A Fuzzy Logic Based Switching Methodology for a Cascaded H-Bridge Multilevel Inverter

ABSTRACT:

In this paper, a unusual switching technique is implemented using a fuzzy logic approach. The proposed technique simplifies the conventional method by eliminating the traditional logic gate design. The fuzzy logic pulse generator acts as a look-up table as well as a pulse generator. Based on the modulation index as input, controlled membership functions (MFs) and rules of the fuzzy logic controller (FLC) opens various possibilities in producing pulses directly. The proposed technique is evaluated on the cascaded multilevel inverter with symmetric and asymmetric operations using selective harmonic elimination pulse width modulation (SHE-PWM). MFs are designed based on the pre-calculated firing conditions for different modulation index values. The hardware verification is carried out to support the proposed switching technique.

KEYWORDS:

1.      Cascaded H-Bridge Multilevel Inverter (CHBMLI)

2.      Fuzzy Logic Controller (FLC)

3.      Membership Function (MF)

4.      Pulse Width Modulation (PWM)

5.      Selective Harmonic Elimination (SHE)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. (a) Symmetrical 7-level CHB MLI and (b) Trinary asymmetrical

9-level CHB MLI.

 EXPERIMENTAL RESULTS:

Fig. 2. (a) Output voltage and load current waveforms for 7 level symmetric CHB MLI at mi = 0:3, (b) Output voltage and load current waveforms  for 7 level symmetric CHB MLI at mi = 0:6, (c) Output voltage and load  current waveforms for 7 level symmetric CHB MLI at mi = 0:9, (d) Output voltage and load current waveforms for 9 level asymmetric CHB MLI at  mi = 0:9, (e) THD spectrum of 7 level output voltage waveform at mi =  0.9 for symmetrical CHB MLI, (f) THD profile of symmetrical CHB MLI for both simulation and experimental at different mi values.

CONCLUSION:

An unusual switching approach is introduced for avoiding look-up table and complex logic gate arrangements to generate the gating pulses for the CHB MLI. In the proposed technique, single FLC works as a pulse generating lookup table which provides gate pules without any mediator. Furthermore, the proposed technique is experimentally validated with symmetrical and asymmetrical CHB MLI for seven and nine level configurations respectively. The proposed technique can be extended to n-level inverters and other MLI configurations.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. Prats, “The age of multilevel converters arrives,” IEEE industrial electronics magazine, vol. 2, no. 2, 2008.

[2] J. Venkataramanaiah, Y. Suresh, and A. K. Panda, “A review on symmetric, asymmetric, hybrid and single dc sources based multilevel inverter topologies,” Renewable and Sustainable Energy Reviews, vol. 76, pp. 788–812, 2017.

[3] D. G. Holmes and T. A. Lipo, Pulse width modulation for power converters: principles and practice. John Wiley & Sons, 2003, vol. 18.

[4] M. S. Dahidah, G. Konstantinou, and V. G. Agelidis, “A review of multilevel selective harmonic elimination pwm: formulations, solving algorithms, implementation and applications,” IEEE Transactions on Power Electronics, vol. 30, no. 8, pp. 4091–4106, 2015.

[5] B. Ozpineci, L. M. Tolbert, and J. N. Chiasson, “Harmonic optimization of multilevel converters using genetic algorithms,” in Power Electronics Specialists Conference, 2004. PESC 04. 2004 IEEE 35th Annual, vol. 5. IEEE, 2004, pp. 3911–3916.

Fuzzy Logic Based MPPT Control for a PV/Wind Hybrid Energy System

ABSTRACT:

In this paper, we present a modeling and simulation of a standalone hybrid energy system which combines two renewable energy sources, solar and wind, with an intelligent MPPT control based on fuzzy logic to extract the maximum energy produced by the two PV and Wind systems. Moreover, other classical MPPT methods were simulated and evaluated to compare with the FLC method in order to deduce the most efficient in terms of rapidity and oscillations around the  maximum power point, namely Perturb and Observe (P&O),  Incremental Conductance (INC) for the PV system and Hill  Climbing Search (HCS) for the Wind generator. The simulation results show that the fuzzy logic technique has a better performance and more efficient compared to other methods due to its fast response, the good energy efficiency of the PV/Wind system and low oscillations during different weather conditions.

KEYWORDS:

1.      Hybrid energy system

2.      MPPT

3.      Fuzzy Logic Control (FLC)

4.      Wind system

5.      Photovoltaic system

6.      PMSG

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Hybrid energy system architecture.

EXPECTED SIMULATION RESULTS:

Fig. 2. PV generator output power for different MPPT techniques.

Fig. 3. PV generator output voltage for different MPPT techniques.

