An Improved Grid Current and DC Capacitor Voltage Balancing Method for Three-Terminal Hybrid AC/DC Microgrid

 ABSTRACT:

 In this paper, a three-terminal AC/DC hybrid microgrid with two DC terminals and one AC terminal is proposed. The proposed system consists of cascaded H-bridge (CHB) converters based AC grid interface and two dual active bridge (DAB) converters based DC subgrid interface that connects two isolated DC buses. In order to reduce the number of power conversion stages and power devices, the DAB converters are directly connected to CHB DC rails according to the system operation requirement. To overcome the imbalanced grid currents and DC rail voltages issues caused by this modified system configuration with only two power conversion stages, an improved method is proposed through the zero-sequence voltage injection in the CHB converters. In addition, to avoid the conflicts between zero-sequence voltage injection and the voltage/current regulation of the system, the impacts of the control parameters to the system stability and dynamic response are investigated. Evaluation results from both three-terminal and five-terminal hybrid AC/DC microgrids show that the generalized effectiveness of the proposed three-phase AC current and DC rail voltage balancing method.

KEYWORDS:

1.      Three-terminal microgrid

2.      Hybrid AC/DC microgrid

3.      Zero-sequence voltage injection

4.      Current balancing control

5.      Voltage balancing control

6.      Grid-voltage sags

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

In this paper, a multi-terminal hybrid AC/DC microgrid structure with two power conversion stages is described in detail and a three-terminal hybrid microgrid with two DC ports is mainly selected for case study. In order to solve the issues of DC capacitor voltages and three-phase grid currents unbalance caused by mismatched DC power between DC ports, an improved control method through the adoption of zero-sequence voltage injection is developed. It has been extensively verified that the grid current and CHB capacitor voltage balancing control can be achieved simultaneously even in the severe case with highly mismatched DC power, grid-voltage sags, or the changes of connection between AC and DC subgrids.

REFERENCES:

[1] P. Ch. Loh, D. Li, Y. K. Chai, and F. Blaabjerg, “Autonomous operation of hybrid microgrid with AC and DC subgrids,” IEEE Trans. Power Electron., vol. 28, no. 5, pp. 2214–2223, May. 2013.

[2] P. Ch. Loh, D. Li, Y. K. Chai, and F. Blaabjerg, “Autonomous control of interlinking converter with energy storage in hybrid AC–DC microgrid,” IEEE Trans. Ind. Appl., vol. 49, no. 3, pp. 1374–1383, May. 2013.

[3] Y. W. Li, D. M. Vilathgamuwa, and P. C. Loh, “Design, analysis and real-time testing of controllers for multi-bus microgrid system,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1195–1204, Sep. 2004.

[4] J. M. Guerrero, J. C. Vasquez, J. Matas, L. G. de Vicuna, and M. Castilla, “Hierarchical control of droop-controlled AC and DC microgrids—Ageneral approach toward standardization,” IEEE Trans. Ind. Electron.,vol. 58, no. 1, pp. 158–172, Jan. 2011.

[5] K. T. Tan, X. Y. Peng, P. L. So, Y. C. Chu, and M. Z. Q. Chen, “Centralized control for parallel operation of distributed generation inverters in microgrids,” IEEE Trans. Smart Grid, vol. 3, no. 4, pp. 1977–1987, Dec.2012.

 

 

An Integrated Hybrid Power Supply for Distributed Generation Applications Fed by Nonconventional Energy Sources

 ABSTRACT:

A new, hybrid integrated topology, fed by photovoltaic (PV) and fuel cell (FC) sources and suitable for distributed generation applications, is proposed. It works as an uninterruptible power source that is able to feed a certain minimum amount of power into the grid under all conditions. PV is used as the primary source of power operating near maximum power point (MPP), with the FC section (block), acting as a current source, feeding only the deficit power. The unique “integrated” approach obviates the need for dedicated communication between the two sources for coordination and eliminates the use of a separate, conventional dc/dc boost converter stage required for PV power processing, resulting in a reduction of the number of devices, components, and sensors. Presence of the FC source in parallel (with the PV source) improves the quality of power fed into the grid by minimizing the voltage dips in the PV output. Another desirable feature is that even a small amount of PV power (e.g., during low insolation), can be fed into the grid. On the other hand, excess power is diverted for auxiliary functions like electrolysis, resulting in an optimal use of the energy sources. The other advantages of the proposed system include low cost, compact structure, and high reliability, which render the system suitable for modular assemblies and “plug-n-play” type applications. All the analytical, simulation, and experimental results of this research are presented.

