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Energy is an important resource, and its main reserves are obviously insufficient compared with consumption. The energy structure is mainly dominated by fossil energy. The pollution emissions from energy utilization are becoming more and more serious. The energy problem has seriously affected the development of new urbanization. This paper studies the optimal scheduling problem of typical urban integrated energy systems participating in different demand response methods. Based on the traditional power demand response model, the demand response model is constructed according to the equivalent thermal parameters. Its model can optimize the electricity and gas load curves and realize the balance of electricity, heat, and gas in an economical and environmentally friendly way. It can also reduce the total cost of the economic operation of the system and reduce the overall carbon emissions of the system. Through the optimization and regulation of multi-type “source-storage-load”, multi-time scale, and multi-objective joint for the distributed thermal power, the matching of thermal and electric hybrid energy and the peak and valley of the power grid can be realized.

In urban construction, all energy infrastructures have been realized by the information structure. However, due to the non-uniform structure of each energy network, the data cannot be more compatible, and the communication guarantee based on the Internet of Things is one of the most urgent problems to be solved. In this paper, a reasonable network computing offloading model is designed in the edge computing layer, and the computing offloading algorithm is introduced. Considering the dependency between subtasks, an optimization problem is established, and a central scheduling algorithm is proposed to solve it. An optimized distributed unloading algorithm is proposed according to the solution idea of the classical distributed unloading algorithm. Simulation results show that the optimized distributed unloading algorithm proposed in this paper has good solving efficiency and performance, and reduces the task processing delay. At the same time, the experimental simulation proves that the efficiency of multiple edge servers in processing subtasks is higher than that of a single server. It is established that changing the convergence speed and communication delay stability margin of the system by changing the system eigenvalue is beneficial to design a better communication network structure to keep the system stable.

This paper presents the modeling of combined heat and power (CHP) systems for microgrid applications. When generating electricity, a CHP unit can recycle waste heat to supply building thermal loads to improve the overall efficiency of a traditional generation system. The ramping capability of a CHP unit makes it an ideal resource for load following and frequency regulation in microgrid operation. In this paper, a CHP model built in Simulink is developed. The CHP model includes three key components: generator, turbine, and absorption chiller. A new isochronous governor control strategy is proposed to provide zero-steady-state-error frequency regulation. The supply of building thermal loads is modeled to facilitate the calculation of the overall CHP system efficiency. The impact of ambient temperature on the maximum electrical output is considered. The developed model is implemented on OPAL-RT for testing the microgrid controller performance in a microgrid system.

In estimating the long term voltage stability of power system, the linearity and accuracy of indice is important. In this paper, a second order indice based on analytic Thevenin equivalent (TE) is proposed for estimating static voltage stability margin. Its analytic expression only using single instant wide area measurements, which make it not be affected by the system inside power change. As a second order indice, its linearity performance well. Compared to conventional voltage stability indice (VSI), such as impedance modulus, the proposed indice has better linearity feature, which can support operators to estimate the remaining power effectively. The performance of proposed VSI is verified on both IEEE 118-bus system and Alberta 2016-bus system.

A combined heat and power (CHP) unit can use its waste heat to supply building thermal loads so that the electrical heating or cooling load is reduced and the overall efficiency is improved. When multiple CHP units are running in a microgrid, it is therefore critical to balance the output of each unit so that both the electricity consumption and the building thermal loads can be satisfied with least cost. This paper presents an optimal microgrid dispatch algorithm for scheduling multiple gas-fired combined heat and power units when the microgrid is disconnected from the main grid. A coordination controller is developed to determine the power output reference for each CHP unit such that the total electric power output of all CHP units are minimized while both electric and thermal demands are met. A few test cases are presented to illustrate the effectiveness of the algorithm.

This paper discusses the effect of load change on the Thevenin equivalent impedance of power systems. In this paper, the Thevenin equivalent impedance influenced by the derivative of active load with respect to reactive load (dP dQ) is analyzed. The Thevenin equivalent impedance forms a closed curve in a complex plane and shrinks to one point when voltage collapses. The magnitude of the Thevenin equivalent impedance at the collapse point is equal to the magnitude of the load impedance. Therefore, the impedance match theory still holds under the effect of the load change. These features are verified on a New England 39-bus system.

It is an important but challenging issue to represent a wind farm using an equivalent model. This paper tries to develop an equivalent representation of a wind farm for power system planning and operation studies using Thevenin equivalent circuit. In the paper, a series string configuration of wind farms with doubly-fed induction generator (DFIG) wind turbines is emphasized, and case studies have been conducted to investigate the characteristics of the equivalent parameters of such a wind farm under different control strategies and wind speeds. Simulation results show that the equivalent parameters are strongly related to the wind speed, particularly when the constant power factor control strategy is employed for wind turbines. It can also be concluded that, compared to the constant power factor case, the constant voltage control scheme possesses better performance and thus is more popular for power system operation and control.

It is an important but challenging issue to represent a wind farm using an equivalent model. This paper tries to find a practical clustering method of a doubly-fed induction generator (DFIG) wind farm for power system simulation. In the paper, the equivalent wind speed for the equivalent model is calculated according to the relationship between power and wind speed. The operating status of DFIG are analyzed for clustering the turbines preliminary and the errors' absolute value integration of output current between the detailed model and the equivalent model during the dynamic process are calculated and analyzed for practical clustering. Simulation results show that the proposed method can perform the dynamic characters of detailed model under homogeneous distributed wind speed case, low wind speed case and high wind speed case effectively.

With the rapid growth of wind power, due to the limit of the system peak load regulation capability, wind turbines were often tripped to guarantee power system security during heating periods in China's north provinces. This paper proposes a thermal-electric decoupling scheme for reduction of wind power trippings. In this study, an outside thermal source is introduced to absorb sufficient wind power and to provide heating services. Thus, the heating output of co-generators could be reduced to lower the minimum forced power of co-generators, which further increases the system peak load regulation capability. An approach is proposed to calculate the wind power tripping rate by using Monte Carlo simulation technique. Case studies have been conducted to demonstrate the effectiveness of the proposed methods, and the results show that the proposed approach could relieve the wind power tripping rate and improve the ability of power system to accommodate wind power.

Load shedding is a very important measure for power system voltage instability prevention. This paper proposes a novel analytical sensitivity index to determine the optimal load shedding locations to avoid voltage instability. An impedance ratio index is first presented to indicate the voltage instability of load buses, and based on this, the sensitivity index is derived to identify and rank the load buses to be shed. Case studies have been conducted on the IEEE 30 bus system, and the simulation results show that the proposed indexes could effectively determine the load shedding locations for voltage instability prevention.