ABSTRACT. Input-series output-parallel (ISOP) dc-dc converter systems require a dedicated input-voltage-sharing (IVS) controlstrategy. A centralized IVS control typically reduces system modularity and reliability. Thus, this paper adopts a decentralized IVS control method to the ISOP-connected three-phase dual-active bridge (DAB3) converter. It contributes to exploring decentralized control methods for ISOP systems by linking the theory of the negative incremental resistance to the instability of the IVS-transfer function. For the stability assessment, closed-loop input impedance models of the DAB3 converter are derived that include the effects of the control and the output-parallel connection into a single-input single-output (SISO) model. The derived analytical models are verified via multitone analyses of a switching model in offline simulations. This way, the stability of the whole ISOP system can be predicted solely based on the SISO model. The model-based stability regions are validated on a real-time simulation system of a two-module system at a switching frequency of 10kHz. Experimental results are presented for an eight-module system with an input voltageof 5kV.

ABSTRACT. Battery energy storage systems (BESS) play an essential role in modern grids by supporting renewable power systems, improving grid power quality through voltage and frequency regulation, and supporting electric vehicle (EV) charging stations. At the same time, and with the rapid growth of EVs, an enormous amount of EV batteries will be retired soon. These second-use EV batteries still have approximately 80% capacity and can be utilized in stationary applications like grid-connected BESSs to reduce the emissions from producing new batteries for energy storage systems. Directly producing multilevel AC from batteries reduces cost by eliminating the need for an explicit conventional inverter. In this paper, a framework is presented for optimizing the multilevel integration of power processing in BESSs, which is particularly applicable to BESSs with heterogeneous second-use batteries.

ABSTRACT. This paper proposes a unified admittance measurement method for three-phase system which is described in the sequence or the synchronous domain only by two-phase excitations in the sequence domain. There are couplings in positive and negative frequency components when the system is asymmetry. A measurement method which scans for a desired frequency range is proposed and it is based on two sets of excitation voltage applications and response current acquisitions at coupling frequencies. Two applications examples, a resistive-inductive (RL) circuit and an IPM motor in each domain, are investigated to validate the proposed measurement method for three-phase admittances.

ABSTRACT. This paper proposes a stability analysis method for a grid-forming inverter with a droop-control in the sequence domain. The analysis is based on the impedance method. First a system operating point is determined and linearized around the point to calculate output admittance of the inverter. Then output responses of the inverter are analyzed for an excitation small-signal in the frequency domain. The feedback control is processed only in the sequence domain. However, the complex conjugate operation in the droop control is found to transform variables equivalently into the synchronous domain. The frequency analysis is processed in a sequence/synchronous mixed domain.

ABSTRACT. Modular power conversion offers many technical and economic advantages as long as power sharing between modules is maintained. Power sharing through decentralized control (requiring no communication between modules and no central controller) offers the greatest flexibility. A droop-less decentralized control strategy has recently been demonstrated to achieve modular power sharing by incorporating nonlinearity in the integrator term in the control loop. This paper experimentally investigates the application of this control to input-parallel-output-parallel (IPOP) converters with buck output stages. It is found that converters with voltage-source-like characteristics at dc (such as voltage-mode CCM buck converters) require special consideration compared to other converters. The paper also explores the effect of this control on transient response. These features are demonstrated experimentally for voltage-mode and current-mode buck converters, including the effects of module-to-module variability.

ABSTRACT. This paper presents a 1~MHz four-phase, five-level coupled inductor flying capacitor multilevel (FCML) converter that tracks signals above the switching frequency. Combining multiple voltage levels, multiple phases, and coupled inductors, the effective switching frequency and achievable control bandwidth are multiplied by 16$\times$ while reducing the required inductor and capacitor sizes. A printed circuit board (PCB) embedded planar coupled inductor is designed to intrinsically balance the flying capacitor voltages, minimize output distortion, minimize output voltage/current ripple, and lower switch blocking voltages. The modular and scalable architecture enables the design of high control bandwidth power amplifiers tracking a signal higher than its switching frequency.

ABSTRACT. This paper introduces digitally controlled multiphase multistage hybrid boost converter (MMHBC) for high voltage capacitor charging applications. Rapid capacitor charging control approach is presented, and topological variations to improve efficiency are examined. The controller provides tight output current regulation, while maintaining real-time current balancing capabilities for superior thermal distribution and converter efficiency. The MMHBC is capable of rapid capacitor bank charging to high voltages by forcing maximum output current at the first stage, which translates into maximal output power during the whole charging period. The controller includes a system governor unit which facilitates additional control aspects for multiphase operation such as phase shedding, soft-start mechanism, and system protection. SMPS operation, rapid capacitor charging, and topological improvements are validated experimentally on a four-phase 12V-to-300V multiphase prototype with a maximum output power of 250W and power density of 2.5kW/Liter.

