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1. A Sub-1V Analog-Assisted Inverter-Based Digital Low-Dropout Regulator with a Fast Response Time at 25mA/100ps and 99.4% Current Efficiency

   https://doi.org/10.1109/CICC.2019.8780173  

   Nguyen, Bai; Tang, Nghia; Zhou, Zhiyuan; Hong, Wookpyo; Heo, Deukhyoun; Tang, Yangyang; Zhang, Philipp (April 2019, 2019 IEEE Custom Integrated Circuits Conference (CICC))

   To mitigate large voltage droop caused by sub-ns dynamic current transitions in system on chips (SoCs), this paper proposes a fully integrated analog-assisted inverter-based digital low dropout regulator (LDO) to obtain a fast response time with 160mV droop at 25mA/100ps featuring 99.4% current efficiency, and 16mV DC load regulation in sub-1V operating range by using a dynamic-step quantizer and a trip-point controller. The proposed quantizer is implemented with an inverter-based flash ADC to achieve high speed without consuming large power while the trip-point controller corrects the DC error of the inverter-based ADC. Besides, the assistant analog LDO is employed to provide fine-grain regulation and remove ripple from the output voltage. 

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2. Cyber Physical Implementation of Improved Distributed Secondary Control of DC Microgrid

   https://doi.org/10.1109/icpee50452.2021.9358705  

   Pragallapati, Nataraj; Ranade, Satish J; Lavrova, Olga (January 2021, 2021 1st International Conference on Power Electronics and Energy (ICPEE))

   null (Ed.)

   This paper presents a cyber physical system implementation of an improved distributed secondary control (IDSC) scheme of islanded dc microgrid (DCMG). The IDSC scheme mitigates the hidden issues of primary control with included droop technique for the distributed generation unit (DGU) in a DCMG by providing the adjustable voltage compensation, improves voltage regulation and enhances the current sharing of all DGUs. The voltage compensation of IDSC is the resultant of two voltage components, i.e., average distributed integral voltage controller and average current controller. The dynamic consensus algorithm is used to obtain the global average values in the for distributed secondary controlusing relatively low bandwidth communication. The impact of communication time delay on the stability in IDSC based DCMG with two DGUs is presented. The performance of IDSC scheme is validated on a microgrid scenario, which includes parallel connection of four DGUs and common load. The real-time cyber physical system of DCMG is implemented on OP AL-RT test platform that combines the device layer on FPGA, control and cyber layers on CPU of OP5700 by using eFPGASim and RT-LAB. 

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3. Frequency regulation for microgrid using genetic algorithm and particle swarm optimization tuned STATCOM

   https://doi.org/10.1002/cta.3319  

   Saxena, Nitin Kumar; Gao, Wenzhong D.; Kumar, Ashwani; Mekhilef, Saad; Gupta, Varun (May 2022, International Journal of Circuit Theory and Applications)

   Abstract This paper presents the genetic algorithm (GA) and particle swarm optimization (PSO) based frequency regulation for a wind‐based microgrid (MG) using reactive power balance loop. MG, operating from squirrel cage induction generator (SCIG), is employed for exporting the electrical power from wind turbines, and it needs reactive power which may be imported from the grid. Additional reactive power is also required from the grid for the load, directly coupled with such a distributed generator (DG) plant. However, guidelines issued by electric authorities encourage MGs to arrange their own reactive power because such reactive power procurement is defined as a local area problem for power system studies. Despite the higher cost of compensation, static synchronous compensator (STATCOM) is a fast‐acting FACTs device for attending to these reactive power mismatches. Reactive power control can be achieved by controlling reactive current through the STATCOM. This can be achieved with modification in current controller scheme of STATCOM. STATCOM current controller is designed with reactive power load balance for the proposed microgrid in this paper. Further, gain values of the PI controller, required in the STATCOM model, are selected first with classical methods. In this classical method, iterative procedures which are based on integral square error (ISE), integral absolute error (IAE), and integral square of time error (ISTE) criteria are developed using MATLAB programs. System performances are further investigated with GA and PSO based control techniques and their acceptability over classical methods is diagnosed. Results in terms of converter frequency deviation show how the frequency remains under the operating boundaries as allowed by IEEE standards 1159:1995 and 1250:2011 for integrating renewable‐based microgrid with grid. Real and reactive power management and load current total harmonic distortions verify the STATCOM performance in MG. The results are further validated with the help of recent papers in which frequency regulation is investigated for almost similar power system models. The compendium for this work is as following: (i) modelling of wind generator‐based microgrid using MATLAB simulink library, (ii) designing of STATCOM current controller with PI controller, (iii) gain constants estimation using classical, GA and PSO algorithm through a developed m codes and their interfacing with proposed simulink model, (v) dynamic frequency responses for proposed grid connected microgrid during starting and load perturbations, (vi) verification of system performance with the help of obtained real and reactive power management between STATCOM and grid, and (vii) validation of results with available literature. 

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4. Robust Control of Solid State Transformer using Dynamic Phasor based model with dq transformation

   https://doi.org/10.1109/NAPS46351.2019.9000398  

   Monika, M.; Meshram, R.; Wagh, S.; Singh, N. M.; Stankovic, A.M. (October 2019, 2019 North American Power symposium)

   A high frequency solid-state transformer (SST) proposed by FREEDM centre is an interesting alternative to conventional distribution transformer in microgrids as it supports additional functionalities such as active-reactive power flow control, fault current limitation and voltage regulation. This paper proposes a dynamic phasor based robust control of SST through the modular control of each stage. The control problem is formulated in frequency domain by representing the system states with time varying Fourier coefficients or dynamic phasors (DP). This formulation transforms the oscillating waveforms of ac circuits to constant or slowly varying variables, hence allow the use of PI controller to track the sinusoidal references. For rectifier and inverter stages of SST, dq transformation is applied on DP which facilitates the design of PI controller to smoothen out the ripples in the output voltage waveform. The controller gains are tuned to reject input and load disturbances and attenuate measurement noise using loop shaping and pole assignment technique. The robustness of the controller is assured analytically against parametric uncertainties using small gain theorem. Simulation results are provided to support the proposed control scheme. Hardwarein- Loop (HIL) simulation is carried out on critical stages using Opal-RT and dSPACE simulators to confirm the effectiveness of the proposed scheme. 

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5. Fast and Secure Operation of Voltage Source Inverter based DERs using Model Predictive Droop Control

   https://doi.org/10.1109/ECCE.2018.8558323  

   Alhosaini, Waleed; Mahmud, Mohammad Hazzaz; Zhao, Yue (September 2018, Fast and Secure Operation of VSI based DERs using Model Predictive Droop Control)

   Reliability of the power grid can be improved by the use of microgrids (MGs) concept, which regulates the voltage and frequency at the point of common coupling (PCC) during normal and/or faulty conditions. Droop characteristics based hierarchical control strategies are commonly used in MGs, where power converters can operate in parallel. However, the need of multiple control loops not only adds complexity to the controller design, but also reduces the dynamic response of the system. In the future power system, grid-tied converters with fast dynamic response are desired to handle the uncertainties induced by high penetration of distributed energy resources. Therefore, this paper presents a novel model predictive control to ensure fast dynamic response of high power three-level converters in stand-alone operating mode as well as grid-tied operating mode. The proposed controller is applied to a MG which consists of a solar inverter connected in parallel with an energy storage system to the PCC, where a local load is tied. Both simulation and experimental results are presented to demonstrate robustness and the high dynamic performance of the proposed controller under rapidly changing atmospheric conditions and different grid operating modes. 

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