Control and Performance Analysis of a Single-Stage Utility-Scale Grid-Connected PV System

IEEE SYSTEMS JOURNAL, VOL. 11, NO. 3, SEPTEMBER 2017

ABSTRACT:

For utility-scale photovoltaic (PV) systems, the control objectives, such as maximum power point tracking, synchronization with grid, current control, and harmonic reduction in output current, are realized in single stage for high efficiency and simple power converter topology. This paper considers a highpower three-phase single-stage PV system, which is connected to a distribution network, with a modified control strategy, which includes compensation for grid voltage dip and reactive power injection capability. To regulate the dc-link voltage, a modified voltage controller using feedback linearization scheme with feedforward PV current signal is presented. The real and reactive powers are controlled by using dq components of the grid current. A small-signal stability/eigenvalue analysis of a grid-connected PV system with the complete linearized model is performed to assess the robustness of the controller and the decoupling character of the grid-connected PV system. The dynamic performance is evaluated on a real-time digital simulator.

 

KEYWORDS:

  1. DC-link voltage control
  2. Feedback linearization (FBL)
  3. Photovoltaic (PV) systems
  4. Reactive power control
  5. Small signal stability analysis
  6. Voltage dip.

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

One of the four 375-kW subsystems.

Fig. 1. One of the four 375-kW subsystems.

  

EXPECTED SIMULATION RESULTS:

(a) PV array voltage for MPPT. (b) PV array (PPV) and grid injected real power (Pg). (c) Grid injected reactive power (Qg).

Fig. 2. (a) PV array voltage for MPPT. (b) PV array (PPV) and grid injected real power (Pg). (c) Grid injected reactive power (Qg).

Grid injected currents and THD.

Fig. 3. Grid injected currents and THD.

PV system response to voltage dip in grid.

Fig. 4 PV system response to voltage dip in grid.

PV system response to a three-phase fault at bus 3.

Fig. 5. PV system response to a three-phase fault at bus 3.

PV system response to an LG fault.

Fig. 6. PV system response to an LG fault.

Pg  response of the whole 1.5-MW PV system.

Fig. 7. Pg  response of the whole 1.5-MW PV system.

 

CONCLUSION:

The proposed modified dc-link voltage controller with FBL technique, using INC MPPT, and real and reactive power controls with enhanced filter for compensation for grid voltage dips has been tested at different insolation levels on a real-time digital simulator (RTDS). Small-signal analysis of a PV system connected to an IEEE 33-bus distributed system is performed. The results from simulation and eigenvalue analysis demonstrate the effectiveness of the FBL controller compared with the controller without FBL. It is found that the FBL controller  outperforms the controllerwithout FBL, as the FBL controller’s  performance is linear at different operating conditions. With grid voltage dip compensator filter, the dynamic performance is much improved in terms of less oscillations and distortion in waveforms. In addition, the eigenvalue analysis shows that the effect of the disturbance in distribution system is negligible on PV system stability as the eigenmodes of the PV system are almost independent of the distribution system. This has been also confirmed by three-phase fault analysis of distribution system in RTDS model. The controller performance is also validated on 4×375 kW PV units connected to the distribution system.

 

REFERENCES:

  • Oprisan and S. Pneumaticos, “Potential for electricity generation from emerging renewable sources in Canada,” in Proc. IEEE EIC Climate Change Technol. Conf., May 2006, pp. 1–10.
  • Petrone, G. Spagnuolo, R. Teodorescu, M. Veerachary, and M. Vitelli, “Reliability issues in photovoltaic power processing systems,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2569–2580, Jul. 2008.
  • Jain and V. Agarwal, “A single-stage grid connected inverter topology for solar PV systems with maximum power point tracking,” IEEE Trans. Power Electron., vol. 22, no. 5, pp. 1928–1940, Jul. 2007.
  • Katiraei and J. Aguero, “Solar PV integration challenges,” IEEE Power Energy Mag., vol. 9, no. 3, pp. 62–71, May-Jun. 2011.
  • H. Ko, S. Lee, H. Dehbonei, and C. Nayar, “Application of voltageand current-controlled voltage source inverters for distributed generation systems,” IEEE Trans. Energy Convers., vol. 21, no. 3, pp. 782–792, Sep. 2006.

