## 1 Introduction  
DC-DC convertors transform the electric energy supplied by a DC source into DC energy, but of another value, adjustable in any event. These are also known as DC variators because they only modify the amplitude of the DC voltage. Most DC-DC convertors run in forced commutation by using the technique of voltage modification as the modulation of the pulse width (pulse width modulation--PWM). The power circuit of a DC-DC convertor is built with semiconductor elements with controlled commutation such as thyristors, GTO myrists, bipolar transistors of MOSFET, or IGBT types. The passing in conduction as well as the blocking of the components are defined through the control and are performed at very precise moments. DC-DC convertors find their applicability in building the supply sources through commutation, in interconnecting the regenerable sources, and in electric drives with DC motors. Based on the ratio between the input and output voltage, DC-DC convertors can be defined in the following categories:  
* STEP-DOWN converters or serial converters (BUCK converters), where the output voltage is lower than the input voltage or at most equal;
* STEP-UP converters or parallel converters (BOOST converters), where the output voltage is higher or at least equal to the input voltage;* STEP--DOWN/UP converters or series-parallel converters (BUCK-BOOST converters), where the output voltage can be lower or higher than the input voltage;
* CUK converters--hybrid converters of boost and buck converters;
* Bridge-type converters.  
The DC-DC buck type can be controlled based on the P&O algorithm in order to run at the maximum power point to transfer a higher quantity of energy from the DC source to the receptor circuit [1; 2; 3]. In order to enhance the energy transfer from a DC source to the receptor circuit, fuzzy logic controllers are used to control the DC-DC convertors [4; 5; 6; 7; 8]. The control of the buck DC-DC converter by means of the algorithm of control through slipping with the input LC filter is presented in [9; 10]. The control of the DC-DC converter to run at the maximum power point can also be performed based on the method of observation of the adaptive perturbation [11]. The MPPT algorithm, performed through the methods CF-P&O-INC, is also used as a strategy of energy management for distributed photovoltaic systems [12]. The use of the red-tailed hawk algorithm for the MPPT algorithm with a single sensor for a photovoltaic system is presented in [13]. Ref. [14] presents a study for improving the design of control systems with a fuzzy logic controller (FLC) of the fuel sources with a membrane to follow the maximum power point (MPPT). An analysis of the modeling, design, and implementation of DC-DC converters was presented in Ref. [15]. DC-DC converters controlled through the MPPT algorithm and neuronal networks have also been used on electrical vehicles with combustion cells [16]. The remote diagnosis and control of a DC-DC converter used for photovoltaic systems were presented in [17], while the use of the control algorithm MPPT for DC-DC converters under partial conditions of shadowing on the photovoltaic panels is presented in Ref. [18].