In this paper a weighting function for voltage unbalance correction is proposed to be integrated into the control of distributed grid-interfacing systems. The correction action can help decrease the negative-sequence voltage at the point of connection with the grid. Based on the voltage unbalance factor and system power capacity, the interfacing converter delivers a small amount of negative-sequence current to the grid and helps correcting the negative-sequence voltage. Although the reduced amplitudes contributed by each individual DG system are very small compared to the total negative-sequence component, many DG system modules can collectively achieve substantial results in the grid. As a practical example, a three-phase grid-interfacing converter servicing sensitive loads with distributed sources is employed to integrate this additional function. Design principles, simulation and experimental results are presented to verify the proposal.

In this paper, a strategy is investigated for control of distributed generators to additionally support the local grid on top of conventional electricity generation. The strategy decouples unbalance and harmonic compensation in the phase sequences and the frequency domain for a grid-connected inverter with local unbalanced and distorting loads. Unlike conventional control schemes for grid-connected converters, the proposed strategy is designed to be sequence-asymmetric for the purpose of unbalanced and harmonic local voltage correction. A frequency-domain Norton equivalent model is derived to illustrate the working principle of the strategy. Accordingly, it is shown that following a frequency-domain decoupled method the fundamental positive-sequence, the harmonic symmetrical sequence, the fundamental zero-sequence and the fundamental negative-sequence components can be regulated independently. Consistent to the model analysis, experiments validate the reduction of the local voltage total harmonic distortion and unbalanced factor when the converter is programmed for both harmonic sinking and voltage unbalance correction.

This paper presents a distributed storage/emergency lighting upgrade circuit that can be added to LED lighting fixtures. In contrast to conventional designs that are mostly supplied by a voltage source, we present an example of an emergency lighting circuit that is supplied by a constant current source (LED driver) in charging/lighting mode. We also compare the performance of the same circuit when it is supplied by a voltage source in emergency lighting mode by the battery. Notwithstanding its low component count, the discussed concept reaches an efficiency of 94%, and has a simple control scheme that provides dimming functionality for non-dimmable LED drivers.

Multiple-output converters have been widely used where individual outputs are required. Compared with conventional separate converters, the advantage of multiple outputs is to have a lower number of active and passive components. In this paper, first, a pulse-width-modulation (PWM)-pulse-frequency-modulation (PFM) method is used for two-output converters that have only one coil and one active switch. Secondly, three-output converter topologies are proposed where the third output is controlled by phase delay (PD). These converters need only two coils and two active switches to regulate three outputs. How to obtain PD at different switching frequencies is discussed next, and a PWM-PFM-PD controlled five-output buck converter is presented. The proposed solution uses only two active switches and two magnetic cores to adjust five-output voltages independently. A modeling and digital control method are proposed in order to regulate the five output voltages. A prototype circuit with independent 15 V/1.5 A, 12 V/1.5 A, 5 V/0.8 A, −5 V/0.6 A and 3.3 V/0.45 A outputs is assembled to validate the analysis, and it was proved that it regulates the output voltages at different loads.

A single-phase grid-connected converter is considered in this paper in the presence of harmonic problems introduced non-linear loads. In order to compensate the harmonics caused by the loads, a local voltage support scheme is proposed. This is an added feature because its implementation is in parallel with a conventional current control method. Distinctively, the measurements of the grid or load current are not needed since the scheme is based on only local measurements. On top of a fundamental part for desired power injection, the converter output current comprises a harmonic part for compensation. Thus, the grid current harmonic distortion is minimized and the enhancement of the local voltage quality is achieved. A comprehensive model analysis indicates that the proposed strategy can help to attenuate harmonics of the local voltage without compromising on the quality of the fundamental current injection. Experimental results validate the effectiveness of the proposed control scheme. Moreover, the impact of grid frequency estimation error on the control strategy's performance is quantified theoretically and experimentally.