Three-phase grid connected PV inverters using the proportional resonance controller

2016 IEEE

ABSTRACT

The development in grid connected three phase inverter has increased the importance of achieving low distortion and high quality current waveform. This paper describes a method of reducing current ripple in a three phase grid connected inverter utilizing Proportional Resonance (PR) controller. The effectiveness of the PR current controller is demonstrated by comparing its performance with that of the Proportional Integral (PI) controller. Simulation and experimental results show that Proportional Resonance (PR) controller achieves better reduction in total harmonic distortion (THD) in the current signal spectrum.

 

KEYWORDS

  1. Grid-connected inverter
  2. LCL filter
  3. PI controller
  4. PR controller.

 

SOFTWARE:MATLAB/SIMULINK

  

BLOCK DIAGRAM:

block diagram

Fig.1. PI controller in synchronous reference scheme.

Fig. 2 PR controller in stationary reference control

SIMULATION RESULTS

Fig.3. The phase grid voltage

Fig.4. The phase current waveform using PI controller

 

Fig.5 The phase current waveform using Proportional resonance  controller

Fig.6. The FFT of the phase current waveform using PI controller

Fig.7. The FFT of the phase current waveform using Proportional Resonance controller

 

CONCLUSION

This paper has considered the impact of the current control scheme of a three-phase grid-connected inverter under normal and abnormal grid conditions using PI and PR controllers. In particular, this work has compared the performance of the industrially accepted PI controller, and the emerging PR controller which is popular in grid connected renewable energy applications. In keeping with the claims of other literature, simulation studies have confirmed that the PR controller shows better performance under normal operating conditions. There is no steady state error output, and the harmonic content of the current waveform is very low. Moreover, in this paper, the effect of grid voltage dips on the performance of the grid connected inverter was considered. Whilst the PI controller demonstrates very good performance, the Proportional Resonance controller offers superior output power regulation, and improved power quality performance. Overall, it suggests that the PR controller is better suited in the event of grid faults, or operation in weak grid environments.

 

REFERENCES

  1. Wuhua and H. Xiangning, “Review of Nonisolated High-Step-Up DC/DC Converters in Photovoltaic Grid-Connected Applications,” IEEE Trans. Ind Electron., vol. 58, pp. 1239-1250, 2011.
  2. Atkinson, G. Pannell, C. Wenping, B. Zahawi, T. Abeyasekera, and M. Jovanovic, “A doubly-fed induction generator test facility for grid fault ride-through analysis,” Instrumentation & Measurement Magazine, IEEE, vol. 15, pp. 20-27, 2012.
  3. Cecati, A. Dell’Aquila, M. Liserre, and V. G. Monopoli, “Design of H-bridge multilevel active rectifier for traction systems,” Industry Applications, IEEE Transactions on, vol. 39, pp. 1541-1550, 2003.
  4. Hassaine, E. Olias, J. Quintero, and V. Salas, “Overview of power inverter topologies and control structures for grid connected photovoltaic systems,” Renewable and Sustainable Energy Reviews, vol. 30, pp. 796-807, 2014.
  5. Nicastri and A. Nagliero, “Comparison and evaluation of the PLL techniques for the design of the grid-connected inverter systems,” in Industrial Electronics (ISIE), 2010 IEEE International Symposium on, 2010, pp. 3865-3870.

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Automatic droop control for a low voltage DC Microgrid

ABSTRACT

A DC microgrid (DC-MG) provides an effective mean to integrate various sources, energy storage units and loads at a common dc-side. The droop-based, in the context of a decentralized control, has been widely used for the control of the DC-MG. However, the conventional droop control cannot achieve both accurate current sharing and desired voltage regulation. This study proposes a new adaptive control method for DC-MG applications which satisfies both accurate current sharing and acceptable voltage regulation depending on the loading condition. At light load conditions where the output currents of the DG units are well below the maximum limits, the accuracy of the current sharing process is not an issue. As the load increases, the output currents of the DG units increase and under heavy load conditions accurate current sharing is necessary. The proposed control method increases the equivalent droop gains as the load level increases and achieves accurate current sharing. This study evaluates the performance and stability of the proposed method based on a linearised model and verifies the results by digital time-domain simulation and hardware-based experiments.

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig. 1 Simplified DC-MG with two DG units

 

EXPECTED SIMULATION RESULTS:

 

Fig. 2 Output currents of the DG units obtained in Simulation Results

a Conventional droop control method with small droop gains

b Conventional droop control method with large droop gains

c Proposed method

 

 

Fig. 3 Output voltages of the DG units obtained in Simulation Results

a Conventional droop control method with small droop gains

b Conventional droop control method with large droop gains

c Proposed method

 

CONCLUSION

This paper presents a new control scheme for DC-MG without using any communication links. In the conventional droop control, small droop gains result in good voltage regulation but inaccurate current sharing, and large droop gains result in accurate current sharing but unacceptable voltage regulation. To overcome this drawback, a new control method is proposed in which the equivalent droop gains automatically change based on the loading condition. The simulation results show and the experimental results verify that by adaptively changing the droop gains according to the load size, both accurate current sharing and desirable voltage regulation are achieved.

