ANALYSIS OF DISCRETE & SPACE VECTOR PWM CONTROLLED HYBRID ACTIVE FILTERS FOR POWER QUALITY ENHANCEMENT

ABSTRACT:

It is known from the fact that Harmonic Distortion is one of the main power quality problems frequently encountered by the utilities. The harmonic problems in the power supply are caused by the non-linear characteristic based loads. The presence of harmonics leads to transformer heating, electromagnetic interference and solid state device mal-functioning. Hence keeping in view of the above concern, research has been carried out to mitigate harmonics. This paper presents an analysis and control methods for hybrid active power filter using Discrete Pulse Width Modulation and Space Vector Pulse Width Modulation (SVPWM) for Power Conditioning in distribution systems. The Discrete PWM has the function of voltage stability, and harmonic suppression. The reference current can be calculated by ‘d-q’ transformation. In SVPWM technique, the Active Power Filter (APF) reference voltage vector is generated instead of the reference current, and the desired APF output voltage is generated by SVPWM. The THD will be decreased significantly by SVPWM technique than the Discrete PWM technique based Hybrid filters. Simulations are carried out for the two approaches by using MATLAB, it is observed that the %THD has been improved from 1.79 to 1.61 by the SVPWM technique.

KEYWORDS:

     1.      Discrete PWM Technique

    2.      Hybrid Active Power Filter

    3.      Reference Voltage Vector, Space Vector

    4.      Pulse Width Modulation (SVPWM)

    5.      Total Harmonic Distortion (THD)

    6.      Voltage Source Inverter (VSI).

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 SIMULATION BLOCK DIAGRAM:

 EXPECTED SIMULATION RESULTS:

Figure 4. Simulation results of balanced linear load (a) The phase-A supply voltage and load current waveforms (b) The phase-A supply voltage and supply current waveforms

Figure 5. Simulation results of unbalanced linear load (a) Three-phase load current waveforms (b) Three-phase supply current waveforms

Figure 6. Simulation results of non-linear load (a) The three-phase source voltage waveforms (b) The three-phase load current waveforms (c) The three-phase source current waveforms

Figure 7. Harmonic spectrum of non-linear load (a) The phase-A load current harmonic spectrum (b) The phase-A source current harmonic spectrum

CONCLUSION:

In this paper, a control methodology for the APF using Discrete PWM and SVPWM is proposed. These methods require a few sensors, simple in algorithm and are able to compensate harmonics and unbalanced loads. The performance of APF with these methods is done in MATLAB/SIMULINK. The algorithm will be able to reduce the complexity of the control circuitry. The harmonic spectrum under non-linear load conditions shows that reduction of harmonics is better. Under unbalanced linear load, the magnitude of three-phase source currents are made equal and also with balanced linear load the voltage and current are made in phase with each other. The simulation study of two level inverter is carried out using SVPWM because of its better utilization of DC bus voltage more efficiently and generates less harmonic distortion in three-phase voltage source inverter. This SVPWM control methodology can be used with series APF to compensate power quality distortions. From the simulated results of the filtering techniques, it is observed that Total Harmonic Distortion is reduced to an extent by the SVPWM Hybrid filter when compared to the Discrete PWM filtering technique i.e. from 1.78% to 1.61%.

REFERENCES:

[1] EI-Habrouk. M, Darwish. M. K, Mehta. P, “Active Power Filters-A Rreview,” Proc.IEE-Elec. Power Applicat., Vol. 147, no. 5, Sept. 2000, pp. 403-413.

[2] Akagi, H., “New Trends in Active Filters for Power Conditioning,” IEEE Trans. on Industry applications, Vol. 32, No. 6, Nov-Dec, 1996, pp. 1312-1322.

[3] Singh.B, Al-Haddad.K, Chandra.A, “Review of Active Filters for Power Quality Improvement,” IEEE Trans. Ind. Electron., Vol. 46, No. 5, Oct, 1999, pp. 960-971.

Micro-grid System Based on Renewable Power Generation Units

ABSTRACT:

Micro-grid system is currently a conceptual solution to fulfil the commitment of reliable power delivery for future power systems. Renewable power sources such as wind and hydro offer the best potential for emission free power for future micro-grid systems. This paper presents a micro-grid system based on wind and hydro power sources and addresses issues related to operation, control, and stability of the system. The micro-grid system investigated in this paper represents a case study in Newfoundland, Canada. It consists of a small hydro generation unit and a wind farm that contains nine variable speed, double-fed induction generator based wind turbines. Using Matlab/Simulink, the system is modelled and simulated to identify the technical issues involved in the operation of a micro-grid system based on renewable power generation units. The operational modes, technical challenges and a brief outline of conceptual approaches to addressing some of the technical issues are presented for further investigation.

