Mahshid Amirabadi

Bio: Mahshid Amirabadi is an academic researcher from Northeastern University. The author has contributed to research in topics: Capacitor & Converters. The author has an hindex of 17, co-authored 72 publications receiving 856 citations. Previous affiliations of Mahshid Amirabadi include Texas A&M University & University of Illinois at Urbana–Champaign.

High-Frequency AC-Link PV Inverter

Abstract: In this paper, a high-frequency ac-link photovoltaic (PV) inverter is proposed. The proposed inverter overcomes most of the problems associated with currently available PV inverters. In this inverter, a single-stage power-conversion unit fulfills all the system requirements, i.e., inverting dc voltage to proper ac, stepping up or down the input voltage, maximum power point tracking, generating low-harmonic ac at the output, and input/output isolation. This inverter is, in fact, a partial resonant ac-link converter in which the link is formed by a parallel inductor/capacitor ( LC) pair having alternating current and voltage. Among the significant merits of the proposed inverter are the zero-voltage turn-on and soft turn-off of the switches which result in negligible switching losses and minimum voltage stress on the switches. Hence, the frequency of the link can be as high as permitted by the switches and the processor. The high frequency of operation makes the proposed inverter very compact. The other significant advantage of the proposed inverter is that no bulky electrolytic capacitor exists at the link. Electrolytic capacitors are cited as the most unreliable component in PV inverters, and they are responsible for most of the inverters' failures, particularly at high temperature. Therefore, substituting dc electrolytic capacitors with ac LC pairs will significantly increase the reliability of PV inverters. A 30-kW prototype was fabricated and tested. The principle of operation and detailed design procedure of the proposed inverter along with the simulation and experimental results are included in this paper. To evaluate the long-term performance of the proposed inverter, three of these inverters were installed at three different commercial facilities in Texas, USA, to support the PV systems. These inverters have been working for several months now.

A Multiport AC Link PV Inverter With Reduced Size and Weight for Stand-Alone Application

Abstract: In this paper, a multiport high-frequency ac link inverter is proposed as the power electronic interface between the photovoltaic (PV) modules, battery energy storage system, and three-phase ac load. In this inverter, a single-stage power conversion unit fulfills all the system requirements, i.e., inverting dc voltage to proper ac, stepping up or down the voltage, generating low harmonic ac current at the output, and input/output isolation. The ac link is formed by a parallel ac inductor/capacitor (LC) pair having low reactive ratings. A single-input/single-output partial resonant inverter has already been proposed by the present authors. This paper verifies the possibility of extending this topology to multiport partial resonant converters. The proposed converter is believed to overcome most of the shortcomings associated with the currently available multiport PV inverters. It is a single-stage ac link power conversion system with zero voltage turn on and soft turn off of the switches, which has very small switching losses, compact size, and light weight. The proposed converter does not contain any electrolytic capacitors at the link, which increases the reliability of this converter to a great extent. In the proposed inverter, PV side and ac side are isolated; however, if galvanic isolation is required, a single-phase high-frequency transformer can be added to the link. This converter can both step up or down the voltage, regardless of the presence of a transformer. Although this configuration is extendable to the grid-connected applications, in this paper, only the stand-alone application is considered. The performance of the proposed multiport inverter is verified through simulations and experiments.

E-Mobility — Advancements and Challenges

Abstract: Mobile platforms cover a broad range of applications from small portable electric devices, drones, and robots to electric transportation, which influence the quality of modern life. The end-to-end energy systems of these platforms are moving toward more electrification. Despite their wide range of power ratings and diverse applications, the electrification of these systems shares several technical requirements. Electrified mobile energy systems have minimal or no access to the power grid, and thus, to achieve long operating time, ultrafast charging or charging during motion as well as advanced battery technologies are needed. Mobile platforms are space-, shape-, and weight-constrained, and therefore, their onboard energy technologies such as the power electronic converters and magnetic components must be compact and lightweight. These systems should also demonstrate improved efficiency and cost-effectiveness compared to traditional designs. This paper discusses some technical challenges that the industry currently faces moving toward more electrification of energy conversion systems in mobile platforms, herein referred to as E-Mobility, and reviews the recent advancements reported in literature.

Soft switched ac-link AC/AC and AC/DC buck-boost converter

Abstract: A novel soft switched AC-link buck-boost converter for medium and high power AC-AC and AC-DC applications is proposed. The proposed configuration uses two bi-directional switches per leg of the converter resulting in 12 bi-directional switches for a three-phase to three-phase topology. Power transfer from input to output is accomplished via a link inductor which is first charged from the input phases, then discharged to the output phases with a precisely controllable current PWM technique. Capacitance in parallel with the link inductor produces low turn-off losses. Turn-on is always at zero voltage as each switch swings from reverse to forward bias. Reverse recovery is with low di/dt and also is buffered due to the link capacitance. The soft switching nature of the converter permits use of slower switches with high link frequencies. Converter operation is bi-directional and supports any input or output power factor or voltage, within the current and voltage capacity of the switches. Simulation results showing converter operation under different conditions are presented along with loss calculations. The topology is expected to offer relatively low weight, compact and efficient power converters and motor drives.

A Single-Stage Soft-Switching High-Frequency AC-Link PV Inverter: Design, Analysis, and Evaluation of Si-Based and SiC-Based Prototypes

Abstract: This paper proposes a high-power-density and reliable inverter topology, which transfers the maximum power of a PV array to the load in one power conversion stage. The single-stage power conversion, along with the soft-switching capability of the proposed three-phase PV inverter promises high efficiency at all operating points. Instead of a capacitive dc link that decouples the dc–dc converter and the voltage source inverter in traditional two-stage PV inverters, a high-frequency capacitive ac link is employed in the proposed inverter, which enables exploiting a very small film capacitor, rather than a bulky electrolytic capacitor, for transferring power. Eliminating electrolytic capacitors prolongs the lifetime of this inverter. Considering the long lifetime of PV modules, this feature is of high importance in PV applications. The high-frequency ac link also allows using high-frequency transformers for providing galvanic isolation. Therefore, this inverter is expected to have a very high power density. This paper presents principles of the operation and control, design, and analysis of this inverter, and verifies the performance of the inverter through two prototypes: a 2-kW Si-based prototype and a 2-kW SiC-based prototype operating at different switching frequencies.

Energy Management of a Fuel Cell/Supercapacitor/Battery Power Source for Electric Vehicular Applications

Abstract: This paper presents an energy management method in an electrical hybrid power source (EHPS) for electric vehicular applications. The method is based on the flatness control technique (FCT) and fuzzy logic control (FLC). This EHPS is composed of a fuel cell system as the main source and two energy storage sources (ESSs)-a bank of supercapacitors (SCs) and a bank of batteries (BATs)-as the auxiliary source. With this hybridization, the volume and mass of the EHPS can be reduced, because the high energy density of BAT and high power density of SC are utilized. In the proposed novel control strategy, the FCT is used to manage the energy between the main and the auxiliary sources, and the FLC is employed to share the power flow in the ESS between the SC and the BAT. The power sharing depends on the load power and the state of charge of the SC and the BAT. EHPS is controlled by the regulation of the stored electrostatic energy in the dc buses. The main property of this strategy is that the energy management in the power source is carried out with a single general control algorithm in different operating modes, consequently avoiding any algorithm commutation. An EHPS test bench has been assembled and equipped with a real-time system controller based on a dSPACE. The experimental results validate the efficiency of the proposed control strategy.

Design and Demonstration of a 3.6-kV–120-V/10-kVA Solid-State Transformer for Smart Grid Application

Abstract: Solid-state transformer (SST) has been regarded as one of the most important emerging technologies for traction system and smart grid application. This paper presents the system design and performance demonstration of a high-voltage SST lab prototype that works as the active grid interface in smart grid architecture. Specifically, the designs of the key components of the system, including both power stage and controller platform, are presented. In addition, the advanced control system is developed to achieve high-performance operation. Furthermore, integration issues of SST with dc microgrid are presented. Lastly, tests under different scenarios are conducted to verify the following advanced features of the presented SST technology: 1) VAR compensation; 2) voltage regulation; 3) source voltage sag operation; and 4) microgrid integration.

Power management and power flow control with back-to-back converters in a utility connected microgrid

Abstract: This paper proposes a method for power flow control between utility and microgrid through back-to-back converters, which facilitates desired real and reactive power flow between utility and microgrid. In the proposed control strategy, the system can run in two different modes depending on the power requirement in the microgrid. In mode-1, specified amount of real and reactive power are shared between the utility and the microgrid through the back-to-back converters. Mode-2 is invoked when the power that can be supplied by the DGs in the microgrid reaches its maximum limit. In such a case, the rest of the power demand of the microgrid has to be supplied by the utility. An arrangement between DGs in the microgrid is proposed to achieve load sharing in both grid connected and islanded modes. The back-to-back converters also provide total frequency isolation between the utility and the microgrid. It is shown that the voltage or frequency fluctuation in the utility side has no impact on voltage or power in microgrid side. Proper relay-breaker operation coordination is proposed during fault along with the blocking of the back-to-back converters for seamless resynchronization. Both impedance and motor type loads are considered to verify the system stability. The impact of dc side voltage fluctuation of the DGs and DG tripping on power sharing is also investigated. The efficacy of the proposed control ar-rangement has been validated through simulation for various operating conditions. The model of the microgrid power system is simulated in PSCAD.

Review of electrical energy storage system for vehicular applications

Abstract: Recently, automotive original equipment manufacturers have focused their efforts on developing greener propulsion solutions in order to meet the societal demand and ecological need for clean transportation, so the development of new energy vehicle (NEV) has become a consensus among governments and automotive enterprises. Efficient electrical energy storage system (EESS) appears to be very promising for meeting the rapidly increased requirements of vehicular applications. It is necessary to understand performances of electrical energy storage technologies. Therefore, this paper reviews the various electrical energy storage technologies and their latest applications in vehicle, such as battery energy storage (BES), superconducting magnetic energy storage (SMES), flywheel energy storage (FES), ultra-capacitor (UC) energy storage (UCES) and hybrid energy storage (HES). The research priorities and difficulties of each electrical energy storage technology are also presented and compared. Afterwards, the key technologies of EESS design for vehicles are presented. In addition, several conventional EESSs for vehicle applications are also analyzed; the comparison on advantages and disadvantages of various conventional EESSs is highlighted. From the rigorous review, it is observed that almost all current conventional EESSs for vehicles cannot meet a high-efficiency of power flow over the full operation range; optimization of EESS and improved control strategies will become an important research topic. Finally, this paper especially focuses on a type of linear engine, a brand new automotive propulsion system used for NEV; the guiding principle of EESS design for the new type of linear engine is proposed, an overview of a novel hybrid EESS based on hybrid power source and series–parallel switchover of UC with high efficiency under wide power flow range for the type of linear engine is presented, and advanced features of the novel hybrid EESS are highlighted.