An energy-based method to locate oscillation sources in power systems is proposed. The energy is identical to the transient energy. The amount of energy is consistent with the oscillation amplitude, and then the component producing energy has negative contribution to the damping and is considered as the oscillation source. The consistency of energy dissipation with damping torque of a generator is proved. A method to compute energy flow in the network based on wide area measurement system data and independent of energy functions is proposed. The energy dissipation or production of a component in the system can be obtained from the net energy flow. The components producing energy are oscillation sources and emergency control actions should be taken on them. The method is validated by simulations and actual oscillation incidents analyses.

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

Due to the coupling of its heat and power output, combined heat and power (CHP) has limited flexibility, which is one of the main reasons for variable renewable energy source (RES) curtailment problem in Northern China. Almost all the existing studies have modelled the CHP's output characteristics as a feasible operation region of electric power and heat power. However, only the extraction steam of a CHP unit that used for district heating can be controlled directly, without considering the extraction steam's heat transfer process, the actual heat power output cannot be precisely decided. Thus this paper proposes a detailed CHP dispatch model based on the principles of heat transfer. A three-stage heat transfer model of the extraction steam is used to describe the heating process. Then, a joint dispatch model concerning CHP units, conventional thermal power units, and RESs is given. Finally, the impacts of different factors on the extraction steam's heat transfer process and its influence for RES accommodation are analyzed. Results show that considering heat transfer process is essential in modelling the CHP plant that used for district heating, especially when the CHP plant is working at a status that deviates from the rated one significantly.

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.

A newly proposed oscillation energy analysis method for power system low frequency oscillation is further developed. The oscillation energy flow in a generator and the energy dissipations of the field winding and the damper winding are studied. The oscillation energy flows into the field winding and the damper winding actually correspond to the electric energy transferred to the windings. The average powers of energy dissipation for oscillation modes with different frequencies are decoupled. For an individual mode, the energy dissipation of generator is computed using eigenvector and energy dissipation coefficient is obtained. The real-part of eigenvalue is negatively proportional to the sum of energy dissipation coefficients of all generators. It means the composite damping of the system comes from the energy dissipations of all generators. Especially in the single-machine system, the energy dissipation coefficient is equal to the damping torque coefficient. The consistency of oscillation energy analysis with damping torque analysis and modal analysis is verified. The energy dissipation leads to a new understanding of damping in power system and can be used for quantitative evaluation of generator damping in both offline and online applications.

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.