| Along with the increasing progress of science and technology, some large-scale equipments, precise instruments have been widely used in industry, petroleum, chemical industry, and other fields. On the other hand, with the increasing use of big power electronic equipments and the non-linear loads in power system, the power quality problem is becoming more and more severe. Unified power quality conditioner (UPQC) is a kind of integrated equipment, its comprehensive power quality regulation abilities include both active power filter function and dynamic voltage restores function. It can not only compensate for harmonic current and reactive current, but also can recover voltage flickers, sag, fluctuate, voltage imbalance and short-time interruption of power system dynamically. Therefore, it becomes the hot research topic of power compensation.The study has been pursued comprehensively and systematically about the circuit structure, compensation instruction detection method and control problem of UPQC, and does the main work as follows.1. Based on the consideration of optimizing UPQC circuit structure and realizing decoupling control, A novel double four-legged topology is proposed in this thesis as the main circuit of UPQC. The single-phase equivalent circuit model is established for discussing the characteristics of UPQC system and power flow under different working patterns. By analyzing its working principle under direct control and indirect control method, it reveals that the task of each converter is consistent.2. Through analyzing the constraints brought by traditional detection methods to compensation instructions detection, a new improved LMS adaptive filtering algorithm is proposed, combined the improved algorithm with the instantaneous reactive power theory, so as to realize harmonic reactive current detection and voltage disturbance identification. In the aspect of voltage compensation instructions detection, a compound voltage compensation strategy is designed for voltage optimal compensation of UPQC and smooth transition of load voltage.3. In view of the voltage tracking control and current tracking control problem, a sliding mode soft switch decoupling control method and a control method based on 3D-SVPWM strategy are put forward respectively. The former method based on decoupling control of four-legged topology, by adopting an improved reaching law, so as to ensure the rapid convergence of control system error and weaken the chattering phenomenon. The latter method expands hysteresis SVPWM control from two dimensional space to three dimensional space, choosing the optimal control vector according to the position of error current space vector and reference voltage space vector, so as to realize high performance current control of four-legged converter.Using software MATLAB/SIMULINK, the simulation model of UPQC control and detection system based on double four-legged topology structure was established. Simulation results revealed that:1. The improved detection method has favorable quickness and accuracy, which is fit for real time detection of UPQC compensation instructions.2. The improved control methods can achieve fast convergence of control error and reduce the steady-state error, which means they have excellent static and dynamic characteristics.3. After compensation of UPQC, the load side voltage recovers to the desired value, meanwhile, the sinusoidal current of grid side and unity power factor are also realized. |
