Key Technologies Research On Unified Power Quality Conditioner (UPQC)

In the process of industrialize and urbanization of our country,the power career have obtained great development.However,with the extensive use of power electronic devices,the input a lot nonlinear load into grid,which effected the stable and save of the grid.Especially in low voltage distributing network of village and town,existing low power factor,unbalance,high harmonic and voltage unqualified,which is due to line length and various load.At present,the power quality compensation devices are single function,large volume and insufficient in compensation quality.The researches in power quality treatment of low voltage distributing network are insufficient,such as needed more precise mathematical model to describe the characteristic of compensation device,more fast detection method to extract compensate component and more stable and high quality control algorithm,which is the key technique of low voltage distributing network power quality compensation,the research is challenging and creating.In order to popularize the applications of power quality comprehensive treatment technique and improve theory research,this paper taken low voltage distributing network unified power quality conditioner as target to study the key technique of comprehensive treatment,and obtained following achievement:Firstly,applied Matlab/Simulink to simulate and obtained the performance of 6 detection algorithms under 8 working conditions.The results shown that DSC detection method is stable and precise,but large in time delay.Thus propose a fast DSC detection method,the converge time is 1/3 of traditional and extract the fundamental frequency sequence precisely in all cases.Secondly,three level 3-phase 3-wire electronic devices without neutral line,commonly neglect the zero component and applied 2D-SVPWM to modulate.Divided into 36 sections,and exist neutral point voltage offset and sub sections division error.Thus proposed an optimal three-dimensional space vector modulation(3D-SVPWM)in three level 3-phase3-wire APF,which consider the zero component and only divided into 12 sections for calculation.Thus shorten calculation and eliminated sub sections division error.The algorithm can be utilized in both 3-phase 3-wire and 3-phase 4-wire electronic devices.Thirdly,the series and parallel unit of unified power quality conditioner(UPQC)are share a DC-link and electrical connect in AC-link,thus exist disturbance in both DC-link and AC-link.This paper proposed resistor separated topology and DC-DC separated topologies of UPQC,both can separate the disturbance in DC-link and improving current compensation performance.Establishes transfer function matrix model of UPQC contain series and parallel converter in equivalent model of transformer,then applying feed-forward decouple method base on unified model to decouple the interaction in AC-link.In addition,analyze the mechanism of series and parallel unit compensation and proposes a coordinate control algorithm base on unity power factor(UPF)detection method to eliminate the repeat compensation of series and parallel converter,the algorithm is simple and stable.Commonly,the parallel active power filter(APF)model without grid impedance,however,low voltage distributing network is a weak network,which must consider the grid impedance.This paper establish a precise model consist of APF,load and grid impedance.And then apply feedback linearization and proportional resonant differentiation(FL-PRD)control in inner current loop.Taken nonlinear load as linear load add harmonics current source,and then applied linear quadratic regulator(LQR)optimal control in inner current loop design without reference current detection and active damping.The proposed algorithm response fast,compensation harmonics well and is robust in a wide range of parameter variations.This paper analysis the characteristics of DC-link voltage,and proposed a simple fuzzy proportional(SFP)control algorithm to regulate the DC-link voltage.This controller obtained excellent performance in harmonics suppression and stability,what's more,the controller is simple.To sum up,this paper research on the key technique of power quality comprehensive treatment in low voltage distributing networks,such as detection method,modulation,modeling,topology of UPQC,decouple control and control algorithm of APF.Which lay the foundation of power quality treatment study and device development,the research achievement can be applied to design and control of other power electronic converter.