Research on reliability assessment method for distributed distribution network power supply with self-healing performance

In distribution networks with distributed power supplies, distributed power supplies can also be used as backup power sources to support the grid. If a distribution network contains multiple distributed power sources, the distribution network becomes a complex power grid with multiple power supplies. When a short-circuit fault occurs at a certain point on the power distribution network, the size, direction and duration of the short-circuit current are no longer single due to the existence of distributed power, and will vary with the location and capacity of the distributed power supply system. The change, in turn, affects the current in the grid, resulting in the generation and propagation of additional current. This power grid of power electronics will cause problems such as excessive standard mis-operation, abnormal heating of the converter and component burnout, and communication system failure. It is of great and practical significance to study the influence of distributed power in distributed power distribution networks.

The location and capacity optimization configuration of distributed power supplies ensures that they. Make better technical and economic use. When the distributed power supply is connected to the distribution network, it will cause the trend size and direction of each branch to change, so that the system loss is not only related to the load size, but also related to the location and capacity of DG. Therefore, it is important to study the rational planning of DG in depth. In order to improve the system network loss effectively, a distributed power distribution power distribution network reactive optimization model with the minimum active loss of the system is established, and an improved multi-target firefly algorithm is proposed for the problem that the traditional firefly algorithm will oscillate repeatedly near the extreme point later in the iteration. In view of the shortcomings of the traditional firefly algorithm, which is easy to precocious and over-dependent on control parameters, the chaotic search strategy and global idea are integrated into the firefly algorithm, and an improved firefly algorithm is proposed, which is applied to solve the planning problem of distributed power supply. The example shows that the proposed algorithm has good practicability and adaptability, and also verifies the practical significance of the proposed model[1].

Aiming at distributed power generation and distribution network scheduling problem, a distributed predictive control algorithm is designed, and an active frequency distributed predictive control model of distributed power grid and grid operating system is established. In the forecasting control period, the Nash equilibrium control solution of the distributed power grid is obtained. Multi-distributed grid-connected power generation online optimization control, through the model predictive control system to achieve safe and stable operation of the grid, and finally, the accuracy of the conclusion is verified by simulation analysis. When the distributed power supply and distribution network are dismounted, the distributed predictive control method can realize the decentralized predictive control state, so that the distributed power supply can run stably, and after the next grid connection, the distribution network will not form a great impact, which is conducive to the stable operation of the distribution network.

As an important field of realizing the "double carbon" goal, low carbon development of electric power industry plays a vital role in realizing the "double carbon" goal of our country. Building urban green electric power system mainly composed of distributed photovoltaic and wind power is an important way to realize low carbon development of electric power industry. In order to accurately grasp the development trend of regional distributed power supply, this paper introduces the concept of distributed power supply permeability, which is defined as the ratio of annual distributed power generation and regional annual power consumption. Firstly, the installed capacity growth model of regional distributed power supply was constructed based on the improved Bass model, and then the annual power generation of distributed power supply was obtained by combining the capacity coefficients of different types of distributed power supply. Secondly, grey theory is used to forecast regional annual electricity consumption. Finally, based on the permeability definition of distributed power supply, the permeability growth curve of distributed power supply in distribution network is drawn and the growth mode is analyzed.

This paper proposes a medium voltage direct current (MVDC) sensor power supply method based on inductive power transfer (IPT). Given that MVDC distribution networks transmit power at high voltages (several tens of kV), control through sensors is necessary to prevent exacerbating MVDC distribution network accidents. Moreover, these high voltages in MVDC distribution networks mean that high voltage insulation is required between the sensor and the distribution line and for any power supply device electrically connected to the sensor. Therefore, this paper proposes a safe and reliable power supply method using the principle of IPT to maintain a suitable insulation distance between the distribution network and the current sensor supply line. After proposing and designing a transmitter/receiver pad and IPT system by considering the current sensor specifications, a 50-W experimental prototype is developed. The experiments demonstrated that the proposed IPT system can resolve concerns about the breakdown of insulation between distribution networks and power supply lines.

