Active and Reactive Power Control of Single Phase Transformerless Grid Connected Inverter for Distributed Generation System

ABSTRACT:

This paper presents a novel approach by which enhancement in power quality is ensured along with power control for a grid interactive inverter. The work presented in this paper deals with modeling and analyzing of a transformer less grid-connected inverter with active and reactive power control by controlling the inverter output phase angle and amplitude in relation to the grid voltage. In addition to current control and voltage control, power quality control is made to reduce the total harmonics distortion. The distorted current flow can compensate for the disturbance caused by nonlinear load. The Simulation of the grid interactive inverter is carried out in MATLAB/SIMULINK environment and experimental results were presented to validate the proposed methodology for control of transformer less grid interactive inverter which supplies active and reactive power to the loads and also makes the grid current to a sinusoidal one to improve the power factor and reduce the harmonics in grid current. This work offers an increased opportunity to provide distributed generation (DG) use in distribution systems as reliable source of power generation to meet the increased load demand which helps to provide a reasonable relief to the customers and utilities to meet the increasing load demand

KEYWORDS:

  1. Grid interactive inverter
  2. Voltage Controller
  3. Current Controller
  4. THD improvement
  5. Reactive power compensation
  6. Intelligent power module

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1: Schematic diagram of grid connected system

Figure 2: grid tie inverter

EXPECTED SIMULATION RESULTS:

Figure 3: Simulation waveforms of current a) when load is controlled rectifier b) inverter current c) grid current d) the reference current

Figure 4: Power flow graph.

Figure 5: grid voltage, load current & grid current

Figure 6: FFT analysis

Figure 7: load current

Figure 8: Injected current

 CONCLUSION:

 The simulation of single phase grid interactive inverter has been carried out with non-linear load and the results obtained from the simulations shows that this control technique improves the power quality ie THD and the power factor. The simulation also shows that power transfer of active and reactive power from the inverter to grid is possible. The reactive power required for the load is completely provided from the inverter. The hardware implementation of the interactive inverter has been conducted using real time workshop in the MATLAB Simulink environment. The half wave rectifier is used as load in the hardware implementation. The results show that the controller is capable for reactive power compensation, and maintaining constant voltage at the grid satisfying standard for grid interconnection. That is the THD is lessthan5% 3.74 and the power factor is .9977 which is near to unity. Energy conservation by load management is possible and a reasonable relief to the customer and voltage profile is maintained at the grid. This work can be extended to cascaded inverter configuration and reliability analysis has to be made as a better option for future studies.

REFERENCES:

[1] EPRI-white paper “Integrating Distributed Resources into electric utility systems ”Technology Review.December2001

[2] Thomas Ackerman “Distributed Generation, a definition’’ Electric power system research,57(3),2001,pp195-204

[3] G. Joos, B.T Ooi, D. McGill is, F.D. Galiana, and R. Marceau, “The potential of distributed generation to provide ancillary services,” at IEEE Power Engineering Society Summer Meeting, 16-20 July 2000, vol. 3, pp. 1762 – 1767

[4] Frede Blaabjerg, Zhechen, Soreren Baekhoej Kjaer “Power electronics as efficient interface in dispersed power generation system” IEEE Transactions on Power Electronics vol:19,no.5, sept2004 pp1184-1194

[5] Yong Yang, Yi Ruan, Huan-qing Shen, Yan-yan Tang and Ying Yang; “Grid-connected inverter for wind power generation system” Journal of Shanghai University, Page(s):.51-56, Vol. 13, No 1,Feb,2009.

A Nested Control Strategy for Single Phase Power Inverter Integrating Renewable Energy Systems in a Microgrid

ABSTRACT:  

In this paper a nested power-current-voltage control scheme is introduced for control of single phase power  inverter, integrating small-scale renewable energy based power generator in a microgrid for both stand-alone and grid-connected modes. The interfacing power electronics converter raises various power quality issues such as current harmonics in injected grid current, fluctuations in voltage across the local loads, voltage harmonics in case of non-linear loads and low output power factor. The proposed nested proportional resonant current and model predictive voltage controller aims to improve the quality of grid current and local load voltage waveforms in grid-tied mode simultaneously by achieving output power factor near to unity. In stand-alone mode, it strives to enhance the quality of local load voltage waveform. The nested control strategy successfully accomplishes smooth transition from grid-tied to stand-alone mode and vice-versa without any change in the original control structure. The performance of the controller is validated through simulation results.

