Power Buffer Research Articles

On the Resilience Analysis of DC Microgrids With Power Buffer Control

On the Resilience Analysis of DC Microgrids With Power Buffer Control

Efficient Fabrication of Disordered Graphene with Improved Ion Accessibility, Ion Conductivity, and Density for High-Performance Compact Capacitive Energy Storage.

High-performance compact capacitive energy storage is vital for many modern application fields, including grid power buffers, electric vehicles, and portable electronics. However, achieving exceptional volumetric performance in supercapacitors is still challenging and requires effective fabrication of electrode films with high ion-accessible surface area and fast ion diffusion capability while simultaneously maintaining high density. Herein, a facile, efficient, and scalable method is developed for the fabrication of dense, porous, and disordered graphene through spark-induced disorderly opening of graphene stacks combined with mechanical compression. The obtained disordered graphene achieves a high density of 1.18gcm-3, sixfold enhanced ion conductivity compared to common laminar graphene, and an ultrahigh volumetric capacitance of 297Fcm-3 in ionic liquid electrolyte. The fabricated stack cells deliver a volumetric energy density of 94.2WhL-1 and a power density of 13.7kWL-1, representing a critical breakthrough in capacitive energy storage. Moreover, the proposed disordered graphene electrodes are assembled into ionogel-based all-solid-state pouch cells with high mechanical stability and multiple optional outputs, demonstrating great potential for flexible energy storage in practical applications.

The impact of marriage equality campaigns on stress: Did a Swiss public vote get under the skin?

Lesbian, gay, bisexual, trans, intersex, and queer (LGBTIQ+) individuals encounter persistent structural inequalities and discrimination that can lead to detrimental psychological and physiological health outcomes. Amid evolving legal landscapes, little attention has been directed toward understanding the physiological health effects of societal shifts on these communities. This study aims to explore the impact of a national marriage equality vote and associated debates on psychological and biological stress among LGBTIQ+ individuals and cisgender, heterosexual, endosex individuals (termed cis-heterosexual) in Switzerland. We gathered longitudinal survey and biological data collected in hair samples among LGBTIQ+ and cis-heterosexual individuals before, during, and after the 2021 national vote (survey data: NT1T2 = 954; NT2T3 = 880; biological data: NT1T2 = 393; NT2T3 = 354). Preregistered analyses reveal a notable increase in biological stress levels (i.e., cortisol and cortisone levels), but not perceived stress, among both LGBTIQ+ as well as cis-heterosexual individuals who were close to them during the campaign. Results further point out the negative impacts of the campaign against marriage equality (i.e., no-campaign) on LGBTIQ+ individuals' biological stress levels as well as on those of their allies. These effects were, however, moderated by exposure to the campaign for marriage equality (i.e., yes-campaign), indicating the powerful buffering effects of the yes-campaign on the impact of discrimination on individuals' health. However, these positive effects appear to come at a cost, potentially impacting the well-being of individuals engaged in advocating for the yes-campaign. This research underscores the lasting impact of political campaigns on individuals' health.

A regulatory power split strategy for energy management with battery and ultracapacitor

Electric vehicle batteries face fast degradation due to the high frequency of charging/discharging cycles and great peak power demands. Lifetime, continuity of supply and power density of these batteries affect the performance of electric vehicles (EVs). Hybrid energy storage systems (HESS) offers a feasible solution by incorporating other energy storage elements like ultra-capacitor (UC) along with battery. Their combination provides higher efficiency and better performance in terms energy/power density. UC can behave like a power buffer when the EV is accelerating and regenerating. The HESS needs a controller that can split the available power between different sub systems as per demand. This paper presents a regulatory control strategy useful in HESS with battery and UC for the speed regulation of a brushless DC (BLDC) motor using a 3-port bidirectional DC-DC converter. The regulatory control strategy monitors the state of charge (SOC) of UC and a fuzzy logic controller regulates the power flow between HESS and the motor. Simulation in MATLAB validates the efficacy of the strategy. Simulation results and hardware evaluation confirm that the regulatory control scheme is effective in splitting the available power according to the load demand and achieves better energy efficiency.

