Fast and accurate detection of symmetrical components is critical for ride-through of asymmetrical faults in grid-forming (GFM) inverter based resources (IBRs). Sequence-decomposed GFM control enables to emulate the behavior of a synchronous machine by an IBR in both positive- and negative-sequences, where current references are generated separately in each sequence from the extracted symmetrical components of the terminal voltage. Cross-coupled dynamics between the stationary frame components attributed by the symmetrical component extraction (SCE) complicates the analysis and design process. In this work, a small-signal model is developed for the analysis and design of such sequence-decomposed GFM control. It is demonstrated that by virtue of its overall structure, sequence-decomposed GFM control enables simplified analysis eliminating the cross-coupled dynamics characteristic to SCE. Subsequently, comparative analysis is presented between delay based and filter based SCE methods focusing on their impact on small-signal stability. Design guidelines are provided along with supporting experimental evidence using a laboratory inverter prototype.
}, author={Awal, M A and Cen, Siye and Rachi, Md Rifat Kaisar and Yu, Hui and Schröder, Stefan and Husain, Iqbal}, year={2023}, month={Jul} } @article{awal_cen_rachi_yu_schröder_husain_2023, title={Modeling, Analysis, and Design for Small-Signal Stability in Sequence-Decomposed Grid-Forming Control}, url={https://doi.org/10.36227/techrxiv.23653152}, DOI={10.36227/techrxiv.23653152}, abstractNote={Fast and accurate detection of symmetrical components is critical for ride-through of asymmetrical faults in grid-forming (GFM) inverter based resources (IBRs). Sequence-decomposed GFM control enables to emulate the behavior of a synchronous machine by an IBR in both positive- and negative-sequences, where current references are generated separately in each sequence from the extracted symmetrical components of the terminal voltage. Cross-coupled dynamics between the stationary frame components attributed by the symmetrical component extraction (SCE) complicates the analysis and design process. In this work, a small-signal model is developed for the analysis and design of such sequence-decomposed GFM control. It is demonstrated that by virtue of its overall structure, sequence-decomposed GFM control enables simplified analysis eliminating the cross-coupled dynamics characteristic to SCE. Subsequently, comparative analysis is presented between delay based and filter based SCE methods focusing on their impact on small-signal stability. Design guidelines are provided along with supporting experimental evidence using a laboratory inverter prototype.
}, author={Awal, M A and Cen, Siye and Rachi, Md Rifat Kaisar and Yu, Hui and Schröder, Stefan and Husain, Iqbal}, year={2023}, month={Jul} } @article{paduani_yu_xu_lu_2022, title={A Unified Power-Setpoint Tracking Algorithm for Utility-Scale PV Systems With Power Reserves and Fast Frequency Response Capabilities}, volume={13}, ISSN={["1949-3037"]}, url={https://doi.org/10.1109/TSTE.2021.3117688}, DOI={10.1109/TSTE.2021.3117688}, abstractNote={This paper presents a fast power-setpoint tracking algorithm to enable utility-scale photovoltaic (PV) systems to provide high quality grid services such as power reserves and fast frequency response. The algorithm unites maximum power-point estimation (MPPE) with flexible power-point tracking (FPPT) control to improve the performance of both algorithms, achieving fast and accurate PV power-setpoint tracking even under rapid solar irradiance changes. The MPPE is developed using a real-time, nonlinear curve-fitting approach based on the Levenberg-Marquardt algorithm. A modified adaptive FPPT based on the Perturb and Observe technique is developed for the power-setpoint tracking. By using MPPE to decouple the impact of irradiance changes on the measured PV output power, we develop a fast convergence technique for tracking power-reference changes within three FPPT iterations. Furthermore, to limit the maximum output power ripple, a new design is introduced for the steady-state voltage step size of the adaptive FPPT. The proposed algorithm is implemented on a testbed consisting of a 500 kVA three-phase, single-stage, utility-scale PV system on the OPAL-RT eMEGASIM platform. Results show that the proposed method outperforms the state-of-the-art.