@article{awal_cen_rachi_yu_schroeder_husain_2024, title={Modeling, Analysis, and Design for Small-Signal Stability in Sequence-Decomposed Grid-Forming Control}, volume={60}, ISSN={["1939-9367"]}, url={https://doi.org/10.1109/TIA.2023.3326423}, DOI={10.1109/TIA.2023.3326423}, 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 and appropriate modeling and analysis method for sequence-decomposed GFM control structures is yet to be reported. In this work, a small-signal model is developed for the analysis and design of such control implementations. 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. The analysis and experiments demonstrate that delay based sequence component extraction method offers greater stability margins under open-load and loaded GFM operations.}, number={1}, journal={IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS}, author={Awal, M. A. and Cen, Siye and Rachi, Md Rifat Kaisar and Yu, Hui and Schroeder, Stefan and Husain, Iqbal}, year={2024}, month={Jan}, pages={865–875} }
 @article{rachi_awal_husain_2023, title={Asymmetrical Fault Ride-Through and Power Oscillation Characterization for Grid-Tied Voltage Source Converters}, volume={59}, ISSN={["1939-9367"]}, DOI={10.1109/TIA.2023.3268280}, abstractNote={As the number of converter-interfaced distributed energy resources connected to the power system continues to increase rapidly, recent grid codes require these grid-tied converters to maintain grid connection during faults to ensure power supply security and reliability. In this work, we analyze the oscillation in the injected real and reactive power that a grid-tied voltage source converter (VSC) introduces as it attempts to contribute to the power quality and improve the voltage at the point of common coupling (PCC) during an asymmetrical fault. We propose a new double sequence current reference generation method that can be utilized to derive a closed-form quantification of the peak value of both the real and reactive power oscillation during asymmetrical fault ride-through (AFRT) analytically. The effect of the resulting bus voltage oscillation and ripple current requirement at twice the grid frequency, corresponding to the real power oscillation, on the input DC bus capacitor and upstream converter is analyzed for facilitating system component sizing. Furthermore, the proposed current reference generation formulation helps control the negative-sequence current injection during fault to assist with fault identification. The theoretical analysis is validated through simulation in PLECS for both asymmetrical and symmetrical fault scenarios. Experimental results for a three-phase, grid-tied VSC operating under both asymmetrical and symmetrical faults are provided to evaluate the performance of the proposed current reference generation method and validate the analysis presented}, number={4}, journal={IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS}, author={Rachi, Md Rifat Kaisar and Awal, M. A. and Husain, Iqbal}, year={2023}, pages={4550–4561} }
 @article{awal_rachi_yu_husain_lukic_2023, title={Double Synchronous Unified Virtual Oscillator Control for Asymmetrical Fault Ride-Through in Grid-Forming Voltage Source Converters}, volume={38}, ISSN={["1941-0107"]}, url={https://doi.org/10.1109/TPEL.2022.3227729}, DOI={10.1109/TPEL.2022.3227729}, abstractNote={In this work, a double synchronous unified virtual oscillator controller is proposed for grid-forming voltage source converters to achieve synchronization to the fundamental frequency positive- and negative-sequence components of unbalanced grid voltage without any phase-locked loop. The proposed controller leverages a positive-sequence virtual oscillator 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 limit the converter output current below/at the maximum value allowable by the converter hardware while retaining synchronization regardless of the nature of grid faults. Consequently, symmetrical and asymmetrical fault ride-through can be achieved without the need for switching to a backup controller. This article presents the implementation and detailed analysis of the double-synchronous structure, which enables simultaneous synchronization to both sequences during current-unconstrained and -constrained operations. Validation of the proposed controller is provided through laboratory hardware experiments.}, number={6}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Awal, M. A. and Rachi, Md Rifat Kaisar and Yu, Hui and Husain, Iqbal and Lukic, Srdjan}, year={2023}, month={Jun}, pages={6759–6763} }
