Maximum power tracking and controlling method of single-stage photovoltaic system

Abstract

The invention relates to a maximum power tracking and controlling method of a single-stage photovoltaic system, belonging to the field of photovoltaic generating system control technology application. The method comprises the following steps of: firstly, starting to search a local maximum power point at the left side of an output power-voltage characteristic curve from the left side of the curve under a current environment condition; commonly deciding the step length and the direction which are superposed to reference voltage Uref of the maximum power point of a photovoltaic array through a differential k of the output power of the photovoltaic array to the voltage and a coefficient C progressively increasing along with the absolute value of the k so as to ensure that the Uref is quickly iterated and converged to the reference voltage corresponding to the local maximum power point at he left side of the curve so as to effectively improve tracking speed and precision; then respectively beginning to search local maximum power points possible of existing at the right side or on the middle part of the curve from the right side or the middle part of the curve in a similar way; and finally, selecting a point with the maximum power to be the solved maximum power point from all the searched local maximum power points.

Description

technical field [0001] The invention relates to a maximum power tracking control method of a single-stage photovoltaic system, which belongs to the application field of photovoltaic power generation system control technology. Background technique [0002] For photovoltaic power generation systems, the most important issue is how to improve the power generation efficiency of the system. Since the single-stage photovoltaic system has only one energy conversion link, the system has a simple structure, high efficiency and stability, and has become a research hotspot at home and abroad. Generally, its control system adopts multi-loop control, that is, the maximum power point tracking MPPT link firstly gives the maximum power point reference voltage U of the photovoltaic array ref , and then control the photovoltaic array output voltage U through a double closed-loop control system composed of a voltage PI controller and a current PI controller pv track u ref . In the entire p...

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Problems solved by technology

However, due to the uncertainty of the intensity of sunlight, the change of the temperature of the photovoltaic array and the nonlinear characteristics of the output power-voltage characteristic curve of the photovoltaic array, the fast and accurate tracking of the maximum power point of the photovoltaic array has become a very complicated problem.

[0003] Since photovoltaic arrays are composed of multiple single photovoltaic cells and diodes connected in series or in parallel, when the intensity of sunlight received by each single photovoltaic cell in the photovoltaic array is equal, that is, when there is no shadow, the output power-voltage characteristic curve However, in many cases, due to the occlusion of opaque objects on the surface of the photovoltaic module or cloudy weather, the intensity of light received by some single photovoltaic cells in the photovoltaic array is different from that of other cells. In this case, the photovoltaic The array output power-voltage characteristic curve is very likely to have a 2-peak shape or a 3-peak shape

However, the current perturbation and observation method and conductance increment method will only converge to a certain peak, that is, the local maximum power point, which cannot guarantee the global maximum power point, resulting in energy waste. At the same time, the perturbation and observation method and conductance increment method It is difficult to ensure fast tracking and high tracking accuracy, which will further cause the loss of photovoltaic array energy

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