Design And Implementation Of 30kVA Diode-clamped Three-level Inverter

With the development of new energy and new infrastructure,medium and high voltage and large capacity inverters are used more and more widely.Because the traditional two-level inverter has large withstand voltage and high output voltage harmonic under medium and high voltage input conditions,the research of three-level inverter has attracted more and more attention.Guided by the project of Foshan joint training base,this thesis designs a 30 k VA diode clamped three-level inverter with good dynamic and static performance and less harmonic content of output voltage.The main work of this thesis is as follows:Firstly,the working process of diode clamped inverter and the three modes of the switch on the bridge arm are analyzed in detail,and the reason of adding dead time is analyzed.The mathematical models in different coordinate systems,the three-level SVPWM space vector distribution and its working principle,the influence of different vectors on the neutral point potential,and the relatively reasonable wave generation timing,the sector judgment and vector action time calculation in the process of target vector synthesis are derived.Secondly,the control structure of feedforward decoupling is deduced by using the diode clamping mathematical model,and the influence of the selection of inner loop feedback variable on the system performance is analyzed.Finally,the inductor current is selected as the inner loop feedback variable.Due to the limitations of traditional PI control,this thesis adopts the compound control structure of PI and repetitive control in parallel,combining the advantages of the two control algorithms.The PI controller parameters of voltage outer loop and current inner loop are designed by zero pole matching method,and the repetitive controller is designed.Finally,a compound control strategy combining double loop PI and repetitive control is built in the simulation environment of MATLAB / Simulink.The simulation results show that the system has good dynamic performance and small output voltage harmonic THD.Then,according to the experimental indexes,the software and hardware system of diode clamped inverter is designed.The hardware system mainly includes the design of output filter parameters of main power circuit,the selection of main power devices,the selection of control circuit chip,the design of peripheral minimum system,the design of driving circuit and voltage and current sampling circuit;The software system mainly includes peripheral initialization and configuration,three-level SVPWM modulation algorithm,PI and repetitive control algorithm.Finally,an experimental prototype with a rated power of 30 k VA is built,the output waveform quality is tested under different power levels,and the dynamic load experiment is carried out.The experimental results verify the consistency between the designed three-level NPC inverter and the theoretical analysis.