 @article{awal_rachi_yu_schroeder_dannehl_husain_2023, title={Grid-Forming Nature Retaining Fault Ride-Through Control}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131145}, abstractNote={A ride-through controller is proposed to enable inverter based resources (IBRs) to retain grid-forming (GFM) nature under current-constrained operation, such as faults or overload conditions. In this context, GFM nature for IBR is denoted by a voltage source behind reactance that preserves synchronism with the grid leveraging power-synchronization. A comparative analysis of existing GFM controllers is presented to demonstrate that the current state-of-the-art, either fails to preserve the GFM nature under fault, or offers only sub-optimal ride-through performance with regard to converter capacity uti-lization and transient stability. The proposed solution maximizes capacity utilization while retaining GFM nature under fault as well as enhances transient stability. Furthermore, detection of fault occurrence and/or clearance is not required and the identical control structure is preserved regardless of normal or fault/overload operation. Hence, the proposed controller avoids recurring fault-mode operation observed for existing GFM controllers at fault clearance especially under weak grid conditions. Experimental results are presented to validate the proposed solution.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Awal, M. A. and Rachi, Md Rifat Kaisar and Yu, Hui and Schroeder, Stefan and Dannehl, Jorg and Husain, Iqbal}, year={2023}, pages={2753–2758} }
 @article{awal_montes_teng_wang_bipu_yu_lukic_husain_2023, title={Medium Voltage Solid State Transformer for Extreme Fast Charging Applications}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131285}, abstractNote={A modular and scalable solid state transformer (SST) with direct medium voltage (MV) AC connectivity is proposed to enable DC extreme fast charging (XFC) of electric vehicles. Single-phase-modules (SPMs), each consisting of an active-front-end (AFE) stage and an isolated DC-DC stage, are connected in input-series-output-parallel (ISOP) configuration. The modular hardware is co-designed with decentralized control of the DC-DC stages where voltage and power balancing are achieved by each SPM using only its local sensor feedback; a centralized controller (CC) regulates the low voltage (LV) DC bus through the AFE stages without any sensor feedback form the SPMs. The controller architecture contrasts sharply with the prior art for MV AC to LV DC SSTs where high-speed bidirectional communication among SPMs and a CC are required for module-level voltage and power balancing, which severely limits the scalability and practical realization of higher voltage and higher power units. Detailed small-signal analysis and controller design guidelines are developed. Furthermore, a soft start-up strategy is presented. The proposed converter and control structure are validated through simulation and experimental results.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Awal, M. A. and Montes, Oscar Andres and Teng, Fei and Wang, Dakai and Bipu, Md Rashed Hasan and Yu, Wensong and Lukic, Srdjan and Husain, Iqbal}, year={2023}, pages={1528–1535} }
 @article{awal_della flora_husain_2022, title={Observer Based Generalized Active Damping for Voltage Source Converters With LCL Filters}, volume={37}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2021.3093504}, abstractNote={An observer-based active damping (AD) controller is proposed along with a unified design and implementation framework for LCL-equipped voltage source converters. The AD controller uses feedback of either of the converter-side current or the grid-side current along with that of the grid voltage. The state of the arts offer observer-based AD only for current-mode control and are limited by their inflexibility to be used in conjunction with established supplementary control methods or by the lack of damping efficacy for all configurations of LCL resonance frequency and the measured current (grid-side vs. converter-side). The proposed AD method is identically applicable for current-mode control and virtual oscillator control (VOC) where explicit voltage/current tracking loops are not used. The proposed AD controller thus overcomes a major limitation of VOC which otherwise offers robust synchronization in reduced/zero-inertia networks and enhanced fault ride-through capability. Simplified design guidelines are presented through comprehensive small-signal analysis including the observer dynamics. The proposed method is shown to be effective for both converter-side and grid-side current measurements irrespective of the LCL resonance frequency relative to the critical frequency. The analysis and design methods are validated through laboratory hardware experiments.}, number={1}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Awal, M. A. and Della Flora, Leandro and Husain, Iqbal}, year={2022}, month={Jan}, pages={125–136} }
 @article{feng_teng_montes_awal_bipu_husain_lukic_2022, title={Passive Capacitor Voltage Balancing of SiC-Based Three-Level Dual-Active-Bridge Converter Using Hybrid NPC-Flying Capacitor Structure}, volume={37}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2021.3119210}, abstractNote={Three-level (TL) dual-active-bridge (DAB) converter serves a critical role in the medium-voltage (MV) solid-state-transformers in which high voltage rating and bidirectional power flow are required. The regular neutral-point-clamping (NPC) topology is easily subjected to capacitor voltage unbalance due to nonideal operating conditions. In this article, a hybrid structure incorporating NPC and flying capacitor (FC) is presented to resolve the voltage unbalance issue. The key advantages include minimal additional hardware efforts and no need to resort to active control. The FC behaves as a buffer to leverage the upper and lower capacitor so that passive voltage balance between the two dc-link capacitors can be achieved on a switching cycle basis. Closed-form analysis further reveals the impact of FC value on voltage unbalance. Moreover, the appropriate modulation scheme, switching condition, and commutation loop are evaluated to provide detailed rule of thumb to the implementation of FC circuit. Analysis shows the FC also brings favorable switching loss performance and is friendly to employ upon fast switching of wide bandgap devices such as SiC. Finally, a 1.6 kV input, 400 V output, 8 kW scaled-down hybrid NPC-FC-based DAB converter is built to validate the above analysis.}, number={4}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Feng, Hao and Teng, Fei and Montes, Oscar Andres and Awal, M. A. and Bipu, Md Rashed Hassan and Husain, Iqbal and Lukic, Srdjan}, year={2022}, month={Apr}, pages={4183–4194} }