KEYWORDS:

  1. Microgrid
  2. Stand-alone mode
  3. Grid-connected mode
  4. Voltage harmonics
  5. Current harmonics
  6. Proportional resonant control
  7. Model predictive control

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of MPVC scheme

EXPECTED SIMULATION RESULTS:

 Fig. 2(a). Steady state grid voltage, load voltage and grid current waveforms with resistive load

Fig. 3(b). Steady state grid voltage, load voltage and grid current waveforms with non-linear load

Fig. 4. THD values of voltage and current waveforms in grid connected mode

Fig. 5(a). Steady state grid voltage, load voltage and filter current waveforms with resistive load

Fig. 6 (b). Steady state grid voltage and load voltage waveforms with non-linear Load

Fig. 7. THD values of load voltage waveform in stand-alone mode

Fig. 8(a). Transient state grid voltage, load voltage and grid current waveforms with change in active power reference

Fig. 9(b). Transient state grid voltage, load voltage and grid current waveforms with change in reactive power reference

Fig. 10(c). Grid voltage, load voltage and grid current waveforms during voltage Sag

(a) Transfer from stand-alone to grid-tied mode

(b) Transfer from grid-tied to stand-alone mode

Fig.11. Grid voltage, load voltage, filter inductor current, grid current

Waveforms

(a) Transfer from stand-alone to grid-tied mode

(b) Transfer from grid-tied to stand-alone mode

Fig.12. Grid current tracking error waveforms

CONCLUSION:

 

In this paper, a nested proportional resonant current and model predictive voltage controller is introduced for control of single phase VSI integrating a RES based plant in a microgrid. This strategy improves the quality of local load voltage and grid current waveforms with both linear and non linear loads. A non-linear load such as the diode bridge rectifier introduces voltage harmonics, but this scheme is successful in achieving low THD values for inverter local load voltage and grid current simultaneously. Simulation results validates the outstanding performance of the proposed controller in both steady state and transient state operations. A smooth transfer of operation modes from stand-alone to grid-tied and vice versa is also achieved by the nested control scheme without changing the control algorithm.

 

REFERENCES:

[1] H. Farhangi, “The path of the smart grid,” IEEE Power and Energy Magazine, vol. 8, no. 1, pp. 18-28, Jan/Feb. 2010.

[2] F. Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.

[3] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” IEEE Trans. on Ind. Electron., vol. 53, no. 5, pp. 1398–1409,  Oct. 2006.

[4] Q. C. Zhong and T. Hornik, “Cascaded Current–Voltage Control to Improve the Power Quality for a Grid-Connected Inverter With a Local  Load,” IEEE Transactions on Ind. Electron., vol. 60, no. 4, pp. 1344- 1355, April 2013.

[5] Y Zhilei, X Lan and Y Yangguang, “Seamless Transfer of Single-Phase Grid-Interactive Inverters Between Grid-Connected and Stand-Alone  Modes,” IEEE Transactions on Power Electronics, vol. 25, no. 6, pp. 1597-1603, June 2010.

An Intelligent Fuzzy Sliding Mode Controller for aBLDC Motor

ABSTRACT:  

Brushless DC (BLDC) motors are one of the most widely used motors, not only because of their efficiency, and torque characteristics, but also because they have the advantages of being a direct current (DC) supplied, eliminating the disadvantages of using Brushes. BLDC motors have a very wide range of speed, so speed control is a very important issue for it. Sliding mode control (SMC) is one of the popular strategies to deal with uncertain control systems. The Fuzzy Sliding Mode Controller (FSMC) combines the intelligence of a fuzzy inference system with the sliding mode controller. In this paper, an intelligent Fuzzy Sliding Mode controller for the speed control of BLDC motor is proposed. The mathematical model of the BLDC motor is developed and it is used to examine the performance of this controller. Conventionally PI controllers are used for the speed control of the BLDC motor. When Fuzzy SMC is used for the speed control of BLDC motor, the peak overshoot is completely eliminated which is 3% with PI controller. Also the rise time is reduced from 23 ms to 4 ms and the settling time is reduced from 46 ms to 4 ms by applying FMSMC. This paper emphasizes on the effectiveness of speed control of BLDC motor with Fuzzy Sliding Mode Controller and its merit over conventional PI controller.

KEYWORDS:

  1. BLDC motors
  2. Sliding Mode Control
  3. Fuzzy Sliding Mode controller
  4. PI Controller

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig 1 Block diagram of BLDC speed control.

EXPECTED SIMULATION RESULTS:

 

Fig 2 Step response with Fuzzy SMC and Fuzzy PI and PI Controllers

Fig 3 Current in the three phases

 

CONCLUSION:

 Fuzzy sliding mode controller for the speed control of BLDC motor is designed and its performance comparison with PI controller is carried out in this paper. Conventionally PI controllers are used for the speed control of BLDC motor and they give moderate performance under undisturbed conditions even though they are very simple to design and easy to implement. But their performance is poor under disturbed condition like sudden changes in reference speed and sudden change in load. The BLDC motor with PI controller shows large overshoot, high settling time and comparatively large  speed variation under loaded condition.

The Fuzzy Sliding Mode Controller combines the intelligence of fuzzy logic with the Sliding Mode technique. The peak overshoot is completely eliminated and the rise time and settling time are improved when Fuzzy SMC is applied for the speed control of BLDC motor. The fluctuation in speed of the motor under loaded condition is also reduced when fuzzy SMC is applied. Thus this controller becomes an ideal choice for applications where very precise and fine control is required.

