@article{tu_du_yu_lu_lukic_2024, title={Privacy-Preserving Robust Consensus for Distributed Microgrid Control Applications}, volume={71}, ISSN={["1557-9948"]}, url={https://doi.org/10.1109/TIE.2023.3274846}, DOI={10.1109/TIE.2023.3274846}, abstractNote={Consensus-based distributed control has been proposed for coordinating distributed energy resources (DERs) in microgrids (MGs). As one key component, distributed average observers are used to estimate the average of a group of reference signals (e.g., voltage, current, or power). State-of-the-art distributed average observers could lead to loss of privacy due to information exchange on the communication channels. The DERs' reference signals, which contain private information, could be inferred by an eavesdropper. In this article, a privacy-preserving distributed average observer is proposed that is based on robust consensus and uses the state decomposition method to preserve privacy. Compared to the existing methods, the proposed observer does not require the knowledge of the reference signal's derivative and gives accurate and smooth estimation, and is thus applicable for MG distributed control applications. A detailed analysis regarding the convergence and privacy properties of the proposed observer is presented. The proposed observer is implemented on hardware controllers and validated in the context of distributed MG control applications through hardware-in-the-loop (HIL) tests.}, number={4}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, author={Tu, Hao and Du, Yuhua and Yu, Hui and Lu, Xiaonan and Lukic, Srdjan}, year={2024}, month={Apr}, pages={3684–3697} }
 @article{tu_du_yu_meena_lu_lukic_2023, title={Distributed Economic Dispatch for Microgrids Tracking Ramp Power Commands}, volume={14}, ISSN={["1949-3061"]}, url={https://doi.org/10.1109/TSG.2022.3189534}, DOI={10.1109/TSG.2022.3189534}, abstractNote={When in grid-connected mode of operation, distributed generators (DGs) within the microgrid (MG) can coordinate to act as a single entity to provide services to the bulk grid. The DGs can coordinate their power production to minimize the total operating cost, which is known as the distributed economic dispatch. Various methods have been proposed to solve the MG economic dispatch problem (EDP) in a distributed fashion, under the assumption that DGs’ power output, in aggregate, follows a constant or slowly varying power command. However, when the MG is providing frequency regulation service, or the internal load is highly dynamic, the MG EDP becomes dynamic, and the state-of-the-art distributed approaches cannot guarantee optimality. In this paper, we propose a distributed economic dispatch algorithm for MGs providing frequency regulation service, as an example of a dispatch profile with ramp commands. A consensus protocol guaranteeing zero steady-state error for ramp inputs is integrated into the EDP to find the optimal solution in a distributed way. With the proposed algorithm, the MG is able to tightly follow a time-varying regulation signal while maintaining an optimal economic dispatch for all the DGs within. We validate the proposed method using regulation signals from PJM and demonstrate the algorithm on a hardware-in-the-loop testbed.}, number={1}, journal={IEEE TRANSACTIONS ON SMART GRID}, author={Tu, Hao and Du, Yuhua and Yu, Hui and Meena, Shweta and Lu, Xiaonan and Lukic, Srdjan}, year={2023}, month={Jan}, pages={94–111} }
 @article{tu_yu_lukic_2023, title={Impact of Virtual Inertia on DC Grid Stability With Constant Power Loads}, volume={38}, ISSN={["1941-0107"]}, url={https://doi.org/10.1109/TPEL.2023.3243138}, DOI={10.1109/TPEL.2023.3243138}, abstractNote={Virtual inertia is an effective control approach to attenuate sudden voltage changes during transient events in low-inertia dc grids. While methods have been proposed to implement virtual inertia, its impact on dc grid stability in the presence of constant power loads (CPLs) remains unclear. In this letter, we perform a rigorous stability analysis for dc grids with CPLs powered by virtual-inertia-enhanced converters. We derive a closed-form stability criterion that can be used to evaluate the impact of virtual inertia on the system stability, and demonstrate that, given a set of system parameters, the stability of a dc grid powering CPLs can be improved for a range of virtual inertia designs. We provide analytical expressions for the optimal virtual inertia that improves stability and for the maximum virtual inertia that does not deteriorate stability. In addition, we present a step-by-step guideline to design a stable dc grid with virtual inertia. Test results are presented to validate the analysis.}, number={5}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Tu, Hao and Yu, Hui and Lukic, Srdjan}, year={2023}, month={May}, pages={5693–5699} }
