Modeling and Control of Multi-Terminal HVDC with Offshore Wind Farm Integration and DC Chopper Based Protection Strategies

ABSTRACT:

Multi-Terminal HVDC based on three-level neutral-clamped voltage source converters (VSC) is an ideal approach for the integration of DFIG wind farms to the power grid. However, dc-link faults and ac faults are major concerns for the safety and consistency of VSC-HVDC system. This paper demonstrates methods employing both full bridge and half bridge DC-DC converters for the fast clearance and protection of dc and ac ground faults respectively. In addition, control strategies incorporating decoupling control and feed-forward compensation on both grid side and wind farm side VSCs are also presented. Normal operations are observed to examine the performance of the MT-HVDC system, and also dc-link fault and three-phase ground fault at inverter side are simulated to verify the effectiveness of the approach employing DC-DC converters to suppress dc current overshoot in case of dc-link fault and mitigate dc voltage overshoot during three-phase ac ground fault. This proposed MT-HVDC transmission system and the fault-ride through capabilities provided by the dc choppers is validated by the simulation studies using detailed Matlab/Simulink model for normal operation, dc and ac ground faults.

KEYWORDS:

1.      VSC-HVDC

2.      DFIG

3.      DC chopper

4.      Faults

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

                                                         Fig. 1 Topology of the proposed multi-terminal VSC-HVDC system.

EXPECTED SIMULATION RESULTS:

Fig. 2 Simulation results of MT-HVDC during normal operation: (a) active power of wind farm, (b) dc voltage, and (c) ac rms current.

Fig. 3 Simulation results of 6 DFIG units during normal operation: (a) active power, (b) reactive power, (c) ac rms voltage, and (d) back-to-back dc-link voltage of DFIG unit.

Fig. 4 Simulation results of MT-HVDC during dc pole-to-pole fault with and without full bridge dc chopper protection: (a) dc voltage, and (b) dc current.

Fig. 5 Simulation results of MT-HVDC during three-phase ac ground fault at inverter side with and without half bridge dc chopper protection: (a) ac rms voltage at inverter side, (b) dc voltage overshoot without protection measures, and (c) dc voltage with protection measures.

CONCLUSION:

This paper investigates a multi-terminal VSC-HVDC system, which integrates two DFIG wind farms to the ac grid. The control strategies of both WFVSC and GSVSC stations are discussed in detail, and two approaches employing both full bridge and half bridge dc choppers are extended and displayed. Simulation studies are carried out in normal, dc pole-to-pole and ac ground fault operations, and the result verifies the effectiveness of the proposed MT-HVDC system in both the performance of wind power delivery and the protection measures for various fault conditions. Specifically, the dc voltage drop and dc current overshoot are eliminated during dc fault with full bridge dc choppers, while only a 8% voltage overshoot is observed with the implementation of half bridge dc choppers in case of three-phase ac ground fault.

REFERENCES:

 [1] S. G. Hernandez, E. M. Goytia and O. A. Lara, “Analysis of wide area integration of dispersed wind farms using multiple VSC-HVDC links,” in Proc. of EPE, Sevilla, pp. 17-26, 2008.

[2] S. Towito, M. Berman, G. Yehuda and R. Rabinvici, “Distribution generation case study: electric wind farm doubly fed induction generators”, in Proc. Convention of Electrical and Electronics Engineering(CEEE), Israel, pp. 393-397, Nov. 2006.

[3] N. Flourentzou, V. G. Agelidis, and G. D. Demetriades, “VSC-based HVDC power transmission systems: an overview,” IEEE Trans. Power Electron., vol. 24, no. 3, pp. 592-602, Mar. 2009.

[4] L. Xu, L. Yao, and C. Sasse, “Grid integration of large DFIG-based wind farms ssing VSC transmission,” IEEE Trans. Power Syst., vol. 22, no. 3, pp.976-984, Aug. 2007.

[5] L. Weimers, “HVDC Light: A new technology for a better environment”, IEEE Power Eng. Review, vol. 18, no. 8, pp.19-20, Aug. 1998.

Inertial Response of an Offshore Wind Power Plant with HVDC-VSC

 ABSTRACT:

This paper analyzes the inertial response of an offshore wind power plant (WPP) to provide ancillary services to the power system grid. The WPP is connected to a high-voltage direct-current voltage source converter HVDC-VSC to deliver the power to the onshore substation. The wind turbine generator (WTG) used is a doubly-fed induction generator (Type 3 WTG). In this paper we analyze a control method for the WTGs in an offshore WPP to support the grid and contribute ancillary services to the power system network. Detailed time domain simulations will be conducted to show the transient behavior of the inertial response of an offshore WPP.