REFERENCES:

[1] Neethu U., Jisha V. R., “Speed Control of Brushless DC Motor : A Comparative Study”, IEEE International Conference on Power  Electronics, Drives and Energy Systems, Vol. 8, No. 12, 16-19 December 2012, Bengaluru India.

[2] Chee W. Lu, “T orque Controller for Brushless DC Motors”, IEEE Transactions on Industrial Electronics, Vol. 46, No. 2, April 1999.

[3] Tony Mathew, Caroline Ann Sam, ”Closed Loop Control of BLDC Motor Using a Fuzzy Logic Controller and Single Current Sensor”, International Conference on Advanced Computing and Communication Systems (ICACCS), Vol. 2, No. 13, 19-21 December 2013, Coimbatore India.

[4] T . Raghu, S. Chandra Sekhar, J. Srinivas Rao,“SEPIC Converter based – Drive for Unipolar BLDC Motor”, International Journal of Electrical  and Computer Engineering (IJECE), Vol.2, No.2, April 2012, pp. 159- 165.

[5] M. A. Jabbar, Hla Nu Phyu, Zhejie Liu, Chao Bi, “Modelling and Numerical Simulation of a Brushless Permanent – Magnet DC Motor in Dynamic Conditions by Time – Stepping T echnique”, IEEE Transactions on Industry Applications, Vol. 40, no. 3, MAY/JUNE 2004.

Power Quality Analysis of a PV fed Seven LevelCascaded H-Bridge Multilevel Inverter

ABSTRACT:  

Efficient DC to DC and DC to AC converters play a vital role in the reliable performance of standalone and grid connected photovoltaic systems. This paper deals with DC to AC conversion by a seven level cascaded H-bridge multilevel inverter for a standalone photovoltaic system. The PV fed seven level cascaded H-bridge multilevel inverter is analyzed in two ways: 1) with equal voltage sources as input to the H bridges and 2) with unequal voltage sources as input. A comparative study of the total harmonic distortion reduction in the PV fed multilevel inverter system with and without equal voltage sources as input is carried out. It is observed that with unequal voltage sources, the total harmonic distortion is increased than that with equal voltage sources as input to the PV fed seven level cascaded H-bridge multilevel inverter. Further, the study attempts to show that with an LC filter at the output stage of the multilevel inverter, the total harmonic reduction is significantly reduced and the power quality of the PV fed multilevel inverter system is highly improved. Results are verified using simulations done in MATLAB/Simulink environment.

KEYWORDS:

  1. Photo voltaic Array (PV Array)
  2. Cascaded Multilevel Inverter
  3. Pulse Width Modulation (PWMJ
  4. Total Harmonic Distortion (THD)

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 Fig.1. Seven level Cascaded H-bridge multilevel inverter

 EXPECTED SIMULATION RESULTS:

Fig.2. (a)Seven level cascaded MLI output voltage (b) Harmonic spectrum of the output voltage

Fig.3.(a) Seven level cascaded MLI output current (b) Harmonic spectrum of the output current

Fig.4. (a) Output voltage of MLI with LC filter (b) Harmonic spectrum of the output voltage with LC filter

Fig.5. (a) Output current of MLI with LC filter (b) Harmonic spectrum of the output current with LC filter

Fig.6. (a) Output voltage of seven level multilevel inverter with unequal

voltage sources (b) Harmonic spectrum of the output voltage

Fig.7. (a) Output Current of seven level MLI with unequal voltage sources

(b) Harmonic spectrum of the output current

Fig.8. (a) Output voltage of seven level cascaded MLI with unequal voltage sources and LC filter (b) Harmonic spectrum of the output voltage with LC filter

Fig.9. (a) Output current of seven level cascaded MLI with unequal voltage sources and LC filter (b) Harmonic spectrum of the output current with LC filter

CONCLUSION:

 In this paper, an analysis of a seven level cascaded H bridge multilevel inverter for a standalone photovoltaic system is carried out 1) with equal voltage sources as input to the H-bridges and 2) with unequal voltage sources as  input. It is found that when equal voltage values are fed as input to the H-bridges of the multilevel inverter, there is a reduction in the total harmonic distortion of the MLI output when compared to that with unequal voltage sources as its input. It is also observed that with an LC filter at the output stage of the multilevel inverter in both the scenarios, the total harmonic reduction is significantly reduced and the power quality of the PV fed multilevel inverter system is highly improved.

 REFERENCES:

[1] Venkatachalam, Jovitha Jerome and J. Karpagam, “An experimental investigation on a multilevel inverter for solar energy applications,” International Journal of Electrical Power and Energy Systems, 2013, pp.157-167.

[2] Ebrahim Babaei, Mohammad Farhadi and Farshid Najaty, “Symmetric and asymmetric multilevel inverter topologies with reduced switching devices,” Electric Power Systems Research, 2012, pp. 122- 130.