KEYWORDS:

1.      Buck-boost

2.      Distributed generation

3.       Fuel cell

4.      Grid-connected

5.      Hybrid

6.       Maximum power point tracking (MPPT)

7.      Photovoltaic

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A compact topology, suitable for grid-connected applications has been proposed. Its working principle, analysis, and design procedure have been presented. The topology is fed by a hybrid combination of PV and FC sources. PV is the main source, while FC serves as an auxiliary source to compensate for the uncertainties of the PV source. The presence of FC source improves the quality of power (grid current THD, grid voltage profile, etc.) fed into the grid and decreases the time taken to reach the MPP. Table IV compares the system performance with and without the FC block in the system. A good feature of the proposed configuration is that the PV source is directly coupled with the inverter (and not through a dedicated dc–dc converter) and the FC block acts as a current source. Considering that the FC is not a stiff dc source, this facilitates PV operation at MPP over a wide range of solar insolation, leading to an optimal utilization of the energy sources. The efficiency of the proposed system in mode-1 is higher (around 85% to 90%) than mode 2 and 3 (around 80% to 85%). A laboratory prototype of the proposed system has shown encouraging results in terms of efficiency, complexity, reliability, EMI concerns, and other features. Table V compares the proposed system and some of the existing HDGS configurations with respect to various parameters and features.

REFERENCES:

[1] J. Kabouris and G. C. Contaxis, “Optimum expansion planning of an unconventional generation system operating in parallel with a large scale network,” IEEE Trans. Energy Convers., vol. 6, no. 3, pp. 394–400, Sep. 1991.

[2] P. Chiradeja and R. Ramakumar, “An approach to quantify the technical benefits of distributed generation,” IEEE Trans. Energy Convers., vol. 19, no. 4, pp. 764–773, Dec. 2004.

[3] Y. H. Kim and S. S. Kim, “An electrical modeling and fuzzy logic control of a fuel cell generation system,” IEEE Trans. Energy Convers., vol. 14, no. 2, pp. 239–244, Jun. 1999.

[4] K. N. Reddy and V. Agarwal, “Utility interactive hybrid distributed generation scheme with compensation feature,” IEEE Trans. Energy Convers., vol. 22, no. 3, pp. 666–673, Sep. 2007.

[5] K. S. Tam and S. Rahman, “System performance improvement provided by a power conditioning subsystem for central station photovoltaic fuel cell power plant,” IEEE Trans. Energy Convers., vol. 3, no. 1, pp. 64–70.

 

An Effective Voltage Controller for Quasi-Z-Source Inverter-Based STATCOM With Constant DC-Link Voltage

 ABSTRACT:

A quasi-Z-source inverter (qZSI) could achieve buck/boost conversion as well as dc to ac inversion in a single-stage topology, which reduces the structure cost when compared to a traditional two-stage inverter. Specifically, the buck/boost conversion was accomplished via shoot-through state which took place across all phase legs of the inverter. In this paper, instead of using traditional dual-loop-based proportional integral (PI)-P controller, a type 2 based closed-loop voltage controller with novel dc-link voltage reference algorithm was proposed to fulfill the dc-link voltage tracking control of a single-phase qZSI regardless of any loading conditions, without the need of inner inductor current loop. A dc–ac boost inverter with similar circuit parameters as a Qzsi was used to verify the flexibility of the proposed controller. The dynamic and transient performances of the proposed controller were investigated to evaluate its superiority against the aforementioned conventional controller. The integrated proposed controller and qZSI topology was then employed in static synchronous compensator application to perform reactive power compensation at the point of common coupling. The effectiveness of the proposed approach was verified through both simulation and experimental studies.