REFERENCES

  • Guerrero, J., Loh, P.C., Lee, T.-L., et al.: ‘Advanced control architectures for intelligent microgrids; part ii: Power quality, energy storage, and ac/dc microgrids’, IEEE Trans. Ind Electron., 2013, 60, (4), pp. 1263–1270
  • Vandoorn, T., De Kooning, J., Meersman, B., et al.: ‘Automatic power-sharing modification of p/v droop controllers in low-voltage resistive microgrids’, IEEE Trans. Power Deliv., 2012, 27, (4), pp. 2318–2325
  • Khorsandi, A., Ashourloo, M., Mokhtari, H.: ‘An adaptive droop control method for low voltage dc microgrids’. 2014 Fifth Power Electronics, Drive Systems and Technologies Conf. (PEDSTC), 2014, pp. 84–89
  • Loh, P.C., Li, D., Chai, Y.K., et al.: ‘Hybrid ac-dc microgrids with energy storages and progressive energy flow tuning’, IEEE Trans. Power Electron., 2013, 28, (4), pp. 1533–1543
  • Loh, P., Li, D., Chai, Y.K., et al.: ‘Autonomous operation of hybrid microgrid with ac and dc subgrids’, IEEE Trans. Power Electron., 2013, 28, (5), pp. 2214–2223

New Perspectives on Droop Control in AC Microgrid

ABSTRACT

Virtual impedance, angle droop and frequency droop control play important roles in maintaining system stability, and load sharing among distributed generators (DGs) in microgrid. These approaches have been developed into three totally independent concepts, but a strong correlation exists. In this letter, their similarities and differences are revealed. Some new findings are established as follows: 1) the angle droop control is intrinsically a virtual inductance method; 2) virtual inductance method can also be regarded as a special frequency droop control with a power derivative feedback; 3) the combination of virtual inductance method and frequency droop control is equivalent to the proportional–derivative (PD) type frequency droop, which is introduced to enhance the power oscillation damping. These relationships provide new insights into the design of the control methods for DGs in microgrid.

 

KEYWORDS

  1. Microgrid
  2. Droop control
  3. Virtual Impedance

 

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

block diagram

Fig. 1 Equivalent output voltage source considering virtual impedance.

 

EXPECTED SIMULATION RESULTS:

Fig. 2 Power response during load change in conventional frequency droop. (a) Active power, (b) reactive power.

Fig. 3 Power response during load change in frequency droop plus virtual reactance. (a) Active power, (b) reactive power.

Fig. 4 Power response during load change in modified frequency droop. (a) Active power, (b) reactive power.

 

CONCLUSION

This letter compares the similarities and differences among three different concepts, virtual impedance method, angle droop and frequency droop control. Although each of them has been well researched, new perspectives are bought to readers by relating all three together. Thus, the inherent relationships are established, and new insights into the controller design are provided. Finally, the modified droop control unifies these three independently developed droop control methods into a generalized theoretical framework. To the reader, this letter explores the possibilities of further enhancing the existing methods and inspiring the development of new methods.

 

REFERENCES

  • M. Guerrero, L. GarciadeVicuna, and J. Matas, “Output impedance design of parallel-connected UPS inverters with wireless load-sharing control,” IEEE Trans. Ind. Electron., vol.52, no.4, pp.1126-1135, Aug.2005.
  • He and Y. Li, “Analysis, design, and implementation of virtual impedance for power electronics interfaced distributed generation,” IEEE Trans. Ind. Appl., vol.47, no.6, pp. 2525-2538, Nov. 2011.
  • Mahmood, D. Michaelson, and J. Jiang, “Accurate reactive power sharing in an islanded microgrid using adaptive virtual impedances,” IEEE Trans. Power Electron., vol.30, no.3, pp. 1605-1617, Mar.2015.
  • Majumder, G. Ledwich, A. Ghosh, S. Chakrabarti, and F. Zare, “Droop control of converter-interfaced microsources in rural distributed generation, ” IEEE Trans. Power Del., vol. 25, no. 4, pp.2768-2778, Oct. 2010.
  • C, Chandorkar, D. M. Divan, and R. Adapa, “Control of parallel connected inverters in standalone ac supply systems,” IEEE Trans. Ind. Appl., vol.29, no.1 pp.136-143, Jan.1993.

