NOVELTY - The device has a measuring unit for measuring a first electric power value generated by a power source (PV) at a first time instant. A controlling unit controls voltage provided by the power source at a second time instant to a first voltage value. A measuring unit measures a second electric power value generated by the power source at the second time instant. A determining unit determines a third power value from a fourth and the second power value. A modifying unit modifies the first voltage value and a second voltage value according to the comparison of the first and third power values.    USE - Device for tracking a maximum power point of a power source e.g. photovoltaic cell, array of cells and fuel cell, in an energy conversion system e.g. direct current (DC)-DC up/down converter circuit and DC/alternating current (AC) inverter circuit.    ADVANTAGE - The device enables comparing the power value with the second power value delivered by the voltage source at the voltage value at the first time instant, so that direction in which the voltage provided by the power to be modified can be determined to get the maximum power from the power source with better robustness against variations of irradiance, thus facilitating tracking of the maximum power point to be robust to climatic variations. The device ensures that a difference between the power values together with the voltage levels indicate the direction of the maximum power point, so that the second voltage value can be set closer to the maximum power point than the first voltage value, thus minimizing power losses by applying first voltage value less frequently than the second voltage value.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for tracking a maximum power point of a power source.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of an energy conversion system.    Power source (PV)    Switch (S)    Controller device (20)    Processor (200)    RAM (203)    Interface (205)