Understanding cycling performance of batteries under varying conditions is crucial for continued development of emerging chemistries. Currently much of this work is focused on cycling single cells in well-controlled lab experiments. There are few module cycling studies in the open literature. Studies of full-sized fielded systems are even rarer. As a result of this data gap, there is limited understanding of how single cell cycling can be used to predict performance of fielded systems prior to their deployment. Sandia National Laboratories (SNL) recently deployed an advanced Zn-MnO 2 secondary battery energy storage system in an off-grid solar plus storage system. Using this deployment as a test case, we will detail how performance and degradation for batteries can vary between the lab and the field. We will also discuss ways that single cell and module lab cycling can be improved to better predict operation in fielded systems. In preparation for this deployment, SNL conducted single cell cycling experiments in the lab to simulate operation in the field and determine the expected life of the systems. The first test program utilized elements of the IEC 61427-1 standard for photovoltaic off-grid application to simulate the temperature and predicted state of charge (SOC) range the cells will be cycled during field operation. The simulated field cycling targeted SOC ranges of 10 to 40% and 80-100% over 150 cycles with temperature varied between -4 and 35 o C to match the ambient conditions in the field during each season. The second type of cycling test was a temperature dependence study to determine how temperature impacted cell degradation. Cells were cycled at C/10 at their full SOC range and at a single temperature until they reached 40% capacity retention. Both cycling studies predicted that low temperature operation would increase the rate of degradation. The system was deployed in May of 2022, and since that time the SNL team has collected a significant amount of performance data to help analyze system level behaviors as compared to observations from cell level testing. These include battery interactions with the solar charge controller, limitations on power inverter settings, and variance between the average system level state of charge and the test protocol. Additionally, the team is analyzing conditions found in the field, with regards to ambient temperature, solar insolation and battery charging rates, and customer usage patterns for comparison with cell-level testing protocol. Observations of the deployed system’s performance indicate there is a need for more nuanced testing protocols for lab testing that can better approximate field conditions. These may include dynamic temperature ranges that vary throughout a charge/discharge cycle, and solar charging assumptions that account for reduced insolation due to cloud cover. This can help further inform the development of charge control algorithms, system hardware and software that can help improve the overall performance of solar microgrid energy storage systems. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2023-02502A

This paper presents a simulation and respective analysis of traveling waves from a 5-bus distribution system connected to a grid-forming inverter (GFMI). The goal is to analyze the numerical differences in traveling waves if a GFMI is used in place of a traditional generator. The paper introduces the topic of traveling waves and their use in distribution systems for fault clearing. Then it introduces a Simulink design of said 5-bus system around which this paper is centered. The system is subject to various simulation tests of which the results and design are explained further in the paper to discuss if and how exactly inverters affect traveling waves and how different design choices for the system can impact these waves. Finally, a consideration is made for what these traveling waves represent in a practical environment and how to properly address them using the information derived in this study.

This paper describes a method of connection and control algorithm for photovoltaic panel-integrated storage that can be interfaced to a grid using commercial dc-ac microinverters. Emulation of an appropriate i-v characteristic allows the integrated panel to operate with any inverter, e.g., peak-power tracking inverter, droop mode or stand-alone. or a battery inverter in droop mode. Rechargeable zinc-manganese dioxide (ZnMnO 2 ) battery cells developed by Urban Electric Power (UEP) are used as a source of energy storage. The batteries are charged with excess solar and discharged in the evening or when additional power is required. A battery management algorithm is developed, charge/discharge data is collected from each cell, and a proof of concept is demonstrated.

This paper discusses a solar photovoltaic (PV) DC microgrid system consisting of a PV array, a battery, DC-DC converters, and a load, where all these elements are simulated in MATLAB/Simulink environment. The design and testing entail the functions of a boost converter and a bidirectional converter and how they work together to maintain stable control of the DC bus voltage and its energy management. Furthermore, the boost converter operates under Maximum Power Point Tracking (MPPT) settings to maximize the power that the PV array can output. The control algorithm can successfully maintain the output power of the PV array at its maximum point and can respond well to changes in input irradiance. This is shown in detail in the results section.

