Artificial Neural Network based Dynamic Voltage Restorer for Improvement of Power Quality

ABSTRACT:  

Dynamic Voltage Restorer (DVR) is a custom power device used as an effective solution in protecting sensitive loads from voltage disturbances in power distribution systems. The efficiency of the control technique, that conducts the switching of the inverters, determines the DVR efficiency.Proportional-Integral-Derivative (PID) control is the general technique to do that. The power quality restoration capabilities of this controller are limited, and it produces significant amount of harmonics – all of which stems from this linear technique’s application for controlling non-linear DVR. As a solution, this paper proposes an Artificial Neural Network (ANN) based controller for enhancing restoration and harmonics suppression capabilities of DVR. A detailed comparison of Neural Network controller with PID driven  controller and Fuzzy logic driven controller is also illustrated, where the proposed controller demonstrated superior performance with a mere 13.5% Total Harmonic Distortion.

KEYWORDS:

  1. Power quality
  2. Dynamic Voltage Restorer (DVR)
  3. PID
  4. Fuzzy logic
  5. Artificial Neural Network (ANN)

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1. Block diagram of the proposed DVR system to mitigate voltage instabilities.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Three phase sag mitigation based on ANN controlled DVR. (a) Instantaneous voltage at stable condition; (b) Instantantaneous voltage when sag occurs; (c) Voltage required to mitigate voltage sag; (d) Output voltage of the inverter circuit; (e) Generated PWM for inverter; (f) Instantaneous voltage after voltage restoration.

 

Fig. 3. Restored Voltage Using (a) PID controller; (b) Fuzzy controller; (c) ANN controller; (d)THD comparison: the least THD can be seen at ANN based DVR, the range of the harmonics is also truncated by a huge amount by this method.

 CONCLUSION:

 DVRs are a popular choice for enhancing power quality in power systems, with an array of control system on offer to drive these devices. In this paper, application of ANN to operate DVR for providing better performance than existing systems to mitigate voltage sag, swell, and harmonics has been demonstrated. Problem statement and theoretical background, structure of the proposed method, training procedure of the ANN used have been described in detail. Simulation results showing the DVR performance during voltage sag have been presented. Comparison of the proposed method with the popular PID controller, and nonlinear Fuzzy controller has been carried out, where the proposed ANN controller appeared as the best option to restore system voltage while mitigating THD to the greatest extent.

REFERENCES:

[1] M. H. Bollen, R. Das, S. Djokic, P. Ciufo, J. Meyer, S. K. Rönnberg, et al., “Power quality concerns in implementing smart distribution-grid applications,” IEEE Transactions on Smart Grid, vol. 8, pp. 391-399, 2017.

[2] V. Khadkikar, D. Xu, and C. Cecati, “Emerging Power Quality Problems and State-of-the-Art Solutions,” IEEE Transactions on Industrial Electronics, vol. 64, pp. 761-763, 2017.

[3] X. Liang, “Emerging power quality challenges due to integration of renewable energy sources,” IEEE Transactions on Industry Applications, vol. 53, pp. 855-866, 2017.

[4] T. Sutradhar, J. R. Pal, and C. Nandi, “Voltage Sag Mitigation by using SVC,” International Journal of Computer Applications, vol. 71, 2013.

[5] F. M. Mahdianpoor, R. A. Hooshmand, and M. Ataei, “A new  approach to multifunctional dynamic voltage restorer implementation for emergency control in distribution systems,” IEEE transactions on power delivery, vol. 26, pp. 882-890, 2011.

A Fuzzy Logic Control Method for MPPT of PV Systems

ABSTRACT:  

Maximum power point trackers are so important in photovoltaic systems to increase their efficiency. Many methods have been proposed to achieve the maximum power that the PV modules are capable of producing under different weather conditions. This paper proposed an intelligent method for maximum power point tracking based on fuzzy logic controller.  The system consists of a photovoltaic solar module connected to a DC-DC Buck-boost converter. The system has been experienced under disturbance in the photovoltaic temperature and irradiation level. The simulation results show that the proposed maximum power tracker could track the maximum power accurately and successfully in all condition tested. Comparison of different performance parameters such as: tracking efficiency and response time of the system shows that the proposed method gives higher efficiency and better performance than the conventional perturbation and observation method.

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1: System used for simulation.