 @article{ghosh_tu_krentz_karsai_lukic_2022, title={An Automated Deployment and Testing Framework for Resilient Distributed Smart Grid Applications}, DOI={10.1109/COINS54846.2022.9854934}, abstractNote={Executing distributed cyber-physical software processes on edge devices that maintains the resiliency of the overall system while adhering to resource constraints is quite a challenging trade-off to consider for developers. Current approaches do not solve this problem of deploying software components to devices in a way that satisfies different resilience requirements that can be encoded by developers at design time. This paper introduces a resilient deployment framework that can achieve that by accepting user-defined constraints to optimize redundancy or cost for a given application deployment. Experiments with a microgrid energy management application developed using a decentralized software platform show that the deployment configuration can play an important role in enhancing the resilience capabilities of distributed applications as well as reducing the resource demands on individual nodes even without modifying the control logic.}, journal={2022 IEEE INTERNATIONAL CONFERENCE ON OMNI-LAYER INTELLIGENT SYSTEMS (IEEE COINS 2022)}, author={Ghosh, Purboday and Tu, Hao and Krentz, Timothy and Karsai, Gabor and Lukic, Srdjan}, year={2022}, pages={73–78} }
 @article{du_tu_lu_wang_lukic_2022, title={Black-Start and Service Restoration in Resilient Distribution Systems With Dynamic Microgrids}, volume={10}, ISSN={["2168-6785"]}, DOI={10.1109/JESTPE.2021.3071765}, abstractNote={The resilience of distribution systems has been challenged by power outages caused by natural disasters, which calls for novel solutions to system restoration. However, the existing black-start (BS) techniques are mainly developed at the transmission level. This problem can be resolved by adopting dynamic microgrids (MGs), i.e., MGs with dynamic and adjustable boundaries nested in the distribution systems. This article proposes a restoration procedure that adopts self-organizing inverters as BS units and achieves distribution system restoration in the context of dynamic MGs. The proposed restoration procedure is structured as a two-stage approach and designed to restore a complete blackout distribution system to the state where the system is ready for seamless main grid reconnection. A framework of dynamic MG operation is developed, which improves the self-healing capability of off-grid distribution systems with automatic sectionalization and flexible reconfiguration. A sequence of actions during restoration is defined, along with distributed controllers designed with considerations of practical operating challenges. The proposed restoration procedure is validated on a 34-bus system using real-time hardware-in-the-loop simulation.}, number={4}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Du, Yuhua and Tu, Hao and Lu, Xiaonan and Wang, Jianhui and Lukic, Srdjan}, year={2022}, month={Aug}, pages={3975–3986} }
 @article{meena_tu_yu_lukic_2022, title={Economic Dispatch in Microgrids using Relaxed Mixed Integer Linear Programming}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE50734.2022.9947665}, abstractNote={Economic dispatch (ED) in a microgrid is vital to supply the load demand with a minimum cost of operation. Considering the large number of discrete variables involved in ED formulation, it is common in practice to use Mixed Integer Linear Programming (MILP) for solving the optimization problem. However, as the problem size increases, the convergence time of MILP can exponentially increase owing to the NP-hard nature of the algorithm. This paper reviews the state of the art ED formulations and proposes an equally optimal and time-efficient method, Relaxed Mixed Integer Linear Programming (RMILP) for executing the day-ahead ED in a microgrid with large problem size. Using the proposed algorithm, ED problems with smaller timesteps can be solved in a reasonable time for large systems. In addition, the load is modeled as a discrete variable which is more realistic from the perspective of load shedding and often ignored in ED formulations in the literature. We apply the proposed approach to the Banshee distribution feeders and show its advantages over conventional methods.}, journal={2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Meena, Shweta and Tu, Hao and Yu, Hui and Lukic, Srdjan}, year={2022} }
