With the rapid development of distributed energy resources, the Isolated Modular Multilevel DC-DC (IMM DC-DC) converter is becoming a promising solution for the interconnection of Medium Voltage (MV) and/or High Voltage (HV) DC grids. In this paper, the detailed mathematical model of the IMM DC-DC converter based on harmonic analysis is firstly established by considering the magnetizing inductance of the high-frequency transformer. Then, the real and reactive powers, transformer primary and secondary side currents, arm currents, and capacitor voltage ripples can be accurately determined. Due to the existence of the large arm inductance, the magnetizing inductance of the transformer is no longer negligible. Comparisons between the study results confirm that the magnetizing inductance has a significant impact on each of the aforementioned variables. The proposed analytical model can help achieve accurate sizing of the major components of the IMM DC-DC converter. The presented analysis is validated by both simulation in the Matlab/Simulink environment and experiment.

The dual-sided permanent magnet linear synchronous motors (PMLSMs) are very good candidates for high-speed Maglev trains due to high power density, fault tolerant capability and more robust gap stability. In this paper, an optimal design of a three-phase dual-sided PMLSM for high power density and high efficiency is investigated. An innovative optimization procedure based on Ansys-Maxwell and optiSLang software is utilized. The detailed finite-element analysis results are carried out to evaluate and verify the performance of the designed machine.

Cryogenic operation of power electronics converters plays a key role in the development of the future electric aircraft systems. Characterization of semiconductor switches in the cryogenic environment is pivotal for implementation of the cryogenic power electronics converters. This paper characterizes two groups of Planar and Trench SiC MOSFETs from room temperature to –175°C. The objective is to explore the impact of the cryogenic environment on static and dynamic behavior of the SiC MOSFETs. The dynamic characteristics of these semiconductor switches are investigated by using a double pulse test circuit. The test circuit is placed inside a cryogenic chamber, which is able to accurately adjust the temperature. Important dynamic characteristics such as voltage and current rise and fall times, turn-on, turn-off, and total switching energy losses are investigated. It is shown that the impacts of the cryogenic environment on the two groups of SiC MOSFETs are not identical. Furthermore, the impact of gate driver output voltage on the switching energy losses is discussed. The static characteristics of the SiC MOSFETs are explored by using the same cryogenic chamber and a curve tracer. Breakdown voltage, gate-source threshold voltage, on-state resistance, body diode forward voltage, and average transconductance are the static parameters that are measured.

Interconnection of Medium Voltage DC (MVDC) grids necessitates reliable and efficient DC-DC converters. Among the existing topologies, the Isolated Modular Multilevel DC-DC (IMM DC-DC) converter is a promising solution. In the technical literature, the impact of the magnetizing inductance of the High Frequency Transformer (HFT) on the operation and control of the converter is neglected. This paper analyzes the IMM DC-DC converter by focusing on the impact of the magnetizing inductance on the operation and control of the converter. Power transfer capability, arm current, reactive power, and soft-switching are discussed by considering the impact of the magnetizing inductance. This paper demonstrates that the magnetizing inductance of the HFT is a key parameter that needs to be carefully selected, as it can improve soft-switching operation, while reducing the power transfer capability of the converter. Simulation studies of a test system in the Matlab/Simulink software environment verify the presented modeling and analysis of the IMM DC-DC converter.

Increasing penetration rate of the renewable energy resources in conjunction with emergence of new dynamic loads such as electric vehicles, necessitate more flexible, efficient, and economical operation of the power grid. To maximize utilization of the power system infrastructure in an efficient and economical way, partially-rated solid-state transformer (PSST) has been proposed to control the power flow. In this paper, new PSSTs based on the AC-AC modular multilevel converter (MMC) are proposed. The proposed PSSTs borrow the salient features of the MMC and are capable of controlling power flow of the grid. Simulation studies in the PSCAD/EMTDC software environment are carried out to validate the performance and effectiveness of the proposed MMC-based PSSTs and the supporting control methods.

