011.

[2] Koutsopoulos and L. Tassiulas, “Challenges in demand load control for the smart grid,” IEEE Netw., vol. 25, no. 5, pp. 16–21, 2011.

[3] M.H.J.Bollen, “Understanding Power Quality Problems: Voltage Sags and Interruptions,” IEEE Press, 2000.

[4] N. Hingorani and L. Gyugyi, Understanding FACTS, Concepts and Technology of Flexible AC Transmission Systems. New York: IEEE Press, 2000.

[5] M. Parvania and M. Fotuhi-Firuzabad, “Demand response scheduling by stochastic SCUC,” IEEE Trans. Smart Grid, vol. 1, no. 1, pp. 89–98, Jun. 2010

A Comparative Study of Different Multilevel Converter Topologies for Battery Energy Storage Application

ABSTRACT:

The integration of Battery Energy Storage Systems (BESS) into the power grids has been proposed as an effective solution for mitigating voltage and frequency instability problems arising from the integration of renewable resources with intermittent patterns. One of the most important applications of BESS is to restore an electric power system to operation without counting on the external transmission network. To prevent potential damage to the expensive equipment of power plant, the converters must generate a high quality and reliable three phase voltage. This research provides a simulation-based investigation in order to scrutinize different multi-level inverter topologies to find the more appropriate multi-level inverter structure for BESS application. The investigation has been done entitled of quantitative and qualitative studies. Throughout the quantitative study, the output specifications of each inverter topology is scrutinized, while other features such as reliability, modularity and functionality are scrutinized as qualitative study. All topologies are simulated in MATLAB/Simulink at the same operating conditions.

KEYWORDS:

1.      Multilevel converter

2.      Battery energy storage

3.      High power application

SOFTWARE: MATLAB/SIMULINK

DIFFERENT TOPOLOGIES:

Fig. 1. One leg representation of multi-level topologies. a) NPCMLI, b)

CCLMLI, c) CMLI, d) ZsMLI, e) QZsMLI.

Fig. 2. Multi-level topologies classification.

EXPECTED SIMULATION RESULTS:

 Fig. 3. Voltage and current waveforms of three level battery source NPC inverter.

Fig. 4. Voltage and current waveforms of three level battery source capacitor clamped inverter.

Fig. 5. Voltage and current waveforms of three level cascaded battery source inverter.

Fig. 6. Voltage and current waveforms of three level Z-source battery connected inverter.

Fig. 7. Voltage and current waveforms of three level Quasi-Z source battery connected inverter.

CONCLUSION:

In this paper the most common multilevel inverter topologies were scrutinized to find the more appropriate topology for BESS application. The investigation has been done entitled of quantitative and qualitative studies. The important output parameters of inverter topologies were investigated as quantitative study, while other features such as reliability, modularity and functionality were scrutinized in qualitative study. Also, various inverter topologies have been evaluated in terms of required capacity in the same operating point. The simulation results proved that the ideal BESS power conversion system, among reviewed multi-level topologies, is Cascaded topology. This topology was chosen for three reasons. First, the efficiency and reliability studies were conducted, and the CMLI was found to be the most efficient and reliable topology with minimum amount of power loss compared to other topologies. Second, it subdivides the battery string and increases the high voltage functionality. Finally, capacitor volume, cost and THD studies were again confirmed the effectiveness of this topology in battery energy storage systems.

REFERENCES:

[1]   H. Abu-Rub, M. Malinowski, and K. Al-Haddad, Power electronics for renewable energy systems, transportation and industrial applications. John Wiley & Sons, 2014.

[2]   T. Soong and P. W. Lehn, “Evaluation of emerging modular multilevel converters for bess applications,” IEEE Transactions on Power Delivery, vol. 29, no. 5, pp. 2086–2094, 2014.

[3]   P. Medina, A. Bizuayehu, J. P. Catal˜ao, E. M. Rodrigues, and J. Contreras, “Electrical energy storage systems: Technologies’ state-of-the-art, techno-economic benefits and applications analysis,” in Hawaii IEEE International Conference on System Sciences, 2014, pp. 2295–2304.