}, number={1}, journal={IEEE TRANSACTIONS ON SUSTAINABLE ENERGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Paduani, Victor Daldegan and Yu, Hui and Xu, Bei and Lu, Ning}, year={2022}, month={Jan}, pages={479–490} } @article{dsouza_muthukaruppan_yu_baran_lukic_vukojevic_2022, title={Assessment of Anti-Islanding Schemes on a Distribution System with High DER Penetration and Dynamic VAR Compensators}, ISSN={["2329-5759"]}, DOI={10.1109/PEDG54999.2022.9923268}, abstractNote={The recently introduced power-electronics-based dynamic VAR compensator (DVC) offers an effective solution in mitigating the impacts that high penetration distributed energy resources (DERs) have on distribution systems. One of the concerns about adopting these devices is their impact on distribution system protection, especially islanding detection. This paper proposes a hardware-in-loop (HIL) test-bed based approach to investigate the performance of islanding detection schemes on a distribution feeder. This approach facilitates the assessment of protection system performance under more realistic conditions by emulating actual devices and a distribution system. The results are based on an actual case study that is outlined to show the effectiveness of existing passive anti-islanding schemes and assess the impact of a DVC on islanding detection.}, journal={2022 IEEE 13TH INTERNATIONAL SYMPOSIUM ON POWER ELECTRONICS FOR DISTRIBUTED GENERATION SYSTEMS (PEDG)}, author={DSouza, Keith and Muthukaruppan, Valliappan and Yu, Hui and Baran, Mesut and Lukic, Srdjan and Vukojevic, Aleksandar}, year={2022} } @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{xu_tu_du_yu_liang_lukic_2021, title={A Distributed Control Architecture for Cascaded H-Bridge Converter With Integrated Battery Energy Storage}, volume={57}, url={https://doi.org/10.1109/TIA.2020.3039430}, DOI={10.1109/TIA.2020.3039430}, abstractNote={Cascaded H-bridge topology has been used in grid-tied converters for battery energy storage system due to its modular structure. To fully utilize the converter's modularity, this article proposes a hierarchical distributed control architecture that consists of primary control, secondary control, and battery state-of-charge (SOC) balancing control. Primary control ensures accurate current tracking, whereas a distributed secondary control based on consensus algorithm is presented to regulate power sharing among modules and is proved to be stable theoretically. A distributed SOC balancing control is further introduced to improve energy efficiency of battery energy storage system. Finally, the hierarchical distributed control strategy is implemented using hardware controllers and a software platform. Besides, a carrier phase shift control is also implemented to achieve multilevel output voltage and harmonic reduction. The experimental results demonstrate the performance of the proposed control scheme effectively.}, number={1}, journal={IEEE Transactions on Industry Applications}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Xu, Bei and Tu, Hao and Du, Yuhua and Yu, Hui and Liang, Hui and Lukic, Srdjan}, year={2021}, month={Jan}, pages={845–856} } @article{awal_rachi_bipu_yu_husain_2021, title={Adaptive Pre-Synchronization and Discrete-Time Implementation for Unified Virtual Oscillator Control1}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE47101.2021.9595171}, abstractNote={Unified virtual oscillator controller (uVOC) is a nonlinear time-domain controller which offers robust synchronization and enhanced fault ride-through for grid-following (GFL) and grid-forming (GFM) converters without the need for switching to a back-up controller. An adaptive pre-synchronization method is proposed for uVOC to enable smooth start-up and seamless connection to an existing grid/network with non-nominal frequency and/or voltage magnitude at the point of coupling (PoC). Furthermore, we evaluate the efficacy of different discretization methods for discrete-time (DT) implementation of the nonlinear dynamics of uVOC and demonstrate that zero-order-hold (ZOH) discretization fails at sampling frequencies up to tens of kHz. DT implementation of uVOC using second-order Runge-Kutta method is presented, which offers a reasonsable compromise between computational overhead and discretization accuracy. In addition, an inductor (L) or an inductor-capacitor-inductor (LCL) type input filter used in typical voltage source converter (VSC) applications leads to voltage deviation at the converter output terminal depending on the power flow. A terminal voltage compensator (TVC) for such voltage deviation is proposed. The efficacy of the proposed methods are demonstrated through laboratory hardware experiments.