Research On Control Strategy Of Three-phase Voltage Type Grid-connected Inverter With Direct Power Control

Energy crisis and environmental pollution problems have become increasingly prominent, people have to explore new development direction of energy. Three-phase voltage source grid-connected inverter is an important transformation device of distributed power supply into the power grid, which plays a role of bridge and link. It has been a hot research topic, and it is widely used in all aspects. However, there exsit many problems, such as the current harmonic pollution, low power factor, the number of sensors and the ability to resist interference. In this paper, the direct power control (DPC) is applied to the grid-connected inverter.In this paper, analyzed the grid-connected inverter's principle of operation and established the mathematical model of three different coordinate systems. On this basis, combined with the instantaneous power theory, A strategy based on voltage-oriented direct power control (VO-DPC) is applied to the inverter. Analysed the basic principle of the structure of the switching vector table, due to heavy use of zero vectors, the instantaneous power's adjustment ability is insufficient, By improving the switching table algorithm, a novel switching vector table is established, enhanced the adjustment ability of instantaneous power.Introduced the concept of virtual flux linkage (VF), combined with SVPWM modulation, the direct power control system based on virtual flux linkage (VF-DPC) was constructed, estimate instantaneous power through virtual flux and the fixed frequency control without AC voltage sensor was realized. In order to solve the DC offset problem of the pure integrator in traditional virtual flux observer, a novel observer is designed. The fuzzy intelligent control method is introduced, which improved the conventional VF-DPC system, thus the IVF-DPC system based on fuzzy control was established.Finally, the system models was built under the Simulink environment, completed a number of simulation experiments. The results show that the VO-DPC realized decoupling control of active power and reactive power, it is simple in structure, no need of complex coordinate transformation, small harmonic pollution and high power factor. IVF-DPC based on fuzzy control not only has the above advantages, but also realize the control without AC voltage sensors. It can operation with high efficiency and reliability, and the robustness is better, so it has a very good application prospects.