Design of an Efficient Dynamic Voltage Restorer for Compensating Voltage Sags, Swells, and Phase Jumps

ABSTRACT:  

This paper presents a novel design of a dynamic voltage restorer (DVR) which mitigate voltage sags, swell, and phase jumps by injecting minimum active power in system and provides the constant power at load side without any disturbance. The design of this compensating device presented here includes the combination of PWM-based control scheme, dq0 transformation and PI controller in control part of its circuitry, which enables it to minimize the power rating and to response promptly to voltage quality problems faced by today’s electrical power industries. An immense knowledge of power electronics was applied in order to design and model of a complete test system solely for analyzing and studying the response of this efficient DVR. In order to realize this control scheme of DVR MATLAB/SIMULINK atmosphere was used. The results of proposed design of DVR’s control scheme are compared with the results of existing classical DVR which clearly demonstrate the successful compensation of voltage quality problems by injecting minimum active power.

KEYWORDS:

1.      Dynamic voltage restorer

2.      Voltage sags

3.      Voltage swells

4.      Phase jumps

5.      PWM-based control

6.      DQ0 transformation

7.      PI controller

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1. Block Diagram of DVR

 EXPECTED SIMULATION RESULTS:

Fig.2.Source Voltage with Sag of 0.5 p.u.

Fig.3.Load Voltage after Compensation through proposed DVR

Fig.4. Load Voltage after Compensation through classical DVR

Fig.5. Voltage injected by proposed DVR as response of Sag

Fig.6.Source Voltage with Swell of 1.5 p.u.

Fig.7. Load Voltage after compensation through proposed DVR

. Fig.8. Load Voltage after Compensation through classical DVR

Fig.9. Voltage injected by DVR as response of Swell

Fig.10. .Load Voltage after Compensation of Phase jump

Fig.11. dq0 form of difference voltage obtained by proposed DVR

Fig.12.dq0 form of difference voltage obtained by classical DVR

CONCLUSION:

As the world is moving towards modernization, the most essential need that it has is of an efficient and reliable power of excellent quality. Nowadays, more and more sophisticated devices are being introduced, and their sensitivity is dependent upon the quality of input power, even a slight disturbance in power quality, such as Voltage sags, voltage swells, and harmonics, which lasts in tens of milliseconds, can result in a huge loss because of the failure of end use equipments. For catering such voltage quality problems an efficient DVR is proposed in this paper with the capability of mitigating voltage sags, swells, and phase jumps by injecting minimum active power hence decreasing the VA rating of DVR. compensation of voltage quality problems using a comparatively low voltage DC battery and by injecting minimum active power.

 REFERENCES:

[1] Kumar, R. Anil, G. Siva Kumar, B. Kalyan Kumar, and Mahesh K. Mishra. "Compensation of voltage sags and harmonics with phasejumps through DVR with minimum VA rating using Particle Swarm Optimization." In Nature & Biologically Inspired Computing, 2009. NaBIC 2009. World Congress on, pp. 1361-1366. IEEE, 2009.

[2] Songsong, Chen, Wang Jianwei, Gao Wei, and Hu Xiaoguang. "Research and design of dynamic voltage restorer." In Industrial Informatics (INDIN), 2012 10th IEEE International Conference on, pp. 408-412. IEEE, 2012.

[3] A. Bendre, D. Divan, W. Kranz, and W. E. Brumsickle, "Are Voltage Sags Destroying Equipment?," IEEE Industry Applications Magazine, vol. 12, pp. 12-21, July-August 2006.

[4] Nielsen, John Godsk, and Frede Blaabjerg. "A detailed comparison of system topologies for dynamic voltage restorers." Industry Applications, IEEE Transactions on 41, no. 5 (2005): 1272-1280.

[5] Zhou, Hui, Jing Zhou, and Zhi-ping Qi. "Fast voltage detection for a single-phase dynamic voltage restorer (DVR) using morphological low-pass filters." In Electric Utility Deregulation and Restructuring and Power Technologies, 2008. DRPT 2008. Third International Conference on, pp. 2042-2046. IEEE, 2008.

An Enhanced Voltage Sag Compensation Scheme for Dynamic Voltage Restorer

 ABSTRACT:  

 This paper deals with improving the voltage quality of sensitive loads from voltage sags using dynamic voltage restorer (DVR). The higher active power requirement associated with voltage phase jump compensation has caused a substantial rise in size and cost of dc link energy storage system of DVR. The existing control strategies either mitigate the phase jump or improve the utilization of dc link energy by (i) reducing the amplitude of injected voltage, or (ii) optimizing the dc bus energy support. In this paper, an enhanced sag compensation strategy is proposed that mitigates the phase jump in the load voltage while improving the overall sag compensation time. An analytical study shows that the proposed method significantly increases the DVR sag support time (more than 50%) compared with the existing phase jump compensation methods. This enhancement can also be seen as a considerable reduction in dc link capacitor size for new installation. The performance of proposed method is evaluated using simulation study and finally, verified experimentally on a scaled lab prototype.

KEYWORDS:

1.      Dynamic voltage restorer (DVR)

2.      Voltage source inverter (VSI)

3.      Voltage sag compensation

4.      Voltage phase jump compensation

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 Basic DVR based system configuration.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for the proposed sag compensation method for 50% sag depth. (a) PCC voltage, (b) load voltage, (c) DVR voltage, (d) DVR active and reactive power, and (e) dc link voltage.

Fig. 3. Simulation results for the proposed sag compensation method for 23% sag depth. (a) PCC voltage, (b) load voltage, (c) DVR voltage, (d) DVR active and reactive power, and (e) dc link voltage.

