Research On Modulation And Control Of T-type Nested Neutral-Point-Clamped Converter

In the development of modern society,energy conservation has become a major theme of human today.With the large-scale application of the motor drive system in various industries,the power consumption control of the motor drive system has attracted widespread attention.In modern motor control system,frequency converters are commonly used to regular speed,control torque and save energy.Due to the limitation of the withstand voltage and current resistance of power devices,the traditional two-level,NPC three-level,FC three-level inverter can not be applied in the higher voltage field.In order to improve the power level of the converter and reduce the pressure of a single power device,researchers began to study higherlevel converters.However,the higher the voltage is,the complexity of its control method will increase exponentially.This thesis mainly studies the T-NNPC four-level inverter topology proposed in recent years.Firstly,the topology of T-NNPC is introduced,and compared with other four-level.topologies,the advantages it existing.The operation principle and the method of controlling the floating capacitors are analyzed,and verified by the in-phase shifting carrier sinusoidal pulse width modulation method.It is found that the switching loss of the modulation method is large.Then this thesis studies the four-level space vector pulse width modulation(SVPWM)method.Firstly,the traditional four-level SVPWM method is introduced.Because of the large number of trigonometric functions in the calculation process,the complexity of the system is increased.The four-level SVPWM modulation method based on space vector mapping simplifies the calculation process and this thesis introduces its detailed operating principle.Based on the principle of SVPWM,an improved flying capacitors control method is proposed.The transition state of T-NNPC four-level topology is analyzed,and an improved dead zone compensation method is given.The SVPWM based on space vector mapping and the proposed improved method are simulated and verified in PLECS software.Finally,a permanent magnet synchronous motor speed control system based on T-NNPC four-level converter is built.Firstly,the mathematical model of permanent magnet synchronous motor are introduced.Then the id=0 control method is selected to build the T-NNPC fourlevel inverter speed control system,and the speed control system was verified by simulation.Then based on the existing hardware platform of the laboratory,the experiment platform of the four-level converter speed control system is built with DSP2833 5+CPLD as the control core.The experimental results show that the system’s good speed regulation performance,and illustrates the practical value of the T-NNPC four-level converter.