[3] Jia-Min Shen, Hurng-Liahng Jinn-Chang Wu and Kuen-Der, “Five-Level Inverter for Renewable Power Generation System, IEEE transactions on energy conversion,” 2013, pp.257-266.

[4] Hui Peng, Makoto Hagiwara and Hirofumi Akagi, “Modeling and Analysis of Switching-Ripple Voltage on the DC Link  between a Diode Rectifier and a Modular Multilevel Cascade Inverter (MMCI),” IEEE transactions on power electronics, 2013, pp.75-84.

[5] Javier Chavarria, Domingo Bie!, Francesc Guinjoan, Carlos Meza and Juan J. Negroni, “Energy-Balance Control of PV  Cascaded Multilevel Grid-Connected Inverters Under LevelShifted and Phase-Shifted PWMs,” IEEE transactions on industrial electronics, 2013, pp.98-111.

 

Evaluation of DVR Capability Enhancement -Zero Active Power Tracking Technique

ABSTRACT:  

This paper presents a utilization technique for enhancing the capabilities of dynamic voltage restorers (DVRs). This study aims to enhance the abilities of DVRs to maintain acceptable voltages and last longer during compensation. Both the magnitude and phase displacement angle of the synthesized DVR voltage are precisely adjusted to achieve lower power utilization. The real and reactive powers are calculated in real time in the tracking loop to achieve better conditions. This technique results in less energy being taken out of the DC-link capacitor, resulting in smaller size requirements. The results from both the simulation and experimental tests illustrate that the proposed technique clearly achieved superior performance. The DVR’s active action period was considerably longer, with nearly 5 times the energy left in the DC-link capacitor for further compensation compared to the traditional technique. This technical merit demonstrates that DVRs could cover a wider range of voltage sags; the practicality of this idea for better utilization is better than that of existing installed DVRs.

KEYWORDS:

 

  1. DVR capability
  2. Energy optimized
  3. Energy source
  4. Series compensator
  5. Voltage stability

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

 

Fig. 1. Circuit diagram model for simulation using MatLab/Simulink.

EXPECTED SIMULATION RESULTS:

Fig. 2. D-axis voltages at the system (VSd), DVR (VDVRd), and load (VLd). during in-phase compensation (simulation).

Fig. 3. Q-axis voltages at the system (VSq), DVR (VDVRq), and load (VLq) during in-phase compensation (simulation).

 

Fig. 4. The overall three-phase voltage signals during in-phase compensation (simulation).

Fig. 5. Real power at source (PS), the DVR (PDVR) and load (PL) during in-phase compensation (simulation).

 

Fig. 6. The DVR DC-side voltage (VDC) during in-phase compensation (simulation).

 

Fig. 7. D-axis voltages at the system(VSd), DVR (VDVRd), and load (VLd) during zero-real power tracking compensation (simulation).

Fig. 8. Q-axis voltages at the system (VSq), DVR (VDVRq), and load (VLq) during zero-real power tracking compensation (simulation)..

Fig. 9. The overall three-phase voltage signals during zero-real power tracking compensation (simulation).

Fig. 10. The DVR DC-side voltage (VDC) during zero-real power tracking compensation (simulation).

CONCLUSION:

 It is clear from both the simulation and experimental results illustrated in this paper that the proposed zero-real power tracking technique applied to DVR-based compensation can result in superior performance compared to the traditional in-phase technique. The experimental test results match those proposed using simulation, although some discrepancies due to the imperfect nature of the test circuit components were seen.

With the traditional in-phase technique, the compensation was performed and depended on the real power injected to the system. Then, more of the energy stored in the DC-link capacitor was utilized quickly, reaching its limitation within a shorter period. The compensation was eventually forced to stop before the entire voltage sag period was finished. When the compensation was conducted using the proposed technique, less energy was used for the converter basic switching process. The clear advantage in terms of the voltage level at the DC-link capacitor indicates that with the proposed technique, more energy remains in the DVR (67% to 14% in the traditional in-phase technique), which guarantees the correct compensating voltage will be provided for longer periods of compensation. With this technique, none (or less) of the real power will be transferred to the system, which provides more for the DVR to cover a wider range of voltage sags, adding more flexible adaptive control to the solution of sag voltage disturbances.

REFERENCES:

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

[2] J. Roldán-Pérez, A. García-Cerrada, J. L. Zamora-Macho, P. Roncero-Sánchez, and E. Acha, “Troubleshooting a digital repetitive controller for a versatile dynamic voltage restorer,” Int. J. Elect. Power Energy Syst., vol. 57, pp. 105–115, May 2014.

[3] P. Kanjiya, B. Singh, A. Chandra, and K. Al-Haddad, “SRF theory revisited to control self-supported dynamic voltage restorer (DVR) for unbalanced and nonlinear loads,” IEEE Trans. Ind. Appl., vol. 49, no. 5, pp. 2330–2340, Sep. 2013.

[4] S. Naidu, and D. Fernandes, “Dynamic voltage restorer based on a four-leg voltage source converter,” IET Generation, Transmission & Distribution, vol. 3, no. 5, pp. 437–447, May 2009.

