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This article presents a new hybrid-mode pulse-frequency-modulation control method for an LLC resonant converter. In the proposed control method, the primary-side resonant current sensing signal of the current-mode control variable is combined with a ramp signal of the voltage-mode control variable to determine an operating frequency. Then, the proposed control method mainly modulates the ramp signal in accordance with the output load condition. Therefore, the control-to-output voltage transfer function has both the current-mode control and voltage-mode control characteristics that provide fast frequency response and stable output voltage regulation in a light-load condition. In addition, since the ramp signal is also used for slope compensation of the resonant current sensing signal, an external slope compensation circuit is not required. A small-signal ac modeling and loop analysis of the proposed method verify the advantages. The proposed control method is implemented into a field programmable gate array (FPGA) board with an analog front-end board. An experiment is carried out on a 288-W LLC resonant converter. The result shows that the proposed control method provides fast dynamic performance and stable operation under a light-load condition without an additional slope compensation circuit. [ABSTRACT FROM AUTHOR]

This letter presents a multi-objective probabilistic model for the optimal selection of pilot buses in secondary voltage regulation (SVR) of transmission grids. The pilot-bus selection (PS) problem is formulated in the form of a stochastic multi-objective optimization problem (SMOP). The resultant SMOP is solved toward the non-dominated sorting genetic algorithm (NSGA-II) together with a fuzzy set theory. The applicability of the proposed PS model is examined on a classical test system as well as a practical transmission grid. [ABSTRACT FROM AUTHOR]

Microgrid islanding can improve the reliability of distribution networks by enabling load to be supplied even after a fault has occured nearby. The generation and load devices in microgrids are commonly interfaced by power electronics, causing a lack of inertia in the network. When microgrids transition from grid-connected to islanded operation after a fault, fast dynamics occur which have to be evaluated to assess stability during and after the transition. Their stability can be evaluated by time-domain simulations, however detailed and validated models of power electronic loads and distributed energy resources are required. This paper proposes component-based models of different types of power electronic loads, and single and three phase distributed energy resources. The models are validated with a variety of voltage and frequency transient experiments. A case study is performed where a modified version of the Cigre European LV residential network is islanded after a fault occurs. The results of the proposed, constant impedance and exponential load models are compared. The results indicate that the proposed models should be used for accurate analysis of the voltage and frequency stability during microgrid islanding simulations. [ABSTRACT FROM AUTHOR]

A current-mode buck regulator with delay-based hysteretic control for microcontroller applications is proposed. Unlike conventional hysteretic buck regulators with accurate explicit hysteretic bands, the proposed design relies only on the inherent delay of a low-speed single-threshold comparator to realize the hysteretic band, and can be seamlessly used across all loads in continuous conduction mode and discontinuous conduction mode without modifying the controller's parameters. Moreover, without additional adaptation circuits or frequency regulation loops, the proposed delay-based hysteretic operation does not increase variations in the switching frequency with process and temperature, and results in even less variations in the switching frequency with the input and output voltages when compared to corresponding designs with accurate explicit hysteretic bands. The simplicity of the design reduces silicon area and quiescent current significantly, which in turns enables achieving high efficiency at both heavy and light load conditions as strictly required by low-power microcontrollers. The regulator is designed in a 65 nm digital CMOS technology. It occupies 0.18 mm2 and supports a wide range of input voltages (1.8–4.2 V), output voltages (0.9–1.5 V), and load current (up to 300 mA). Measurement results show that the proposed regulator achieves 95% peak efficiency, while achieving between 62% and 87% efficiency at 10-μA load across all operating conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a circuit structure that can improve the power-conversion efficiency \eta e of an AC–DC boost converter. The circuit uses a 1:1 transformer and a voltage boost circuit composed of an inductor, a capacitor, and a diode. The transformer forces the converter to operate in continuous conduction mode for input current, and thereby reduces input ripple. The voltage boost circuit enables the switch to operate in critical conduction mode, so the power loss due to turn-on of switch and reverse recovery of diode is minimized. The proposed converter has high \eta e over a wide range of AC input voltage $V_{{\rm{ac}}}:\,\eta _{e}= 92.9\% $ at $V_{{\rm{ac}}}= {\text{85}}\,{\text{V}} and \eta e= 97.4\% at V{\rm{ac}}= {\text{265}}\,{\text{V}}, when the converter was operated at DC output voltage of 400 V and output power of 500 W. The temperature of the switch stabilized at ∼84 °C for $V_{{\rm{ac}}}= {\text{85}}\,{\text{V}}$ , at ∼70 °C for $V_{{\rm{ac}}}= {\text{110}}\,{\text{V}}$, and at ∼42 °C for $V_{{\rm{ac}}}= {\text{220}}\,{\text{V}}$, whereas that in other AC–DC converters either failed or stabilized at much higher levels. The proposed converter is well suited to systems that require an input voltage range of 85–265 V in root-mean-square value. [ABSTRACT FROM AUTHOR]

