| With an increasing demand for high quality power from related industries andimportant departments, high-performance PWM inverters have attracted more and moreattention. At the same time, due to the development of semiconductor power devices, aswell as improved steadily of various control methods, numerical control has replacedtraditional analog control by virtue of its superior control ability and easier standardizedproduction to meet the requirement of power modularization. Nowadays the combinationof traditional control methods and digital control methods is usually adopted. However,the traditional control methods under mathematical control is sometimes not so good asthe original analog control, so a detailed modeling and analysis as well as a direct controldesign in discrete domain is presented in this paper to acquire the accurate digital controlmethod.This paper mainly concentrated on double closed-loop digital control technology forouter ring of voltage and inner ring of the inverter power current. The basic knowledge ofinverter, the development of digital control method and both the advantages anddisadvantages of digital control methods compared with traditional control methods areintroduced first.Next, the modeling and analysis for the inverter is adopted and the impact on theinverter output voltage are discussed. A mathematical model of the inverter in discretedomain derived from the circuit principle is acquired in which the dead zone, a beat lagand zero-order hold are of more importance and are more detailed elaborated. The deadzone effect is modeled and analyzed particularly while its equivalent damping is thenanalyzed approximatelyThe controller is designed in discrete domain according to the acquired model, and itscut-off frequency is analyzed to get appropriate parameters for controllers in inner currentloop and outer voltage loop through stability criterion analysis such as root locus analysisand bode diagram analysis. The accuracy of the model is verified by comparing thestability of the model and simulation while the adaptability of the circuit to the changes inparameters of the proposed double-loop controllers is analyzed. Results show that the proposed double-loop controller has good robustness.Finally, experiments are carried outto verify the accuracy and precision of theoretical analysis. |
