Research On The Photovoltaic Grid-connected System With The Function Of Power Quality Improvement

With the depletion of the traditional fossil energy, solar power gradually become the focus in the world. Due to the characteristics of susceptible to environmental change, photovoltaic(PV)grid-connected in the large scale will have adverse impact on power grid, such as unstable output power of the PV system will cause the irregular and frequent action of grid-connected inverter power switch, which brings harmonic problems to the power grid. Moreover, with the development of power grid, more and more nonlinear resistance loads connect to the end of the grid, which may also influence the power quality. According to the above problems, this paper proposed a PV grid-connected system which can compensate harmonic and reactive current of the power grid. The detail content as follows:Firstly, the topology and working principle of PV grid-connected system and active power filter were analyzed. Then the feasibility of unified control of the two was explored in theory.The topology of PV grid-connected system with the function of power quality improvement was achieved. The mathematical model of the system was established based on the analysis of its working principle.Secondly, the pre-modeling of PV grid-connected system was analyzed. At first, PV cell engineering mathematics model was established. Based on the model, Matlab simulation module was set. Then, the mathematics model and the output characteristic in series, parallel,and series-parallel arrays of the PV cells under partially shading were carried on. The maximum power point location and the maximum power point mechanism were analyzed theoretically.The validity of the theoretical derivation was verified through the Matlab modeling and simulation. Power output of PV array under the condition of the partially shading had the characteristic of local maximum power points. So this paper proposed a global tracking MPP control algorithm. The effectiveness of the algorithm was verified by simulation.Finally, the control strategy of the system was studied and the effectiveness of the system was verified by simulation. The current closed-loop control structure of the system was established firstly. The PV grid-connected active current instruction, DC side voltage control signal and harmonic reactive current signal in power grid was deducted gradually. Thegrid-connected current instruction signal was achieved after instruction signal synthesis. Then the tracking control strategy of instruction current signal was analyzed. Using a proportional integral resonant current tracking control strategy can no-difference track the instruction current signal and ensure the stability of the system. Based on the above work, Matlab simulation module of system was built, and the simulation module was analyzed from three aspects. The simulation results showed that the system achieved the desired goal. In the process of transporting active power, the system can also compensate harmonic reactive current of the power grid at the same time.