Research On Novel Voltage-doubling Multilevel Inverter Topology And Its Modulation Strategy

The new type of electric power system is high speed development,new type application scenarios constantly emerging,such as the low voltage dc power distribution of the power electronic technology rapid development provides the inexhaustible power,at the same time on the performance of the power electronic equipment various new requirements are put forward.Switched-capacitive multilevel inverter with high voltage gain and low output harmonics has been widely used in new transmission and distribution equipment,new energy power generation,motor drive and other fields.In the field of power electronics,the new multilevel inverter topology with high voltage gain and its control method is one of the research hotspotsThis thesis takes double-voltage gain five-level inverter circuit as the research object,and carries out research from three aspects: circuit topology,modulation method and grid-connected application.The main research contents are as follows:(1)A new six-switch double-voltage gain five-level inverter topology is proposed,which is composed of two half-bridge units and a switched-capacitor unit.The time-sharing series and parallel operation of DC input power supply and capacitor can be realized through the carrier cascade modulation strategy,so as to realize the autonomous boost of the circuit and the five-level output voltage waveform.The proposed inverter topology has the advantages of fewer switching devices,capacitor voltage self-balancing,low voltage stress and simple modulation strategy.(2)A new hybrid T-type five-level boosting inverter topology is proposed.The topology is composed of a double voltage charging unit and T+I inverter unit.The DC input power and the capacitor run in series and parallel by using the carrier cascade modulation strategy,which realizes the autonomous voltage boosting and five-level voltage output of the circuit.Different from the new six-switch double voltage gain five-level inverter topology,the charging and discharging process of the voltage charging unit in this inverter topology is independent of the inverter process,and the control algorithm is simple.And can realize the current bidirectional flow.Aiming at the problems of surge current and capacitance voltage fluctuation when the topology is started,the optimization of voltage doubling circuit and the closed-loop control method are studied.(3)Research on grid-connected application of a new type multilevel inverter with double voltage gain is carried out.The working principle of grid-connected single-phase multilevel inverter is analyzed,and the comparison between SRF-PLL and SOGI-PLL is analyzed.At the same time,the working characteristics of L,LC and LCL filters also are analyzed.Combined with PR control algorithm,the grid-connected working process and output characteristics of the new voltage doubling five-level inverter are simulated and verified by experiments.The results show that the new five-level inverter has the advantages of double voltage gain,low output harmonics and self-balancing capacitor voltage.Figure[59]Table[8]Reference[61]...