 EXPECTED SIMULATION RESULTS:

 Fig. 2: case 1: changing the solar radiation

Fig. 3: Case 1: performance of FLC method

Fig. 4: Case I: performance of P&O method

Fig, 5: Case 2: changing the solar radiation

Fig, 6: Case 2: performance of FLC method

Fig, 7: Case 2: performance of P&O method

Fig, 8: Changing the temperature

Fig, 9: Performance of FLC method

Fig, 10: Performance of P&O method

CONCLUSION:

 Photovoltaic model using Matlab/STMULTNK and design of appropriate DC-DC buck-boost converter with a maximum power point tracking facility are presented in this paper. A new method for MPPT based fuzzy logic controller is presented and compared with the conventional P&O MPPT method. The models are tested under disturbance in both solar radiation and photovoltaic temperature. Simulation results show that the proposed method effectively tracks the maximum power point under different ambient conditions.The oscillation around MPP is decreased and the response is faster in compared with the conventional methods. Comparing the tracking efficiency of both methods indicates that the proposed method has a higher efficiency than the conventional P&O MPPT method.

 REFERENCES:

[1] Jancarle L. Dos Santos, Fernando L. M. Antunes and Anis Chehab, “A Maximum Power Point Tracker for PV Systems Using a High Performance Boost Converter”, Solar Energy, Issue 7, Vol. 80, pp. 772- 778,2005.

[2] Ting-Chung Yu and Tang-Shiuan Chien, “Analysis and Simulation of Characteristics and Maximum Power Point Tracking for Photovoltaic Systems”, Conference,P prpo.c 1e3ed3i9n g- s1 3o4f4 ,PT aoiwpeeri, 2E0l0e9c.t ronics and Drive Systems

[3] Roberto Faranda, Sonia Leva, “Energy Comparison of MPPT techniques for PV Systems”, Wseas Transctions on Power System, Issue 6, Vol. 3, pp. 446-455, June 2008.

[4] D. P. Hohm and M. E. Ropp, “Comparative Study of Maximum Power Point Tracking Algorithms using an experimental, programmable, maximum power point tracking test bed”,P roceedings of Photovoltaic Specialists Conference ,pp. 1699 – 1702, USA,2000.

[5] Trishan Esram and Patrick 1. Chapman, “Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques”, Energy ConverSion, Issue 2, Vol. 22, pp. 439 – 449, May 2007.

Performance Recovery of Voltage Source Converterswith Application to Grid-connected Fuel Cell DGs

ABSTRACT:  

Most common types of distributed generation (DG) systems utilize power electronic interfaces and, in particular,  three-phase voltage source converters (VSCs) which are mainly  used to regulate active and reactive power delivered to the grid. The main drawbacks of VSCs originate from their nonlinearities, control strategies, and lack of robustness against uncertainties. In this paper, two time-scale separation redesign technique is proposed to improve the overall robustness of VSCs and address the issues of uncertainties. The proposed controller is applied to a grid-connected Solid Oxide Fuel Cell (SOFC) distributed generation system to recover the trajectories of the nominal system despite the presence of uncertainties. Abrupt changes in the input dc voltage, grid-side voltage, line impedance and PWM malfunctions are just a few uncertainties considered in our evaluations. Simulation results based on detailed model indicate that the redesigned system with lower filter gain (_) achieves more reliable performance in compare to the conventional current control scheme. The results also verified that the redesigned controller is quite successful in improving the startup and tracking responses along with enhancing the overall robustness of the system.

KEYWORDS:

  1. Power converters
  2. Solid oxide fuel cell (SOFC)
  3. Distributed generation (DG)
  4. Time-scale separation redesign

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig. 1. Schematic diagram of a grid-connected SOFC power plant with redesigned controller.

 EXPECTED SIMULATION RESULTS:

 Fig. 2. Active (top) and reactive (bottom) output power in case 1 (input dc

voltage) uncertainty using PI and redesigned controller.

Fig. 3. Output voltage (top) and current (bottom) of each SOFC array in case

1 (input dc voltage) uncertainty using PI and redesigned controller.

Fig. 4. Active (top) and reactive (bottom) output power in case 2 (grid-side

voltage) uncertainty using PI and redesigned controller.

Fig. 5. d-axis (top) and q-axis (bottom) currents of the VSC in case 2 (gridside

voltage) uncertainty using PI and redesigned controller.

Fig. 6. Active (top) and reactive (bottom) output power in case 3.1 (line

resistance) uncertainty using PI and redesigned controller.

Fig. 7. Active (top) and reactive (bottom) output power in case 3.2 (line

inductance) uncertainty using PI and redesigned controller.

Fig. 8. Additive random Gaussian noises on duty ratio of phase a (top), b

(middle), and c (bottom) of the VSC.

