Small Disturbance Analysis Of Grid-connected PV Power System

With the depletion of non-renewable energy sources gradually, developing thesustainable energy has become the project of global attention. As one of the mostrepresentative of the new energy, Photovoltaic (PV) power generation develops rapidly everyyear, especially after2009. Today, grid-connected PV power generation technology growstowards to maturity. But with the scale expanding and capacity increasing of grid-connectedPV power generation, its stability problem begins to be concerned about by more people. Andsmall disturbance stability problem is unavoidable in a real system. So it is necessary toresearching the small disturbance stability of grid-connected PV power system.On the other hand, comparing with the conventional power generation system,grid-connected PV power generation has some differences including the intermittent of solarenergy, PV system containing a large number of power electronic devices and the limitedreactive power regulating capability of PV system, which cause the operation characteristicsof PV system having the differentiation with those of conventional power generators. So thesmall disturbance stability study of PV power system needs for further analysis.This paper researches the small disturbance stability of grid-connected PV system usingeigenvalues analysis method, and its theoretical basis is the Lyapunov stability theory. Firstly,this paper establishes the mathematical model of two-steps grid-connected PV system,including mathematical models of solar cells, DC-DC converter, the maximum power pointtracking control, the inverter, grid-connected control and network, and then linearizesmathematical model nearby the equilibrium point to get the system state matrix, bycalculating the eigenvalues of the state matrix to determine the stability of the system.Furthermore this paper uses eigenvalues sensitivity and eigenvalues track to get the result thathow controller parameters have influence on the distribution of eigenvalues, and optimizesthe distribution of values through adjusting the controller parameters.What’s more, after increasing the load in the model of the PV system, this paper revealsmechanism of small disturbance instability causing by the lack of reactive power and leadingto voltage drop by using eigenvalue analysis method, then by adding reactive powercompensator device to restrain system instability phenomenon, and through the theoreticalanalysis, finds that the greater the reactive power compensation device in the steady state gainis, the better stability of system. Finally using the Matlab/Simulink simulation to test aboveprocedure, the result is consistent with the theoretical analysis.