[5] T. Jimichi, H. Fujita, and H. Akagi, “A dynamic voltage restorer equipped with a high-frequency isolated dc-dc converter,” IEEE Trans. Ind. Appl., vol. 47, no. 1, pp. 169– 175, Jan. 2011.

 

Adaptive Reactive Power Control Using Static VAR Compensator (FC-TCR & TCR)

ABSTRACT:

  Flexible AC transmission system (FACTS) is a technology, which is based on power electronic devices, used to enhance the existing transmission capabilities in order to make the transmission system flexible and independent operation. The FACTS technology is a promising technology to achieve complete deregulation of Power System i.e. Generation, Transmission and Distribution as complete individual units. The loading capability of transmission system can also be enhanced nearer to the thermal limits without affecting the stability.

FACTS

Complete close-loop smooth control of reactive power can be achieved using shunt connected FACTS devices. Static VAR Compensator (SVC) is one of the shunt connected FACTS device, which can be utilized for the purpose of reactive power compensation.. This paper attempts to design and simulate the Fuzzy logic control of firing angle for SVC (TCR & FC-TCR) in order to achieve better, smooth and adaptive control of reactive power. The design, modeling and simulations are carried out for λ /8 Transmission line and the compensation is placed at the receiving end (load end). The results of both SVC (TCR & FC-TCR) devices

KEYWORDS:

  1. Fuzzy Logic
  2. FACTS and SVC

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1. Single Phase equivalent circuit and fuzzy logic control structure of SVC

EXPECTED SIMULATION RESULTS:

 

Fig.2. Uncompensated voltages for R=500 Ω

Fig.3. Compensated voltages for R=500 Ω with TCR

Fig.4. Compensated voltages for R=500 Ω with FC-TCR

Fig.5. Active and Reactive powers of the Tr.line R=200 Ω after compensation with FC-TCR

Fig.6. Active and Reactive powers of the Tr.line for R=200 Ω after compensation with TCR

CONCLUSION:

This paper presents an “online Fuzzy control scheme for SVC” and it can be concluded that the use of fuzzy controlled SVC (TCR & FC-TCR) compensating devices with the firing angle control is continuous, effective and it is a simplest way of controlling the reactive power of transmission line. It is observed that SVC devices were able to compensate over voltages. Compensating voltages are shown in Fig.15 and Fig.16.

SVC

The use of fuzzy logic has facilitated the closed loop control of system, by designing a set of rules, which decides the firing angle given to SVC to attain the required voltage. The active and reactive power compensation with SVC devices was shown in Fig.17 and Fig.18. With MATLAB simulations [4] [5] and actual testing it is observed that SVC (TCR & FC-TCR) provides an effective reactive power control irrespective of load variations.

 REFERENCES:

 [1] Narain. G. Hingorani, “Understanding FACTS, Concepts and Technology Of flexible AC Transmission Systems”, by IEEE Press

USA

[2] Bart Kosko, “Neural Networks and Fuzzy Systems A Dynamical Systems Approach to Machine Intelligence”, Prentice-Hall of India New Delhi, June 1994.

[3] Timothy J Ross, “Fuzzy Logic with Engineering Applications”, McGraw-Hill, Inc, New York, 1997.

[4] Laboratory Manual for Transmission line and fuzzy Trainer Kit Of Electrical Engineering Department NIT Warangal

[5] SIM Power System User Guide Version 4 MATLAB Manual Periodicals and Conference Proceedings:

Optimized Control Strategy for a Medium-Voltage DVR—Theoretical Investigations and Experimental Results

ABSTRACT:  

Most power quality problems in distribution systems are related to voltage sags. Therefore, different solutions have been examined to compensate these sags to avoid production losses at sensitive loads. Dynamic Voltage Restorers (DVRs) have been proposed to provide higher power quality. Currently, a system wide integration of DVRs is hampered because of their high cost, in particular, due to the expensive DC-link energy storage devices. The cost of these DC-link capacitors remains high because the DVR requires a minimum DC-link voltage to be able to operate and to compensate a sag. As a result, only a small fraction of the energy stored in the DC-link capacitor is used, which makes it impractical for DVRs to compensate relatively long voltage sags. Present control strategies are only able to minimize the distortions at the load or to allow a better utilization of the storage system by minimizing the needed voltage amplitude. To avoid this drawback, an optimized control strategy is presented in this paper, which is able to reduce the needed injection voltage of the DVR and concurrently to mitigate the transient distortions at the load side. In the following paper, a brief introduction of the basic DVR principle will be given.  Next, three standard control strategies will be compared and an optimized control strategy is developed in this paper. Finally, experimental results using a medium-voltage 10-kV DVR setup will be shown to verify and prove the functionality of the presented control strategy in both symmetrical and asymmetrical voltage sag conditions.

KEYWORDS:

  1. Asymmetrical voltage sag
  2. Dynamic voltage restorer (DVR)
  3. In-phase compensation
  4. Optimized compensation
  5. Pre-sag compensation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig. 1. Basic concept of a DVR.

