Look ahead dynamic security-constrained economic dispatch considering frequency stability and smart loads

Abstract

Conventional economic dispatch models aim to determine the optimal production of generation units under the steady state operation constraints. Due to the growing integration of low inertia power generation technologies (e.g. wind, solar, etc.), considering stability constraints, in particular, frequency stability, a theme of this work, becomes a crucial need in nowadays security-constrained economic dispatch (SCED) programs. This paper develops a new look ahead dynamic (i.e. multi-period) security-constrained economic dispatch model, further considering frequency stability constraints (DSCED-FSC). The aim of the DSCED-FSC is to optimize the cost of power generation subject to operation and frequency stability constraints under normal and contingency conditions. The proposed DSCED-FSC secures N-1 contingencies for both thermal limits and frequency stability. The system frequency response is included in DSCED-FSC model by linearizing the discretized rotor angle swing equation. The dynamic models of governors and load damping are considered in the discretized system frequency response. The safety of system frequency response under generation outages is provided by activating generators' governors, inertial response and load damping as the primary frequency reserve. In addition to primary frequency reserve, the demand elasticity of smart motor loads is utilized to avoid the activation of under frequency load shedding (UFLS) relays under severe generation outages. The proposed DSCED-FSC model is formulated as a mixed integer linear programming (MILP) problem. The nonlinear AC power flow equations are linearized using Taylor series expansions and piecewise linear (PWL) approximation techniques. The efficacy of the proposed DSCED-FSC model in supporting system frequency is investigated using the IEEE 118-bus test system.