Research On Novel Cascaded Converter For Medium-High Voltage

Cascaded converter is the reseach subject of this paper.First, it extends the concept of basic power electronics units, and after analysing the structure of the symmetric H-bridge circuit, it presents a new type of asymmetric H-bridge topology and analyses the combination principle for the two structures. Then a new topology of the four-level inverter is given, and also its operating principle and all states.Then a special SHEPWM algorithm is put forward for the circuit switching control with a desired output wave, according to the features of the new topology. Compared with the former converters, the obvious advantage of this new topology lies in reducing the quantity of switches but not reducing the number of the electrical levels, and also lies in reducing the system loss and increasing the efficiency effectively. The SHEPWM algorithm can optimize the output wave while keeping a lower switch frequency, and make the advantage of this system in hige-power application more outstanding.Second, traditional converters usually adopt diodes with a big capacitor as the rectifier in each power cell at the input side. In this way the power factor is low and may generate a great deal of harmonic which infuse into the power grid and cause harmonic pollution. The paper takes the APFC as a part of the rectifier, and by simulation gets the conclusion that taking the APFC not only reduces the harmonic pollution to power grid, but also improves the converter's performance.Last, the hardware design of the control system is presented. This design has something of significance for the further research of the medium-high voltage converter.