Research On Coordinated Control Strategy Of Photovoltaic Grid-connected Inverter And APF

Recent years,although photovoltaic power-generating has been favored by people due to its advantages of green and abundant resources,the low utilization rate and intermittentness limited its application.On the other hand,as the increasing development of power electronics technology,the proportion of using nonlinear load increases year by year in consumption,it inevitably aggravates the harmonic pollution to the power grid.The most effective means to harmonic control currently is the use of Active Power Filter(Active Power Filter,APF),but APF also faced with the development problem of single function and high cost.Both photovoltaic power generating and APF has broad application prospects,but limited by its own shortcomings,for this reason,this paper studies a photovoltaic grid-connected inverter and APF collaborative control strategy.Comparing with both only one used under the topology structure basically unchanged,this system can not only realize the photovoltaic grid-connecting but also realize the function of APF,thus making up for the shortcomings and limitations when one of two used alone.In this paper,first compared and analyzed the topological structure and working principle of photovoltaic grid-connecting device and APF,verified the possibility of coordinating control between,the two theoretically,indicating three kinds of working methods in the system for coordinating control strategy.Measuring the harmonic and reactive power component in the system based on ip-iq of instantaneous reactive power theory;synthesis method of instruction current in coordinating control strategy between photovoltaic grid-connecting and APF is studied.Considering the traditional software PLL is susceptible to the change of complex grid,an improved software phase-locked loop(Third Order Generalized.Integrator-Phase Locked Loop,TOGI-PLL)based on the third-order generalized integrator is discussed.The phase locked loop can accurately lock the phase of the power grid voltage when voltage of the power grid is asymmetric and even there are harmonic and DC components.In this paper,focused on the SVPWM current tracking control method of single hysteresis ring,and its regional judgment is optimized.An improved double-hysteresis current tracking control method based on SVPWM is proposed,which makes the effect of current tracking control more ideal.Based on the above research,the simulation model is established by using MATLAB/Simulink software,and simulated three working modes of the system:working in complete photovoltaic grid-connecting;complete APF,as well as unified work of grid-connecting with APF,and the simulation results verifies the correctness and feasibility of the coordinating control strategy.Designed and constructed the hardware experiment platform based on TMS320F28335 control chip,which mainly do the experiments on TOGI-PLL,ip-iq harmonic current detection method and double hysteresis loop SVPWM current tracking control strategy,etc.The results also prove that the core control algorithm used in each module is reasonable and feasible.