With the increase in wind power integration in power systems, wind power uncertainty can no longer be neglected in the determination of the day-ahead power generation schedules. Aiming to achieve the best economy of power generation of the system, this study proposes a unit commitment (UC) optimal model for thermal plants, considering the fuel costs required for compensating for the wind power below schedule. The AC power flow equations are included as constraints based on the second-order cone programming (SOCP) method. SOCP is further improved here by considering line loss as constraint to guarantee the validity of its solution. Research shows that generators with lower minimum-output and fuel-cost rates are preferred to be online and that reasonable wind curtailment is beneficial for reducing the generation cost. Finally, AC power flow verification is carried out and the results suggest that the improved SOCP method could model the AC power flow equations correctly. The proposed methodology can be effective in making UC decisions for power grids with high wind power penetration.
High voltage AC (HVAC) transmission system is preferred to be used in off-shore wind power plant which is located within 40km from the seashore. Capacitance of HVAC cables is naturally higher than that of overhead lines, and it should be properly compensated. P model of three-core XLPE cable which is widely used in off-shore wind power plant was applied in the paper. Based on this model, impacts of reactive power compensation on HVAC transmission system, including capacity and location of compensation equipment, were analyzed and simulated then. Research showed that inductive compensation at off-shore side of the cable is more effective to decrease power loss along the cable and increase its transmission capacity than that at onshore side, while the latter is more appropriate to improve the power factor at onshore access point of the wind power plant to grid. Compensation capacity was optimized to realize the best economy with designated certain parameters of HVAC system by Sequential Quadratic Programming (SQP) method. Finally by SQP costs of 35kV and 220kV HVAC transmission system were compared, critical distance and transmission capacity of these two systems adoption were found. These results can be a reference of HVAC transmission system design of off-shore wind power plant.
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