Unified Power Quality Controlof Three-phase Photovoltaic Grid System

With the rapid development of the industry, as well as traditional fossilfuels dwindling, worldwide environmental pollution and energy shortage havebecome important factors restricting the sustainable development of humansociety. Solar energy is an important member of the new energy, it has thefollowing advantages: unlimited, easy to use, no pollution, do not damage theenvironment. At present, the development of the global photovoltaic powergeneration is very rapid, the existing power system will be more and moreaccess to photovoltaic power. Compared to traditional power generationtechnology, photovoltaic technology is influenced by the external environment.The output power is intermittent and it uses a lot of power electronic devices,the amount of non-linear and impact load.These factors bring many new powerquality problems.In this article, a complete three-phase photovoltaic grid power generationsystem is studied. Through the study of photovoltaic power generation and, andcontrol strategy, it analysis the system of power quality problems and theirsolution. This article focuses on the following aspects of the detailed analysisand simulation study:Firstly, according to the working principle of the solar cell, the electricalcharacteristics of the solar cell is analyzed. A MATLAB simulation model isestablished, which can simulate the output characteristics of photovoltaic cellsin different light intensities and battery temperature. By controlling the dutycycle of the Boost circuit Photovoltaic, Maximum Power Point Tracking(MPPT) is achieved, using perturbation and observation method. Simulationresults show that the model is responsive to light intensity, temperature changes,and be able to quickly and accurately to achieve maximum power tracking,versatile and dynamic performance;Secondly, the mathematical model of a three-phase photovoltaicgrid-connected inverter based on the rotating coordinate system is established.On this basis, a three-phase space vector inverter based on voltage and currentdouble closed-loop decoupled control is designed to achieve active inverter,reducing the total harmonic distortion of the system current waveform toimprove the output current waveform. It has excellent dynamic and steady-state performance, as well as satisfying the grid-connected PV requirements.Thirdly, the Dynamic Voltage Rrestorer (DVR) is modeled and simulatedagainst the three-phase photovoltaic grid system voltage distortion. On thebasis of analysis of the basic principle of the dynamic voltage restorer, thedistortion of the voltage detection method is improved. A three-phase dq0transform detection algorithm is used to establish the common model of thethree-phase balanced and unbalanced voltage detection. The control strategybased on incremental parameter fuzzy self-tuning PID controller is designed, sothat the DVR is able to compensate for the photovoltaic power due to changesin light intensity and temperature of the battery side voltage distortion, as wellas improving the power quality of photovoltaic power station.Finally, the active filter is modeled and simulated against the thethree-phase photovoltaic grid system harmonic problems. Based on analysis ofthe basic principles of the shunt active power filter, the harmonic currentdetection method is improved. Improvedi p iqharmonic current detectionmethod which based on the delay integral gain links is proposed. And thecurrent control strategy which based on variable frequency hysteresis spacevoltage vector is proposed. The current tracking performance of the active filteris improved. The active filter suppresses the user side of the harmonic currenton the condition of the non-ideal linear load, as well as improving the powerquality of photovoltaic power station.