One of the most prominent issues facing smart grid development is the Load Frequency Control (LFC) problem. A promising approach to solving this issue is to use distributed optimization techniques. The Distributed Model Predictive Control (DMPC) technology has been leveraged to solve the LFC problem. While the theory of MPC and DMPC has been developed for decades, the lack of easy-to-implement DMPC tools has been a barrier for researchers and practitioners to adopt DMPC technology in real-world applications. In this paper, we apply an open-source DMPC toolbox, namely MPCTools, to solve the LFC problem of a multi-area power generation system. The simulation is established in MATLAB Simulink and the simulation results show the effectiveness of the DMPC strategy using MPCTools.

This article presents a novel fault detection, characterization, and fault current control algorithm for a standalone solar-photovoltaic (PV) based dc microgrids. The protection scheme is based on the current derivative algorithm. The overcurrent and current directional/differential comparison based protection schemes are incorporated for the dc microgrid fault characterization. For a low impedance fault, the fault current is controlled based on the current/voltage thresholds and current direction. Generally, the droop method is used to control the power-sharing between the converters by controlling the reference voltage. In this article, an adaptive droop scheme is also proposed to control the fault current by calculating a virtual resistance Rdroop, and to control the converter output reference voltage. For a high impedance fault, differential comparison method is used to characterize the fault. These algorithms effectively control the converter pulsewidth and reduce the flow of source current from a particular converter, which helps to increase the fault clearing time. Additionally, a trip signal is sent to the corresponding dc circuit breaker (DCCB), to isolate the faulted converter, feeder or a dc bus. The dc microgrid protection design procedure is detailed, and the performance of the proposed method is verified by simulation analysis.

This paper proposes a combined adaptive droop-based load sharing, maximum power point tracking (MPPT), and energy management of photovoltaic (PV)-based dc microgrid system. A proportional droop index (PDI) algorithm is introduced, which is a function of normalized current sharing difference and voltage deviation at the output side of the converter. The proposed method calculates adaptive virtual resistance $R_{\textrm {droop}}$ , which allows the PV converter to operate at MPP or load sharing mode. By fine-tuning $R_{\textrm {droop}}$ values, the proposed method eliminates poor voltage regulation issues of the conventional droop method. The control of the hybrid energy storage system (HESS) with a battery and a supercapacitor (SC) is also discussed to stabilize the dc grid voltage and energy management of the dc microgrid. The detailed analysis and the design procedure of low-voltage (LV) dc microgrid systems are explained, and the effectiveness of the proposed method is verified by simulation and experimental studies.

Successful system protection is critical to the performance of the DC microgrid system. This paper proposes an adaptive droop based fault current control for a standalone low voltage (LV) solar-photovoltaic (PV) based DC microgrid protection. In the proposed method, a DC microgrid fault is detected by the current and voltage thresholds. Generally, the droop method is used to control the power sharing between the converters by controlling the reference voltage. In this paper, this scheme is extended to control the fault current by calculating an adaptive virtual resistance R droop , and to control the converter output reference voltage. This effectively controls the converter pulse width, and reduces the flow of source current from a particular converter which helps to increase the fault clearing time. Additionally, a trip signal is sent to the corresponding DC circuit breaker (DCCB), to isolate the faulted converter, feeder or a DC bus. The design procedure is detailed, and the effectiveness of proposed method is verified by simulation analysis.

Successful system protection is critical to the feasibility of the DC microgrid system. This work focused on identifying the types of faults, challenges of protection, different fault detection schemes, and devices pertinent to DC microgrid systems. One of the main challenges of DC microgrid protection is the lack of guidelines and standards. The various parameters that improve the design of protection schemes were identified and discussed. Due to the absence of physical inertia, the resistive nature of the line impedance affects fault clearing time and system stability during faults. Therefore, the effectiveness of protection coordination systems with communication were also explored. A detailed literature review was done to identify possible grounding schemes and protection devices needed to ensure seamless power flow of grid-connected DC microgrids. Ultimately, it was identified that more analyses and experimentation are needed to develop optimized fault detection schemes with reduced fault clearing time.

This study discusses a droop-based proportional load sharing control of parallel connected dc-dc converters in photovoltaic (PV)-based low-voltage dc microgrid. Droop control is the popular scheme for power sharing in dc microgrid. In this study, proportional droop index (PDI) algorithm with droop (R-droop) shifting is introduced to improve the load sharing performance of the dc microgrid, which is a function of normalised current sharing difference and voltage deviation in the output side of the converters. This proposed control method calculates adaptive virtual resistance, Rdroop, and allows the converter to share the load current based on PV power available. By incorporating a new Rdroop shifting method with PDI, the proposed scheme eliminates the trade-off between current sharing and voltage regulation of the conventional method. The detailed analysis and design procedures are explained, and the effectiveness of the proposed method is verified by detailed simulation and experimental studies.