KEYWORDS:

1.      Renewable power generation

2.      Distributed generation

3.     Micro-grid, Simulation.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. The micro-grid system currently under investigation

EXPECTED SIMULATION RESULTS:

                            Fig. 2. (a) Wind speed profile, (b) WPGS output power, (c) HGU output power, (d) Voltage at bus 1

                    Fig. 3. (a) Micro-grid frequency (Hz), (b) WPGS output power, (c) HGU output power, (d) Voltage at bus 1

                    Fig. 4. (a) Micro-grid frequency (Hz), (b) WPGS output power, (c) HGU output power, (d) Voltage at bus 1

             

CONCLUSION:

Micro-grid operation of a system based on renewable power generation units is presented in this paper. The system behavior and technical issues involved with three operational modes in micro grid scheme are identified and discussed. The investigation is performed based on simulation results using Matlab/Simulink software package. Simulation results indicate that dump load and suitable storage system along with proper control scheme are additionally required for the operation of the study system in a micro-grid scheme. A control coordinator and monitoring system is also required to monitor micro-grid system state and decide the necessary control action for an operational mode. The required control schemes development for the proposed micro-grid system is currently under investigation by the authors.

REFERENCES:

[1] T. Ackermann and V. Knyazkin, “Interaction between distributed generation and the distribution network: Operation aspects”, Second Int. Symp. Distributed Generations: Power System Market Aspects, Stockholm, Sweden, 2002.

[2] C. Abbey, F. Katiraei, C. Brothers, “Integration of distributed generation and wind energy in Canada”, Invited paper IEEE Power Engineering Society General Meeting and Conference, Montreal, Canada, June 18-22, 2006.

[3] Frede Blaabjerg, Remus Teodorescu, Marco Liserre, Adrian V. Timbus, “Overview of control and grid synchronization for distributed power generation systems”, IEEE Transactions on Industrial Electronics, Vol. 53, No. 5,October 2006.

[4] F. Katiraei, C. Abbey, Richard Bahry, “Analysis of voltage regulation problem for 25kV distribution network with distributed generation”, IEEE Power Engineering Society General Meeting, Montreal, 2006.           

[5] R. H. Lasseter, “Microgrids (distributed power generation)”, IEEE Power Engineering Society Winter Meeting, Vol. 01, pp. 146-149, Columbus, Ohio, Feb 2001.

Performance comparison of SVC and SSSC with POD controller for Power System Stability

ABSTRACT:

 Steady state and transient problems in a power system have undesirable consequences on the system. It can limit the amount of power that can be transmitted in the system and consequently leads to voltage instability and at times it may also result into total voltage collapse.The main objective of this paper is a comparative investigate in enhancement of volatge stability via static synchronous series compensator (SSSC) and static var compensator (SVC) externally controlled by a POD controller. The new designed P.O.D controller is very efficient for voltage stability under transient conditions. This paper discusses and demonstrates the comparision between the SVC with P.O.D controller and SSSC with P.O.D controller,applied to power system for effectively regulating system voltage for different types of faulted condition. One of the major reasons for installing a SVC is to improve dynamic voltage control and thus increase system load ability during transient condition. This work is presented to present the transmission line voltage stability & machine oscillation damping stability by using SVC & SSSC with POD controller & compared their performance to enhance the stability of a power system. Simulation results shows that SVC with POD controller is more effective to enhance the voltage stability and increase transmission capacity in a power system.

KEYWORDS:

1.      FACTS

2.      Power system

3.       POD Controller

4.      SVC(Static VAR compensator)

5.      SSSC(static synchronous series compensator)

6.      Voltage Stability.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 Single line diagram of a 2-machine power system

 SIMULATION DIAGRAM:

Fig. 2 Simulation Diagram of the SSSC

Fig. 3 Simulation Diagram of SVC Controller

EXPECTED SIMULATION RESULTS:

Fig. 4(a) Simulation Results of SSSC without POD

Fig. 4(b) Simulation Results of SSSC without POD

Fig. 5(a) Simulation Results of SSSC with POD

Fig. 5(b) Simulation Results of SSSC with POD

Fig. 6 Simulation results of SVC Controller

  

 Fig. 7(a) Bus voltages in p.u for 1-phase fault (without SVC)

                     

Fig. 7(b) Bus Voltages in p.u for 1-phase fault (with  SVC)

   

             

CONCLUSION:

This paper explains, the FACTS controllers that are used to mitigate the power quality problems. The standard FACTS controller for a particular type of problem is also given. The simulation results give the clear observation of how the FACTS devices improve the power quality. The simulation work is done on Static Var Compensator (SVC) and Static Synchronous Series Compensator(SSSC).SVC and SSSC are providing better power quality under variation of source voltage and when the system is suddenly loaded. The thesis includes the simulation results of the SVC and SSSC only. The future work given as the simulation results of the systems for various power quality problems with all remaining FACTS devices. Then it can be very easy to find an exact FACTS device for a particular type of power quality problem. Installations of SSSC and SVC controllers at all suitable locations will naturally improve the voltage stability of a power system. But, keeping in mind, the cost of the controllers and the optimization task, the number of controllers and their sizes are minimized. Taking corrective actions to keep the system voltage secured under all possible line outage contingency will not be economical or it may not be necessary. Therefore, only the most critical line outage contingency is considered. The line outage is ranked according to the severity and the severity is taken on the basis of increased reactive power generation and real power losses. Outage of other lines has no much impact on the system and therefore they are not given importance.

REFERENCES:

[1] 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.

 [2] 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.

 [3] Molina, M.G. and P. E. Mercado, “Evaluation of Energy Storage Systems for application in the Frequency Control”, Proc. 6th COBEP, Florianópolis, Brazil, 2001, pp. 479-484.

[4] M. Noroozian, L. Angquist, M. Ghandhari, G. Andersson,1997, “Use of UPFC for Optimal Power Flow Control,” IEEE Transactions on Power Delivery, 12(4), pp. 1629-1634.

[5] M. Ghandhari, G. Andersson, I.A. Hiskens, 2001, “Control Lyapunov Functions for Series Devices,” IEEE Transactions on Power Delivery, 16(4), pp. 689-694.

Application of Synchronous Static Series Compensator (SSSC) on Enhancement of Voltage Stability and Power Oscillation Damping

Application of Synchronous Static Series Compensator (SSSC) on Enhancement of Voltage Stability and Power Oscillation Damping

ABSTRACT:

This paper investigates the problem of controlling and modulating power flow in a transmission line using a Synchronous Static Series Compensator (SSSC). The studies, which include detailed techniques of twelve pulse and PWM controlled SSSC, are conducted and the control circuits are presented. The developed control strategies for both twelve-pulse and PWM-controlled SSSC use direct manipulations of control variables instead of typical d-q transformations. The complete digital simulation of the SSSC within the power system is performed in the MATLAB/ Simulink environment using the Power System Block set (PSB). Simulation results validate that Voltage and Power Oscillation can be damped properly using of Synchronous Static Series Compensator (SSSC).

KEYWORDS:

1. SSSC

2. Reactive compensation

3. Control strategy

4. FACTS

5. PWM control
6. Voltage stabilization.

SOFTWARE: MATLAB/SIMULINK

FUNCTIONAL BLOCK DIAGRAM:

Fig 1. Functional model of SSSC

                                       

CIRCUIT DIAGRAM:

Fig 2. Static Synchronous Series Compensator (SSSC) used for power oscillation damping

EXPECTED SIMULATION RESULTS:

                                            Fig 3. A. SSSC Dynamic Response for Reactive Power     

                              

                                                                              Fig 3 .B. SSSC Dynamic Response for Voltage

                                            Fig 4. A. System without SSSC under a three-phase fault   for Reactive Power

                                                          Fig 4. B. System without SSSC under a three phase fault  for Voltage

     

                                                  Fig 5. A. System with SSSC under a three-phase fault for  Reactive Power  

                                                         Fig 5. B. System with SSSC under a three-phase fault for Voltage

CONCLUSION:

This paper analyzed the problem of controlling and modulating power flow in a transmission line using a Synchronous Static Series Compensator (SSSC). The studies, which include detailed techniques of twelve pulse and PWM controlled SSSC, are conducted and the control circuits are presented. The SSSC operating conditions and constraints are compared to the operating conditions of other FACTS devices, showing that the SSSC offers several advantages over others. However, at the present time the total cost of a SSSC installation is higher than the cost of other FACTS devices. Comparisons of two implemented control strategies clearly show that the PWM based and phase controller have both disadvantages and advantages, which makes the design process somewhat complicated. The dc voltage pre-set value in PWM-based controllers has to be carefully selected. As the modulation ratio lies between zero and one, the dc voltage should not be lower than the maximum of the requested SSSC output phase voltage in order to obtain proper control. On the other hand, if the dc side voltage is too high, the rating of both the GTO valves and dc capacitor has to be increased, which means higher installation costs. Not only that, a higher dc side voltage means a lower amplitude modulation ratio, and the lower modulation ratio results in higher harmonic distortion. Phase control allows the dc voltage to change according to the power system conditions, which is clearly advantageous, but it requires a more complicated controller and special and costly series transformers. Also, Simulation results validate that Voltage and Power Oscillation can be damped properly using of Synchronous Static Series Compensator (SSSC).