[4]   E. H. Allen, R. B. Stuart, and T. E. Wiedman, “No light in august: power system restoration following the 2003 north american blackout,” IEEE Power and Energy Magazine, vol. 12, no. 1, pp. 24–33, 2014.

[5]   L. Yutian, F. Rui, and V. Terzija, “Power system restoration: a literature review from 2006 to 2016,” Journal of Modern Power Systems and Clean Energy, vol. 4, no. 3, pp. 332–341, 2016.

A Comparative Study of Different Multilevel Converter Topologies for High Power Photovoltaic Applications

ABSTRACT:

This paper investigates the modern topology of multilevel converters, which are suitable for use in high power photovoltaic applications with the focus on achieving lower total harmonic distortion and better efficiency. Multilevel converters offer several advantages compared to conventional types. Multilevel converters provide high quality output while using the low switching frequency. It affects the switching losses, size of semiconductor switches and harmonic filters. This research investigates various topologies of multilevel converter for high power photovoltaic applications and compares their THD, efficiency, number of required semiconductors and other important characteristics. All topologies are simulated using MATLAB/Simulink in the same operating conditions. Finally, the more suitable multilevel topology is selected with respect to the simulation results.

KEYWORDS:

1.      Photovoltaic

2.      Multilevel converter

3.      Qualitative study

4.      High power application

SOFTWARE: MATLAB/SIMULINK

DIFFERENT TOPOLOGIES:

Fig 1: a) NPC b) Capacitor clamped c) Cascade d) Z-source e) Quasi Z-source f) Hybrid

EXPECTED SIMULATION RESULTS:

Fig.2. Three level NPC inverter voltage and current waveforms.

Fig. 3. Three level Capacitor clamped voltage and current waveforms.

Fig. 4. Voltage and current waveforms of three level cascaded inverter.

Fig.5. Voltage and current waveforms of three level Z source inverter.

Fig.6. Voltage and current waveforms of three level Quasi Z source.

Fig. 7. Voltage and current waveforms of three level hybrid model.

CONCLUSION:

The price analysis of the converter shows that multilevel converters are more economic than conventional types in the case of medium and high power applications. In This research, different multilevel converter topologies have been investigated and compared in order to find the most suitable topology, which is appropriate to use in the PV applications. Six multilevel topologies, which were proposed in the literature, have been investigated. The investigation was done via quantitative and qualitative study. In quantitative study, important output parameters of proposed multilevel topologies were evaluated using Matlab/Simulink at the same operating point. Also, a qualitative analysis has been performed to investigate some advantages and disadvantages of each topology, which cannot be considered in the simulation. The results prove that quasi Z-source converter has better performance in comparison with other types.

REFERENCES:

[1]   Nabae, I. Takahashi and H. Akagi, “A new neutral point clamped PWM inverter”, IEEE Trans. Ind. Appl., IA-17 (5) 518–523, 1981.

[2]   T. A. Meynard, H. Foch, P. Thomas, J. Couralt, R. Jakob, and m. Naherstaedt, “Multicel converters: Basic consepts and industry application”, IEEE Trans. Ind. Electron., 49 (5), 955-964, 2002.

[3]   M. F. Escalante, J. C. Vannier, and A. Arzande, “Flying capacitor multilevel inverters and DTC motor drive applications”, IEEE Trans. Ind. Elect., 49 (4), 809–815, 2002.

[4]   S. S. Fazel, S. Bernet, D. Krug and K. Jalili,“Design and comparison of 4 kV Neutral-pointclamped, flying capacitor and series-connectd H-bridge multilevel converters”, IEEE Trans. Ind. Appl., 43(4), 1032-1040, 2007.

[5]   J. V. Núñez, “Multilevel Topologies: Can New Inverters Improve Solar Farm Output? ” Solar industry journal, 5, 12, 2013.