Distributed power access brings a lot of impact to the entire power grid, especially to the distribution network related with it directly, such as power flow, power quality, power distribution reliability and so on. Distributed power access to the distribution network changes the radiation mode with single power supply into network mode with multi-power supply, the operation mode is complicated, Therefore, the traditional reliability assessment method is no longer applicable; need further study of new methods. Firstly, the influence of distributed power access on the traditional reliability algorithm is studied in this paper, and establishes the Isolated island partitioning model and Isolated island partitioning process, and makes Dynamic solution. Based on the existing assessment methods, this paper presents a method of distribution network reliability assessment based on load and power stochastic functions according to different characteristics of distributed power supply and traditional power supply, and the actual example shows that the distribution Power supply can improve the reliability index of distribution network and improve user's power quality.

At present, the research on the planning problem of distributed power access distribution network is mostly carried out under the condition that the target annual load is known, and the impact of the differential load growth in different stages and the multi-scenario timing characteristics of the distribution network components are not considered. Aiming at this problem, an optimal access location and capacity calculation method for multi-period and multi-scenario distributed power supply based on OpenDSS is proposed. Firstly, the simulation principle and advantages of OpenDSS are explained from the aspects of model construction and power flow calculation. Secondly, the optimal power supply access model with multiple time slots and multiple scenarios is established with the goal of minimum planning end value. Thirdly, a model solving method based on particle swarm optimization is proposed. Finally, a typical example is chosen to calculate the optimal planning scheme of distributed power supply under multi-period, and the rationality of the model is verified.

Voltage unbalance in power systems feeding AC traction power systems is a worldwide known problem. One of the main aspects of this problem is the negative effect of voltage unbalance on motor loads causing operating problems and economic damage. It is necessary to perform unbalanced power flow studies and calculate voltage unbalance indexes to assess this negative effect of voltage unbalance and the develop of compensating measures during the design stage. Usually, calculations of the AC traction power supply system and the distribution network feeding it are carried out separately during the design of new lines of railways electrified by alternating current (AC) and reconstructing of existing ones. This approach is a source of deviations in the power flow studies because the lack of consideration of mutual influences between the traction power system and the distribution power system. In this paper, we compare a digital model in which the traction power supply system and the distribution network are modeled separately with a model that considers mutual influences between the traction and external power supply systems, including power flows through the traction network caused by the distribution network (transit currents). For digital modeling of these processes, authors used ETAPTM software with eTraXTM package. It allows to run unbalanced power flow studies when the generation and load are being changed over time, including train movement. During a separate simulation of the traction power system and distribution network, traction network was modelled using the equivalent sources connected to traction substation buses and the distribution network was modeled taking into account the fact that traction load was given from the simulation of the traction power system. The traction load was considered as lumped loads connected to the traction substation buses.At the same time, in both cases, the unbalanced power flow study was carried out by the phase domain method. Based on the results of two models comparison, it was concluded that the combined model containing a traction power supply system and distribution network, is more effective in terms of improving the accuracy of assessment voltage unbalance in accordance with current regulatory and technical documents on power quality.

Because the distributed power supply is connected to the distribution network, its structure has also changed the original traditional method. The original single power supply method was originally used. The network provided is a radial network and it is connected to the distributed power supply. Later, it became a structure with small- and medium-sized power supplies inside, and its network power supply became dual or multiple power supplies. Such a structural change affected the coordination of power distribution protection devices, which would impose current on the distribution network. Protection has a negative impact. This paper aims to study the adaptive current protection technology of distribution network with distributed power based on local information. On the basis of analyzing the characteristics of distributed power, the classification of distributed power, and the operation mode of distributed power, according to the access of IIDG, as well as different influences of relay protection of distribution network, an improved protection scheme with adaptive current quick-break protection as the main protection is proposed, so that different fault characteristics of the distribution network have different setting values, and then simulation experiments are carried out on this scheme. The experimental results show that the setting value of three-phase short-circuit fault proposed in this paper can well protect the protection range, which is larger than the traditional protection setting and self-adaptive setting.

