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Cascaded multilevel power factor correction (PFC) converters show great potential for applications that require high ac voltage input but low dc-bus voltage output, such as telecom power supply, battery formation, and Internet data centers. They are compact and put less voltage stress on power switches. To provide multidc outports with fewer power switches, a cascaded half-bridge-based multilevel multiport bridgeless PFC is proposed in this article. Compared with cascaded full-bridge multilevel PFC, the number of switches per power cell for the proposed PFC is reduced by half while maintaining the same dc outports. Due to the multilevel voltage, the volt–second on the boost inductor decreases, reducing the current ripple of the proposed PFC by $2n$ times with the same boost inductance as the conventional totem-pole PFC. By splitting the power into $2n$ cells with low voltage, the total switching losses are also reduced by $2n$ times with the same equivalent switching frequency. In addition, the proposed rectifier also reduces conduction losses as lower voltage switches with smaller conduction loss are adopted in half-bridge cells compared with conventional totem-pole PFC rectifiers. Finally, these benefits are analyzed and validated with experiments.

Unprecedented expansion of renewable, energy storage, and fast charger system applications has diversified the bidirectional converter designs over the past decade. This article presents a new dual-active bridge (DAB) converter topology, which employs parallel and series switches arrangements for low-voltage bridge configurations. The additional switch inclusion provides high dc conversion gain, which enables attractive fast charger applications. The performance of the proposed DAB-based converter with wide dc range has been investigated through several design techniques and comparisons. The use of use of silicon carbide (SiC) devices in higher power conversion significantly improves switching losses. However, unsupervised design will result in significant switching losses and increased electromagnetic emissions. Since the DAB-based converter's high switching frequency allows operation with smaller magnetics, the system stray capacitance plays a critical role. The common-mode current propagated through the system's stray capacitance generates undesired electromagnetic interferences (EMI) and impacts the soft-switching achievable range. To overcome the common-mode current circulation issue, design solutions have been employed to reduce the emergence of system stray capacitance. A harmonic analysis is further discussed along with evaluation of transformer design comparisons. The experimental results show the performance of the DAB-based converter in bidirectional operation and improved common mode current generation with respect to EMI emissions. The simulation and experimental results have been performed using a 5 kW rated power DAB-based converter with SiC power semiconductors.

CLLC resonant converters are an attractive option for battery charging applications due to their bidirectional power flow and high efficiency. Pulse frequency modulation (PFM) is the simple method to drive CLLC converters. However, PFM cannot regulate the output voltage under the light-load condition properly, which leads to high switching and core losses. Phase-shift modulation techniques, such as dual-phase-shift (DPS) modulation, can overcome this challenge. However, more improvements are demanded due to high circulating currents in phase-shift modulations. In this article, an improved modulation technique based on triple phase shift (TPS) has been applied in CLLC converters to improve the light-load efficiency. TPS modulation like any other phase-shift modulation keeps the switching frequency of CLLC converters fixed at the resonant frequency under the light-load condition and regulates the output voltage by its three phase-shift parameters. The improved TPS modulation has lower circulating current at the same average output current compared to DPS modulation. Therefore, higher efficiency, smaller peak, and RMS current values can be achieved under the light-load condition. In addition, the proposed TPS modulation has a better flexibility in regulating the output voltage under the light-load condition due to an extra phase-shift parameter compared to DPS modulation. The proposed TPS modulation has been analyzed thoroughly in this article, and a proper selection of phase-shift values has been explained to improve the efficiency of the converter. Finally, advantages of the improved TPS modulation have been validated by simulation and a 1-kW experimental setup.