With ever-increasing demand of feature-rich portable electronics, single-inductor multiple-output (SIMO) converters are becoming a cost-effective option to provide different supply voltages while maintaining a long battery life. A single-discharge (SDC) control scheme is proposed to simplify the SIMO design, to achieve low cross-regulation, and to support wide range of loads with reasonable power efficiency. A SDC SIMO buck converter with four outputs composed of comparators, phased-locked loop, finite state machine (FSM) controller, and an output stage, is prototyped using TSMC's 0.18-μm BCD process. In addition to the basic switching functions, the FSM controller provides a state skipping feature to allow no-load regulation. Its functionality is verified experimentally and can convert an input voltage from 2.7 to 3.7 V to 1, 1.2, 1.5, and 1.8 V outputs. The simulated peak power conversion efficiency is 86% with a combined output power ranging from 150 to 300 mW. The packaged SDC SIMO converter ICs exhibit a lower measured peak efficiency of 73%, with a cross-regulation of 0.24 mV/mA due to the parasitic bond-wire resistance. The converter prototype can support a wide range of loading conditions, from open circuit to a total output power of 1 W. [ABSTRACT FROM PUBLISHER]

The POWER9TM family of chips is fabricated in 14-nm silicon-on-insulator finFET technology using 17 levels of copper interconnect. The 695-mm2 24-core microprocessor features a new core based on an execution slice microarchitecture. The chip contains 8 billion transistors and has 120 MB of eDRAM L3 cache. The processor features an adaptive clock strategy to reduce timing margin needed during power supply droop events by embedding analog voltage-droop monitors that direct a digital phase-locked loop to immediately reduce clock frequency in response to a droop event. The scale-out chip IO subsystem supports up to 300-GB/s accelerator bandwidth using new 25-Gb/s links, 48 lanes of PCIeGen4 totaling 192 GB/s, eight ports of 2667 MT/s DDR4, and 256 GB/s of symmetric multiprocessor (SMP) interconnect. The scale-up chip adds additional SMP bandwidth and replaces the DDR4 memory interface with eight ports of differential memory interfaces with 230 GB/s of bandwidth resulting in 12.9 Tb/s of total off-chip bandwidth. [ABSTRACT FROM AUTHOR]

Two main methods for controlling switching converters exist in the literature. The direct one is the voltage mode control, which suffers from some disadvantages such as slow response to load variations and an input voltage-dependent total loop gain. The current mode control can overcome these problems but at the expense of extra cost and more complex control design. V1 concept is a new promising control technique for designing voltage mode control of buck-type converters with an optimal response similar to current mode control. In this paper, the dynamics and the stability of buck converters under V1 control are studied. In particular, subharmonic oscillation limits in the parameter space are addressed. First, a closed-loop state-space model is derived and then used to formulate an analytical matrix-form expression for predicting the stability limit of the system. Using this expression, multi-parametric stability boundaries are obtained. It is shown that the equivalent series inductance of the output capacitor can narrow the stability region. It is also demonstrated that the integral action in the feedback loop of a V1-controlled buck converter has a negligible effect on the subharmonic oscillation boundary. The theoretical analysis is validated through numerical simulation of the circuit-level switched model of the system. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

It is often assumed that the input voltage source of a switch‐mode power supply is constant or shows negligible small variations. However, the last assumption is no longer valid when a fuel‐cell stack is used as input source. A fuel‐cell stack is characterised by low and unregulated DC output voltage, in addition, this voltage decreases in a non‐linear fashion when the demanded current increases; henceforth, a suitable controller is required to cope the aforementioned issues. In this study, an average current‐mode controller is designed using a combined model for a fuel‐cell stack and a boost converter; moreover, a selection procedure for the controller gains ensuring system stability and output voltage regulation is developed. The proposed energy system uses a fuel‐cell power module (polymer electrolyte membrane fuel cells) and a boost converter delivering a power of 900 W. Experimental results confirm the proposed controller performance for output voltage regulation via closed‐loop gain measurements and step load changes. In addition, a comparison between open‐ and closed‐loop measurements is made, where the controller robustness is tested for large load variations and fuel‐cell stack output voltage changes as well. [ABSTRACT FROM AUTHOR]