Fig. 9. Active (top) and reactive (bottom) output power in case 4 (duty

ratio) uncertainty using PI and redesigned controller.

 CONCLUSION:

 This paper presents a new control technique based on two time-scale separation redesign for the VSC of a grid connected SOFC DG system. A three-phase VSC is used to regulate active and reactive power delivered to the grid. In addition, variations in the input dc voltage, line impedance, grid-side voltage and duty ratio are mathematically formulated as additive uncertainties based on the nonlinear model of the VSC. As a result, the proposed controller is able to address the issues of robustness and further enhance the system stability in the presence of uncertainties. The redesigned controller also presents a fast and accurate startup response and delivers superior decoupling performance as compared to the conventional PI controller. Moreover, the redesigned controller significantly reduces the maximum overshoot in the output power while the system with a conventional controller exhibits deterioration in the output response which leads to excessive current and voltage variations in the FC arrays.

REFERENCES:

[1] P. Kundur, Power System Stability and Control. New York, NY, USA:McGraw-Hill, 1994.

[2] R. Seyezhai and B. L. Mathur, “Modeling and control of a PEM fuel cell based hybrid multilevel inverter,” International Journal of Hydrogen Energy, vol. 36, pp. 15029-15043, 2011.

[3] T. Erfanmanesh and M. Dehghani, “Performance improvement in gridconnected fuel cell power plant: An LPV robust control approach,”

International Journal of Electrical Power & Energy Systems, vol. 67, pp. 306-314, 2015.

[4] S. A. Taher and S. Mansouri, “Optimal PI controller design for active power in grid-connected SOFC DG system,” International Journal of Electrical Power & Energy Systems, vol. 60, pp. 268-274, 2014.

[5] R. Teodorescu, M. Liserre, and P. Rodriguez, Grid Converters for Photovoltaic and Wind Power Systems. Hoboken, NJ, USA: John Wiley & Sons, 2011.

Modeling, Analysis and Testing of Autonomous Operation of an Inverter-Based Microgrid

ABSTRACT:  

The analysis of the small-signal stability of conventional power systems is well established, but for inverter based microgrids there is a need to establish how circuit and control features give rise to particular oscillatory modes and which of these have poor damping. This paper develops the modeling and analysis of autonomous operation of inverter-based microgrids. Each sub-module is modeled in state-space form and all are combined together on a common reference frame. The model captures the detail of the control loops of the inverter but not the switching action. Some inverter modes are found at relatively high frequency and so a full dynamic model of the network (rather than an algebraic impedance model) is used. The complete model is linearized around an operating point and the resulting system matrix is used to derive the eigenvalues. The eigenvalues (termed “modes”) indicate the frequency and damping of oscillatory components in the transient response. A sensitivity analysis is also presented which helps identifying the origin of each of the modes and identify possible feedback signals for design of controllers to improve the system stability. With experience it is possible to simplify the model (reduce the order) if particular modes are not of interest as is the case with synchronous machine models. Experimental results from a microgrid of three 10-kW inverters are used to verify the results obtained from the model.

KEYWORDS:

  1. Inverter
  2. Inverter model
  3. Microgrid
  4. Power control
  5. Small-signal stability

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Typical structure of inverter-based microgrid.

 EXPECTED SIMULATION RESULTS:

 Fig. 2. Active power (filtered) response of micro-sources with 3.8 kW of step

change in load power at bus 1.

Fig. 3. Reactive power exchange between the micro sources with 3.8 kW of

step change in load power at bus 1 (Initial values: Q1 =0, Q2 = 􀀀200, Q3 =

+200; Final values: Q1 = +600, Q2 = 􀀀300, Q3 = 􀀀200).

Fig. 4. Active power (filtered) response of micro-sources with 16.8 kW and

12 kVAR RL load step change at bus 1.

Fig. 5. Reactive power (filtered) response of micro-sources with 16.8 kW and

12 kVAR RL load step change at bus 1.

Fig. 6. Output voltage (d-axis) response with 27 kW of step change in load

power at bus 1.

Fig. 7. Inductor current (d-axis) response with 27 kW of step change in load

power at bus 1.

 CONCLUSION:

 In this paper, a small-signal state-space model of a microgrid is presented. The model includes inverter low frequency dynamics dynamics, high frequency dynamics, network dynamics, and load dynamics. All the sub-modules are individually modeled and are then combined on a common reference frame to obtain the complete model of the microgrid.