 @article{ravuri_yu_chatterji_tu_lukic_2021, title={A Compact 50kW High Power Density, Hybrid 3-Level Paralleled T-type Inverter for More Electric Aircraft Applications}, ISSN={["2473-7631"]}, DOI={10.1109/ITEC51675.2021.9490099}, abstractNote={The demand for high performing, lightweight, reliable inverters, increased the scope of wide bandgap and high-switching frequency based solutions. To achieve such high efficiency inverters, it is vital to focus on the system level design considerations to maximize the benefits of these advanced technologies. This paper presents an improved design based on considerations to further reap the benefits of choosing the right inverter topology; increased capabilities through paralleling devices, with reduced total number of switches; and designing a planarized inverter with PCB based busbar. Appropriate thermal analysis and heatsink design has aided in increased system power density along with the overall efficiency. Demonstration of a SOkW 3-phase 3-level paralleled T-type SiC inverter operating at 40kHz switching frequency for aircraft applications is shown to evaluate the benefits of proposed design methodology. The prototype achieves a high power density of 11kW/L.}, journal={2021 IEEE TRANSPORTATION ELECTRIFICATION CONFERENCE & EXPO (ITEC)}, author={Ravuri, Likhita and Yu, Hui and Chatterji, Arindam and Tu, Hao and Lukic, Srdjan}, year={2021}, pages={652–657} }
 @article{awal_tu_xu_lukic_husain_2021, title={Circulating Reactive Power and Suppression Strategies in DC Power Electronics Networks}, ISSN={["1048-2334"]}, DOI={10.1109/APEC42165.2021.9487129}, abstractNote={In DC electrical networks consisting of pulse-width-modulated converters, large circulating reactive power may be caused by parallel resonance among the passive filters and the parasitic elements of the interconnecting power-line cables. Such undesired circulating currents at switching frequencies and their harmonics lead to larger ripple in the network voltage, shorter component lifetime, and increased loss. In this work, the condition for such resonances is derived analytically and two suppression methods, namely, an inductor-capacitor (LC) trap filter and an L-termination filter, are proposed. Through analysis, we demonstrate that the proposed methods can guarantee resonance suppression in a generic DC network consisting of arbitrary N converters. Systematic design rules are developed. The analysis and suppression methods are validated through laboratory experiments.}, journal={2021 THIRTY-SIXTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2021)}, author={Awal, M. A. and Tu, Hao and Xu, Bei and Lukic, Srdjan and Husain, Iqbal}, year={2021}, pages={796–803} }
 @article{yu_awal_tu_husain_lukic_2021, title={Comparative Transient Stability Assessment of Droop and Dispatchable Virtual Oscillator Controlled Grid-Connected Inverters}, volume={36}, ISSN={["1941-0107"]}, url={https://doi.org/10.1109/TPEL.2020.3007628}, DOI={10.1109/TPEL.2020.3007628}, abstractNote={With the increasing integration of power electronics interfaced distributed generators, transient stability assessment of grid-connected inverters subjected to large grid disturbances is of vital importance for the secure and resilient operation of the power grid. Dispatchable virtual oscillator control (dVOC) is an emerging approach to implement nonlinear control of grid-forming inverters. Through coordinate transformation, a simple first-order nonlinear power angle dynamic equation is uncovered from the complex oscillator dynamics. Furthermore, this article proposes a concise and straightforward graphical approach to assess transient stability of dVOC using vector field on the circle. To provide a more in-depth analysis, a complete large-signal model is derived and the impact of dVOC voltage amplitude dynamics is analyzed. For comparison, transient stability of the currently prevalent droop control is also assessed using phase portraits. Salient transient stability features of dVOC and droop control during grid faults are summarized and compared. The theoretical analysis is validated by controller hardware-in-the-loop testbed using industry-grade hardware.}, number={2}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Yu, Hui and Awal, M. A. and Tu, Hao and Husain, Iqbal and Lukic, Srdjan}, year={2021}, month={Feb}, pages={2119–2130} }
 @article{du_lu_wang_chen_tu_lukic_2021, title={Dynamic Microgrids in Resilient Distribution Systems With Reconfigurable Cyber-Physical Networks}, volume={9}, ISSN={["2168-6785"]}, DOI={10.1109/JESTPE.2020.2981921}, abstractNote={Modern distribution systems energized by inverter-interfaced distributed generators (DGs) operate as coupled cyber-physical networks (C/P-networks), where the controllable components in the P-network are coordinated through the C-network. The concept of dynamic microgrids (MGs) operation has been adopted to enable distribution system autonomous operation with varying electric boundaries. To further enhance the system operation resiliency and flexibility, dynamic MGs operation with reconfigurable C/P-networks is discussed in this article. An evaluation framework is proposed to assess the operational feasibility of distribution feeders with multiple inverter-based dynamic MGs and come out with possible restoration solutions in the context of cross-layer C/P-network reconfiguration. Furthermore, distributed controllers are developed for components with different operating characteristics to realize seamless system topology variations and provide coordinated secondary regulation in various operation modes. The proposed evaluation framework, along with the developed distributed controller, has been validated using a hardware-in-the-loop (HIL) real-time CPS testbed.}, number={5}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Du, Yuhua and Lu, Xiaonan and Wang, Jianhui and Chen, Bo and Tu, Hao and Lukic, Srdjan}, year={2021}, month={Oct}, pages={5192–5205} }
