The Research Of A Cascade High Voltage Inverter With Energy-feedback Function

Since the1990s, with the improving of awareness of energy saving, inverters are widelyused. The technology of low voltage inverters is well developed, while high voltageinverters are falling behind. Due to the constraint of the voltage level of power devices, it isdifficult to get high voltage output using a single device. But the emerging of multi-leveltechnology makes it possible to use many low voltage devices to construct a high voltageinverter. There are some different topologies of mutil-level technology, most of which arenot able to feedback energy to the grid， when the motor is in regenerative or brakingcondition. The paper introduces PWM rectifier structure to cascade mutil-level convertersto get energy-feedback function as well as good quality of input current. The converters ofthis new structure will make enormous economic benefits and be competitive in the market.In the paper, the new structure will be analyzed, especially the control strategy of therectifier side and inverter side. We have designed hardware and software of the invertersystem. The main content of this paper is listed below:(1)The energy feedback principle of induction motor is explained, and we made simulationto verify the constraints of traditional cascade mutil-level inverters.(2)The structure of this new inverter is described. Based on the model of PWM rectifier,two control strategies are proposed: fixed switching frequency direct current control,predict current control. They are based on different ideas, the former making use ofcontinuous model while the latter making use of discrete model. Simulations arepresented to show the difference.(3)The carrier phase-shift PWM control strategy of H-bridge is analyzed by means ofmathematical analysis. The carrier phase-shift modulation is an effective way to reducevoltage harmonics and produce high voltage output. A simulation on the new typeinverter system was made, including PWM rectifier control、H-bridge control andmotor control. (4)The hardware components are chosen after computing。The control circuits are designedbased on the structure of DSP&FPGA which are connected by external bus. Thehuman-machine interface is set up using a touch screen. The principle and programmingmethod of the screen is introduced.In the last,I made a summary to my work. Some useful conclusions are proposed and someshortcomings are pointed out in this paper.