Fig. 4. Mechanical power of wind turbine for different MPPT techniques.

Fig. 5. Power coefficient (Cp) for different MPPT techniques.

CONCLUSION:

In this work, an intelligent control based on fuzzy logic is developed to improve the performance and reliability of a PV/Wind hybrid energy system, also the implementation of the other conventional MPPT algorithms for compared with the FLC technique. For a best performance analysis of MPPT techniques on the system, the simulations are carried out under different operating conditions. Simulation results show that the fuzzy controller has a better performance because it allows with a fast response and high accuracy to achieve and track the maximum power point than the P&O, INC and HCS methods for the PV and Wind generators respectively.

REFERENCES:

[1] A.V. Pavan Kumar, A.M. Parimi and K. Uma Rao, “Implementation of MPPT control using fuzzy logic in solar-wind hybrid power system,” IEEE International Conference on Signal Processing, Informatics, Communication and Energy Systems (SPICES), India, 19-21 February, 2015.

[2] C. Marisarla and K.R. Kumar, “A hybrid wind and solar energy system with battery energy storage for an isolated system,” International Journal of Engineering and Innovative Technology, vol. 3, n°3, pp. 99-104, ISSN 2277-3754, September 2013.

[3] L. Qin and X. Lu, “Matlab/Simulink-based research on maximum power point tracking of photovoltaic generation,” Physics Procedia, 24, pp.10- 18, 2012.

[4] B. Bendib, F. Krim, H. Belmili, M. F. Almi and S. Boulouma, “Advanced fuzzy MPPT controller for a stand-alone PV system,” Energy Procedia, 50, pp.383-392, 2014.

[5] H. Bounechba, A. Bouzid, K. Nabti and H. Benalla, “Comparison of perturb & observe and fuzzy logic in maximum power point tracker for pv systems,” Energy Procedia, 50, pp.677-684, 2014.

Evaluation of Battery System for Frequency Control in Interconnected Power System with a Large Penetration of Wind Power Generation

ABSTRACT:

Recently, a lot of distributed generations such as wind power generation are going to be installed into power systems. However, the fluctuation of these generator outputs affects the system frequency. Therefore, introduction of battery system to the power system has been considered in order to suppress the fluctuation of the total power output of the distributed generation. For frequency analysis, we use the interconnected 2-area power system model. It is assumed that a small control area with a large penetration of wind power plants is interconnected into a large control area. In this system, the tie line power fluctuation is very large as well as the system frequency fluctuation. It is shown that the installed battery can suppress these fluctuations and that the effect of battery on suppression of fluctuations depends on the battery capacity. Then, the required battery capacity for suppressing the tie line power deviation within a given level is calculated.

KEYWORDS:

1.      Battery

2.       Distributed Generation

3.      Frequency

4.      Load Frequency Control (LFC)

5.      Power System

6.      Tie Line Power

7.      Wind Power Generation

SOFTWARE: MATLAB/SIMULINK

2-AREA POWER SYSTEM:

Fig. 1. 2-area power system model for frequency control.

EXPECTED SIMULATION RESULTS:

Fig.2. Impact of LFC control method.

Fig. 3. Behaviors of tie line power flow, system frequency and battery

output with/without battery (Kb = 0.5, Tb = 0.5).

Fig. 4 Behaviors of tie line power and output and stored energy of battery

(9OMWh, 1500MW)

CONCLUSION:

In this paper, we have analyzed the impact of installed wind power generation and battery on the system frequency and the tie line power. In 2-area power systems, the tie line power fluctuation is remarkably large as well as the system frequency fluctuation. It has been made clear that the installed battery can suppress these fluctuations and that the effect of battery on suppression of these fluctuations depends on battery capacity. If the stored energy of battery reaches the full capacity, the battery output changes to zero suddenly and the large fluctuation is caused. Therefore, the stored energy    needs to be controlled within the rated storage capacity Based on this need, the required battery capacity for suppressing the tie line power deviation within a reference level has been calculated. If battery and LFC generator are controlled cooperatively, installation of battery with a larger capacity makes it possible to decrease LFC capacity of the conventional generators.  In the near future, a new method to calculate the optimal  battery storage capacity (MWh) and the appropriate power converter capacity (MW) for various kinds of wind power generation patterns and an effective control method of the battery system for reducing the battery capacity and LFC capability of the conventional power plants will be studied.

REFERENCES:

[1] W. El-Khattam and M. M. A. Salama, "Distributed generation technologies, definitions and benefits," Electric Power Systems  Research, vol. 71, issue 2, pp. 1 19-128, Oct. 2004.

