Voltage Control in Power Systems: Preliminary Results T. Geyer, G. Ferrari-Trecate, T. Geyer, G. Ferrari-Trecate, M. Morari Automatic Control Laboratory Swiss Federal Institute of Technology (ETH) in collaboration with Mats Larsson ABB
Power system: overview Generator 1: infinite bus Generator 2: generates limited power Capacitor bank: stabilizes power system Transformer: steps down voltage controls load voltage Load: consumes power Network: connects components
Power system: overview (ctd.) hybrid system: discrete manipulated variables logic and finite state machine nonlinearities pwa functions 3 major submodels: generator 2 transformer load
Hybrid model dimensions: 2 ordinary diff. equations 1 finite state machine 29 algebraic equations: 11 linear, 18 nonlinear 6 states: 2 continuous, 4 discrete 4 manipulated variables: 1 continuous, 3 discrete model available: in modelica as pwa discrete-time approx. in MLD form and ?
control objectives: stabilizeV 4m (cont.) min. load shedding s L (disc.) manipulated variables: ultc voltage reference: V 4m,ref (cont.) capacitor switching: s C (disc.) load shedding: s L (disc.) disturbance: line outage (disc.) Control problem
Optimal Control Problem Subject to Dynamics (in MLD form): Soft constraints on bus voltages :
Receding Horizon Control Optimize at time t (with new measurements) Only apply the first optimal move u(t) Repeat the whole optimization at time t +1 Advantage of on-line optimization: Feedback!
Tuning of Cost Function Violation of soft constraints is penalized by: Choose weight R on u such that: No constraint violation:nominal control: > ultc voltage reference > capacitor bank Constraint violation:emergency control: > all controls including load-shedding
Preliminary Results
Conclusions Control problem: MPC is able to stabilize the load voltage V 4m with N=2 and T s =15sec without using load-shedding solution time 8sec..2min (PC with 1GHz) but: there remains a control error Outlook: observer model reduction reachability analysis large-scale problem