 EXPECTED SIMULATION RESULTS:

 Fig. 2. Measured voltages during a long, balanced sag.

Fig. 3. Measured voltages during a long, unbalanced sag.

CONCLUSION:

 Voltage sags are a major problem in power systems due to the increased integration of sensitive loads. DVR systems are able to compensate these short voltage sags. The control and the design  of these systems are critical. Present control strategies are able either to minimize load distortions or the needed voltage amplitude. Both requirements are of utmost importance, especially the needed voltage amplitude for compensating a voltage sag leads to a strict limitation of the range of operation without oversizing the converter significantly.

In this paper, the basic concept of an optimized solution is presented. Based on a combination of the pre-sag and in-phase compensation methods, the proposed optimized DVR control strategy can react to a short voltage sag avoiding disturbances to the protected load. While for a long voltage sag, the proposed method is still able to generate the appropriate voltage without over modulation (or oversized DC-link capacitor) and with minimized load voltage transient distortions. Furthermore, medium voltage level experimental results are presented to verify the feasibility of this control strategy in both balanced and unbalanced voltage sag situations. Although, the effect of the control strategy has only been shown for long but shallow sags, similar results occur for deep sags or large phase jumps.

In this study, it was found that the required voltage amplitude of the DVR with the proposed optimized control strategy was reduced by 25%, compared to the pre-sag controller. In other words, the maximum compensation time is increased by approximately the same amount. Taking into consideration that a phase jump of 12 is not extremely high and that the advantages increases with larger phase jumps, an even higher gain is  possible in practical systems. Summarizing all advantages up, it can be stated that the compensation time of existing DVR systems under pre-sag control can be significantly improved when applying the proposed optimized strategy. In newly designed DVRs, the DC-link capacitance can be decreased without reducing the range of operation.

 REFERENCES:

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

[2] A. Kara, D. Amhof, P. Dähler, and H. Grüning, “Power supply quality improvement with a dynamic voltage restorer (DVR),” in Proc. Appl.Power Electron. Conf., 1998, no. 2, pp. 986–993.

[3] P. Dähler, M. Eichler, O. Gaupp, and G. Linhofer, “Power quality devices improve manufacturing process stability,” ABB Rev., vol. 1, pp.  62–68, 2001.

[4] W. 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.

[5] C. Meyer and R. De Doncker, “Solid-state circuit breaker based on active thyristor topologies,” IEEE Trans. Power Electron., vol. 21, no.2, pp. 450–458, Nov. 2006.

Dynamic Modular Modeling of Smart Loads Associated with Electric Springs and Control

ABSTRACT:  

Smart loads associated with electric springs (ES) have been used because fast demand-side management for smart grid. While simplified dynamic ES models have been used because power system simulation, these models do not include the dynamics of the power electronic circuits and control of the ES.This paper presents a dynamic and modular ES model that can incorporate controller design and the dynamics of the power electronic circuits. Based on experimental measurements, the order of this dynamic model has been reduced so that the model suits both circuit and system simulations.

SMART LOADS

The model is demonstrated with the radial chordal decomposition controller for both voltage and frequency regulation. The modular approach allows the circuit and controller of the ES model and the load module to be combined in the d-q frame. Experimental results based on single and multiple smart loads setup are provided to verify the results obtained from the model simulation. Then the ES model is incorporated into power system simulations including an IEEE 13 node power system and a three-phase balanced microgrid system.

KEYWORDS:

  1. Electric spring
  2. Parameter estimation
  3. Radial-chordal decomposition
  4. Smart loads
  5. Microgrids

 SOFTWARE: MATLAB/SIMULINK

   SCHEMATIC DIAGRAM:

 

 Fig. 1 System setup in Phase III.

 EXPECTED SIMULATION RESULTS:

 

 

(a)Full results of experiment and the theoretical model.

(b)Zoom in results of experiment and the theoretical model.

(c) Full results of experiment and the estimated model.

(d) Zoom in results of experiment and the estimated model.

Fig. 2 Experimental and simulation (theoretical and estimated models) results of ES output voltage.

(a) PCC Voltage (Vg).

(b) Voltage output of ES (Ves).

(c) Current of the Smart load (Isl).

(d) P-Q power of the smart load.

Fig. 3 Experimental and simulation results on Phase II setup                                             with  a ZIP load.

(a) PCC Voltage (Vg).

(b) Voltage output of ES (Ves).

(c) Current of the Smart load (Isl).

(d) P-Q power of the smart load.

Fig. 4 Simulation results on Phase II setup with a thermostatic                                                               load.

(a) PCC voltage (Vg1/2/3).

(b)Voltage output of ES 1 (Ves1).

(c) Voltage output of ES 2 (Ves2).

(d) Voltage output of ES 3 (Ves3).

(e) P-Q power of smart load 1.

(f) P-Q power of smart load 2.

(g) P-Q power of smart load 3.

