liserre lecture 12 by H1a4PA5Z

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									Ancillary Services of Distributed Power Generation Systems




        Ancillary Services of Distributed Power
                  Generation Systems

                                            Marco Liserre
                                              liserre@poliba.it




Marco Liserre                                                     liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                                                  Agenda


    Definition of ancillary services
    Active and reactive capability of DPGS
    Power Flow through a line
    Droop Control
    Services at Load Level
    Services at Electric Power System (EPS) Level




Marco Liserre                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                          Definition of ancillary services

         The IEEE 1547.3 “IEEE Guide for Monitoring, Information Exchange, and Control of
          Distributed Resources Interconnected with Electric Power Systems” defines ancillary
          services only those provided by DPGS at the Electric Power Systems Area


         They are: load regulation, energy losses, spinning and non-spinning reserve, reactive
          supply.


         However future ancillary services may include also power quality enhancement


         Moreover they can also be defined at Load Level (e.g. UPS functionality)


         Ancillary services contribute to a systemic approach to the management of the new
          power system characterized by an higher inflow from DPGS


         Anyway ancillary services could facilitate the penetration of RES in power systems




Marco Liserre                                                                              liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                          Definition of ancillary services
        Ancillary services are based on the specific characteristic of inverter-based
         DPGS that can be used to inject active, reactive power and harmonics in the
         grid (the second and third even if the energy source is not available)

        Some of the ancillary services are similar to those that traditional power plant
         provide to contribute to the safe and stable system operation


        However DPGS ancillary services are mainly considered at a distribution level
         hence part of the features of active distribution grid (smart grid) and not at
         transmission level (where traditional power plants are usually connected)


        Moreover when a DPGS is LV-connected the grid frequency and the grid
         voltage cannot be controlled independently since low-voltage distribution lines
         have a not negligible resistance


        Hence these issues can not be considered as a mere transposition of known
         concepts at a different level since they are involved in a wider change of the
         power system
Marco Liserre                                                                      liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                      Active and reactive capability of the
                              inverter-based DPGS
                                                                                                   P                                      P

    Active      and     reactive power                                                                                              V
     management of the DPGS depends                                                            E
                                                                                                                                              VL

     on the grid converter                                              Ig   0                         VL         Q         Ig       E                  Q
             P                                                  P                              V

                                                                                                                 (a)                                    (b)

                                                                                                   P                                      P
                            Q                                       Q

                                                                                                                       Ig
                                                                                       V                                         V

                                                                                       E                    VL    Q              E       VL             Q
                                                                             Ig
    full power converter           half power converter (DFIG)
                                                                                                                 (c)                                    (d)
                                    P                                                              P                                      P

                           EPCC                                                           V                                        V
                                            Vtrasf &distr                                                   VL
                                                                                  
                                                           Q                                                    Q                                     Q
                 Ig        Egrid                                                       E                                             E             VL
                                                                             Ig                                        Ig


                                                                                                                 (e)                                    (f)




Marco Liserre                                                                                                                                 liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                              Power Flow through a line

    P
       1
       Z
                               
          EV cos   E 2 cos   EV sin  sin  
                                                
       1
                               
    Q   EV cos   E 2 sin   EV sin  cos  
       Z                                       

     In case of an inductive line
         EV                            EV cos   E 2
      P    sin                    Q
         X                                  X
     The previous equations can be used for:

           controlling the power sharing among different systems feeding/absorbing power (parallel
            operation of inverters for UPS applications or micro-grid)

           Support of voltage profile and frequency in the EPS area where the DPGS is connected

           Support of the load by DPGS (UPS functionality)

    The equations are the basis of the droop control that is the most straightforward way of
    relating P,f and Q,V
Marco Liserre                                                                                      liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                    Droop control technique: inductive line
               Using short-line model and complex phasors, the analysis below is valid for
                both single-phase and balanced three-phase systems.
               At the section A       V         VV                              VA2        VV
                                   PA  A cos   A B cos              QA      sin   A B sin    
                                        Z         Z                               Z          Z
                        A I
                                Z        B
                                                                                  VA
                                                                             
