Research And Realization On Mpptalgorithms For Photovoltaic System

As the whole world is under the double pressures of environmental pollution andenergy crisis, the solar power is becoming an important part of the world’s energy for theadvantages of large reserves, no pollution, and no restrict to region. In the photovoltaicpower generation system, improving the conversion efficiency of the photovoltaic array isone of the critical problems, which can be effectively solved by MPPT（Maximum PowerPoint Tracking). The present study of MPPT control focus on the trade-off between theresponse speed and the steady accuracy by adjusting the tracking step. Aiming at theproblem above and based on the existing research and technology, this thesis mainlyresearch on photovoltaic MPPT algorithm from the several aspects as follows:(1) An improved P&O (Perturb and Observe) MPPT algorithm based on thefractional-order differential compensation is proposed to improve the steady-state accuracyat the premise of fast response speed, in which the fractional-order differential of power istaken into account and provides additional information. The power oscillates can berejected as the fractional-order differential is characterized by filtering and the result withboth the low steady-state losses and the high algorithm efficiency can be received bycombing the first-order differential with the fractional-order one. Moreover, the intuitivetheoretical analysis for this improved method is given. The improved method is simulatedby MATLAB/Simulink. A comparison of the traditional control method and the proposedone shows that the proposed method can be used to reduce the power losses and increasethe tracking efficiency effectively.(2) An improved variable step-size P&O MPPT algorithm based on coordinatetransformation is proposed to improve the response speed at the premise of the highsteady-state accuracy. Taking the voltage of maximum power point as a benchmark, thevoltage coordinate is transformed into the natural logarithm coordinate on both sides of PVarray output characteristic curve, respectively. The PV array output characteristic curvescan be compressed with the different ratio as the natural logarithm is characterized bynonlinear of increase, to realize tracking with variable step-size, which adjusts by real-timevoltage. The simulation results show that the proposed control algorithm can start rapidly,track the MPP rapidly and accurately with external environment change and improve theefficiency of photovoltaic array.(3) Experiments for the proposed P&O MPPT algorithm based on the fractionaldifferential compensation are implemented on MPPT photovoltaic system experimental platform, and compared with the traditional P&O algorithm for comprehensiveperformance. Experiments include the one with indoor photovoltaic array and the other onewith outdoor ordinary photovoltaic array. The experimental results show that comparedwith the traditional P&O algorithm, the proposed P&O MPPT algorithm based onfractional differential compensation can obviously improve the steady performance undertwo kinds of experimental environment.