 

Control Strategy of Three-Phase Battery Energy Storage Systems for Frequency Support in Microgrids and with Uninterrupted Supply of Local Loads

 

ABSTRACT

Frequency control in autonomous microgrids (MG) with high penetration of renewable energy sources represents a great concern to ensure the system stability. In this regard, this paper presents an enhanced control method for battery energy storage systems (BESS) to support the frequency of MG and with the ability of disconnecting from the MG to supplying in the island mode a local consumer. A frequency controller, combining a conventional droop control with an inertia emulation function, governs the BESS active power transfer during the primary frequency control level. The BESS may also provide voltage support in the point of common coupling with the MG. Moreover, the proposed BESS may compensate, partially or totally, the power absorbed by the local loads in order to improve the MG frequency response. When the MG power quality worsens below a certain level, in terms of voltage and frequency, the BESS detaches from the MG and continues to operate islanded.

The reconnection is accomplished following a smoothly resynchronization of the local voltage with the MG, without disturbing the local loads supply. Additionally, this paper also discusses about the aspects related to the BESS management and its integration within the proposed system. The simulation and experimental results assess the feasibility of the proposed control solutions. Frequency control in autonomous microgrids (MG) with high penetration of renewable energy sources represents a great concern to ensure the system stability. In this regard, this paper presents an enhanced control method for battery energy storage systems (BESS) to support the frequency of MG and with the ability of disconnecting from the MG to supplying in the island mode a local consumer. A frequency controller, combining a conventional droop control with an inertia emulation function, governs the BESS active power transfer during the primary frequency control level. The BESS may also provide voltage support in the point of common coupling with the MG.

Moreover, the proposed BESS may compensate, partially or totally, the power absorbed by the local loads in order to improve the MG frequency response. When the MG power quality worsens below a certain level, in terms of voltage and frequency, the BESS detaches from the MG and continues to operate islanded. The reconnection is accomplished following a smoothly resynchronization of the local voltage with the MG, without disturbing the local loads supply. Additionally, this paper also discusses about the aspects related to the BESS management and its integration within the proposed system. The simulation and experimental results assess the feasibility of the proposed control solutions.

 

KEYWORDS

  1. Battery energy storage systems (BESS)
  2. Frequency control
  3. Inverter, microgrid (MG)
  4. Seamless transfer

 

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

 

 

 

 

 

Fig. 1 BESS Structure

 

EXPECTED SIMULATION RESULTS:

 

 

 

 

 

Fig. 2. MG frequency (Top) and BESS active power (Bottom) for different operating conditions (simulation results).

 

 

 

 

 

Fig. 3 MG frequency (Top) and BESS active power (Bottom) for different levels of the local load compensation

 

CONCLUSION

This paper presented a Battery Energy Storage Systems BESS mainly designed to provide frequency support in MG, but having special control features. The BESS can operate both connected to the MG (G-mode) or in (I-mode), whereas the transition between the two states is seamlessly coordinated by an original control method. The BESS may serve local sensitive consumers connected on the local bus, by including special control functions to protect them in adverse MG operating conditions. The BESS management is also taking into discussion from the perspective of its influence upon the proposed controller performance. Simulations and experimental results were provided to validate the proposed BESS. An improved frequency controller, with conventional droop and virtual inertia was proposed and in the simulation results, it proved to be an efficient solution, resulting in faster damping of the MG frequency oscillations. Moreover, by partially or totally compensating the local loads, the MG is relieved by the corresponding power disturbance produced by their stochastic operation and thus the MG frequency deviation can be diminished.

By this approach, the BESS along with the local loads may be considered as a sort of smart load. The transition between G-mode to I-mode took place when the PCC power quality worsened and the experimental results showed a clean transfer without important voltage and frequency variations. The transition between I-mode to G-mode included a smoothly synchronization period of the local voltage with the MG voltage, after which the switching to G-mode did not disturb either the local loads or the MG. During I-mode, the local loads are supplied directly by the BESS and the presented experimental results including a comprehensive operating case, proved that the voltage control quality falls into the required standards. Future studies are intended to be carried out on the system availability to contribute to the MG power quality improvement.

