A Comparative Study of Energy Management Schemes for a Fuel-Cell Hybrid Emergency Power System of More-Electric Aircraft

ABSTRACT:  

This paper presents a comparative analysis of different energy management schemes for a fuel-cell-based emergency power system of a more-electric aircraft. The fuel-cell hybrid system considered in this paper consists of fuel cells, lithium-ion batteries, and supercapacitors, along with associated dc/dc and dc/ac converters. The energy management schemes addressed are state of the art and are most commonly used energy management techniques in fuel-cell vehicle applications, and they include the following: the state machine control strategy, the rule-based fuzzy logic strategy, the classical proportional–integral control strategy, the frequency decoupling/fuzzy logic control strategy, and the equivalent consumption minimization strategy. The main criteria for performance comparison are the hydrogen consumption, the state of charges of the batteries/supercapacitors, and the overall system efficiency. Moreover, the stresses on each energy source, which impact their life cycle, are measured using a new approach based on the wavelet transform of their instantaneous power. A simulation model and an experimental test bench are developed to validate all analysis and performances.

KEYWORDS:

1.      Batteries

2.      Dc–dc converters

3.      Energy management

4.      Fuel cells

5.      Hybridization

6.      Optimization

7.      Supercapacitors

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Proposed system block diagram using AFLC

 EXPERIMENTAL RESULTS:

Fig. 2. DC/DC converter model validation. (a) Fuel-cell boost converter. (b) Battery boost converter. (c) Battery buck converter.

Fig. 3 DC/AC converter model validation.

Fig. 4. Simulation and experimental results for all EMS schemes. (a) Simulation results for state machine control. (b) Experimental results for state machine

control. (c) Simulation results for rule-based fuzzy logic. (d) Experimental results for rule-based fuzzy logic. (e) Simulation results for classical PI control.

(f) Experimental results for classical PI control. (g) Simulation results for frequency decoupling and fuzzy logic. (h) Experimental results for frequency decoupling

and fuzzy logic. (i) Simulation results for ECMS. (j) Experimental results for ECMS.

CONCLUSION:

This paper has presented a performance comparison of different energy management schemes for a fuel-cell hybrid emergency system of MEA. The hybrid system is modeled and  validated with experiments. Five state-of-the-art commonly used energy management schemes are studied through simulations and experimental tests on a 14-kW fuel-cell hybrid  system. The same initial condition is used for all the schemes, and the experimental results are close to simulations. The criteria for performance comparison are the hydrogen consumption, the battery SOC, the overall efficiency, and the stress seen by each energy source. The latter is measured using a new approach based on wavelet transform. Compared with the other schemes, the state machine control scheme provided slightly better efficiency (80.72%) and stresses on the battery  and supercapacitor (σ of 21.91 and 34.7, respectively). The classical PI control scheme had the lowest fuel consumption (235 g of H2 consumed) and more use of the battery energy (SOC between 70%–51%). As expected, the lowest fuel-cell stress (σ of 12.04) and the lowest use of the battery energy (SOC between 70%–59%) were achieved with the frequency decoupling and fuzzy logic scheme but at the expense of more fuel consumption (245 g of H2 consumed) and lower overall efficiency (79.32%). The dc-bus or supercapacitor voltage was maintained nearly constant (≈270 Vdc) for all the schemes. To conclude, the energy management system suitable for MEA should be a multischeme EMS, such that each scheme is chosen based on a specific criterion to prioritize. As an example, depending on the operating life of each energy source, the EMS can be chosen to either minimize the stress on the fuelcell system, the battery system, or the supercapacitor system, hence maximizing the life cycle of the hybrid power system. In addition, if the target is to reduce the fuel consumption, the strategy based on the classical PI or ECMS could be selected. An alternative is to design a multiobjective optimization EMS  to optimize all the performance criteria, which is the next topic for further studies.

REFERENCES:

[1] P. Thounthong and S. Rael, “The benefits of hybridization,” IEEE Ind. Electron. Mag., vol. 3, no. 3, pp. 25–37, Sep. 2009.

[2] P. Thounthong, S. Rael, and B. Davat, “Control strategy of fuel cell and supercapacitors association for a distributed generation system,” IEEE  Trans. Ind. Electron., vol. 54, no. 6, pp. 3225–3233, Dec. 2007.

[3] Z. Amjadi and S. Williamson, “Power-electronics-based solutions for plug-in hybrid electric vehicle energy storage and management systems,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 608–616, Feb. 2010.

