Online: November 23,2020 DOI: 10.7500/AEPS20200707003
Abstract:Quantity regulation is a basic regulation mode of district heating networks. First, aiming at the characteristics that the flow is variable and it in the turbulent resistance square area with the quantity regulation, a second-order cone relaxation method for pressure drop of hydraulic branch is proposed, and a penalty cost term is introduced to ensure exact relaxation. Next, according to the characteristics of the stable thermal condition of quantity regulation, a equivalent heat loss method of thermal branch is proposed. The heat loss of the pipeline is equivalent to the load to form a lossless pipeline, which realizes the independent analysis of hydraulic and thermal models. Then, combined with the branch flow model of the distribution network, a joint power flow model of the district heat-electric system is built. Furthermore, a joint optimal power flow model with the form of convex-concave programming for district heat-electric system is established. Finally, the optimization model is transformed into a second-order cone programming problem and solved equentially. Simulation cases show that compared with the non-convex accurate model, the proposed method retains a high solution accuracy, improves the solving speed significantly, and can obtain the global optimal solution.
Online: November 23,2020 DOI: 10.7500/AEPS20200513005
Abstract:This paper analyzes the difficulty of accurately calculating the load deviation of power generation and consumption and system loss in market clearing and calculation of locational marginal price (LMP) in China. First, two kinds of LMP calculation models are proposed, which are both involved in the methods of allocating the network loss by using loss distribution factors and allocating load deviation by using load deviation distribution factors. The accurate calculation of system network loss and load deviation is realized. Then, the iteration-based LMP model uses the bus load as the initial point to prepare a power generation plan. After each solution, the deviation between the total generation and the system load is allocated to all nodes to correct their loads. The LMP is solved by multiple iterations. The two-stage LMP model establishes a coupling model that considers the system network loss and load deviation based on the system load. In the first stage, the load deviation is calculated; in the second stage, the deviation is fixed to calculate the LMP. Finally, the effectiveness of the proposed model is verified by comparing the LMP of the proposed method and the direct allocation method of network loss, and analyzing the influence of different load deviation levels and load deviation distribution factors on the LMP.
Online: November 23,2020 DOI: 10.7500/AEPS20200506004
Abstract:The prevalence of distributed renewable energy provides a new way for constructing a clean and efficient smart grid. Meanwhile, it also leads to some difficulties at demand side such as more random behaviors of end users, more difficult energy management, and less efficient equipment utilization. To deal with these new challenges and fully invoke demand-side flexibility, energy sharing as an innovative distributed operation paradigm emerges at the right moment. This paper presents the concept of demand-side energy sharing and analyzes its potential in smoothing uncertainty, enhancing operation economy and improving equipment utilization efficiency. The key points and basic requirements in designing energy sharing mechanism are elaborated. On this basis, the domestic and international researches on energy sharing mechanism design are summarized into five categories from the perspectives of cooperative game and non-cooperative game. Current research progress and remaining problems are also concluded. Further, future research direction is previewed from two aspects, i.e. the internal design and external connection, of the demand-side energy sharing market.
Online: November 23,2020 DOI: 10.7500/AEPS20200430026
Abstract:With the increasing penetration of new energy in distribution networks, a series of reliability issues, e.g., voltage over-limit and power flow overloading, have become severe threatens. Therefore, an awareness method of voltage spatial-temporal distribution with high proportion of new energy penetration is proposed. Due to the absence of power flow models of the distribution network in practice, a data-driven method is designed to make short-term prediction for nodal voltage awareness with high accuracy. The proposed method is composed of three sectors: numerical weather prediction (NWP) based distributed wind power and photovoltaic forecasting, in which the relationship between meteorological data and distributed energy output is developed; generalized regression neural network (GRNN) based learning mechanism for constructing voltage sensitivity matrix, in which nodal power-voltage mapping of data-driven is developed without a power flow model of distribution network; and kernel density estimation (KDE) based GRNN sample correction method for avoiding the forecasting errors because of the local density deviation of the original sample. Case studies based on IEEE 33-bus and Venezuela 141-bus distribution systems demonstrate the effectiveness of the proposed method. Compared with similar methods, the proposed KDE-GRNN has a significant advantage of forecast precision and rate of convergence.
Online: November 23,2020 DOI: 10.7500/AEPS20200427004
Abstract:With the wide application of information and communication technology in distribution network, the degree of cyber physical coupling of distribution network is gradually deepened. The existing reliability model of the cyber-physical system (CPS) of distribution network is difficult to accurately evaluate the reliability of complex scenarios in practical engineering application. In this paper, multi-state reliability models are established for coupling components based on their failure cases, and cyber failure scenarios of distribution network are traversed based on full binary tree topology. Thus, a novel reliability analysis method is proposed. This method takes into account the actual fault handling process and transfer capacity constraints, and is applicable for all distribution network topologies with open-loop operation. It provides a feasible method for evaluating the reliability of the stock CPS of distribution network. Finally, taking an actual distribution network in a city as an example, the feasibility and effectiveness of the proposed reliability evaluation method of the CPS of distribution network is verified.
