Improving the Dynamic Performance of Wind

Farms with STATCOM

ABSTRACT:

When integrated to the power system, large wind farms can pose voltage control issues among other problems. A thorough study is needed to identify the potential problems and to develop measures to mitigate them. Although integration of high levels of wind power into an existing transmission system does not require a major redesign, it necessitates additional control and compensating equipment to enable (fast) recovery from severe system disturbances. The use of a Static Synchronous Compensator (STATCOM) near a wind farm is investigated for the purpose of stabilizing the grid voltage after grid-side disturbance such as a three phase short circuit fault. The strategy focuses on a fundamental grid operational requirement to maintain proper voltages at the point of common coupling by regulating the voltage. The DC voltage at individual wind turbine (WT) inverters is also stabilized to facilitate continuous operation of wind turbines during disturbances.

KEYWORDS:

1.      Wind turbine

2.      Doubly-fed Induction Generator

3.      STATCOM

4.      Three phase fault

5.      Reactive power support.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

Wind turbines have to be able to ride through a fault without disconnecting from the grid. When a wind farm is connected to a weak power grid, it is necessary to provide efficient power control during normal operating conditions and enhanced support during and after faults. This paper explored the possibility of connecting a STATCOM to the wind power system in order to provide efficient control. An appropriately sized STATCOM can provide the necessary reactive power compensation when connected to a weak grid. Also, a higher rating STATCOM can be used for efficient voltage control and improved reliability in grid connected wind farm but economics limit its rating. Simulation studies have shown that the additional voltage/var support provided by an external device such as a STATCOM can significantly improve the wind turbine’s fault recovery by more quickly restoring voltage characteristics. The extent to which a STATCOM can provide support depends on its rating. The higher the rating, the more support provided. The interconnection of wind farms to weak grids also influences the safety of wind turbine generators. Some of the challenges faced by wind turbines connected to weak grids are an increased number and frequency of faults, grid abnormalities, and voltage and frequency fluctuations that can trip relays and cause generator heating.

REFERENCES:

 [1] http://www.awea.org/newsroom/releases/Wind_Power_Capacity_012307. html, accessed Nov. 2007.

[2] T. Sun, Z. Chen, F. Blaabjerg, “Voltage recovery of grid-connected wind turbines with DFIG after a short-circuit fault,” 2004 IEEE 35th Annual Power Electronics Specialists Conf., vol. 3, pp. 1991-97, 20-25 June 2004.

[3] E. Muljadi, C.P. Butterfield, “Wind Farm Power System Model Development,” World Renewable Energy Congress VIII, Colorado, Aug- Sept 2004.

[4] S.M. Muyeen, M.A. Mannan, M.H. Ali, R. Takahashi, T. Murata, J. Tamura, “Stabilization of Grid Connected Wind Generator by STATCOM,” IEEE Power Electronics and Drives Systems Conf., Vol. 2, 28-01 Nov. 2005.

[5] Z. Saad-Saoud, M.L. Lisboa, J.B. Ekanayake, N. Jenkins, G. Strbac, “Application of STATCOMs to wind farms,” IEE Proceedings – Generation, Transmission, Distribution, vol. 145, pp.1584-89, Sept 1998.

A Versatile Control Scheme for a Dynamic Voltage

Restorer for Power-Quality Improvement

ABSTRACT:

This paper presents a control system based on a repetitive controller to compensate for key power-quality disturbances, namely voltage sags, harmonic voltages, and voltage imbalances, using a dynamic voltage restorer (DVR). The control scheme deals with all three disturbances simultaneously within a bandwidth. The control structure is quite simple and yet very robust; it contains a feed forward term to improve the transient response and a feedback term to enable zero error in steady state. The well-developed graphical facilities available in PSCAD/EMTDC are used to carry out all modeling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation.