KEYWORDS:

1.      Control system analysis

2.      Flexible ac transmission systems

3.      Quasi-Z-source inverter (qZSI)

4.      Reactive power control

5.      Static volt-ampere reactive (VAR) compensators.

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

A voltage controller based on type 2 compensator incorporating a novel dc-link voltage reference algorithm was proposed for single-phase dc–ac boost inverter and qZSI topologies. When compared with the traditional dual-loop-based PI-P controller, the proposed controller showed simpler design procedures to attain its control parameters without using trial and error method. In addition, the proposed controller demonstrated stability and excellent dynamic and transient performances even though Qzsi was operating in discontinuous conduction mode. Furthermore, constant qZSI dc-link voltage was achieved by the proposed dc-link voltage reference algorithm regardless of any loading conditions. The proposed qZSI was employed in STATCOM application to perform reactive power compensation at the PCC, where all the aforementioned advantages were realized in both the simulation and experimental works.

REFERENCES:

[1] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 504–510, Mar./Apr. 2003.

[2] J. Anderson and F. Z. Peng, “Four quasi-z-source inverters,” in Proc. IEEE Power Electron. Spec. Conf., 2008, pp. 2743–2749.

[3] Y. Li, J. Anderson, F. Z. Peng, and D. Liu, “Quasi-z-source inverter for photovoltaic power generation systems,” in Proc. 24th Annu. IEEE Appl. Power Electron. Conf. and Expo.,, 2009, pp. 918–924.

[4] T. W. Chun, H. H. Lee, H. G. Kim, and E. C. Nho, “Power control for a PV generation system using a single-phase grid-connected quasi z-source inverter,” in Proc. IEEE 8th Int. Conf. Power Electron. ECCE Asia, 2011, pp. 889–893.

[5] D. Vinnikov, I. Roasto, R. Strzelecki, and M. Adamowicz, “Step-up DC/DC converters with cascaded quasi-z-source network,” IEEE Trans. Ind. Electron., vol. 59, no. 10, pp. 3727–3736, Oct. 2012.

 

 

Aggregation of EVs for Primary Frequency Control of an Industrial Microgrid by Implementing Grid Regulation & Charger Controller

 ABSTRACT:

 After nearly a century with internal combustion engines dominating the transportation sector, it now appears that electric vehicles (EVs) are on the brink of enjoying rapid development due to numerous useful features they possess, such as less operational cost and reduced carbon emissions. EVs can act as load as well as source, by utilizing the technique known as Vehicle-to-Grid (or Grid-to-Vehicle technique if EVs are used as a load). This technique adds key features to an industrial microgrid in the form of primary frequency control and congestion management. In this paper, two controllers (grid regulation and charger controller) are proposed by considering different charging profiles, state of charge of electric vehicle batteries, and a varying number of electric vehicles in an electric vehicle fleet. These controllers provide bidirectional power flow, which can provide primary frequency control during different contingencies that an industrial microgrid may face during a 24-hour period. Simulation results prove that the proposed controllers provide reliable support in terms of frequency regulation to an industrial microgrid during contingencies. Furthermore, simulation results also depict that by adding more electric vehicles in the fleet during the vehicle-to-grid mode, the frequency of an industrial microgrid can be improved to even better levels. Different case studies in this article constitute an industrial microgrid with varied distributed energy resources (i.e. solar and wind farm), electric vehicles fleet, industrial and residential load along with diesel generator. These test cases are simulated and results are analyzed by using MATLAB/SIMULINK.