 

REFERENCES

  • European Commission, Energy Roadmap 2050, 2011. [Online].Available: http://ec.europa.eu/energy/energy2020/roadmap/index_en.htm
  • Bevrani, A. Ghosh, and G. Ledwich, “Renewable energy sources and frequency regulation: Survey and new perspectives,” IET Renew. Power Gen., vol. 4, no. 5, pp. 438–457, Sep. 2010.
  • Tan, Q. Li, and H. Wang, “Advances and trends of energy storage technology in Microgrid,” Int. J. Elect. Power Energy Syst., vol. 44, no. 1, pp. 179–191, Jan. 2013.
  • Bottrell, M. Prodanovic, and T. C. Green, “Dynamic stability of a microgrid with an active load,” IEEE Trans. Power Electron., vol. 28, no. 11, pp. 5107–5119, Nov. 2013.
  • A. P. Lopes, F. J. Soares, and P. M. R. Almeida, “Integration of electric vehicles in the electric power system,” Proc. IEEE, vol. 99, no. 1, pp. 168–183, Jan. 2011.

A Novel Three-Phase Three-Leg AC/AC Converter Using Nine IGBTs

ABSTRACT:

This paper proposes a novel three-phase nine-switch ac/ac converter topology. This converter features sinusoidal inputs and outputs, unity input power factor, and more importantly, low manufacturing cost due to its reduced number of active switches. The operating principle of the converter is elaborated; its modulation schemes are discussed. Simulated semiconductor loss analysis and comparison with the back-to-back two-level voltage source converter are presented. Finally, experimental results from a 5-kVA prototype system are provided to verify the validity of the proposed topology.

 

KEYWORDS:

  1. AC/AC converter
  2. pulse width modulation (PWM)
  3. reduced switch count topology

 

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:Fig: 1 B2B 2L-VSC.

Fig: 2 Proposed nine switch ac to ac converter with a quasi dc link

 

EXPECTED SIMULATION RESULTS:

  

Fig. 3. Measured rectifier and inverter waveforms (CF-mode operation). (a) Input and output voltages. (b) Voltage spectrum. (c) Input and output currents.

Fig. 4. Measured waveforms and spectrum (VF mode operation). (a) Input and output voltages. (b) Spectrum.

Fig. 5. Measured waveforms when the inverter output frequency has a step increase from 30 to 120 Hz, while the rectifier input frequency remains at 60 Hz. (a) Input and output voltages. (b) Input and output currents.

 

CONCLUSION:

A novel nine-switch PWMac/ac converter topology was proposed in this paper. The topology uses only nine IGBT devices for ac to ac conversion through a quasi dc-link circuit. Compared with the conventional back-to-back PWM VSC using 12 switches and the matrix converter that uses 18, the number of switches in the proposed converter is reduced by 33% and 50%, respectively. The proposed converter features sinusoidal inputs and outputs, unity input power factor, and low manufacturing cost. The operating principle of the converter was elaborated, and modulation schemes for constant and VF operations were developed. Simulation results including a semiconductor loss analysis and comparison were provided, which reveal that the proposed converter, while working in CF mode, has an overall higher efficiency than the B2B 2L-VSC at the expense of uneven loss distribution. However, the VF-mode version requires IGBT devices with higher ratings and dissipates significantly higher losses, and thus, is not as attractive as its counterpart. Experimental verification is carried out on a 5-kVA prototype system.

 

REFERENCES:

 Wu, High-power Converters and AC Drives. Piscataway, NJ: IEEE/Wiley, 2006.

  • Singh, B. N. Singh, A. Chandra, K. Al-Haddad, A. Pandey, and D. P. Kothari, “A review of three-phase improved power quality AC– DC converters,” IEEE Trans. Ind. Electron., vol. 51, no. 3, pp. 641–660, Jun. 2004.
  • Blaabjerg, S. Freysson, H. H. Hansen, and S. Hansen, “A new optimized space-vector modulation strategy for a component-minimized Voltage source inverter,” IEEE Trans. Power Electron., vol. 12, no. 4, pp. 704–714, Jul. 1997.
  • L. A. Ribeiro, C. B. Jacobina, E. R. C. da Silva, and A. M. N. Lima, “AC/AC converter with four switch three phase structures,” in Proc. IEEE PESC, 1996, vol. 1, pp. 134–139.