This work presents a novel mixed-signal control scheme for a boost power factor correction (PFC) rectifier. The digital controller modulates the inductor peak current to produce a low-distortion ac line current in discontinuous conduction mode (DCM) and continuous conduction mode (CCM), without the need for average current sensing. A lookup table (LUT) optimizes efficiency at low input currents, by allowing operation at 125–500-kHz DCM based on calculated thresholds. At high input currents, the converter operates at 1-MHz CCM for reduced inductor footprint. An analog off-time generator with a digital frequency locked loop facilitates CCM operation, eliminating the need for slope compensation in the current loop and reduces frequency variations. The LUT is programmed with an adaptive output voltage of 250/450 V for low/high mains line voltage (85–265 Vrms) to optimize efficiency over a broad range of conditions. The 150-W PFC prototype operates up to 1 MHz with a peak efficiency of 95% and a total harmonic distortion of 5%. [ABSTRACT FROM AUTHOR]

A resonant switched capacitor converter with high efficiency over a wide and continuous conversion ratio range is introduced. The efficiency of the topology depends primarily on the conduction losses and is decoupled, to a large extent, from the voltage conversion ratio. This is an advantage over classical switched capacitor converters, for which the efficiency is strongly related to the conversion ratio. The operation principle applies three zero current switching states to charge, discharge, and balance the remaining charge of the flying capacitor. This results in a gyrator, i.e., a voltage-dependent current source, with a wide range of voltage conversion ratios (smaller as well as greater than unity) as well as bidirectional power flow capabilities. The analytical expressions for the conversion ratio and expected efficiency are provided and validated through simulations and experiments. The experimental verifications of the converter demonstrate peak efficiency of 96% and above 90% efficiency over a wide range of voltage gains and loading conditions. In addition, the system was found to be highly efficient at the extreme cases of both light and heavy loads. [ABSTRACT FROM AUTHOR]

Switching power suppliers are described through a mixed analog/digital model. The analog (nonlinear) part is represented by the power circuit and the digital one by the control driving the (MOSFET) switches. We present a general, efficient, and reliable technique to determine, versus variations of design parameters, 1) the periodic steady-state behavior of these circuits discussing stability, 2) periodic time varying transfer functions, and 3) to straightforwardly evaluate the performances of the controller. The proposed simulation approach resorts to the saltation matrix operator to define fundamental matrix for hybrid dynamical systems. This extends conventional simulation and analysis techniques such as the shooting method, the periodic linear phasor, and the Floquet multipliers evaluation to mixed analog/digital circuits. The effectiveness of the approach, representing an alternative viewpoint with respect to commonly adopted analysis strategies, is shown by designing a version of a voltage regulator module for a computer and by investigating its limits versus its output filtering capacitance. [ABSTRACT FROM AUTHOR]

Full-bridge single-stage (FBSS) ac-dc converters allow to regulate both the output voltage and the input current that achieves a near sinusoidal waveform using only the four bridge transistors. Independent of this feature, these converters still need to be optimized in order to become an interesting and attractive solution for modern switch mode power supplies with power factor corrector (PFC) function. One of the most important improvements needed is the downsizing of the dc bus capacitor C b with the inherent cost reduction. However, this action introduces complex issues in the regulation of the input current and it is also responsible for the generation of high output voltage ripple. The new contribution of this paper consists in the introduction of a set of power circuit optimizations and control techniques in a FBSS PFC converter that solves the referred issues in order to enable the reduction of the dc bus capacitor's size and cost. These procedures are based in the use of a free wheeling circuit that improves the light load operation and in the application of one shot nonlinear modulator, in order reduce the output voltage ripple even when the dc bus ripple is high. The possibility of using, in the proposed topology, a reduced ratio capacitance/watt lower than the typical values used in commercial applications (0.7-0.5 μF/W for 385-450 V, respectively), while maintaining the accurate input current regulation, is also theoretically proved. The developed concepts, solutions and design criteria are detailed described in the paper. The correspondent theoretical study is verified trough experimental results token in an optimized FBSS topology prototype. [ABSTRACT FROM AUTHOR]

