Experimental validation of the solid state substation with embedded energy storage concept

This paper proposes the concept of integrating the energy storage within a Medium Voltage to Low Voltage solid state substation in order to provide new features compatible with the requirements from future more intelligent grids. The principles for the system development are presented and the role of each subsystem is explained. The experimental evaluation of the 1.9kVrms/25kVA substation with 1.5MJ of supercapacitor storage consists of subsystem tests showing the waveform quality, step transients as well as system tests of the efficiency, ride-through and power peak shaving operation

Multiport Converter Topologies for Distributed Energy System Applications

In the midst of a present-day global energy renaissance, power electronics has evolved into a top-tier technology discriminator in distributed energy resource (DER) systems. Faced with the formidable task of integrating various types of DER technologies into singular systems, there is a growing appetite for multiport converter (MPC) design. In response, three unique DER MPC topologies are presented: the power sharing converter (PSC), the multi-level nine switch converter (ML9SC), and the modular fuel cell hybrid energy storage (MFC+HES) converter. First, low-voltage and medium-voltage PSC architectures are shown to decouple series-connected source currents and enable independent control. Multidimensional modeling and analysis is then discussed. Next, three system designs are discussed: single-zone, dual-zone, and multi-zone. Each implements PSC technology and high-frequency isolated full-bridge converters to interface multiple fuel cell sources to a medium voltage grid via a single multilevel neutral point clamped inverter interface. A 1-MW simulation and a reduced-scale hardware prototype offer collaborative insight into the inherit benefits of the proposed PSC systems: increased output power, operational flexibility, thermal balancing, source availability, and cost-effectiveness. Secondly, the ML9SC is presented as a component-minimized multi-port converter with low cost, high efficiency, high power quality, and low noise. The multiport characteristic of the ML9SC can be effectively employed in uninterruptible power systems, six-phase wind generators, and doubly-fed induction wind generators. Next, operating constraints and modulation index limits are analyzed at different operating conditions. Loss breakdown is analyzed and compared with the conventional back-to-back multi-level converter. Finally, simulation results are included as proof of concept. Lastly, the proposed MFC+HES converter integrates energy-dense MFC technology with power-dense storage technology. System modularization and hybridization are discussed initially, followed by a selection between supercapacitors and lithium-ion batteries (LIBs). Next, system topology and design is discussed, and the MFC and LIBs are electrically modeled such that Middlebrook’s Extra Element Theorem can mitigate unwanted system resonance and optimize system design. Simulation and hardware results for a 100W MFC+HES system realizes a 300% boost current response capability as well as the following system benefits: limp-home capability, evenly distributed heat/aging, and maximized output power

Industrial applications of power electronics

Electronic applications use a wide variety of materials, knowledge, and devices, which pave the road to creative design, development, and the creation of countless electronic circuits with the purpose of incorporating them in electronic products. Therefore, power electronics have been fully introduced in industry, in applications such as power supplies, converters, inverters, battery chargers, temperature control, variable speed motors, by studying the effects and the adaptation of electronic power systems to industrial processes. Recently, the role of power electronics has been gaining special significance regarding energy conservation and environmental control. The reality is that the demand for electrical energy grows in a directly proportional manner with the improvement in quality of life. Consequently, the design, development, and optimization of power electronics and controller devices are essential to face forthcoming challenges. In this Special Issue, 19 selected and peer-reviewed papers discussing a wide range of topics contribute to addressing a wide variety of themes, such as motor drives, AC-DC and DC-DC converters, electromagnetic compatibility and multilevel converters.publishersversionpublishe

Special Power Electronics Converters and Machine Drives with Wide Band-Gap Devices