                                                                       I    VB              XI     Vq
                VA 0                              VB                           RI

                                                                                          Vd

                                                                  RPA  XQA                               XPA  RQA
                                          Vd  VA  VB cos                          Vq  VB sin  
                                                                     VA                                      VA



               For a mainly inductive line   XPA                          XQA
                                                            VA  VB 
                                              VAVB                         VA


Marco Liserre                                                                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                Droop control technique: inductive line
        The angle δ can be controlled regulating the active power P whereas the inverter
         voltage VA is controllable through the reactive power Q.
        Control of the frequency dynamically controls the power angle and, thus, the real
         power flow.
        Thus by adjusting P and Q independently, frequency and amplitude of the grid
         voltage are determined

                V  V0  kq Q  Q0                        f  f0  k p  P  P 
                                                                                  0
                    V                                          f


                   V0                                         f0
                     V                                         f




                                Q1 Q     Q2Q                            P1   P0   P2 P
                                    0

        From another point of view to share the P and Q among several units working in
         parallel

Marco Liserre                                                                            liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




                Implementation of the droop characteristics




                   *  G p ( s )  ( P  P* )                Vc , Ic voltage and current of the converter

                V  V *  Gq ( s )  (Q  Q* )                  Ig grid current
                                                                Gp(s) , Gq(s) compensators transfer functions

Marco Liserre                                                                                          liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                        Droop control technique: RL line
        Distribution lines have a not negligible resistive nature, hence more complex formula
         have to be considered

        In case the aim is to control the active power injected by the DPGS and the reactive
         power exchanged with the grid the following equations can be used



                                                                    1
                                                             PC       E V  E  cos   EV    sin  
                                                                    Z                                    


                                                                    1
                                                             QG       E (V  E  sin   EV    cos  
                                                                    Z                                     


                                                    tan   X / R

        However they are dependent on the grid impedance nature


Marco Liserre                                                                                        liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                  Droop control technique: P/Q decoupling
       In order to remove from active and reactive powers the dependence of line impedance
        the following transformation is proposed:


                P '  PC sin   QG cos 

            Q '  P cos   QG sin 
                   C

           that leads to

                     EV
                P'     sin                In these formula active and reactive
                      Z                     powers are clearly related to the phase
                                            (frequency) and amplitude of the voltage
                     EV
                Q'     cos   E 2         how it was in the pure inductive case
                      Z

           hence the control laws can be formulated as

             Gp (s)  P  PC*  sin   QG  QG  cos  
                                                   *                         that express the reference
                        C                                                  amplitude and phase of the
                                                                             voltage produced by the DPGS
           V  V *  Gq (s)  P  P*  cos   QG  QG  sin  
                             C C
                                                  *    *
                                                                 
                                                                             to have the desired P and Q

Marco Liserre                                                                                 liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


            Implementation of the droop characteristics
                      with P Q decoupling




                      mi  m p s            Gq ( s )  n p
         G p ( s) 
                          s


Marco Liserre                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                               Stability and robustness analysis
       Using the small-signal analysis it is possible to check stability margin and robustness
        respect to parameter variation such as the grid inductance

                                                                                                     mi  mp s
     pmeas ( s)  2
     ˆ
                         o2
                                     
                                               ˆ                  ˆ
                                      E sin  v( s )  VE cos   ( s) 
                                                                          
                                                                                         ˆ
                                                                                         ( s)                 
                                                                                                                  E sin  v(s)  VE cos   ( s)
                                                                                                                           ˆ                ˆ       
                   s  2o s  o 2                  Z                  
                                                                                                        s

     qmeas ( s )  2
     ˆ
                         o2
                  s  2o s  o 2 
                                      E cos  v( s )  VE sin   ( s ) 
                                     
                                                ˆ
                                                       Z
                                                                  ˆ
                                                                         
                                                                                         v(s)  np  E cos v(s)  VE sin   (s)
                                                                                         ˆ                  ˆ                ˆ             
                                                                         




                                                              4                   1
                2 1     1
                                                         3                   2        1

                   2                                         5
                                                                                   2



