Model Predictive Power Control Of Single-Phase Three-level Rectifier

Single-phase three-level rectifier is widely used in photovoltaic grid-connected inverter,electric vehicle,high-speed railway traction system and other related fields,because of its characteristics of bidirectional energy flow,unit power-factor operation and low harmonic content,which has achieved great economic and social benefits.In recent years,with the rapid development of power electronics technology,the demand for power quality is also improving.Especially with the continuous increase of highspeed railway mileage,higher requirements are put forward for the dynamic response ability of single-phase rectifier control system and the performance stability of ac-dc side under steady-state condition.Therefore,it's of great engineering application value to study the control strategy of single-phase three-level rectifier.This paper takes single-phase three-level rectifier as the research object,takes improving the system dynamic response speed,reducing the harmonic content on the current side and ensuring the stable output of voltage on the dc side as the main objectives,and starts with the selection of control theory and optimization of control algorithm,which is described as follows:To begin with,on the basis of building up mathematical model related to singlephase three-level rectifier and analyzing its working principle in detail,this paper introduces the SVPWM modulation algorithm and neutral voltage balance control,and the switching state of tubes in rectifier is controlled combined with direct power control.At the same time of introducing the related wave trap and phase-locked loop design,this paper verifies the accuracy and feasibility of the proposed theory by simulation.Next,after establishing the prediction model of single-phase rectifier in discrete time domain,the principle and implementation of FCS-MPC algorithm based on PI outer ring are introduced and analyzed,including the establishment of value function and the definition process of network side current in static coordinate system.Compared with the traditional space vector modulation algorithm mentioned above,the proposed control algorithm has the advantages of lower ac side harmonic content at the same switching frequency.In addition,because in the traditional FCS-MPC algorithm based on the PI outer ring,the overall control performance of system is affected by the parameters of the outer-ring PI controller,which may lead to the shortcomings of slow dynamic response or overshoot.Therefore,an improved FCS-MPC algorithm based on the dynamic reference setting of the outer ring is proposed.In the control algorithm,the concept of dynamic reference design is adopted to replace PI control in the voltage outer loop.By deducing the expression based on dynamic reference design,it is used to define the relevant formulas of the reference current on the grid side and the reference voltage on the dc side in the static reference coordinate system.Compared with the traditional FCS-MPC algorithm,the simulation verifies that the improved algorithm has the advantages of faster dynamic response speed,smaller voltage drop of the output voltage on the dc side and smaller fluctuation after entering the steady-state.Finally,this paper builds a low-power experimental platform with DSP as the control core,and on this basis,the algorithms proposed in this paper are compared and verified.