A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating

ABSTRACT

 The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology.

KEYWORDS

1.      Average switching frequency

2.      Dc-link voltage

3.      Hybrid topology

4.      Non-stiff source

5.      Unified power quality conditioner (UPQC)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Equivalent circuit of proposed VSI topology for UPQC compensated system (modified topology).

EXPECTED SIMULATION RESULTS

   

Fig. 2. Simulation results before compensation (a) load currents (b) terminal voltages.

Fig. 3. Simulation results using conventional topology. (a) DC capacitor voltages (top and bottom). (b) Source currents after compensation. (c) Voltage across the interfacing inductor in phase-a of the shunt active filter. (d) Shunt active filter currents. (e) Terminal voltages with sag, DVR-injected voltages,

and load voltages after compensation.

   

Fig. 4. Simulation results with modified topology. (a) Voltage across series capacitor and load voltage in phase-a. (b) Inverter output voltage in leg-a of shunt active filter. (c) DC and fundamental values of voltage across series capacitor and inverter output voltage.

Fig. 5. Simulation results using modified topology. (a) DC capacitor voltages. (b) Source currents after compensation. (c) Voltage across the interfacing inductor in phase-a of the shunt active filter. (d) Shunt active filter currents. (e) Terminal voltages with sag, DVR injected voltages, and load voltages after compensation.

    

CONCLUSION

A modified UPQC topology for three-phase four-wire system has been proposed in this paper, which has the capability to compensate the load at a lower dc-link voltage under nonstiff source. Design of the filter parameters for the series and shunt active filters is explained in detail. The proposed method is validated through simulation and experimental studies in a three-phase distribution system with neutral-clamped UPQC topology (conventional). The proposed modified topology gives the advantages of both the conventional neutral-clamped topology and the four-leg topology. Detailed comparative studies are made for the conventional and modified topologies. From the study, it is found that the modified topology has less average switching frequency, less THDs in the source currents, and load voltages with reduced dc-link voltage as compared to the conventional UPQC topology.

REFERENCES

[1] M. Bollen, Understanding Power Quality Problems: Voltage Sags and Interruptions. New York: IEEE Press, 1999.

[2] S. V. R. Kumar and S. S. Nagaraju, “Simulation of DSTATCOM and DVR in power systems,” ARPN J. Eng. Appl. Sci., vol. 2, no. 3, pp. 7–13, Jun. 2007.

[3] B. T. Ooi, J. C. Salmon, J. W. Dixon, and A. B. Kulkarni, “A three phase controlled-current PWM converter with leading power factor,” IEEE Trans. Ind. Appl., vol. IA-23, no. 1, pp. 78–84, Jan. 1987.

[4] Y. Ye, M. Kazerani, and V. Quintana, “Modeling, control and implementation of three-phase PWM converters,” IEEE Trans. Power Electron., vol. 18, no. 3, pp. 857–864, May 2003.

[5] R. Gupta, A. Ghosh, and A. Joshi, “Multiband hysteresis modulation and switching characterization for sliding-mode-controlled cascaded multilevel inverter,” IEEE Trans. Ind. Electron., vol. 57, no. 7, pp. 2344–2353, Jul. 2010.

Transformer-less dynamic voltage restorer based on buck-boost converter

ABSTRACT

In this study, a new topology for dynamic voltage restorer (DVR) has been proposed. The topology is inspired by the buck-boost ac/ac converter to produce the required compensation voltage. This topology is able to compensate different voltage disturbances such as sag, swell and flicker without leap of the phase angle. The mass of the proposed topology has been reduced due to lack of injection topology. In addition to, the required compensation energy is directly delivered from the grid through the grid voltage. Therefore, the massive dc-link capacitors are not required to implement. To verify the qualification of the topology, the simulation results by MATLAB/SIMULINK software have been presented. Moreover, an experimental prototype of the case study has been designed and tested.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Proposed topology

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for sag compensation

Fig. 3 Simulation results for swell compensation

Fig. 4. Simulation results

CONCLUSION

In this paper a new topology for DVR using buck-boost ac/ac converter was proposed. This topology contains five bidirectional switches, an inductor and a capacitor. Unlike the conventional topologies, the proposed DVR does not have any injection transformer due to the structural features. Because of direct connection to the grid, the storage elements are not required in the proposed topology. Therefore, this topology has less physical volume, mass and price in comparison with traditional topologies. Any kind of voltage disturbances can be compensated by the proposed topology and the effective operation has been confirmed by simulation and experimental results.

