Design And Implementation Of Three-phase Four-legged Inverter System

With the rapid development of modern society, inverter technology has become an important part of power electronic technology. Inverter technology is mainly used in all the fields where we need convert DC to DC, such as driving of ac motor, uninterrupted power supply, variable frequency power and reactive compensation. Inverter technology can transform poor primitive DC to excellent AC which can meet the requirement of voltage and frequency of loading conditions. The paper focuses the research and design on three-phase four-legged inverter through control strategy and the design of software and hardware.At the beginning, in this paper, the topology of three-phase inverters with unbalanced load and the equivalent circuit is analyzed in detail. Before studying controlling the output waveform of three-phase four-legged inverter, the paper studies the control method of single-phase inverter, and then based the control method of single-phase inverter proposes a three-phase four-wire inverter control method. A double feedback loop control scheme, which is outer control loop and inner control loop, is proposed for single-phase power supply through sinusoidal inverter. The outer control loop uses two PI controllers for the independent control as magnitude and phase to ensure a highly steady precise of the voltage output from inverted power supply. The inner control loop added a proportion of the controller, reduced the filter inductor, to ensure a fast response to the voltage output and reduce waveform distortion.This paper elaborates the design method and hardware structure of three-phase four-legged inverter, especially introduces the design of control circuit including the design of software and hardware. The control system of three-phase four-legged inverter is consisted by a PLC, a touch screen and central control unit.This paper proposes the program of designing the control circuit and detailed introduces the design of the hardware and software of central control unit. In the hardware, the paper designs the small systems of DSP and FPGA which compose the central control unit, and introduces the design of PLC and HMI in detail. In the software, first the control algorithm is realized on DSP and FPGA, and second the control system realizes logic control and command control through designing the program of PLC, and then the program of dealing with data and transmitting data is realized on PLC according to Modbus agreement.At last, the paper provides the waveforms of three-phase four-legged inverter, and analyzes the results.