Research On Modeling And Model Predictive Control Strategy Based On NPC Inverter

In recent years,with the rapid development of renewable energy,distributed new energy grid connected technology has been widely used and studied.It is not only required to be able to generate power when the system is stable,but also could transfer the stable power to the power grid in system failures or grid voltage umbalance cause by three-phase umbalance loads.In this paper,a new control scheme called Finite-Control-Set Model Predictive Control(FCS-MPC)which is proposed in recent years for power electronic control is studied.According to the defects of FCS-MPC scheme,the corresponding improvement scheme is put forward,and the improved FCS-MPC technology is applied to the control of the three-level Neutral Point Clamped(NPC)grid connected inverter.This paper first introduces several traditional grid connected inverter control strategy.By comparing the advantages and disadvantages of various control strategies,the Finite-Control-Set Model Predictive Current Control(FCS-MPCC)technology used in this paper is proposed.On the basis of this,the control principle of FCS-MPCC technology is introduced in detail.The construction process of FCS-MPCC technology is discussed from the aspects of system modeling,system discretization and cost function establishment.About the discretization of the system,this paper gives three different methods.To deal with the problem that the FCS-MPCC needs high processing speed,this paper gives three methods to reduce the amount of calculation.The simulation comparison shows that the proposed Space Vector Pulse Width Modulation(SVPWM)sector principle selection method of switch state could reduce the calculation burden of the controller.After the classical FCS-MPCC technology is improved,the control strategy is applied to the control of NPC inverter.This paper introduces three kinds of phase-locked loop structure.The tracking accuracy of traditional single reference coordinate system based on unbalanced power system is analyzed in detail.SOGI-PLL and DDSRF-PLL are proposed to solve this problem.The DDSRF-PLL is adopted to lock the phase of the grid voltage after comparing of simulation and experiment.After this,two control strategy of grid connected inverter under unbalanced grid voltage are proposed.They are positive and negative sequence separation phase locked method based on DDSRF-PLL and the method based on new power theory without PLL.These two control strategies are applied to the control of NPC inverter by using improved FCS-MPCC technology.A Simulink-Real-Time hardware simulation system based PCI-6229 is established.Through the main circuit design calculations,a grid connected inverter prototype is built.Experimental results show that the control algorithm used in this paper has a good control effect.