A STATCOM-Control Scheme for Grid Connected Wind Energy System for Power Quality Improvement

ABSTRACT:

Injection of the wind power into an electric grid affects the power quality. The performance of the wind turbine and thereby power quality are determined on the basis of measurements and the norms followed according to the guideline specified in International Electro-technical Commission standard, IEC-61400. The influence of the wind turbine in the grid system concerning the power quality measurements are-the active power, reactive power, variation of voltage, flicker, harmonics, and electrical behavior of switching operation and these are measured according to national/international guidelines. The paper study demonstrates the power quality problem due to installation of wind turbine with the grid. In this proposed scheme STATic COMpensator (STATCOM) is connected at a point of common coupling with a battery energy storage system (BESS) to mitigate the power quality issues.

The battery energy storage is integrated to sustain the real power source under fluctuating wind power. The STATCOM control scheme for the grid connected wind energy generation system for power quality improvement is simulated using MATLAB/SIMULINK in power system block set. The effectiveness of the proposed scheme relives the main supply source from the reactive power demand of the load and the induction generator. The development of the grid co-ordination rule and the scheme for improvement in power quality norms as per IEC-standard on the grid has been presented.

 

KEYWORDS:

  1. International electro-technical commission (IEC)
  2. power quality
  3. wind generating system (WGS)

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

  statcom

Fig.1.System operational scheme in grid system.

 

EXPECTED SIMULATION RESULTS:

  

Fig. 1. Three phase injected inverter Current.

Fig. 2. (a) Source Current. (b) Load Current. (c) Inverter Injected Current. (d) Wind generator (Induction generator) current.


Fig. 3. (a) DC link voltage. (b) Current through Capacitor, 
STATCOM output voltage.

Fig. 5. Supply Voltage and Current at PCC.


Fig.6.(a) Source Current. (b) FFT of source current.                

Fig.7.(a) Source Current. (b) FFT of source current

 

CONCLUSION:

The paper presents the STATCOM-based control scheme for power quality improvement in grid connected wind generating system and with non linear load. The power quality issues and its consequences on the consumer and electric utility are presented. The operation of the control system developed for the STATCOM-BESS in MATLAB/SIMULINK for maintaining the power quality is simulated. It has a capability to cancel out the harmonic parts of the load current. It maintains the source voltage and current in-phase and support the reactive power demand for the wind generator and load at PCC in the grid system, thus it gives an opportunity to enhance the utilization factor of transmission line. The integrated wind generation and STATCOM with BESS have shown the outstanding performance. Thus the proposed scheme in the grid connected system fulfills the power quality norms as per the IEC standard 61400-21.

 

REFERENCES:

 Sannino, “Global power systems for sustainable development,” in IEEE General Meeting, Denver, CO, Jun. 2004.

  • S. Hook, Y. Liu, and S. Atcitty, “Mitigation of the wind generation integration related power quality issues by energy storage,” EPQU J., vol. XII, no. 2, 2006.
  • Billinton and Y. Gao, “Energy conversion system models for adequacy assessment of generating systems incorporating wind energy,” IEEE Trans. on E. Conv., vol. 23, no. 1, pp. 163–169, 2008, Multistate.
  • Wind Turbine Generating System—Part 21, International standard-IEC 61400-21,
  • Manel, “Power electronic system for grid integration of renewable energy source: A survey,” IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1002–1014, 2006, Carrasco.

Improving the Dynamic Performance of Wind Farms with STATCOM

ABSTRACT:

When integrated to the power system, large wind farms can pose voltage control issues among other problems. A thorough study is needed to identify the potential problems and to develop measures to mitigate them. Although integration of high levels of wind power into an existing transmission system does not require a major redesign, it necessitates additional control and compensating equipment to enable (fast) recovery from severe system disturbances. The use of a Static Synchronous Compensator (STATCOM) near a wind farm is investigated for the purpose of stabilizing the grid voltage after grid-side disturbance such as a three phase short circuit fault. The strategy focuses on a fundamental grid operational requirement to maintain proper voltages at the point of common coupling by regulating the voltage. The DC voltage at individual wind turbine (WT) inverters is also stabilized to facilitate continuous operation of wind turbines  during disturbances.

 

KEYWORDS:

  1. Wind turbine
  2. Doubly-fed Induction Generator
  3. STATCOM
  4. Three phase fault
  5. Reactive power

 

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

wind farm with statcom

Fig. 1. Block diagram of a Doubly-fed induction generator

Fig. 2 Test System

EXPECTED SIMULATION RESULTS: 

Fig. 3. Voltage at the fault bus (Load bus) , Voltage at the fault bus (Zoomed version)

Fig. 4. Reactive power in the system with no compensating device, Reactive power in the system with mechanically switched capacitors

Fig. 5. Reactive and active power of the 25 MVA STATCOM for Case 3, AC and DC busbar voltages of the STATCOM for Case III.