}, journal={2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Awal, M. A. and Rachi, Md Rifat Kaisar and Bipu, Md Rashed Hassan and Yu, Hui and Husain, Iqbal}, year={2021}, pages={3418–3424} } @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{long_yu_xie_lu_lubkeman_2021, title={Diesel Generator Model Parameterization for Microgrid Simulation Using Hybrid Box-Constrained Levenberg-Marquardt Algorithm}, volume={12}, ISSN={["1949-3061"]}, url={https://doi.org/10.1109/TSG.2020.3026617}, DOI={10.1109/TSG.2020.3026617}, abstractNote={Existing generator parameterization methods, typically developed for large turbine generator units, are difficult to apply to small kW-level diesel generators in microgrid applications. This article presents a model parameterization method that estimates a complete set of kW-level diesel generator parameters simultaneously using only load-step-change tests with limited measurement points. This method provides a more cost-efficient and robust approach to achieve high-fidelity modeling of diesel generators for microgrid dynamic simulation. A two-stage hybrid box-constrained Levenberg-Marquardt (H-BCLM) algorithm is developed to search the optimal parameter set given the parameter bounds. A heuristic algorithm, namely Generalized Opposition-based Learning Genetic Algorithm (GOL-GA), is applied to identify proper initial estimates at the first stage, followed by a modified Levenberg-Marquardt algorithm designed to fine tune the solution based on the first-stage result. The proposed method is validated against dynamic simulation of a diesel generator model and field measurements from a 16kW diesel generator unit.}, number={2}, journal={IEEE TRANSACTIONS ON SMART GRID}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Long, Qian and Yu, Hui and Xie, Fuhong and Lu, Ning and Lubkeman, David}, year={2021}, month={Mar}, pages={943–952} } @article{awal_rachi_yu_husain_lukic_2021, title={Double Synchronous Unified Virtual Oscillator Control for Asymmetrical Fault Ride-Through in Grid-Forming Voltage Source Converters}, url={https://doi.org/10.36227/techrxiv.14776125.v2}, DOI={10.36227/techrxiv.14776125.v2}, abstractNote={A double synchronous unified virtual oscillator controller (dsUVOC) is proposed for grid-forming voltage source converters to achieve synchronization to the fundamental frequency positive- and negative-sequence components of unbalanced or distorted grids. The proposed controller leverages a positive- and a negative-sequence virtual oscillator, a double-sequence current reference generator, and a double-sequence vector limiter. Under fault conditions, the controller enables to clamp the converter output current below the maximum value limited by the converter hardware while retaining synchronization without a phase-locked-loop (PLL) regardless of the balanced or unbalanced nature of grid faults. Consequently, balanced and unbalanced fault ride-through can be achieved without the need for switching to a back-up controller. The paper presents the systematic development of the double-synchronous structure along with detail design and implementation guidelines. Validation of the proposed controller is provided through extensive control-hardware-in-the-loop (CHIL) and laboratory hardware experiments.}, author={Awal, M A and Rachi, Md Rifat Kaisar and Yu, Hui and Husain, Iqbal and Lukic, Srdjan}, year={2021}, month={Dec} } @article{awal_rachi_yu_husain_lukic_2021, title={Double Synchronous Unified Virtual Oscillator Control for Asymmetrical Fault Ride-Through in Grid-Forming Voltage Source Converters}, url={https://doi.org/10.36227/techrxiv.14776125.v1}, DOI={10.36227/techrxiv.14776125.v1}, abstractNote={A double synchronous unified virtual oscillator controller (dsUVOC) is proposed for grid-forming voltage source converters to achieve synchronization to the fundamental frequency positive- and negative-sequence components of unbalanced or distorted grids. The proposed controller leverages a positive- and a negative-sequence virtual oscillator, a double-sequence current reference generator, and a double-sequence vector limiter. Under fault conditions, the controller enables to clamp the converter output current below the maximum value limited by the converter hardware while retaining synchronization without a phase-locked-loop (PLL) regardless of the balanced or unbalanced nature of grid faults. Consequently, balanced and unbalanced fault ride-through can be achieved without the need for switching to a back-up controller. The paper presents the systematic development of the double-synchronous structure along with detail design and implementation guidelines. Validation of the proposed controller is provided through extensive control-hardware-in-the-loop (CHIL) experiments.