Normally, a two stage power conversion system is used to convert a low dc voltage to high amplitude ac voltage. These two stage power conversion systems are very bulky, more complex in control and less efficient, etc when they are used, especially for low input dc voltages. In this paper a high gain dc-ac inverter topology is presented, which can produce an instantaneous output voltage higher or lower than the input dc voltage without any intermediate power conversion stage or transformers. Coupled inductor is used in this circuit in order to achieve high gain. The two stage power conversion will be done in a single stage by this converter. The proposed topology posses several desirable features like high gain, less loss and less size etc. The various modes of operation and steady state analysis of the proposed topology are presented. The proposed topology is simulated using MATLAB/SIMULINK, simulation results are presented to validate the proposed idea.

Several control methods are available in the literature for maximum power point (MPP) tracking, load sharing etc. in a photovoltaic (PV) based microgrid system. This paper proposes an adaptive droop based MPP tracking and load sharing of PV based dc microgrid. For this, proportional droop index (PDI) algorithm is introduced, which is a function of normalized current sharing difference and losses in the output side of the converters. This proposed control method calculates adaptive virtual resistance Rdroop, and allows the converter to operate at MPP. By fine tuning Rdroop values, the proposed method also eliminates poor voltage regulation issues of the conventional droop method. The detailed analysis and design procedure are explained and the effectiveness of proposed method is verified by detailed simulation analysis.

This paper gives an overview about droop based power sharing issues of parallel connected dc-dc converters in low voltage dc microgrid. Droop control is the popular technique for power sharing in dc microgrid. The main drawbacks of the conventional droop methods are, poor current sharing and drop in dc grid voltage due to large droop gain. In this paper, a modified figure of merit called proportional droop index (PDI) is introduced in order to improve the power sharing performance of the dc microgrid, which is a function of normalized current sharing difference and losses in the output side of the converters. This proposed control method which calculates instantaneous virtual resistance, R droop , and allows the converter to share the load current based on input power to the converters. By using R droop shifting, the proposed method also eliminates the tradeoff between current sharing and voltage regulation. The detailed analysis and design procedure are explained and the effectiveness of proposed method is verified by detailed simulation analysis.

This paper discuss the relationship between load sharing and circulating current for parallel connected dc-dc converters. In the proposed algorithm a new figure-of-merit called Droop Index is introduced, which is a function of normalized current sharing difference and losses in the output side of the converters. This algorithm minimizes the circulating current and current sharing difference between the converters based on the virtual resistance, Rdroop values. This also eliminates the trade-off between current sharing difference and voltage regulation. By calculating negative Rdroop values, the algorithm gives better performance and low voltage regulation. The detailed analysis and design procedure are explained for two dc-dc boost converters connected in parallel. The effectiveness of proposed method is verified using MATLAB simulation.

This paper addresses load current sharing and circulating current issues of parallel-connected DC-DC converters in low-voltage DC microgrid. Droop control is the popular technique for load current sharing in DC microgrid. The main drawbacks of the conventional droop method are poor current sharing and drop in dc grid voltage due to the droop action. Circulating current issue will also arise due to mismatch in the converters output voltages. In this work, a figure of merit called droop index (DI) is introduced in order to improve the performance of dc microgrid, which is a function of normalized current sharing difference and losses in the output side of the converters. This proposed adaptive droop control method minimizes the circulating current and current sharing difference between the converters based on instantaneous virtual resistance Rdroop. Using Rdroop shifting, the proposed method also eliminates the tradeoff between current sharing difference and voltage regulation. The detailed analysis and design procedure are explained for two DC-DC boost converters connected in parallel. The effectiveness of the proposed method is verified by detailed simulation and experimental studies.

This paper investigates the relationship between current sharing difference and circulating current for two parallel connected dc-dc converters. In the proposed algorithm a new figure-of-merit called Droop Index is introduced, which is a function of normalized current sharing difference and losses in the output side of the converters. This algorithm minimizes the circulating current and current sharing difference between the converters. Although there may exist a trade-off between current sharing difference and voltage regulation, the proposed droop index algorithm gives better performance and low voltage regulation. The detailed analysis and design procedure are explained for two dc-dc boost converters connected in parallel. The effectiveness of proposed method is verified using MATLAB simulation.