Fig. 6. Reactive and active powers of only the STATCOM for Case 4, Reactive power and terminal voltage of only the the MSC for Case 4.

Fig. 7. Reactive powers of the system with a STATCOM and MSC

Fig. 8. Reactive power of the 125 MVA STATCOM for Case 5.

 

CONCLUSION:

Wind turbines have to be able to ride through a fault without disconnecting from the grid. When a wind farm is connected to a weak power grid, it is necessary to provide efficient power control during normal operating conditions and enhanced support during and after faults. This paper explored the possibility of connecting a STATCOM to the wind power system in order to provide efficient control. An appropriately sized STATCOM can provide the necessary reactive power compensation when connected to a weak grid. Also, a higher rating STATCOM can be used for efficient voltage control and improved reliability in grid connected wind farm but economics limit its rating. Simulation studies have shown that the additional voltage/var support provided by an external device such as a STATCOM can significantly improve the wind turbine’s fault recovery by more quickly restoring voltage characteristics. The extent to which a STATCOM can provide support depends on its rating. The higher the rating, the more support provided. The interconnection of wind farms to weak grids also influences the safety of wind turbine generators. Some of the challenges faced by wind turbines connected to weak grids are an increased number and frequency of faults, grid abnormalities, and voltage and frequency fluctuations that can trip relays and cause generator heating.

 

REFERENCES:

  • http://www.awea.org/newsroom/releases/Wind_Power_Capacity_012307. html, accessed Nov. 2007.
  • Sun, Z. Chen, F. Blaabjerg, “Voltage recovery of grid-connected wind turbines with DFIG after a short-circuit fault,” 2004 IEEE 35th Annual Power Electronics Specialists Conf., vol. 3, pp. 1991-97, 20-25 June 2004.
  • Muljadi, C.P. Butterfield, “Wind Farm Power System Model Development,” World Renewable Energy Congress VIII, Colorado, Aug- Sept 2004.
  • M. Muyeen, M.A. Mannan, M.H. Ali, R. Takahashi, T. Murata, J. Tamura, “Stabilization of Grid Connected Wind Generator by STATCOM,” IEEE Power Electronics and Drives Systems Conf., Vol. 2, 28-01 Nov. 2005.
  • Saad-Saoud, M.L. Lisboa, J.B. Ekanayake, N. Jenkins, G. Strbac, “Application of STATCOMs to wind farms,” IEE Proceedings – Generation, Transmission, Distribution, vol. 145, pp.1584-89, Sept 1998.

A FACTS Device Distributed Power Flow Controller (DPFC)

ABSTRACT:

This paper presents a new component within the flexible ac-transmission system (FACTS) family, called distributed power-flow controller (DPFC). The DPF Controller is derived from the unified power-flow controller (UPFC). The DPFC can be considered as a UPFC with an eliminated common dc link. The active power exchange between the shunt and series converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third- harmonic frequency. The DPFC employs the distributed FACTS (D-FACTS) concept, which is to use multiple small-size single-phase converters instead of the one large-size three-phase series converter in the UPFC. The large number of series converters provides redundancy, thereby increasing the system reliability. As the D-FACTS converters are single-phase and floating with respect to the ground, there is no high-voltage isolation required between the phases. Accordingly, the cost of the DPFC system is lower than the UPFC. The DPFC has the same control capability as the UPFC, which comprises the adjustment of the line impedance, the transmission angle, and the bus voltage. The principle and analysis of the DPFC are presented in this paper and the corresponding experimental results that are carried out on a scaled prototype are also shown.

 

KEYWORDS:

  1. AC–DC power conversion
  2. Load flow control
  3. Power electronics
  4. Power semiconductor devices
  5. Power-transmission

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

facts device

Fig. 1. DPFC control block diagram.

 

EXPECTED SIMULATION RESULTS:

 Fig. 2. DPFC operation in steady state: line current.       

               

Fig. 3. DPFC operation in steady sta te:series converter voltage.

Fig. 4. DPFC operation in steady state: bus

Fig. 5. Reference voltage for the series converters. voltage and current at the Δ side of the transformer


Fig. 6. Step response of the DPFC: series converter

Fig. 7. Step response of the DPFC: linecurrent. voltage.

Fig. 8. Step response : active and reactive power injected by the series converter at the fundamental frequency.

