PhD Dissertation Defense Presentation Wednesday, September 11th, 2013 9:30am 11:00am C103 Engineering Research Complex THEORETICAL ANALYSIS AND REDUCTION TECHNIQUES OF DC CAPACITOR RIPPLES AND REQUIREMENTS IN INVERTERS By Xi Lu Advisor: Dr. Fang Zheng Peng Department of Electrical and Computer Engineering Michigan State University
ABSTRACT THEORETICAL ANALYSIS AND REDUCTION TECHNIQUES OF DC CAPACITOR RIPPLES AND REQUIREMENTS IN INVERTERS By Xi Lu DC link capacitor is an important component for many conventional topologies, such as three-phase voltage source inverter (VSI), H-bridge VSI and etc. Minimization of the dc capacitor is an essential step towards developing and manufacturing compact low-cost inverter systems for high temperature operation, long life and high reliability. Traditionally, the dc capacitance has been determined according to empirical equations and computer simulations, which provides little insights into how to minimize the dc capacitor. In order to achieve an optimum minimization of the dc capacitor, an accurate theory to calculate the dc capacitor voltage ripple and current ripples must be developed first, then pulse-width modulation (PWM) and control techniques or topological improvements can be further developed to minimize both dc voltage and current ripples. This dissertation is mainly divided into two parts. First half is minimizing the capacitor ripple and requirements for three-phase VSI; while second half is for H-bridge VSI. In the first half of the dissertation, it proposes an accurate theory of calculating the dc link capacitor voltage ripples and current ripples for inverters and PWM rectifiers. The results are analyzed and summarized into graphs according to the theory, which helps find the right capacitance value for a given voltage ripple tolerance and the rms ripple current that the capacitor has to absorb. In hybrid electric vehicle (HEV) applications, the high voltage battery pack is connected to the dc link bus through a dc-dc converter. Based on the above-proposed theory, a PWM
modulation method for the dc-dc converter is developed to further reduce the dc capacitor current ripples and requirements. To verify the proposed theory and PWM method, a 150 kw inverter prototype has been built. The comparison between the calculation result and experimental result shows that they are in close agreement. For the second half of the dissertation, contributions for H-bridge inverters are made for photovoltaic and FACTs systems. As the demand of the renewable energy increases every year, the photovoltaic (PV) systems have been playing an important part in supplying energy for the global consumption. In order to connect PV modules to the grid without inserting any bulky low frequency step-up transformers, the cascaded H-bridge multilevel inverters are utilized to increase the output voltage level up to the grid voltage (e.g. 13.8 kv). The 2ω harmonic component on the dc link side of the H-bridge inverters has long been a thorny problem, which requires a huge dc link capacitor bank to absorb this 2ω low frequency current ripple in order to maintain the dc link voltage ripple under a tolerable value. This dissertation presents a simple 3 rd harmonic injection method for the cascaded H-bridge multilevel inverters for photovoltaic systems. This approach achieves a 50% to 75% reduction of the dc link capacitance, without adding any extra components or increasing the control complexity. Same 2ω harmonic problem exists in FACTs devices, which is typically implemented by an H-bridge inverter. A new topology and control method are proposed to significantly reduce the dc capacitance to minimum by only adding a phase leg and an ac capacitor with the value of 1/10 of the original dc capacitance.
Publications Journals 1. Baoming Ge, Xi Lu, Xianhao Yu, Maosong Zhang, and Fang Z. Peng, Multiphase-Legs Coupling Current Balancer for Parallel Operation of Multiple MW Power Modules, IEEE Transactions on Industrial Electronics, 2014 2. Shao Zhang, Shuai Jiang, Xi Lu, Baoming Ge, and Fang Z. Peng, Resonance Issues and Damping Techniques for Grid-connected Inverters with Long Transmission Cable,, IEEE Transactions on Power Electronics, vol.29, no.1, pp.110,120, Jan. 2014 Conference Proceedings and Presentations: 3. Shuai Jiang, Shao Zhang, Xi Lu, Baoming Ge and Fang Zheng Peng, Resonance Issues and Active Damping in HVAC Grid-Connected Offshore Wind Farm Energy Conversion Congress and Exposition (ECCE), 2013 IEEE 