[2] N. Jaleeli, L. S. VanSlyck, D. N. Ewart, L. H. Fink, and A. G. Hoffmann, "Understanding automatic generation control," IEEE Trans. Power Syst., vol. 7, pp. 1106-1122, Aug. 1992.

[3] A. Murakami, A. Yokoyama, and Y. Tada, "Basic study on battery capacity evaluation for load frequency control (LFC) in power system  with a large penetration of wind power generation," T. IEE Japan, vol. 126-B, no. 2, pp. 236-242, Feb. 2006. (in Japanese)

[4] P. Kunder, "Power System Stability and Control, " McGraw-Hill, 1994.

[5] A. J. Wood and B. F. Wollenberg, "Power Generation Operation and  Control," 2nd ed., Wiley, New York, 1966.

Shunt Isolated Active Power Filter With Common DC Link Integrating Braking Energy Recovery in Urban Rail Transit

 ABSTRACT:

In urban rail transit, there is a large number of harmonics brought by diode rectifiers, and shunt

active power filters (APFs) are an effective method of harmonics rejection. Traditional shunt APFs work with a dedicated DC link leading to complexity, while those with a common DC bus but using non-isolated topologies bring serious problems of zero-sequence circulating current (ZSCC), which introduce losses and provoke poor quality. Consequently, this paper first analyzes the limitations of traditional non-isolated APFs on modulation radio. Based on the analysis, this paper put forward a novel isolated APF with a common DC link based on existing diode rectifiers in urban rail transit, which realizes braking energy recovery as an additional function. To this end, harmonics brought by diode rectifiers are reduced while rejecting ZSCC. Meanwhile, braking energy can feedback to the city grid with lower harmonics. Finally, simulation and experiment using a 1-kW prototype converter verify the feasibility and validity of the proposed converter on harmonics suppression and braking energy recovery.

KEYWORDS:

1.      Active power filter (APF)

2.       LLC series resonant converter

3.      Soft switching

4.      Braking energy recovery

5.      Zero sequence circulating current (ZSCC)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Topology of the shunt isolated APF with common DC link integrating braking energy recovery based on HFPET and LLC converter.

 EXPECTED SIMULATION RESULTS:

Figure 2. Load current iL(A), grid current i_g(A) and circulating current i_cc(A). ZSCC of shunt APF directly connected to 3-phase grid without HFPET i_{cc_nonisolated} (A) and ZSCC of shunt isolated APF with HFPET i_{cc_isolated} (A).

Figure 3. Simulation results of current on side of grid i_ga(A), i_gb(A), i_gc (A) and voltage of DC traction grid U_dc (V) under periods of without APF (running process of train), with APF (running process of train), mode switching period and braking energy recovery.

Figure 4. Simulation waves of non-linear load current i_La(A) and

feedback current i_fa (A).

CONCLUSION:

In urban rail transit, harmonics need to be suppressed and braking energy also should be utilized to reduce losses. In this paper, focuses on the problems of harmonics in urban rail transit while braking energy recovery is also included. Based on traditional shunt non-isolated APFs, it is shown that ZCSS   would occur without an isolated HFPET, the amplitude of which is 23% of the load current which brings high losses and increases current stress of the switches. Two types of potential loops of ZCSS are analyzed and equivalent circuits are built for accurate analysis, which shows that the modulation radio of the inverter would be constrained at the upper limit of π/6 to guarantee no ZSCC. Consequently, a shunt isolated  APF with a common DC link integrating braking energy recovery is put forward to realize suppression of harmonics and elimination of ZSCC together with energy feedback. In this topology, the LLC series resonant converter operates in soft-switching condition of ZVS and ZCS, bringing high efficiency and wide voltage range. Closed-loop control strategy of voltage and current during period of APFs and braking energy recovery are designed respectively. During the process of starting and running of the train, the voltage of the DC bus is lower than the reference voltage, the converter  is operating as the APF without ZSCC. In the process of braking, the voltage of the DC bus rises so that APF is paused and braking energy recovery is put into use. Simulation based on MATLAB/Simulink and PLECS has been done to verify analysis on characteristics of soft-switching and eliminating harmonics. A 1-kW prototype based on DSP and CPLD has been built to realize compensation of harmonics and energy feedback. All the needs are well satisfied and this novel converter combine two functions together and restrain ZCSS to realize an high DC voltage utilization with a smaller area  and volume compared to traditional methods of achieving the APF and braking energy recovery.

 REFERENCES:

[1] W. Xu, ``Comparisons and comments on harmonic standards IEC 1000-3-6 and IEEE Std. 519,'' in Proc. 9th Int. Conf. Harmon. Qual. Power, Orlando, FL, USA, Oct. 2000, pp. 260_263.