In the context of increasing energy shortage, the application of various renewable and dispersed energy sources for power generation and energy supply will become increasingly widespread. As a small local power grid containing multiple distributed power sources connected to the distribution network, micro grid (MG) can be linked to the distribution network to operate, or can be disconnected from the distribution network to operate when the grid fails or when is needed. Due to the randomness of distributed power and load operation in MG, the direction of power transmission between MG and the distribution network is also uncertain. When the distributed power generation capacity of MG is small and the load level is high, MG must absorb electrical energy from the distribution network to meet the demand of the internal load of itself, which is equivalent to operating in the load state; and when the amount of power generated by the distributed power supply is large, the excess power will be sent back to the distribution network, which is equivalent to the power supply state, and this case will have a great impact on the original protection of the distribution network. In this paper, through the establishment of MG and distribution network grid structure simulation, the impact of MG to distribution network protection in power supply state and load state is analyzed respectively and a variety of improvement measures are proposed based on the actual situation.

Distributed power supply connected to distribution network brings impact on system voltage distribution as well as tidal current analysis, which causes degradation of system power quality. For this reason, a system optimization model is needed to analyze and optimize system voltage and tidal current. The linearized second-order cone relaxation optimization algorithm for distribution networks with distributed power sources is proposed. First, the distribution network branch tide model is introduced to analyze the tide of the distribution network with distributed power supply access; based on this, the distributed distribution network tide optimization model is established. Secondly, the distributed distribution network tidal optimization model is simplified, and the multi-time second-order cone relaxation optimization algorithm is proposed for the non-convex nonlinearity in tidal analysis, and the segmental linearization is performed for the non-convex nonlinearity of capacitor bank and on-load regulator transformer. Finally, a modified IEEE33 node test system is used on the MATLAB simulation platform to verify the tidal optimization of this distributed distribution network tidal optimization system. The simulation results show that the tidal optimization algorithm can reasonably dispatch the output of on-load regulating transformers, capacitor banks and distributed power sources, effectively reduce the network loss and the voltage deviation of the grid.

Distributed energy access and energy storage configuration are important links in the design of an active distribution network, and research on their design methods is essential to support the scientific development of an active distribution network. Therefore, on the basis of full research and demonstration, the content of the scheme design of the active distribution network and the technical principle of the overall design of the active distribution network are first determined, so that they can play the role of macro instruction in the scheme design. In addition, this paper deeply studies the capacity allocation of distributed generation and energy storage systems in the active distribution network, puts forward a general method for optimal allocation of distributed generation access and energy storage capacity, and provides design information and technical support for the active distribution network method.

Aiming at the influence of distributed power on the voltage of distribution lines and power flow distribution, a method containing reactive voltage control for 10kV distribution network with distributed power supply is proposed. Firstly, the influence of accessing distributed power supply on the voltage characteristics of distribution network is analyzed. Then, a grid reactive power control method for balancing the operation times and optimization effects of equipment is proposed. The control precision of reactive power compensation equipment is optimized by dynamically adjusting the power factor, avoid the frequent operation of the equipment; finally, a decentralized and superior control method is proposed. By detecting the distributed power source's point of integration, the reactive power and voltage situations at the point are evaluated, and the differentiated control is performed according to different voltage levels. The simulation experiment results show that the proposed dual-layer reactive voltage control method can significantly reduce the active loss and improve the voltage pass rate.

This paper proposes a distributed power supply consumption metering assessment index system and method for rural energy internet, which can be used in the dispatch and design departments of power companies. The method can solve the problems that exist in the existing distribution system, such as the lack of basis for siting and capacity determination and access of large-scale distributed power units, and the single and one-sided assessment index of distributed power consumption capacity. Firstly, analysing the characteristics of the new rural power grid, considering the impact of the uncertainty of distributed power supply output, organically combine the influencing factors of power quality, power supply reliability and operational safety and establish a multi-dimensional index evaluation system to measure the ability of distributed power sources to consume. Finally, the improved fuzzy estimation is used to determine the consumption capacity of the rural grid. The data of a rural grid operation is analysed by case study to accurately assess the consumption capacity of distributed power sources in the area.

The large-scale access of distributed power generation to the distribution network changes the power flow characteristics of the distribution network, and has a certain impact on the voltage quality and network loss of the distribution network.This paper analyzes the distributed power supply access to run the distribution of high permeability, from two levels of regional and local area presented depicting regional and local distribution network given distributed power ability and level of index system, was proposed based on time sequence simulation area - local two-phase given distribution network distributed power supply capability evaluation method, is put forward in this paper is verified by an example of evaluation index system and evaluation of the effectiveness of the algorithm.