Research On Detect And Control Techniques Of Unified Power Quality Conditioner

Unified power quality conditioner (UPQC) is a device multi- function and it can settle many power quality problem which is one of the most important equipment among the custom power devices. UPQC can not only improve the current quality of the power network but also enhance the voltage quality of the power load. Now it is not widely used in industrial application and its detecting and control technique need to consummate further. This dissertation is dedicated to investigate its signal detecting, control models and control strategies and give the new detecting and control strategy. These researches are significant to improve the cosmically industrial applications of UPQC.There are negative sequence elements, zero sequence elements and other harmonics ingredients in voltage and current signals. The dq0 transformation method based on the instantaneous reactive power theory is the most popular method to UPQC in compensating the non-fundamental elements of the signal. The calculation of the dq0 method is large, its hardware in utility is complex and it is not suitable to the single-phase UPQC. A novel non-positive fundamental sequence voltage and current detecting method is presented based on analyzing the function of trigonometric function in detecting the fundamental positive sequence voltage and current. It achieved the expression of fundamental positive sequence voltage and fundamental positive sequence current by using a few calculation of pending test signals multiplies with a cosine function and a sine function. The compensation of the non- fundamental positive sequence ingredients is established on this method. Furthermore, this method can follow the change of the frequency and primal phase angle in dynamic and real-time. It increased the adaptability when parameters of system had changed.The double-loop strong coupling problem was existed in the model of some power devices if they were transformed from abc coordinate system to dq coordinate system. So the entirely decoupling control is impracticability. It is the same with the model of UPQC. According to it, a novel decoupling method is proposed in this paper: The model is established by adding a transformation from dq system toαβsystem which has got from abc system to dq system. The elements of each coordinate are decoupled completely in this new model. Using this new method, the entirely decoupling model of UPQC has achieved. The decoupling model of UPQC is advantage to the decoupling control and control system design under some control modes and control manners. It is helpful to enhance the control results and system design.The UPQC control can be sort of series/voltage shunt/current and series/current shunt/voltage mode based on the different control objects of series part and shunt part. Both modes can be controlled by open-loop and close-loop manner. Different control strategies were proposed under two control modes and control manners. Method which calculated the reference value and detecting term was presented under different control strategies. The parameter calculations are taken full advantage of UPQC decoupling model in open-loop control. Otherwise, as the control object is auto-conditioning by given error signals in close-loops, it is independent of UPQC series and shunt model. Yet, it is very important to design the parameters of close-loops. Simulation and experient results show every kind of control mode can realize the control objects of UPQC. The results of two control modes are almost the same when they are under same control manner.The PI controller, which is restricted to its quantity and capability of parameters, is always used in UPQC DC voltage control and the control capability is difficult to achieve perfect. The fractional PIλDμcontroller has more parameters than traditional PID controller and it expands the optimization field of controller design and control rule. It is introduced into the UPQC DC voltage control. The simulation shows that the control results by using PIλDμcontroller are helpful to enhance the dynamic control capability than the traditional PI control. This research work is supported by National Nature Science Foundation of China (50467002).