Application Of Selective Harmonic Elimination Pulse Width Modulation In Multilevel Inverters

With development of human society and progress of technology,the demand for electricity is getting bigger.At the same time,the capacity and voltage level of electric power equipment are increasing.As a result of these,the efficiency of electrical equipment has become the focus.In a variety of electrical equipment,the multi-level inverters play an important role in motor drive,photovoltaic power generation,AC-DC power grid and other fields.Among many modulation methods of multi-level inverters,the selective harmonic elimination pulse-width modulation(SHEPWM)is widely used in high-capacity and high-voltage inverters by virtue of the advantages such as:low switching frequency,low switching loss and high efficiency.This paper introduced the application of SHEPWM in varies kinds of multi-level inverters.And it analyzed its existing problems and solutions according to different situations.The details are as follows:Firstly,according to the basic principle of three-level T-type inverter,this paper analyzed the existing problems and solutions of scholars at home and abroad.And then this paper proposed a novel SHEPWM for the neutral-point voltage balance algorithm.The algorithm can restore balance quickly of the neutral-point voltage balance when the neutral-point voltage is unbalanced.And the fluctuation range is smaller after the neutral-point voltage balance.Compared with the traditional SHEPWM,this algorithm is significant.Secondly,this paper analyzed the advantages of parallel three-level T-type inverters.A novel SHEPWM was proposed for the parallel three-level T-type inverters.In the case of the same switching frequency,this method can eliminate more harmonics than the traditional SHEPWM.And the quality of system output waveform is better.However,the zero-sequence circulating currents of this method is larger.Therefore,based on the proposed SHEPWM,two kinds of zero-sequence circulating currents suppression methods for parallel three-level T-type inverters were proposed in this paper.The performance and effectiveness of the proposed methods were confirmed by simulation.Thirdly,this paper introduced the working principle of H-bridge cascade multilevel inverter.And the module power and device loss equalization strategy of H-bridge cascade multilevel inverter was introduced.This paper analyzed the advantages and disadvantages of different equalization strategies.At the same time,the SHEPWM was applied to the H-bridge cascade multilevel inverter to reduce switching losses and improve system efficiency.Simulation results were provided to verify the effectiveness of the SHEPWM for the H-bridge cascade multilevel inverter.Finally,the experimental platform of three-level T-type inverter based on dSPACE was built.This paper analyzed the design and working principle of the hardware circuit of the system in detail.The sampling circuit,protection circuit,driver circuit and other circuits of H bridge cascade multi-level inverter based on DSP&FPGA were designed.And then their working principle were analyzed.At the same time,based on the experimental platform,the validities of the control strategies proposed in this paper were verified by experiments.