CIRED 2003 Beta session 4 a Distributed Generation

CIRED’ 2003 Beta session 4 a: Distributed Generation Controllability of DG helps managing Distribution Grids J. A. Peças Lopes (jpl@fe. up. pt) Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Exploiting DG to improve system operation • DG has been considered as non controllable and non dispatchable, since all the energy production has priority to be absorbed by the network; • The increase in DG foreseen for the next years will require a different approach regarding the way how DG units will be operated: – Concepts of controllability should be developed and exploited: • Participation in reactive power control; • Interruptability; • Delivery of ancillary services (primary and secondary reserves, according to the conversion technology and primary energy sources); • Participation in system restoration strategies; – Development of concepts related with control of clusters of DG and virtual power stations; Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Main characteristics of DG units and controlability concepts • Three main types of energy conversion systems can be found among DG units: – Conventional synchronous machines (cogeneration, CHP, mini -hydro); – Asynchronous generators (wind power, mini-hydro); – AC/DC/AC electronic conversion systems used together with synchronous or induction machines (micro-turbines, fuel cells, wind generators). • Classification (according to primary energy source and conversion system used): – Non- controllable (Ex: Wind park with asynchronous stall generators); – Partially controllable (Ex: Wind park with synchronous variable speed gen. and AC/DC/AC converters); – Controllable (Ex: Mini-hydro or Cogeneration plant with synchronous units). Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation DG units used to optimise the distribution system operation • DG can be used to optimise the operation strategy of distribution networks. The Problem can be formulated an optimisation problem: Min (active power losses) Subj. to: Vmax < Vi < Vmin Sij max < Sij Qgmaxi< Qgi < Qgmini taking into account the type of generator Qimpor max < Qimpor Transformer tap limits are kept Control variables: Qg, capacitor banks and transformer taps The need to use a motor of optimisation (Evolutionary Particle Swarm Optimisation – EPSO) Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Some results of the participation of DG in Voltage VAR control • Test System: 60 k. V distribution network with a large penetration of DG (mini-hydro and wind generation). Activate control on reactive power generated in the DG Units. Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Some results of the participation of DG in Voltage VAR control • Changes in active Losses – Peak load scenario – A clear reduction on actives losses was obtained Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Some results of the participation of DG in Voltage VAR control • Results concerning voltage in network busses Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Dynamic Impacts • Dynamic behaviour impacts need to be addressed using adequate DG modelling and DG equivalent representation: – Considering disturbances resulting from DG operation; – Considering disturbances in distribution networks; – Considering disturbances in the transmission system Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Dynamic behavior analysis • Scenario: Week peak with maximum dispersed generation • Disturbance: Outage of Power Plant H: 7, 346 MVA, production of 6, 692+j 3, 03 MVA, injection of 2, 678+j 1, 081 MVA (tg j = 0, 404) • Voltage profile: • 60 k. V bus at the substation Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Dynamic behavior analysis 15 k. V bus of the feeder where the power plant was connected 15 k. V bus of the feeder where the power plant was not connected Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Dynamic behavior analysis (Impact in the other generators) Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Relay coordination • • Under voltage relay coordination is needed; Energy conversion systems need to able to withstand low voltages during short-circuits up-stream. Frequency changes Changes in contractual inter-area power flows Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Impacts on Operation • • • Load flows become bi-directional; Voltage profiles have different patterns; Losses change as a function of the production and load levels; Congestion in system branches is a function of the production and load levels; Short-circuit levels increase; Power quality may be affected; Voltage transients will appear as a result of connection disconnection of generators; Risk of islanding operation; Reliability may be reduced; System dynamic behavior may be largely affected; Protections coordination is needed; Barcelona– May 2003

CIRED’ 2003 Beta session 4 a: Distributed Generation Conclusions • The future: – DG units should be more actively used to help in the management of the distribution grid; – New DMS tools need to be developed: • • Topology processor with capabilities of identification of energised areas; Voltage and reactive power control; Load and current forecasting; Load flow including new generator models and load allocation algorithms to allow load flow to run; • Optimum network reconfiguration; • State estimation (considering that some DG units will not be monitored and new pseudo-measures need to be defined); – Cluster control strategies should be implemented, involving the development of local dispatch centres; – Development of DMS training simulators for distribution grids with large amounts of DG (steady state and dynamic behaviour). Barcelona– May 2003