The model was analyzed in terms of the system eigenvalues and their sensitivity to different states. With the help of this analysis the relation between different modes and system parameters was established. It was observed that the dominant low-frequency modes are highly sensitive to the network configuration and the parameters of the power sharing controller of the micro sources. The high frequency modes are largely sensitive to the inverter inner loop controllers, network dynamics, and load dynamics.

Results obtained from the model were verified experimentally on a prototype microgrid. It was observed that the model successfully predicts the complete microgrid dynamics both in the low and high frequency range.

Small signal modeling has had a long history of use in conventional power systems. The inverter models (and the inclusion of network dynamics) illustrated in this paper allow microgrids to be designed to achieve the stability margin required of reliable power systems.

 REFERENCES:

[1] R. H. Lasseter, “Microgrids,” in Proc. Power Eng. Soc.Winter Meeting, Jan. 2002, vol. 1, pp. 305–308.

[2] A. Arulapalam, M. Barnes, A. Engler, A. Goodwin, and N. Jenkins, “Control of power electronic interfaces in distributed generation microgrids,” Int. J. Electron., vol. 91, no. 9, pp. 503–523, Sep. 2004.

[3] R. Lassetter, “Integration of Distributed Energy Resources: The CERTS Microgrid Concept,” CERT Rep., Apr. 2002.

[4] M. S. Illindala, P. Piagi, H. Zhang, G. Venkataramanan, and R. H. Lasseter, “Hardware Development of a Laboratory-Scale Microgrid Phase 2: Operation and Control of a Two-Inverter Microgrid,” Nat. Renewable Energy Rep., Mar. 2004.

[5] Y. Li, D. M. Vilathgamuwa, and P. C. Loh, “Design, analysis and realtime testing of a controller for multibus microgrid system,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1195–1204, Sep. 2004.

Grid to Vehicle and Vehicle to Grid Energy Transfer using Single-Phase Bidirectional ACDC Converter and Bidirectional DC – DC converter

ABSTRACT:

 In this paper, a configuration of a single-phase bidirectional AC-DC converter and bidirectional DC-DC converter is proposed to transfer electrical power from the grid to an electrical vehicle (EV) and from an EV to the grid while keeping improved power factor of the grid. In first stage, a 230 V 50 Hz AC supply is converted in to 380V dc using a single-phase bidirectional AC-DC converter and in the second stage, a bidirectional buck–boost dc-dc converter is used to charge and discharge the battery of the PHEV (Plug-in Hybrid Electric Vehicle). In discharging mode, it delivers energy back to the grid at 230V, 50 Hz. A battery with the charging power of 1.2 kW at 120V is used in PHEV. The buck-boost DC-DC converter is used in buck mode to charge and in a boost mode to discharge the battery. A proportional-integral (PI) controller is used to control the charging current and voltage. Simulated results validate the effectiveness of proposed algorithm and the feasibility of system.

KEYWORDS:

  1. Plug-in Hybrid Electric Vehicle (PHEV)
  2. Bidirectional AC-DC Converter
  3. DC-DC Converter
  4. Vehicle to grid (V2G)
  5. Electric drive vehicle (EDVs)

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 Fig.1 Proposed configuration for V2G and G2V Energy transfer

 EXPECTED SIMULATION RESULTS:

 Fig.2 Charging and discharging of PHEV battery (Full profile)

               Fig.3 Charging and discharging of PHEV battery (in large view)

Fig.4. Discharging and Charging of PHEV battery demonstrating unity

Power factor operation

Fig.5 Waveform and harmonics spectrum of the discharging grid current

Fig.6 Waveform and harmonics spectrum of the Charging grid current

CONCLUSION:

The proposed converter has delivered the AC current to/and from the grid at unity power factor and at very low current harmonics which ultimately prolongs the life of the converter and the battery and minimizes the possibility of distorting the grid voltage. It also enables V2G interactions which could be utilized to improve the efficiency of the grid.

REFERENCES:

[1] Young-Joo Lee, Alireza Khaligh, and Ali Emadi, “Advanced Integrated Bidirectional AC/DC and DC/DC Converter for Plug-In Hybrid Electric Vehicles,” IEEE Trans. on Vehicular Tech. vol. 58, no. 8, pp. 3970-3980, Oct, 2009.

[2] Bhim Singh, Brij N. Singh, Ambrish Chandra, Kamal Al-Haddad, Ashish Pandey and Dwarka P. Kothari, “A review of single-phase improved power quality ac–dc converters,” IEEE Trans. Industrial Electronics, vol. 50, no. 5, pp. 962-981, Oct. 2003.

