Research On Novel Dual-output Neutral-point-clamped Three-level Inverter

Power electronics converter is now widely used in the fields of national defense,aviation,industry and so on.Inverters,as one of the power electronics converters that can convert input DC into AC,have been widely used.But now with the gradual development of electrical equipment,the use of six-phase synchronous motor and some applications requiring dual motor drive are gradually emerging.For this application,the proposal of dual output inverter is particularly important.Previously,the nine-switch inverter(Nine Switch Inverter,NSI)proposed by scholars is a two-level dual-output inverter,and has been widely used.However,the traditional two-level inverter is limited in the application of high voltage and large power.On the basis of existing circuit research,according to the characteristics and formation rules of these topology structures,a novel dual-output neutral-point-clamped three-level inverter(Dual-Output Neutral-Point-Clamped Three-Level-Inverter,DO-NPC-TLI)is proposed.The DO-NPC-TLI achieves two sets of independent three-phase AC outputs with 20 power switches and 12 clamp diodes.The topology of DO-NPC-TLI is described.According to its double output structure,it is divided into two working modes: inverter 1 effective mode and inverter 2 effective mode.Each working mode is divided into three working states,and the current flow path and output level state corresponding to each working state are analyzed in detail.The voltage stress and current stress of each power device are analyzed with 6 working states.On this basis,a feasible modulation method suitable for its structure is proposed.In this paper,a VSVPWM strategy for DO-NPC-TLI is proposed based on the idea of time-division modulation of NSI,space vector pulse-width modulation(Space Vector Pulse Width Modulation,SVPWM)and virtual space vector pulse-width modulation(Virtual Space Vector Pulse Width Modulation,VSVPWM)of NPC-TLI.A switching cycle is divided into two parts,and each group of inverters works for 1/2 cycle.Modulation process is completed within their respective effective cycle according to the reference vector of each group of inverters.To simplify the space vector modulation process,a carrier pulse width modulation(Carrier-based Pulse Width Modulation,CBPWM)strategy based on VSVPWM strategy is proposed.According to the duty ratio and switching sequences of VSVPWM strategy,the modulation wave expressions are calculated.Combined with triangular carrier and logic comparison,the driving signals of switches are obtained.CBPWM strategy avoids a lot of trigonometric function calculation,omits the judgment of small sectors,and can realize the effective modulation of the circuit only through simple and regular modulation waves and logical comparison.On this basis,the switching sequences are optimized and the CBPWM strategy is optimized.The optimized strategy simplifies the logical comparison part and reduces the number of modulated waves,and the modulated waves are summed up into three groups of formulas,which can realize the effective modulation of the circuit.The simulation platform was built by MATLAB/Simulink and the experimental platform was built by DSP and FPGA.The correctness of the simulation and experimental results also indirectly indicated the feasibility of the proposed DO-NPC-TLI topology structure and the effectiveness of the modulation strategy.