4. Shao Zhang, Shuai Jiang, Xi Lu, Baoming Ge and Fang Zheng Peng, Auto-tuning based Resonance Damping of Gridconnected Voltage Source Inverters with Long Transmission Cable, Energy Conversion Congress and Exposition (ECCE), 2013 IEEE 5. Weigui Ji, Xi Lu, Yuan Ji, Yingbin Tang, Feng Ran, and Fang Zheng Peng, "Low cost battery equalizer using buck-boost and series LC converter with synchronous phase-shift control," Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE, pp.1152,1157, 17-21 March 2013 6. Shao Zhang, Xi Lu, Yang Liu, Baoming Ge, and Fang Zheng Peng, "Nine IGBTs based UPFC topology and control for renewable power integration," Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE, pp.1294,1300, 17-21 March 2013 7. Dong Cao, Xi Lu, Xianhao Yu, and Fang Zheng Peng, Zero Voltage Switching Double-Wing Multilevel Modular Switched-Capacitor DC-DC Converter with Voltage Regulation, Applied Power Electronics Conference and Exposition (APEC), pp.2029,2036, 17-21 March 2013 8. Baoming Ge, Xi Lu, Xianhao Yu, Maosong Zhang, and Fang Zheng Peng, Current Balancer for Parallel Operation of Multiple MW Power Modules, Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE, pp.2295,2301, 17-21 March 2013 9. Xi Lu, Baoming Ge and Fang Zheng Peng, "Minimizing DC Capacitance Requirement of Cascadeded H- Bridge Multilevel Inverters for Photovoltaic Systems by 3 rd Harmonic Injection," Applied Power Electronics Conference and Exposition (APEC), 2012 Twenty-Seventh Annual IEEE, pp.240-245, 5-9 February 2012 10. Xi Lu, Wei Qian and Fang Zheng Peng, "Modularized Buck-Boost + Cuk Converter for High Voltage Series Connected Battery Cells," Applied Power Electronics Conference and Exposition (APEC), 2012 Twenty- Seventh Annual IEEE, pp.2272-2278, 5-9 February 2012 11. Xi Lu and Fang Zheng Peng, "Theoretical Analysis of DC Link Capacitor Current Ripple Reduction in the HEV DC-DC Converter and Inverter System Using a Carrier Modulation Method," Energy Conversion Congress and Exposition (ECCE), 2012 IEEE, pp.2833,2839, 15-20 Sept. 2012 12. Xi Lu, Wei Qian, Dong Cao, Fang Zheng Peng and Jianfeng Liu, "A carrier modulation method for minimizing the dc link capacitor current ripple of the HEV DC-DC converter and inverter systems," Applied Power Electronics Conference and Exposition (APEC), 2011 Twenty-Sixth Annual IEEE, pp.800-807, 6-11 March 2011
13. Shuai Jiang, Yuan Li, Xi Lu, Baoming Ge and Fang Zheng Peng, "Practical control implementation for 100 kva three-phase four-wire online voltage regulator," Applied Power Electronics Conference and Exposition (APEC), 2011 Twenty-Sixth Annual IEEE, pp.749-756, 6-11 March 2011 14. Jianfeng Liu, Shuai Jiang, Dong Cao, Xi Lu and Fang Zheng Peng, "Sliding-mode control of quasi-z-source inverter with battery for renewable energy system," Energy Conversion Congress and Exposition (ECCE), 2011 IEEE, vol., no., pp.3665-3671, 17-22 Sept. 2011 15. Dong Cao, Xianhao Yu, Xi Lu, Wei Qian and Fang Zheng Peng, "A double-wing multilevel modular capacitorclamped dc-dc converter with reduced capacitor voltage stress," Energy Conversion Congress and Exposition (ECCE), 2011 IEEE, vol., no., pp.545-552, 17-22 Sept. 2011 16. Xi Lu, Craig Rogers, F. Z. Peng, "A double Fourier analysis development of THD for PWM inverters: A theoretical method for motor loss minimization," Energy Conversion Congress and Exposition (ECCE), 2010 IEEE, pp.1505-1510, 12-16 Sept. 2010 17. Wei Qian, Jorge Cintron-Rivera, Sangmin Han, Xi Lu, Fang Z. Peng, Management and Control of Energy Storage Systems, the Joint 2010 IEEE Nanotechnology Materials and Devices Conference and 1 st IEEE International Symposium on Energy, Environment, Safety and Security (NMDC 2010 & 1st IEEE EESS), 12-15 October, 2010, The Clement Monterey, Monterey, California, USA 18. Xi Lu, Honnyong Cha, F.Z. Peng, "Optimizing capacitance in SPWM converter/inverter for series hybrid electric bus systems," Vehicle Power and Propulsion Conference, 2009. VPPC '09. IEEE, pp.852-858, 7-10 Sept. 2009 19. Xi Lu, F. Z. Peng, "Minimizing DC capacitor current ripple and DC capacitance requirement of the HEV converter/inverter systems," Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE, pp.1191-1198, 20-24 Sept. 2009 20. Honnyong Cha, Craig Rogers, Xi Lu, F.Z. Peng, "Design of high efficient and high density integrated magnetics for interleaved DC-DC boost converter for series hybrid electric bus," Vehicle Power and Propulsion Conference, 2009. VPPC '09. IEEE, pp.1428-1433, 7-10 Sept. 2009