 @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{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{luo_awal_yu_husain_2021, title={FPGA-Based High-Bandwidth Motor Emulator for Interior Permanent Magnet Machine Utilizing SiC Power Converter}, volume={9}, ISSN={["2168-6785"]}, DOI={10.1109/JESTPE.2020.3015179}, abstractNote={A high-bandwidth (>20 kHz) motor emulator (ME) prototype for ac machines, utilizing field programmable gate array (FPGA)-based hybrid model predictive control (MPC) and a high fidelity motor model and implemented with a voltage source power converter, and fast-switching SiC devices, is presented in this article. The hybrid MPC incorporates a unique gate stitching modulation strategy that synchronizes the inverter switching state with the ME switching state for an accurate representation of the emulated motor currents in the physical inverter hardware output. The gate stitching MPC hybrid algorithm avoids the need for an excessively high switching frequency of the ME power converter. The developed high-bandwidth ME can emulate up to the switching ripple current of the inverter under test (IUT) where the current slope can change up to six times within one switching period when using space vector pulse width modulation (PWM). The FPGA-based fast iterating online motor model is another key component which along with the high-performance ME current regulation algorithm can accurately emulate the motor current. The bandwidth achieved far exceeds that of existing ME solutions that can only emulate fundamental current and only a few orders of harmonic content. The high bandwidth also allows the use of a small line inductor, which reduces the size and cost of the ME system. Simulation and experiment results are provided to the FPGA implementation and validate the high-bandwidth current emulating capability.}, number={4}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Luo, Yukun and Awal, M. A. and Yu, Wensong and Husain, Iqbal}, year={2021}, month={Aug}, pages={4340–4353} }
 @article{bipu_awal_cen_zabin_khan_lubkeman_husain_2021, title={Secondary Voltage and Frequency Regulation for Grid Re-Synchronization in Microgrid with Unified Virtual Oscillator Controlled Multi-port Converters}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE47101.2021.9595901}, abstractNote={Unified Virtual Oscillator Controller (uVOC) is a type of oscillator based nonlinear time domain controller that achieves faster primary control response than conventional droop control as no phase-locked loop (PLL) is required. uVOC can be used effectively for either grid following or grid-forming voltage source converters. Grid-forming converter is essential for a microgrid to operate in islanded mode in addition to the more common grid-connected mode. In this paper, a secondary regulation scheme is proposed to augment the capability of uVOC based on a Multi-port Converter (MPC) by adding voltage and frequency regulation for grid re-synchronization. With this method, changing primary controller is not required and seamless transition is achieved. To implement this secondary regulation, communication or data exchange between different components is required. The network connectivity is implemented based on the RIAPS platform, an open-source distributed operating system developed for real-time control of microgrid/smartgrid systems. Finally, the suitability of proposed secondary regulation with uVOC based MPC was verified through simulation and experiment on a microgrid testbed.}, journal={2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Bipu, Md Rashed Hassan and Awal, M. A. and Cen, Siye and Zabin, Salina and Khan, Mehnaz and Lubkeman, David and Husain, Iqbal}, year={2021}, pages={900–905} }
 @article{awal_husain_2021, title={Transient Stability Assessment for Current-Constrained and Current-Unconstrained Fault Ride Through in Virtual Oscillator-Controlled Converters}, volume={9}, ISSN={["2168-6785"]}, DOI={10.1109/JESTPE.2021.3080236}, abstractNote={Unified virtual oscillator controller (uVOC) inherits the rigorous analytical foundation offered by oscillator-based grid-forming (GFM) controllers and enables fast overcurrent limiting and fault ride through (FRT). Control design for effective FRT requires transient stability analysis. Existing transient stability analysis methods and studies are limited in either considering only current-unconstrained scenarios or neglecting the simultaneous power-angle and voltage dynamics. Under current-constrained faults, the voltage and power-angle dynamics are strongly coupled and both play critical roles in determining transient stability. Therefore, decoupled analysis of the two, typically used in transient stability studies, does not offer comprehensive insight into the system dynamics. In this work, a comprehensive modeling and analysis method for transient stability in uVOC-based converters is developed under both current-saturated and current-unsaturated symmetrical ac faults. We utilize a phase-plane analysis of the overall system in a single graphical representation to obtain holistic insights into the coupled voltage and power-angle dynamics. The FRT controller and the analysis method have been validated through simulations and hardware experiments. The results demonstrate that uVOC is not constrained by a critical clearing angle unlike droop and virtual synchronous machine (VSM)-type second-order controllers.