Fig. 5 Experimental and simulation results on Phase III setup.

(a) Power delivered by the renewable energy source.

(b)Phase A voltage of node 634 (Vs).

(c) Power absorbed in phase A of node 634.

(d)Sum power absorbed by smart load 1,2 and 3.

(e) Power absorbed by smart load 4.

(f) Power absorbed by smart load 5.

Fig. 6 Simulation results on Phase IV setup.

(a) Utility frequency

(b) PCC voltage (Vg)

Fig. 7 Simulation results on Phase V setup.

CONCLUSION:

 In this paper, the dynamic model of an ES is firstly analyzed as a theoretical model in state space. An order-reduced model is derived by estimation based on experimental measurements. A theoretical model of the order of 6 with 4 inputs has been simplified into a 2nd-order model with 2 inputs. The RCD control is adopted as the outer-controller module in the smart load. Two models of noncritical loads, namely ZIP and thermostatic load models, are analyzed to cooperate with the ES. The estimated ES model (the inner model), outer controller and the load model can be modelled separated as modules and then combined to form the smart load model.

RCD

The modular approach offers the flexibility of the proposed model in outer-controller design and the noncritical load selection. The results obtained from the proposed model are compared with experimental measurements in different setups because model verification. The proposed model has been tested because voltage and frequency regulation. This simplified modular modeling method could pave the way because future work on modeling widely-distributed ESs in distribution networks so that various control strategies can be studied.

REFERENCES:

[1] J.M. Guerrero, J.C. Vasquez, J. Matas, M. Castilla and L. Garcia de Vicuna, “Control strategy for flexible microgrid based on parallel line-interactive UPS systems”, IEEE Transaction on Industrial Electronics, vol. 56, no.3, pp. 726-735, Mar. 2009.

[2] P. Khayyer and U. Ozguner, “Decentralized control of large-scale storage-based renewable energy systems”, IEEE Transactions on Smart Grid, vol. 5, no.3, pp. 1300-1307, May 2014.

[3] Yang, Y., H. Wang, F. Blaabjerg, and T. Kerekes. “A Hybrid Power Control Concept for PV Inverters With Reduced Thermal Loading.” IEEE Transaction on Power Electronics, vol 29, no. 12, pp. 6271– 6275, Dec. 2014.

[4] A. H. Mohsenian-Rad, V. W. S. Wong, J. Jatskevich, R. Schober, and A. Leon-Garcia, “Autonomous demand-side management based on game-theoretic energy consumption scheduling for the future smart grid,” IEEE Transaction Smart Grid, vol. 1, no. 3, pp. 320– 331, Dec. 2010.

[5] A. J. Conejo, J. M. Morales and L. Baringo, “Real-time demand response model,” IEEE Trans. Smart Grid, vol. 1, no. 3, pp. 236–242, Dec. 2010.

Enhancement of Voltage Stability and Power Oscillation Damping Using Static Synchronous Series Compensator with SMES

 ABSTRACT:  

The power system network is becoming more complex nowadays and it is very difficult to maintain the stability of the power system. The main purpose of this paper proposes a 12-pulse based Static Synchronous Series Compensator (SSSC) with and without Superconducting Magnetic Energy Storage (SMES) for enhancing the voltage stability and power oscillation damping in multi area system.

MATLAB

Control scheme for the chopper circuit of SMES coil is designed. A three area system is taken as test system and the operation of SSSC with and without SMES is analysed for various transient disturbances in MATLAB / SIMULINK environment.

KEYWORDS

Static Synchronous Series Compensator (SSSC)

Superconducting Magnetic Energy Storage (SMES)

Multi area system

Transient disturbances

 SOFTWARE: MATLAB/SIMULINK

 SINGLE LINE DIAGRAM:

 Fig. 1 Single line diagram of the test system with SSSC with SMES

 EXPECTED SIMULATION RESULTS:

Fig. 2.Simulation result of test system

Fig. 3 Power output for Case (a) and (b)

                                                  (a) With fault

 

                                                          (b) Case (a)

                                   (c) Case (b)                     Time (sec)

Fig. 4 Simulation result of Voltage with fault

 Fig. 5 Simulation result for current with fault

Fig, 6 Simulation result for P & Q with fault

 CONCLUSION:

The dynamic performance of the SSSC with and without SMES for the test system are analysed with Matlab/simulink. In this paper SMES with two quadrant chopper control plays an important role in real power exchange.

SSSC

SSSC with and without has been developed to improve transient stability performance of the power system. It is inferred from the results that the SSSC with SMES is very efficient in transient stability enhancement and effective in damping power oscillations and to maintain power flow through transmission lines after the disturbances.

REFERENCES:

[1] S. S. Choi, F. Jiang and G. Shrestha, “Suppression of transmission system oscillations by thyristor controlled series compensation”, IEE Proc., Vol.GTD-143, No.1, 1996, pp 7-12.