KEYWORDS:

1.      Dynamic voltage restorer (DVR)

2.      Harmonic distortion

3.      Power quality (PQ)

4.      Repetitive control

5.      Voltage sag.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

EXPECTED SIMULATION RESULTS:

CONCLUSION:

The use of dynamic voltage restorers in PQ-related applications is increasing. The most popular application has been on voltage sags amelioration but other voltage-quality phenomena may also benefit from its use, provided that more robust control schemes than the basic PI controller become available. A case in point is the so called repetitive controller proposed in this paper, which has a fast transient response and ensures zero error in steady state for any sinusoidal reference input and for any sinusoidal disturbance whose frequencies are an integer multiple of the fundamental frequency. To achieve this, the controller has been provided with a feed forward term and feedback term. The design has been carried out by studying the stability of the closed loop system including possible modeling errors, resulting in a controller which possesses very good transient and steady-state performances for various kinds of disturbances. A key feature of this control scheme is its simplicity; only one controller is required to eliminate three PQ disturbances, namely, voltage sags, harmonic voltages, and voltage imbalances. The controller can be implemented by using either a stationary reference frame or a rotating reference frame. In this paper, the highly developed graphical facilities available in PSCAD/EMTDC have been used very effectively to carry out all aspects of the system implementation. Comprehensive simulation results using a simple but realistic test system show that the repetitive controller and the DVR yield excellent voltage regulation, thus screening a sensitive load point from upstream PQ disturbances.

REFERENCES:

[1] M. H. J. Bollen, “What is power quality?,” Elect. Power Syst. Res., vol. 66, no. 1, pp. 5–14, July 2003.

[2] J. G. Nielsen and F. Blaabjerg, “A detailed comparison of system topologies for dynamic voltage restorers,” IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1272–1280, Sep./Oct. 2005.

[3] V. K. Ramachandaramurthy, A. Arulampalam, C. Fitzer, C. Zhan, M. Barnes, and N. Jenkins, “Supervisory control of dynamic voltage restorers,” Proc. Inst. Elect. Eng., Gen., Transm. Distrib, vol. 151, no. 4, pp. 509–516, Jul. 2004.

[4] P. T. Nguyen and T. K. Saha, “Dynamic voltage restorer against balanced and unbalanced voltage sags: Modelling and simulation,” in Proc. IEEE Power Eng. Soc. General Meeting, Jun. 2004, vol. 1, pp. 639–644, IEEE.

[5] M. H. J. Bollen, Understanding Power Quality Problems: Voltage Sags and Interruptions.. Piscataway, NJ: IEEE Press, 2000.

Natural Harmonic Elimination of Square-Wave Inverter for Medium-Voltage Application

ABSTRACT:

In this paper, a low-frequency square-wave inverter with a series-connected pulse width modulation (PWM) inverter is investigated for high-power applications. The series compensators produce only the desired harmonic voltages to make the net output voltage sinusoidal with small PWM switching harmonics only. An open-loop control strategy for the series compensator is proposed in this paper. This strategy indirectly sets the compensator dc bus voltage to the desired level. No external dc source or active power at fundamental frequency is required to control this dc bus voltage. Different variations of this basic strategy are presented in this paper for medium voltage applications. Theoretical analysis of this strategy is presented in this paper with simulation and experimental results.

KEYWORDS:

1.      AC motor drives

2.      Power conversion

3.      Power conversion harmonics.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 EXPECTED SIMULATION RESULTS:

CONCLUSION:

In this paper, an open-loop natural control of voltage source inverter has been proposed mainly for high-power applications. The main square-wave inverter is built with high-voltage low switching- frequency semiconductor devices like integrated gate commutated thyristors (IGCTs). The series compensators are IGBT-based inverters and operate from relatively low dc bus voltages at high switching frequencies. The series compensators produce only the desired harmonic voltages to make the net output voltage sinusoidal. For medium-voltage application, several compensating PWM inverters are connected in series. Each cell compensates one particular harmonic only. As the order of harmonics increases, the required dc bus voltage level drops. This enables to exploit higher switching frequency for higher order harmonic cell. It has been established both theoretically and experimentally that the dc bus of the compensators do not require any external dc source or closed-loop controller for this proposed strategy. The active power at harmonic frequencies keeps the compensator dc bus voltage charged. For variable speed drives applications, the magnitude of the fundamental output voltage should be controlled by regulating the dc bus voltage of the square-wave inverter. For static synchronous compensator (STATCOM) applications, the limited variation of this dc bus voltage may also be required. This can be achieved by drawing small active power at fundamental frequency from the grid.

REFERENCES:

 [1] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral point clamped PWM inverter,” IEEE Trans. Ind. Appl., vol. IA-17, no. 5, pp. 518–523, Sept./Oct. 1981.

[2] M. D.Manjrekar, P. K. Steimer, and T. A. Lipo, “Hybrid multilevel power conversion system: A competitive solution for high-power applications,” IEEE Trans. Ind. Appl., vol. 36, no. 3, pp. 834–841, May/Jun. 2000.