KEYWORDS:

1.      HVDC

2.       Inertial response

3.       Offshore wind turbine

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Test system schematic

EXPECTED SIMULATION RESULTS:

Fig. 2. ΔT order applied to the controller of the DFIG

Fig. 3. DFIG rotating speed, 150 MW

Fig. 4. DFIG electromagnetic torque, 150 MW

Fig. 5. HVDC link voltage , 150 MW

Fig. 6. HVDC link current, 150 MW

Fig. 7. Real and reactive power (rectifier side), 150 MW

Fig. 8. Real and reactive power (inverter side), 150 MW

Fig. 9. DFIG rotating speed, 180 MW

Fig. 10. DFIG electromagnetic torque, 180 MW

Fig. 11. HVDC link voltage , 180 MW

Fig. 12. HVDC link current, 180 MW

Fig. 13. Real and reactive power (rectifier side), 180 MW

Fig. 14. Real and reactive power (inverter side), 180 MW

Fig. 15. DFIG rotating speed, 200 MW, 12 m/s

Fig. 16. DFIG electromagnetic torque, 200 MW, 12 m/s

Fig. 17. HVDC link voltage , 200 MW, 12 m/s

Fig. 18. HVDC link current, 200 MW, 12 m/s

CONCLUSION:

Detailed time domain simulations were conducted in order to analyze the transients present on the inertial response of an offshore WPP delivering power through an HVDC-VSC link. Several results from transient behavior are presented, these results show that an offshore WPP connected to the grid via an HVDC-VSC link is able to deliver inertial response if it is requested.

These results are important as the WPP importance for the power system is growing and its performance during contingencies must be asured.

REFERENCES:

[1] A. Bodin, “HVDC Light—A Preferable Power Transmission System for Renewable Energies.” Proceedings of the 2011 Third International Youth Conference on Energetics; July 7–9, 2011, Leiria, Portugal

[2] M. de Prada Gil, O. Gomis-Bellmunt, A. Sumper, and J. Bergas-Jané, “Analysis of a Multi-Turbine Offshore Wind Farm Connected to a Single Large Power Converter Operated with Variable Frequency.” Energy (36: 5), May 2011; pp. 3272–3281

[3] Feltes, C., and Erlich, I. “Variable Frequency Operation of DFIG-Based Wind Farms Connected to the Grid Through VSC-HVDC Link.” IEEE Power Engineering Society General Meeting, June 24–28, 2007, Tampa, Florida.

[4] N. Miller, K. Clark, M. Cardinal, and R. Delmerico, "Grid-friendly wind plants controls: GE Wind CONTROL—Functionality and field tests," presented at European Wind Energy Conf., Brussels, Belgium, 2008.

[5] N. W. Miller, K. Clark, and M. Shao, “Impact of frequency responsive wind plant controls on grid performance,” presented at 9th International Workshop on Large-Scale Integration of Wind Power, Quebec, Canada, Oct. 18–19, 2010.

Harmonics Reduction And Power Quality Improvement By Using DPFC

ABSTRACT:

The DPFC is derived from the unified power-flow controller (UPFC). The DPFC can be considered as a UPFC with an eliminated common dc link. The active power exchange between the shunt and series converters which is through the common dc link in the UPFC is now through the transmission lines at the third-harmonic frequency. The DPFC employs the distributed concept, in which the common dc-link between the shunt and series converters are eliminated and three-phase series converter is divided to several single-phase series distributed converters through the line. According to the growth of electricity demand and the increased number of non-linear loads in power grids harmonics, voltage sag and swell are the major power quality problems. DPFC is used to mitigate the voltage deviation and improve power quality. Simulations are carried out in MATLAB/Simulink environment. The presented simulation results validate the DPFC ability to improve the power quality.

KEYWORDS:

1.      Load flow control

2.      FACTS

3.      Power Quality

4.       Harmonics

5.      Sag and Swell Mitigation

6.       Distributed Power Flow Controller

7.       Y–Δ transformer

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. DPFC configuration

EXPECTED SIMULATION RESULTS:

Fig 2. three phase voltage sag waveform without DPFC

Fig. 3 three phase voltage sag waveform with DPFC

Fig.4 3-ϕ load current swell waveform without DPFC

Fig.5 Mitigation of 3-ϕ load current swell with DPFC

              

Fig.6 Total harmonic distortion of load voltage without DPFC

.

Fig.7 Total harmonic distortion of load voltage with DPFC

CONCLUSION:

This paper has presented a new concept called DPFC. The DPFC emerges from the UPFC and inherits the control capability of the UPFC, which is the simultaneous adjustment of the line impedance, the transmission angle, and the bus voltage magnitude. The common dc link between the shunt and series converters, which is used for exchanging active power in the UPFC, is eliminated. This power is now transmitted through the transmission line at the third-harmonic frequency. The series converter of the DPFC employs the DFACTS concept, which uses multiple small single-phase converters instead of one large-size converter. The reliability of the DPFC is greatly increased because of the redundancy of the series converters. The total cost of the DPFC is also much lower than the UPFC, because no high-voltage isolation is required at the series-converter part and the rating of the components of is low. To improve power quality in the power transmission system, the harmonics due to nonlinear loads, voltage sag and swell are mitigated. To simulate the dynamic performance, a three-phase fault is considered near the load. It is shown that the DPFC gives an acceptable performance in power quality improvement and power flow control.