Fig.9. Step response: bus voltage and current at the Δ of the transformer

 

CONCLUSION:

 This paper has presented a new concept called Distributed power flow controller. It emerges from the UPFC and inherits the control capability of the UPFC, which is the simultaneous adjustment of the line impedance, the transmission angle, and the bus-voltage magnitude. The common dc link between the shunt and series converters, which is used for exchanging active power in the UPFC, is eliminated. This power is now transmitted through the transmission line at the third-harmonic frequency. The series converter of the DPFC employs the D-FACTS concept, which uses multiple small single-phase converters instead of one large-size converter. The reliability of the DPFC is greatly increased because of the redundancy of the series converters. The total cost of this controller is also much lower than the UPFC, because no high-voltage isolation is required at the series-converter part and the rating of the components of is low. The DPFC concept has been verified by an experimental setup. It is proved that the shunt and series converters in the DPFC can exchange active power at the third-harmonic frequency, and the series converters are able to inject controllable active and reactive power at the fundamental frequency.

 

REFERENCES:

 -H. Song and A. Johns, Flexible ac Transmission Systems (FACTS) (IEE Power and Energy Series), vol. 30. London, U.K.: Institution of Electrical Engineers, 1999.

  • G. Hingorani and L. Gyugyi, Understanding FACTS : Concepts and Technology of Flexible AC Transmission Systems. New York: IEEE Press, 2000.
  • Gyugyi, C.D. Schauder, S. L.Williams, T. R. Rietman,D. R. Torgerson, andA. Edris, “The unified power flowcontroller:Anewapproach to power transmission control,” IEEE Trans. Power Del., vol. 10, no. 2, pp. 1085–1097, Apr. 1995.
  • -A. Edris, “Proposed terms and definitions for flexible ac transmission system (facts),” IEEE Trans. Power Del., vol. 12, no. 4, pp. 1848–1853, Oct. 1997.
  • K. Sen, “Sssc-static synchronous series compensator: Theory, modeling, and application,” IEEE Trans. Power Del., vol. 13, no. 1, pp. 241–246, Jan. 1998.

Matrix Converters: A Technology Review

ABSTRACT

The matrix converter is an array of controlled semiconductor switches that connects directly the three-phase source to the three-phase load. This converter has several attractive features that have been investigated in the last two decades. In the last few years, an increase in research work has been observed, bringing this topology closer to the industrial application. This paper presents the state-of-the-art view in the development of this converter, starting with a brief historical review. An important part of the paper is dedicated to a discussion of the most important modulation and control strategies developed recently. Special attention is given to present modern methods developed to solve the commutation problem. Some new arrays of power bidirectional switches integrated in a single module are also presented. Finally, this paper includes some practical issues related to the practical application of this technology, like overvoltage protection, use of filters, and ride-through capability.

KEYWORDS

  1. AC–AC power conversion
  2. Converters
  3. Matrix

 

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 matrix converter

Fig. 1. Simplified circuit of a 3 x 3 matrix converter

 

EXPECTED SIMULATION RESULTS:

Phase output voltage

Fig. 2. Typical waveforms. (a) Phase output voltage. (b) Load current.

maximum voltage ratio

Fig. 3. Illustrating maximum voltage ratio of 50%.

voltage ratio improvement
Fig. 4. Illustrating voltage ratio improvement to 87%.

Line-to-line voltage and current

Fig. 5. Line-to-line voltage and current in the load with the indirect method. Output frequency of 50 Hz.

CONCLUSION:

 After two decades of research effort, several modulation and control methods have been developed for the matrix converter, allowing the generation of sinusoidal input and output currents, operating with unity power factor using standard processors. The most important practical implementation problem in the matrix converter circuit, the commutation problem between two controlled bidirectional switches, has been solved with the development of highly intelligent multistep commutation strategies. The solution to this problem has been made possible by using powerful digital devices that are now readily available in the market.

 

REFERENCES:

 Gyugi and B. Pelly, Static Power Frequency Changers: Theory, Performance and Applications. New York: Wiley, 1976.

  • Brandt, “Der Netztaktumrichter,” Bull. ASE, vol. 62, no. 15, pp. 714–727, July 1971.
  • Popov, “Der Direktumrichter mit zyklischer Steuerung,” Elektrie, vol. 29, no. 7, pp. 372– 376, 1975.
  • Stacey, “An unrestricted frequency changer employing force commutated thyristors,” in Proc. IEEE PESC’76, 1976, pp. 165–173.
  • Jones and B. Bose, “A frequency step-up cycloconverter using power transistors in inverse-series mode,” Int. J. Electron., vol. 41, no. 6, pp. 573–587, 1976.
  • MATRIX Converter