Grid interfacing-converter-systems

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  • Situations/Problems of existing grids; driving to the next generation of grid; before that, take a look the existing grid
  • Situations/Problems of existing grids; driving to the next generation of grid; before that, take a look the existing grid
  • Depends on large central power stations; centralized control; unidirectional; Difficult to upgrade the existing grid due to increasing power demand; Context: current flow through the feeder and transformer impedance introduce voltage drop, ant that means voltage appearing at the user sides can be shaped/influenced by the current.
  • Voltage quality problems, steady-state ones and transient ones; main features in the grid and conventional solutions; fluctuations (including voltage and frequency) Context: can be even worse due to the change of existing grid
  • Flexible operation; Bottom-up solutions Flexibility, complexity, reliability, quality …… concepts, ideas, detailed power electronic control, implementations… Context: a smart operation of a future grid can be complex, but also must be smartly organized so as to achieve smart and flexible control, some concepts have been proposed, and what we proposed?
  • Converter systems with enhanced voltage quality basic electricity energy delivery from DG to the grid integrate previously proposed control and solutions protect local system from grid disturbances power flow control under disturbed situations for grid support
  • Grid interfacing-converter-systems

    1. 1. Grid-Interfacing Converter Systems with Enhanced Voltage Quality Fei Wang
    2. 2. Contents <ul><li>Introduction </li></ul><ul><li>Grid-interfacing systems </li></ul><ul><li>Structure and functionalities </li></ul><ul><li>Control design and implementation </li></ul><ul><li>Conclusions </li></ul>
    3. 3. Transition to the future grid <ul><li>Improving energy efficiency </li></ul><ul><li>Applying sustainable energy </li></ul><ul><li>Growing electricity consumption </li></ul><ul><li>Demanding high-quality electricity </li></ul>
    4. 4. Conventional electricity grid <ul><li>Central power station </li></ul><ul><li>Top-down centralized control </li></ul><ul><li>Unidirectional power flow </li></ul>Generation Transmission Distribution Loads
    5. 5. Voltage quality problems <ul><li>Harmonics </li></ul><ul><li>Dips </li></ul><ul><li>Unbalance </li></ul><ul><li>Fluctuations </li></ul>Generation Transmission Distribution Loads
    6. 6. Distributed generation in the grid Energy Storages Distributed Generation Distribution networks Grid-interfacing converters
    7. 7. Path to the future grid
    8. 8. Path to the future grid
    9. 9. Series-parallel grid-interfacing systems <ul><li>Independent distributed sources powered dc bus </li></ul>
    10. 10. Series-parallel grid-interfacing systems <ul><li>Common distributed sources powered dc bus with isolation techniques </li></ul>
    11. 11. Series-parallel grid-interfacing systems <ul><li>An example of coupling the utility grid and a local grid/micro-grid </li></ul>
    12. 12. Series-parallel grid-interfacing systems <ul><li>Adapted series-parallel structure </li></ul><ul><li>Common distributed sources powered dc bus </li></ul>
    13. 13. Reconfiguring system functionalities <ul><li>Conventional power quality enhancement </li></ul><ul><ul><li>Unified PQ conditioners (UPQC) </li></ul></ul><ul><ul><li>UPQC + energy storage (batteries, super-capacitors, distributed sources, etc. ) </li></ul></ul>
    14. 14. Reconfiguring system functionalities <ul><li>Circuit presentation of the proposed grid-interfacing system </li></ul><ul><ul><li>Subscripts: </li></ul></ul><ul><ul><li>+, - : positive and negative sequence; </li></ul></ul><ul><ul><li>1: fundamental components </li></ul></ul><ul><ul><li>h : harmonics </li></ul></ul>
    15. 15. Reconfiguring system functionalities <ul><li>Multi-level control objectives </li></ul><ul><li>- Level 1: Maintaining good voltage quality for local loads </li></ul><ul><ul><li>Dispatching power within the local grid (micro-grids) </li></ul></ul><ul><li>- Level 2: Active power filtering function </li></ul><ul><li>- System Level: Grid interactive control, grid support, power transfer </li></ul>
    16. 16. Comparison with shunt systems <ul><ul><li>(a) Series-parallel system </li></ul></ul><ul><ul><li>(b) Shunt-connected system </li></ul></ul>
    17. 17. Control design and implementation <ul><li>Employed configuration of the laboratory system </li></ul>
