【摘要】：近年來,能源問題和環(huán)境問題愈加嚴(yán)重,解決好這兩大問題關(guān)系到人類能否實現(xiàn)可持續(xù)發(fā)展。在此背景下分布式發(fā)電系統(tǒng)得到了迅速的發(fā)展,智能電網(wǎng)的建設(shè)成了電網(wǎng)發(fā)展必然趨勢。智能電網(wǎng)能夠靈活的分配能量,改善電能質(zhì)量,更加安全可靠。固態(tài)變壓器就是智能電網(wǎng)的核心設(shè)備之一。固態(tài)變壓器主要功能有:管理系統(tǒng)能量,使能量分布更加合理;對輸入交流側(cè)進行功率因數(shù)校正;隔離電網(wǎng)和用戶,提高用電安全;為分布式發(fā)電系統(tǒng)和儲能設(shè)備提供直流接口。本文研究的固態(tài)變壓器主電路拓?fù)錇槿嗳壥侥K級聯(lián)型結(jié)構(gòu),三級式拓?fù)渲饕ㄝ斎爰�、中間級和輸出級。輸入整流級把輸入的工頻交流電壓轉(zhuǎn)換為直流電壓。為了提高輸入電壓等級,整流級采用模塊級聯(lián)型結(jié)構(gòu),每相由三個PWM整流橋級聯(lián)而成。中間隔離級實現(xiàn)整流輸出電壓的電壓等級的轉(zhuǎn)換和隔離。每個整流模塊后接一個雙有源橋(Dual active bridge,DAB)DC-DC變換器。DAB模塊由一個高頻變壓器和兩個對稱的全橋電路組成,DAB輸出電壓并聯(lián),為分布式發(fā)電系統(tǒng)和儲能設(shè)備提供直流接口。逆變級把DAB輸出的直流電壓逆變?yōu)楣ゎl交流電壓供用戶使用。通過對主電路拓?fù)浣Y(jié)構(gòu)的分析,確定了輸入級采用載波移相的調(diào)制方法、DAB級采用單移相控制的控制方式。載波移相控制下,整流級級聯(lián)H橋輸入電壓為七電平,更接近于正弦波;單移相控制下DAB級高頻變壓器漏感電流在一個周期內(nèi)有六種工作狀態(tài),通過分析各工作狀態(tài),得出傳輸功率與各電氣量之間的關(guān)系。建立電路的小信號模型,推導(dǎo)出電路傳遞函數(shù)。提出了整流級采用基于三相dq變換的共同占空比控制和DAB級采用電壓跟隨的控制策略。共同占空比控制下,各整流級輸出平均電壓穩(wěn)定在設(shè)定值上。電壓跟隨控制使DAB輸出電壓按一定比例跟隨輸入電壓。為了解決系統(tǒng)各模塊電路參數(shù)不匹配引起的整流級輸出電壓不均衡和DAB級傳輸功率不均衡的問題,論文提出了功率均衡控制的控制策略。該功率均衡控制策略不需要電流傳感器,降低了成本。為了驗證理論的正確性,在PSIM軟件中對整個系統(tǒng)進行了仿真,并搭建硬件平臺進行實驗驗證。仿真結(jié)果和實驗結(jié)果都驗證了所提出理論的正確性。
[Abstract]:In recent years, energy and environment problems become more and more serious. In this context, the distributed generation system has been developed rapidly, and the construction of smart grid has become an inevitable trend of grid development. Smart grid can distribute energy flexibly, improve power quality, and be more safe and reliable. Solid state transformer is one of the core equipments of smart grid. The main functions of solid-state transformer are as follows: managing system energy, making energy distribution more reasonable, correcting input AC side power factor, isolating power grid and users, improving power safety; Provide DC interface for distributed generation system and energy storage equipment. The main circuit topology of solid-state transformer in this paper is three-phase three-stage modular cascade structure. The three-stage topology mainly includes input stage, intermediate stage and output stage. Input rectifier level converts input power frequency AC voltage to DC voltage. In order to improve the input voltage level, the rectifier stage adopts a modular cascade structure, each phase is cascaded by three PWM rectifier bridges. The intermediate isolation stage realizes the conversion and isolation of the voltage level of the rectified output voltage. Each rectifier module is followed by a dual-active bridge (Dual active bridge,DAB) DC-DC converter. The dab module consists of a high-frequency transformer and two symmetrical full-bridge circuits, which provide a DC interface for distributed generation system and energy storage equipment. The inverter stage converts DC voltage output from DAB to power frequency AC voltage for user's use. Based on the analysis of the topology of the main circuit, the modulation method of input stage using carrier phase shift and the control mode of DAB stage adopting single phase shift control are determined. Under carrier phase shift control, the input voltage of rectifier cascaded H bridge is seven levels, which is closer to sine wave, and the leakage inductance current of DAB high frequency transformer has six working states in one cycle. The relation between transmission power and electrical quantity is obtained. The small signal model of the circuit is established and the circuit transfer function is derived. A common duty cycle control based on three-phase dq transform and a voltage following control strategy for DAB stage are proposed. Under the common duty cycle control, the average output voltage of each rectifier stage is stable on the set value. The voltage following control causes the DAB output voltage to follow the input voltage in a certain proportion. In order to solve the problems of unbalanced output voltage of rectifier stage and unbalanced transmission power of DAB stage caused by the mismatch of circuit parameters in each module of the system, the control strategy of power equalization control is proposed in this paper. The proposed power equalization control strategy does not require current sensors and reduces the cost. In order to verify the correctness of the theory, the whole system is simulated in PSIM software, and the hardware platform is built for experimental verification. Simulation results and experimental results verify the correctness of the proposed theory.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM41

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