22 - 24 September 2010
Lyngby - Denmark




     EES-UETP Electric   Vehicle Integration into Modern Power Networks




  ...
Introduction


Large scale deployment of EV

• Steady-state impacts related with
voltage drops and branch overloads

Grid ...
Introduction


• Renewable energies need to increase their
penetration in the generation mix in order to
reduce CO2 emissi...
The MERGE control concept


•   A two level hierarchical control approach needs to be adopted:

     • Local control house...
EV Voltage / Frequency support modes



                                  Local Control


              Voltage Control


...
Conceptual Framework For EV Integration


• EV must be an active element
within the power system

• The Upper Level contro...
Delivery of Primary Reserve / Local Frequency Control
Methodology
   Primary domain of application: Islanded grids (island...
Primary Reserve
EV Electronic Grid Interface Modelling

•   For frequency control the envisioned
    response from EVs is ...
Primary Reserve
EV Electronic Grid Interface Modelling
     
                                                             ...
Primary Reserve
Evaluation of the performance of grid

   Case Study: small island normally fed from Diesel generation
Primary Reserve
Scenarios characterization
                                                                      Scenario ...
Primary Reserve
Scenarios characterization
•   Sudden shortfall on wind speed may jeopardize current power quality
    sta...
Primary Reserve
Grid Modelling

•   A single bus model of the system was
    developed using Matlab/Simulink:
      Wind ...
Primary Reserve
Results – Scenario 1
                              50.5                                                   ...
Primary Reserve
Results – Scenario 2
                              50.5                                                   ...
Primary Reserve
Conclusions
•   It is possible to verify that system dynamic performance was improved dramatically
    whe...
Implementation of EV Grid Interfaces

 Power Electronic Converter:
 The “Black Box” interface between the Low Voltage Grid...
Implementation of EV Grid Interfaces
POWER CONVERTER – SINGLE & THREE PHASE TOPOLOGIES

Three-Phase, Three-level, Bidirect...
EV Grid Interfaces

 Low Level Control:
 Closed loop control which outputs high frequency signals for each switch

 Three‐...
EV Grid Interfaces

   High Level Control: outputs the battery charging current reference for the Low
   Level Control
Cha...
EV Grid Interfaces

  Droop Control: outputs the droop charging current reference to the Charge
  Control
  Reacts to Volt...
Secondary frequency control


•   Load variations or changes in generation output (namely from variable
    generation uni...
Secondary Reserve
AGC operation with EV
• Modification of the active power set-points of generators and EV

• Some modific...
Secondary Reserve
Evaluating the Contribution of EV for Secondary Frequency Control



• Definition of a case-study: Portu...
Secondary Reserve
Case-Study – Definition
                                                                           12


...
Secondary Reserve
Case-Study – Definition

  • Example of a windy day in the Portuguese system in the Autumn of 2009
Secondary Reserve
Case-Study – Dynamic Modeling
• Transmission system with 2 control areas (Portugal and Spain)

• 5 tie l...
Secondary Reserve
Case-Study – Disturbance and Scenario Definition
     Winter valley period (6 a.M.)
                    ...
Secondary Reserve
Results – Interconnection active Power Flow
                    1000
                                   ...
Secondary Reserve
Results – Used Reserve Levels
               Reserve Used Without EV Participating in Secondary Control
...
Secondary Reserve
Results – Frequency Evolution

                                                             With partici...
Secondary Reserve
Results – Electrical Current in the Line 16-18
             0.75
                                       ...
Secondary Reserve
Results – Electrical Current in the Line 20-21
               1
                                        ...
Secondary Reserve
Results – Area Control Error for Portugal
            3000
                                             ...
Secondary Reserve
Conclusions
• Three main conclusions that can be drawn from these studies:

     1.   Improvement of the...
Final Conclusions


• A specific EV grid interface needs to be adopted in order to allow EV to participate
in the provisio...
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J. A. P. Lopes, "Smart EV grid interfaces responding to frequency variations to maximize renewable energy integration," in Electric Vehicle Integration into Modern Power Networks, DTU, Copenhagen, 2010