    18. 18. Control design and implementation <ul><li>Overall control structure </li></ul><ul><ul><li>Parallel converter </li></ul></ul><ul><li>Series converter </li></ul>
    19. 19. Control design – parallel converter <ul><li>Control diagram of the parallel converter </li></ul>
    20. 20. Control design – parallel converter <ul><li>Instability improvement under no-load conditions </li></ul>Bode plots of the plant transfer function Feedforward loop
    21. 21. Control design – parallel converter <ul><li>Selective harmonic regulation </li></ul>Bode plots of the open-loop transfer function with multiple PR controllers Multiple PR controllers
    22. 22. Control design – parallel converter <ul><li>Disturbance sensitivity improvement </li></ul>System sensitivity to current disturbances Inner current feedback loop
    23. 23. Control design – series converter <ul><li>Control diagram of the series converter </li></ul>
    24. 24. Control design – series converter Inverter output voltage to feedback current when Bode plots of open-loop transfer function
    25. 25. Laboratory system
    26. 26. Experimental results <ul><li>Output voltages of the parallel converter </li></ul><ul><li>(tested under a single-phase nonlinear load) </li></ul>(a) WITHOUT low-order harmonic compensation (b) WITH low-order harmonic compensation
    27. 27. Experimental results <ul><li>Emulation of active filter function with low-order harmonic current injection </li></ul>Frequency spectra of the phase current Series-converter current Injected series voltage
    28. 28. Experimental results <ul><li>Test under a distorted grid condition </li></ul>Distorted grid voltage (6.7%THD) Output voltage of the series-converter Output voltage of the parallel converter Currents delivered to the grid
    29. 29. Experimental results <ul><li>Test under unbalanced voltage dips </li></ul>Grid voltage (phase a & b dip to 80%) Output voltage of the series-converter Output voltage of the parallel converter Currents delivered to the grid
    30. 30. Conclusions and recommendations <ul><li>All common grid disturbances at the distribution level can be mitigated by the proposed approach </li></ul><ul><li>The voltage quality can be improved at both user and grid side, combing with distributed power generation </li></ul><ul><li>Grid interaction control integrating grid-impedance adaptability </li></ul><ul><li>Scaled up grid-interfacing systems for smart-grid research </li></ul>
    31. 31. References <ul><li>Selected papers </li></ul><ul><li>1. Wang, F., Benhabib, M.C., Duarte, J.L., Hendrix, M.A.M., Sequence-decoupled controller for three-phase grid-connected inverters. IEEE Applied Power Electronics Conference and Exposition (APEC ), 2009, pp. 121-127. </li></ul><ul><li>2. Wang, F., Benhabib, M.C., Duarte, J.L., Hendrix, M.A.M., High performance stationary frame filters for symmetrical sequences or harmonics separation under a variety of grid conditions. IEEE APEC , 2009, pp. 1570-1576. </li></ul><ul><li>3. Wang, F., Duarte, J.L., Hendrix, M.A.M., Ribeiro, P. F., Modeling and analysis of grid harmonic distortion impact of aggregated DG Inverters. IEEE Transactions on Power Electronics , in press, Oct. 2010. </li></ul><ul><li>4. Wang, F., Duarte, J.L., Hendrix, M.A.M., Design and analysis of active power control strategies for distributed generation inverters under unbalanced grid faults. IET Generation, Transmission & Distribution , vol. 4, iss. 8, pp. 905-916, Aug. 2010. </li></ul><ul><li>5. Wang, F., Duarte, J.L., Hendrix, M.A.M., Pliant active and reactive power control for grid-interactive converters under unbalanced voltage dips. IEEE Transactions on Power Electronics , in press, May 2010. </li></ul><ul><li>10. Wang, F., Duarte, J.L., Hendrix, M.A.M., Control of grid-interfacing inverters with integrated voltage unbalance correction. IEEE Power Electronics Specialists Conference (PESC) , 2008, pp. 310-316. </li></ul><ul><li>11. Wang, F., Duarte, J.L., Hendrix, M.A.M., Grid-interfacing converter systems with enhanced voltage quality for smart grid application - concept and implementation. IEEE Transactions on Power Electronics , submitted for review, Oct. 2010. </li></ul><ul><li>12. Wang, F., Duarte, J.L., Hendrix, M.A.M., Reconfiguring grid-interfacing converters for power quality improvement. IEEE Young Researchers Symposium IAS/PELS/PES Benelux Chapter , 2008, pp. 1-6. </li></ul><ul><li>b. Ph. D. dissertation </li></ul><ul><li>Wang F., Flexible operation of grid-interfacing converters in distribution networks: bottom-up solutions to voltage quality enhancement. Eindhoven University of Technology , 2010. </li></ul>

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