A Fuzzy Logic Controller for Autonomous Operation of a Voltage Source Converter-Based Distributed Generation System

ABSTRACT

This paper presents a fuzzy logic controller (FLC) for autonomous (islanded) operation of an electronically interfaced distributed generation unit and its load. In the grid connected mode, the voltage-sourced converter is operated in the active and reactive power (PQ) control mode, where a conventional control scheme is used to control the active and reactive power exchange with the grid. In the islanded mode, the proposed FLC is used to control the voltage of the islanded system despite the load variability and uncertainties. In addition, this paper also presents the use of the black-box nonlinear optimization technique to tune the parameters of the membership functions of the FLC in order to achieve optimal performance. The salient features of the proposed FLC are: 1) efficient to deal with the nonlinear systems; 2) design does not depend on the mathematical model of the system; and 3) less sensitive to the parameters variation than the conventional controllers. The frequency of the islanded system is dictated through the use of an internal oscillator. The effectiveness of the proposed FLC in controlling the voltage of the islanded system, irrespective of the load variability, is extensively validated based on simulation studies in the PSCAD/EMTDC environment. Moreover, the paper highlights the superiority of the proposed FLC over the conventional proportional-integral controllers through comparing the transient responses of the system based on both controllers.

KEYWORDS

1.     Autonomous operation

2.     Distributed generation (DG)

3.      Fuzzy logic controller (FLC)

4.      Voltage source converter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Single line diagram of the DG system

 EXPECTED SIMULATION RESULTS

Fig. 2. Responses for transition from grid-connected to islanded mode. (a) V_d. (b) V_q. (c) Load voltage (rms). (d) Load real power. (e) Load reactive power. (f) Three-phase load voltage using FLC. (g) Three-phase converter currents using FLC.

Fig. 3 Responses for the change of the load resistance R from 76 to 152 Ω(a) V_d. (b) V_q. (c) Load voltage (rms). (d) Load real power. (e) Load reactive power. (f) Three-phase load voltage using FLC. (g) Three-phase converter currents using FLC.

Fig. 4. Responses for the change of the load resistance R from 76 to 304 Ω(a) V_d. (b) V_q. (c) Load voltage (rms). (d) Load real power. (e) Load reactive power. (f) Three-phase load voltage using FLC. (g) Three-phase converter currents using FLC.

Fig. 5. Responses for change of the load inductance L from 111.9 to 222 mH. (a) V_d. (b) V_q. (c) Load voltage (rms). (d) Load real power. (e) Load reactive power. (f) Three-phase load voltage using FLC. (g) Three-phase converter currents using FLC.

Fig. 6. Responses for connecting a nonlinear load in parallel to the load. (a) V_d. (b) V_q. (c) Load voltage (rms). (d) Load real power. (e) Load reactive power. (f) Three-phase load voltage using FLC. (g) Three-phase converter currents using FLC.

Fig. 7. Responses for connecting a three-phase induction motor in parallel to the load. (a) Vd. (b) Vq. (c) Load voltage (rms). (d) Load real power. (e) Load reactive power. (f) Three-phase load voltage using FLC. (g) Three-phase converter currents using FLC. (h) Motor speed. (i) Developed torque.

CONCLUSION

This paper has presented the application of a FLC to the autonomous operation of an electronically coupled DG unit and its local load with the purpose of achieving better transient responses despite the load variability and uncertainty. A detailed dynamic model of the system under study and the control strategy are investigated. The system performance using the FLC is evaluated through the following case studies:

1) transition from the grid-connected mode to the islanded mode;

2) change of the RLC load parameters;

3) switching of a nonlinear load;

4) motor energization.

The simulation results have shown that the system performance using the proposed FLC has a better damped response and a faster transient behavior in comparison with that obtained using the conventional PI controller. It can be concluded that the FLC guarantees a robust stability and efficient performance irrespective of the load uncertainty.

REFERENCES

[1] N. Hatziargyriou, H. Asano, R. Iravani, and C. Marnay, “Microgrids,” IEEE Power Energy Mag., vol. 5, no. 4, pp. 78–94, Jul./Aug. 2007.

[2] R. A. Walling, R. Saint, R. C. Dugan, J. Burke, and L. A. Kojovic, “Summary of distributed resources impact on power delivery systems,” IEEE Trans. Power Del., vol. 23, no. 3, pp. 1636–1644, Jul. 2008.

[3] F. Katiraei, M. R. Iravani, and P.W. Lehn, “Micro-grid autonomous operation during and subsequent to islanding process,” IEEE Trans. Power Del., vol. 20, no. 1, pp. 248–257, Jan. 2005.

[4] P. Piagi and R. H. Lasseter, “Autonomous control of microgrids,” in Proc. IEEE Power Eng. Soc. (PES) Gen. Meeting, Montreal, QC, Canada, Jun. 2006, Paper no. 1708993.

[5] H. Nikkhajoei and R. H. Lasseter, “Distributed generation interface to the CERTS microgrid,” IEEE Trans. Power Del., vol. 24, no. 3, pp. 1598–1608, Jul. 2009.

