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The reserve scheduling is important for integrated energy systems to cope with sudden disturbances such as fluctuations of renewable energy. The existing reserve scheduling approaches for integrated energy systems need iterations of calculation to guarantee the feasibility of the gas-fired units’ reserve, leading to problem of high computational burden. In this paper, a two-layer optimization model is proposed to set the boundary of the gas-fired units’ power and reserve, so that the scheduling result can meet the gas network constraints. The proposed two-layer optimization framework can avoid repeated loop iterations, resulting in low computational complexity. Testing results verify the effectiveness of the proposed method.

Due to the capacity of thermal storage, electric water heater (EWH) is one of the best candidates for demand response programs. However, few attentions are given to the modeling and optimization of EWHs with thermostatically-controlled automatic water mixer (TCAWM). In this paper, differential thermodynamic model is established for EWHs with TCAWM and a piecewise linear approximation method is performed for the nonlinear thermodynamic model. The multi-objective optimization model is established by introducing an index reflecting the comfort degree of users, so that the optimal energy usage of the EWH can be obtained by mixed integer linear programming. Testing examples verify the effectiveness of the proposed method.

As a kind of important demand side resource, the thermostatically controlled loads (TCLs) play an important role in the peak load shifting and load balancing programs. This paper establishes a state-queuing (SQ) model for the large-scale TCLs, and estimates the system states based on the Kalman-filtering. Based on state estimation, the control strategy, whose parameters are optimized by the genetic algorithm (GA), is designed to damp the power fluctuation of the TCLs. Finally, the effectiveness of the proposed method is verified.

With the development of the energy internet, the integrated energy system that takes the power system as the main body and integrates heat energy, natural gas and other energy forms has gradually become a new situation of energy utilization. In view of the uncertainty of wind power and load, an integrated electricity and natural-gas energy system scheduling model considering multi-energy storage systems was established in this paper. Finally, testing results verify the effectiveness of the proposed method.

This paper proposed the drawback of Doubly Fed Induction Generator (DFIG) during voltage drops. Since the stator winding of DFIG is directly connected to the grid, DFIG is sensitive to the grid fault, especially to voltage drops. With the increasing capacity of wind turbines, the wind turbines need to meet the certain ability to across low voltage. The research of dynamic behavior based on DFIG during voltage drops is important to provide the evidence to protecting circuit. Due to the electromagnetic transient process of DFIG, this paper analyzed the analytical expressions of stator current? rotor current and the dc bus voltage both in symmetrical short-circuit and asymmetric short-circuit. The simulation results in PSCAD/EMTDC proved the correctness of the theoretical expression.

This paper proposes a low-voltage ride-through (LVRT) protection scheme without fault current limiter (FCL) on the grid-side inverter (GSI), based on energy balance characteristics of permanent magnet synchronous generator (PMSG) wind power systems during the grid voltage drop. The scheme utilizes a series dynamic braking resistor (SDBR) to consume the excess active power from the PMSG transmitting to the grid during the voltage drop. A detailed design procedure and control strategy for the SDBR is presented. The theoretical analysis and the PSCAD/EMTDC simulation results prove that the proposed protection scheme can boost GSI voltage, limit GSI over-current, stabilize DC-link voltage, guarantee the safe and stable operation of the converters, and then improve LVRT capability of PMSG wind power system.