ABSTRACT. The multiphase series capacitor buck (SCB) converter is an attractive candidate voltage regulator module (VRM) in point-of-load (POL) applications. However, there needs tobe more discussion on the control issue and technique toachieve the fast-transient requirement for the SCB converter.This paper discusses the voltage stress and oscillation issue inthe SCB converter when applying the phase overlap transientimprovement control. A partial phase overlap transient controlwith simple implementation is proposed to achieve good transientperformance while maintaining the device voltage stress and avoiding flying capacitor voltage oscillation. The simulation andexperimental results under load step-up transient show theeffectiveness of the proposed control.

ABSTRACT. This paper presents various phase activation sequences to increase the output voltage of an N-phase Series-Capacitor (SerC) Buck converter, bypassing the traditional input-to-output voltage conversion limit of 1/N². Phase counts up to 16 are analysed with output voltages increasing by a factor of up to 7. With the increased output voltage now available to higher phase count configurations, the DPWM resolution can be increased by a factor of N by employing a novel method of minor duty increments (MDI). An experimental discrete prototype of an 11-phase, 48V-to-1.0V SerC Buck was fabricated to validate both the increase in the output voltage ceiling and DPWM resolution, as well as the MDI-DPWM output voltage linearity.

ABSTRACT. Hybrid switched-capacitor (SC) converters have gained popularity due to their efficient switch utilization and use of energy-dense capacitors, which allows them to achieve high efficiency and power density even at large conversion ratios. The Dickson converter is one such popular hybrid SC converter, as it can achieve the theoretical minimum switch stress rating. However, unlike other hybrid SC topologies that can automatically achieve full soft-charging by adding a single augmenting inductor at the output, certain Dickson variants require split-phase switching, wherein extra sub-phases are inserted into the control scheme in order to soft-charge all flying capacitors. Traditionally, split-phase timing has been calculated analytically, sometimes using imprecise models. This paper instead proposes an active control technique for detecting hard-charging events on the flying capacitors, such that the split-phase timing can be automatically tuned to converge on soft-charging operation. While this method is demonstrated on a resonant Dickson converter in this work, the technique can be applied to regulating split-phase applications and used to detect hard-charging events in general.

ABSTRACT. High breakdown voltage, low on-resistance, and high speed have made wide-bandgap power semiconductors suitable for many applications such as wireless power transfer, electric vehicles, hybrid and electric aircraft, and aerospace. However, the maximum power density of these devices is limited by the channel temperature rise. Thus, accurate temperature measurement of the active area is essential in research on wide-bandgap power semiconductors, which is often hampered by packaging and cooling methods. Employing temperature sensitive electrical parameters (TSEP) is a promising approach for the temperature measurement of power semiconductors. This paper uses a vector of three TSEPs, i.e., the gate-source voltage biased at weak, moderate, and strong inversion regions, to extract more information for accurate temperature measurement of the active area in GaN FETs.

ABSTRACT. The operation and failure modes of the flying capacitor multicell converter topology are well-known and the protections for Si IGBT-based converters are well established. However, when it comes to high voltage SiC MOSFET-based converters there are some particularities like shorter energy withstanding time, higher dv⁄dt and fault propagation that requires specific remedies. This paper provides an assessment of the failure modes for 7-level 13.8 kV AC 22 kV DC converter using 10 kV SiC MOSFET, an analysis of the fault propagation mechanisms between cells and the design of a transient voltage suppressor (TVS) diode-based protection module to prevent it.

ABSTRACT. On-Board Chargers (OBCs) comprising an ac-dc front-end and a subsequent isolated dc-dc converter stage represent a crucial component of Electric Vehicles (EVs), and must be able to charge the EV battery from both, a three-phase mains and a single-phase mains. Further, a lightweight and compact realization of the OBC is key in mobile applications. This requirement for high gravimetric and volumetric power density is often hindered by the large (electrolytic) dc-link capacitor required to buffer the power pulsation at twice the mains frequency in single-phase operation, which can be omitted by employing an active Power Pulsation Buffer (PPB) circuit allowing to minimize the overall capacitor volume. This paper introduces the Smart-dc-Link (S-Link)concept which improves the OBC performance by utilizing the active PPB circuitry also in three-phase operation: There, the S-Link facilitates a six-pulse dc-link voltage variation enabling a substantial switching loss reduction in the ac-dc converter front-end, while advantageously the dc output voltage can be kept constant.