Scaling considerations and optimal control for an offshore wind powered direct air capture system

The optimal design and operation of an offshore wind powered direct air capture (DAC) system is complex owing to the intermittent energy supply and the modularity of the units. A solid amine DAC process involves multiple individual units which undergo periodic loading to capture carbon dioxide (CO2) from ambient air, followed by regeneration to produce pure CO2 for utilisation or sequestration. The modular nature of a solid DAC process is exploited in this study to investigate the optimal design and coordinated operation of multiple DAC units mounted on a single 15 MW offshore wind turbine platform, with battery energy storage for additional short term power buffering. Important design parameters considered include the number of independently controllable units, the cyclic capacity of each unit (proportional to the amount of adsorbent) and the battery capacity and maximum power ratings. The design study results highlighted the diminishing returns to the CO2 capture rate with scaling, with a full design optimisation based upon cost estimations left for future work as the technology matures. It was found the optimal configuration was 14 DAC units, each with a cyclic capacity of 2000 kg CO2 , giving a total annual capture rate of 45 600 ton yr−1 and a wind utilisation factor of 96.6%. Furthermore, it was found that a rules-based control strategy based on high and low loading limits was competitive with a machine learning based controller and outperformed a model predictive control scheme.

Plug-and-Play of Grid-Forming Units in DC Microgrids Assisted With Power Buffers

Plug-and-Play of Grid-Forming Units in DC Microgrids Assisted With Power Buffers

Model-Based Dynamic Event-Triggered Distributed Control of Linear Physically Interconnected Systems and Application to Power Buffers

Model-Based Dynamic Event-Triggered Distributed Control of Linear Physically Interconnected Systems and Application to Power Buffers

Gain-Scheduled Structured Control in DC Microgrids

Power buffers are electronic converters that shield direct current (dc) microgrids from the effects of abrupt load changes. By promoting collective behaviors, distributed control solutions can improve the overall grid performance, as power buffers can collectively react to abrupt load changes. In this article, a novel gain-scheduled structured control scheme for power buffers is proposed. The control objective is to regulate both the stored energy and the input impedance of the power buffers in a distributed fashion, while guaranteeing, at the same time, the closed loop stability regardless of load changes occurring within predefined ranges. The proposed controller is expressed as a gain-scheduled state feedback law, whose coefficients depend affinely on the scheduling parameters. The structure of the controller gain is chosen to reflect the topology of the communication network implementing the distributed controller. In this article, the existing theory is extended to deal with such control problem, providing a novel strategy, which can be used to design gain-scheduled controllers for the considered class of structured feedback systems. Simulation results using a high-fidelity dc microgrid simulator verify the effectiveness of the proposed approach.

Development of control strategy for community battery energy storage system in grid-connected microgrid of high photovoltaic penetration level

The focus of this paper is to develop a control strategy for a community battery bank in a grid-connected microgrid in which a significant level of photovoltaic generation is embedded. In order to minimize the capacity of the community battery, the power transfer capacity of the interconnection link between the microgrid and the external grid system is utilized to safe maximum levels. Through Empirical Mode Decomposition analysis of the net power flows of the microgrid, the daily and seasonal modes of the net power oscillations are identified as the two dominant low-frequency components. Whence a rule-based operational strategy is developed to control the power flows of the community battery via a novel dynamic referencing scheme for the state-of-charge of the battery bank. The battery control scheme counteracts the dominant daily and seasonal modes of oscillations of the net power. The numerical calculations performed for a case study shows that the proposed scheme leads to an approximately 16% decrease in the required battery capacity for particular growth rate of solid-electrolyte interphase film in the battery bank. The scheme does not require the forecasting of the net power, and thus, it has an increased degree of robustness when the community battery undertakes the power buffering task.

Event‐triggered control of power buffers in DC microgrids over an unreliable network

AbstractPower buffers can help improve the inertia in DC microgrids and supply the additional power demand during short load transients. This article investigates distributed event‐triggered control of power buffers over an unreliable network, subject to packet losses and transmission delays. For each power buffer, a distributed event‐triggered control law regulates the input impedance while altering its stored energy. Moreover, a dynamic event‐triggered communication mechanism determines the time sequence of control updates and data transmissions among power buffers. An appealing feature of this mechanism is a designable positive minimum inter‐event time despite packet losses and transmission delays. The closed‐loop system is shown to be exponentially stable. Controller/hardware‐in‐the‐loop studies validate the theoretical findings.

The Impact of Hybrid Energy Storage System on the Battery Cycle Life of Replaceable Battery Electric Vehicle

Compared with batteries, ultracapacitors have higher specific power and longer cycle life. They can act as power buffers to absorb peak power during charging and discharging, playing a role in peak shaving and valley filling, thereby extending the cycle life of the battery. In this article, a replaceable battery electric coupe SUV equipped with a lithium iron phosphate (LiFePO4) power battery is taken as the research object, and a vehicle dynamics simulation model is established on the MATLAB/Simulink platform. Parameter matching and control optimization for a hybrid energy storage system (HESS) are conducted. Through a proven semiempirical cycle model of the LiFePO4 power battery, the operating cycle life model is derived and used to estimate the battery cycle life. World Light Vehicle Test Cycle (WLTC) simulation results show that the HESS with 308 ultracapacitors can extend the cycle life of the LiFePO4 power battery by 34.24%, thus significantly reducing the operation cost of the battery replacement station.

