Utilizing the flexibility provided by the thermal system components, for example, pipelines in the district heating network (DHN), building envelopes as well as thermal energy storage (TES) devices, can be an effective way for power system to solve the wind curtailment problem which closely relates to the limited flexibility of combined heat and power (CHP). However, almost all the previous studies ignored heat transfer (HT) constraints when modelling these abovementioned thermal system components. HT constraint is one of the most important constraints in thermal system analysis, without considering it may result in infeasibility for the dispatch results. Hence in this study we propose a detailed model for these three components, namely DHN, building envelopes as well as TES devices, with consideration of HT constraints. This model can be further simplified to consider different combinations of these components by setting relevant model parameters. An iteration solution to deal with such nonlinear HT constraints is put forward. The effectiveness of the proposed model is verified by case studies. The simulation results demonstrate that considering HT constraints is necessary when try to exploit the flexibility provided by these thermal system components, or we may overestimate their benefit

Frequency support provided by wind turbine generator (WTG) is important for frequency security of the power system with high proportion of wind power. A WTG initially operating at the optimal point and utilizing rotor kinetic energy for frequency support can only provide temporary frequency support, and avoiding second frequency drop is a critical issue. Synthetic inertia control, which is actually PD control, is the most widely studied control strategy, but its optimality is not well studied. In this paper, a functional optimization model of optimal control strategy for WTG temporary frequency support considering coordination with synchronous generator (SG) is built. The problem is solved with numerical method to obtain the optimal output power curves of WTGs. The optimal control strategy is then obtained with system response fitting. The coordination strategy of multiple WTGs for temporary frequency support based on the releasable rotor kinetic energy is also proposed. Practical realization of the proposed control strategy is presented. The effectiveness of the proposed control strategy is verified with real-time simulation of an actual power system with detailed electromagnetic transient model on the RT-LAB platform.

To cope with the uncertainty and variability of wind power, it is important for the power system to maintain adequate reserve capacity. The energy storage ability of the district heating system (DHS) provides considerable flexibility for the combined heat and power (CHP) units, and hence CHP can also participate in reserve capacity service. However, the CHP operation is restricted not only by its power condition, but also by the DHS heating condition, which brings difficulty in quantifying the CHP reserve flexibility. This paper focuses on properly assessing and utilizing the available reserve capacity of the CHP units as well as addressing the DHS heating constraints. The particularity for CHP reserve assessment is firstly analyzed and summarized as the component-coupling feature and the heating-dependency feature. Based on this, the regulating region method is proposed to describe the heating-restricted reserve capacity of the CHP units. Further, an integrated power and heat dispatch approach is developed which utilizes the regulating region to formulate the available CHP reserve capacity. Finally, the numerical simulation is performed to demonstrate the necessity of precisely assessing the available reserve capacity of the CHP units and the benefit of utilizing this potential reserve flexibility for wind accommodation.

Negative damping of prime movers is a major cause of sustained frequency oscillations in power systems. Increasing the damping torque of prime movers by adjusting governor parameters is an effective measure to prevent frequency oscillations. The oscillation frequency is volatile and turbine parameters change with loading conditions. To guarantee robustness and adaptability, the governor parameters should be adjusted to ensure sufficient damping torque over the entire range of oscillation frequency and under different turbine parameters. An optimization model of governor parameters is proposed. A constraint of the model is that the damping torque of the prime mover over the entire oscillation frequency range, and under different turbine parameters, must be greater than the threshold. The composite dynamic performance of primary frequency regulation under different loading conditions is the optimization objective. Test results validate the proposed method. The stability of the frequency oscillation mode under different conditions can be guaranteed.

Heat transfer (HT) is a major constraint in thermal system analysis. However, when discussing utilizing the flexibility provided by the heating sector, for example using thermal energy storage (TES) to increase operational flexibility of combined heat and power (CHP), the HT process is often ignored. This may mean infeasibility of the resulting schedules. In response to this, this paper proposes a general TES model which takes detailed HT analysis into account. By setting the relevant parameters, this model can be used to describe the HT process for both sensible heat (SH) and latent heat (LH) TES devices. An iteration method is proposed to deal with the nonlinearity introduced by the HT constraints, and to solve the joint nonlinear dispatch problem for CHP with TES. The simulation results show that explicitly considering the HT process is essential to realistically assess and therefore make full use of the flexibility provided by TES. Moreover, the comparison between LH and SH TES shows that LH can provide more flexibility for the system, especially when the starting energy level in the TES device is low.