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J. A. P. Lopes, "Smart EV grid interfaces responding to frequency variations to maximize renewable energy integration," in Electric Vehicle Integration into Modern Power Networks, DTU, Copenhagen, 2010

  1. 1. 22 - 24 September 2010 Lyngby - Denmark EES-UETP Electric Vehicle Integration into Modern Power Networks Smart EV grid interfaces responding to frequency variations to maximize renewable energy integration João A. Peças Lopes INESC Porto / FEUP (jpl@fe.up.pt)
  2. 2. Introduction Large scale deployment of EV • Steady-state impacts related with voltage drops and branch overloads Grid restrictions may limit the growth of EV penetration, if no additional measures are adopted. Solution: Active management of EV batteries • Dynamic issues  EV participating in primary frequency control  EV participating in AGC (secondary frequency control) o
  3. 3. Introduction • Renewable energies need to increase their penetration in the generation mix in order to reduce CO2 emissions • There are renewable power sources characterized by some variability • In isolated Grids if EVs participate in primary frequency control, major benefits to the integration of RES in large scale are expected • When parked and plugged-in, EVs will either absorb energy (and store it) or provide electricity to the grid when (the V2G concept). • Existing EV grid interfaces are passive devices that do not allow the required flexibility
  4. 4. The MERGE control concept • A two level hierarchical control approach needs to be adopted: • Local control housed at the EV grid interface, responding locally to grid frequency changes and voltage drops; • Upper control level designed to deal with: • “short-term programmed” charging to deal with branch congestion, voltage drops • Delivery of reserves (secondary frequency control); • Adjustments in charging acoording to the availability of power resources (renewable sources).
  5. 5. EV Voltage / Frequency support modes Local Control Voltage Control Coordinated Control Primary Control (local control) Frequency Control Secondary Control
  6. 6. Conceptual Framework For EV Integration • EV must be an active element within the power system • The Upper Level control requires interactions with: • An Aggregating entity to allow:  Reserve management Electricity Market Operators  Market negotiation
  7. 7. Delivery of Primary Reserve / Local Frequency Control Methodology Primary domain of application: Islanded grids (islands or networks operated in islanding conditions) 1. An isolated system has been characterized in terms of available generation and load. These components were modeled connected to a single bus system, where the several types of generation are then modeled individually together with the load. 2. A sudden change on wind power generation was simulated in order to assess its impact on the system’s frequency. Several scenarios were created for this purpose. 3. EV penetration was then characterized and the model for EV connections, featuring V2G, has been developed. This model was included in the single bus system and, finally, its effects on the system’s dynamic behaviour were evaluated running simulations in the same conditions as defined in 2.
  8. 8. Primary Reserve EV Electronic Grid Interface Modelling • For frequency control the envisioned response from EVs is shown in the figure: P  When facing frequency deviations Pmax EVs may slow down/speed up their charging or even inject active power into the grid  A dead band for battery premature exhaustion prevention is required EV consumption  Prated MW/Hz proportional gain f controls the reaction to frequency deviations Dead Band Pmin PInjection PConsumption Droop control for EVs V2G mode
  9. 9. Primary Reserve EV Electronic Grid Interface Modelling   • A PQ inverter control logic was adopted • Set-points for active power controlled by a proportional gain that reacts to frequency deviations v,i v,i v  v  k( iref i ) * iact ireact P, Q 1   TQ s  1 Control loop for EVs active power set-point  PQ inverter control system
