Voltage stability of the power grid with integrated wind turbines

There has been a transition from non-renewable fossil fuels to renewable and clean energy sources. A result of this transition is the installation of a significant amount of wind turbines. The increasing presence of wind power requires additional voltage stability analysis of the power system. This is due to the considerable voltage fluctuations produced by changes in the wind speed which may affect some commercial and industrial loads. This problem is substantially more important as grid capacity is pushed to its limit. As a result, there is an interest in steady state and transient voltage stability analysis of the power grid with integrated wind turbines. This thesis studies the effect of wind speed variation on motor-type industrial loads, fed from the grid via a weak connection - long distribution line, in combination with a partial supply from locally installed distributed energy source - wind turbine. Two types of studies were conducted: 1) studies that involve a three phase fault on the strong line, and 2) studies that involve the continuous steady state operation of the wind turbine with typical wind variations. Type one studies examine the transient voltage stability of the system. They compare the static load model to a dynamic load model. In addition, the accuracy of constant power factor PV curves is compared to the equivalent circuit of induction machine PV curves at predicting a voltage collapse. It will be demonstrated that the dynamic load model and the equivalent circuit of induction machine PV curves is the only combination considered that accurately predicts the transient voltage stability of the system. The effect of a weak line (WL), between the grid and the load, is compared to a medium strength line (ML). Other factors which will be varied are: the post fault re-closing times and the load composition. Type two studies focus on the continuous operation of wind turbines. These cases explore the steady state voltage stability of fixed speed wind turbines (FSWT) compared to doubly fed induction generator (DFIG) wind turbines. The dependence on wind power is increased to determine their penetration limit. It will be shown that the use of the DFIG wind turbine produces less voltage fluctuations and has the potential for larger penetration in the power system.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat