Showing papers by "Srdjan Lukic published in 2022"

Gate Driver Power Supply with Air-gapped Transformer for Medium Voltage Converters

Abstract: In this paper, a gate driver power supply (GDPS) for SiC MOSFETs in medium-voltage power converters is presented. The main design considerations of the proposed GDPS are high voltage isolation, low coupling capacitance, and regulated output voltage. We present a design procedure for the transformer with an air gap to achieve the design objectives. Due to the air gap, the coupling factor of the proposed transformer is significantly lower than that of transformers without air gaps. Therefore, a series-series compensation network is designed to drive the loosely coupled magnetic link to achieve high-efficiency power transfer and stable output voltage. The input and output voltages of the proposed power supply are designed to be 24 VDC, and the rated output power is 20 W. The proposed transformer exceeds a partial discharge inception voltage of 20 kV RMS and has a coupling capacitance of 2.1 pF. The enclosure of the power supply is characterized by a creepage distance of 152 mm and a clearance distance of 80 mm between the input and output terminals of the GDPS. Compared with the commercially available high voltage gate driver power supply ISO5125I-120, the output power of the developed power supply is increased by four times, and the isolation strength doubled.

Decentralized Interleaving of Cascaded H-Bridge Multi-Level Converters

Abstract: This document proposes a simple method to decentralize the interleaving for cascaded H bridge (CHB) converters. In the proposed approach, a single signal sent from the Central controller (CC) to Local Controllers (LC) contains information about the desired pulse width and is synchronized with respect to other LC. While centralized controllers need individual signals for each of the CHB modules, the proposed method requires a single signal per phase which decreases the number of PWM channels needed. A detailed explanation of the proposed method is presented. Experimental results are presented that show the interleaving of two CHB modules for an example DC to AC application.

Design and Implementation of DC-Transformer using 10 kV SiC MOSFET for Medium-Voltage Extreme Fast Charger

Abstract: The medium-voltage (MV) electric vehicle (EV) fast charger is foreseen as a feasible way to improve efficiency and power density of future EV charging infrastructure. The emerging 10 kV SiC MOSFET enables direct connection to MV utility using a single-module in basic topology, achieving a noticeable enhancement of system simplicity. In this paper, an active neutral- point-clamped (ANPC) based dual-active-bridge (DAB) converter using 10 kV SiC MOSFET is presented. The design and implementation of critical components including busbar, isolated gate driver and MV transformer are elaborated subsequently. The tradeoff between insulation of MV system against power density is discussed. The dc-transformer (DCX) is tested under a 10 kV to 700 V voltage ratio, with 99.1 % efficiency at 30 kW power throughput.

An Automated Deployment and Testing Framework for Resilient Distributed Smart Grid Applications

Abstract: Executing distributed cyber-physical software processes on edge devices that maintains the resiliency of the overall system while adhering to resource constraints is quite a challenging trade-off to consider for developers. Current approaches do not solve this problem of deploying software components to devices in a way that satisfies different resilience requirements that can be encoded by developers at design time. This paper introduces a resilient deployment framework that can achieve that by accepting user-defined constraints to optimize redundancy or cost for a given application deployment. Experiments with a microgrid energy management application developed using a decentralized software platform show that the deployment configuration can play an important role in enhancing the resilience capabilities of distributed applications as well as reducing the resource demands on individual nodes even without modifying the control logic.

Assessment of Anti-Islanding Schemes on a Distribution System with High DER Penetration and Dynamic VAR Compensators

Abstract: The recently introduced power-electronics-based dynamic VAR compensator (DVC) offers an effective solution in mitigating the impacts that high penetration distributed energy resources (DERs) have on distribution systems. One of the concerns about adopting these devices is their impact on distribution system protection, especially islanding detection. This paper proposes a hardware-in-loop (HIL) test-bed based approach to investigate the performance of islanding detection schemes on a distribution feeder. This approach facilitates the assessment of protection system performance under more realistic conditions by emulating actual devices and a distribution system. The results are based on an actual case study that is outlined to show the effectiveness of existing passive anti-islanding schemes and assess the impact of a DVC on islanding detection.

Economic Dispatch in Microgrids using Relaxed Mixed Integer Linear Programming

Abstract: Economic dispatch (ED) in a microgrid is vital to supply the load demand with a minimum cost of operation. Considering the large number of discrete variables involved in ED formulation, it is common in practice to use Mixed Integer Linear Programming (MILP) for solving the optimization problem. However, as the problem size increases, the convergence time of MILP can exponentially increase owing to the NP-hard nature of the algorithm. This paper reviews the state of the art ED formulations and proposes an equally optimal and time-efficient method, Relaxed Mixed Integer Linear Programming (RMILP) for executing the day-ahead ED in a microgrid with large problem size. Using the proposed algorithm, ED problems with smaller timesteps can be solved in a reasonable time for large systems. In addition, the load is modeled as a discrete variable which is more realistic from the perspective of load shedding and often ignored in ED formulations in the literature. We apply the proposed approach to the Banshee distribution feeders and show its advantages over conventional methods.

Impact of Virtual Inertia on DC Grid Stability With Constant Power Loads

Abstract: Virtual inertia is an effective control approach to attenuate sudden voltage changes during transient events in low-inertia dc grids. While methods have been proposed to implement virtual inertia, its impact on dc grid stability in the presence of constant power loads (CPLs) remains unclear. In this letter, we perform a rigorous stability analysis for dc grids with CPLs powered by virtual-inertia-enhanced converters. We derive a closed-form stability criterion that can be used to evaluate the impact of virtual inertia on the system stability, and demonstrate that, given a set of system parameters, the stability of a dc grid powering CPLs can be improved for a range of virtual inertia designs. We provide analytical expressions for the optimal virtual inertia that improves stability and for the maximum virtual inertia that does not deteriorate stability. In addition, we present a step-by-step guideline to design a stable dc grid with virtual inertia. Test results are presented to validate the analysis.

A Comprehensive Approach towards Multi-Objective EMI Filter Design Optimization in High-Frequency SiC-based Motor Drives

Abstract: With rapid penetration of high-frequency, high-density power electronics into the industry, controlling the system generated EMI becomes one of the major design challenges. Designing practical optimized EMI filters require simultaneous consideration of multiple aspects - including electromagnetic couplings, magnetic materials, practical component parasitics and their impacts at high-frequencies, and also the overall manufacturing costs. The multi-dimensional nature of the problem often results in overcompensated designs that hurt the system efficiency and power density. This paper focuses on a comprehensive design platform (developed in MATLAB) towards designing high-density, optimized, highly efficient EMI filters by analyzing the generated noise spectrum and evaluating a vast array of potential solutions before outputting an optimized filter solution. The proposed tool includes database-based component selection, optimal topology selection, multistage filter design, overall optimization for volume, mass, cost and total loss. The proposed filter has been thoroughly evaluated in a PSIM simulation environment emulating the hardware in CRD300DA12E-XM3, a 300kW three-phase inverter from Wolfspeed with an RL load representing a motor drive application. A 20kHz switching frequency is chosen and impacts of the motor high-frequency characteristics on the generated EMI noise spectrum of the overall system have been analyzed.