}, author={Awal, M A and Rachi, Md Rifat Kaisar and Yu, Hui and Husain, Iqbal and Lukic, Srdjan}, year={2021}, month={Jun} } @article{awal_rachi_yu_husain_lukic_2021, title={Double Synchronous Unified Virtual Oscillator Control for Asymmetrical Fault Ride-Through in Grid-Forming Voltage Source Converters}, url={https://doi.org/10.36227/techrxiv.14776125}, DOI={10.36227/techrxiv.14776125}, abstractNote={A double synchronous unified virtual oscillator controller (dsUVOC) is proposed for grid-forming voltage source converters to achieve synchronization to the fundamental frequency positive- and negative-sequence components of unbalanced or distorted grids. The proposed controller leverages a positive- and a negative-sequence virtual oscillator, a double-sequence current reference generator, and a double-sequence vector limiter. Under fault conditions, the controller enables to clamp the converter output current below the maximum value limited by the converter hardware while retaining synchronization without a phase-locked-loop (PLL) regardless of the balanced or unbalanced nature of grid faults. Consequently, balanced and unbalanced fault ride-through can be achieved without the need for switching to a back-up controller. The paper presents the systematic development of the double-synchronous structure along with detail design and implementation guidelines. Validation of the proposed controller is provided through extensive control-hardware-in-the-loop (CHIL) and laboratory hardware experiments.}, author={Awal, M A and Rachi, Md Rifat Kaisar and Yu, Hui and Husain, Iqbal and Lukic, Srdjan}, year={2021}, month={Dec} } @article{quan_huang_yu_2020, title={A Novel Order Reduced Synchronous Power Control for Grid-Forming Inverters}, volume={67}, url={https://doi.org/10.1109/TIE.2019.2959485}, DOI={10.1109/TIE.2019.2959485}, abstractNote={Nowadays, the grid-forming inverter, also referred as the voltage-controlled inverter, has gained greater attention due to its advantages in providing power support to the grid. The power control is central to grid-forming inverters in realizing grid-support functionalities, such as the droop control or virtual inertia emulation. However, in these controls, the dynamic response of the instantaneous power usually suffers from overshoots and oscillations. To improve the dynamic response of the injected instantaneous power, this letter introduces a novel synchronous active power control for the voltage-controlled grid-connected inverter. The droop coefficient can be released from adjusting the damping factor of the system. A novel design method is proposed to reduce the second-order power loop to a first-order model. Consequently, the droop and reference-following controls operate like a first-order system with an excellent dynamic response. Moreover, the virtual inertia can be designed freely without affecting the performance of the power control. The correctness of the control is verified experimentally.}, number={12}, journal={IEEE Transactions on Industrial Electronics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Quan, Xiangjun and Huang, Alex Q. and Yu, Hui}, year={2020}, month={Dec}, pages={10989–10995} } @article{du_tu_yu_lukic_2020, title={Accurate Consensus-based Distributed Averaging with Variable Time Delay in Support of Distributed Secondary Control Algorithms}, volume={11}, url={http://dx.doi.org/10.1109/tsg.2020.2975752}, DOI={10.1109/tsg.2020.2975752}, abstractNote={Distributed secondary control has been widely used in hierarchical control structures, where multiple distributed generators (DGs) need to coordinate to regulate system voltage and frequency. In these systems, consensus algorithms determine the average of a group of dynamic states (e.g., voltages measured by a group of DGs). To be useful, consensus algorithms must be computationally efficient, stable and accurate. In practice, numerous practical implementation challenges significantly affect the consensus equilibrium. In this paper, we quantify the accuracy deviations of the distributed average observer algorithms proposed in the literature to demonstrate the problems with the state-of-the-art distributed averaging techniques. A novel approach is proposed that achieves accurate average tracking in the presence of time-varying communication delays among agents. In our implementation, time synchronization of all distributed controllers is enabled by a novel software platform, called Resilient Information Architecture Platform for the Smart Grid (RIAPS). The proposed distributed average observer is implemented on hardware controllers and its effectiveness is validated in a controller hardware-in-the-loop testbed.