Improved MPPT algorithms for rapidly changing environmental conditions Dezso Sera * , Tamas Kerekes * , Remus Teodorescu * and Frede Blaabjerg * * Aalborg University/Institute of Energy Technology, Aalborg, Denmark Abstract—The first part of this paper intends to give an overview of the Maximum Power Point Tracking methods for Photovoltaic (PV) inverters presently reported in the literature. The most well-known and popular methods, like the Perturb and Observe (P&O), the Incremental Conductance (INC) and the Constant Voltage (CV), are presented. These methods, especially the P&O, have been treated by many works, which aim to overcome their shortcomings, either by optimizing the methods, or by combining them. In the second part of the paper an improvement for the P&O and INC method is proposed, which prevents these algorithms to get confused during rapidly changing irradiation conditions, and it considerably increases the efficiency of the MPPT. I. INTRODUCTION PV solar electricity together with solar thermal has the highest potential of all the renewable energies since solar energy is a practically unlimited resource, available everywhere. The power delivered by the PV module depends on the irradiance, temperature, and shadowing conditions. The PV panel has a nonlinear characteristic, and the power has a Maximum Power Point (MPP) at a certain working point, with coordinates VMPP voltage and IMPP current. Since the MPP depends on solar irradiation and cell temperature, it is never constant over time; thereby Maximum Power Point Tracking (MPPT) should be used to track its changes. The penetration of PV systems as distributed power generation systems has been increased dramatically in the last years. In parallel with this, Maximum Power Point Tracking (MPPT) is becoming more and more important as the amount of energy produced by PV systems is increasing. II. MAXIMUM POWER POINT TRACKING METHODS Many MPPT techniques have been reported in the literature, but there are three main methods, which are the most widely used: [1]  Perturb and Observe (P&O)  Incremental Conductance (INC)  Constant Voltage (CV) The first two are so called ‘hill-climbing’ methods, and they are using the fact that on the V-P characteristic, on the left of the MPP the variation of the power against voltage dP/dV > 0, while at the right, dP/dV < 0. (see Fig. 1) [14] The CV method is based on the fact that generally the ratio V MPP /V OC ≈ 0.76 [1]. P V dP/dV = 0 dP/dV < 0 dP/dV > 0 MPP Fig. 1 Sign of the dP/dV at different positions on the power characteristic A. The Perturb and Observe (P&O) method The most commonly used MPPT algorithm is the Perturb and Observe (P&O), due to its ease of implementation in its basic form. In Fig. 1, if the operating voltage of the PV array is perturbed in a given direction and dP/dV > 0, it is known that the perturbation moved the array's operating point toward the MPP. The P&O algorithm would then continue to perturb the PV array voltage in the same direction. If dP/dV < 0, then the change in operating point moved the PV array away from the MPP, and the P&O algorithm reverses the direction of the perturbation. [1] The advantage of the P&O method is that it is easy to implement. However, it has some limitations, like oscillations around the MPP in steady state operation, slow response speed, and even tracking in wrong way under rapidly changing atmospheric conditions. [1][2][3][5][6][8] Fig. 2 The flowchart of the P&O MPPT method