Power electronic converters play a key role in power generation, storage, and consumption. The major portion of power losses in the converters is dissipated in the semiconductor switching devices. In recent years, new power semiconductors based on wide band-gap (WBG) devices have been increasingly developed and employed in terms of promising merits including the lower on-state resistance, lower turn-on/off energy, higher capable switching frequency, higher temperature tolerance than conventional Si devices. However, WBG devices also brought new challenges including lower fault tolerance, higher system cost, gate driver challenges, and high dv/dt and resulting increased bearing current in electric machines. This work first proposed a hybrid Si IGBTs + SiC MOSFETs five-level transistor clamped H-bridge (TCHB) inverter which required significantly fewer number of semiconductor switches and fewer isolated DC sources than the conventional cascaded H-bridge inverter. As a result, system cost was largely reduced considering the high price of WBG devices in the present market. The semiconductor switches operated at carrier frequency were configured as Silicon Carbide (SiC) devices to improve the inverter efficiency, while the switches operated at fundamental output frequency (i.e., grid frequency) were constituted by Silicon (Si) IGBT devices. Different modulation strategies and control methods were developed and compared. In other words, this proposed SiC+Si hybrid TCHB inverter provided a solution to ride through a load short-circuit fault. Another special power electronic, multiport converter, was designed for EV charging station integrated with PV power generation and battery energy storage system. The control scheme for different charging modes was carefully developed to improve stabilization including power gap balancing, peak shaving, and valley filling, and voltage sag compensation. As a result, the influence on the power grid was reduced due to the matching between daily charging demand and adequate daytime PV generation. For special machine drives, such as slotless and coreless machines with low inductance, low core losses, typical drive implementations using conventional silicon-based devices are performance limited and also produce large current and torque ripples. In this research, WBG devices were employed to increase inverter switching frequency, reduce current ripple, reduce filter size, and as a result reduce drive system cost. Two inverter drive configurations were proposed and implemented with WBG devices in order to mitigate such issues for 2-phase very low inductance machines. Two inverter topologies, i.e., a dual H-bridge inverter with maximum redundancy and survivability and a 3-leg inverter for reduced cost, were considered. Simulation and experimental results validated the drive configurations in this dissertation. An integrated AC/AC converter was developed for 2-phase motor drives. Additionally, the proposed integrated AC/AC converter was systematically compared with commonly used topologies including AC/DC/AC converter and matrix converters, in terms of the output voltage/current capability, total harmonics distortion (THD), and system cost. Furthermore, closed-loop speed controllers were developed for the three topologies, and the maximum operating range and output phase currents were investigated. The proposed integrated AC/AC converter with a single-phase input and a 2-phase output reduced the switch count to six and resulting in minimized system cost and size for low power applications. In contrast, AC/DC/AC pulse width modulation (PWM) converters contained twelve active power semiconductor switches and a common DC link. Furthermore, a modulation scheme and filters for the proposed converter were developed and modeled in detail. For the significantly increased bearing current caused by the transition from Si devices to WBG devices, advanced modeling and analysis approach was proposed by using coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which took into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. Possible bearing current issues in axial-flux machines, and possibilities of computation time reduction, were also discussed. Two experimental validation approaches were proposed: the time-domain analysis approach to accurately capture the time transient, the stationary testing approach to measure bearing capacitance without complex control development or loading condition limitations. In addition, two types of motors were employed for experimental validation: an inside-out N-type PMSM was used for rotating testing and stationary testing, and an N-type BLDC was used for stationary testing. Possible solutions for the increased CMV and bearing currents caused by the implementation of WGB devices were discussed and developed in simulation validation, including multi-carrier SPWM modulation and H-8 converter topology

Grid-Connected Energy Storage Systems: State-of-the-Art and Emerging Technologies