}, number={4}, journal={IEEE Transactions on Smart Grid}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Du, Yuhua and Tu, Hao and Yu, Hui and Lukic, Srdjan}, year={2020}, pages={2918–2928} } @article{xie_yu_long_zeng_lu_2020, title={Battery Model Parameterization Using Manufacturer Datasheet and Field Measurement for Real-Time HIL Applications}, volume={11}, url={https://doi.org/10.1109/TSG.2019.2953718}, DOI={10.1109/TSG.2019.2953718}, abstractNote={This paper presents a novel battery model parameterization method using actual field measurement and manufacturer datasheet for real-time hardware-in-the-loop (HIL) applications. It is critical that real-time HIL models can accurately reproduce field test results so that tests can be conducted on HIL testbeds instead of in the field. In the past, numerical heuristic optimization algorithms were often used to derive parameters for battery models. However, the deterministic algorithms often reach a locally optimal solution and stochastic heuristic searching strategies suffer from low searching efficiency. Therefore, in this paper, we propose a global-local searching enhanced genetic algorithm (GL-SEGA). By applying the generalized opposition-based learning mechanism, GL-SEGA can efficiently explore the global solution space. By using the trust-region-reflective method to perform the local search, the GL-SEGA can improve the accuracy and convergence in its local exploitations. Field measurements and manufactory datasheets are used to test and validate the accuracy and robustness of the GL-SEGA algorithm.}, number={3}, journal={IEEE Transactions on Smart Grid}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Xie, Fuhong and Yu, Hui and Long, Qian and Zeng, Wente and Lu, Ning}, year={2020}, month={May}, pages={2396–2406} } @article{awal_yu_lukic_husain_2020, title={Droop and Oscillator Based Grid-Forming Converter Controls: A Comparative Performance Analysis}, volume={8}, ISSN={["2296-598X"]}, DOI={10.3389/fenrg.2020.00168}, abstractNote={Two distinct approaches, one droop-based phasor-domain modeled and the other non-linear oscillator-based time-domain modeled, have emerged for the analysis and control of power electronic converters at the system interface layer where these converters are integrating distributed energy resources (DERs). While the droop-type controllers are based on distinct time-scale separation of control loops, purposefully slowing down the response of the DERs, the oscillator-based controllers deliver fast dynamic response with accurate power sharing capability as well as stability guarantee. In this paper, we analyze both the droop- and oscillator-type converters in the context of grid forming converters with respect to steady state terminal response, transient stability, and harmonic compensation in converter output current or in network voltage. Simulation and experimental results are provided to demonstrate the easier implementation of oscillator-based controls that can also achieve supplementary control objectives pertinent to power quality.}, journal={FRONTIERS IN ENERGY RESEARCH}, author={Awal, M. A. and Yu, Hui and Lukic, Srdjan and Husain, Iqbal}, year={2020}, month={Oct} } @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{tu_du_yu_dubey_lukic_karsai_2020, title={Resilient Information Architecture Platform for the Smart Grid: A Novel Open-Source Platform for Microgrid Control}, volume={67}, url={https://doi.org/10.1109/TIE.2019.2952803}, DOI={10.1109/TIE.2019.2952803}, abstractNote={Microgrids are seen as an effective way to achieve reliable, resilient, and efficient operation of the power distribution system. Core functions of the microgrid control system are defined by the IEEE Standard 2030.7; however, the algorithms that realize these functions are not standardized, and are a topic of research. Furthermore, the corresponding controller hardware, operating system, and communication system to implement these functions vary significantly from one implementation to the next. In this article, we introduce an open-source platform, resilient information architecture platform for the smart grid (RIAPS), ideally suited for implementing and deploying distributed microgrid control algorithms. RIAPS provides a design-time tool suite for development and deployment of distributed microgrid control algorithms. With support from a number of run-time platform services, developed algorithms can be easily implemented and deployed into real microgrids. To demonstrate the unique features of RIAPS, we propose and implement a distributed microgrid secondary control algorithm capable of synchronized and proportional compensation of voltage unbalance using distributed generators. Test results show the effectiveness of the proposed control and the salient features of the RIAPS platform.