| With the increasing severity of energy and environment problems, renewable energy is competitively developed all over the world. Wind energy, which is clean and abundant, is attached great importance to and becomes the fastest developing renewable energy. In order to reduce negative effects on the power system to which wind farm is connected, now wind farms are always connected to the high-voltage power system in our country. However, with the maturity of wind power technology and the coordinated development of wind power and smart grid, it is foreseeable that there will be more and more wind power penetration into the low-voltage distribution network. Therefore, it will be practically meaningful to study impacts on low-voltage distribution network caused by the penetration of wind power. The thesis mainly focuses on the following aspects:First, the steady-state models of two typical kinds of wind farms are studied, which are based on constant-speed constant-frequency induction generator and variable-speed constant-frequency doubly-fed induction generator (DFIG) respectively. For the former type, the steady-state model of induction generator is established, and the power loss of transformers is taken into account while modeling wind farm. Besides, a reactive power compensation method which is fit for wind farm is proposed. For the latter, the paper mainly focuses on the steady-state model of DFIG which operates in the mode of constant power factor. Based on the model, a simplified model of DFIG is proposed, which dramatically makes the process of power flow calculation simplified.Second, impacts on voltage stability and power loss of distribution network are analysed from theoretical perpective. Based on the steady-state models, simulations from different aspects are carried out on a practical distribution network which is interconnected with the two typical kinds of wind farms. And simulation results show that voltage stability and power loss of distribution network can be affected by different operation conditions of wind farm, such as the different reactive power compensation conditions, the change of connecting location to distribution network, the variation of the output of active power and wind turbine power factor and so on.At last, to cope with the impacts on voltage stability and power loss, a few countermeasures are proposed, such as planning of rational installed capacity of wind power, selection of appropriate interconnecting location, allocation of moderate amount of spinning reserve capacity, adoption of proper reactive power compensation method, application of superconducting magnetic energy storage (SMES) devices and HVDC Light and so on. |