 KEYWORDS:

1.      Industrial Microgrid

2.      Vehicle to Grid

3.      Electric Vehicle

4.      Grid to Vehicle

5.      Primary Frequency Control

6.      State of Charge

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This paper studies the impact of EVs’ charging on an industrial microgrid. The control scheme is implemented through grid regulation and charger controllers which provide bidirectional power flow. This dual power flow not only provides charging power to EVs but also ensures frequency regulation through active and reactive power support. The charging station consists of a central AC/DC VSC station that injects power into an industrial microgrid and minimizes frequency deviations. Different contingencies have been simulated and their impact on primary frequency is observed. Simulation results prove that the proposed bidirectional charging strategy contributes effectively towards frequency regulation. The frequency is well regulated within the acceptable margin when V2G mode is enabled for EVs’ charging/discharging as compared to when V2G mode was disabled. Frequency regulation improves even further by increasing the number of EVs in the fleet as more vehicles contribute to grid regulation mode. Hence, simulation results prove the robustness of the proposed controllers.

REFERENCES:

[1] P. Zhou and M. Wang, "Carbon dioxide emissions allocation: A review," Ecological Economics, vol. 125, pp. 47-59, 2016.

[2] N. Zhang, K. Yu and Z. Chen, "How does urbanization affect carbon dioxide emissions? A cross-country panel data analysis," Energy Policy, vol. 107, pp. 678-687, 2017.

[3] M. A. Abdelbaky, X. Liu and D. Jiang, "Design and implementation of partial offline fuzzy model-predictive pitch controller for large-scale wind-turbines," Renewable Energy, vol. 145, pp. 981-996, 2020/01/01/ 2020.

[4] M. A. Abdelbaky, X. Liu and X. Kong, "Wind Turbines Pitch Controller using Constrained Fuzzy-Receding Horizon Control," in 2019 Chinese Control And Decision Conference (CCDC), 2019, pp. 236-241.

[5] P. Weldon, P. Morrissey and M. O’Mahony, "Long-term cost of ownership comparative analysis between electric vehicles and internal combustion engine vehicles," Sustainable Cities and Society, vol. 39, pp. 578-591, 2018.

A Transient Component Based Approach for Islanding Detection in Distributed Generation

ABSTRACT:

 In this paper, transient response of the microgrid caused due to unintended switching events and faults have been investigated in distributed generation (DG) system. The proposed technique is based on two new criteria; i) transient index value (TIV) and ii) positive sequence superimposed current angle at PCC. The proposed method utilizes three phase voltage signals at DG end to compute the TIV. The performance of the proposed integrated approach has been evaluated on a sample test system and a practical distribution network consisting of combined heat and power plant, wind turbine generators, and photovoltaic system. The simulation results demonstrate that the proposed technique exhibits high reliability and leads to faster detection of islanding condition as compared to the existing passive islanding detection methods not only for zero active and reactive power mismatch conditions, but also for transient events caused due to nonlinear loads.

 KEYWORDS:

1.      Distributed generation

2.      Islanding condition

3.      Least square approach

4.      Power mismatch

5.      Voltage signal

 SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

In this paper, two criterion-based approach using TIV derived from three phase voltages and sign of PSSC angle was proposed for islanding detection. For the detection of islanding event in microgrid system, the voltage from DG end and current signal injected to PCC are accessed. The detection methodology has been tested for different critical conditions such as low active and reactive power mismatch and results obtained were accurate and reliable. Also, the method is not prone to false detection even during severe non-islanding conditions such as capacitor switching, fault conditions, switching of large block of load and opening of DG end breakers. The presence of nonlinear load has no effect on the detection using proposed algorithm. With the proposed approach, the non-detection zone had reduced and hence the reliability of the operation was assured. Because of faster detection capacity (less than one cycle) and simple computational procedure, more reliable and secured way to detect islanding phenomenon is possible in the digital platform using the proposed integrated technique.

REFERENCES:

[1] IEEE Standard 929-2000: ‘IEEE standard for Interconnecting Distributed Resources with Electric Power Systems’, 2003.

[2] M. A. Redfern, O. Usta, and G. Fielding, “Protection against loss of utility grid supply for a dispersed storage and generation unit”, IEEE Trans Power Del., vol. 8, no. 3, pp. 948-954, Jul. 1993.