}, number={11}, journal={IEEE Transactions on Industrial Electronics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Tu, Hao and Du, Yuhua and Yu, Hui and Dubey, Abhishek and Lukic, Srdjan and Karsai, Gabor}, year={2020}, month={Nov}, pages={9393–9404} } @article{awal_yu_husain_yu_lukic_2020, title={Selective Harmonic Current Rejection for Virtual Oscillator Controlled Grid-Forming Voltage Source Converters}, volume={35}, ISSN={0885-8993 1941-0107}, url={http://dx.doi.org/10.1109/tpel.2020.2965880}, DOI={10.1109/TPEL.2020.2965880}, abstractNote={Virtual oscillator control (VOC) is a nonlinear grid-forming controller that simultaneously achieves the functionality of output voltage control and primary control layers in a power electronics interfaced distributed generation (DG) unit. Unlike conventional phasor-based primary control methods such as the droop control and virtual synchronous machine control, VOC is a time-domain controller that can guarantee almost global asymptotic synchronization. However, the high-frequency dynamics has largely been ignored in the analysis of VOC in prior art; as a result, VOC-based DGs fail to suppress harmonic current in the presence of harmonic distortion in the network-side voltage. In this work, we demonstrate that frequency-domain method can be used for oscillator-based converters in the high-frequency range, specifically, for harmonic mitigation in the converter output current. We propose a virtual impedance-based selective harmonic current suppression method, and demonstrate that it is better to use the network-side current feedback rather than that of the converter-side current for VOC implementation with virtual impedance control. Established harmonic rejection strategies for grid-following and conventional grid-forming converters are compared with the proposed method for VOC. Through impedance-based analysis, we demonstrate that the proposed method augments the passivity range of the converter terminal response with a much simpler implementation. The proposed harmonic suppression strategy is validated through hardware experiments using a single-phase inverter prototype.}, number={8}, journal={IEEE Transactions on Power Electronics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Awal, M A and Yu, Hui and Husain, Iqbal and Yu, Wensong and Lukic, Srdjan M.}, year={2020}, month={Aug}, pages={8805–8818} } @inproceedings{a distributed control architecture for cascaded h-bridge converter_2019, url={http://dx.doi.org/10.1109/apec.2019.8722268}, DOI={10.1109/apec.2019.8722268}, abstractNote={Cascaded H-bridge topology has been used in grid-tied converter for battery energy storage system due to its modular structure. To fully utilize the converter’s modularity, we propose a hierarchical distributed control architecture that consists of primary control and secondary control. Primary control ensures correct current tracking, but may lead to unequal power output among modules. A distributed secondary control based on consensus algorithm is presented to establish equal power sharing among modules. Further, a carrier phase shift control is implemented to achieve multilevel output voltage and harmonic reduction. Finally, the effectiveness of the presented control strategy is verified through experiments.}, booktitle={2019 IEEE Applied Power Electronics Conference and Exposition (APEC)}, year={2019}, month={Mar} } @inproceedings{a new distributed voltage controller for enabling volt-var support of microgrids in grid-connected operation_2019, url={http://dx.doi.org/10.1109/pesgm40551.2019.8973481}, DOI={10.1109/pesgm40551.2019.8973481}, abstractNote={Voltage support is one of ancillary services that can be provided by grid-connected microgrids. This paper presents a new microgrid-level voltage controller to enable microgrids to contribute to distribution system voltage regulation. Like the Volt-Var droop control of the smart inverters, the proposed controller makes sure that the voltage and reactive power flow at microgrid point of common coupling (PCC) follows a proportional relationship. To increase flexibility and avoid centralized computation, a distributed controller design is developed using the distributed averaging algorithm in order to achieve reactive power sharing among multiple distributed energy resources (DERs) within the microgrid. A large signal analysis is performed to study the stability and dynamic characteristics of the closed-loop system. Simulation results show that the proposed controller is effective in providing voltage regulation for distribution systems with multi-microgrid architecture.