Dynamic Voltage Restorer Using Switching Cell Structured Multilevel AC-AC Converter

IEEE Transactions on Power Electronics, 2016

ABSTRACT:

Dynamic voltage restorer (DVR) technology has become a mature power quality product. In high-power applications, DVR using a multilevel converter is commonly used. However, DVR using a multilevel direct pulse width modulation (PWM) ac-ac converter has not been well studied. This paper presents a new DVR topology using a cascaded multilevel direct PWM ac-ac converter. In the proposed scheme, the unit cell of the multilevel converter consists of a single-phase PWM ac-ac converter using switching cell (SC) structure with coupled inductors. Therefore, the multilevel converter can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed DVR. This improves the reliability of the DVR system. The output voltage levels of the multilevel converter increase with the number of cascaded unit cells, and a high ac output voltage is obtained by using low-voltage-rating switching devices. Furthermore, a phase-shifted PWM technique is applied to significantly reduce the size of the output filter inductor. A 1-kW prototype of single-phase DVR is developed, and its performance is experimentally verified. Finally, the simulation results are shown for a three-phase DVR system.

 

KEYWORDS:

  1. Commutation problem
  2. coupled inductor
  3. direct PWM AC-AC converter
  4. dynamic voltage restorer (DVR)
  5. multilevel converter
  6. pulse width modulation (PWM)
  7. switching cell (SC)

 

SOFTWARE: MATLAB/SIMULINK

 

CIRCUIT DIAGRAM:

Fig. 1. Three-phase DVR systems using VSI [2]. (a) DVR with energy storage. (b) DVR with no energy storage.

 

EXPECTED SIMULATION RESULTS:

 

Fig. 2. Simulated waveforms of the three-phase DVR ( voa=vob=voc=220 Vrms,Po=3kW, )

 

CONCLUSION:

In this paper, a new DVR system, employing the proposed cascaded multilevel direct PWM ac-ac converter, was presented. Compared with the conventional DVR topologies using the VSI, the proposed scheme has the advantages of fewer power stages, higher efficiency, and the elimination of bulky dc-link capacitor. In addition, unlike the existing DVR with the direct PWM ac-ac converter, the proposed DVR ensures stable operation because the proposed cascaded multilevel ac-ac converter has the following unique advantages over the conventional ac-ac converters.

  • It is immune to EMI noise because the switching devices are not damaged by the EMI noise’s misgating on- or off.
  • The commutation problem found in the conventional ac-ac converters can be effectively eliminated without using either dedicated soft commutation strategy or lossy RC snubber circuits.
  • It operates properly even with highly distorted input voltage, which is impossible with the conventional approach using soft commutation strategy.

Furthermore, the proposed multilevel ac-ac converter can obtain high ac output voltage with low-voltage-rating switching devices by cascading unit cells. The equivalent output frequency of the multilevel converter is increased by using a phase-shifted PWM technique, which reduces the size of the output LC filter. The performance of the proposed DVR is successfully verified by using a 1-kW prototype. Finally, a three-phase DVR system using the proposed scheme is verified through simulation.

 

REFERENCES:

  • -H. Kwon, G. Y. Jeong, S.-H. Han, and D. H. Lee, “Novel line conditioner with voltage up/down capability,” IEEE Trans. Ind. Electron., vol. 49, no. 5, pp. 1110–1119, Oct. 2002.
  • 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.
  • C. Aeoliza, N. P. Enjeti, L. A. Moran, O. C. Montero-Hernandez, and S. Kim, “Analysis and design of a novel voltage sag compensator for critical loads in electrical power distribution systems,” IEEE Trans. Ind. Appl., vol. 39, no. 4, pp. 1143–1150, Jul./Aug. 2003.
  • E. Brumsickle, R. S. Schneider, G. A. Luckjiff, D. M. Divan, and M. F. McGranaghan, “Dynamic sag correctors: Cost-effective industrial power line conditioning,” IEEE Trans. Ind. Appl., vol. 37, no. 1, pp. 212– 217, Jan./Feb. 2001.

Improved Fault Ride Through Capability in DFIG Based Wind Turbines Using Dynamic Voltage Restorer With Combined Feed-Forward and Feed-Back Control

IEEE ACCESS, volume 5, date of current version October 25, 2017.

ABSTRACT: This paper investigates the fault ride through (FRT) capability improvement of a doubly fed induction generator (DFIG)-based wind turbine using a dynamic voltage restorer (DVR). Series compensation of terminal voltage during fault conditions using DVR is carried out by injecting voltage at the point of common coupling to the grid voltage to maintain constant DFIG stator voltage. However, the control of the DVR is crucial in order to improve the Fault Ride Through capability in the DFIG-based wind turbines. The combined feed-forward and feedback (CFFFB)-based voltage control of the DVR verifies good transient and steadystate responses. The improvement in performance of the DVR using CFFFB control compared with the conventional feed-forward control is observed in terms of voltage sag mitigation capability, active and reactive power support without tripping, dc-link voltage balancing, and fault current control. The advantage of utilizing this combined control is verified through MATLAB/Simulink-based simulation results using a 1.5-MW grid connected DFIG-based wind turbine. The results showgood transient and steady-state response and good reactive power support during both balanced and unbalanced fault conditions.

 

 KEYWORDS:

  1. Doubly-fed induction generator (DFIG)
  2. Dynamic voltage restorer (DVR)
  3. Fault Ride-Through (FRT)
  4. Low Voltage Ride Through (LVRT)
  5. Combined feed forward feedback control
  6. MPPT

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

fault ride through

Fig. 1. Schematic Diagram of DVR with DFIG.