Design and Analysis of an On-Board Electric Vehicle Charger for Wide Battery Voltage Range

ABSTRACT:

The scarcity of fossil fuel and the increased pollution leads the use of Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV) instead of conventional Internal Combustion (IC) engine vehicles. An Electric Vehicle requires an on-board charger (OBC) to charge the propulsion battery. The objective of the project work is to design a multifunctional on-board charger that can charge the propulsion battery when the Electric Vehicle (EV) connected to the grid. In this case, the OBC plays an AC-DC converter. The surplus energy of the propulsion battery can be supplied to the grid, in this case, the OBC plays as an inverter. The auxiliary battery can be charged via the propulsion battery when PEV is in driving stage. In this case, the OBC plays like a low voltage DC-DC converter (LDC). An OBC is designed with Boost PFC converter at the first stage to obtain unity power factor with low Total Harmonic Distortion (THD) and a Bi-directional DC-DC converter to regulate the charging voltage and current of the propulsion battery. The battery is a Li-Ion battery with a nominal voltage of 360 V and can be charged from depleted voltage of 320 V to a fully charged condition of 420 V. The function of the second stage DC-DC converter is to charge the battery in a Constant Current and Constant Voltage manner. While in driving condition of the battery the OBC operates as an LDC to charge the Auxiliary battery of the vehicle whose voltage is around 12 V. In LDC operation the Bi-Directional DC-DC converter works in Vehicle to Grid (V2G) mode. A 1KW prototype of multifunctional OBC is designed and simulated in MATLAB/Simulink. The power factor obtained at full load is 0.999 with a THD of 3.65 %. The Battery is charged in A CC mode from 320 V to 420 V with a constant battery current of 2.38 A and the charging is switched into CV mode until the battery current falls below 0.24 A. An LDC is designed to charge a 12 V auxiliary battery with CV mode from the high voltage propulsion battery.

KEYWORDS:

1.      Bi-directional DC-DC converter

2.      Boost PFC converter

3.      Electric vehicle

4.      Low voltage DC-DC converter

5.      Vehicle-to-grid.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig 1 Block Diagram of Power distribution in EV

EXPECTED SIMULATION RESULTS:

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Fig 2 Simulated Results of Charging operation of the propulsion battery (a)Voltage and (b)Current in Beginning Point(c)voltage and (d)current in Nominal Point (e)voltage and (f)current in Turning Point(g)voltage and (h)current in End Point

Fig 3 DC link voltage and current during G2V operation (The current is multiplied by 100 for batter visibility)

Fig 4 Voltage and Current of Auxiliary battery during charging (Current is multiplied by 10 for better visibility)

CONCLUSION:

An On-Board Electric Vehicle charger is designed for level 1 charging with a 230 V input supply. Different stages of an OBC is stated and the challenges are listed. The developments have been implemented to overcome key issues. A two stage charger topology with active PFC converter at the front end followed by a Bi-directional DC-DC converter is designed. The active PFC which is a Boost converter type produces less than 5 % THD at full load. Moreover, the PFC converter is applicable to wide variation in loads. The detailed design of the power stage, as well as the controller, is discussed with the simulated results.

A second stage DC-DC converter is designed and simulated for the charging current and voltage regulation. The converter performs very precisely by charging the propulsion battery in CC/CV mode over a wide range of voltage. A V2G controller has been developed for the DC-DC converter in order to supply power to the grid from the propulsion battery. A new Low-Voltage DC-DC converter is proposed to charge the Auxiliary battery via the propulsion battery utilizing the same OBC. The battery voltage and current waveforms are presented and the performance of the designed converter is verified.

REFERENCES:

[1] “No Title,” https://en.wikipedia.org/wiki/Electric_vehicle. .

[2] S. S. Williamson, Energy management strategies for electric and plug-in hybrid electric vehicles. Springer, 2013.

[3] a. Emadi and K. Rajashekara, “Power Electronics and Motor Drives in Electric, Hybrid Electric, and Plug-In Hybrid Electric Vehicles,” IEEE Trans. Ind. Electron., vol. 55, no. 6, pp. 2237–2245, 2008.

[4] M. Yilmaz and P. T. Krein, “Review of charging power levels and infrastructure for plug-in electric and hybrid vehicles,” 2012 IEEE Int. Electr. Veh. Conf. IEVC 2012, vol. 28, no. 5, pp. 2151–2169, 2012.

[5] H. Wang, S. Dusmez, and A. Khaligh, “Design and analysis of a full-bridge LLC-based PEV charger optimized for wide battery voltage range,” IEEE Trans. Veh. Technol., vol. 63, no. 4, pp. 1603–1613, 2014.

Neuro-fuzzy current controller for three-level cascade inverter based D-STATCOM

ABSTRACT:

Distribution STATCOM (D-STATCOM) is a custom power device connected in parallel to power system. In this paper, Neuro-Fuzzy Controller (NFC) which has robust structure is proposed for control of D-STATCOM’s dq-axis currents. Designed NFC is first order Mamdani type NFC structure and has two inputs, one output and six layers. DSTATCOM is based on three-level cascaded inverter and this inverter is controlled with Sinusoidal Pulse Width Modulation (SPWM) technique. dSPACE’s DS1103 control card is used for real-time implementation of D-STATCOM’s control algorithm. The performance of D-STATCOM using NFC is evaluated by changing of reference reactive current (iqref) as on-line. Under this condition, some experimental results obtained from experimental setup are given.