[2] M. Qasim, P. Kanjiya, and V. Khadkikar, ``Optimal current harmonic extractor based on unified ADALINEs for shunt active power filters,'' IEEE Trans. Power Electron., vol. 29, no. 12, pp. 6383_6393, Dec. 2014.

[3] P. H. Henning, H. D. Fuchs, A. D. L. Roux, and H. D. T. Mouton, ``A 1.5-MW seven-cell series-stacked converter as an active power filter and regeneration converter for a DC traction substation,'' IEEE Trans. Power Electron., vol. 23, no. 5, pp. 2230_2236, Sep. 2008.

[4] A. S. Lock, E. R. C. da Silva, M. E. Elbuluk, and D. A. Fernandes, ``An APF-OCC strategy for common-mode current rejection,'' IEEE Trans. Ind. Appl., vol. 52, no. 6, pp. 4935_4945,  Dec. 2016.

[5] H. Hu, Z. He, and S. Gao, ``Passive filter design for china high-speed rail-way with considering harmonic resonance and characteristic harmonics,'' IEEE Trans. Power Del., vol. 30, no. 1, pp. 505_514, Feb. 2015.

Coordination control of hybrid AC/DC Microgrid

 ABSTRACT:

The hybrid AC/DC microgrid is considered to be the more and more popular in power systems as increasing DC loads. In this study, it is presented that a hybrid AC/DC microgrid is modelled with some renewable energy sources (e.g. solar energy, wind energy), typical storage facilities (e.g. batteries), and AC, DC load, and also the power could be transformed smoothly between the AC and DC sub-grids by the bidirectional AC/DC converter. Meanwhile, coordination control strategies are proposed for power balance under various operations. In grid-connected mode, the U–Q (DC bus voltage and reactive) or PQ method is adopted for the bidirectional AC/DC converter according to the amount of exchange power between AC and DC system in order to improve the DG utilisation efficiency, protecting the converter and maintain the stable operation of the system. In islanded mode, V/F control is applied to stabilising the entire system voltage and frequency, achieving the power balance between the AC and DC systems. Finally, these control strategies are verified by simulation with the results showing that the control scheme would maintain stable operation of the hybrid AC/DC microgrid.

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Compact hybrid AC/DC microgrid system

 EXPECTED SIMULATION RESULTS:

Fig. 2 AC bus voltage and current of A phase in grid-connected mode

Fig. 3 SOC of the battery in grid-connected mode

Fig. 4 Power of wind, DC side power flowed into AC side and the output

of battery in grid-connected mode

Fig. 5 PV output power versus 50*solar irradiation in islanded mode

Fig. 6 DC bus voltage with the influence of solar irradiance variation

and pulse load

Fig. 7 SOC of the battery in islanded mode

Fig. 8 AC bus voltage and current of A phase in islanded mode

Fig. 9  Power of wind, DC side power flowed into AC side and the output

of battery in islanded mode

 CONCLUSION:

In this paper, the coordination control strategies are proposed for the hybrid AC/DC microgrid, operating in grid-connected mode and islanded mode. The control strategies are verified with Matlab/ Simulink under various operations and load conditions. The simulation results show that the control strategies of the hybrid AC/DC microgrid system are efficient. In grid-connected mode, both the bidirectional AC/DC converter and the batteries can keep the DC bus voltage stable, and ensure the converter smoothly operates in U–Q or PQ methods under the various solar irradiation conditions. In islanded mode, the AC bus voltage and frequency are provided by bidirectional AC/DC converter, the battery is to maintain DC bus stability and system power balance under pulse load and various solar irradiation conditions.

REFERENCES:

[1] Unamuno, E., Barrena, J.: ‘Hybrid ac/dc microgrids – part I: review and classification of topologies’, Renew. Sust. Energy Rev., 2015, 52, pp. 1251– 1259

[2] Khederzadeh, M., Sadeghi, M.: ‘Virtual active power filter: a notable feature for hybrid ac/dc microgrids’, IET Gener. Transm. Distrib., 2016, 10, (14), pp. 3539–3546

[3] Salomonsson, D., Soder, L., Sannino, A.: ‘An adaptive control system for a dc microgrid for data centers’, IEEE Trans. Ind. Appl., 2008, 44, (6), pp. 1910– 1917

[4] Anand, S., Fernandes, B.G., Guerrero, J.M.: ‘Distributed control to ensure proportional load sharing and improve voltage regulation in low-voltage dc microgrids’, IEEE Trans. Power Electron., 2013, 28, (4), pp. 1900–1913

[5] Wu, W., Wang, H., Liu, Y., et al.: ‘A dual buck-boost AC/DC converter for DC nanogrid with three terminal outputs’, IEEE Trans. Ind. Electron., 2017, 64, (1), pp. 295–299