[2] M.W. Tsang and D. Sutanto, “Power System Stabiliser using Energy Storage”, 0-7803-5935-6/00 2000, IEEE

[3] Hingorani, N.G., “Role of FACTS in a Deregulated Market,” Proc. IEEE Power Engineering Society Winter Meeting, Seattle, WA, USA, 2006, pp. 1-6.

[4] Molina, M.G. and P. E. Mercado, “Modeling of a Static Synchronous Compensator with Superconducting Magnetic Energy Storage for Applications on Frequency Control”, Proc. VIII SEPOPE, Brasilia, Brazil, 2002, pp. 17-22.

[5] Molina, M.G. and P. E. Mercado, “New Energy Storage Devices for Applications on Frequency Control of the Power System using FACTS Controllers,” Proc. X ERLAC, Iguazú, Argentina, 14.6, 2003, 1-6.

A New Protection Scheme for HVDC Converters against DC Side Faults with Current Suppression Capability

ABSTRACT:  

Voltage-source converters (VSCs) and half bridge Modular Multilevel Converters (MMCs) are among the most popular types about HVDC converters. One about their serious drawbacks is their vulnerable nature to DC side faults, because the freewheeling diodes act because a rectifier bridge and feed the DC faults. The severity of DC side faults can be limited by connecting double thyristor switches across the semiconductor devices. By turning them on, the AC current contribution into the DC side is eliminated and the DC-link current will freely decay to zero. The main disadvantages about this method are: high dv/dt stresses across thyrsitors during normal conditions, and absence of bypassing therefore the freewheeling diodes during DC faults as they are sharing the fault current with thyristors.

HVDC

This paper proposes a new protection scheme for HVDC converters (VSCs as well as MMCs). In this scheme, the double thyristor switches are combined and connected across the AC output terminals of the HVDC converter. The proposed scheme provides advantages such because lower dv/dt stresses and lower voltage rating of thyristor switches, in addition to providing full separation between the converter semiconductor devices and AC grid during DC side faults. A simulation case study has been carried out to demonstrate the effectiveness of the proposed scheme.

KEYWORDS:

  1. DC side faults
  2. Double Thyristor Switch
  3. Fault current suppression
  4. Protection of VSC-HVDC
  5. Protection of MMC-HVDC

 SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1. Description of simulated case study

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for VSC case: (a) converter line voltage , (b) per-phase grid current, (c) DC-link current, (d) thyristors currents for different protection schemes, (e) freewheeling diode current for different protection scheme, and (f) dv/dt stresses across each thyristor for different protection schemes.

Fig. 3. Simulation results for three-level MMC (n=2): (a) converter line voltage , (b) per-phase grid current, (c) DC-link current, (d) thyristors currents for different protection schemes, (e) freewheeling diode current for different protection scheme, and (f) dv/dt stresses across each thyristor for different protection schemes.

 CONCLUSION:

 Depending on AC circuit breakers (ACCBs) to protect HVDC converters against DC side faults is a risk because the full AC fault current is passing through the freewheeling diodes until tripping the ACCBs is achieved. Hence, the need therefore complex DC breakers has emerged because the alternative. In this paper, a protection scheme therefore both VSC-HVDC and MMCHVDC converters against DC side faults is proposed. The proposed scheme provides complete separation between the AC side and the HVDC converters during DC faults which allows the DC-link current to freely decay to zero (the grid current contribution into DC fault is eliminated).

VSC

A comparison between the proposed scheme and other existing schemes (STSS, and DTSS) is presented. With the same number of thyristors, the proposed scheme is able to accomplish the task of the DTSS, but with back-to-back thyristor switches exposed to lower dv/dt stresses, and possessing lower voltage (33% compared to other schemes), but higher current rating (200% compared to other schemes). Implementation of the proposed scheme is less complex because it is connected across the AC terminals of the converter not across semiconductor devices because in the single and double thyristor switch schemes.

REFERENCES:

[1] N. Flourentzou, V.G. Agelidis, G.D. Demetriades, “VSC-Based HVDC Power Transmission Systems: An Overview”, IEEE Transactions on Power Electronics ,Vol. 24 , No. 3, pp. 592 – 602, March 2009.

[2] P. Lundberg,M. Callavik, M. Bahrman, P. Sandeberg, “High-Voltage DC Converters and Cable Technologies for Offshore Renewable Integration and DC Grid Expansions” IEEE Power and Energy Magazine, Vol. 10 , No. 6 , pp. 30-38, Nov. 2012.

[3] Lidong Zhang et al. “Interconnection of two very weak ac systems by VSC-HVDC links using power-synchronization control”, IEEE Trans. on Power Systems, vol. 26 , no. 1, pp.344-355, 2011.

[4] J. M. Espi, J.Castello, “Wind turbine generation system with optimized dc-link design and control”, IEEE Trans. on Ind. Electron. , vol. 60, no.3, pp. 919- 929, 2013.

[5] S. Cole, R. Belmans, “Transmission of bulk power”, IEEE Ind. Electron. Magazine, vol. 3, no.3, pp.19-24, Sept. 2009.