  10. 10. Primary Reserve Evaluation of the performance of grid Case Study: small island normally fed from Diesel generation
  11. 11. Primary Reserve Scenarios characterization Scenario 1 Scenario 2 PDiesel1,2 (kW) 1500 1500 • Isolated system composed by:  4 diesel units PDiesel3,4 (kW) 1800 1800  2 wind turbines (1 more for scenario PWind (kW) 1320 1980 2) PPV (kW) 100 100  Mild PV penetration  Load ranging from 1770kW to Installed power 4200kW Scenario 1 Scenario 2 • Vehicles: PTotal load (kW) 2172 2172  1 vehicle per household Pload (kW) 1770 1770  2150 vehicles  323 (15%) EVs PEV load (kW) 402 402  3 EV types: PEV available (kW) 851 851 o 1xPHEV: 1.5kW o 2xEVs: 3kW and 6kW Pwind (kW) 900 1272 o Charging time: 4h Psync1 (kW) 636 450 Psync2 (kW) 636 450 Valley hour operation (load plus generation dispatch)
  12. 12. Primary Reserve Scenarios characterization • Sudden shortfall on wind speed may jeopardize current power quality standards under EN 50.160 for isolated systems • Large frequency excursions due to wind power changes become a limiting factor to the integration of Intermittent Renewable Energy Sources like wind power) 10 9 Wind Speed (m/s) 8 7 6 5 0 1 2 3 4 Time (s) Disturbance applied to the case study
  13. 13. Primary Reserve Grid Modelling • A single bus model of the system was developed using Matlab/Simulink:  Wind speed suffers time domain changes  Electrical component and their links in a steady state frequency domain model • To each generation a dynamic model was assigned:  diesel generator  4th order model, with frequency regulation performed through conventional proportional and integral control loops  Wind generator  simple induction machine Isolated system single-line diagram
  14. 14. Primary Reserve Results – Scenario 1 50.5 3 2.5 System Frequency (Hz) 50 PDiesel (MW) 2 1.5 49.5 1 49 0.5 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Time (s) Time (s) PW = 1.3 MW; EV - charge mode PW = 1.3 MW; EV - freq. control 1.5 0.1 0 1 -0.1 PWind (MW) 0.5 PEV (MW) -0.2 -0.3 0 -0.4 -0.5 -0.5 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Time (s) Time (s)
  15. 15. Primary Reserve Results – Scenario 2 50.5 3 2.5 System Frequency (Hz) 50 PDiesel (MW) 2 1.5 49.5 1 49 0.5 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Time (s) Time (s) PW = 2.0 MW; EV - charge mode PW = 2.0 MW; EV - freq. control 1.5 0.1 0 1 -0.1 PWind (MW) 0.5 PEV (MW) -0.2 -0.3 0 -0.4 -0.5 -0.5 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Time (s) Time (s)
  16. 16. Primary Reserve Conclusions • It is possible to verify that system dynamic performance was improved dramatically when EVs are participating in frequency control • Further sensitivity analysis is still needed to identify the best control parameters for the droop control mode of the electronic grid interface used by the EVs 50.3 PW = 1.3 MW; EV - charge mode 50.2 PW = 1.3 MW; EV - freq. control System Frequency (Hz) 50.1 PW = 2.0 MW; EV - freq. control 50 49.9 49.8 49.7 49.6 49.5 49.4 49.3 0 1 2 3 4 5 6 7 8 9 10 Time (s) • The presence of a considerable amount of storage capability connected at the distribution level also allows the operation of isolated distribution grids with large amounts of IRES and/or microgeneration units connected to it
  17. 17. Implementation of EV Grid Interfaces Power Electronic Converter: The “Black Box” interface between the Low Voltage Grid (AC) and EV Battery (DC) Design Requirements Converter Functions Three-Phase Three Leg Grid physical ⁄ v ► Converter connection Single-Phase Two Leg Converter Battery charge AC/DC conversion Rectifier + ⁄ + ► + V2G capability DC/AC conversion Inverter Grid “clean” interface Low harmonic content Controlled Three ⁄ ► Level Converter Small displacement factor 17
  18. 18. Implementation of EV Grid Interfaces POWER CONVERTER – SINGLE & THREE PHASE TOPOLOGIES Three-Phase, Three-level, Bidirectional Converter: Power Matrix Convert of switches er Time Variant Power Non-linear Convert System er 18