   

REFERENCES

[1]         Hietpas, S.M., Naden, M.: ‘Automatic voltage regulator using an AC voltagevoltage converter’, IEEE Trans. Ind. Appl., 2000, 36, (1), pp. 33–38

[2]         Vilathgamuwa, D.M., Member, S., Perera, A.A.D.R., et al.: ‘Dynamic voltage restorer’, 2003, 18, (3), pp. 928–936

[3]         Wijekoon, H.M., Vilathgamuwa, D.M., Choi, S.S.: ‘Interline dynamic voltage restorer: an economical way to improve interline power quality’, IEE Proc. Gener. Transm. Distrib., 2003, 150, (5), pp. 513–520

[4]         Wang, B., Member, S., Venkataramanan, G., et al.: ‘Operation and control of a dynamic voltage restorer using transformer coupled H-bridge converters’, 2006, 21, (4), pp. 1053–1061

[5]         Babaei, E., Farhadi Kangarlu, M.: ‘Voltage quality improvement by a dynamic voltage restorer based on a direct three-phase converter with fictitious DC link’, IET Gener. Transm. Distrib., 2011, 5, (8), p. 814

Sensitive Load Voltage Compensation Performed by a Suitable Control Method

 IEEE Transactions on Industry Applications , 2016

ABSTRACT

This work proposes the usage of a repetitive-based control to dynamically restore the voltage applied to sensitive and critical loads of power system. The control intrinsically is able to wipe off harmonic distortion and relies on simple transfer function. As a consequence, there is no need to apply harmonic selective filters. Furthermore, the control system is able to work out on sinusoid references and, thus, avoids the need of employing the dq transform. A recursive least-squares is also included to the control system in order to assure the synchronization of the voltages to be restored. The design of the control parameters along with the system stability is discussed. The experimental results are produced with a setup of a three phase series compensator. The scenarios for emulating faulty voltages are the same for experimental and simulated results. The results corroborate the usage of the proposed method.

KEYWORDS

1.      Bode plot

2.      DVR-Dynamic voltage restorer

3.      Nyquist stability

4.      Repetitive control

5.      Sensitive load

6.      Series compensator

7.      Voltage quality

8.      Voltage sag.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Series compensation system. (a) Electrical grid with compensation

to sensitive load. (b) Single-phase equivalent circuit for the feed of sensitive load.

EXPECTED SIMULATION RESULTS:

Fig. 2. Sagged grid scenario. (a) Sagged and controlled output voltages. (b) Detail of the correction instant.

Fig. 3 Sagged/distorted grid and controlled output voltages.

Fig. 4. Sagged grid and controlled output voltages with RLS algorithm included.

Fig. 5. Sagged/distorted grid scenario. (a) Sagged/distorted and controlled output voltages. (b) Detail of the correction instant.

CONCLUSION

This paper has proposed a repetitive control technique to be applied to a series compensator which protects critical loads against voltage distortions from the power grid. The system stability is assured by a low-pass filter which attenuates the resonant peaks from the repetitive controller above a frequency value. This value should be greater than the expected highest harmonic interference endured by the system. The low-pass filter is cascaded with the repetitive controller. The control system is implemented in the discrete domain, employing the trapezoidal integration. Three scenarios including harmonics and sag interferences have been used to test the proposed control system. The controller has proved to be effective to mitigate them. Furthermore, an experimental setup of the series compensator has been mounted to verify the simulations. The results corroborate the proposed controller.

REFERENCES

[1]         S. Jothibasu and M. Mishra, “An improved direct AC-AC converter for voltage sag mitigation,” IEEE Trans. Ind. Electron., vol. 62, no. 1, pp. 21–29, Jan. 2015.

[2]         M. R. Alam, K. M. Muttaqi, and A. Bouzerdoum, “Characterizing voltage sags and swells using three-phase voltage ellipse parameters,” IEEE Trans. Ind. Appl., vol. 51, no. 4, pp. 2780–2790, Apr. 2015.

[3]         H. Hao and X. Yonghai, “Control strategy of PV inverter under unbalanced grid voltage sag,” in IEEE Energy Conversion Congress and Exposition, ECCE, vol. 1, no. 1, Sept. 2014, pp. 1029–1034.

