Study On Linear Active Disturbance Rejection Control Strategy For SiC MOSFET Three Level Grid Connected Converter

The neutral point clamped(NPC)three level grid connected converter has been extensively used in medium-high voltage and high power grid connected system due to its superiority of low output voltage harmonic content,high effiency,low device voltage etc..However,the quality of grid current will be degraded in the case of grid voltage fluctuation,distortion,harmonic contaminated,and perturbation of system parameters such as filter inductance.In order to improve the quality of grid current,anti-disturbance performance and stability,the ability of disturbance rejection and control strategy for SiC MOSFET three level grid connected converter were studied in this paper.The main contents are as follows:Firstly,the principle of three level grid connected converter was analyzed,and its mathematical model was established.Based on mastering the construction and principle of active disturbance rejection controller(ADRC),the variable parameter anti-saturation linear active disturbance rejection controller(VPAS-LADRC)was designed,the system dynamic performance was promoted,meanwhile,the inherent drawback of large current overshoot for LADRC controller was constrained.Secondly,in order to adapt the requirement of digital control system practically,the discrete model of three level grid connected system under LADRC control was built in this paper.The stability of closed control system was analyzed by Jury criterion,and the discrete stable domain range was derivated.It was closely related to the parameters of LADRC controller and sample period.Compared with the stability range without upper bounds in continuous domain,it meant a lot to the selection of controller parameters practically.In addition,the influence of LADRC parameters on the performance of observer and rapidity,stability,anti-disturbance ability for control system was analyzed.The optimum range of LADRC parameters was determined,and the characteristic of LADRC parameters was obtained when LADRC control system achieved the strongest anti-disturbance performance.Thirdly,the multiple objection optimum function including system response speed and tracking accuracy of output current was established,and the LADRC parameters were optimized through harmony search algorithm under different sample periods.The Matlab simulation model of VPAS-LADRC three level grid connected converter was built,its performance under grid voltage fluctuation,distortion,the mid-point in DC side unbalance and filter inductance changing was analyzed.The results showed that the current overshoot was decreased effectively,both the quality of grid current and anti-disturbance performance were improved.Finally,the SiC MOSFET overcurrent protection circuit based on drain source voltage detection was designed in this paper.On the three level grid connected converter experimental platform with TMS320F28335 as the minimum system,the grid connected experiment under VPAS-LADRC control was accomplished,the validity and feasibility of method and design in this paper were verified.