Research On Resonances Analysis And Control For Multiple Inverters In A Micro-grid

In recent years, more and more attention paid to the micro-grid by the social from all walks of life. Compared to the traditional grid, the micro-grid has the advantages of less investment, pollution-free, the reliability of power supply and without the need of long distance power transmission. Micro-grid not only provided power separately but also grid-connected to the main grid. But if the resonance happen in the micro-grid, it not only cause the lower power quality, but also even cause the grid equipment damage. So, it is necessary for resonances analysis in the micro-grid.Firstly, in this paper we discuss the advantages and disadvantages of several commonly used inverter control methods, then we choose deadbeat control as the inverter control mode. According to the principle of deadbeat control, we set up the mathematical model of single-phase inverter. Then, we establish the model of single inverter and multiple inverters connected with the grid. If we are equivalent the inverter to a current source, the output current can be expressed by internal reference current, the other inverter reference current and the voltage of the grid. The coefficient is defined as internal resonance factor, parallel resonance factor and series resonance factor. In this way, we can set up the relationship of the inverters in the micro-grid. Then we can use a mathematic equation to show the all kinds of affects for the output current.Secondly, by drawing the several bode plots of the different resonance factor, we can find that the internal resonance factor and series resonance factor will appear a public resonance peak in the multiple inverter micro-grid system. In this system, the resonance caused by the LCL filter has a great influence for the public resonance peak. It is effectively to restrain the resonance by improving the performance of LCL filter. On this basis, this paper puts a new model of LCL filter with the virtual impedance. The harmonic current can be obtained by the harmonic voltage and virtual impedance. Then the harmonic current will feedback to the controller to compensate the harmonic voltage. The improved control method will effectively restrain harmonic component of output current.Once more, the deadbeat control simulation model of single phase inverter can be build through the MATLAB/SIMULINK. The effectiveness can be verified in this system. Subsequently, we can verify the effectiveness and correctness of the improved deadbeat control by injecting the disturbance harmonic.Finally, in this paper, the actual system of hardware and software will be designed. According to the software design, the flow chart of software can be draw. At the end of this paper the programs will be downloaded to the control panel, and we can get the experimental date and waveform.