1,720,994 research outputs found
A Unidirectional Flying Chain-link Modular Multilevel Rectifier (FCL-MMR) with Reduced Energy Storage for Offshore Wind Integration
No full textIn recent years, the Modular Multilevel Converter (MMC) has been widely recognised as the state-of-art for AC/DC conversion stages in the integration of offshore wind energy through HVDC links. The MMC guarantees high power quality, efficiency, reliability and flexibility. However, in applications where the power flow is mostly unidirectional, the capabilities of the MMC are not fully exploited, resulting in a converter whose weight and volume are not optimised. This aspect is particularly challenging in offshore applications where the platform cost is a key factor. A more traditional solution could be the use of an AC/DC converter based on diode rectifiers, providing minimum size and complexity at the cost of poor AC power quality, requiring large active/passive filters. This paper proposes a new unidirectional AC/DC converter, named Flying Chain-link Modular Multilevel Rectifier (FCL-MMR), that combines a three-phase diode rectifier with modular chain-links of submodules (SMs) that enable the control of sinusoidal AC currents and, if needed, the exchange of reactive power with the offshore AC grid. This is achieved with a limited number of submodules characterized by low energy storage requirements. The conversion concept and the theoretical analysis are presented and SM selection criteria is discussed. The proposed converter has been validate in Plecs simulation. © 2018 IEEE
Digital Time-Optimal Phase Shedding in Multiphase Buck Converters
No full textThis letter proposes a time-optimal digital controller for the phase shedding (PS) in multiphase buck converters. PS is an established technique to improve the efficiency of multiphase converters at light load by changing the active number of phases depending on the load-current level. In order to minimize the output-voltage deviation and the transient time during PS, a minimum time algorithm is investigated. The proposed technique is insensitive to the power stage parameters, as its operation relies only on a feedforward action, depending on the steady-state duty cycle and the number of phases to be turned on or turned off. The proposed approach is validated through experimental tests on a synchronous buck converter
Model Predictive Control for Isolated DC/DC Power Converters with Transformer Peak Current Shaving
No full textIn this paper a Model Predictive Control, suitable for isolated DC/DC power converters and featuring optimization on converter operations, is proposed. The control is designed based on a specific a current-fed DC/DC converter topology, named Active-Bridge-Active-Clamp converter. This topology is particularly suitable for batteries interface, utilizing its interleaved structure in order to achieve an effective current ripple cancellation at the low voltage terminals. However, the increased complexity of the ABAC converter requires a specific modulation implementation and a detailed converter modeling. For such reasons, the operating principle of the ABAC converter is firstly introduced and mathematical models of the ABAC are developed in this paper. Subsequently, a Model Predictive Control is proposed and implemented aiming to achieve terminal current regulation, improve dynamic performance and reduce current stress in a wide DC voltage operating range, whilst maintaining a fixed switching frequency and a reduced prediction horizon. Simulation results for a 10kW ABAC converter are provided to validate the theoretical claims. © 2018 IEEE
Analytical Model for Reluctance and Cage Rotor Bar Magnetic Gear
No full textMagnetic gearboxes are becoming more attractive in gearing areas because of their high torque density and high efficiency. In this article, we proposed a 2-D analytical model in a coaxial magnetic gearbox by considering design aspects that can make the design process more reliable, efficient, and cost effective. The proposed analytical model is based on the solution of Laplace's and Poisson's equations for each subdomain, i.e., magnets, airgap, slots, and bars. The global solution is obtained using the boundary and continuity conditions. The analytical model can be used as a design tool for a magnetic gearbox with more design aspects compared with previously proposed methods. The analytical results of field distribution, induced bar current, and electromagnetic torque are obtained and compared with finite-element analysis (FEA)
Parameters mismatch analysis for the Active-Bridge-Active-Clamp (ABAC) converter