[3] M.C. Kisacikoglu, B. Ozpineci and L.M. Tolbert, “Examination of a PHEV bidirectional charger system for V2G reactive power compensation,” in Proc. of Twenty-Fifth Annual IEEE Applied Power Electronics Conference and Exposition (APEC), 2010, 21-25 Feb.2010, pp.458-465.

[4] M.C. Kisacikoglu, B. Ozpineci and L.M. Tolbert, “Effects of V2G reactive power compensation on the component selection in an EV or PHEV bidirectional charger,” in Proc. of Energy Conversion Congress and Exposition (ECCE), 2010 IEEE, 12-16 Sept. 2010, pp.870-876.

[5] W. Kempton and J. Tomic, “Vehicle-to-grid power fundamentals: Calculating capacity and net revenue,” J. Power Sources, vol. 144, no. 1, pp. 268–279, Jun. 2005.

Single-Phase AC/AC Buck-Boost Converter with Single-Phase Matrix Topology

ABSTRACT:

 This paper deals with a new family of single-phase AC/AC buck-boost converter based on singlephase matrix topology. The proposed converter provides a wider range of output AC voltage in which the output voltage can be bucked and in-phase/out-of-phase with the input voltage; and the output voltage can be boosted and in-phase/out-of-phase with the input voltage. A commutation strategy is employed to realize snubberless operation. The operating principles, circuit analysis and experimental results based on TMS320F2812 DSP are presented.

 KEYWORDS:

  1. Z-source converter
  2. Single-phase matrix converter (SPMC)
  3. PWM AC/AC converter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1: Proposed topology.

 EXPECTED SIMULATION RESULTS:

 

(a) Buck in-phase

 

 (b) Buck out-of-phase

Fig. 2: Experimental results for buck mode with Vi = 70 Vrms/60Hz, D = 0.3. (a) Region (I) (buck inphase). (b) Region (III) (buck out-of-phase). Top: vi; Bottom: vo. (x-axis: 10ms/div., y-axis: 100V/div)

(a) Boost in-phase

(b) Boost out-of-phase

Fig. 3: Experimental results for boost mode with Vi = 50 Vrms/60Hz, D = 0.7. (a) Region (II) (boost in-phase). (b) Region (IV) (boost out-of-phase). Top: vi; Bottom: vo. (x-axis: 10ms/div., y-axis: 100V/div)

CONCLUSION:

In this paper a new family of single-phase Z-source AC/AC buck-boost converter based on singlephase matrix converter topology has been presented. The proposed converter has following fertures:the output voltage can be bucked-boosted and in-phase with the input voltage; the output voltage can be bucked-boosted and out-of-phase with the input voltage. In order to provide a continuous current path, the safe-commutation strategy is employed. Steady-state analysis and experimental results were illustrated. By duty-ratio control, the proposed converter becomes “solid-state transformers” with a continuously variable turn ratio. The proposed converter can be used as dynamic voltage restorer (DVR) to compensate voltage sags and swells in AC/AC line conditioning without any energy-storage devices requirement. The feature which the output voltage is bucked-boosted and in-phase with the input voltage is used for voltage sag compensation. The feature which the output voltage is bucked boosted and out-of-phase with the input voltage is used for voltage swell compensation.

 REFERENCES:

[1] Fang X. P., Qian Z. M., Peng F. Z.: Single-phase Z-source PWM AC-AC converters, IEEE Power Electronics Letters, vol. 3, no. 4, 2005, pp. 121-124.

[2] Tang Y., Xie S., Zhang C.: Z-source AC-AC converters solving commutation problem, IEEE Trans. Power Electronics, vol. 22, no. 6, 2007, pp. 2146-2154.

[3] Kwon B. H., Mim B. D., Kim J. H.: Novel commutation technique of AC-AC converters, IEE Proc. Electr. Power Appl., vol. 145, no. 4, July 1998, pp. 295-300.

[4] Wheeler P. W., Rodriguez J., Clare J. C., Empringham L., Weinstein A.: Matrix converter: a technology review, IEEE Trans. on Ind. Electronics, vol. 49, no. 2, April 2002, pp. 276-288.

[5] Nguyen M. K., Jung Y. G., and Lim Y. C.: Single-phase Z-source buck-boost matrix converter, in proc. Of IEEE Applied Power Electronics Conference and Exposition, APEC’09, pp. 846-850, 2009.