The modular multilevel converter (MMC) has become the most attractive converter topology for medium/high-power applications. However, uneven power loss distribution and thermal loading among the semiconductor devices of each submodule (SM) compromise the reliability and lifetime of the converter. In this paper, an active thermal loading control method for the MMC is proposed to simultaneously (i) minimize the total semiconductor power loss and (ii) balance the thermal loading of the semiconductor devices within each submodule. In the proposed method, a multi-objective optimization problem is formulated and solved to establish a trade-off between the total power loss and the power loss of the semiconductor devices with the highest thermal loading. Subsequently, the Pareto optimal solutions for circulating currents, output common-mode voltage, and capacitor voltages are explored. Performance and effectiveness of the proposed method are verified by simulation and experimental studies.

The modular multilevel converter (MMC) has become a potential candidate for medium/high-power applications including high-voltage direct current (HVDC) transmission, adjustable speed drive, and static var compensation systems. One of the technical challenges associated with the control of an MMC is the choice of pulse width modulation (PWM) strategy along with a submodule (SM) capacitor voltage balancing algorithm without imposing high computational burden on the controller and/or unnecessary switching transitions among the SMs. This paper proposes a distributed PWM strategy with an improved SM capacitor voltage balancing algorithm which aims at reducing the computational burden of the controller, the electro-magnetic interference and the switching frequency. The validity of the proposed PWM strategy and the SM capacitor voltage balancing algorithm is confirmed by simulation and experimental results.

Accurate battery models and precise calculation of the battery state-of-charge (SOC) are necessary for maximizing battery performance, realizing safe operation, and extending the operating range of hybrid electric and plug-in hybrid vehicles. In this paper, by taking various temperatures and charging/discharging current rates into consideration, a comprehensive battery model is developed in which the parameters are extracted based on experimental data. Furthermore, an online SOC estimation method based on the developed model and the Extended Kaiman Filter (EKF) is proposed. The accuracies of the battery model and the SOC estimation method at various temperatures and current rates are evaluated and validated based on a set of simulation and experimental studies.

This paper proposes a multivariable digital control design methodology for the voltage regulation of an islanded single distributed generation (DG) unit microgrid and its dedicated load. The controller design methodology is based on a family of spectral Multi-Input Multi-Output (MIMO) models of the microgrid system and performs open-loop shaping and system decoupling simultaneously by a convex optimization approach. The control design procedure includes: (i) the determination of a family of nonparametric models of the system at various operating points, (ii) the determination of the class of the controller, and (iii) system open-loop shaping by convex minimization of the summation of the square second norm of the errors between the system open-loop transfer functions and a desired open-loop transfer function. Based on the proposed design methodology, twodq-augmented voltage controllers are proposed to regulate the load voltages of a single-DG-unit microgrid. The proposed controllers guarantee the robust stability and satisfactory dynamic response of the system in spite of load parametric uncertainties and also the presence of nonlinear load. This paper describes the theoretical aspects involved in the design procedure of the controllers and evaluates the performance of the controllers based on simulation studies and experiments.

The modular multilevel converter (MMC) is one of the most potential converter topologies for medium/high power/voltage applications. One of the main technical challenges of an MMC is to eliminate/minimize the circulating currents within the legs. Circulating currents, if not properly controlled, increase the amplitude of capacitor voltage variations, rating values of the converter components and converter losses. This paper proposes a closed-loop circulating current control strategy for an MMC to specifically minimize the amplitude of capacitor voltage variations. The proposed strategy is based on adding an offset signal to the modulating signal of each arm. To minimize the amplitude of the capacitor voltage oscillations, an optimal circulating current component is determined and used as a reference signal for the current control of each MMC leg. Performance of the proposed control strategy is evaluated based on simulation studies in the MATLAB/Simulink environment. The reported study results demonstrate effectiveness of the proposed strategy to reduce the amplitude of the capacitor voltage oscillations.