Online: November 23,2020 DOI: 10.7500/AEPS20200322004
Abstract:Dispatching and control cloud (DCC) is an important part of the “three clouds” planning of State Grid Corporation of China. Aiming at the characteristics of hierarchical deployment design, which combines unification and distribution of dispatching and control cloud, Combined with the two-level deployment system framework of leading nodes for national dispatching and control center-regional power grid dispatching and control center and provincial collaborative nodes, based on the concept of cloud computing, oriented to power grid regulation business, basic architecture of infrastructure as a service (IaaS) layer for dispatching and control cloud is designed. The virtualization (sharing and dynamic deployment) of hardware resources, standardization of data and service-oriented application of dispatching and control cloud platform are realized. On the other hand, technologies of virtualization of server and storage resources, domain name system, load balance, read-write separation etc. are introduced into IaaS layer architecture, which provides basic support for dispatching and control cloud nodes to adopt dual-site mode, and it realizes that each node of the cloud can provide external services and remote active-active application at the business level at the same time.
Online: November 19,2020 DOI: 10.7500/AEPS20200812006
Abstract:The quantitative analysis method of the complementarity between wind power output and photovoltaic power output based on weather classification can scientifically guide the optimal dispatch of wind-photovoltaic complementary power generation system. In order to overcome the shortcomings of the existing weather classification methods that principal component analysis cannot extract nonlinear features, and t-SNE based algorithm does not consider the actual distribution of samples, a weather classification and complementarity analysis method for wind and photovoltaic power output based on kernel principal component analysis (KPCA) and self-organizing feature map (SOFM) neural network is proposed. Firstly, the KPCA is employed to extract the feature vectors based on numerical weather prediction data. Then, a weather pattern classification model based on SOFM neural network is constructed by using the feature vectors as input conditions. Finally, Based on the evaluation indicators for complementary rate of fluctuation and complementary rate of ramp, the complementary degree and the optimal grid-connected capacity ratio of wind and photovoltaic power output under different weather patterns are quantitatively analyzed from two perspectives of flucaturation and ramp. The results demonstrate that the fluctuation complementarity and the optimal grid-connected capacity ratio of wind and photovoltaic power output have obvious difference under different weather patterns, which verified the effectiveness of the proposed method.
Online: November 19,2020 DOI: 10.7500/AEPS20200622004
Abstract:In recent years, the continuous growth of the installed capacity of renewable energy has brought new problems to the stability of power system. An analysis method based on frequency response matrix is proposed to calculate the influence of wind power grid conncetion on the low-frequency oscillation mode in power system. The result shows that the phase sum of some elements in the frequency response matrix of synchronous grid and wind turbine system determines the influence of wind power at different access points on the low-frequency oscillation mode. Compared with the traditional analysis method, vector margin method only needs to obtain the low-frequency oscillation mode and the transfer function matrix of wind turbine system and synchronous grid system without the calculation of eigenvectors and residue. The process is simple and the result is intuitive. When multiple wind turbines are integrated to the system simultaneously, the influence of each wind turbine can be observed visually in a two-dimensional complex plane. The effectiveness of the analysis results can be verified by the case of Inner Mongolia grid.
Online: November 19,2020 DOI: 10.7500/AEPS20200518007
Abstract:Compared with the previous projects, the main difficulties in the system design of Chongqing-Hubei project of China are that the engineering DC voltage is higher, capacity is larger, requirements for fault ride-through and AC/DC protection etc. are improved, but the transient stress level of fully-controlled power electronic devices is limited and the extreme mode of AC power grid deteriorates. In view of the limited transient stress level of the device, this paper proposes the accurate calculation method of rising rate for the arm fault current in the converter, the independent arm blocking strategy of overcurrent protection for valve base controller, the dynamic setting strategy of valve over-voltage protection. They solve the problem that the device safety and fault ride-through capability cannot be taken into account under the weak device capability. Aiming at the problems of high-frequency instability and weak-system instability of AC grid and flexible DC system in extreme modes, the instability mechanism and the practical engineering methods solving the instability are proposed. To meet the special requirements of AC breaker failure the protection and DC differential protection under the access of 500 kV AC power grid, the corresponding solutions and advices are proposed.
Online: November 19,2020 DOI: 10.7500/AEPS20200225010
Abstract:The real-time power grid impedance information obtained by grid-connected inverters can be used in power grid status monitoring, fault diagnosis, and grid-connected equipment stability control, to improve the intelligent level of grid-connected equipment and power grid regulation. Since the injected disturbance signal is often applied to the current control loop of the inverter, the impedance measurement frequency band is limited by the bandwidth of the controller. In order to improve the accuracy of high-frequency impedance measurement, this paper proposes a power grid impedance measurement method based on Sobol quasi-random pulse width modulation (SQRPWM) by taking advantages of the characteristic of frequency spectrum shift of random pulse width modulation and the uniformity of Sobol quasi-random sequence. The frequency boundary of SQRPWM is optimized and designed according to the system bandwidth and stability constraints. The feasibility of the proposed impedance measurement scheme based on SQRPWM and the mixed impedance measurement scheme combined with the single pulse and SQRPWM is verified on the experimental platform of Starsim. The results show that the proposed impedance measurement scheme has the advantages of small disturbance and high measurement accuracy at a high frequency. Moreover, if the proposed method is combined with the current-disturbance based impedance measurement method, the frequency band of the power grid impedance measurement can be further expanded and the broadband impedance information can be obtained.