High penetration of renewable energy resources in the power system results in various new challenges for power system operators. One of the promising solutions to sustain the quality and reliability of the power system is the integration of energy storage systems (ESSs). This article investigates the current and emerging trends and technologies for grid-connected ESSs. Different technologies of ESSs categorized as mechanical, electrical, electrochemical, chemical, and thermal are briefly explained. Especially, a detailed review of battery ESSs (BESSs) is provided as they are attracting much attention owing, in part, to the ongoing electrification of transportation. Then, the services that grid-connected ESSs provide to the grid are discussed. Grid connection of the BESSs requires power electronic converters. Therefore, a survey of popular power converter topologies, including transformer-based, transformerless with distributed or common dc-link, and hybrid systems, along with some discussions for implementing advanced grid support functionalities in the BESS control, is presented. Furthermore, the requirements of new standards and grid codes for grid-connected BESSs are reviewed for several countries around the globe. Finally, emerging technologies, including flexible power control of photovoltaic systems, hydrogen, and second-life batteries from electric vehicles, are discussed in this article.This work was supported in part by the Office of Naval Research Global under Grant N62909-19-1-2081, in part by the National Research Foundation of Singapore Investigatorship under Award NRFI2017-08, and in part by the I2001E0069 Industrial Alignment Funding. (Corresponding author: Josep Pou.

High Power, Medium Frequency, and Medium Voltage Transformer Design and Implementation

Many industrial applications that require high-power and high-voltage DC-DC conversion are emerging. Space-borne and off-shore wind farms, fleet fast electric vehicle charging stations, large data centers, and smart distribution systems are among the applications. Solid State Transformer (SST) is a promising concept for addressing these emerging applications. It replaces the traditional Low Frequency Transformer (LFT) while offering many advanced features such as VAR compensation, voltage regulation, fault isolation, and DC connectivity. Many technical challenges related to high voltage stress, efficiency, reliability, protection, and insulation must be addressed before the technology is ready for commercial deployment. Among the major challenges in the construction of SSTs are the strategies for connecting to Medium Voltage (MV) level. This issue has primarily been addressed by synthesizing multicellular SST concepts based on modules rated for a fraction of the total MV side voltage and connecting these modules in series at the input side. Silicon Carbide (SiC) semiconductor development enables the fabrication of power semiconductor devices with high blocking voltage capabilities while achieving superior switching and conduction performances. When compared to modular lower voltage converters, these higher voltage semiconductors enable the construction of single-cell SSTs by avoiding the series connection of several modules, resulting in simple, reliable, lighter mass, more power dense, higher efficiency, and cost effective converter structures. This dissertation proposes a solution to this major issue. The proposed work focuses on the development of a dual active bridge with high power, medium voltage, and medium frequency control. This architecture addresses the shortcomings of existing modular systems by providing a more power dense, cost-effective, and efficient solution. For the first time, this topology is investigated on a 700kW system connected to a 13kVdc input to generate 7.2kVdc at the output. The use of 10kV SiC modules and gate drivers in an active neutral point clamped to two level dual active bridge converter is investigated. A special emphasis will be placed on a comprehensive transformer design that employs a multi-physics approach that addresses all magnetic, electrical, insulation, and thermal aspects. The transformer is designed and tested to ensure the system’s viability

Power quality improvement utilizing photovoltaic generation connected to a weak grid

Microgrid research and development in the past decades have been one of the most popular topics. Similarly, the photovoltaic generation has been surging among renewable generation in the past few years, thanks to the availability, affordability, technology maturity of the PV panels and the PV inverter in the general market. Unfortunately, quite often, the PV installations are connected to weak grids and may have been considered as the culprit of poor power quality affecting other loads in particular sensitive loads connected to the same point of common coupling (PCC). This paper is intended to demystify the renewable generation, and turns the negative perception into positive revelation of the superiority of PV generation to the power quality improvement in a microgrid system. The main objective of this work is to develop a control method for the PV inverter so that the power quality at the PCC will be improved under various disturbances. The method is to control the reactive current based on utilizing the grid current to counteract the negative impact of the disturbances. The proposed control method is verified in PSIM platform. Promising results have been obtaine

Experimental validation of the solid state substation with embedded energy storage concept

This paper proposes the concept of integrating the energy storage within a Medium Voltage to Low Voltage solid state substation in order to provide new features compatible with the requirements from future more intelligent grids. The principles for the system development are presented and the role of each subsystem is explained. The experimental evaluation of the 1.9kVrms/25kVA substation with 1.5MJ of supercapacitor storage consists of subsystem tests showing the waveform quality, step transients as well as system tests of the efficiency, ride-through and power peak shaving operation