   Root locus for 0.00002 < mp                          Root locus for 0.000002 < mi                               Root locus diagram for grid
     < 0.001 and mi=0.0002                               < 0.0018 and mp=0.00006                                 inductance variations: 8.5 mH
                                                                                                                        < Lg’< 5000 mH
Marco Liserre                                                                                                                       liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



    Voltage support provided by the DPGS at load level

                 Ig                Iload

                 Lg                                               Ig                   E                                    Ig                   E
                                                         Ic                                         VLg           Ic                                       VLg
    E                  Ic                        Vload                   Iload                                                     Iload         Vload
                                                                                       Vload
                                                
                                                              current-controlled converter in normal                   voltage-controlled converter in normal
                                                                            conditions                                               conditions
               CURRENT CONTROLLED
            grid-feeding component adjusting
             reactive power according to grid
                    voltage variations


                                                                                               Ig
                  Ig
                                   Iload

                                                                                                        E
                  Lg                                                                                                           VLg
     E                 Vc                        Vload
                                                                                                          Iload
                                                                                                                           Vload
                                                                                     Ic


              VOLTAGE CONTROLLED
               grid-supporting component
             controlling its output voltage in                                          compensation of a voltage dip of 0.15 pu
             order to stabilize load voltage



Marco Liserre                                                                                                                                 liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



    Voltage support provided by the DPGS at load level


                     Ig = 0
                                                 E                      In normal conditions the shunt controller
                                                               VLg       provides a current IC = Iload
                                    Iload = Ic
                                                       Vload
                                                                        In case of voltage dips it provides the
                                   normal conditions                     active power required by the load and it
                                                                         injects the reactive power needed to
                                                                         stabilize the load voltage
                Ig
                                                                        The amount of reactive         power is
                                                                         inversely proportional to      the grid
                                     E                 VLg               impedance
                                                       Vload
                                     Iload                              A large inductance will help in mitigating
                                                                         voltage sags although it is not
                              Ic                                         recommendable during normal operation



                compensation of a voltage dip of 0.15 pu


Marco Liserre                                                                                             liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




       PV system with shunt-connected multifunctional
                         converter


                Ig       Lg*                                  The voltage sags compensation
                                                 LOAD          requires a large-rated converter
                                         Iload
          E
                                                              However the PV shunt-connected
                                        Ic                     converter is already rated for
                               Vc’




                                                               supplying full power
                                                              An inductance Lg* of 0.1 pu is placed
                 PV                                            on the grid line (inductive line)
                array
                                                              It is possible to control the voltage
                                PV converter                   frequency and amplitude adjusting
                                                               active     and     reactive    power
                                                               independently.



Marco Liserre                                                                               liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




                             Multifunctional PV inverter




       The droop controller provides the reference for the voltage control

Marco Liserre                                                           liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




                                                                      Voltage control
                                                                               LOAD

                     E       Ig                                       Iload
                                                                                         The PV inverter is voltage controlled
                                                                                         The current injection is controlled
                                                         Ic                               indirectly
                                                                                         The voltage error is pre-processed by
                                                                                          the repetitive controller (the periodic
                                                                                          signal generator of the fundamental
          Vc’                                       Ic
                 -
                         Repetitive            +
                                                    -                                     component and of the selected
      Vref +              control
                                             Iref
                                                              PI
                                                                                          harmonics)
                                                                                         The PI controller improves           the
                                                                                          stability of the system
                                                                                         The voltage in the PCC is constant
                                                                                          and equal to the desired value
                                                                                         In presence of a voltage dip Ig is
                                                                                          forced to be phase-shifted by almost
                                    2   N 1              2                          90° with respect to the corresponding
                     FDFT  z        i 0   kNh cos  N h i  Na    z i
                                                                        
                                    N        
                                                                                          grid voltage
               the 3rd and the 5th harmonics are compensated
Marco Liserre                                                                                                          liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




                                  Simulation results: grid normal conditions

                      10
    current[A]




                       0

                      -10
                                                                                                     1800
                            0   0.5   1   1.5   2     2.5     3   3.5   4   4.5   5                                                             P
                                                                                                     1600
                                                    time[s]                                                                                     Q
                      10                                                                             1400

                                                                                                     1200
    current[A]




                       0




                                                                                      P[W], Q[Var]
                                                                                                     1000

