Abstract
The secure operation of 110-kV networks should be considered in the optimal generation dispatch of regional power grids in large central cities. However, since 110-kV lines do not satisfy the premise of R << X in the direct current power flow (DCPF) model, the DCPF, which is mostly applied in the security-constrained unit commitment (SCUC) problem of high-voltage power grids, is no longer suitable for describing the active power flow of regional power grids in large central cities. Hence, the quadratic active power flow (QAPF) model considering the resistance of lines is proposed to describe the network security constraints, and an SCUC model for power system with 110-kV network and pumped-storage hydro (PSH) units is established. The analytical expressions of the spinning reserve (SR) capacity of PSH units are given considering different operational modes, and the SR capacity of PSH units is included in the constraint of the SR capacity requirement of the system. The QAPF is a set of quadratic equality constraints, making the SCUC model a mixed-integer nonlinear non-convex programming (MINNP) model. To reduce the computational complexity of solving the model when applied in actual large-scale regional networks, the QAPF model is relaxed by its convex hull, and the SCUC model is transformed into a mixed-integer convex programming (MICP) model, which can be solved to obtain the global optimal solution efficiently and reliably by the mature commercial solver GUROBI (24.3.3, GAMS Development Corporation, Guangzhou, China). Test results on the IEEE-9 bus system, the PEGASE 89 bus system and the Shenzhen city power grid including the 110-kV network demonstrate that the relaxed QAPF model has good calculation accuracy and efficiency, and it is suitable for solving the SCUC problem in large-scale regional networks.
Highlights
security-constrained unit commitment (SCUC) is an optimization problem in power grids to determine the generator units’ on-off states and power output within a certain dispatch period while minimizing the total operation cost
The quadratic active power flow (QAPF) model is relaxed by its convex hull, which transforms a quadratic equality into two convex inequality constraints
It can be noticed that some of the relative deviation of the active power of lines computed by the direct current power flow (DCPF) model is greater than 20%, whereas the maximum relative deviation of the active power of lines computed by the QAPF model is less than 5%, which is more accurate
Summary
SCUC is an optimization problem in power grids to determine the generator units’ on-off states and power output within a certain dispatch period while minimizing the total operation cost. With load demand increasing rapidly and the scale of grids expanding quickly, the regional grids in metropolises are becoming complicated Since these grids are mainly composed of 110-kV networks, the secure operation of 110-kV networks should be considered when optimizing the generation dispatch scheduling of these regional grids. Benders decomposition is applied to deal with the SCUC problem with ACPF constraints considering wind power uncertainty, computational efficiency may decrease significantly as the scale of the network expands [11,12,13,14]. The contribution of PSH units should be considered in the scheduling of day-ahead generation dispatch in large-scale regional grids.
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