 @article{zhang_tu_she_sadilek_ramabhadran_hu_earls_2021, title={High-Efficiency Silicon Carbide-Based Buck-Boost Converter in an Energy Storage System: Minimizing Complexity and Maximizing Efficiency}, volume={27}, ISSN={["1558-0598"]}, DOI={10.1109/MIAS.2020.3024495}, abstractNote={Energy storage (es) systems are key enablers for the high penetration of renewables. The buck-boost converter in a dc-coupled architecture for integrated photovoltaic (PV) and ES systems shows promising performance with a lower cost and higher efficiency. Silicon carbide (SiC) devices can benefit ES converters as well as the whole ES system. This article focuses on the development of a high-efficiency, SiC-based buck-boost converter in an ES system while emphasizing its unique design considerations. First, the topologies of the buck-boost converter, considering system requirements and device rating/availability, are discussed. A two-level voltage source converter (VSC) with paralleled discrete SiC devices in mature packages (e.g., TO-247) is selected because of its smaller converter complexity and better device availability. Then, the gate drive and layout design for current sharing between paralleled devices are presented. The impact of a device parameter mismatch (e.g., threshold voltage) on switching loss is also evaluated. Moreover, control and protection schemes for the buck-boost converter are discussed. Finally, a 60-kW ES converter with four 1,700-V SiC MOSFETs is prototyped and experimentally demonstrates up to 99.48% efficiency and satisfactory short circuit performance.}, number={3}, journal={IEEE INDUSTRY APPLICATIONS MAGAZINE}, author={Zhang, Zheyu and Tu, Hao and She, Xu and Sadilek, Tomas and Ramabhadran, Ramanujam and Hu, Huan and Earls, William}, year={2021}, pages={51–62} }
 @article{du_tu_lu_lukic_2021, title={Privacy-Preserving Distributed Average Observers in Distribution Systems With Grid-Forming Inverters}, volume={12}, ISSN={["1949-3061"]}, DOI={10.1109/TSG.2021.3105651}, abstractNote={Information security is critical for the safe and secure operation of distribution systems. Distributed averaging has been frequently utilized to coordinate multiple inverter-interfaced distributed generators (DGs) within the distribution grid. Unfortunately, state-of-the-art dynamic consensus-based average observers lead to loss of privacy due to neighboring information exchange, i.e., the local states of each DG that contain private information could be inferred by the neighboring DGs. In this paper, to avoid privacy disclosure and guarantee the effectiveness of distributed averaging, a privacy-preserving distributed average observer is proposed. The proposed observer adopts an algorithm-based approach in privacy preservation. Compared to the existing distributed privacy-preserving algorithms in the literature, the proposed observer achieves accurate averaging and does not introduce additional restrictions on the communication network topology. Two-fold obfuscation is implemented to mask the true values of one agent’s local states from its neighbors during the average seeking. Particularly, the true values are randomly deviated at each agent locally before publishing, and the true values of the deviations are further masked using dynamic weights that vary randomly. Additionally, the proposed observer supports “plug-and-play” functionality and is robust against communication delays. The proposed observer is implemented on hardware controllers, and its observation and privacy-preserving performance are validated in a controller hardware-in-the-loop (HIL) testbed.}, number={6}, journal={IEEE TRANSACTIONS ON SMART GRID}, author={Du, Yuhua and Tu, Hao and Lu, Xiaonan and Lukic, Srdjan}, year={2021}, month={Nov}, pages={5000–5010} }