REFERENCES:

 [1] “Static Synchronous Compensator,” CIGRE, Working group 14.19, 1998.

[2] N. G. Hingorani and L. Gyugyi, Understanding FACTS, Concepts and Technology of Flexible AC Transmission Systems. Piscataway, NJ: IEEE Press, 2000.

[3] R. Mohan and R. K. Varma, Thyristor-Based FACTS Controllers for Electrical Transmission Systems. Piscataway, NJ: IEEE Press, 2002.

[4] L. Gyugyi, N. G. Hingorani, P. R. Nannery, and N. Tai “Advanced StaticVar Compensator Using Gate Turn- Off Thyristors for Utility Applications”, CIGRE, 23– .203, August 26 September 1, 1990, France

[5] J. Arrillaga, B. Barrett, N. A. Vovos “Thyristor Controlled Regulating Transformer for Variable Voltage Boosting”, IEE Proceedings, No. 10, October 1976.

Design and Specifications of SVPWM Controlled Three Phase Three Wire Shunt Active Power Filter for Harmonic Mitigation

Abstract

The most important part of the shunt active power filters is generating of gate signal for Voltage Source Inverters (VSI). In this paper the proposed Space Vector Pulse Width Modulation (SVPWM) is implemented in a closed loop control system for a shunt active power filter. The reference harmonic components are extracted from the sensed nonlinear load currents by applying the Synchronous Reference Frame (SRF) theory, where a three-phase thyristor bridge rectifier with R-L load is taken as the nonlinear load. The switching control algorithms of the proposed SVPWM would be generating appropriate switching gates to the voltage source inverter. The shunt active power filter generates the actual compensating harmonic current based on the switching gates provided by the controller. For showing the performance of proposed method a typical system has been simulated by MATLAB/SIMULINK. The proposed active power filter is able to improve about 30.18% of the total harmonic distortion (THD) for the distorted line current caused by an uncontrolled rectifier as the nonlinear load and to meet IEEE 519 standard recommendations on harmonics level.

Keywords

1.                  Power Quality

2.                  Shunt Active Power Filter

3.                  Synchronous Reference Frame Theory

4.                  Space Vector Pulse Width Modulation (SVPWM).

Software: Matlab/Simulink

Block Diagram                     Fig 1. Block diagram of proposed Shunt active power filter for a 3phase 3 wire system

Simulation Results:

Fig 2. Three phase voltage and load currents for before Compensation-simulation results:(a) a-phase voltage, volts, (b) a-phase load current, Amps 

Fig 3. %THD source current before compensation 

 Fig 4. Reference compensation-(a) a-phase compensation currents, Amps (b) b-phase compensation currents, Amps (c) c-phase compensation current, Amps.

 Fig 5. %THD source current after compensation

Fig 6. Source Voltages and Currents in three phases after compensation-(a)a-phase source voltage, (b)a-phase source current

Conclusion

In this paper, a novel simplified control method, which is suitable for digital control realization, for the active power filter using SVPWM is proposed. The objectives of this project have been achieved by reducing the harmonic components that exist in a power system with a chosen nonlinear load. This most recent aimed on the one hand to prove the effectiveness of the SVPWM in the contribution in the switching power losses reduction in shunt active filter. The proposed closed loop filtering control system mainly consists of the harmonics isolator, the hysteresis tolerance comparators conjunction with the space vector pulse width modulation controller and the active power filter. The combination of these components enables the closed loop control system to be implemented. The proposed system is able to compensate the harmonics caused by a three phase uncontrolled diode rectifier and it provides positive results by reducing the percentage of THD of the line current. The shunt active filter is found effective to meet IEEE 519 standard recommendations on harmonics level.      

References

[1] Singh.B, A1-Haddad.K, Chandra.A, “Review of active filters for power quality improvement”, IEEE Trans. Ind. Electron.,(46), 5, Oct, 1999, pp. 960-971

[2] E1-Habrouk. M, Darwish. M. K, Mehta. P, “Active power filters-A review,” Proc. IEE-Elect. Power Applicat., vol. 147, no. 5, Sept. 2000, pp. 403-413.

[3] Akagi, H., “New trends in active filters for power conditioning,” IEEE Trans. On Industry Applications, (32), 6, Nov-Dec, 1996, pp. 1312-1322

[4] Peng Fangzheng, “Application issues of active power filters,” IEEE Industry Applications Magazine, v 4, n 5, Sep-Oct, 1998, pp. 21-30

[5] Akagi.H, Kanazawa.Y, and Nabae.A, “Instantaneous reactive power compensators comprising switching device without energy storage components,” IEEE Trans. on Industry Applications, (20), 3, 1984, pp. 625-630.