A Decentralized Power Allocation Strategy for Dynamically Forming Multiple Hybrid Energy Storage Systems Aided With Power Buffer

Multiple hybrid energy storage systems (HESSs) consisting of batteries and super-capacitors (SCs) are widely used in DC microgrids to compensate for the power mismatch. According to their specific energy and power characteristics, batteries and SCs are used to compensate low-frequency and high-frequency power mismatches, respectively. This paper proposes a decentralized power allocation strategy for dynamically forming multiple HESSs aided with a novel power buffer. The power buffer is a device combing a capacitor and a bidirectional DC-DC converter, it is used as an interface between the batteries and DC bus, allowing easy Plug-and-Play of different energy storage units and effective and efficient power allocation. First, the power buffer and SCs split the power mismatch into a low-frequency and high-frequency part with a modified I-V droop control. Then the power buffer transfers the low-frequency mismatch to the batteries for compensation based on their respective state-of-charges (SoCs), while the high-frequency part is dealt by the SCs directly. This new scheme further allows elimination of the DC bus voltage deviations. Finally, the real-time hardware-in-loop (HIL) tests of three case studies confirm the effectiveness of the proposed control strategy.

Burst Mode Control of Active-Power-Decoupling Integrated Active Clamp Flyback PFC Rectifiers

To mitigate the bulky and heavy twice-line frequency power buffer in single-phase power-factor-correction (PFC) rectifiers while maintaining a lower cost, active-power-decoupling integrated active clamp flyback (iACF) PFC rectifier is recently proposed in the literature. The solution inherits all the benefits of conventional ACF converters such as low component count, leakage energy recycling, and soft-switching while being able to reduce the size of the power buffer in the system without hardware modifications. However, existing modulation and control strategies, based on Continuous-Conduction-Mode (CCM), can only achieve a high efficiency at heavy load but not at light load. This paper proposes a new modulation to improve the light-load efficiency of iACF PFC rectifiers. By combining CCM and burst mode of operation, this new modulation method can maintain all good features of CCM while effectively reducing the operating frequency, thus reducing the switching losses of the system at light load. This paper firstly reviews the existing light-load modulation methods for ACF converters and limitations of applying these methods to iACF are highlighted. The detailed operating principles of the proposed modulation method are explained, and controller implementation that supports simultaneous full-load, medium load and ultra-light load operation is developed. A 100-W laboratory iACF prototype is developed to verify the feasibility of the proposal, showcasing a 4-point average efficiency 91.9%, superior to the conventional two-stage solutions.

Three-Mode Variable-Frequency ZVS Modulation for Four-Switch Buck+Boost Converters With Ultra-High Efficiency

This article introduces a three-mode variable-frequency zero-voltage switching (ZVS) modulation method for the four-switch buck+boost converter. This method makes this circuit concept well suited for applications, such as wireless power charging of electric vehicles, where this circuit operates as a power buffer between the resonant converter and the battery with the function to implement the required charging profile. Herein, the buck+boost converter operation is subdivided into three operating regions according to the converter static voltage gain, i.e., buck-, buck-boost- and boost-type modes. A ZVS turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> triangular current mode (TCM) control is adopted for buck-type and boost-type modes. In the buck-boost-type mode when the input-to-output voltage gain is close to unit, all the possible modulation cases are studied thoroughly based on the phase shift of the two half bridges in a full switching period. The selection of the most suitable modulation scheme is performed to minimize the rms value of the inductor current while taking into account the simplification of the practical implementation. Closed-form equations are derived, which makes it easy to implement in practice. The proposed strategy is described, analyzed, and finally verified through a 3 kW surface mounted device (SMD) silicon carbide (SiC) <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> -based laboratory prototype with designed input voltage of 300–600 V and the typical output voltage of 400 V class battery. The efficiency from the measured results is remarkably high, i.e., between 99.2% and 99.6% in a power range from 1 to 3 kW. Finally, tests for the operating mode transitions demonstrated the feasibility of the proposed modulation method. The power density of this converter is 4.86 kW/L.