[3] W. Wang, J. Kliber, G. Zhang, W. Xu, B. Howell, and T. Palladino, “A power line signaling based scheme for anti-islanding protection of distributed generators-part II: field test results”, IEEE Trans. Power Del. ,vol. 22, no. 3, pp. 1767-1772, Jul. 2007.

[4] W. Xu, G. Zhang, C. Li, W. Wang, G. Wang, and J. Kliber, “A power line signaling based technique for anti-islanding protection of distributed generators-part 1: scheme and analysis,” IEEE Trans. Power Del., vol. 22, no. 3, pp. 1758-1766, Jul. 2007.

[5] P. Gupta, R. S. Bhatia, and D. K. Jain, “Active ROCOF relay for islanding detection,” IEEE Trans. Power Del., vol. 32, no. 1, pp. 420-429, Feb.2017.

 

A simplified phase-shift PWM-based feedforward distributed MPPT method for grid-connected cascaded PV inverters

ABSTRACT:

The modularity and decreased filter size properties have made cascaded multilevel inverters (MLIs) more applicable than conventional two-level inverters, especially in high and medium power photovoltaic (PV) applications. However, partial shading of PV modules will affect negatively the output power of the unshaded modules. There are several existing solutions in the literature to address this challenge, however almost all of them suffer from complex implementations, low efficiency, and high cost. This paper presents a new simplified feedforward distributed maximum power point tracking (MPPT) method for three-phase grid-connected cascaded MLIs. The cascaded MLI provides a modular, and highly efficient single stage power conversion for PV systems. The proposed distributed MPPT method is depending on the phase-shift pulse width modulation (PSPWM) method with a simplified implementation. The proposed method is developing a feedforward signal that is proportional to the maximum power of the individual module. Then, the current controller, and the modulating signal are multiplied with the proportionality factor of the module maximum power. Furthermore, a modified modulation compensation method without using proportional-integral (PI) controllers is introduced to solve the problem of the unbalanced three-phase PV output currents that results from PV power mismatches and shading. A case study is implemented for 15 kW PV system to investigate the performance of the proposed method. In addition, comprehensive comparisons with the previous attempts in the literature are provided to verify the superior performance of the new proposed control method.

KEYWORDS:

1.      Distributed maximum power point tracking (MPPT)

2.      Cascaded multilevel inverter

3.      Phase-shift PWM (PS-PWM)

4.      Photovoltaic (PV)

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

This paper presents a distributed MPPT method for grid-tied PV systems with cascaded H-bridge inverters. The proposed method is based on employing a feedforward control method for extracting the MPPT of individual modules through adapting the percentage sharing of each module. The proposed method is superior solution for PV system grid integration due to its simple implementation, signal stage power conversion, no added complexity with increasing the number of connected modules, and it eliminates the need for individual control loop for each module. The proposed distributed MPPT method is validated through various operating scenarios of the selected case study. The results show the ability of the proposed distributed MPPT to extract MPPT of each PV module at normal and partial shading conditions. Moreover, the proposed modulation compensation method shows the injection of balanced output currents, even if at partial shading condition. The relative performance of the proposed distributed MPPT method is also compared with the most notable methods in the literature according to various performance criteria, including ability to extract individual MPPT, implementation complexity, system cost, THD content and balance output currents, and system efficiency. The comparisons show the validity and superiority of the presented distributed MPPT method over the notable candidates in the literature.

REFERENCES:

Abdalla, I., Corda, J., Zhang, L., 2013. Multilevel DC-link inverter and control algorithm to overcome the PV partial shading. IEEE Trans. Power Electron. 28 (1), 14–18.

Abdalla, I., Corda, J., Zhang, L., 2016. Optimal control of a multilevel DC-link converter photovoltaic system for maximum power generation. Renew. Energy 92 (Jul.), 1–11.

Al-Dhaifallah, M., Nassef, A.M., Rezk, H., Nisar, K.S., 2018. Optimal parameter design of fractional order control based INC-MPPT for PV system. Sol. Energy 159 (Jan.), 650–664.