REFERENCES:

[1] S.Masoud Barakati Arash Khoshkbar sadigh and Mokhtarpour.Voltage Sag and Swell Compensation with DVR Based on Asymmetrical Cascade Multicell Converter North American Power Symposium (NAPS),pp.1-7,2011.

[2] Zhihui Yuan, Sjoerd W.H de Haan, Braham Frreira and Dalibor Cevoric “A FACTS Device: Distributed Power Flow Controller (DPFC)” IEEE Transaction on Power Electronics, vol.25, no.10, October 2010.

[3] Zhihui Yuan, Sjoerd W.H de Haan and Braham Frreira “DPFC control during shunt converter failure” IEEE Transaction on Power Electronics 2009.

[4] M. D. Deepak, E. B. William, S. S. Robert, K. Bill, W. G. Randal, T. B. Dale, R. I. Michael, and S. G. Ian, “A distributed static series compensator system for realizing active power flow control on existing power lines,” IEEE Trans. Power Del., vol. 22, no. 1, pp. 642–649, Jan. 2007.

[5] D. Divan and H. Johal, “Distributed facts—A new concept for realizing grid power flow control,” in Proc. IEEE 36th Power Electron. Spec. Conf. (PESC), 2005, pp. 8–14.

Designing of Multilevel DPFC to Improve Power Quality

ABSTRACT:

According to growth of electricity demand and the increased number of non-linear loads in power grids, providing a high quality electrical power should be considered. In this paper, Enhancement of power quality by using fuzzy based multilevel power flow controller (DPFC) is proposed. The DPFC is a new FACTS device, which its structure is similar to unified power flow controller (UPFC). In spite of UPFC, in DPFC the common dc-link between the shunt and series converters is eliminated and three-phase series converter is divided to several single-phase series distributed converters through the line. This eventually enables the DPFC to fully control all power system parameters. It, also, increases the reliability of the device and reduces its cost simultaneously. In recent years multi level inverters are used high power and high voltage applications .Multilevel inverter output voltage produce a staircase output waveform, this waveform look like a sinusoidal waveform leads to reduction in Harmonics. Fuzzy Logic is used for optimal designing of controller parameters. Application of Fuzzy Multilevel DPFC for reduction of Total Harmonic Distortion was presented. The simulation results show the improvement of power quality using DPFC with Fuzzy logic controller.

KEYWORDS:

1.      FACTS

2.       Power Quality

3.      Multi Level Inverters

4.      Fuzzy Logic

5.       Distributed Power Flow Controller component

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1: The DPFC Structure.

EXPECTED SIMULATION RESULTS:

Fig.2: 5 Level Voltage Waveform

Fig.3: Three Phase output Voltage and Current Waveform

Fig.4: Supply Voltage and Current Waveform with unity PF

Fig.5: THD without fuzzy

Fig.6: THD with fuzzy

CONCLUSION:

In this paper Fuzzy Logic Controller technique based distributed power flow controller (DPFC) with multilevel voltage source converter (VSC) is proposed. The presented DPFC control system can regulate active and reactive power flow of the transmission line. We are reducing the THD value from 24.84% to 0.41% by using this technic as shown in fig’s (12) & (13).The series converter of the DPFC employs the DFACTS concept, which uses multiple converters instead of one large-size converter. The reliability of the DPFC is greatly increased because of the redundancy of the series converters. The total cost of the DPFC is also much lower than the UPFC, because no high-voltage isolation is required at the series converter part and the rating of the components are low. Also results show the valid improvement in Power Quality using Fuzzy Logic based Multilevel DPFC.

REFERENCES:

[1] K Chandrasekaran, P A Vengkatachalam, Mohd Noh Karsiti and K S Rama Rao, “Mitigation of Power Quality Disturbances”, Journal of Theoretical and Applied Information Technology, Vol.8, No.2, pp.105- 116, 2009

[2] Priyanka Chhabra, “Study of Different Methods for Enhancing Power Quality Problems”, International Journal of Current Engineering and Technology, Vol.3, No.2, pp.403-410, 2013

[3] Bindeshwar Singh, Indresh Yadav and Dilip Kumar, “Mitigation of Power Quality Problems Using FACTS Controllers in an Integrated Power System Environment: A Comprehensive Survey”, International Journal of Computer Science and Artificial Intelligence, Vol.1, No.1, pp.1-12, 2011

[4] Ganesh Prasad Reddy and K Ramesh Reddy, “Power Quality Improvement Using Neural Network Controller Based Cascaded HBridge Multilevel Inverter Type D-STATCOM”, International Conference on Computer Communication and Informatics, 2012

[5] Lin Xu and Yang Han, “Effective Controller Design for the Cascaded Hbridge Multilevel DSTATCOM for Reactive Compensation in Distribution Utilities”, Elektrotehniski Vestnik, Vol.78, No.4, pp.229- 235, 2011