}, booktitle={2019 IEEE Power & Energy Society General Meeting (PESGM)}, year={2019}, month={Aug} } @inproceedings{observer based admittance shaping for resonance damping in voltage source converters with lcl filter_2019, url={http://dx.doi.org/10.1109/ecce.2019.8913194}, DOI={10.1109/ecce.2019.8913194}, abstractNote={An observer based resonance damping controller is proposed for voltage source converters (VSCs) with LCL input filter connected to any arbitrary AC network. In prior art, design and analysis of observer based current controllers has been performed either in z-domain taking a discrete approximation of the LCL filter or in continuous-time but with the observer discretized for digital implementation; both methods introduce significant modelling error in the high frequency range. We use a continuous-time equivalent of the discrete observer and develop a comprehensive model of the VSC including the effects of discretization, controller delay, and PWM process. Leveraging the model, we propose a dual-loop current controller with an inner admittance shaping loop that achieves internal stability of the VSC by damping the LCL resonance without the need for additional sensors; moreover, passive converter admittance is achieved almost up to the Nyquist frequency which provides sufficient condition for stability for any uncertain network impedance that may lead to harmonic resonance within that frequency range. The resonance damping capability of the proposed controller is validated through hardware experiments.}, booktitle={2019 IEEE Energy Conversion Congress and Exposition (ECCE)}, year={2019}, month={Sep} } @inproceedings{passivity-oriented discrete-time voltage controller design for grid-forming inverters_2019, url={http://dx.doi.org/10.1109/ecce.2019.8912988}, DOI={10.1109/ecce.2019.8912988}, abstractNote={Passivity theory provides a promising approach to guarantee microgrid system stability. If all converters in the system can be made passive, prevention of electrical resonance can be achieved. To that end, a passivity-oriented discrete-time voltage controller for grid-forming inverters is proposed in this –paper. Compared with existing methods, the approach ensures not only –superior reference tracking performance and load disturbance rejection capability, but also provides passive output impedance, and therefore, guaranteed stable inverter operation under weak grid condition. A comparison study is carried out and the proposed controller design method is validated by hardware-in-the-loop (HIL) experiments.}, booktitle={2019 IEEE Energy Conversion Congress and Exposition (ECCE)}, year={2019}, month={Sep} } @inproceedings{a hardware-in-the-loop real-time testbed for microgrid hierarchical control_2018, url={http://dx.doi.org/10.1109/ecce.2018.8557737}, DOI={10.1109/ecce.2018.8557737}, abstractNote={To maintain a stable, flexible and economic operation of a microgrid, hierarchical control architecture consisting of primary, secondary and tertiary control is proposed. However, the differences in dynamics of microgrid, bandwidths of control levels and speed of communication channels make it difficult to comprehensively validate the performance of the hierarchical control schemes. In this paper we propose a hardware-in-the-loop real-time testbed for microgrid hierarchical control. The proposed testbed can be used to validate control performance under different microgrid operating modes (grid-tied or islanded), different primary control schemes (current or voltage mode) and different secondary control approaches (centralized or distributed). The integration of industry-grade hardware that runs primary and secondary control into the testbed allows for complete emulation of microgrid operation, and facilitates the study of the effects of measurement noise, sampling and communication delays.}, booktitle={2018 IEEE Energy Conversion Congress and Exposition (ECCE)}, year={2018}, month={Sep} } @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{an adaptive interleaving algorithm for multi-converter systems_2018, url={http://dx.doi.org/10.1109/pedg.2018.8447801}, DOI={10.1109/pedg.2018.8447801}, abstractNote={To integrate DC distributed generation (DG) with micro-source into the existing AC grid, a DC distribution bus can be used to couple on-site photovoltaics (PV), battery energy storage systems (BESS), and DC loads. If the converters connected to the DC bus are interleaved, the DC bus capacitor size could be minimized. In this paper, we propose an interleaving algorithm for multi-converter systems to minimize the current harmonics at switching frequency on the DC bus. The proposed algorithm is implemented using Resilient Information Architecture Platform for Smart Grid (RIAPS) platform. Hardware-in-the-Loop (HIL) simulation results based on Opal- RT are presented to validate its performance. The influence of synchronization frequency on the proposed algorithm are also considered.