Since microgrids with renewable generation and energy storage can achieve high reliability, they present an attractive solution for powering critical loads. Microgrids should be carefully planned and optimized to meet the power requirements of critical loads and justify their economic viability. Conventional microgrid design approaches consider a fixed power architecture, focusing mainly on improving the financial aspects of the design by sizing its energy sources. This paper introduces a new Vectorial Microgrid Optimization (VMO) design method for critical loads. The proposed VMO improves the microgrid design by 1) incorporating the selection of the microgrid power conversion architecture and the size of the energy sources into a unified design strategy, 2) implementing multi-objective optimization to find the desired balance between the microgrid power supply availability, net present cost, and power efficiency. Through the use of graph theory, the proposed VMO automates the architecture selection process. The benefits of the proposed VMO method are highlighted in a critical load case-study to find the optimal microgrid design. The obtained microgrid design is compared with the results of existing microgrid planning tools and the standard industry approach for powering critical loads.

Modern architectures of transformerless, three-phase-grid-connected photovoltaic (PV) inverter for 1000- and 1500-V commercial/residential applications are analyzed and compared from the point of view of the energy harvested during one year period, system efficiency, and power density. Scenarios for different ac grid voltage levels and inverters topologies are analyzed based on one- and two-stage solutions. The architectures with and without included dc/dc stage are compared from the point of view of the optimized power density. In the case of the two-stage PV inverter architecture, the mini-boost converter concept, presented in previous publications, is extended and the standard boost topology that employs 1200-V rated IGBTs and diodes is replaced by a multilevel, hybrid power converter topology that exhibits high efficiency due to the partial power processing and new classes of 900- and 650-V SiC and GaN devices employed. The inverter’s output filter design space (DS) has been researched from the point of view of the dc bus voltage variation. The cases are analyzed for fully controlled bus voltage at its minimum value and when allowed to vary in the full MPP range. Optimization results of the output filter DSs for the minimum and maximum operating dc bus voltage are compared in terms of the occupied volume in order to investigate whether it is possible to obtain more compact inverter stage by better control of dc bus voltage. The results show that in the case of controlled low dc bus voltage level, it is feasible to design a filter that occupies up to 50% less volume than the filter designed for the full MPP voltage variation. Even more, this can be achieved by maintaining the system efficiency. The simulation and experimental results complement the analysis of the 1000- and 1500-V grid-connected PV inverter systems.

Synchronous rectification (SR) technologies for $LLC$ resonant converters are essential to high-power, low-voltage battery chargers considering the excessive current stress on the rectifiers. Mainstream SR controllers employ an adaptive approach that measures the drain–source voltage during the SR turn-on phase ( $v_{\text {ds.on}}$ ). However, $v_{\text {ds.on}}$ is low-magnitude and sensitive to the voltage across parasitic inductors and capacitors. The distortion of $v_{\text {ds.on}}$ causes SR mistriggering, undermining the efficiency. This article proposes a noise-tolerant SR strategy based on the volt-second product (VSP) of SR drain–source voltage in the turn-off phase and rectifier current conduction time. The proposed method determines SR ON-time using high-magnitude voltage signals, which are tolerant of parasitic effects. In steady-state operation, the VSP method reduces the SR ON-time error caused by circuit parasitic components, whereas in transient operation, the algorithm dynamically adjusts SR ON-time to maintain a safe operation margin, preventing rectifier reverse current flow. Details of the implementation and timing sequence are provided to demonstrate the simplicity and effectiveness of the VSP SR algorithm. Experimental results show that compared with conventional adaptive SR, the proposed VSP SR decreases the ON-time error by 64% in the above-resonance operation and removes the reverse current in the below-resonance operation, which reduces the total loss by 3%.

Traditional voltage-mode and dual-loop current-mode linear schemes are widely used for controlling the fundamental dc–dc converters due to their simple implementation and fixed-frequency. Pulse-Width-Modulation (PWM) operation. While the dynamic response can be improved by pushing the control bandwidth, lower stability margins may lead to unexpected peak deviations in the inductor current and capacitor voltage, causing failures due to magnetic saturation or excessive voltage overshoot. The concept of dual-loop geometric-based control is introduced in this article by combining geometric state-plane analysis for the outer voltage loop with traditional current-control techniques for the inner loop. The traditional linear voltage compensator is replaced by a geometric alternative that can control the time-domain evolution of the state variables, providing a fast and reliable transient response by following a desired geometrical path to reach the steady-state operating point. In this way, stringent dynamic requirements can be successfully addressed by shaping the state variables’ time evolution by employing a simple geometric equation to define the voltage compensator. Circular trajectories are implemented using simple parametric equations resulting in remarkably well-defined, reliable transient behavior. Experimental results of dual-loop geometric controlled platforms validate the proposed control concept and highlight the strong contribution to the applied field made by this innovative controller.