  19. 19. EV Grid Interfaces Low Level Control: Closed loop control which outputs high frequency signals for each switch Three‐Phase currents control : Sliding‐Mode Vectorial Control ‐ Nearly sinusoidal phase currents = Low harmonic distortion ‐ Currents in phase with voltages =  Small displacement factor ‐ Static and dynamic phase current following ‐ Capacitor voltage equalization ‐ Robustness = immunity to disturbances Grid/Battery charging current control: Proportional‐Integral external loop ‐ “Current source” converter behaviour ‐ Dynamic current following and near to zero static error High Level Control: Defines a current reference to Low Level Control Charge Control  Grid/battery requirements: charging current, end of charge, Minimum and  maximum SOC levels … Droop‐control  Grid frequency or voltage control: set‐point, dead‐band and slope 19
  20. 20. EV Grid Interfaces High Level Control: outputs the battery charging current reference for the Low Level Control Charge Control: provides the charging current reference within the battery constraints 20
  21. 21. EV Grid Interfaces Droop Control: outputs the droop charging current reference to the Charge Control Reacts to Voltage and Frequency local deviations according to respective droop functions Central control units establish and communicate droop defining parameters Charging Current Reference = output of Frequency Droop or Voltage Droop within Battery Charge Constraints 21
  22. 22. Secondary frequency control • Load variations or changes in generation output (namely from variable generation units) provoke load / generation imbalances that lead to: 1. frequency changes and 2. inter-area power unbalances regarding scheduled power flows • EV battery charging can be considered as very flexible loads, capable of providing fast reserves (through the aggregators) • An increased robustness of operation can be achieved • The reserve levels can be reduced (depending on the hour of the day, taking into account that the number of grid plugged vehicles) 22
  23. 23. Secondary Reserve AGC operation with EV • Modification of the active power set-points of generators and EV • Some modifications need to be introduced in conventional AGC systems:  redefinition of the partipation factors and  introduction of an additional block to communicate with EV aggregators • These control functionalities to be provided by EV are intended to keep the scheduled system frequency and established interchange with other areas within ini predefined limits, enabling further deployment of IRES Pe 1 + fp1 + Pref1 fi fi + B fpm + Prefm - + fREF Pe ini + ACE m -KI/s + Pif1 + - ini Pa 1 + m k - + + -  Pe i 1 ini i   Pa ini i 1 i fpA1 + Prefa1 Pifn Aggregators PifREF fpAk + Prefak - ini Pa k
  24. 24. Secondary Reserve Evaluating the Contribution of EV for Secondary Frequency Control • Definition of a case-study: Portugal /Spain (European interconnected system)  Grid selection  Modeling • Setting up a contingency / disturbance • Evaluating the system dynamic performance:  Without the participation of EV  With the participation of EV
  25. 25. Secondary Reserve Case-Study – Definition 12 10 • Portuguese transmission/generation 8 % of EV Cha rging network, including existing tie lines with 6 Spain (equivalent) 4 • Technical constraints  Portugal will 2 not export more than 1500 MW or 0 1 5 9 13 17 21 import more than 1400 MW Hours Percentage of EV charging during a typical day, under a smart charging strategy (EV  30% of total fleet) Installed capacity • 30% EV penetration  20% PHEV  1.5 kW  40% EV1  3 kW  40% EV2  6 kW • EV load was following a smart charging scheme
  26. 26. Secondary Reserve Case-Study – Definition • Example of a windy day in the Portuguese system in the Autumn of 2009
  27. 27. Secondary Reserve Case-Study – Dynamic Modeling • Transmission system with 2 control areas (Portugal and Spain) • 5 tie lines interconnecting areas 1 and 2 at 400 kV • Generator equivalents per technology at each substation node:  Conventional generator  4th order model synchronous machine o Thermal units  simple governor and a three stage thermal turbine with reheat o Hydro units  governor with transient droop compensation and a typical hydro turbine o IEEE type 1 voltage regulator was used  Wind generators  3rd order model squirrel cage simple induction machine o undervoltage relay setting  0.9 p.u. • Voltage levels: 150 kV, 220 kV and 400 kV • One AGC per area Proportional Control 1 R Cvopen Pmecmax Pe - - Synchronous + Governor Turbine + Pref Pmec Generator (AGC signal) Cvclose 0