Ando, Y., Oku, T., Yasuda, M., Shirahata, Y., Ushijima, K., Murozono, M., 2017. A compact SiC photovoltaic inverter with maximum power point tracking function. Sol. Energy 141, 228–235.

Azizi, A., et al., 2018. Impact of the aging of a photovoltaic module on the performance of a grid-connected system. Sol. Energy 174, 445–454.

A Novel High-Gain DC-DC Converter Applied in Fuel Cell Vehicles

 ABSTRACT:

The DC-DC converter for fuel cell vehicles should be characterized by high-gain, low voltage stress, small size and high-efficiency. However, conventional two-level, three-level and cascaded boost converters cannot meet the requirements. A new non-isolated DC-DC converter with switched-capacitor and switched-inductor is proposed in this paper, which can obtain high-gain, wide input voltage range, low voltage stresses across components and common ground structure. In this paper, the operating principle, component parameters design, and comparisons with other high-gain converters are analyzed. Moreover, the state-space averaging method and small-signal modeling method are adopted to obtain the dynamic model of converter. Finally, simulation and experimental results verify the effectiveness of the proposed topology. The input voltage of the experimental prototype ranges from 25V to 80V. The rated output voltage is 200V and rated power is 100W. The maximum efficiency is 93.1% under rated state. The proposed converter is suitable for fuel cell vehicles.

KEYWORDS:

1.      Fuel cell vehicles

2.      DC-DC converter

3.      Switched-capacitor and switched- inductor

4.      High-gain

5.      Low voltage stress

SOFTWARE: MATLAB/SIMULINK

 CONCLUSION:

This paper presents a non-isolated DC-DC converter topology for fuel cell vehicles. The proposed converter can obtain high-gain and wide input voltage range. The voltage gain can reach 2(1−d)/(1−2d) and duty cycle d<0.5 while achieving high-gain. The voltage stresses across components are less than half of the output voltage, which is beneficial to reduce the size and cost of the converter. In addition, the circuit topology is a common ground structure, which can avoid EMI and safety problems. The converter can always maintain the stability of the output voltage by closed-loop control. There are not the voltage overshoot and impulse current during soft-start process by adopting the soft-start program. Under the rated state, the measured maximum efficiency of the prototype is 93.1%. The proposed converter is suitable for fuel cell vehicles.

REFERENCES:

[1] G. Du, W. Cao S. Hu Z. Lin and T. Yuan “Design and Assessment of an Electric Vehicle Powertrain Model Based on Real-World Driving and Charging Cycles ” IEEE Trans. Veh. Technol., vol. 68, no. 2, pp. 1178-1187, Feb. 2019.

[2] Z. Geng, Q. Chen, Q. Xia D. S. Kirschen and C. Kang “Environmental Generation Scheduling Considering Air Pollution Control Technologies and Weather Effects ” IEEE Trans. Power Syst., vol. 32, no. 1, pp. 127-136, Jan. 2017.

[3] H. Bi P. Wang and Y. Che “A Capacitor Clamped H-Type Boost DC-DC Converter With Wide Voltage-Gain Range for Fuel Cell Vehicles ” IEEE Trans. Veh. Technol., vol. 68, no. 1, pp. 276-290, Jan. 2019.

[4] L. Li, S. Coskun, F. Zhang R. Langari and J. Xi “Energy Management of Hybrid Electric Vehicle Using Vehicle Lateral Dynamic in Velocity Prediction ” IEEE Trans. Veh. Technol., vol. 68, no. 4, pp. 3279-3293, Apr.2019.

[5] N. Elsayad, H. Moradisizkoohi, and O. A. Mohammed “A Single-Switch Transformerless DC-DC Converter With Universal Input Voltage for Fuel Cell Vehicles: Analysis and Design ” IEEE Trans. Veh. Technol., vol. 68, no. 5, pp. 4537-4549, Mar. 2019.