[4] G. Renouard-Vallet, M. Saballus, G. Schmithals, J. Schirmer, J. Kallo, and A. K. Friedrich, “Improving the environmental impact of civil aircraft  by fuel cell technology: Concepts and technological progress,” Energy  Environ. Sci., vol. 3, no. 10, pp. 1458–1468, 2010.

[5] G. Renouard-Vallet, M. Saballus, G. Schmithals, J. Schirmer, J. Kallo, and A. K. Friedrich, “Fuel cells for aircraft applications,” ECS Trans., vol. 30, no. 1, pp. 271–280, 2011.

Control and operation of a solar PV-battery grid-tied system in fixed and variable power mode

ABSTRACT:  

In this work, a simple phase-locked loop – less control is presented for a single-stage solar photovoltaic (PV) – battery-grid-tied system. As compared to traditional solar PV systems, the system has reduced losses due to the absence of boost converter and a flexible power flow due to the inclusion of a storage source (battery). The synchronous reference frame theory is used to generate the pulses for switching the voltage-source converter (VSC), while maximum power is extracted from the solar PV array by using perturb and observe-based maximum power point tracking technique. The inherent feature of shunt active filtering by the VSC has also been incorporated in this system. Test results for the system operation under fixed power and variable power mode are studied on a prototype developed in the laboratory. During fixed power mode, a fixed amount of power is fed to the grid, whereas in variable power mode the power fed to the grid varies. Test results obtained are in accordance with the IEEE-519 standard. This work is a basis for the upcoming power market, where solar PV consumers can manage the generated electricity and maximise their profit by selling the power to the grid judiciously.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig.1 Proposed topology

EXPERIMENTAL RESULTS:

Fig. 2 Performance of the system at steady state under fixed power mode

(b) vgab, iga, ila and iaspv, (c) Vdc, Ipv, Vbat and Ibat

Fig. 3 Impact of a decrease in load and insolation level during fixed power mode

(a)     vgab, iga, ila and iaspv, (b) Vdc, Ipv, Vbat and Ibat. Impact of a decrease in solar insolation during fixed power mode (c) vgab, iga, Ipv and iaspv, (d) Vdc, Ipv, Vbat and Ibat

Fig. 4 Impact of increase in solar insolation during fixed power mode

(a)     vgab, iga, Ipv and iaspv, (b) Vdc, Ipv, Vbat and Ibat. Performance of the system at steady state under variable power mode

Fig. 5 Performance of the system at steady state under variable power mode

 (d) Grid power

Fig. 6 Impact of load unbalancing and solar variations on solar PV-battery-grid-tied system

(a)     vgab, igc, ilc and icspv, (b) Vdc, Ipv, Vbat and Ibat. Impact of solar variation on solar PV-battery-grid-tied system (c) vgab, iga, ila and Ipv, (d) Vpv, Vbat, Ibat and iaspv

Fig. 7 Impact of solar variation and battery disconnection on solar PV-battery-grid-tied system

 (c) vgab, iga, ila and iaspv, (d) Vdc, Ipv, Vbat and Ibat

CONCLUSION:

A solar PV-battery-grid-tied system has been implemented in this work. P&O-based MPPT technique has been used to extract maximum power from the solar PV array, while SRF theory has been used to control the VSC. No PLL has been used here, the grid voltage vector angle with the α-axis, has been utilised to obtain the reference grid currents. The system's operation under fixed power mode is analysed, wherein a fixed amount of power is fed to the grid irrespective of the insolation and load variation. The battery gets charged/discharged in order to adjust these variations. Moreover, during the variable power mode, under load disconnection and solar insolation increase, the power fed to the grid increases. Even if the battery gets disconnected, the power generated by the solar PV array is fed to the grid and the load without any issue. Moreover, all these test results obtained are in accordance to an IEEE-519 standard.

