Stability Analysis of Grid-Connected Photovoltaic Systems Here, P is the solution of the following Ric- cati equation: A T P + PA - PBR -1 B T P + Q = 0 and K = R -1 B T P is the optimal gain matrix. The matrix Q and R are appropriately chosen weighting parameters such that Q T = Q 0 and R T > 0. There are no specific guidelines concerning the form that Q but in the most of the cases it is a diagonal matrix and R=1. u = - k 1 z 1 = - k 1 h ( x ) = - ( i - I ref ) Substituting all these values into (14), the following feedback linearizing control law can be obtained: u = Ri + e L ( i - I ref ) Ri + e - L ( i - I ref ) - = v v v (15) FEEDBACK LINEARIZING CONTROLLER DESIGN FOR GRID-CONNECTED PV SYSTEM For single-phase grid-connected PV system the control law can be written as: This is the final control law for a single-phase grid-connected PV system, which is to be imple- mented through the inverter of the system. The block diagram representation of the proposed system with this controller is shown in Figure 7. LYAPUNOV FUNCTION FOR GRID- CONNECTED PV SYSTEM