With the number of electric vehicles (EVs) on the rise, there is a need for an adequate charging infrastructure to serve these vehicles. The emerging extreme fast-charging (XFC) technology has the potential to provide a refueling experience similar to that of gasoline vehicles. In this article, we review the state-of-the-art EV charging infrastructure and focus on the XFC technology, which will be necessary to support the current and future EV refueling needs. We present the design considerations of the XFC stations and review the typical power electronics converter topologies suitable to deliver XFC. We consider the benefits of using the solid-state transformers (SSTs) in the XFC stations to replace the conventional line-frequency transformers and further provide a comprehensive review of the medium-voltage SST designs for the XFC application.

Extreme Fast Charging of Electric Vehicles: A Technology Overview

A power generation system including a photovoltaic (PV) module to generate direct current (DC) power is provided. The system includes a controller to determine a maximum power point for the power generation system and a boost converter for receiving control signals from the controller to boost the power from the PV module to a threshold voltage required to inject sinusoidal currents into the grid. A DC to alternating current (AC) multilevel inverter is provided in the system to supply the power from the PV module to a power grid. The system also includes a bypass circuit to bypass the boost converter when an input voltage of the DC to AC multilevel inverter is higher than or equal to the threshold voltage.

Solar inverter and control method

Fuel cell power systems offer a unique combination of high efficiency, wide size range, modularity, and compatibility with cogeneration. The development of complete energy systems that realize the benefits offered by fuel cell technology requires a basic understanding of fuel cell system components as well as the associated power electronics for different applications. This paper explains the basic characteristics of a fuel cell system, describes the different types of fuel cells and their current state of development, and discusses the potential application of these systems to transportation and stationary power. Particular emphasis is given to the electrical characteristics of the fuel cell, which is a relatively stiff power source. Power electronic systems are essential for making the fuel cell electrical output compatible with most loads. Options for dc–dc and dc–ac power conversion circuits are given with a discussion of the distinct features of each circuit that can be used for system planning purposes. The interaction between a fuel cell and a single-phase ac inverter load is highlighted because of the widespread applicability of this particular combination.

Fuel Cell Power Systems and Applications

Since most of renewable energy resources are dc type, dc microgrids find more attention in deregulated power systems for improvement of reliability and efficiency of the system. In dc microgrids, there is no zero-crossing in current and voltage; so the circuit breaking and fault current limiting are serious concerns. Conventional thyristor-based dc fault current limiters are attractive solutions for tackling this problem. However, they impose permanent interruption on the system in case of temporary fault. In this paper, a novel hybrid circuit breaker (HCB) is proposed to improve power quality of the system by adopting different limiting behaviors for permanent and temporary faults. The proposed HCB transfers load power through a mechanical circuit breaker (MCB) under normal condition. Upon fault occurrence in both sides of the HCB, the fault current is transferred from the MCB to a current limiting path incorporating a zero voltage switching (ZVS) transition mechanism. The HCB limits the fault current for a predefined duration and then interrupts the faulty feeder. In case of temporary fault, the current is returned to the MCB in ZVS. The HCB operation principle is discussed in different operation modes. Capabilities of the proposed HCB are tested and verified by different experiments carried out on a prototype.

Hybrid DC Circuit Breaker and Fault Current Limiter With Optional Interruption Capability

This paper proposes a new modular flexible power electronic transformer (FPET). The proposed FPET is flexible enough to meet future needs of power electronic centralized systems. The main feature of the FPET is the independent operation of modules each of which contains one port. Each port can be considered as input or output, because bidirectional power flow is provided. The modules are connected to a common dc link that facilitates energy transfer among modules as well as ports. Therefore, a multiport system is developed, which the ports can operate independently. This merit is important for applications, where input and output voltages are different in many parameters. A comparison study is carried out to clarify the pros and cons of expandable FPET. In addition, the measurement results of a laboratory prototype are presented to verify the capabilities of FPET in providing different output waveforms and controlling load side reactive power.

Flexible Power Electronic Transformer

A multilevel converter-based, intelligent, universal transformer includes back-to-back, interconnected, multi-level converters coupled to a switched inverter circuit via a high-frequency transformer. The input of the universal transformer can be coupled to a high-voltage distribution system and the output of the universal transformer can be coupled to low-voltage applications. The universal transformer is smaller in size than conventional copper-and-iron based transformers, yet provides enhanced power quality performance and increased functionality.

Multilevel converter based intelligent universal transformer

A multifunction hybrid intelligent universal transformer includes a conventional transformer coupled with power electronics on the secondary side to enhance the functionality of power conversion. The universal transformer includes features for overcoming the deficiencies associated with conventional transformers, including voltage sag compensation, instantaneous voltage regulation, outage compensation, capacitor switching protection, harmonic compensation, single-phasing protection, DC output, and variable frequency output.

Multifunction hybrid intelligent universal transformer

A universal hybrid solid-state switchgear for power transmission or distribution systems incorporates a fast mechanical switch and solid-state power electronics switching circuits to provide circuit breaker and fault current limiting applications.

Multifunction hybrid solid-state switchgear

A photovoltaic (PV) integrated variable frequency drive system having a variable frequency drive and an energy source. The variable frequency drive having a back end inverter, a DC bus electrically connected to the back end inverter, and an active front end electrically connected to the DC bus to facilitate bi-directional power flow to and from a power grid. The energy source being electrically connected to the DC bus.

Photovoltaic integrated variable frequency drive

An apparatus for DC fast charging of an electric vehicle includes an active front end AC-DC converter and an isolated DC-DC converter. The active front end AC-DC converter is adapted to rectify a medium voltage alternating current (AC) from a utility grid to a high voltage direct current (DC). The isolated DC-DC converter is adapted to transform the high voltage DC to a low voltage DC for charging the electric vehicle.

Jih-Sheng Lai

Papers

Multilevel converter based intelligent universal transformer

Multifunction hybrid intelligent universal transformer

Multifunction hybrid solid-state switchgear

Photovoltaic integrated variable frequency drive

Medium voltage stand alone dc fast charger