                                                                                                      800
                      -10
                            0   0.5   1   1.5   2     2.5     3   3.5   4   4.5   5                   600
                                                    time[s]                                           400
                       2
         current[A]




                                                                                                      200
                       0
                                                                                                       0
                       -2
                                                                                                     -200
                                                                                                            0   1      2             3   4          5
                            0   0.5   1   1.5   2     2.5     3   3.5   4   4.5   5
                                                                                                                           time[s]
                                                    time[s]


                        inverter current Ic (top), load current Iload (middle),                      active and reactive power provided by the PV
                                                                                                           inverter
                        grid current Ig (bottom).



Marco Liserre                                                                                                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




                  Simulation results: voltage sag of 0.15 pu




                                                              active and reactive power provided by the PV
                                                                    inverter




                E = grid voltage             Ic = inverter
                     current
                Ig = grid current      Iload = load current


Marco Liserre                                                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                             Voltage harmonic mitigation

                                                                               Experimental results
                                                                               obtained in case of
                                                                               distorting load and without
                                                                               shunt converter: A grid
                                                                               voltage [300V/div], C load
                                                                               voltage [300V/div], 1 load
                                                                               current [10V/div].



   Experimental results in case of distorting load and shunt converter connected to the grid: A) grid
   voltage [300V/div], C) load voltage [300V/div], 1) load current [10V/div].




                                                             Without compensation (Black bar), with
                                                                   compensation (white bar)



Marco Liserre                                                                                     liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems




                 Experimental setup: Politecnico di Bari


                                                                      Isolation     AC power
         DC source       Grid Converter          Filter      Load   transformer Lg*  Source
                           1-ph VSI                                                 1 x 240 V

            DC
           power                                             LOAD
           supply
                                                    LC



                           PWM

                             acquisition
                             board and
                               control




Marco Liserre                                                                          liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



        Experimental results: voltage dip duration equal
                            to 1.5 s




                                                                                                  without droop control




                grid voltage E (top) : voltage dip of 0.15 pu, load voltage Vload (middle), grid current Ig
                      (bottom)


Marco Liserre                                                                                                 liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                Reactive power compensation at the PCC


                       upgrade for 600 kW WT systems using 300 kW back-to-back converter


                               High wind condition

                               High wind condition + reactive power compensation




                   reduction in mechanical stress

                   reactive power control without capacitor banks


Marco Liserre                                                                               liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



     Voltage support provided by the DPGS at EPS area
      The reactive power injection by grid-connected systems can enhance the voltage
      profile
      The goal is to reduce the active power supplied by the low-voltage feeder,
      injecting reactive power to support the voltage amplitude decreasing the current
      and as a consequence the losses
                                                                        without reactive   with reactive power
                                                                        power injection          injection
                                                                         grid   inverter   grid         inverter
                                                             f (Hz)     50      50         50       50
                                                             E (V)      228     228        228      230
                                                             P (kW)     24.5    0          21.3     0
                                                             Q (kVar)   n.a.    0          n.a.     16.5




Marco Liserre                                                                                     liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


  Power Quality Enhancement provided by the DPGS at
                      EPS area
          Active filter operation
          Only current is
           compensated
          The WTs are cleaning the
           line current




Marco Liserre                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems


                                           Conclusions
    Ancillary services are considered as those services that the DPGS can provide
     to the grid in order to behave more similarly to a traditional power plant
    However DPGS are connected at distribution network level, hence new
     problems and new possibilities arises
    Moreover DPGS are usually installed to meet demand of local loads hence
     they could be used to provide ancillary services also to the loads
    In general if the full power of the DPGS is managed by a PWM inverter, full
     control on active and reactive power and on the harmonics can be used to
     make DPGS contributing to the stabile and safe operation of the EPS area
     where it is connected and even to allow micro-grid operation
    Since all the ancillary services are connected to the management of the power
     flow in the grid hence the power flow theory and the consequent droop control
     are useful to guarantee the desired dynamic performances and robustness
     against grid impedance variation