Nine-level Asymmetrical Single Phase MultilevelInverter Topology with Low switching frequency andReduce device counts

ABSTRACT:

 This paper presents a new asymmetrical singlephase multilevel inverter topology capable of producing ninelevel output voltage with reduce device counts. In order to obtain the desired output voltage, dc sources are connected in all the combination of addition and subtraction through different switches. Proposed topology results in reduction of dc source, switch counts, losses, cost and size of the inverter. Comparison between the existing topologies shows that the proposed topology yields less component counts. Proposed topology is modeled and simulated using Matlab-Simulink software in order to verify the performance and feasibility of the circuit. A low frequency switching strategy is also proposed in this work. The results show that the proposed topology is capable to produce a nine-level output voltage with less number of component counts and acceptable harmonic distortion content.

KEYWORDS:

  1. Multilevel inverter
  2. Asymmetrical
  3. Total Harmonic Distortion (THD)
  4. Low-frequency switching

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Proposed nine level inverter topology.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for proposed nine level inverter topology; (a)

and (b) are switching pulses, (c) Level generator output voltage.

Fig. 3. Simulation Output results at 50Hz fundamental frequency for R = 150ohm, L= 240, P.F = 0.9

Fig. 4. Simulation Output results at 50Hz fundamental frequency for R =150ohm, L= 240, P.F = 0.9

 CONCLUSION:

In this paper a new single-phase multilevel inverter topology is presented. Proposed topology is capable of producing nine-level output voltage with reduce device counts. It can be used in medium and high power application with unequal dc sources. Different modes of operation are discussed in detail. On the bases of device counts, the proposed topology is compared with conventional as well as other asymmetrical nine-level inverter topologies presented in literature. Comparative study shows that, for nine level output, the proposed topology requires lesser component counts then the conventional and other topologies. Proposed circuit is modeled in Matlab/Simulink environment. Results obtained shows that topology works properly. Detailed Simulation analysis is carried out. THD obtained in the output voltage is 8.95% whereas the each harmonic order is < 5%, satisfies harmonic Standard (IEEE-519).

REFERENCES:

[1] J. Rodriguez, L. G. Franquelo, S. Kouro, J. I. Leon, R. C. Portillo, M. A.M. Prats and M. A. Perez, “Multilevel Converters: An Enabling Technology for High-Power Applications”, IEEE Proceeding, Vol 97, No. 11, pp.1786 – 1817, November 2009.

[2] J. R. Espinoza, “Inverter”, Power Electronics Handbook, M. H. Rashid, Ed. New York, NY, USA: Elsevier, 2001,pp. 225 -269.

[3] L. M. Tolbert and T. G. Habetler, “Novel multilevel inverter carrierbased PWM method”, IEEE Transactions on Indsutrial Apllications”, Vol. 35, No. 5, pp. 1098-1107, September 1999.

[4] S. Debnath, J. Qin, B. Bahrani, M. Saeedifard and P. Barbosa, “Operation, Control and Applications of the Modular Multilevel Converter: A Review”, IEEE Transactions on Power Electronics, Vol. 30, No. 1, pp. 37-53, January 2015.

[5] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. C. Portillo and M. A. M. Prats, “The Age of Multilevel Converters Arrives”, IEEE Industrial Electronics magazine, Vol. 2, No. 2 pp. 28-39, June 2008.

Operation and Control of Smart Transformer for Improving Performance of Medium Voltage Power Distribution System

ABSTRACT:  

Smart transformer (ST) is a power electronic based transformer equipped with effective control and communication. It is expected to play a significant role in future power distribution system, however, their operational features in the medium voltage (MV) power distribution systems are yet not explored. In this paper, operation and control of ST are presented for improving its performance and operational range in a power distribution system consisting of two radial feeders in a city center. For investigating the performance of ST in above system, one conventional power transformer (CPT) is replaced by the ST whereas other feeder is continued to be supplied through the CPT. In this scheme, the ST is operated such that it makes total MV grid currents of the combined system balanced sinusoidal with unity power factor. Therefore, in addition to providing continuous and reliable operation of ST based loads, the ST can also improve the performance of the loads which are supplied by the CPT in a different feeder. Moreover, the proposed scheme eliminates the need of power quality improvement devices at the other feeder. Therefore, the scheme also makes the application of ST in the distribution system cost effective. Simulation results validate the suitability of ST in improving the performance of multiple feeder medium voltage power distribution system.

KEYWORDS:

  1. Smart transformer (ST)
  2. Medium voltage rectifier
  3. Power distribution system

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig. 1. A schematic of conventional power distribution system consisting of

two radial feeders in a city center.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulated waveforms when ST is not compensating for feeder II. (a) PCC voltages. (b) Grid currents. (c) MV rectifier currents (d) Feeder II currents.

