【摘要】：隨著化石能源的不斷消耗,人類正在面臨嚴(yán)重的能源危機(jī),為了改善能源供應(yīng)結(jié)構(gòu),可再生能源的開發(fā)利用得到了更多的重視。太陽能被認(rèn)為最清潔的可再生能源,但是光伏發(fā)電具有間歇性,通過增加儲能單元可保證電能的持續(xù)供應(yīng)。雙向DC/DC變換器可實(shí)現(xiàn)能量的雙向流動,在儲能單元控制中起著關(guān)鍵的作用。LLC諧振變換器因其高功率密度,高轉(zhuǎn)換效率得到了廣泛應(yīng)用。本文主要研究了具有LLC諧振特性的雙向DC/DC變換器,并對基于頻率調(diào)制的最大功率跟蹤算法做了研究。本文以帶儲能單元的戶用光伏發(fā)電系統(tǒng)應(yīng)用為背景,以雙向半橋LLC諧振變換器做研究對象。通過基波分析法分析了變換器穩(wěn)態(tài)的正、反向工作原理與特性,歸納出變換器正、反向不對稱工作的異同點(diǎn),為變換器設(shè)計(jì)提供了基礎(chǔ),并通過仿真分析了變換器不同工作方向下的主要波形。為了滿足雙向半橋LLC諧振變換器低電壓環(huán)境工作要求,分析了變換器交錯(cuò)并聯(lián)控制原理,研究了LLC諧振狀態(tài)下驅(qū)動信號占空比變化對變換器電壓增益的影響,提出了基于占空比與頻率混合調(diào)制的均流控制策略,通過頻率調(diào)制調(diào)節(jié)變換器輸出電壓,同時(shí)以變換器各模塊諧振電流均值之差作為變量通過占空比調(diào)制實(shí)現(xiàn)電流平衡。仿真分析表明,混合調(diào)制可有效解決變換器交錯(cuò)并聯(lián)回流問題,實(shí)現(xiàn)變換器模塊間的等功率輸出。為了使光伏電池時(shí)刻以最大功率輸出,分析了光伏電池輸出特性與變換器諧振特性的關(guān)系,采用了中值變頻最大功率跟蹤算法,通過等分變換器開關(guān)頻率區(qū)間,比較中值開關(guān)頻率點(diǎn)光伏電池輸出功率,確定下一個(gè)等分區(qū)間,最終實(shí)現(xiàn)光伏電池最大功率輸出。仿真分析表明,中值變頻調(diào)制MPPT響應(yīng)速度快,跟蹤誤差小,可實(shí)現(xiàn)光伏電池最大功率有效跟蹤。根據(jù)課題指標(biāo)要求,設(shè)計(jì)了交錯(cuò)并聯(lián)雙向半橋LLC諧振變換器樣機(jī),實(shí)驗(yàn)結(jié)果表明變換器工作原理與特性分析的正確性,實(shí)現(xiàn)了變換器模塊間電流平衡,驗(yàn)證了中值變頻調(diào)制MPPT的仿真與實(shí)驗(yàn)結(jié)果的一致性。
[Abstract]:With the continuous consumption of fossil energy, mankind is facing a serious energy crisis. In order to improve the structure of energy supply, more attention has been paid to the development and utilization of renewable energy. Solar energy is considered to be the cleanest renewable energy, but photovoltaic power generation is intermittent, by adding energy storage units to ensure the continued supply of electricity. Two-way DC/DC converter can realize bidirectional flow of energy, which plays a key role in energy storage unit control. LLC resonant converter is widely used because of its high power density and high conversion efficiency. In this paper, the bidirectional DC/DC converter with LLC resonance is studied, and the maximum power tracking algorithm based on frequency modulation is studied. In this paper, the application of household photovoltaic power generation system with energy storage unit is taken as the background, and the bi-directional half-bridge LLC resonant converter is taken as the research object. The principle and characteristics of steady-state forward and reverse operation of the converter are analyzed by the fundamental analysis method, and the similarities and differences of the forward and reverse asymmetric operation of the converter are summarized, which provide the basis for the design of the converter. The main waveforms of the converter in different working directions are analyzed by simulation. In order to meet the requirements of low voltage environment of bi-directional half-bridge LLC resonant converter, the principle of interleaved parallel control is analyzed, and the effect of the duty cycle of driving signal on the voltage gain of LLC resonant converter is studied. A current-sharing control strategy based on mixed modulation of duty cycle and frequency is proposed. The output voltage of the converter is regulated by frequency modulation, and the difference of resonant current mean of each module of the converter is taken as the variable to achieve current balance through duty cycle modulation. The simulation results show that the hybrid modulation can effectively solve the problem of interlaced parallel reflux and realize the equal power output between the converter modules. In order to make the photovoltaic cell output with maximum power at all times, the relationship between the output characteristic of photovoltaic cell and the resonant characteristic of the converter is analyzed. The median variable frequency maximum power tracking algorithm is adopted, and the switching frequency range of the equilateral converter is adopted. The output power of photovoltaic cell at median switching frequency point is compared and the next equipartition interval is determined to realize the maximum power output of photovoltaic cell. The simulation results show that the median frequency modulation (MPPT) has high response speed and low tracking error, and it can effectively track the maximum power of photovoltaic cells. According to the requirements of the project, the prototype of the interleaved bi-directional half-bridge LLC resonant converter is designed. The experimental results show that the principle and characteristic analysis of the converter are correct, and the current balance between the converter modules is realized. The simulation and experimental results of median frequency conversion modulation (MPPT) are verified.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM46

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