Marco Liserre                                                             liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                                              References
   1.    IEEE 1547.3, IEEE Guide for Monitoring, Information Exchange, and Control of Distributed
         Resources Interconnected with Electric Power Systems, 2007
   2.    Tsai-Fu Wu, Hung Shou Nien, Hui-Ming Hsieh, Chih-Lung Shen “PV power Injection and Active
         Power Filtering with Amplitude-Clamping and Amplitude-Scaling Algorithms”, IEEE
         Transactions on Industry Applications, vol. 43, no. 3, May/June 2007.
   3.    Josep M. Guerrero, José Matas, Luis García de Vicuña, Miguel Castilla, Jaume Miret, “Wireless-
         Control Strategy for Parallel Operation of Distributed-Generation Inverters”, IEEE Transactions
         on Industrial Electronics , vol.53, no.5, Oct. 2006, pp. 1461-1470.
   4.    Josep M. Guerrero, José Matas, Luis García de Vicuña, Miguel Castilla, Jaume Miret,
         “Decentralized Control for Parallel Operation of Distributed Generation Inverters Using
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         2007, pp. 994-1004.
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         Power Electronics,vol.22, no.4,July 2007, pp.1107-1115.
   6.    P. Wang, N. Jenkins, M.H.J. Bollen, “Experimental investigation of voltage sag mitigation by an
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         October 1998.
   7.    P. Mattavelli, F. Pinhabel Marafao, “Repetitive-Based Control for Selective Harmonic
         Compensation in Active Power Filter”, IEEE Transactions on Industrial Electronics, vol. 51, no.
         5, October 2004, pp. 1018-1024.



Marco Liserre                                                                                liserre@ieee.org
Ancillary Services of Distributed Power Generation Systems



                                              References
   8.    R. A. Mastromauro, M. Liserre, T. Kerekes, A. Dell’Aquila, “A Voltage Controlled Grid
         Connected Photovoltaic System with Power Quality Conditioner Functionality”, accepted for
         publication on IEEE Transactions on Industrial Electronics, forthcoming issue.
   9.    M. Bollen, Understanding Power Quality Problems: Voltage Sags and Interruptions; Piscataway,
         NJ: IEEE Press, 1999.
   10.   M. Routimo; M. Salo; H. Tuusa; “Current sensorless control of a voltage-source active power
         filter”, Applied Power Electronics Conference and Exposition, 2005. APEC 2005. Twentieth
         Annual IEEE, vol.3, Iss., 6-10, March 2005 pp. 1696- 1702.
   11.   R. R. Sawant and M. C. Chandorkar, “Methods for multi-functional converter control in three-
         phase four-wire systems”, IET Power Electron., vol. 2 , no. 1, Jan. 2009, pp. 52-66.
   12.   S.-J. Lee, H. Kim, S.-K. Sul, F. Blaabjerg, “A novel control algorithm for static series
         compensator by use of PQR instantaneous power theory,” IEEE Trans. Ind. Electron., vol. 19,
         no. 3, May. 2004, pp.814-827.
   13.   J. M. Guerrero, L. García de Vicuña, J. Matas, M. Castilla, J. Miret, “Output impedance Design
         of Parallel-Connected UPS Inverters With Wireless Load-Sharing Control”, IEEE Trans. Ind.
         Electron., vol.52, no.4, Aug. 2005, pp. 1126-1135.
   14.   J. M. Guerrero, L. García de Vicuña, J. Matas, M. Castilla, Jaume Miret, “A Wireless Controller
         to Enhance Dynamic Performance of Parallel Inverters in Distributed Generation Systems,”
         IEEE Trans. Power Electron., vol. 19, no. 5, Sep. 2004, pp. 1205-1213.
   15.   J. C. Vasquez, R. A. Mastromauro, J. M. Guerrero, M. Liserre, “Voltage Support Provided by a
         Droop-Controlled Multifunctional inverter”, accepted to be published on IEEE Transactions on
         Industrial Electronics, forthcoming issue.
   16.   C.-C. Shen and C.-N. Lu, “A voltage sag index compatibility between equipment and supply”,
         IEEE Trans. On Power Delivery, vol. 22, no. 2, April 2007, pp. 996-1002.

Marco Liserre                                                                                liserre@ieee.org

								
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