}, booktitle={2018 9th IEEE International Symposium on Power Electronics for Distributed Generation Systems (PEDG)}, year={2018}, month={Jun} } @inproceedings{decentralized synchronization of ac-stacked voltage source converters_2018, url={http://dx.doi.org/10.1109/ecce.2018.8557380}, DOI={10.1109/ecce.2018.8557380}, abstractNote={A decentralized control method is proposed for a system of multiple voltage source converters (VSC) stacked in series on the AC side. Using the proposed method, a group of low-voltage rated VSC modules can be utilized to implement converters for medium/high voltage grid-tied applications. Each converter module can maintain synchronization using only its local measurements without any communication or any form of centralized synchronization signal. A mathematical model of such a system consisting of $N$ number of VSC modules employing the proposed control scheme is presented and a linearized model is developed for small signal stability assessment. The proposed method is robust against grid frequency variation and can naturally correct power sharing errors among modules caused by sensor inaccuracies or reference mismatches. Real time simulation results are presented to validate the proposed controller.}, booktitle={2018 IEEE Energy Conversion Congress and Exposition (ECCE)}, year={2018}, month={Sep} } @article{analysis and design of current control schemes for lcl-type grid-connected inverter based on a general mathematical model_2017, url={http://dx.doi.org/10.1109/tpel.2016.2602219}, DOI={10.1109/tpel.2016.2602219}, abstractNote={For the LCL-type grid-connected inverter, there are basically three current control schemes, namely the grid current control, the inverter-side inductor current control, and the weighted average current control. This paper builds a general mathematical model to describe the three current control schemes. In this model, the grid current is an equivalent target control variable, the capacitor current feedback serves as a damping solution, and the computation and pulse-width modulation delays are taken into account. Based on the general mathematical model, a comparative analysis of different control schemes is carried out in terms of the grid current stability. It reveals that when the inverter-side inductor current is controlled, the grid current shows the same stability as the inverter-side inductor current; but when the weighted average current is controlled, both the grid current and the inverter-side inductor current are critically stable even though the weighted average current can be easily stabilized. Moreover, the general mathematical model also provides a unified perspective to design different control schemes, which makes the controller parameter tuning more straightforward and effective. In this way, a set of controller parameters which yields high robustness against the grid-impedance variation can be selected for all the three current control schemes. Finally, a 6-kW prototype is built, and experiments are performed to verify the theoretical analysis.}, journal={IEEE Transactions on Power Electronics}, year={2017}, month={Jun} } @inproceedings{stability analysis of cascade ac system based on three-phase voltage source pwm rectifier_2014, url={http://dx.doi.org/10.1109/peac.2014.7037969}, DOI={10.1109/peac.2014.7037969}, abstractNote={In cascade AC systems, the impedance interaction between the source module and the load module may cause overall system instability. The generalized Nyquist stability criterion can be applied to characterize the stability of cascade three-phase AC systems. But it is usually very complicated and cannot directly reveal effective control strategy to alleviate the interaction problem. Based on three-phase voltage source PWM rectifier, this paper proposes a simplified stability criterion for three-phase AC systems. An input impedance regulator design method is introduced to alleviate the interaction problem. Finally, a 20kW prototype is built and tested. The experimental results confirm the proposed stability criterion and the input impedance regulator design method.}, booktitle={2014 International Power Electronics and Application Conference and Exposition}, year={2014}, month={Nov} }