Published in IET Renewable Power Generation Received on 5th October 2010 Revised on 29th January 2011 doi: 10.1049/iet-rpg.2010.0175 ISSN 1752-1416 Comparison of direct maximum power point tracking algorithms using EN 50530 dynamic test procedure T. Andrejas ˇic ˇ M. Jankovec M. Topic ˇ Faculty of Electrical Engineering, Laboratory of Photovoltaics and Optoelectronics, University of Ljubljana, Trz ˇas ˇ ka cesta 25, 1000 Ljubljana, Slovenia E-mail: tine.andrejasic@fe.uni-lj.si Abstract: Three direct maximum power point tracking (MPPT) algorithms with non-adaptive voltage step are evaluated in the light of their performance for photovoltaic systems under dynamic conditions for a resistive load. A microcontroller-based buck – boost DC–DC converter platform is used to implement and compare the algorithms. Dynamic test procedures from a new standard for inverter efficiency determination EN 50530 were implemented to evaluate dynamic MPPT algorithms’ efficiency and their dependence. Experimental results show that MPPT algorithms’ regulating frequency and regulating voltage step play a crucial role in the dynamic performance of direct algorithms. A range of regulating frequencies and voltage steps were examined. If proper parameter values are chosen, all algorithms perform well and close to each other. Detailed evaluation was performed with determining partial MPPT efficiency under different irradiance slopes. Results show that at least 10 Hz should be used to satisfy the 99% tracking efficiency over all slopes in the range from 0.5 to 100 W/m 2 /s as specified by EN 50530 standard. Further increase of regulating frequency would result in higher slope efficiency only at dynamic conditions. 1 Introduction Renewable electrical energy sources such as solar power are becoming increasingly important owing to the limited fossil fuels resources and their negative environmental impact. Since the photovoltaic (PV) systems are still one of the more expensive ways of producing electricity, it is important to maximise their output power under any operational and ambient conditions. PV generators have non-linear current – voltage characteristics with their specific instantaneous maximum power point (P MPP ) that is dependent on solar irradiance (G), ambient temperature, wind speed and other ambient parameters. In order for the PV generator to operate at the P MPP , switching mode pulse-width modulation direct current-to- direct current (DC–DC) or direct current-to-alternating current (DC–AC) converter with a maximum power point tracking (MPPT) algorithm must be inserted between the PV generator and an electric load. The converter’s primary task is to continuously adapt the input load impedance that the PV generator feels, to track the instantaneous P MPP of the PV generator. Many MPPT algorithms for the DC–DC and DC–AC converters have been developed in the last decades. Direct methods are those that use voltage or current measurement or both. They regulate the operating point of the generator near the P MPP by periodically adjusting the voltage (V PV ) of the PV generator or duty cycle of the DC–DC/DC–AC converter with regulating frequency ( f reg ) with an adaptive or a constant voltage step irrespective to solar irradiance, module temperature, shading, degradation etc. Indirect methods are based on monitoring of accompanying non- electrical parameters (solar irradiance, ambient temperature etc.) that rely on prior characterisation or databases of PV generator data, on which the assumed P MPP is calculated and afterwards tracked. Major direct and indirect methods have been reviewed in [1, 2]. The weakness of indirect methods is that they are not immune to aging or shading of the PV generator [3]. Since the first MPPT algorithm patented in 1969 [4], the authors have been comparing the algorithms and their improvements by their dynamic response to a step in irradiance or PV generator’s temperature. The steps applied were not consistent through studies and developments of new and improved algorithms; therefore it has been difficult to objectively compare their performance. Based on intensive study of operating dynamic conditions a test procedure with two sequences for measurement of dynamic MPPT algorithm efficiency was proposed [5]. The developed procedure is a part of a recently introduced standard for testing DC–AC inverters efficiency EN 50530 [6]. Besides the dynamic, static MPPT algorithm efficiency and start-up/shut-down test were defined. The overall inverter efficiency is determined by the static MPPT efficiency and conversion efficiency, instead of only conversion efficiency that was used before, while the start- up/shut-down test determines the minimum operating power of the inverter. Dynamic test procedure from the standard was used to evaluate the performance, in particular the dynamic IET Renew. Power Gener., 2011, Vol. 5, Iss. 4, pp. 281–286 281 doi: 10.1049/iet-rpg.2010.0175 & The Institution of Engineering and Technology 2011 www.ietdl.org