CONCLUSION:

In this paper an enhanced sag compensation scheme is proposed for capacitor supported DVR. The proposed strategy improves the voltage quality of sensitive loads by protecting them against the grid voltage sags involving the phase jump. It also increases compensation time by operating in minimum active power mode through a controlled transition once the phase jump is compensated. To illustrate the effectiveness of the proposed method an analytical comparison is carried out with the existing phase jump compensation schemes. It is shown that compensation time can be extended from 10 to 25 cycles (considering presag injection as the reference method) for the designed limit of 50% sag depth with 450 phase jump. Further extension in compensation time can be achieved for intermediate sag depths. This extended compensation time can be seen as considerable reduction in dc link capacitor size (for the studied case more than 50%) for the new installation. The effectiveness of the proposed method is evaluated through extensive simulations in MATLAB/Simulink and validated on a scaled lab prototype experimentally. The experimental results demonstrate the feasibility of the proposed phase jump compensation method for practical applications.

REFERENCES:

[1] J.A. Martinez and J.M. Arnedo, “Voltage sag studies in distribution networks- part I: System modeling,” IEEE Trans. Power Del., vol. 21,no. 3, pp. 338–345, Jul. 2006.

[2] J.G. Nielsen, F. Blaabjerg and N. Mohan, “Control strategies for dynamic voltage restorer, compensating voltage sags with phase jump,” in Proc. IEEE APEC, 2001, pp. 1267–1273.

[3] J.D. Li, S.S. Choi, and D.M. Vilathgamuwa, “Impact of voltage phase jump on loads and its mitigation,” in Proc. 4th Int. Power Electron. Motion Control Conf., Xian, China, Aug. 14–16, 2004, vol. 3, pp. 1762– 176.

[4] M. Sullivan, T. Vardell, and M. Johnson, “Power interruption costs to industrial and commercial consumers of electricity, IEEE Trans. Ind App., vol. 33, no. 6, pp. 1448–1458, Nov. 1997.

[5] J. Kaniewski, Z. Fedyczak and G. Benysek "AC Voltage Sag/Swell Compensator Based on Three-Phase Hybrid Transformer With Buck- Boost Matrix-Reactance Chopper", IEEE Trans. Ind. Electron., vol.61, issue. 8, Aug 2014.

An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage

ABSTRACT:  

For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q-axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method.

KEYWORDS:

1.      Fluctuating dc-link voltage

2.      q-axis current pulsation

3.      Suppression

4.      Torque pulsation

5.      Traction drive

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Circuit schematic of the ac/dc/ac traction drive system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of two methods in the asynchronous modulation mode. (a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional method. (d) and (e) Stator current and torque with the proposed method. (f) DC-link voltage of the inverter without and with the proposed method.

(g) Transition waveforms of the stator current without and with the proposed method.

Fig. 3. Spectrum analysis of the simulation results of the two methods in the asynchronous modulation mode. (a)–(c) Stator current without compensation, with the conventional method, and with the proposed method. (d)–(f) Torque without compensation, with the conventional method, and with the proposed method.

Fig. 4. Simulation results of the two methods in the synchronous modulation mode. (a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional method. (d) (e) Stator current and torque with the proposed method.

Fig. 5. Simulation results of the two methods in the square-wave modulation mode. (a) Line voltage of the motor. (b) and (c) Stator current and torque with the conventional method. (d) and (e) Stator current and torque with the proposed method.

CONCLUSION:

A closed-loop torque and current pulsation suppression method for railway traction drives under fluctuating dc-link voltage is proposed. This method aims to eliminate the q-axis current pulsation component in the FOC system through output frequency compensation. The torque pulsation suppression is achieved on the basis of q-axis current pulsation elimination automatically. A resonant controller is proposed for the closed loop control of q-axis current and dynamic compensation of the output frequency. Different from the conventional feed forward open-loop frequency compensation method, the torque pulsation with the proposed method is suppressed through the elimination of the q-axis current pulsation component rather than the beat component in the output voltage. The effectiveness of the proposed method have been verified by simulation and experiments on traction drives with the inverter operated in asynchronous, synchronous, and square wave modulation modes, respectively. The results have been compared to those with the conventional feed forward frequency compensation method based on fluctuating dc-link voltage detection. Both simulation and experimental results show that the suppression of stator current and torque pulsation are obvious in different modulation modes with the proposed control method using the same dc-link capacitance.

The proposed suppression method can reduce the sensitivity of the system to variations of the grid frequency. However, the fluctuating component in the dc-link voltage will be increased with the proposed method compared with the LC resonant filter solution.

REFERENCES:

[1] R. J. Hill, “Electric railway traction. II. Traction drives with three-phase induction motors,” Power Eng. J., vol. 8, no. 3, pp. 143–152, Jun. 1994.

[2] A. Steimel, “Electric railway traction in Europe,” IEEE Ind. Appl. Mag., vol. 2, no. 6, pp. 6–17, Nov./Dec. 1996.

[3] H. Ouyang, K. Zhang, P. Zhang, Y. Kang, and J. Xiong, “Repetitive compensation of fluctuating DC link voltage for railway traction drives,” IEEE Trans. Power Electron., vol. 26, no. 8, pp. 2160–2171, Aug. 2011.

[4] J. Klima, M. Chomat, and L. Schreier, “Analytical closed-form investigation of PWM inverter induction motor drive performance under DC bus voltage pulsation,” IET Electr. Power Appl., vol. 2, no. 6, pp. 341–352, Nov. 2008.

[5] A. Cheok, S. Kawamoto, T. Matsumoto, and H. Obi, “AC drive with particular reference to traction drives,” in Proc. 4th Int. Conf. Adv. Power Syst. Control, Oper. Manage., 1997, pp. 348–353.