Research On Voltage Stability Of Micro-grid With Series Combination Of Micro-source

In this thesis, aiming at the problems that exist in the structure of AC, DC and hybrid micro-grid, an AC micro-grid with series combination of micro-sources is studied. The existing of wind, solar and other combination micro-source in the micro-grid system achieves the complementary use of nature resources. And structure of the inverter in series such that the lower DC voltage capable of outputting a high AC voltage, while significantly reducing the harmonic content of the system output voltage. A plurality of series subsystems includes hybrid micro-sources and inverter units within the system, to some extent, improve the reliability of system operation. However, due to the randomness and uncertainty of the natural conditions of the outside world, stable operation of the system is still the problem worthy of study, and voltage stability is an integral part of the stable system. So the voltage stability issues of the AC micro-grid with series combination of micro-sources are studied.Firstly, the specific structure of AC micro-grid with series combination of micro-sources is given, several major micro-sources in the structure are introduced, and inverter unit failure and redundancy series subsystem access methods, the improvement measures of micro-grid voltage stability and the influence of wind and solar disturbance to voltage stability of AC micro-grid with series combination of micro-source is analyzed.Secondly, in order to achieve the subsystem power balance control and stability control for the DC link voltage, using the carrier amplitude variation and phase shift method. And basing on this, the system voltage characteristics are analyzed. As inverter unit output series, the current flowing through each of the micro-source inverter is equivalent, the essence of power control for each unit is the control of the fundamental output voltage amplitude. Under the condition of the total fundamental output voltage component remains constant, each micro-source inverter output power can be changed by changing the modulation of carrier amplitude variation and phase shift method. Furthermore, a kind of micro-source output voltage control method based on multi quasi proportional resonant is studied and the multi quasi proportional resonant controller is designed, so as to suppress the influence of non-linear loads on output voltage of AC micro-grid with series combination of micro-sources in islanding mode.Finally, the models of V/f control, Droop control and series subsystem consisting of photovoltaic, wind micro-source and energy storage system are set up. The simulation analysis based on the AC micro-grid with series combination of micro-source both with resistive loads and nonlinear loads of rectifier type under islanding operation modes is made, and the voltage stability of system is analyzed.