The proliferation of photovoltaic (PV) installations across the globe has accelerated dramatically in the past decade covering home, rural, mobile, industrial, and utility-scale applications. In all these cases, improving payback time and energy production for PV installations is a very complex design tradeoff that involves multiple variables such as irradiance fluctuations, inverter efficiency, operating temperature variation, and PV panel type. In this paper, a detailed multivariate study of PV plant design is presented, resulting in an improved technique to increase the potential benefits of solar plants with lower capital costs. This new approach includes detailed consideration of the probabilistic hourly temperature and solar irradiation profile of the installation site, the efficiencies and operating areas of different grid-tie inverters, and detailed models of different PV modules in the optimal design process. The harvested energy, total costs, and payback time are the objective functions in this approach, while the number of series and parallel panels, the tilt angle, and inverter topology and PV module type are determined from a list of possible candidates. The optimization process is implemented for a sample system, and the results are compared to both a traditional and design software approach. It is seen that by applying the proposed approach with lower capital costs, the harvested energy, financial benefits, and the payback time can be improved by 9.3%, 1%, and 6.95%, respectively. Several case studies are then presented to investigate the sensitivity and robustness of the design with regard to the ambient temperature variation, solar irradiation fluctuation, and available surface area for PV module installation.

Solar plants based on single-stage conversion photovoltaic (PV) inverters (no dc-dc boost stage) have gained popularity due to their simplicity, high efficiency, and cost effectiveness. Existing PV plants mostly operate under 1000 V and are subject to wide dc-bus voltage variations due to the effect of PV cell temperature and the voltage of the maximum power point (well below the open-circuit voltage). In particular, attractive locations, such as U.S.-Canada mountain and central regions, are subject to extreme PV surface temperatures, making the dc-bus voltage variation a challenge for single-stage solar inverters. This paper investigates 1500 V solar inverters with a focus on dc-bus voltage range extension capabilities through novel modulation and power devices utilization. A comparative analysis with the existing 1000 V solar inverters is presented to illustrate the significant advantages of the wide dc-bus range in 1500 V systems. A lower voltage limit in the dc-bus is achieved by employing a novel voltage reactive power dc-bus control strategy and modified modulation. A higher dc-bus peak voltage is obtained by maximizing the use of power switches. As a result, the 1500 V inverter dc-bus voltage is significantly extended to capture energy under extreme PV surface temperatures, greatly improving the limited range of traditional 1000 V inverters. Simulations and experimental results using a three-phase three-level neutral point-clamped inverter level are presented to validate the proposed dc-bus extension range, control strategy, and modulation scheme.

The addition of a more distributed generation in the electrical grid is poised to rapidly improve the sustainability of electric power generation and energy security, while reducing cost. The electrical grid is an aging century-old large infrastructure mainly based on large (GW) electrical central power stations that have slow dynamics. Grid integration of distributed generators requires advanced power electronic conversion and control systems to successfully incorporate energy sources and storage systems with high efficiency, power quality, and reliability. The emerging adoption of distributed grid-connected converters brings unprecedented new capabilities and opportunities to support the electrical grid and increase the flexibility of distribution systems (existing ac and forthcoming dc). Future and novel technologies involved in the advancement of renewable and CO2 neutral distributed generation will include work in the areas of topologies, modulation, controllers, energy storage, and power quality, among other technical solutions to enable high penetration and reliable operation. As well, new innovations foresee the use of power converters to provide new ancillary functions for grid support and adopt evolving standards and grid codes.

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