The high-frequency magnetic linked solid-state transformer (SST) has the tremendous potential to solve the issues related to interfacing the grid with renewable energy sources and the non-linear loads as well as to provide the additional control functionalities. Several H-bridges are usually connected in series for the medium voltage grid integration of the SST. The number of the dual active bridge modules and the number of high-frequency magnetic links (HFMLs) usually increase with the increase of the number of series connected H-bridges. This increases the possibility of parameter mismatches and system instability. Therefore, the multiple-active bridge (MAB) dc-dc converter concept has been proposed for next generation SST, where multiple H-bridges share the same HFML. This configuration reduces the number of HFML and increases the cross-coupling power transfer capability. However, the design process of the MAB converter involves a multi-physics research in the field of power electronics, magnetics, switching, control, and energy management. In this paper, the detailed analytical modelling and the control technique of the silicon carbide (SiC)-based MAB converter are investigated. The small and large signal average models of the converter are developed and a voltage balance controller is designed for the better understanding of the controller characteristics. The effect of connecting several H-bridges to a single HFML is investigated in detail. Moreover, to reduce the switching loss, the converter topology adopts the SiC-based switching devices instead of the traditional silicon (Si)-based devices and the nanocrystalline magnetic material is used for the HFML design due to its low specific core loss. A scaled down laboratory prototype of the MAB converter is implemented in the laboratory and can be utilized as a basic building block for the next generation SST.

This paper presents a new hybrid three-phase cascaded modular multilevel inverter developed with reduced switch count for harvesting renewable energy. The basic module of the proposed inverter consists of six switches, three asymmetric dc links, and two blocking diodes. The inverter can generate six positive voltage states, which are negatively polarized by the end-side H-bridge unit. As a result, higher number of voltage levels are obtained with minimum number of switches that ensure reduced total harmonic distortion in the grid current. Additionally, the proposed inverter can operate at comparatively lower switching frequency, which decreases the switching loss. Most of the switches in each individual module conduct for a small period resulting in low conduction losses. The reduced switch count with the low switching and conduction losses increases the compactness and the efficiency of the proposed inverter. Multiple high-frequency magnetic links are utilized for the dc sources required for the proposed inverter to achieve inherent dc-link voltage balancing ability and galvanic isolation. The performance of the proposed inverter is validated by simulation and experimental investigations.

The pulse width modulation (PWM) techniques are becoming the game changer for multi-pulse power converter fed multilevel inverter-based induction motor drive (IMD) due to their significant impacts on power quality. In this paper, a new level shifted carrier-based PWM technique is proposed for a 5-level cascaded H-bridge (CHB) multilevel inverter driven by a 36-pulse ac-dc converter based IMD. To meet the power quality demand of IEEE-519 at grid side, a modular transformer is used, and the transformer is coupled to form a 36-pulse ac-dc converter. A 5-level CHB multilevel inverter is utilized on the motor side, which uses the proposed carrier based PWM technique for switching action to ensure superior performance of the IMD. The proposed PWM technique is named as third-harmonic injected inverted sinusoidal carrier PWM (THI2SCPWM), which utilizes 3 ^rd harmonic injection principle with inverted sinusoidal signal to form the proposed carrier signal. The 5-level CHB inverter used in the IMD shows less power loss and total harmonic distortion (THD) with the proposed THI2SCPWM technique. Moreover, the IMD with the THI2SCPWM shows low stator voltage THD, stator current THD, and smooth dynamic response. Apart from these, the THI2SCPWM mitigates the torque ripple of the IMD. The motor drive system with the THI2SCPWM technique is modeled and its performance is simulated on MATLAB/Simulink environment. A scaled down experimental setup is utilized to validate the superiority of the proposed PWM technique.

Due to global warming and shortage of fossil fuels, the grid-connected solar photovoltaic (PV) system has gained significant popularity all over the world. The modular multilevel cascaded (MMC) inverter is the natural choice for step-up transformer and line filter less direct medium voltage grid integration of solar PV systems. However, power quality and loss are the important issues while connecting the PV system to the medium voltage grid through MMC inverter. Modulation technique is the key to maintain output power quality, e.g., total harmonic distortion (THD) and to ensure low switching and conduction losses. In this paper, an advanced modulation technique named “triangle saturated common mode pulse width modulation (TSCMPWM)” control is proposed for a 3-phase 5-level MMC inverter-based grid-tied PV system. Compared to traditional modulation techniques, the proposed TSCMPWM control offers the lowest voltage THD as well as lower inverter power losses. Performance of the proposed modulation technique is evaluated in MATLAB/Simulink environment and tested with a reduced scale prototype test platform. Both simulation and experimental results show the effectiveness of the proposed modulation technique.

This article investigates the use of a dual-slope delta modulation (DSDM) technique to control a dynamic voltage restorer (DVR) that can mitigate the voltage sag problems in power systems. Traditionally, the DVR uses a pulsewidth modulation technique to control the power electronic switches in a voltage source inverter (VSI). However, the VSI suffers from several disadvantages, such as ripples in the output voltage, high dv/dt, and high total harmonic distortion. To overcome these problems, this article proposes a novel DSDM technique for a current source inverter (CSI) based DVR. The proposed DSDM technique generates the switching pulses for the power electronic switches in the CSI to produce the required missing voltage waveforms with the necessary phase angle jump to restore the load voltage to its nominal value following power systems faults. The DVR usually requires an energy storage device to support the system voltage during voltage sag, which is referred to as a storage-energy-supplied (SES) DVR. However, the energy storage device makes the DVR bulkier and costlier. A line-energy-supplied (LES) DVR scheme has been proposed in the literature that can eliminate the need for the energy storage device and hence has the potential to reduce the cost of the DVR. To validate the proposed DSDM technique, different types of fault-induced voltage sags are simulated in a radial distribution system. The proposed DSDM technique is tested to control the CSI-based SES-DVR and LES-DVR to mitigate the voltage sag. The simulation results show that the proposed DSDM technique is effective to mitigate the voltage sags by accurately injecting the required missing voltage both in magnitude and phase angle.

A data-driven smart solid-state transformer (SST) is an attractive building block for reliable and automated distribution power grids. An SST can work as an energy buffer unit in a completely embedded framework, similar to the information internet router, which facilitates a seamless information flow between the local grids and the data centers. An SST connects two or more electric subsystems and then distributes the energy to other subsystems based on a data-driven energy dispatch and intelligent management algorithm. The modern SST-based distribution grid has been envisioned to integrate several renewable energy sources, energy storage devices, and dc or ac loads in a standardized protocol-based plug-n-play technique, which may form a dc or an ac zonal microgrid system. Energy-efficient monitoring, coordination, control management, and economic dispatch are crucial issues for the optimal operation of an SST. This article proposes a data-driven coordinated control strategy for a three-stage multiple active bridge converter-based SST topology, which can ensure improved power quality of the distribution grid. A step-by-step controller design methodology is developed, which can coordinate several control data according to the various SST functionalities. The article presents the simulation and experimental results that validate the effectiveness of the proposed coordinated control approach.