@article{liu_youssef_chescheir_appelboom_poole_arellano_skaggs_2019, title={Effect of controlled drainage on nitrogen fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent}, volume={217}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2019.02.018}, abstractNote={Application of livestock manure has become a principal nutrient source in groundwater and surface water. The goal of this research was to investigate the effect of controlled drainage (CD) on nitrogen (N) fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent (SLE). A four-year field experiment was conducted on a naturally poorly drained pasture in eastern North Carolina. The 1.25 ha experimental field was artificially drained by subsurface drains installed at 1.0 m depth and 12.5 m spacing. Two treatments, replicated twice were implemented: conventional drainage (FD) and CD. The CD management protocol was more intensive compared to previous studies. The drain outlets of CD plot were set at 36 cm below soil surface all year round except several days before irrigation application when water table depth was shallower than 65 cm below surface. Controlled drainage significantly reduced drainage flow and TN loading via subsurface drain lines by an average of 397 mm yr−1 (93%) and 34.5 kg N ha−1 yr−1 (94%), respectively. DRAINMOD hydrologic simulations indicated that 96% of the reduction in predicted drain flow was attributed to increased lateral seepage. The nitrogen that did not drain from the field in response to CD was lost via enhanced denitrification (67%) and lateral seepage to adjacent fields (33%). This study clearly demonstrated how CD management affects the N fate and transport through seepage and denitrification process.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Liu, Yu and Youssef, Mohamed A. and Chescheir, George M. and Appelboom, Timothy W. and Poole, Chad A. and Arellano, Consuelo and Skaggs, R. Wayne}, year={2019}, month={May}, pages={440–451} }
 @inproceedings{zhou_liu_bhattacharya_huang_2010, title={New inductor current feedback control with active harmonics injection for inverter stage of solid state transformer}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78751540900&partnerID=MN8TOARS}, DOI={10.1109/iecon.2010.5675216}, abstractNote={Solid state transformer (SST) is considered the key unit for power processing and conversion in the future distributed renewable energy network. The role of SST is to enable the active management of distributed energy resources, energy storage devices and different type of loads in a distribution grid. Inverter stage of SST supplies sinusoidal voltage to the users. In this paper an improved inductor current control based on active harmonics injection is proposed to overcome the drawback of inferior performance of conventional inductor current feedback control for the nonlinear loads. The inductor current overshoot during the load transient is investigated by using both capacitor current feedback control and inductor current feedback control. The inductor current feedback control has the capability to limit current overshoot even with a smaller inductor, which shows the potential to further reduce the size and weight of the passive components.}, booktitle={IECON Proceedings (Industrial Electronics Conference)}, author={Zhou, X. and Liu, Y. and Bhattacharya, Subhashish and Huang, A.}, year={2010}, pages={593–598} }
 @inproceedings{li_liu_bhattacharya_huang_2009, title={An optimum PWM strategy for 5-level active NPC (ANPC) converter based on real-time solution for THD minimization}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72449155137&partnerID=MN8TOARS}, DOI={10.1109/ecce.2009.5316229}, abstractNote={The recently introduced active NPC (ANPC) converter is becoming an attractive topology of multilevel converter family. This paper presents the analysis of the 5-level ANPC converter with an optimum PWM strategy to achieve the minimized total harmonic distortion (THD) for high power or high frequency applications. Instead of relying on the conventional look-up table based on off-line calculated solutions, the switching angles of the optimum PWM are calculated through a real-time algorithm, which is time-efficient and therefore easy to implement in real-time by digital processors. The control scheme of balancing the floating capacitors voltages is also proposed. Simulation results verify the performance of the proposed strategies.}, booktitle={2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009}, author={Li, J. and Liu, Y. and Bhattacharya, Subhashish and Huang, A.Q.}, year={2009}, pages={1976–1982} }