Practical switching devices have finite turn-on and turn-off times. To avoid short circuit, a blanking time is added between turn-off and turn-on of the complementary working switches in a switching-leg. The blanking time, also referred to as deadtime, is one of the dominant sources of output current and voltage distortion in pulse-width modulated (PWM) power amplifiers. Extensive studies exist on elimination, minimization, and compensation of the effect. Most techniques achieve a reduction of the distortion but are not capable of completely removing it. The dual-buck (DB) converter does not suffer from blanking-time-related distortion. However, blanking time is not the only source of switching-leg-induced distortion. This paper focuses on the effects of semiconductor device parameters on the output quality of the DB converter. It is shown that, ideally, the forward voltages of the diodes and switches have no effect on the output quality. Measurements on a prototype, industrial power stack based, DB converter show a 100 times improvement of the open-loop spurious free dynamic range when compared to conventional PWM converters.

The aim of this paper is to analyse the stability of grid-connected converters using repetitive control for voltage harmonic compensation. Supplementary to an earlier proposed control strategy to upgrade grid-connected converters for add-on voltage support, the stability analysis of the overall system is presented. A straightforward procedure is proposed and a couple of stability conditions are derived. The analysis is broken down into two sub-parts and therefore, the Nyquist's criterion can be easily applied. Simulations and experiments support the stability model analysis. The proposed method is not limited to the application with voltage support but also applicable for other converter systems based on repetitive-control algorithms.

SummaryThis paper presents a 7.7‐mm2 on‐chip LED driver based on a DC/DC resonant hybrid‐switched capacitor converter operating in the MHz range with and without output capacitor. The converter operation allows continuously dimming the LED while keeping control on both peak and average current. Also, it features no flickering even in the absence of output capacitor and for light dimmed down to 10% of the nominal value. The capacitors and switches of the LED driver are integrated on a single IC die fabricated in a low‐cost 5 V 0.18‐μm bulk CMOS technology. This LED driver uses a small (0.7 mm2) inductor of 100 nH, which is 10 times smaller value than prior art integrated inductive LED drivers, still showing a competitive peak efficiency of 93% and achieving a power density of 0.26 W/mm2 (0.34 W/mm3).

This paper considers a three-phase four-wire grid-interfacing voltage-source inverter with local unbalanced and distorting loads. A sequence-decoupled resonant control strategy is proposed to support the local voltage on top of conventional active power regulation. The local voltage at the point of common connection, which is traditionally used for grid synchronization for distributed generators, is also used for sensing unbalanced and harmonic voltages. Therefore, measurements of load currents for unbalanced and harmonic compensation can be eliminated with the proposed approach.

In this paper an add-on control method is proposed to damp oscillations in the LCL filter of a grid connected converter. An observer is used to estimate the capacitor current, and successively, a conventional active damping technique is applied. Since the capacitor current is estimated from already available measurements, the proposed active damping method does not need an extra current sensor for the capacitor current. Model analysis and simulation validate the effectiveness of the proposed control method.

This paper presents a LED driver IC based on a self-resonant Hybrid-Switched Capacitor Converter (H-SCC) operating in the MHz range. Capacitors and switches of the LED driver are integrated on-chip in a low-cost 5V 0.18μm bulk CMOS technology. The effective chip area is 7.5mm 2 . A conventional SMD output capacitor and a 6.4 mm 2 150nH SMD air-core inductor are enough to operate the driver in a compact PCB area. Integrated zero-current detection (ZCD) circuitry enables self-resonant operation and Zero-Current Switching independently of the output current, inductor tolerances and/or parasitics, improving the converter efficiency at light loads. A ZCD threshold control enables continuous conduction mode too, to improve efficiency at large currents. The experimental results show a peak efficiency of 92.2% and a maximum power density of 373mW/mm 2 . The LED driver is able to control a 700mA LED down to 10% of its nominal current and can adjust to LED voltage variations, avoiding the need for LED binning.

A strategy for voltage harmonics suppression is proposed to upgrade existing grid-connected inverters. It utilizes the already available measurement of the voltage at the point of common connection and the inverter output current. As a result, on top of conventional power injection, the inverter is equipped with an additional feature for harmonics compensation. Model analysis, simulation and experiments verify the effectiveness of the proposed strategy.