[4]         Y. W. Li, D. M. Vilathgamuwa, F. Blaabjerg, and P. Loh, “A robust control scheme for medium-voltage-level DVR implementation,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2249–2261, Aug. 2007.

[5]         S. Jothibasu and M. Mishra, “A control scheme for storageless DVR based on characterization of voltage sags,” IEEE Trans. Power Del., vol. 29, no. 5, pp. 2261–2269, Oct. 2014.

Self-tuned fuzzy-proportional–integral compensated zero/minimum active power algorithm based dynamic voltage restorer

ABSTRACT:

Voltage sag is the most common and severe power quality problem in the recent times due to its detrimental effects on modern sensitive equipment. Generally, direct-on-line starting of the three-phase induction motor (IM) and various kinds of short circuit fault are directly responsible for this event. This study investigates the impacts of starting and stopping of two threephase IMs on the load voltage profile. To be more critical, two three-phase short circuit faults and one unsymmetrical fault are also simulated in the same network at different instants of time. A simple control algorithm of a real power optimised dynamic voltage restorer (DVR) with a reduced power factor strategy is presented to protect the sensitive load from these types of detrimental events. A novel fuzzy-proportional–integral based self-tuned control methodology is implemented in the proposed work to compensate the loss in the DVR circuit as well as to regulate the load voltage and the direct current link voltage. The results show the effectiveness of the adopted control scheme in DVR application to mitigate the voltage sag.

SOFTWARE: MATLAB/SIMULINK

DIAGRAM:

Fig. 1 Investigated distributed test system with DVR

  

EXPECTED SIMULATION RESULTS:

Figure 2. Voltage profile of load and DVR (a) Without DVR, (b) DVR voltage, (c) With DVR, (d) DC voltage

Figure 3 Torque profile of IMs (a) Motor 1without DVR, (b) Motor 2 without DVR, (c) Motor 1 with DVR, (d) Motor 2 with DVR

Figure 4. Pertaining to unsymmetrical fault (a) Load voltage without DVR, (b) DVR voltage, (c) Load voltage with DVR

Figure 5. Active DVR power profile pertaining to (a) In-phase compensation, (b) Present technique

CONCLUSION:

This study divulges a simple yet robust reduced power factor controlled energy optimised algorithm in DVR to offer a common solution to mitigate the severe voltage sag. Minimisation of energy delivered may increase the life of the ESU, therefore limits the expenditure indirectly. The self-tuned fuzzy-PI scheme also plays a significant role to regulate the active power through the DVR as well as to compensate the load voltage and DVR losses. The results obtained in this work shows that the proposed DVR solution provides a good and satisfactory level of compensation. The system voltage has been compensated nearly up to its nominal value. The DC voltage is also very fairly regulated. The application of DVR reduces the level of oscillation in the torque profile of the IM. The proposed method is also compared with other strategies surfaced in the existing literature and it is unfold that the proposed strategy offers better harmonic compensation and it also provides better damping in the load voltage. Thus, it may be concluded that the proposed control technique of DVR, operated by adaptive fuzzy control scheme, may be justified for utilising the same as a common sag mitigating device. Within the context of the present study, the work is ended with simulation only. However, the same may be tested on an experimental bench.

REFERENCES:

[1]      McGranaghan, M.F., Mueller, D.R., Samotyj, M.J.: ‘Voltage sags in industrial systems’, IEEE Trans. Ind. Appl., 1993, 29, (2), pp. 397–403

[2]      Moreno-Munoz, A., De-la-Rosa, J.J.G., Lopez-Rodriguez, M.A., et al.: ‘Improvement of power quality using distributed generation’, Int. J. Electr. Power Energy Syst., 2010, 32, (10), pp. 1069–1076

[3]       Bollen, M.H.J.: ‘Understanding power quality problems’ (Wiley-IEEE Press, Hoboken, NJ, USA, 1999)

[4]      Honrubia-Escribano, A., Gomez-Lazaro, E., Molina-Garcia, A., et al.: ‘Influence of voltage dips on industrial equipment: analysis and assessment’, Int. J. Electr. Power Energy Syst., 2012, 41, pp. 87–95

[5]      Kamble, S., Thorat, C.: ‘Characteristics analysis of voltage sag in distribution system using rms voltage method’, ACEEE Int. J. Electr. Power Eng., 2012,3, (1), pp. 55–61