KEYWORDS:

1.      D-STATCOM

2.      Neuro-Fuzzy Current Controller

3.      SPWM

4.       Three-Level Cascade Inverter

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig.1. Three-level cascaded inverter based D-STATCOM

EXPECTED SIMULATION RESULTS:

 Fig.2. Changing of dc link voltages

Fig.3. iqref tracking performance of iq

Fig.4. Phase-a current and voltage waveforms of D-STATCOM

Fig.5. Changing of modulation index

Fig.6. Changing of phase angle

CONCLUSION:

In this paper, NFC is developed to synthesize the current control loop of D-STATCOM. NFC which is a combination of ANN and FLC gives the D-STATCOM a good dynamic response and excellent tracking ability in changing of iqref. Experimental results show that Neuro-Fuzzy current controlled D-STATCOM can provide the desired reactive power exact and fast within own rated power limits even in the worst operating condition.

REFERENCES:

[1] S. Mohagheghi, “Adaptive Critic Designs Based Neuro-Controllers for Local and Wide Area Control of a Multimachine Power System with A Static Compensator,” Phd. Thesis, Georgia Institute of Technology, 2006.

[2] C. Schauder, H. Mehta, “Vector Analysis and Control of Advanced Static VAr Compensators,” Generation, Transmission and Distribution, IEE Proceedings C, vol.140, pp. 299-360, 1993.

[3] V. Blasko, V. Kaura, “A New Mathematical Model and Control of A Three-Phase AC-DC Voltage Source Converter,” IEEE Transactions on Power Electronics, vol.12, pp. 116-123, 1997.

[4] P. W. Lehn, M. R. Iravani, “Experimental Evaluation of STATCOM Closed Loop, IEEE Transactions on Power Delivery,” vol.13, pp. 1378-1384, 1998.

[5] P. Rao, M. L. Crow, Z. Yang, “STATCOM Control for Power System Voltage Control Applications,” IEEE Transactions on Power Delivery, vol.15, pp.1311-1317, 2000.

Cascaded Control of Multilevel Converter based STATCOM for Power System Compensation of Load Variation

 ABSTRACT:

 The static synchronous compensator (STATCOM) is used in power system network for improving the voltage of a particular bus and compensate the reactive power.It can be connected to particular bus as compensating device to improve the voltage profile and reactive power compensation. In this paper, a multi function controller is proposed and discussed. The control concept is based on a linearization of the d-q components with cascaded controller methods. The fundamental parameters are controlled with using of proportional and integral controller. In closed loop method seven level cascaded multilevel converter (CMC) is proposed to ensure the stable operation for damping of power system oscillations and load variation.

KEYWORDS:

1.      FACTS

2.       PWM

3.       CMC

4.       STATCOM

SOFTWARE: MATLAB/SIMULINK

 TEST SYSTEM:

Figure 1.STATCOM network connection.

 EXPECTED SIMULATION RESULTS:

Figure 2. Load terminal dq0 Currents with Load variation

Figure 3. Source terminal dq0 Currents with Load variation.

Figure 4. Iqref output for load rejection.

Figure 5. Source Voltage for load rejection with AGC.

Figure 6. THD of output Voltage of Cascaded Multilevel converter.

Figure 7. THD of output Current of Cascaded Multilevel Converter

Figure 8.Source Active and Reactive power.

Figure 9. Power factor in Load and Source Bus

Figure 10.Three phase Supply Voltage of multilevel converter.

CONCLUSION:

The cascaded controller is designed for seven level CMC based STATCOM. This control scheme regulates the capacitor voltage of the STATCOM and maintain rated supply voltage for any load variation with in the rated value. It has been shown that the CMC is able to reduce the THD values of output voltage and current effectively. The CMC based STATCOM ensures that compensate the reactive power and reduce the harmonics in output of STATCOM.

 REFERENCES:

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

[2] P. Lehn and M. Iravani, Oct.1998, “Experimental evaluation of STATCOM closed loop dynamics”, IEEE Trans. Power Delivery, vol.13, pp.1378-1384.

[3] Mahesh K.Mishra and Arindam Ghosh, Jan 2003, ”Operation of a D-STATCOM in Voltage Control Mode”, IEEE Trans. Power Delivery, vol.18, pp.258-264.

[4] Arindam Ghosh, Avinash Joshi, Jan 2000, ”A New Approach to Load Balancing and Power Factor Correction in Power Distribution System”, IEEE Trans. Power Delivery, vol.15, No.1, pp. 417-422.

[5] Arindam Ghosh, Gerard Ledwich, Oct 2003,”Load Compensating DSTATCOM in Weak AC Systems”, IEEE Trans. Power Delivery, vol.18, No.4, pp.1302-1309.