Preventive Control For Transient Security In Two-machine Power System Based On Trajectory Sensitivity Method

Modern electric power system has become increasingly large and complex. Due to the outburst failure or disturb caused by factors such as extreme weather, cascading collapse in transient process may occurred and even leading to a massive blackout. When sudden disturbance breaking, the parameters of regional power grid need to be ensured in a safe range to avoid unwanted outages and blackouts. With the higher demands for the quality of power, strengthening research on power system preventive control for transient security has an important and practical significance.The main work is as follows:(1) Using dynamic equivalence technology to simplify power systems is considered to be an effective measure in dynamic security analysis. Suitable generator model and load model are chosen to be the basis to study the complex power system. By analyzing the relation of several main variables in power system, it can be known that phase angle of voltage may affect other parameters. Basing on this point, the thesis hope to control the parameters by adjusting phase angle. Following this idea, a control strategy is proposed, TCPST can be applied in transmission lines. By choosing proper phase angle to ensure parameters in a safe range and system in a safe operation.(2) According to the classification of power system stability, the operation security is analyzed from two perspectives which are voltage security and angle security. Load bus voltage and frequency deviation of generator are chosen as the safety index of system. Two equivalent simplified models of power system are constructed as the basis for dynamic security analysis and preventive control. Adding thyristor controlled phase shift transformer(TCPST) in the above-mentioned models then the new models are formed.(3) How to choose a proper shifting-phase angle dynamically according to the current state of the system is a key point in preventive control. The thesis presents a preventive control scheme based on trajectory sensitivity method. The state trajectory can be calculated by initial state and system differential equation model. If the trajectory is not in the safe region, the state sensitivity with respect to the shifting-phase angle is needed and the current shifting-phase angle can also be obtained by judge whether the next moment trajectory is in safe range, thus the purpose of safe operation and preventive control can be realized.Theory analysis and simulation results have verified the validation of the proposed method. TCPST can improve the active and reactive power distribution by adjusting the phase-shifting angle of TCPST. Load bus voltage and the frequency deviation of generator can be controlled in a safe range respectively thus the generator trip can be avoided.