Research On Discontinuous Pulse Width Modulation And Related Problems For Three-Level Converters

With the development of new energy technologies,three-level converters are widely used in power conversion,motor drive and other fields.This paper deeply analyzes the working principle of the neutral point clamped(NPC)three-level converter and its typical modulation method.This paper focuses on the switching loss and neutral point potential fluctuation problem of the three-level converter.First,it outlines the application of three-level converter under the background of photovoltaic grid-connected power generation and the popularization of new energy vehicles.It summarizes the recent domestic and foreign research status of three-level converters from topologies and modulation strategies,and further summarizes the key problems of switching loss reduction and neutral point potential balance in three-level converter control.Second,the the three-level converter experimental platform design is introduced from the aspects of hardware design and software design,and the operation and control principle of the three-level converter is briefly introduced.The output level of three-level converter and its commutation path during level switching are analyzed,and the mathematical model in the ?? frame is established.Based on this,a double closed-loop control method is proposed,in which the PI regulator is used as the voltage outer loop and the deadbeat controller is used as the current inner loop.Typical three-level converter modulation methods are introduced,which are CBPWM,SVPWM,VSVPWM and SHEPWM method respectively.Their basic working principles as well as the switching loss reduction capability or the neutral point potential balance capability are briefly analyzed.Then,nine kinds of clamping modes of the traditional discontinuous pulse width modulation method are analyzed.The clamp mode of the traditional DPWMI-IV and its performance in the reduction of switching loss and midpoint potential balance are briefly analyzed through simulation and experiments.Finally,serveral DPWM methods with different switching loss reduction requirements are proposed.These include discontinuous pulse width modulationfor different power factors(PF_DPWM),discontinuous pulse width modulation for minimum switching losses(SLMDPWM),and discontinuous pulse width modulation for neutral point potential balance(NPBDPWM).After elaborated on the above three DPWM methods,the feasibility of the proposed method was theoretically verified by the Matlab/Simlink simulation model.Finally,the experimental results shows that the proposed PF_DPWM method can obtain the switching loss reduction capability under any load condition,the SLMDPWM method can achieve the minimum switching loss,and the NPBDPWM method can achieve the neutral point potential balance capability while the switching loss reduction.