Research On The Wave Control Of Three Phase Inverter

With the rapid development of power electronics technology, the inverter is widelyapplied in the fields of medical, industrial, transportation, military, bank and so on. Theinverter guarantees the normal operation of the electronic device, while it can also outputhigh-quality power to ensure the technical and economic characteristics of electricalequipment. Inverter applications can be divided into: AC stabilized power supply, powertransmission and power inverter, power system applications and new energy supply system.In the application of AC stabilized power supply, the waveform control technology hasbeen one of the hottest researches.In this paper, with a100kVA combined three-phase inverter as a research object,research on the waveform control of three-phase inverter technology was carried out. Thispaper mainly study the composite control strategy of PI control plus repetitive control andfeedforward control of output current. This paper focuses on the establishment of amathematical model of PWM inverter, design of the repetitive controller, CompositeControl strategy and the output current feedforward controller.Firstly, this thesis introduced two different types of main circuit topologies of thethree-phase PWM inverter, which were compared from the three aspects of power levels,control methods and conditions. Then a circuit model of single-phase PWM inverter wasestablished. After that, mathematical models in different coordinate systems of combinedthree-phase inverter were established. These models were continuous-time state spacemodel, the transfer function model and the block diagram model. Finally the frequencycharacteristics test of the plant was taken to determine the equivalent resistance of thecircuit model of the inverter and lay the foundation of the design for controller.On the basis of the mathematical model of PWM inverter, the paper started the designof the controller. Repetitive controller was designed around the three parts: the principle of repetitive control, inspection standards and design process. Since the cutoff frequency ofthe LC filter is low, the traditional design method of repetitive controller is difficult toachieve satisfactory control effect. Therefore this paper used a more appropriate repetitivecontroller design methods. In order to improve the dynamic characteristics of repetitivecontroller, PI controller was added into the control system parallel with repetitive controller.This paper also made the steady-state and dynamic simulation and take the steady-stateexperiments to prove the effectiveness and feasibility of the designed controller.In the end, in order to eliminate the effect of load disturbance on the steady-state errorfor improving the steady-state characteristics of the control system, this paper introducedfeedforward control of output current. The basic principle of feedforward control of outputcurrent was introduced firstly. Then the control system block diagram was simplified. Afterthat, Derivation of the transfer function of feedforward control of output current was madeand a proportional feedforward control strategy was adopted. Finally, the simulation provedthat feedforward control of output current not only reduced the steady-error of outputvoltage, but also improved the dynamic characteristics of the system.