Research On Three-phase T-type Three-level Non-isolated Grid-connected Inverter

There are several advantages of the three-phase three-level inverter. Its outputvoltage harmonic content as well as the value of dv/dt and EMI is quite small. So itis a hotspot in the high-pressure high-power inverter application research. Thethree-phase diode-neutral-point-clamped three-level inverter is a main type oftopology of three-phase three-level inverters and it has been widely applied. Thethree-phase T-type three-level inverter is an advanced type of topology based on thethree-phase diode-neutral-point-clamped three-level inverter. The neutral point ofthe inverter is clamped by series-opposing switches of each bridge arm. In this way,the output voltage of the inverter has three levels. Compared with the three-phasediode-neutral-point-clamped three-level inverter, two clamping diodes are reducedin each phase of the inverter, which can reduce the losses and inverter size. It is avery promising topology.In this paper, the three-phase T-type three-level non-isolated photovoltaicgrid-connected inverter is introduced. Its principles and commutating process areanalyzed. The space vector modulation method and its implementation steps areillustrated. Common mode current suppression and neutral point potential balancecontrol are two main problems of the three-phase T-type three-level non-isolatedphotovoltaic grid-connected inverter. Firstly, main methods to solve the twoproblems are introduced respectively. And the advanced space vector modulation isanalyzed, which is a way to solve the problems. Then a synthetic method isproposed, which inhibits common-mode current by low pass filter and controls theneutral point potential balance by advanced space vector modulation. Thensimulations on the mentioned methods are conducted in the Matlab/Simulinkenvironment, and the simulation results verify the effectiveness of these methods.At last, the hardware design of the three-phase T-type three-level grid-connectedinverter is introduced.