本文以數位控制實現具備援之功能三相三階換流器並聯系統。此系統使用虛擬電阻下垂控制法，作為並聯運轉之控制策略。其優點為不需要在換流器之間進行即時通訊，且能依據不同容量分擔負載的需求。
在換流器部分，本文則採用T型式拓樸架構，此架構所使用元件數少，效率高，且能有效減少輸出電壓諧波含量。採用一種注入零序訊號的載波脈寬調變作為其控制方式，相比於同樣得到大量使用之空間向量脈寬調變方式，其有調變波形生成容易、不需判斷空間向量區間的特性，同時依然保留空間向量調變電壓利用率高之優點。最後實際製作兩臺6 kW換流器，印證所提理論之可行性。

This thesis proposes the design and implementation of a digitally-controlled three phase three level inverter parallel system with redundancy feature. This system uses the virtual resistance droop control method as the control strategy for parallel operation. The advantage is that it does not need instant communication between the inverters, and can share the load according to different capacities.
The proposed three level circuit is using T-type topology. The benefits of this topology are using fewer components, high efficiency and the lower output voltage THD. This thesis uses a variant of Carrier-Based PWM(CBPWM) as the control scheme. Compare to Space Vector PWM(SVPWM), the modulation waveform of Carrier-Based PWM is easy to produce and there is no need to determine the location of the space vector, but still get the profit of high voltage utilization. Finally, two 6 kW inverters are actually produced to confirm the feasibility of the proposed theory.

[1]Lekha Sejpal, Comparison of Two-Level and Three-Level Neutral-Point Clamped Inverters in Automotive Applications, University of Concordia, 2013.
[2]S. M. Shin, J. H. Ahn and B. K. Lee, “Maximum Efficiency Operation of Three-Level T-type Inverter for Low-Voltage and Low-Power Home Appliances,” JEET, vol. 10, no. 2, pp. 586-594, 2015.
[3]蔡興，＂多電平換流器技術及其原理綜述＂，南昌高專學報，第5期，頁數：180-184，2011年10月。
[4]Mohan, Undeland , Robbins，電力電子學，江炫章譯，第三版，全華出版社，2016年，第8-1~8-10頁。
[5]Y. Jiao, F. C. Lee and S. Lu, “Space Vector Modulation for Three-Level NPC Converter With Neutral Point Voltage Balance and Switching Loss Reduction,” IEEE Trans. Power Electron., vol. 29, no. 10, pp. 5579-5591, Oct. 2013.
[6]S. Floten and T. S. Haug, Modulation Methods for Neutral-Point-Clamped Three-Level Inverter, Norwegian University of Science and Technology, Jun. 2010.
[7]A. M. Hava, R. J. Kerkman, and T. A. Lipo, “Simple Analytical and Graphical Tools for Carrier Based PWM Methods,” IEEE Power Electronics Specialists Conference, vol. 2, pp. 1462-1471, June 1997.
[8]R. Burgos, R. Lai, Y. Pei, F. Wang, D. Boroyevich and J. Pou, “Space Vector Modulator for Vienna-Type Rectifiers Based on the Equivalence Between Two-Level and Three-Level Converters: A Carrier-Based Implementation,” IEEE Trans. Power Electron., vol. 23, no. 4, Jun. 2008.
[9]Duan Shanxu, Meng Yu, Xiong Jian, Kang Yong and Chen Jian, "Parallel operation control technique of voltage source inverters in UPS," Proceedings of the IEEE 1999 International Conference on Power Electronics and Drive Systems. PEDS'99 (Cat. No.99TH8475), Hong Kong, 1999, pp. 883-887 vol.2.
[10]W. A. Tabisz, M. M. Jovanovic and F. C. Lee, "Present and future of distributed power systems," [Proceedings] APEC '92 Seventh Annual Applied Power Electronics Conference and Exposition, Boston, MA, USA, 1992, pp. 11-18.
[11]Z. Li, X. Sun and J. Chai, "Proportional power sharing control for parallel-connected inverters," 2011 4th International Conference on Electric Utility Deregulation and Restructuring and Power Technologies (DRPT), Weihai, Shandong, 2011, pp. 1647-1651.
[12]J. M. Guerrero, Luis Garcia de Vicuna, J. Matas, M. Castilla and J. Miret, "Output impedance design of parallel-connected UPS inverters with wireless load-sharing control," in IEEE Transactions on Industrial Electronics, vol. 52, no. 4, pp. 1126-1135, Aug. 2005.
[13]K. De Brabandere, B. Bolsens, J. Van den Keybus, A. Woyte, J. Driesen and R. Belmans, "A Voltage and Frequency Droop Control Method for Parallel Inverters," in IEEE Transactions on Power Electronics, vol. 22, no. 4, pp. 1107-1115, July 2007.
[14]Q. Zhong, "Robust Droop Controller for Accurate Proportional Load Sharing Among Inverters Operated in Parallel," in IEEE Transactions on Industrial Electronics, vol. 60, no. 4, pp. 1281-1290, April 2013.
[15]J. M. Guerrero, N. Berbel, J. Matas, J. L. Sosa and L. G. de Vicuna, "Droop Control Method with Virtual Output Impedance for Parallel Operation of Uninterruptible Power Supply Systems in a Microgrid," APEC 07 - Twenty-Second Annual IEEE Applied Power Electronics Conference and Exposition, Anaheim, CA, USA, 2007, pp. 1126-1132.
[16]Q. Zhong and Y. Zeng, "Universal Droop Control of Inverters With Different Types of Output Impedance," in IEEE Access, vol. 4, pp. 702-712, 2016.
[17]L. Ruiming and W. Shengtie, "Power distribution of parallel converters in islanded microgrid using virtual resistance droop control," 2018 13th IEEE Conference on Industrial Electronics and Applications (ICIEA), Wuhan, 2018, pp. 1671-1675.
[18]Y. Chen, A. Luo and Z. Peng, "Robust droop multiple loop control method for resistance output parallel inverters," 2nd IET Renewable Power Generation Conference (RPG 2013), Beijing, 2013, pp. 1-4.
[19]Y. Guan, J. M. Guerrero, X. Zhao and J. C. Vasquez, "Comparison of a synchronous reference frame virtual impedance-based autonomous current sharing control with conventional droop control for parallel-connected inverters," 2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), Hefei, 2016, pp. 3419-3426.
[20]TEXAS INSTRUMENTS, User guides TIDA-01606, "10-Kw Three Level Three phase Grid Tie Inverter, "March 2018.
[21]王嘉紋，＂具浮點運算數位信號處理器之三相交流-直流-交流功率換流器研製＂，國立臺灣科技大學電機研究所碩士論文，民國九十九年。
[22]A. V. Timbus, R. Teodorescu, F. Blaabjerg, M. Liserre and A. Dell'Aquila, "Independent synchronization and control of three phase grid converters," International Symposium on Power Electronics, Electrical Drives, Automation and Motion, 2006. SPEEDAM 2006., Taormina, 2006, pp. 1246-1251.
[23]Fang Zheng Peng and Jih-Sheng Lai, "Generalized instantaneous reactive power theory for three-phase power systems," in IEEE Transactions on Instrumentation and Measurement, vol. 45, no. 1, pp. 293-297, Feb. 1996.