 @article{du_lu_tu_wang_lukic_2020, title={Dynamic Microgrids With Self-Organized Grid-Forming Inverters in Unbalanced Distribution Feeders}, volume={8}, ISSN={["2168-6785"]}, DOI={10.1109/JESTPE.2019.2936741}, abstractNote={In contrast to conventional static microgrids (MGs), MGs with dynamic and adjustable territories (i.e., dynamic MGs) are proposed and implemented in this article. Dynamic MGs are commonly dominated by grid-forming inverters and nested in unbalanced distribution feeders. Unlike balanced systems where only positive-sequence components exist, proper operation of unbalanced dynamic MGs presents additional challenges. A distributed secondary control strategy is developed in this article for distributed generators (DGs) interfaced with grid-forming inverters in unbalanced dynamic MGs by providing coordinated regulations on both positive- and negative-sequence system models. System frequency and voltage are under constant regulation, along with voltage unbalance (VU) management for multiple critical load buses (CLBs). The proposed control strategy enables seamless system transition during unbalanced dynamic MGs reconfiguration and guarantees proportional positive- and negative-sequence power-sharing among connected DGs with respect to system topology variation. Detailed controller designs are provided and stability analyses are derived. The proposed control strategy is fully implemented in hardware controllers and validated on a hardware-in-the-loop (HIL) MG testbed.}, number={2}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Du, Yuhua and Lu, Xiaonan and Tu, Hao and Wang, Jianhui and Lukic, Srdjan}, year={2020}, month={Jun}, pages={1097–1107} }
 @article{awal_yu_tu_lukic_husain_2020, title={Hierarchical Control for Virtual Oscillator Based Grid-Connected and Islanded Microgrids}, volume={35}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2019.2912152}, abstractNote={Virtual oscillator control (VOC) is a nonlinear time domain controller that achieves significantly faster primary control response in islanded microgrids, compared to droop or virtual synchronous machine (VSM) control. Despite its superior performance, adoption of VOC is limited due to the lack of compatible secondary regulation or grid synchronization techniques. This is attributed to the nonlinear nature of VOC that complicates secondary control design, and the third-harmonic component in VOC output voltage that severely restricts grid-tied operation. To leverage the faster primary control response characteristics of VOC, we propose a compatible hierarchical control structure that enables operation and seamless transition between islanded and grid-connected modes. In the islanded mode, the controller achieves voltage and frequency regulation and grid synchronization; in the grid-tied mode, notch filters are used to suppress harmonic currents and tertiary level power reference tracking is achieved. The proposed controllers are validated through a series of real-time hardware-in-the-loop tests and hardware experiments using laboratory inverter prototype and state-of-the-art controls and communications hardware.}, number={1}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Awal, M. A. and Yu, Hui and Tu, Hao and Lukic, Srdjan M. and Husain, Iqbal}, year={2020}, month={Jan}, pages={988–1001} }
 @article{dubey_karsai_volgyesi_metelko_madari_tu_du_lukic_2019, title={Device Access Abstractions for Resilient Information Architecture Platform for Smart Grid}, volume={11}, ISBN={1943-0663}, DOI={10.1109/LES.2018.2845854}, abstractNote={This letter presents an overview of design mechanisms to abstract device access protocols in the resilient information architecture platform for smart grid, a middleware for developing distributed smart grid applications. These mechanisms are required to decouple the application functionality from the specifics of the device mechanisms built by the device vendors.}, number={2}, journal={IEEE EMBEDDED SYSTEMS LETTERS}, author={Dubey, Abhishek and Karsai, Gabor and Volgyesi, Peter and Metelko, Mary and Madari, Istvan and Tu, Hao and Du, Yuhua and Lukic, Srdjan}, year={2019}, month={Jun}, pages={34–37} }
 @article{du_tu_lukic_2019, title={Distributed Control Strategy to Achieve Synchronized Operation of an Islanded MG}, volume={10}, ISBN={1949-3061}, DOI={10.1109/TSG.2018.2861679}, abstractNote={To seamlessly transition a microgrid (MG) from islanded to grid-connected mode, it is necessary to synchronize the magnitude, frequency, and phase of the MG voltage to the voltage of the main grid. In this paper, we propose a distributed control strategy to achieve synchronized operation of an islanded MG supported by multiple controllable distributed generators (DGs). The proposed method utilizes a pinning-based consensus algorithm to ensure explicit coordination between magnitude, frequency, and phase angle regulation while ensuring proportional power sharing. System frequency is regulated by all the DGs in proportion to their capacity, while a selected DG eliminates the phase and magnitude regulation errors. Controller design criteria is based on small-signal stability analysis. The proposed control strategy is implemented in hardware controllers and its effectiveness is demonstrated using a real-time hardware-in-the-loop MG testbed.}, number={4}, journal={IEEE TRANSACTIONS ON SMART GRID}, author={Du, Yuhua and Tu, Hao and Lukic, Srdjan}, year={2019}, month={Jul}, pages={4487–4496} }