A 10-Bit 20 Channel LCD Column Driver Using Compact DAC

A 20-channel liquid crystal display (LCD) driver architecture is implemented with [Formula: see text]m CMOS technology. This work presents a novel design of 10-bit compact and high-resolution two-stage DAC to improve the linearity and uniformity of each channel performance. A complete column driver, including a compact DAC, low power buffer, global R-string and multiplexing circuit design, is implemented, and the layout of this 20-channel, 10-bit LCD driver is generated using [Formula: see text]m CMOS technology. All the circuit blocks of the proposed LCD column driver were simulated using the EDA tool HSPICE and layout generation by Laker. This work also realizes a high-performance class AB operational amplifier with a gain of 140[Formula: see text]dB for the proposed LCD driver. The 10-bit compact LCD driver has a 1.4 mV LSB and an output voltage of 1.7 V is achieved for the input range of 0.25–1.7[Formula: see text]V. The compact DAC voltage selector with decoder in this design uses fewer switches in comparison to conventional tree-type RDAC, occupying a smaller chip area with fast response. The proposed design is sufficiently robust for high-color depth and resolution LCD driver applications. The experimental results exhibit maximum differential nonlinearity (DNL) and integral nonlinearity (INL) of 0.065 LSB and −0.12 LSB, respectively. The one channel area is [Formula: see text]m and the settling time is [Formula: see text]s for the [Formula: see text] and 20[Formula: see text]pF driving load.

A New PFC Front End With Constant DC-Link Voltage, Reduced Buffer Capacitance, and Soft Switching

Critical conduction mode (CRM) boost power factor correction (PFC) front end is one of the most popular solutions to universal ac–dc applications below 300 W for its simplicity and high efficiency. However, its power density is largely limited by the need for a relatively bulky inductor and a buffer capacitor. This article introduces a new PFC front end that enables simultaneous size reduction of both the inductor and the buffer capacitor by achieving zero-voltage-switching of all switches and active power buffering. A 100-W universal input prototype is built, measuring a 96.7% peak efficiency and 50.8-W/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> power density. Compared to a typical CRM boost PFC front end, the prototype achieves a 47% size reduction of the magnetics, a 21% size reduction of the buffer capacitor, and an almost constant dc-link voltage, while maintaining comparable efficiency performance.

Power Decoupling Rectifier With Common-Ground Concept for Lighting Applications

The lightweight and the electrolytic capacitor-less are the development trends of microconverters for transportation lighting applications. Some solutions available to address the power fluctuations are caused by electrolytic capacitor-less. However, the leakage currents caused by nonisolated converters have been little studied. Given this, an improved transformerless single-phase rectifier based on the virtual dc-bus concept is proposed in this letter. This solution connects the negative of the LED array directly to the grid neutral, thus shorting the stray capacitance to the ground, suppressing leakage currents, and improving system reliability. In addition, the active pulsating power buffering solution is introduced with only one additional power switch due to the sharing of cells. Finally, the experimental results verify the correctness and superior performance of the proposed solution.

Robust Control of Power Buffers in DC Microgrids

Power buffers are dc-dc converters with large capacitors to provide inertia during microgrid transients. This power buffer converter precedes the point-of-load (PoL) converter; the later converter is tasked with regulating the load voltage. By controlling the input impedance of the power buffer, the impact of abrupt load changes on the resistive dc network is cushioned. In practice, dc microgrids might need to support uncertain loads. Such loads, however, have not been treated for power buffers with proper robust controllers. Herein, load uncertainties are represented using polytopic models, and state feedback controllers are developed by solving the resulting linear matrix inequalities. Centralized, decentralized, and distributed control schemes are accommodated in the presence of uncertain loads. Proposed robust controllers are validated for a dc microgrid, populated with power buffers, in a controller/hardware-in-the-loop environment.

Resilient Decentralized Control of Power Buffers in DC Microgrids

Resilient Decentralized Control of Power Buffers in DC Microgrids

Distributed Dynamic Event-Triggered Control of Power Buffers in DC Microgrids

This article investigates distributed event-triggered control (ETC) of power buffers in a direct current (DC) microgrid. In order to facilitate the control design, a linear interconnected system model is derived that captures the physical coupling among power buffers. Then, a distributed ETC law regulates the stored energy and input impedance of each power buffer, and a decentralized dynamic event-triggering mechanism determines when each power buffer communicates with its neighboring buffers. This strategy eliminates the need for both continuous controller updates and continuous communication among the power buffers. The resulting closed-loop system is shown to be exponentially stable under a mild assumption on the communication network. The proposed event-triggering mechanism guarantees not only the exclusion of the Zeno behavior but also the existence of a positive minimum interevent time that can be adjusted by the control design parameters. Simulation studies validate the effectiveness of the proposed theoretical results for a multibuffer DC microgrid.