REFERENCES:

[1] Esram, T., Chapman, P.L.: ‘Comparison of photovoltaic array maximum power point tracking techniques,’ IEEE Trans. Energy Convers., 2007, 22, (2), pp. 439–449

[2] Deshpande, A., Patil, S.L., Deopare, H.: ‘Comparative simulation of conventional maximum power point tracking methods’. Proc. Int. Conf. Computing, Communication and Automation (ICCCA), 2016, pp. 1025–1028

[3] Sahu, H.S., Nayak, S.K.: ‘Numerical approach to estimate the maximum power point of a photovoltaic array,’ IET Gener. Transm. Distrib., 2016, 10, (11), pp. 2670–2680

[4] Libo, W., Zhengming, Z., Jianzheng, L.: ‘A single-stage three-phase grid connected  photovoltaic system with modified MPPT method and reactive power compensation,’ IEEE Trans. Energy Convers., 2007, 22, (4), pp. 881– 886

[5] Jain, S., Agarwal, V.: ‘A single-stage grid connected inverter topology for solar PV systems with maximum power point tracking,’ IEEE Trans. Power Electron., 2007, 22, (5), pp. 1928–1940

A New Design Method of an LCL Filter Applied in Active DC-Traction Substations

ABSTRACT:  

This paper concentrates on the LCL filter with damping resistance intended to connect the shunt active power filter of an active DC-traction substation to the point of common coupling with the transmission grid. In order to find design conditions and conceive a design algorithm, attention is directed to the transfer functions related to currents and the associated frequency response. The mathematical foundation of the design method is based on the meeting the requirements related to the significant attenuation of the high-frequency switching current, concurrently with the unalterated flow of the current that needs to be compensated by active filtering. It is pointed out that there are practical limitations and a compromise must be made between the two requirements. To quantify the extent to which the harmonics to be compensated are influenced by imposing the magnitude response at both highest harmonic frequency to be compensated and switching frequency, a performance indicator is defined. As an additional design criterion, the damping power losses are taken into consideration. The validity and  effectiveness of the proposed method are proved by simulation results and experimental tests on a laboratory test bench of  small scale reproducing the specific conditions of a DC-traction substation with six-pulse diode rectifier.

KEYWORDS:

1.      DC-traction substations

2.      LCL filter

3.      Passive damping

4.      Regeneration

5.      Shunt active power filters

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the active DC-traction substation.

 EXPERIMENTAL RESULTS:

Fig. 2. Voltages and currents in the TT’s primary in traction regime.

Fig. 3. Harmonic spectrum of the current in the primary of TT.

Fig. 4. Bode magnitude diagram for Cf =10F, Rd =27; L2 =1.48mH.

Fig. 5. LCL filter input current.

Fig. 6. Current flowing through the capacitor of the interface filter.

Fig. 7. Harmonic spectra of the LCL filter input current (black bars) and

output current (yellow bars) for harmonic order k[1, 37].

Fig. 8. Voltages and currents upstream of PCC during the operation in

traction regime.

Fig. 9. Succesive traction (filtering) and braking (regeneration) regimes: (a)

phase voltage (blue line) and supply current (green line); (b) DC-capacitor

voltage (black line) and DC-line voltage (red line).

CONCLUSION:

A new design method of an LCL filter with damping resistance intended to couple the three-phase VSI of an active DC-traction substation to the power supply has been proposed in this paper. The following elements of originality are outlined.

1) The theoretical substantiation is based on the frequency response from transfer functions related to currents, taking into account the existence of the series damping resistances.

2) The expressed amplitude response and resonance frequency highlight their dependence on only pairs L2Cf and RdCf, It is a very important finding for the conceived design algorithm.

3) The expression of the power losses in the damping resistances is highlighted and an equivalent resistance is introduced as a quantitative indicator of them.

4) By considering the switching frequency as main parameter and taking into consideration the frequency of the highest order harmonic to be compensated, the design algorithm is based on the imposition of the associated attenuations.

5) In the substantiation of the design algorithm, a detailed analysis is performed on the existence of physical-sense solutions, providing the domain in which the values of the parameters must be located.

6) As a large number of parameters values sets can be obtained, a new performance indicator (MPI) is proposed, to quantify the extent to which the harmonics to be compensated are influenced.

The analysis and the simulation results achieved for an active DC-traction substation with six-pulse diode rectifier and LCL coupling filter have indicated that the proposed method is valid and effective. The experimental tests conducted in a laboratory test bench of small scale reproducing the specific conditions of a DC-traction substation illustrate good performance of the system for active filtering and regeneration connected to the power supply by the passive damped LCL filter.

The design proposal can be applied in any three-phase LCL-filter-based shunt active power filter.

REFERENCES:

[1] A. Ghoshal and V. John, “Active damping of LCL filter at low switching to resonance frequency ratio,” IET Power Electron., vol. 8, no. 4, pp. 574–582, 2015.