 @article{tu_feng_srdic_lukic_2019, title={Extreme Fast Charging of Electric Vehicles: A Technology Overview}, volume={5}, ISSN={["2332-7782"]}, DOI={10.1109/TTE.2019.2958709}, abstractNote={With the number of electric vehicles (EVs) on the rise, there is a need for an adequate charging infrastructure to serve these vehicles. The emerging extreme fast-charging (XFC) technology has the potential to provide a refueling experience similar to that of gasoline vehicles. In this article, we review the state-of-the-art EV charging infrastructure and focus on the XFC technology, which will be necessary to support the current and future EV refueling needs. We present the design considerations of the XFC stations and review the typical power electronics converter topologies suitable to deliver XFC. We consider the benefits of using the solid-state transformers (SSTs) in the XFC stations to replace the conventional line-frequency transformers and further provide a comprehensive review of the medium-voltage SST designs for the XFC application.}, number={4}, journal={IEEE TRANSACTIONS ON TRANSPORTATION ELECTRIFICATION}, author={Tu, Hao and Feng, Hao and Srdic, Srdjan and Lukic, Srdjan}, year={2019}, month={Dec}, pages={861–878} }
 @inproceedings{tu_lukic_2018, title={A hybrid communication topology for modular multilevel converter}, DOI={10.1109/apec.2018.8341535}, abstractNote={Modular multilevel converter with large number of modules is a potential topology for many applications such as high-voltage DC (HVDC) and solid state transformers (SST). However, the communication between the controller and the modules becomes complex if the number of modules is high. If conventional star topology communication where the controller has direct connection to all the modules is used, the wiring can be cumbersome and the cost can be high. Another possible solution is ring topology communication. Because the modules are connected in series and each module imposes some delay, ring topology has a limited communication speed. In this paper, we proposed a hybrid communication topology to combine star and ring topology. The proposed communication topology reduces the cycle time by 30% compared to ring topology for MMC with 30 modules while increases negligible cost.}, booktitle={Thirty-third annual ieee applied power electronics conference and exposition (apec 2018)}, author={Tu, H. and Lukic, S.}, year={2018}, pages={3051–3056} }
 @inproceedings{yu_tu_lukic_2018, title={A passivity-based decentralized control strategy for current-controlled inverters in AC microgrids}, DOI={10.1109/apec.2018.8341200}, abstractNote={As a conventional stability analysis method of AC microgrid, the impedance based method needs a comprehensive impedance model of all the subsystems. It may fall short when the AC microgrid is interfaced by large number of converters with different parameters, or the microgrid has a time-varying structure, both of which would make the system modeling extremely complicated. This paper proposed a passivity margin criterion for AC microgrid, which decentralizes the stability target to each individual converter. The system will be stable with satisfactory margin as long as each converter is designed in accordance with the criterion, regardless of the system variations. A passivity realization approach for current-controlled LCL-type inverter is derived. The conclusions are verified on an OPAL-RT based Hardware-in-the-Loop platform.}, booktitle={Thirty-third annual ieee applied power electronics conference and exposition (apec 2018)}, author={Yu, Hui and Tu, H. and Lukic, Srdjan}, year={2018}, pages={1399–1406} }
 @inproceedings{tu_lukic_2017, title={Comparative study of PES net and SyCCo bus: Communication protocols for modular multilevel converter}, DOI={10.1109/ecce.2017.8095966}, abstractNote={Due to its modularity and scalability, modular multilevel converter is a promising topology for medium voltage applications, such as energy storage or motor drives. Because of the large number of modules, the wiring can become complex if the conventional star topology communication network is used. To solve this issue, a communication link that uses a ring topology to connect the central controller and the modules provides an efficient solution. The information exchanged on this link includes real time data, such as duty cycle, measurements and fault feedback. Thus, a dedicated high-speed communication protocol is needed. This paper reviews two possible protocols for modular multilevel converter communication, PES Net and SyCCo bus. After introducing the operating principles, their performance is compared and discussed. SyCCo bus is implemented using Altera Cyclone IV FPGA. Tests are conducted to analyze the communication delay of SyCCo bus. The implementation is made open source.}, booktitle={2017 ieee energy conversion congress and exposition (ecce)}, author={Tu, H. and Lukic, S.}, year={2017}, pages={1487–1492} }