Modeling And Analysis Of Power System With Distributed Energy Resources

The aggravation of environmental pollution and energy shortage, promotes the extensive application of distributed generation (DG) and accelerates the application process of other distributed energy sources (DER) such as electric vehicle (EV) and battery storage (BS). Large-scale application of DER is helpful to improve the reliability and economy of power grid, promote clean energy and renewable energy application in electric power production. The application also affects the voltage level, line capacity and short-circuit capacity of the power system, threats the safe operation of the power grid seriously. How to ensure the safe operation of power system under the premise of improve the economy and reliability of the power grid operation, and the permeability of distributed energy is a problem to be solved including distributed energy grids. How to realize economic operation, reliable operation of power system and improve the penetration leve of DER under the premise of safe operation for, it is a urgent problem to solve for power grid containing DER.Aimed at solving above problems.the paper makes mathematical model for power grid containing DER, puts forward key line identification model and wind power allowed capacity model in the aspect of grid security analysis, proposes intentional island partition model and reliability evaluation model in the aspect of grid reliability analysis,presents optimal scheduling model in the aspect of grid economy analysis. The main outputs of this paper are displayed as follows:The paper develops vulnerable line identification model based on hybrid flow betweenness. The model covers actual power flow distribution characteristics, maximum transmission capacity of line, the influence of generator capacity and load level. Electrical coupling degree between the lines and outage transfer distribution factor are also considered in this model to quantify physical network connection and fault effect between lines. With a more comprehensible physical background, hybrid flow betweenness can effectively evaluate the importance of lines in the network structure and power transmission of power network. Transient energy margin is used to evaluate influence on power system's vulnerability caused by vulnerable line faults to verify the critical lines. Tenacity and power supply can can reasonably depict breadth and depth of the effects on system state change caused by vulnerable line faults, the two indexes are introduced to evaluate the vulnerability of power grid DG under different failure modes. Under intentional attack mode and global attack mode, the paper further studys on the influence of DG on grid vulnerability.The paper proposes penetration level calculation model for wind farm considering the uncertainty of wind speed and load based on robust linear optimization method. The model applied box set to cover uncertainty of wind speed and load to ensure node voltage and line capacity can meet constraints in the worst case, ensure the safe operation of the power system.Optimized duality theory is used to simplify the model and convert uncertainty quantities in constraints to certainty quantities,so the allowed capacity of single wind farm can be calculated.Under the condition of multi wind farms, a bi-level optimization model to calculate allowed capacity are proposed, the model avoids inaccuracy caused by accumulation of allowed capacity of single wind farm.This paper proposes a novel intentional island model of a distribution system with DG. This paper abstracts the distribution network with DGs to the layered directed tree according to its radial structure and power restoration process. In consideration of grade, controllability, capacity, level and electrical betweenness of load, the model weights load and maximizes total load weight in the island. The proposed model considers power balance, node voltage, phase angle and transmission capability of the branch, and network connectivity to meet practical engineering requirements. The improved Dijkstra algorithm formulates a search rule to select the load that can be divided into an island in descending order of the shortest path between the load node and DG node. An optimal island partition scheme is achieved through three stages:origin island, baby island and mature island. Meanwhile, scheme adjustment and constraint checking are used alternately to balance objective functions and constraints.The paper proposes reliability evaluation model of distribution network with multi DERs based on combined power generation system (CPGS) composed by DG, BS and EV.The EV in CPGS can be divided into regular EV and ruleless EV according the driving behavior, to model charging load and discharging capacity. Based on statistical data of petrol vehicles and probability distribution of charging start instant and charging time, the statistical model can be built to describe the charging load and discharging capacity of ruleless EV. The charge and discharge curve of regular EV also can be drawn on the basis of daily dispatch Tablele. The CPGS takes charge and discharge curve of EV, daily load and power generation of DG into consideration to calculate its power supply time during island. Combined with fault duration, the power supply time during island will be used to analyze and determine interruption times and duration of loads in island. Then the Sequential Monte Carlo method completes the reliability evaluation of distribution system with multi DERs.The paper proposes the economic scheduling model of virtual power plant (VPP) with multi DERs based unified market covering day-ahead market and real time market.The unified market breaks the limit that day-ahead market should purchase and sell electricity according to forecasting load, optimizes electricity traded in day-ahead market to minimize overall costs and maximize overall profits. Combined electricity trading model in unified market and operating model with constraint condition of elements in VPP, the work develops the optimal scheduling of VPP, reasonably allocates electricity among distributed generation, interruptible load, energy storage system and electric vehicle in VPP and optimizes electricity transaction between VPP and unified market to achieve maximum economic benefits.