No full textThe Dual-Active-Bridge has become the most common choice in modern isolated, bidirectional DC/DC conversion stages where high efficiency, galvanic isolation and large voltage conversion ratios are required. However, in low voltage high current applications, the current ripple on the low voltage side may be considerably high, thus requiring large capacitive filtering. As an alternative to the standard Dual-Active-Bridge, an Active Bridge, Active Clamp (ABAC) converter is presented in this paper which simplifies the low voltage side filtering by cancelling the load current ripple through interleaving. This paper introduces the ABAC topology operated with Single Phase Shift modulation and analyses the impact of different parameters mismatch on DC current sharing and current ripple cancellation between the interleaved channels. The theoretical findings are validated in simulation and experiment on a 10-kW ABAC converter. © 2017 IEEE
Analysis of Low-Frequency-Oscillations in Single- Phase AC Systems by LTP Theory
No full textThe paper presents the analysis of a single-phase active rectifier, with DC constant power load, affected by Low-Frequency Oscillation (LFO) behaviour. Conventional LTI analysis tools might fail to reveal the LFO phenomenon, whereas the LTP (Linear Time Periodic) approach, here exploited with analytical derivation and detailed simulations, provides superior results. © 2018 EPE Association
Parallel-connected bidirectional converters for avionic applications
No full textThis paper proposes a fully FPGA controlled Bi-Directional Converter (BDC) for avionic applications. The dissertation starts with an overview of the proposed converter, followed by the description and the mathematical analysis of the Dual Active Bridge (DAB) topology. Then, the control laws for both single and parallel modes are presented. In particular, the discussion on the paralleling of power converters with current sharing is the main contribution of this study. Simulations and experimental evaluations that illustrate the behavior of the BDC unit are given throughout all the specific sections
Time optimal, parameters-insensitive digital controller for DC-DC buck converters
No full textIn this paper a digital control approach is investigated for time-optimal load step response of DC-DC synchronous buck converters intended for point-of-load applications employing low-ESR ceramic output capacitors. Unlike previously reported approaches, the proposed technique is insensitive to the power stage parameters, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected. An asynchronous A/D converter has been employed, realized in a standard 0.35 mum CMOS process. The A/D converter quantizes the output voltage and triggers a nonlinear, event-based digital controller whenever a quantization level transition is detected. Time-optimal response is based solely on output voltage measurements and on the knowledge of the steady-state duty cycle, a number easily available within the digital controller. Effectiveness and properties of the proposed robust time-optimal approach are validated through both computer simulations and experimental tests on a synchronous buck converter prototype and a VHDL implementation of the control algorithm on an FPGA device
Parameter-Independent Time-Optimal Digital Control for Point-of-Load Converters
No full textIn this paper, a digital control approach is investigated for time-optimal load step response of DC-DC synchronous buck converters intended for point-of-load (PoL) applications and employing low-equivalent series resistance ceramic output capacitors. Unlike previously reported approaches, the proposed technique is insensitive to converter parametric variations and design uncertainties, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected. In its most general formulation, the proposed technique automatically incorporates adaptive voltage positioning (AVP) regulation, according to the typical droop design guidelines for powering modern microprocessors. A simpler version, suitable for voltage-mode controlled PoL converters not requiring AVP positioning, is also presented. The technique employs an asynchronous A/D conversion scheme, which quantizes the converter state variables and triggers a nonlinear, event-based digital controller whenever a quantization level transition is detected. Additional sensing requirements are not needed, since the time-optimal transient is achieved through the measurement of the output voltage and, whenever AVP regulation is needed, of the phase currents. Effectiveness and properties of the proposed robust time-optimal approach are validated through both computer simulations and experimental tests on a synchronous buck converter prototype and a VHDL implementation of the control algorithm on an field programmable gate array device
Time optimal, parameters-insensitive digital controller for VRM applications with Adaptive Voltage Positioning
No full textA digital control approach is investigated for time-optimal load step response of Voltage Regulation Modules (VRM) equipped with low-ESR ceramic output capacitors. The proposed time-optimal technique is insensitive to the power stage parameters, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected and automatically incorporates Adaptive Voltage Positioning (AVP) regulation. The proposed robust time-optimal approach is validated through both computer simulations and experimental tests on a synchronous buck converter prototype
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