[3] R. H. Wilkinson, T. A. Meynard, and H. du T. Mouton, “Natural balance of multicell converters: The general case,” IEEE Trans. Power Electron., vol. 21, no. 6, pp. 1649–1657, Nov. 2006.

[4] H. Akagi, S. Inoue, and T. Yoshii, “Control and performance of a transformer less cascade PWM STATCOM with star configuration,” IEEE Trans. Ind. Appl., vol. 43, no. 4, pp. 1041 1049, Jul./Aug. 2007.

[5] S. S. Fazel, S. Bernet, D. Krug, and K. Jalili, “Design and comparison of 4-kV neutral-point-clamped, flying-capacitor, and series-connected Hbridge multilevel converters,” IEEE Trans. Ind. Appl., vol. 43, no. 4, pp. 1032–1040, Jul./Aug. 2007.

Improved Z-Source Inverter with Reduced Z-Source Capacitor Voltage Stress and Soft-Start Capability

ABSTRACT:

This paper proposes an improved Z-source inverter topology. Compared to the traditional Z source inverter, it can reduce the Z-source capacitor voltage stress significantly to perform the same voltage boost, and has inherent limitation to inrush current at startup. The control strategy of the proposed Z-source inverter is exactly the same as the traditional one, so all the existing control strategy can be used directly. A soft-start strategy is also proposed to suppress the inrush surge and the resonance of Z-source capacitors and inductors. The operation principle of the proposed topology and comparison with the traditional topology are analyzed in detail. Simulation and experimental results are given to demonstrate the new features of the improved topology.

KEYWORDS:

1.      Inrush current

2.      Soft start

3.      Z-source inverter.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 EXPECTED SIMULATION RESULTS:

CONCLUSION:

This paper has presented a new Z-source inverter topology. Compared to the previous Z-source inverter, the improved topology has several merits.

1) The Z-source capacitor voltage stress is reduced greatly to perform the same boost ability; thus, low-voltage capacitors can be utilized to reduce the system cost and volume;

2) The inrush current and resonance of Z-source capacitors and inductors in traditional topology can be suppressed with a proper soft-start strategy. Simulation and experimental results verified the aforesaid merits of the proposed topology.

REFERENCES:

 [1] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 504–510, Mar./Apr. 2003.

[2] Q. Tran, T. Chun, J. Ahn, and H. Lee, “Algorithms for controlling both the DC boost and AC output voltage of Z-source inverter,” IEEE Trans. Ind. Electron., vol. 54, no. 5, pp. 2745–2750, Oct. 2007.

[3] F. Z. Peng, M. Shen, and Z. Qian, “Maximum boost control of the Z-source inverter,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 833–838, Jul. 2005.

[4] M. Shen, J. Wang, A. Joseph, F. Z. Peng, L. M. Tolbert, and D. J. Adams, “ConstantBoost control of the Z-source inverter to minimize current ripple and voltage stress,” IEEE Trans. Ind. Appl., vol. 42, no. 3, pp. 770–777, May/Jun. 2006.

[5] P. C. Loh, D. M. Vilathgamuwa, Y. S. Lai, G. T. Chua, and Y. Li, “Pulsewidth modulation of Z-source inverters,” IEEE Trans. Power Electron., vol. 20, no. 6, pp. 1346–1355, Nov. 2005.

COMPENSATION OF SAGS AND SWELLS VOLTAGE USING DYNAMIC VOLTAGE RESTORER (DVR) DURING SINGLE LINE TO GROUND AND THREE-PHASE FAULTS

ABSTRACT:

This paper deals with modelling and simulation technique of a Dynamic Voltage Restore (DVR). The DVR is a dynamic solution to protect sensitive loads against voltage sags and swells. The DVR can be implemented to protect a group of medium voltage or low voltage consumers. The new configuration of DVR has been proposed using improved d-q-0 controller technique. This study presents compensation of sags and swells voltage during single line to ground (SLG) fault and three-phase fault. Simulation results carried out by Matlab/Simulink verify the performance of the proposed method.