[2] G. E. Mejia Ruiz, N. Munoz, and J. B. Cano, “Modeling, analysis and design procedure of LCL filter for grid connected converters,” in Proc. 2015 IEEE Workshop Power Electron. and Power Quality Appl. (PEPQA), pp. 1–6.

[3] M. Hanif, V. Khadkikar, W. Xiao, and J. L. Kirtley, “Two degrees of freedom active damping technique for filter-based grid connected PV systems,” IEEE Trans. Ind. Electron., vol. 61, no. 6, pp. 2795–2803,June 2014.

[4] X. Wang, F. Blaabjerg, and P. C. Loh, “Grid-current-feedback active damping for LCL resonance in grid-connected voltage source converters,” IEEE Trans. Power Electron., vol. 31, pp. 213–223, 2016.

[5] W. Xia, J. Kang, “Stability of LCL-filtered grid-connected inverters with capacitor current feedback active damping considering controller time delays,” J. Mod. Power Syst. Clean Energy, vol. 5, no. 4, pp. 584–598, July 2017.

Modelling and Simulation of Standalone PV Systems with Battery supercapacitor Hybrid Energy Storage System for a Rural Household

ABSTRACT:  

This paper presents the comparison between the standalone photovoltaic (PV) system with battery-supercapacitor hybrid energy storage system (BS-HESS) and the conventional standalone PV system with battery-only storage system for a rural household. Standalone PV system with passive BS-HESS and semi-active BS-HESS are presented in this study. Two control strategies, Rule Based Controller (RBC) and Filtration Based Controller (FBC), are developed for the standalone PV system with semi-active BS-HESS with the aim to reduce the battery stress and to extend the battery lifespan. The simulation results show that the system with semi-active BS-HESS prolongs the battery lifespan by significantly reducing the battery peak current up to 8.607% and  improving the average SOC of the battery up to 0.34% as compared to the system with battery only system.

KEYWORDS:

1.     Renewable energy

2.     PV

3.     Hybrid energy storage system

4.     Supercapacitor

5.     Battery

6.     Control strategy

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Simulink Models. (a) Standalone PV system with Battery-only Storage. (b) Standalone PV System with Passive BS-HESS. (c) Standalone PV system with Semi-Active BS-HESS.

EXPERIMENTAL RESULTS:

Fig. 2. 24-hours Profiles. (a) Solar Irradiation Profile. (b) Load Demand (c) PV Power Output.

Fig. 3. Battery Current. (a) Battery-only (b) Passive BS-HESS. (c) Semi-active BS-HESS (RBC). (d) Semi-active BS-HESS (Moving Average).

Fig. 4. Supercapacitor Current. (a) Passive BS-HESS. (b) Semi-active BS-HESS (RBC). (c) Semi-active BS-HESS (Moving Average).

CONCLUSION:

The BS-HESS shows the positive impact to the battery and the overall system. The passive BS HESS is easy to be implemented, but the improvement is not significant as it cannot be controlled. Therefore, semi-active BS-HESS is a better configuration that improves the battery lifespan and maximizes the level of utilization of the supercapacitor. The system with semi-active BS-HESS (moving average filter) has significantly smoothened the battery current. The system with semi-active BS-HESS (RBC) shows a great capability in battery peak current reduction and the prevention of battery deep discharge by reducing the peak power demand by 8.607% and improving the average SOC of the battery by 0.34% as compared to the system with battery-only system.

REFERENCES:

[1] Kan SY, Verwaal M, and Broekhuizen H, The use of battery-capacitor combinations in photovoltaic powered products, J. Power Sources 2006, 162: 971–974.

[2] Chong LW, Wong YW, Rajkumar RK, Rajkumar RK, and Isa D, Hybrid energy storage systems and control strategies for stand-alone renewable energy power systems, Renew. Sustain. Energy Rev. 2016, 66, pp: 174–189.

[3] Kuperman A and Aharon I, Battery-ultracapacitor hybrids for pulsed current loads: A review, Renew. Sustain. Energy Rev. 2011, 15: 981– 992.

[4] Dougal RA, Liu S, and White RE, Power and life extension of battery-ultracapacitor hybrids, IEEE Trans. Components Packag. Technol 2002., 25: 120–131.

[5] Kuperman A, Aharon I, Malki S, and Kara A, Design of a semiactive battery-ultracapacitor hybrid energy source, IEEE Trans. Power Electron.2013, 28: 806–815.