 @inproceedings{liu_p._g._c._huang_langston_steurer_litzenberger_anderson_adapa_et al._2009, title={Controller hardware-in-the-loop validation for a0 10 MVA ETO-based STATCOM for wind farm application}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72449158355&partnerID=MN8TOARS}, DOI={10.1109/ecce.2009.5316033}, abstractNote={This paper reports experimental validation of a Static Synchronous Compensation (STATCOM) by controller hardware-in-the-loop (CHIL) testing with a real-time digital simulator (RTDS). The controller is designed and developed for a 10 MVA STATCOM for voltage regulation at the PCC of a 50 MW wind farm connected to a 69kV utility grid. Emitter Turn-off (ETO) thyristors are switching devices in the multilevel inverter. The STATCOM controller was developed for a cascade multilevel inverter and has been validated on a laboratory test-bench. The CHIL testing of the controller is done with detailed scaled model of the 50 MW wind farm and 69kV utility system. The experimental results from the RTDS for both steady state and dynamic changes in the STATCOM output validate the STATCOM controller design and performance.}, booktitle={2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009}, author={Liu, Y. and P., Liang Z. and G., Song Z. and C., Bhattacharya W. and Huang, S. and Langston, A. and Steurer, J. and Litzenberger, M. and Anderson, W. and Adapa, L. and et al.}, year={2009}, pages={1398–1403} }
 @inproceedings{huang_liu_chen_li_song_2009, title={Emitter turn-off (ETO) thyristor, ETO light converter and their grid applications}, DOI={10.1109/pes.2009.5275226}, abstractNote={In today's electric power system, solid state power electronics technology plays more and more important roles and the demand for mega-watt level power ratings is increasing. The development of mega-watt power converters strongly depends on the state-of-the-art of power semiconductor technology, cooling technology and digital controller. The authors have been involved in the development of the Emitter Turn-Off (ETO) thyristor, an emerging power semiconductor switch for high power applications. Packed with advanced features as well as superior performance, ETO based power electronics systems are very attractive for various grid applications. In this paper, the authors will present the ETO device, ETO Light converter that are under development at the NSF FREEDM Systems Center. Moreover, the authors will explain how these developments will facilitate grid applications: static synchronous compensator (STATCOM) without/with energy storage, direct connection of wind turbine, High Voltage Direct Current (HVDC) application, power flow control and solid-state circuit breaker and current limiter.}, booktitle={2009 ieee power & energy society general meeting, vols 1-8}, author={Huang, A. and Liu, Y. and Chen, Q. and Li, J. and Song, W. C.}, year={2009}, pages={1861–1868} }
 @article{liu_hong_huang_2009, title={Real-Time Algorithm for Minimizing THD in Multilevel Inverters With Unequal or Varying Voltage Steps Under Staircase Modulation}, volume={56}, ISSN={["1557-9948"]}, url={http://dx.doi.org/10.1109/tie.2009.2015360}, DOI={10.1109/TIE.2009.2015360}, abstractNote={Different modulation methods have been proposed to control the multilevel inverters. This paper focuses on the staircase modulation that is very popular for multilevel inverters with low switching frequencies. Nonreal-time algorithms for the staircase modulation cannot be applied practically in multilevel inverters with varying voltage steps, since the sizes of lookup tables would be huge. We propose a real-time algorithm for multilevel inverters with unequal or varying voltage steps under the staircase modulation. The algorithm results in the minimal total harmonic distortion (THD) of the output voltage of the inverter, which is proved by rigorous mathematical derivations in this paper. A new expression of THD is presented to simplify the derivation significantly. Computational complexity of the algorithm is analyzed to estimate the time cost of the calculation. We implemented the algorithm on a digital signal processor and provide experimental results that verify the performance of the proposed algorithm.}, number={6}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Liu, Yu and Hong, Hoon and Huang, Alex Q.}, year={2009}, month={Jun}, pages={2249–2258} }