The success of electric vehicles (EVs) greatly depends on battery size, cost, lifetime, and capacity. The battery capacity of EVs has to contain enough energy to allow EV users to drive, at least, the minimum distance that internal combustion engine vehicles take. However, even with very efficient EVs and combining all the available highly efficient EV technologies, the battery capacity still needs to be large. Thus, one alternative to reduce the battery size is to improve the charging infrastructure by implementing sufficient public/private fast-charging locations, which will significantly increase the EV driving range with relatively low battery capacities. However, this kind of infrastructure requires charging with higher current capability, due to the high power levels involved in the fast-charging process. In this paper, a bidirectional dc/dc converter with six inverter legs connected to a three-phase output is proposed. The converter is similar to a three-phase dual-active-bridge (DAB) converter with more inverter legs in parallel. These additional inverter legs increase the converter current capability, without affecting the DAB main characteristics, preserving similar modulation techniques and DAB advantages. An accurate study about the proposed topology is carried out in this paper, and simulations and experimental results are shown for a 20-kW prototype, validating the theoretical analysis.

This paper presents a LED driver based on a new Hybrid-Switched Capacitor Converter (H-SCC) operating in the MHz range, which uses the internal pulsed nodes of a Dickson converter and an LC output network to provide output current dimming. The converter is implemented using 5V integrated capacitors and switches in a 0.18μm bulk CMOS technology. The experimental results show that the proposed LED driver has a power density of 122mW/mm2 and an efficiency of 79%, and only needs a small 40nH inductor.

In this paper, a multiple output dc-dc converter is proposed. Pulse frequency modulation (PFM), pulse width modulation (PWM) and phase delay (PD) methods are used to regulate output voltages. Two of the output voltages are regulated by PWM, 2 of them by PFM, and the other one by PD. Five regulated outputs are obtained by using only two active switches. The switches can be operated at different switching frequencies. A hardware prototype was implemented that has 1.5V/0.5A, 3.3V/1A, 12V/0.5A, -12V/0.5A and 5V/1A outputs and the efficiency is 89% at the rated power.

A digital control method combining primary-side sensing, observer and model-predictive-control techniques is proposed. A conventional isolated Flyback converter is chosen for demonstrating the method. The only measured signal is the drain-source voltage over the switch. Following a procedure of signal processing, state estimation and constraint problem formulation, the controller determines the optimal duty cycle ratio. The advantages of the proposed method include minimal overshoot and fast stabilization, converter state restriction, and measurement network simplification.

This paper proposes a four-degree-of-freedom control method for a dual active Flexbattery H-Bridge converter, which operates similarly to dual-active- bridge converters. The Flexbattery pack is constructed from multiple modular units and each unit contains one voltage source, one inductor and four switches. Due to the cascaded structure of the pack, it is able to generate high-frequency square-waveform signals with tunable amplitudes and duty cycles. Distinct from the well-known unified triple-phase-shift approach, the proposed control method includes one additional degree of freedom. The tunable control variables become one voltage amplitude, two duty cycles, and the phase shift. By taking the third harmonic into account, the proposed four-degree-of-freedom control method further reduces the circulating current.

In this study, a three-phase bidirectional dc/ac converter is proposed using a direct ac/ac converter and a six-leg converter, to avoid the use of dc-link capacitors and to increase the current capability at the dc side. To link the six-leg inverter to the direct ac/ac converter, three single-phase high-frequency transformers are implemented to simplify the topology, which will attract the industry. The direct ac/ac converter used in the study demonstrates reduced complexity and simpler modulation techniques compared with a conventional matrix converter. The analysis starts with the description of the proposed dc/ac converter for single phase, which is subsequently extended to a three-phase dc/ac converter. A 20 kW prototype was built to verify and to validate the theoretical study of the proposed converter.

A scheme is presented to integrate a primary-side-sensing technique into a model-predictive-controller for a Flyback converter. The control circuit consists of a signal processor, an observer, and a model-predictive controller. Besides inheriting the advantages of model-predictive-control, e.g. optimal tradeoff between overshoot, fast stabilization and constraints handling, the proposed controller saves on hardware by applying primary-side-sensing.