Fig. 3. Simulated waveforms when ST is compensating for feeder II. (a) PCC voltages. (b) Grid currents. (c) MV rectifier currents (d) Feeder II currents.

Fig. 4. Simulated waveforms during transient conditions when load in feeder II is changed. (a) PCC voltages. (b) Grid currents. (c) MV rectifier currents (d) Feeder II currents.

 CONCLUSION:

 In this paper, the operation and control of a futuristic power distribution system consisting of two radial feeders with one CPT replaced by an ST is presented. It is shown that the ST can compensate for the loads connected at the feeder supplied by the CPTs, in addition to supplying their own loads. This scheme has potential to eliminate the requirement of power quality improvement devices such as STATCOM, power factor correcting capacitors, etc., connected at the second feeder. This ancillary feature in the medium voltage power distribution systems has potential to make application of ST more attractive and cost effective.

REFERENCES:

[1] S. Bifaretti, P. Zanchetta, A. Watson, L. Tarisciotti, and J. Clare, “Advanced power electronic conversion and control system for universal and flexible power management,” Smart Grid, IEEE Transactions on, vol. 2, no. 2, pp. 231–243, Jun. 2011.

[2] X. She, R. Burgos, G. Wang, F. Wang, and A. Huang, “Review of solid state transformer in the distribution system: From components to field application,” in Energy Conversion Congress and Exposition (ECCE),

2012 IEEE, Sep. 2012, pp. 4077–4084.

[3] S. Alepuz, F. Gonzalez, J. Martin-Arnedo, and J. Martinez, “Solid state transformer with low-voltage ride-through and current unbalance management capabilities,” in Industrial Electronics Society, IECON 2013 – 39th Annual Conference of the IEEE, Nov. 2013, pp. 1278–1283.

[4] S.-H. Hwang, X. Liu, J.-M. Kim, and H. Li, “Distributed digital control of modular-based solid-state transformer using dsp+fpga,” Industrial Electronics, IEEE Transactions on, vol. 60, no. 2, pp. 670–680, Feb. 2013.

 

A Unity Power Factor Converter with Isolation for Electric Vehicle Battery Charger

ABSTRACT:  

This paper deals with a unity power factor (UPF) Cuk converter EV (Electric Vehicle) battery charger having a high frequency transformer isolation alternatively of only a single segment front end converter used in vehicle’s traditional battery chargers. The operation of the proposed converter is defined in a number modes of the converter factors i.e. DCM (Discontinuous Conduction Mode) or CCM (Continuous Conduction Mode) alongside with the best plan equations.

PFC

In this way, this isolated PFC converter makes the input current sinusoidal in structure and improves input power factor to unity. Simulation effects for the proposed converter are proven for charging a lead acid EV battery in regular current constant voltage (CC-CV) mode. The rated full load and various enter supply conditions have been viewed to show the extended power quality indices as compared to conventional battery chargers. These indices observe the global IEC 61000-3-2 general to provide harmonic free input parameters for the proposed&nbsp; circuit.

KEYWORDS:

  1. UPF Cuk Converter
  2. Battery Charger
  3. Front end converter
  4. CC-CV mode
  5. IEC 61000-3-2 standard

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig. 1 General Schematic of an EV Battery Charger with PFC CUK Converter

 EXPECTED SIMULATION RESULTS:

 

(a)

 (b)

 (c)

Fig.2 Simulated performance of the isolated Cuk converter in rated condition (a) rated input side and output side quantities (b-c) harmonic analysis of the current at source end

(a)

(b)

(c)

Fig.3 Simulated performance of the isolated Cuk converter while input is varied to 270V (a) rated input side and output side quantities (b-c) harmonic analysis of the current at source end

(a)

(b)

(c)

Fig.4 Simulated performance of the isolated Cuk converter while input is reduced to 270V (a) rated input side and output side quantities (b-c) harmonic analysis of the current at source end

(a)

(b)

 (c)

Fig.5 Simulated performance of the isolated Cuk converter at light load condition (a) rated input side and output side quantities (b-c) harmonic analysis of the current at source end

 

CONCLUSION:

 An isolated Cuk converter based battery charger for EV with remarkably improved PQ indices along with well regulated battery charging voltage and current has been designed and simulated. The converter performance has been found satisfactory and well within standard for rated as well as different varying input rms value of supply voltages. The considerably improved THD in the current at the source end makes the proposed system an attractive solution for efficient charging of EVs at low cost. The proposed UPF converter performance has been tested to show its suitability for improved power quality based charging of an EV battery in CC-CV mode. Moreover, the cascaded dual loop PI controllers are tuned to have the smooth charging characteristics along with maintaining the low THD in mains current.