}, number={6}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Awal, M. A. and Husain, Iqbal}, year={2021}, month={Dec}, pages={6935–6946} }
 @article{awal_husain_2021, title={Unified Virtual Oscillator Control for Grid-Forming and Grid-Following Converters}, volume={9}, ISSN={["2168-6785"]}, DOI={10.1109/JESTPE.2020.3025748}, abstractNote={A unified virtual oscillator controller (uVOC) is proposed, which enables a unified analysis, design, and implementation framework for both grid-forming (GFM) and grid-following (GFL) voltage-source converters (VSCs). Oscillator-based GFM controllers, such as dispatchable virtual oscillator control (dVOC), offer a rigorous analytical framework with enhanced synchronization but lack effective fault handling capability, which severely limits practical application. The proposed uVOC facilitates synchronization with an arbitrarily low grid voltage and fast overcurrent limiting; this enables effective fault ride-through unlike existing GFM controllers which typically switch to a back-up controller during the fault. GFM operation with uVOC is achieved in both grid-connected and islanded modes with seamless transitions between the two. In GFL converters, bidirectional power flow control and dc bus voltage regulation are achieved with uVOC. No phase-locked loop (PLL) is required for either GFL or GFM operation circumventing the synchronization issues associated with PLLs in weak grid applications. Detail small-signal models for GFM and GFL operation have been developed, and the systematic design guidelines for controller parameters are provided. The proposed controller is validated through hardware experiments in a hybrid ac–dc microgrid.}, number={4}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Awal, M. A. and Husain, Iqbal}, year={2021}, month={Aug}, pages={4573–4586} }
 @article{awal_husain_2021, title={Unified Virtual Oscillator Control for Synchronization Under Ultra-Weak Grid Conditions}, ISSN={["1048-2334"]}, DOI={10.1109/APEC42165.2021.9487212}, abstractNote={A unified virtual oscillator controller (uVOC) with fast power control response is proposed for enhanced synchro-nization under ultra-weak grid conditions. The recently proposed uVOC offers a unified analysis, design, and implementation framework for both grid-following and grid-forming converters; leveraging its superior synchronization capability, enhanced fault ride-through response is achieved without the need for a back-up controller during faults. In this work, we propose an improved uVOC design and implementation which enables fast power-flow control. Through analysis, we demonstrate that the proposed controller retains synchronization as long as a feasible equilibrium exists. Furthermore, using dynamic reactive power control the feasible power-flow range is extended under ultra-weak grid conditions. Systematic design guidelines for controller parameters are presented. The analysis and design are validated through hardware experiments.}, journal={2021 THIRTY-SIXTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2021)}, author={Awal, M. A. and Husain, Iqbal}, year={2021}, pages={105–110} }
 @article{awal_bipu_montes_feng_husain_yu_lukic_2020, title={Capacitor Voltage Balancing for Neutral Point Clamped Dual Active Bridge Converters}, volume={35}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2020.2988272}, abstractNote={A capacitor voltage balancing method is proposed for a full-bridge neutral point diode clamped (NPC) dual-active bridge (DAB) converter. In existing literature, capacitor voltage balancing is achieved by actively selecting between the small voltage vectors, i.e., connecting either the upper or the lower capacitor on the dc bus to the transformer winding, on the basis of measured voltage mismatch. These balancing methods are dependent on the direction of power flow through the DAB converter. In this work, we propose a voltage balancing controller, which is independent of power flow direction and does not require adjustments of active voltage vectors through the modulator. Irrespective of the direction of transformer current, by dynamically shifting the switching instants of the inner switch pairs in the two NPC legs during the free-wheeling/zero voltage vector time, either of the two capacitors can be selectively charged without introducing any offsets in the voltage-second seen by the transformer. A simple bidirectional phase-shift modulator is designed to facilitate voltage balancing irrespective of power flow direction or mode of operation. The proposed method is highly and universally effective under any converter operating condition and was verified and demonstrated through analysis, simulation, and hardware experiments using a laboratory prototype.}, number={10}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Awal, M. A. and Bipu, Md Rashed Hassan and Montes, Oscar Andres and Feng, Hao and Husain, Iqbal and Yu, Wensong and Lukic, Srdjan}, year={2020}, pages={11267–11276} }