 

 EXPECTED SIMULATION RESULTS:

 DVR using CFFFB control

Fig 2. DVR using CFFFB control: (a) supply voltage with 35 % balanced sag in pu, (b) load voltage in pu, and (c) DVR injection voltage in Volts.

Fig. 3. (a) Active Power of DFIG with CFFFB control DVR with 35 % balanced sag in pu. (b) Reactive Power of DFIG with CFFFB control DVR with 35 % balanced sag in pu. (c) Rotor speed control of DFIG with CFFFB controlled DVR with 35 % balanced sag in pu. (d) DC-link voltage with CFFFB controlled DVR with 35 % balanced sag in pu. (e) Stator current (GSC current) of DFIG with CFFFB controlled DVR with 35 % balanced sag in pu. (f) Rotor current (RSC current) of DFIG with CFFFB controlled DVR with 35 % balanced sag in pu.

DVR using CFFFB control

Fig. 4 DVR using CFFFB control: (a) supply voltage with 35 % unbalanced sag of Phase A (in red) in pu, (b) load voltage in pu, and (c) DVR injection voltage in Volts.

Fig. 5. (a) Active Power of DFIG with CFFFB control DVR with 35 % unbalanced sag in pu. (b) Reactive Power of DFIG with CFFFB control DVR with 35 % unbalanced sag in pu. (c) Rotor speed control of DFIG with CFFFB controlled DVR with 35 % unbalanced sag in pu. (d) DC-link voltage with CFFFB controlled DVR with 35 % unbalanced sag in pu. (e) Stator current (GSC current) of DFIG with CFFFB controlled DVR with 35 % unbalanced sag in pu. (f) Rotor current (RSC current) of DFIG with CFFFB controlled DVR with 35 % unbalanced sag in pu.

 DVR using CFFFB control

Fig. 6. DVR using CFFFB control: (a) supply voltage with short circuit three phase to ground fault in pu, (b) load voltage in pu, and (c) DVR injection voltage in Volts.

 DVR using CFFFB control

Fig. 7 (a) Active Power of DFIG with CFFFB control DVR with short circuit three phase to ground fault in pu. (b) Reactive Power of DFIG with CFFFB control DVR with short circuit three phase to ground fault in pu (c) Rotor speed control of DFIG with CFFFB controlled DVR with short circuit three phase to ground fault in pu. (d) DC-link voltage with CFFFB controlled DVR with short circuit three phase to ground fault in pu. (e) Stator current (GSC current) of DFIG with CFFFB controlled DVR with short circuit three phase to ground fault in pu. (f) Rotor current (RSC current) of DFIG with CFFFB controlled DVR with short circuit three phase to ground fault in pu.

Fig. 8 Harmonic spectrum of DVR Load voltage with Feed Forward control shows THDD5.24 %.

Fig. 9 Harmonic spectrum of DVR Load voltage with CFFFB control shows THDD4.47 %.

  

CONCLUSION:

This paper investigates the performance of DVR with combined Feed-Forward and Feed-Back control for the FRT capability improvement in DFIG based wind turbines. Series compensation scheme using DVR proves to be very effective with good reactive power compensation scheme, voltage control and power flow control. The performance comparison suggests that the operation of DVR is a good suit for improving FRT capability in DFIG based variable speed wind turbines as per grid code standards. The investigated combined Feed Forward and Feed Back (CFFFB) control has many advantages like simplicity with limited controller complexity. The controller is used to investigate the improvement in performance of Fault Ride Through capability operation in DFIG wind turbine while modifying the voltage control of a DVR. The DVR proves to deliver very good transient voltage control, fault current control and reactive power support. The controller contributes in better harmonic compensation compared to conventional control as per IEEE 519 standards. The simulation results performed using a 1.5 MW DFIG based wind turbine connected to electrical grid show better performance of DVR with the combined Feed-Forward and Feed-Back control for improving the Fault Ride Through capability of DFIG based wind turbines.

 

REFERENCES:

  • A. J. Amalorpavaraj, K. Palanisamy, S. Umashankar, and A. D. Thirumoorthy, “Power quality improvement of grid connected wind farms through voltage restoration using dynamic voltage restorer,” Int. J. Renew. Energy Res., vol. 6, no. 1, pp. 53_60, Mar. 2016.
  • A. J. Amalorpavaraj, P. Kaliannan, and U. Subramaniam, “Improved fault ride through capability of DFIG based wind turbines using synchronous reference frame control based dynamic voltage restorer,” ISA Trans., vol. 70, no. 1, pp. 465_474, Jul. 2017.
  • Morren and S. W. H. D. Haan, “Ridethrough of wind turbines with doubly-fed induction generator during a voltage dip,” IEEE Trans. Energy Convers., vol. 20, no. 2, pp. 435_441, Jun. 2005.
  • Holdsworth, X. G. Wu, J. B. Ekanayake, and N. Jenkins, “Comparison of _xed speed and doubly-fed induction wind turbines during power system disturbances,” IEE Proc.-Gen. Transmiss. Distrib., vol. 150, no. 3, pp. 343_352, May 2003.
  • D. Hansen and G. Michalke, “Fault ride-through capability of DFIG wind turbines,” Renew. Energy, vol. 32, no. 9, pp. 1594_1610, Jul. 2007.

Dynamic voltage restoration projects in hydearbad

Dynamic voltage restoration (DVR)

Dynamic voltage restoration (DVR) is a method of overcoming voltage sags that occur in electrical power distribution.These are a problem because spikes consume power and sags reduce efficiency of some devices. DVR saves energy through voltage injections that can affect the phase and wave-shape of the power being supplied.

Devices used for DVR include static var devices, which are series compensation devices that use voltage source converters (VSC). The first such system in North America was installed in 1996 – a 12.47 kV system located in Anderson, South Carolina.

Dynamic Voltage Restoration

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