| As the global energy demand increases year by year,a general consensus is forming to vigorously develop renewable energies,such as wind and photovoltaic energies.Nowadays,the capacity of photovoltaic power generation grows rapidly,and the transmission loss gains much attention.An effective way has been adopted by improving the voltage level of photovoltaic dc-bus.However,meanwhile,it gives rise to some new problems such as voltage stress of power devices.To address this issue,this paper devotes to the topology and the corresponding control strategy of multilevel inverter.The main research work is as follows:A hybrid clamped six level(HC-6L)inverter is proposed.The derivation process of the topology is given.Accordingly,all the switch state combinations are listed,where the harmful switch states and invalid switch state are removed,leaving the eight applicable switch state.The switching principle between the eight switch states is revealed.To display the advantage,it is compared with the existing HC-6L inverter.The modulation strategy of the proposed HC-6L inverter is analyzed.Especially,the influence of the switch states on the energy absorption of flying capacitor is given.By reasonably arrange the redundant states,a voltage balance method of flying capacitor is proposed.On the other hand,it is found that the output voltage will be distorted during the dead time in some state transition processes.The distortion mechanism is presented and a two-stage dead time method is proposed to alleviate the distortion.The state space average model of the three-phase HC-6L inverter was established.In dq coordinate system,the controller parameters of the outer voltage and inner current loop are designed,respectively.The simulation model of the three-phase HC-6L was built in Matlab / Simulink,and a 6k W prototype was built in the laboratory.The simulation and experimental results verify the the practicability of the proposed topology and the effectiveness of the proposed control method. |
PDF Full Text Request