【摘要】：近年來,我國不斷面臨一次能源短缺的威脅,面對日益嚴(yán)峻的環(huán)境問題,開發(fā)新能源并解決新能源發(fā)電接入電網(wǎng)的一系列問題顯得十分重要。為了避免分布式能源并網(wǎng)對大電網(wǎng)造成的沖擊,而提出的既可為區(qū)域內(nèi)負(fù)荷提供冷熱電聯(lián)供,也能與電網(wǎng)并聯(lián)運(yùn)行的小型電網(wǎng)被稱為微網(wǎng)。其中由微電源、電力電子接口、儲能及負(fù)荷組成的以直流方式傳輸?shù)奈㈦娋W(wǎng)就是直流微電網(wǎng)。該文針對直流微電網(wǎng)中主要電力電子變流器的控制方法展開了討論與研究。首先,為了應(yīng)對離網(wǎng)運(yùn)行時(shí)的不平衡交流負(fù)載,該文在三相DC/AC逆變器原有的拓?fù)浣Y(jié)構(gòu)上增加了一條零序電流分量的通路,形成一種新型中線拓?fù)浣Y(jié)構(gòu),這種添加了中線的三相逆變器能夠在負(fù)載不平衡的情況下保證逆變器輸出電壓不發(fā)生畸變。其次,當(dāng)直流微電網(wǎng)作為直流微源并入大電網(wǎng)的時(shí)候需要其能夠友好平滑地接入大電網(wǎng),采用虛擬同步發(fā)電機(jī)控制方法的并網(wǎng)接口逆變器可以自動(dòng)的參與配網(wǎng)調(diào)節(jié),在實(shí)現(xiàn)分布式電源并網(wǎng)的同時(shí)改善接入點(diǎn)電能質(zhì)量,并且能消除本地負(fù)荷大量切投引起的電壓波動(dòng),保證輸出電壓質(zhì)量。與大電網(wǎng)并聯(lián)運(yùn)行時(shí),能夠抑制大電網(wǎng)電壓畸變時(shí)產(chǎn)生的影響維持逆變器直流側(cè)電壓基本穩(wěn)定。最后,針對直流微電網(wǎng)中最常見直流負(fù)荷——電動(dòng)汽車的充電問題提出了一種基于虛擬直流發(fā)電機(jī)的柔性直流變換器控制方法,通過這種方法控制的雙向直流變換器在恒壓充電模式時(shí),能穩(wěn)定負(fù)荷側(cè)電壓不受母線電壓發(fā)生擾動(dòng)時(shí)的影響實(shí)現(xiàn)恒壓充電,同樣在恒流充電模式中也能過濾母線波動(dòng)影響使輸出電流恒定,且由于考慮了直流發(fā)電機(jī)的慣性環(huán)節(jié),因此負(fù)荷側(cè)電壓、電流的變化是一個(gè)緩和震蕩過程,有效提升了電動(dòng)汽車充電的穩(wěn)定性。該文在PSCAD/EMTDC中搭建了一個(gè)簡單的直流微電網(wǎng)模型,該模型中包含了帶不平衡負(fù)載的三相四橋臂逆變器、基于虛擬同步發(fā)電機(jī)的并網(wǎng)接口逆變器、以及基于虛擬直流發(fā)電機(jī)的雙向直流變換器。通過仿真和實(shí)驗(yàn),驗(yàn)證了虛擬同步發(fā)電機(jī)及虛擬直流發(fā)電機(jī)控制策略的可行性以及中線拓?fù)浣Y(jié)構(gòu)針對不平衡負(fù)載的有效性,為直流微電網(wǎng)的進(jìn)一步研究奠定基礎(chǔ)。
[Abstract]:In recent years, China is facing the threat of primary energy shortage. In the face of increasingly severe environmental problems, it is very important to develop new energy and solve a series of problems of new energy generation connected to power grid. In order to avoid the impact of distributed energy grid connection on large power grid, the proposed small power grid, which can not only provide the combined cooling and heat supply for the local load, but also run in parallel with the power grid, is called microgrid. The DC microgrid, which consists of micro-power supply, power electronic interface, energy storage and load, is DC microgrid. In this paper, the control methods of main power electronic converters in DC microgrid are discussed and studied. First of all, in order to deal with the unbalanced AC load in off-grid operation, this paper adds a zero-sequence current component path to the original topology of three-phase DC / AC inverter, and forms a new midline topology. The three-phase inverter with neutral line can ensure that the output voltage of the inverter is not distorted when the load is unbalanced. Secondly, when the DC microgrid is incorporated into the large power grid as a DC microsource, it is necessary that the DC microgrid can be connected to the large power grid in a friendly and smooth manner, and the grid-connected interface inverter using the virtual synchronous generator control method can automatically participate in the distribution network regulation. The power quality of the access point can be improved while the distributed power supply is connected to the grid, and the voltage fluctuation caused by the local load cutting can be eliminated, and the output voltage quality can be guaranteed. When running in parallel with large power grid, the DC side voltage of inverter is basically stable when the influence of voltage distortion in large power grid can be restrained. Finally, a flexible DC converter control method based on virtual DC generator is proposed for charging the most common DC load-electric vehicle in DC microgrid. The bidirectional DC / DC converter controlled by this method can stabilize the load side voltage in constant voltage charging mode and realize constant voltage charging without the influence of bus voltage disturbance. In the same constant current charging mode, the output current is constant by filtering the effect of bus fluctuation, and because the inertia link of DC generator is considered, the variation of load side voltage and current is a mild oscillation process. Effectively improves the electric vehicle charging stability. In this paper, a simple DC microgrid model is built in PSCAD / EMTDC. The model includes three-phase four-leg inverter with unbalanced load and grid-connected interface inverter based on virtual synchronous generator. And the bidirectional DC converter based on virtual DC generator. Through simulation and experiment, the feasibility of control strategy of virtual synchronous generator and virtual DC generator and the validity of midline topology for unbalanced load are verified, which lays a foundation for further research on DC microgrid.
【學(xué)位授予單位】：長沙理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TM46

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