UPF

The proposed UPF converter topology have the inherent advantage of low ripples in input and output side due to the added input and output side inductors. Therefore, the life cycle of the battery is increased. MATLAB based simulation shows the performance assessment of the proposed charger for the steady state and dynamics condition which clearly state that the proposed charger can sustain the sudden disturbances in supply for charging the rated EV battery load. Moreover, during whole disturbances in supply voltage, the power quality parameters at the input side, are maintained within the IEC 61000-3-2 standard and THD is also very low.

REFERENCES:

[1] Limits for Harmonics Current Emissions (Equipment current ≤ 16A per Phase), International standards IEC 61000-3-2, 2000.

[2] Muhammad H. Rashid, “Power Electronics Handbook, Devices, Circuits, and Applications”, Butterworth-Heinemann, third edition, 2011.

[3] N. Mohan, T. M. Undeland, and W. P. Robbins, Power Electronics: Converters, Applications and Design. Hoboken, NJ, USA: Wiley, 2009.

[4] B. Singh, S. Singh, A. Chandra and K. Al-Haddad, “Comprehensive Study of Single-Phase AC-DC Power Factor Corrected Converters With High-Frequency Isolation”, IEEE Trans. Industrial Informatics, vol. 7, no. 4, pp. 540-556, Nov. 2011.

[5] A. Abramovitz K. M. Smedley “Analysis and design of a tapped-inductor buck–boost PFC rectifier with low bus voltage” IEEE Trans. Power Electron., vol. 26 no. 9 pp. 2637-2649 Sep. 2011.

The Application of Electric Spring in Grid-ConnectedPhotovoltaic System

ABSTRACT:  

The characteristics of distributed photovoltaic system power generation system is intermittent and instability. Under the weak grid conditions, when the active power of the PV system injected into the grid is fluctuant, the voltage of supply feeder will increase or decrease, thus affecting the normal use of sensitive load. The electric spring can transfer the energy injected into the supply feeder to the wide-voltage load, which is in series with the ES, to ensure the voltage stability of the sensitive load in the system. In this paper, a grid-connected photovoltaic simulation model with electric spring is built in Matlab / simulink. The voltage waveforms on the ES and sensitive load is obtained under the condition of changing the active power injected into the supply feeder by the grid-connected photovoltaic system. Thought the analysis of the waveforms, we can find that the Electric spring is a kind of effective method to solve the voltage fluctuation of the supply feeder in the grid-connected PV system.

KEYWORDS:

  1. Electric spring
  2. Grid-Connected Photovoltaic System
  3. Voltage Regulation
  4. Photovoltaic Consumption

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Figure 1. The photovoltaic system model with Electric spring

 EXPECTED SIMULATION RESULTS:

Figure 2. The effective value of line voltage when the active power of PV system decreases

Figure 3. The line voltage when the active power of PV system increases (with ES)

 CONCLUSION:

 This paper applies the electric spring to the PV system to solve the problem that the bus voltage fluctuates due to the power fluctuation during the PV power injected into the bus. By building a simulation model in Matlab /Simulink, it is proved that the voltage on the bus can be effectively stabilized after adding the electric spring in the grid-connected photovoltaic system. When the active power of the PV fluctuates, the electric spring can transfer the voltage fluctuation on the bus to the wide-voltage load, in order to ensure that the bus voltage stability in the vicinity of the given value. Therefore, this is an effective method to solve the fluctuation of the bus voltage in PV grid connected system.

REFERENCES:

  1. Hui S Y R, Lee C K, Wu F. Electric springs—A new smart grid technology[J]. IEEE Transactions on Smart Grid, 2012, 3(3): 1552-1561.
  2. F. Kienzle, P. Ahein, and G. Andersson, “Valuing investments in multi-energy conversion, storage, and demand-Side management systems under uncertainty,” IEEE Trans Sustain. Energy, vol. 2, no. 2, pp. 194–202,Apr. 2011.
  3. C. K. Lee and S. Y. R. Hui, “Input voltage control bidirectional power converters,” US patent application, US2013/0322139, May 31, 2013.
  4. CHEN Xu, ZHANG Yongjun, HUANG Xiangmin. Review of Reactive Power and Voltage Control Method in the Background of Active Distribution Network[J]. Automation of Electric Power Systems,2016,40(01):143-
  5. Lee S C, Kim S J, Kim S H. Demand side management with air conditioner loads based on the queuing system model[J]. IEEE Transactions on Power Systems, 2010, 26 (2): 661-668.