KEYWORDS:

1.      Dynamic Voltage Restorer

2.      Voltage Sags

3.      Voltage Swells

4.      Single Line to Ground (SLG) Fault

5.      Three-Phase Fault.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

CONCLUSION:

The DVR modeling and simulation has been shown by the aid of Matlab/Simulink. The control system is based on dq0 technique which is a scaled error, between source side of the DVR and its reference for compensating sags and swells. The simulation shows that the DVR performance is efficient in mitigation of voltage sags and swells. According to the simulation results, the DVR is able to compensate the sags and swells during single line to ground (SLG) fault and three-phase fault. As result of the FFT analysis, the compensated load voltage by the DVR has appropriate THD. The DVR handles both balanced and unbalanced situations without any difficulties. It injects an appropriate voltage component to correct any anomaly rapidly in the supply voltage; in addition, it keeps the load voltage balanced and constant at the nominal value.

REFERENCES:

[1] D.M. Vilathgamuwa, A.A.D.R. Perera, S.S. Choi, “Voltage Sag Compensation with Energy Optimized Dynamic Voltage Restorer”, IEEE Trans. on Power Del., Vol. 11, No. 3, pp. 928-936, July 2003.

[2] P. Boonchiam, N. Mithulananthan, “Understanding of Dynamic Voltage Restorers through Matlab Simulation”, Thammasat Int. J. Sc. Tech., Vol. 11, No. 3, July-Sept. 2006.

[3] IEEE Std. 1159-2009, “Recommended Practice for Monitoring Electric Power Quality”, pp. 1-81 June 2009.

[4] V. Salehi, S. Kahrobaee, S. Afsharnia, “Power Flow Control and Power Quality Improvement of Wind Turbine Using Universal Custom Power Conditioner”, IEEE Conference on Industrial Electronics, Vol. 4, pp. 1688-1892, July 2002.

[5] B.H. Li, S.S. Choi, D.M. Vilathgamuwa, “Design Considerations on the Line-Side Filter Used in the Dynamic Voltage Restorer”, IEE Proc. Gener. Transmission Distrib., Issue 1, Vol. 148, pp. 1-7, Jan. 2001.

Comparison of Control Algorithms for Shunt Active Filter for Harmonic Mitigation

ABSTRACT:

 Shunt Active Filter generates the reference current, that must be provided by the power filter to compensate harmonic currents demanded by the load. This paper presents different types of SRF methods for real time regeneration of compensating current for harmonic mitigation. The three techniques analyzed are the Synchronous Reference Frame Theory (SRF), SRF theory without synchronizing circuit like phase lock loop (PLL) also called instantaneous current component theory and finally modified SRF theory. The performance of Shunt Active Power Filter in terms of THD (Total Harmonic distortion) of voltage and current is achieved with in the IEEE 519 Standard. The comparison of all methods is based on the theoretical analysis and simulation results obtained with MATLAB/SIMULINK

KEYWORDS:

1.      Synchronous Reference Frame

2.      Instantaneous current component theory

3.      Modified SRF

4.      Active Filter

5.      Harmonics

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

CONCLUSION:

This paper presents the compensation performance of all the different SRF techniques under sinusoidal voltage source condition as shown in table-1. Results are similar with gained source THD under IEEE 519, but under various filter type the chebyshev type filter is having superior performance compare to Butterworth filter for all methods. The Synchronous Reference Frame method is one of the most common and performing methods for detection of harmonics in active filters. An Improved Synchronous Reference Frame Method for the control of active power filters was presented. It is called Filtered Modified Reference Frame Method (FMRF) and is based on the same principle as the Synchronous Reference Frame method. However, this new method explores the fact that the performance of the active filter to isolate harmonics depends on the speed of the system that determines the rotating reference frame, but doesn’t depend on its position. So, the delay introduced by the ac voltage filters, used for the detection of the reference frame, has no influence on the detection capability of the method. Compared with other methods, this new method presents some advantages due to its simplicity and its rudeness to perturbations on the ac network.

REFERENCES:

[1] M.J. Newman, D.N.Zmood, D.G.Holmes, “Stationary frame harmonic reference generation for active filter systems”, IEEE Trans. on Ind. App., Vol. 38, No. 6, pp. 1591 – 1599, 2002.

[2] V.Soares,P.Verdelho,G.D.Marques,“ An instantaneous active reactive current component method for active filters” IEEE Trans. Power Electronics, vol. 15, no. 4, July- 2000, pp. 660–669.

[3] G.D.Marques, V.Fernao Pires, Mariusz Mlinowski, and Marian Kazmierkowski, “An improved synchronous Reference Method for active filters,” the International conference on computer as a tool, EUROCON 2007, Warsaw, September - 2007, pp. 2564-2569.