Traditional digital power factor correction (PFC) uses three sensors to measure the input and output voltages and the input current. Each sensor, especially the input current one, increases the cost of the system and generates power losses in case of resistive sensors. This paper presents a controller for boost PFC converters. It uses precalculated duty cycles generated offline, and applies them to the switch. In order to control the converter with nonnominal conditions, just one analog-to-digital converter (ADC) is used, which measures the output voltage. Measuring the average and the ripple of the output voltage with this ADC, the controller takes compensation action for changes in the input voltage but also in the load of the converter. The average value is used to control the input voltage changes, while the ripple value is used to control load changes. These two loops present low frequency bandwidth, so the ADC and the whole system can be low cost. Finally, a comparator is used to detect the zero-crossing of the input voltage, so the precalculated values are synchronized with the ac mains. In this way, the converter only uses one ADC and one comparator, both with low bandwidth. Results show that high power factor and normative compliance are reached, even under nonnominal conditions. [ABSTRACT FROM AUTHOR]

LLC resonant converter is one of the most suitable circuit topologies that have been introduced for designing constant output voltage switched-mode power supplies. In this paper, a design procedure is introduced for using this converter as a wide output range voltage source. Unlike constant output voltage applications which need small converter inductance ratio and narrow switching frequency variations, for wide output range applications, large values of these parameters are needed simultaneously and should be optimized. Instead of minimizing the components stresses, leading to a great value of the inductance ratio, proper choice of the converter parameters resulting in a smaller inductance ratio has been done. Maximum value of the capacitor in parallel with the power MOSFETs drain-sources has been derived to realize the zero voltage switching operation in the converter inductive region. Soft switching is achieved for all power devices under all operating conditions. A prototype of the converter has been tested for different regulated output voltages (35-165 Vdc) under different loads (0-3 Adc) and input voltages (320-370 Vdc) for using an ion implanter arc power supply, with maximum efficiency value of 94.7%. Experimental results confirm the high performance of the wide output range LLC resonant converter even under the worst case conditions. [ABSTRACT FROM AUTHOR]

A hysteretic mixed-signal controller for high-frequency switch-mode power supplies that achieves both very fast transient response and constant switching frequency under steady-state operation is presented. The mixed-signal controller combines three control loops: analog nonlinear current loop, digital linear voltage loop, and digital frequency loop. To eliminate the sampling delay associated with conventional digital controllers and improve the transient response performance, the fast nonlinear loop is built with a simple analog hardware. The nonlinear current loop is designed based on the hysteretic control of the output capacitor current. To guarantee the constant switching frequency, under different operating conditions, a digital frequency loop is proposed and implemented. The digital frequency loop eliminates undesirable switching frequency variation, associated with the conventional hysteretic controllers, by digitally adjusting the hysteretic bands around the output voltage reference. The controller operation is experimentally verified with a 5-MHz buck converter. Experimental results demonstrate fast transient response while the constant switching frequency is maintained under steady-state operation. [ABSTRACT FROM AUTHOR]

LLC-LC resonant converter is a suitable circuit topology to design switched-mode power supplies for wide-output-voltage and wide-output-load applications. In this paper, a design procedure is introduced to optimize this converter. Unlike soft switching techniques for pulse width modulated converters, which usually apply an active auxiliary circuit to reduce switching losses and EMI, in the proposed converter, not only such circuits are not used, but also all of the parasitic elements are merged to the converter's main components. Zero-voltage switching (ZVS) operation is realized for all power devices under all operating conditions. Thus, this converter is a suitable choice for high-switching-frequency operation. The converter parameters have been designed to minimize the components' current and voltage stresses. In addition, the frequency variation range has been reduced in order to use the magnetic components, optimally. Developed prototype of the converter has been tested for different output voltages (25-165 Vdc) under different loads (0-3 Adc) and input voltages (320-370 Vdc) for being used as ion implanter arc power supply. For regulating and adjusting the designed prototype converter output voltage, its switching frequency varies from 177 to 314 kHz. The converter's maximum efficiency is approximately equal to 96.6%. [ABSTRACT FROM AUTHOR]