 @article{liu_huang_song_bhattacharya_tan_2009, title={Small-Signal Model-Based Control Strategy for Balancing Individual DC Capacitor Voltages in Cascade Multilevel Inverter-Based STATCOM}, volume={56}, ISSN={["1557-9948"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-67649366309&partnerID=MN8TOARS}, DOI={10.1109/TIE.2009.2017101}, abstractNote={This paper presents a new feedback control strategy for balancing individual DC capacitor voltages in a three-phase cascade multilevel inverter-based static synchronous compensator. The design of the control strategy is based on the detailed small-signal model. The key part of the proposed controller is a compensator to cancel the variation parts in the model. The controller can balance individual DC capacitor voltages when H-bridges run with different switching patterns and have parameter variations. It has two advantages: 1) the controller can work well in all operation modes (the capacitive mode, the inductive mode, and the standby mode) and 2) the impact of the individual DC voltage controller on the voltage quality is small. Simulation results and experimental results verify the performance of the controller.}, number={6}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, author={Liu, Yu and Huang, Alex Q. and Song, Wenchao and Bhattacharya, Subhashish and Tan, Guojun}, year={2009}, month={Jun}, pages={2259–2269} }
 @article{wang_huang_sung_liu_baliga_2009, title={Smart Grid Technologies}, volume={3}, ISSN={["1941-0115"]}, DOI={10.1109/MIE.2009.932583}, abstractNote={The need for power semiconductor devices with high-voltage, high- frequency, and high-temperature operation capability is growing, especially for advanced power conversion and military applications, and hence the size and weight of the power electronic system are reduced. Development of 15-kV SiC IGBTs and their impact on utility applications is discussed.}, number={2}, journal={IEEE INDUSTRIAL ELECTRONICS MAGAZINE}, author={Wang, Jun and Huang, Alex Q. and Sung, Woongje and Liu, Yu and Baliga, B. Jayant}, year={2009}, month={Jun}, pages={16–23} }
 @article{liu_bhattacharya_song_huang_2008, title={Control Strategy for Cascade Multilevel Inverter based STATCOM with Optimal Combination Modulation}, ISBN={["978-1-4244-1667-7"]}, ISSN={["0275-9306"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-52349084808&partnerID=MN8TOARS}, DOI={10.1109/pesc.2008.4592734}, abstractNote={Static synchronous compensation (STATCOM) is a flexible AC transmission system (FACTS) device connected in shunt to the network for generating or absorbing reactive power. The STATCOM is used to regulate voltage, control power factor and stabilize power flow. The transformerless STATCOM is attractive due to low cost and power losses. Cascaded multilevel inverters are viable topologies for the transformerless STATCOM since each power semiconductor device only sustains low voltage. To meet IEEE 519 standard and keep low switching frequency, an optimal combination modulation strategy is used, which leads to some challenges in designing the controller, such as extra switching and the balancing of individual dc capacitor voltages. In this paper, the design of the controller is specified. Simulation results and experimental results are shown to verify the performance of the proposed control strategy.}, journal={2008 IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE, VOLS 1-10}, author={Liu, Yu and Bhattacharya, Subhashish and Song, Wenchao and Huang, Alex Q.}, year={2008}, pages={4812–4818} }
 @article{liu_luo_2008, title={Trinary hybrid 81-level multilevel inverter for motor drive with zero common-mode voltage}, volume={55}, ISSN={["0278-0046"]}, DOI={10.1109/TIE.2007.909072}, abstractNote={This paper proposes a trinary hybrid 81-level multilevel inverter for motor drive. Benefiting from the trinary hybrid topology of the inverter, 81-level voltages per phase can be synthesized with the fewest components. Bidirectional DC-DC converters are used not only to inject power to the DC links of the inverter but also to absorb power from some DC links in cases with a lower modulation index. The higher bandwidth of DC-DC converters alleviates the ripples of DC-link voltages caused by the load current. The space vector modulation used here, which selects voltage vectors that generate a zero common-mode voltage in the load, works at a low switching frequency. With up to 81-level voltages per phase, the total harmonic distortion is small, and the relationship between the fundamental load voltage and the modulation index is precisely linear. A vector controller is used to control an induction motor, which results in a high dynamic response for speeds or torques. The performance of the proposed inverter for the motor drive is confirmed by simulation and experiment.}, number={3}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, author={Liu, Yu and Luo, Fang Lin}, year={2008}, month={Mar}, pages={1014–1021} }