Studies On Composite Load Modeling Of Distribution Network Considering Distributed Generation

With the fast development of renewable and clean energy generation, there will be a series of new theory and practical problems to be solved. One of them is the modeling of power systems. Based on the background stated above, this dissertation studies the composite load modeling of distribution power network considering distributed generation. The main work and contributions are as below:1. Aiming at the disadvantages of the structure of traditional induction motor load model, a novel"synthesis induction-motor model considering distribution network"is established. In this model, the distribution network is equivalent to a line connecting to a terminal transformer, which can describe the influence of OLTC (on-load tap changer) and reactive power compensation. The model achieves the unity of the physics environment, parameters identification environment and simulation applying environment of composite load at the power substation. The results of modeling test based on simulation measured data shows that the"synthesis induction-motor model considering distribution network"has excellent identifiability, generalization, and the composite describing capability. Its integral performance is better than traditional induction motor model. This model provides the basis and effective structure for research on load modeling of distribution network considering distributed generation.2. The composite load model of distribution network including wind power generation (WG) is studied with MATLAB Simulation toolbox and theory of measurement-based method. The research proves that the WG could be considered as generalized dynamic load which consumes negative power, and could be described by asynchronous generator. In order to describe the synthetic load characteristic of distribution network including WG, the author proposes a kind of generalized composite load model that is constituted by asynchronous machine in parallel with static load. In the model, the ratio of dynamic load can be any real numerical value. The validity of this composite load model with any ratio of dynamic load is testified by modeling of three typical operation modes under different capacity of wind power generation.3. Using the typical IEEE 14 node distribution network as simulation environment, the author systematically studied the impact of WG on composite load characteristics, which consider some impotent influential elements such as capacity ratio, location, and the connecting mode to the distribution network and so on. It has been proved that the influence of capacity is apparently greater than that of location, and the effect of dispersed WG is smaller than that of the centralized, hence the dispersed connection one have advantage to the safe and stable operation of power system. Using the measured data from simulation, the validity of generalized composite load model is tested through fitting result, average error and identification parameters. At the same time, the generalized composite load model of asynchronous machine with any ratio of dynamic load is proposed, and its superiority is also tested.4. For the sake of studying on the composite load modeling of distribution network with photovoltaic (PV) and fuel cell (FC), the PV and FC grid-connected power system is established and the model of each function module and control strategy are expounded. It is pointed out that the PV and FC could be considered as generalized static load which consumes negative power, and could be described by constant power model. Based on this, the generalized composite load model of equivalent static load in parallel with induction motor is proposed to describe the synthetic load characteristic of distribution network including PV and FC. The validity of this generalized composite load model is testified by modeling of three typical modes under different capacity of PV and FC.5. In order to study the composite load modeling of distribution network with microturbine (MT), the model of each function module and control strategy are expounded with establishing of the MT generation system. It is pointed out that the MT could be considered as generalized dynamic load which consumes negative power, and could be described by a first-order differential state equation. And the generalized composite load model of equivalent dynamic load consisted of MT and induction motor in parallel with static load is proposed to describe the synthetic load characteristic of distribution network including MT. The validity of the composite load model is testified by modeling to three different typical capacity of MT.