  28. 28. Secondary Reserve Case-Study – Disturbance and Scenario Definition Winter valley period (6 a.M.) Simplified Portuguese Transmission C1 Network Control Area 1 Control Area 2 C15 C16 C17 H W11 ~ C2 H ~ T ~ N ~ W2 H ~ W1 C7 H 1 2 ~ W6 11 10 150 kV 400 kV C5 C6 17 12 ~ W4 ~ W5 H H 13 400 kV 220 kV 14 15 220 kV 400 kV 16 4 3 C8 H ~ W7 ~ ~ W3 C3 C4 H TG 220 kV 400 kV 18 6 5 C9 22 220 kV TG ~ W8 150 kV C11 23 TC ~ 19 ~ 8 220 kV W9 150 kV C10 400 kV 400 kV 20 21 H 7 • Event  300 ms fault at line 15-16 C12 TC C13 TC C14 H ~ ~ W10 ~ • Impact of EV in the AGC operation: 1. EV are not used for AGC 24 25 9 operation Equivalent Generator Types ~ C(TC): Conventional Fuel or Coal ~ C(TG): Conventional Gas ~ C(H): Conventional Hydro 2. EV are obtaining active power ~ N: Conventional Nuclear W: Wind set-points from the AGC, through the aggregation units
  29. 29. Secondary Reserve Results – Interconnection active Power Flow 1000 With participation of EV Without participation of EV 500 0 -500 (MW) -1000 interconnection -1500 P -2000 -2500 -3000 -3500 0 100 200 300 400 500 600 700 800 900 Time (s)
  30. 30. Secondary Reserve Results – Used Reserve Levels Reserve Used Without EV Participating in Secondary Control Used Reserve (MW) Reserve (MW) t=2min t=15min Hydro 461 461 461 Thermal 590 211 256 EV 0 0 0 Total 1049 672 717 Reserve Used With EV Participating in Secondary Control Used Reserve (MW) Reserve (MW) t=2min t=15min Hydro 461 192 316 Thermal 590 31 74 EV 581 581 581 Total 1630 804 971
  31. 31. Secondary Reserve Results – Frequency Evolution With participation of EV 50.2 Without participation EV 50.1 Frequency (Hz) 50 49.9 49.8 49.7 -10 -5 0 5 10 15 20 25 30 Time (s)
  32. 32. Secondary Reserve Results – Electrical Current in the Line 16-18 0.75 With participation of EV Without participation of EV 0.7 0.65 0.6 (p.u.) 0.55 16-18 0.5 I 0.45 0.4 0.35 0 20 40 60 80 100 120 Time (s)
  33. 33. Secondary Reserve Results – Electrical Current in the Line 20-21 1 With participation of EV Without participation of EV 0.95 0.9 0.85 (p.u.) 0.8 20-21 I 0.75 0.7 0.65 0 20 40 60 80 100 120 Time (s)
  34. 34. Secondary Reserve Results – Area Control Error for Portugal 3000 With participation of EV Without participation of EV 2000 1000 ACE (MW) 0 -1000 -2000 -3000 0 100 200 300 400 500 600 700 800 900 Time (s)
  35. 35. Secondary Reserve Conclusions • Three main conclusions that can be drawn from these studies: 1. Improvement of the system robustness of operation 2. Increase of the system reserve levels that can be effectively mobilized for secondary control use 3. Increase safe integration of renewable power sources in the system • Fast reaction of EV + communication + control architecture = fast and effective AGC operation • When EV are participating in secondary frequency control, further integration of IRES in interconnected grids is possible • Additional economical and environmental benefits are expected from the adoption of EV smart control strategies, mainly due to avoided start-up of expensive and highly pollutant generation units that compose the tertiary control • As a counterpart EV owners must be properly remunerated when participating in the provision of this type of ancillary services in order to make this concept efficient and with sufficient adherence
  36. 36. Final Conclusions • A specific EV grid interface needs to be adopted in order to allow EV to participate in the provision of ancillary reserve services; • This on board device can be integrated with the EV battery management system • The adoption of such control approach allows increased dynamic robustness of operation to the system • Large penetration levels of renewable variable power generation are feasible, specially in isolated grids. .

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