Design And Study On 250kVA Three Level Middle Voltage Inverter

The multi-level inverter can provide high voltage and high quality output with utilization of normal-voltage-rating power devices,which makes multi-level inverter desirable for high-power and high-voltage applications. And it has been widely investigated in the power electronics field.The energy dissipation of high voltage is very serious in our country. If we carry out the variable frequency(VF) speed regulation with multi-level inverter, that will bring considerable value not only in economy but also to society. Because the products used in our country are most from abroad, development of the VF speed regulation products of our own country makes great sense.In this thesis, the development of high voltage motor drive systems and the multi-level technique are summarized. The detailed structures and operating principles of several multi-level topologies are presented and explained. The operating principles of the diode-clamped three-level inverter and the SVPWM strategy are analyzed in detail. The key points of hardware construction of 250kVA inverter are introduced here by:component and material selection,principles and design of gate drive circuits with optical couple isolation, delay protection circuit, voltage and current detecting circuit, tempatrue detecting circuit.Two groups of switching power supplies are designed for the system. In addition, the experience and essential points in high voltage power inverter hardware design are summarized.Two methods to control the neutral point potential are proposed in this thesis which can solve the neutral point potential problem owned by three-level inverter.One is based on the hardware and the other is based on software.At last, the hardware and the control strategy are tested by doingexperiments.A series of experiment waveforms of the whole system are given.