Control Strategy Research For Converter With Wide Inductance Variation

Inverter based on pulse width modulation(PWM) is the most widely used power electronic converter device, which plays an important role in many walks of life. Therefore, improving grid inverter power density, reliability and performance, and reducing the cost is very important. Selection of inverter passive filter inductor cores is very important, because it directly affect the efficiency, volume, costs and control performance of the system. Air gap ferrite and magnetic powder core material, with high resistivity, can achieve lower loss. So it is widely used in many places. However, because the linearity of air gap ferrite and magnetic powder core materials in large current is bad, the inductance value changes greatly, which will seriously affect the control stability, filtering effect, static and dynamic effect. This paper aims at researching the grid inverters, especially in view of control strategy research when the filter inductance widely changes.First, this paper introduces the basic working principle and main circuit topology of the three-phase grid inverter and deduces the mathematical model of the ABC, αβ, and dq coordinates.Secondly, this paper introduces the three-phase grid inverter system based on PI control strategy control strategy, mainly introduces the design of current loop PI controller parameters under nominal inductor value and analyze the stability of the current loop when filtering inductance widely change.Thirdly, study the control strategy based on the theory of the h-infinity mixed sensitivity. Overview of robust control theory Brief and theory of h-infinity mixed sensitivity and principles of the selection of weight function. Finally, focusing on design process of h-infinity mixed sensitivity controller when the filter inductance widely changes, and do the performance test to verify the feasibility of the control strategy.In addition, because h-infinity mixed sensitivity control has the shortcoming of lacking control precision, h-infinity mixed sensitivity is proposed combined with repetitive control of current loop control strategy. The paper introduces the basic idea of repetitive control at first, and Focusing on design process of the parameters of the repetitive controller, and check on the stability of composite control system.Finally, the simulation of PI control strategy, h-infinity mixed sensitivity control strategy, H-infinity mixed sensitivity control and repetitive control composite control strategy has been done when the filter inductance widely changes. H-infinity mixed sensitivity control and repetitive control with the combination of hybrid control strategy can be either remain robust stability or realize high precision control at the same time.