A New Framework for Cycle-by-Cycle Digital Control of Megahertz-Range Variable Frequency Buck Converters

Cui, Xiaofan; Avestruz, Al-Thaddeus

doi:10.1109/compel.2018.8460055

Cited by 12 publications

(7 citation statements)

References 9 publications

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“…In DC microgrids, reasonable control of power converters enables the regulation of output voltages to smooth the power flow and provide electric power with high quality. Recently, different schemes of current-mode control for converters have been studied due to its unique advantages in current regulation [4] [19]. Here we suppose that the power converters in the microgrid are distributed-controlled in current mode.…”

Section: The Modeling Of DC Microgrids With Closed-loop Converter Con...mentioning

confidence: 99%

“…However, linearized models of microgrids are not always applicable. The first reason is that from the perspective of a dynamic system, the power converter dynamics can be approximated by a nonlinear statespace averaging model only if the system bandwidth is well below the switching frequency [4]. The challenge here is that the feasible region of the averaging model shrinks sharply when we perform linearization for nonlinear systems with high bandwidth.…”

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confidence: 99%

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Large-Signal Stability Criteria in DC Power Grids With Distributed-Controlled Converters and Constant Power Loads

Chang

Cui

Wang

et al. 2020

IEEE Trans. Smart Grid

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The increasing adoption of power electronic devices may lead to large disturbance and destabilization of future power systems. However, stability criteria are still an unsolved puzzle, since traditional small-signal stability analysis is not applicable to power electronics-enabled power systems when a large disturbance occurs, such as a fault, a pulse power load, or load switching. To address this issue, this paper presents for the first time the rigorous derivation of the sufficient criteria for largesignal stability in DC microgrids with distributed-controlled DC-DC power converters. A novel type of closed-loop converter controllers is designed and considered. Moreover, this paper is the first to prove that the well-known and frequently cited Brayton-Moser's mixed potential theory (published in 1964) is incomplete. Case studies are carried out to illustrate the defects of Brayton-Moser's mixed potential theory and verify the effectiveness of the proposed novel stability criteria.Index Terms-large-signal stability criteria, power electronicsenabled power systems, distributed-controlled power converters, constant power loads, potential theory. I. INTRODUCTIONOWER systems are going through a paradigm shift from electric machine-based to power electronics-based, with a huge number of different players on the supply side [1]-[3]. Nowadays, thousands of distributed energy resources (DERs) are being integrated into power systems through power electronics components such as solar panels, wind turbines, and energy storage systems; however, the integration of numerous power electronic components and constant power loads (CPLs) destabilizes power systems and leads to critical oscillations. Consequently, one of the crucial challenges of this new paradigm is to keep the whole power system stable. The stability issues faced by DC microgrids are especially severe and urgent due to their unique properties. First, the low inertia of DC microgrids sharply weakens their stability; and second, owing to their advantage of smooth control, DC microgrids are unprecedentedly more promising than AC power systems given the increasing penetration of DERs. Therefore, the purpose of this paper is to solve the stability issues in power-converterdominated DC microgrids.Recent works related to stability analysis in DC microgrids can be categorized according to the type of disturbance and the number of converters, as shown in Table I. Most of the stability studies of DC microgrids are performed using small-signal and linearized models, especially for large-scale DC microgrids

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Section: The Modeling Of DC Microgrids With Closed-loop Converter Con...mentioning

confidence: 99%

mentioning

confidence: 99%

Large-Signal Stability Criteria in DC Power Grids With Distributed-Controlled Converters and Constant Power Loads

Chang

Cui

Wang

et al. 2020

IEEE Trans. Smart Grid

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“…The sensing of the current extremum requires a single-point measurement, which is especially vulnerable when the switching frequency approaches the frequency band of the interference. Interference can lead to instabilities including those that manifest as subharmonics of the equilibrium switching frequency [5]. The modeling of this interference within a control conditioning framework and the effect on the dynamics were logically delineated and rigorously derived in theory in Part I of this paper.…”

Section: Introductionmentioning

confidence: 99%

“…Fig.25: A 30 W, 5 MHz current-mode buck converter using constant on-time cycle-by-cycle digital control[5]. The digital controller is implemented in Xilinx Artix-7 FPGA.…”

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confidence: 99%

Overcoming High Frequency Limitations of Current-Mode Control Using a Control Conditioning Approach -- Part II: Implementation and Hardware

Cui¹,

Avestruz²

2022

Preprint

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This article is the second part of a paper series about interference in extremum (i.e., peak or valley) current-mode control, which applies to both fixed and variable switching frequency power converters. Specifically, this part presents three control conditioning methods that mitigate the adverse effect of interference. These methods are new ways to use: (i) slope compensation; (ii) low-pass filtering; and (iii) the phenomenon of comparator-overdrive-delay, for control conditioning. The stability criterion, closed-loop dynamics, and transient performance are derived with mathematical rigor for each method. The design tradeoffs are illustrated, discussed, and compared. The effectiveness of all three methods are demonstrated and validated in hardware using a power converter operating at multi-MHz switching frequencies.

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“…In addition, for variable switching-frequency power converters, sampling measurements at a fixed-rate is susceptible to distortion in measurement quality due to unmodeled switching transients. As an alternative, event-driven control is starting to draw attention in power electronics as it can alleviate the requirement for high complexity sampling hardware without sacrificing the performance significantly [9], [18].…”

Section: Introductionmentioning

confidence: 99%

Correct-by-construction control synthesis for buck converters with event-triggered state measurement

Yang

Cui

Avestruz

et al. 2019

2019 American Control Conference (ACC)

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In this paper, we illustrate a new correct-byconstruction switching controller for a power converter with event-triggered measurements. The event-triggered measurement scheme is beneficial for high frequency power converters because it requires relatively low-speed sampling hardware and is immune to unmodeled switching transients. While providing guarantees on the closed-loop system behavior is crucial in this application, off-the-shelf abstraction-based techniques cannot be directly employed to synthesize a controller in this setting because controller cannot always get instantaneous access to the current state. As a result, the switching action has to be based on slightly out-of-date measurements. To tackle this challenge, we introduce the out-of-date measurement as an extra state variable and project out the inaccessible real state to construct a belief space abstraction. The properties preserved by this belief space abstraction are analyzed. Finally, an abstraction-based synthesis method is applied to this abstraction. We demonstrate the controller on a constant on-time buck voltage regulator plant with an event-triggered sampler. The simulation verifies the effectiveness of our controller.

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A New Framework for Cycle-by-Cycle Digital Control of Megahertz-Range Variable Frequency Buck Converters

Cited by 12 publications

References 9 publications

Large-Signal Stability Criteria in DC Power Grids With Distributed-Controlled Converters and Constant Power Loads

Large-Signal Stability Criteria in DC Power Grids With Distributed-Controlled Converters and Constant Power Loads

Overcoming High Frequency Limitations of Current-Mode Control Using a Control Conditioning Approach -- Part II: Implementation and Hardware

Correct-by-construction control synthesis for buck converters with event-triggered state measurement

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