Energy Conversion And Control Technique Investigation For Building Integrated Photovoltaic System

Growing concerns about energy crisis and environmental issues have attracted a great deal of interest in the development and application of the building integrated photovoltaic (BIPV) system using the nonpolluting renewable solar energy. The BIPV, as an important policy to mitigate energy and environmental issues and implement sustainable development, integrates organically photovoltaic power system into buildings, and can reduce the investment costs, shorten energy pay-back time, and improve the energy efficiency of buildings. The basic analysis theory and design method of energy conversion and control for building integrated photovoltaic system are investigated from the sight on power electronics, including energy conversion configuration, converter topology, control and energy management of the BIPV system.The photovoltaic modules acting as facade elements with generating electricity function in the BIPV system generally have different installation orientations and angles, moreover these modules are easy to be affected by partial shadows created by the surrounding buildings. The conventional energy conversion configurations based on centralized, string and multi-string technology have the problem of low energy efficiency and bad performance under the partial shading and mismatch condition, therefore they are difficulty to sever as high performance BIPV system. In order to improve these problem, the dc-module-based BIPV system consisting of photovoltaic dc building module and centralized inverter module is proposed in this paper. The calculation and evaluation models of energy efficiency for the BIPV systems with different energy conversion configurations are set up firstly, and then the energy efficiencies of these system is evaluated quantificationally under different partial shading and mismatch conditions, finally their comprehensive performances are compared.Photovoltaic dc building module as the core of the dc-module-based BIPV system integrates photovoltaic module, facade element and high performance dc-dc converter with the functions of maximum power point tracking (MPPT) and power line carrier communication into a whole constituting a novel photovoltaic building materials. The selection, design and analysis methods of the suitable dc-dc converter are researched. An active maximum power point tracking (AMPPT) technique based on the active P-V characteristic correction (APVC) of photovoltaic module is proposed. The proposed technique corrects the P-V characteristic with multi-maximum point to a single maximum point characteristic firstly, secondly the conventional MPPT algorithm can be used to achieve excellent tracking performance, finally an engineering design method of the key parameters of incremental conductance algorithm is presented.The leakage current suppression, low frequency ripple current suppression and the coordinate control of the photovoltaic dc building modules and centralized inverter module are the important issues in the centralized inverter module of the dc-module-base BIPV system. A single-phase hybrid bridge three-level inverter topology and its modulating strategy are proposed to suppress the leakage current in this paper, and its output filter design method is given to satisfy the need of the double-mode inverter with grid-connection and stand-alone. The propagation model of the low frequency ripple current in dc-module-based BIPV system is derived, and its effect to the utility efficiency of the photovoltaic module is analyzed. The design method of the input filter capacitor considering to suppress low frequency ripple current and improve the photovoltaic module utility efficiency is given. At first, the essence of coordinate control for the dc-module-based BIPV system is opened out, the second the accurate model for the dc bus voltage control is established, at last its control strategy is investigated.In order to satisfy the need of some building loads on the power quality and reliability, the concept of dc-module-base BIPV system is extended to multi-energy hybrid BIPV system, which can integrate effectively the other generation and storage unit based on wind turbine, fuel cell, battery and so on. Three energy conversion configurations are presented to response the demand for some building loads, then the problems of energy flow and energy balance under stand alone operation mode are analyzed. The definition, constitution and object of energy management for multi-energy hybrid BIPV system are discussed. The basic principle of energy balance control and energy management strategy under the grid-connection and stand-alone mode are analyzed firstly, and then the modeling method of energy management for multi-energy hybrid BIPV system is researched, finally its time-domain stability analysis is performed.