 @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{awal_yu_husain_2020, title={Passivity-Based Predictive-Resonant Current Control for Resonance Damping in LCL-Equipped VSCs}, volume={56}, ISSN={["1939-9367"]}, DOI={10.1109/TIA.2019.2959594}, abstractNote={In this article, we propose a frequency-domain passivity-based damping controller combined with predictive current control for LCL-filter-equipped voltage source converters (VSCs) connected to an arbitrary ac network to achieve passive VSC input admittance almost up to the Nyquist frequency. The controller guarantees resonance damping in the corresponding frequency range irrespective of the network impedance seen by the VSC. Resonant current compensation is added to eliminate the steady-state tracking error and to achieve superior disturbance rejection. We have used impedance-based method for the analysis of harmonic resonance instabilities caused by current controllers. The developed passivity-based predictive-resonant current controller is analytically shown to stabilize interactions among multiparalleled VSCs. Resonance damping capability of the proposed method is validated through simulation and hardware experiments.}, number={2}, journal={IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS}, author={Awal, M. A. and Yu, Wensong and Husain, Iqbal}, year={2020}, pages={1702–1713} }
 @article{hafiz_awal_queiroz_husain_2020, title={Real-Time Stochastic Optimization of Energy Storage Management Using Deep Learning-Based Forecasts for Residential PV Applications}, volume={56}, ISSN={["1939-9367"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85084192067&partnerID=MN8TOARS}, DOI={10.1109/TIA.2020.2968534}, abstractNote={A computationally proficient real-time energy management method with stochastic optimization is presented for a residential photovoltaic (PV)-storage hybrid system comprised of a solar PV generation and a battery energy storage (BES). Existing offline energy management approaches for day-ahead scheduling of BES suffer from energy loss in real time due to the stochastic nature of load and solar generation. On the other hand, typical online algorithms do not offer optimal solutions for minimizing electricity purchase costs to the owners. To overcome these limitations, we propose an integrated energy management framework consisting of an offline optimization model concurrent with a real-time rule-based controller. The optimization is performed in receding horizon with load and solar generation forecast profiles using deep learning-based long short term memory method in rolling horizon to reduce the daily electricity purchase costs. The optimization model is formulated as a multistage stochastic program where we use the stochastic dual dynamic programming algorithm in the receding horizon to update the optimal set point for BES dispatch at a fixed interval. To prevent loss of energy during optimal solution update intervals, we introduce a rule-based controller underneath the optimization layer in finer time resolution at the power electronics converter control level. The proposed framework is evaluated using a real-time controller-hardware-in-the-loop test platform in an OPAL-RT simulator. The proposed real-time method is effective in reducing the net electricity purchase cost compared to other existing energy management methods.}, number={3}, journal={IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS}, author={Hafiz, Faeza and Awal, M. A. and Queiroz, Anderson Rodrigo and Husain, Iqbal}, year={2020}, pages={2216–2226} }
 @inproceedings{awal_husain_yu_2017, title={Predictive current control for stabilizing power electronics based AC power systems}, DOI={10.1109/ecce.2017.8096792}, abstractNote={Frequency domain passivity theory is used to evaluate harmonic resonance instabilities in a system with multiple grid-tied voltage source converters (VSCs), and subsequently, a stabilizing controller using predictive current control (PCC) method is proposed to prevent such instabilities. The input admittance of VSCs using PCC can achieve passivity almost up to the Nyquist frequency. This research demonstrates that a very simple and easy implementation of PCC can extend the controller delay dependent stability range of converter side current control for VSCs equipped with LCL-filters up to that point. The alternative approaches achieved stability over similar frequency range by combining complicated active damping techniques with proportional-integral or proportional-resonant type controllers. The frequency domain analysis of the proposed PCC based method is validated via simulation and hardware experiments. The controller is experimentally shown to achieve stable operation irrespective of model imperfections.}, booktitle={2017 ieee energy conversion congress and exposition (ecce)}, author={Awal, M. A. and Husain, I. and Yu, Wensong}, year={2017}, pages={4634–4641} }