Wooyoung Choi

High-Speed Electric Machines: Challenges and Design Considerations

High speed electric machines have been widely used in many applications nowadays and are gaining more attention. However, many special design challenges exist for HSEMs. This paper aims to discuss major challenges and design considerations for HSEMs. Four different loss components of high speed design are discussed and the methods to reduce each loss component are elaborated. Bearing options for HSEMs are compared. In addition, the rotor dynamics and thermal challenges are discussed in detail, following with some design suggestions and considerations.

Comparative Analysis on Conducted CM EMI Emission of Motor Drives: WBG Versus Si Devices

Silicon carbide (SiC) MOSFETs and gallium nitride (GaN) high-electron mobility transistors are perceived as future replacements for Si IGBTs and MOSFETs in medium- and low-voltage drives due to their low conduction and switching losses. However, it is widely believed that the already significant conducted common-mode (CM) electromagnetic interference (EMI) emission of motor drives will be further exacerbated by the high-speed switching operation of these new devices. Hence, this paper investigates and quantifies the increase in the conducted CM EMI emission of a pulse width modulation inverter-based motor drive when SiC and GaN devices are adopted. Through an analytical approach, the results reveal that the influence of dv/dt on the conducted CM emission is generally limited. On the other hand, the influence of switching frequency is more significant. Lab tests are also conducted to verify the analysis.

Core loss estimation of high speed electric machines: An assessment

High speed electric machines have been gaining significant interest over the last several years. This is mainly due to several advantages including increased power density and lower cost. High speed machines can allow for the elimination of gear box to achieve higher reliability and reduced maintenance of the full drive system. One of the challenges with designing high speed machine is accurate estimation of core loss. This paper will introduce both opportunities and challenges of estimating core loss for high speed electric machines. First, this paper will summarize core loss characterization and modeling based on physical and mathematical formulation. The limitation of classical Steinmetz equation is explained and a modified Steinmetz equation with variable coefficients is presented to improve accuracy of the core loss estimation for wide frequency and flux density range. Several contributing factors are also reviewed for estimation of core loss with consideration of arbitrary excitation waveform, flux density distribution, and the skin effect. This paper explains a core loss model for permanent magnet electric machines and discusses the dependency of core loss on machine dimensions as well. Finally, future opportunities are suggested for core loss estimation of high speed machines.

Achieving high efficiency using SiC MOSFETs and reduced output filter for grid-connected V2G inverter

This paper describes a comprehensive analysis of a three-phase two-level silicon carbide (SiC) MOSFET V2G inverter including the LCL filter design. The efficiency is compared between the SiC MOSFET and Si IGBT. Using a SiC device enables the inverter to operate at high switching frequency and this leads to improved efficiency up to 99.05% at 10 kHz and 97.71% at 100 kHz switching frequency. The output LCL filter is also designed based on a specific switching frequency and the filter value is most significantly reduced at the highest switching frequency. The SiC inverter and LCL filter is simulated using LTSpice and MATLAB Simulink.

Reactive power control of grid-connected inverter in vehicle-to-grid application for voltage regulation

Vehicle-to-grid is a promising concept, which has a potential to provide ancillary services to the power grid such as peak load reduction, spinning and non-spinning reserve, and voltage and frequency regulation. This paper investigates the control method of a grid-connected inverter in vehicle to grid application for voltage regulation through reactive power control. The control technique is to maintain the point of common coupling voltage at a nominal value when there is sag or swell on grid voltage. The required power is mathematically derived as a function of the balanced sag or swell factor and phase angle of compensated voltage. The proposed control technique is simulated using MATLAB Simulink and Simpower tools.

Effect of grid inductance on grid current quality of parallel grid-connected inverter system with output LCL filter and closed-loop control

Grid-connected inverters (GCIs) are power electronics interfaces to connect distributed energy resources into the grid. In order to improve the performance of distributed energy resources as well as maintain the high power quality of the grid, it is important to understand the characteristic of GCIs with appropriate controllers depending on its applications. This paper presents a study on the effect of grid inductance on quality of the grid current when there are multiple parallel-connected inverters to the grid. The model includes three-phase two-level voltage source inverters, output LCL filter, the grid, and voltage-oriented PI controller with a power controller. Parallel GCI systems are mathematically modeled. Frequency responses of grid current are investigated according to different grid inductances. A parallel grid-connected inverter system is simulated using MATLAB Simulink in order to present the effect of grid inductance on grid current and power quality.

Closed-Form Solution for Axial Flux Permanent-Magnet Machines With a Traction Application Study

This research attempts to find a new closed-form solution for axial flux permanent-magnet (AFPM) machines and applies it in a traction application example. The machine types considered are with toroid and overlapping windings. The proposed closed-form solution includes analytical derivations for winding lengths, resistances, and inductances as functions of fundamental air-gap flux density and inner-to-outer diameter ratio. Finite-element analysis is used to verify the accuracy of the proposed analytical calculations. Furthermore, a parametric analysis is performed on inductances, resistances, phase back-EMFs, phase terminal voltages, efficiencies, and torque speed capability to compare for both winding types. The proposed solution should assist traction machine designers to ascertain benefits and limitations of the toroid and overlapping winding types in traction application as well as to achieve faster design results.

Reviews on grid-connected inverter, utility-scaled battery energy storage system, and vehicle-to-grid application - challenges and opportunities

The purpose of this paper is to review three emerging technologies for grid-connected distributed energy resource in the power system: grid-connected inverters (GCIs), utility-scaled battery energy storage systems (BESSs), and vehicle-to-grid (V2G) application. The overview of GCIs focuses on topologies and functions. Different functions of utility-scaled BESS are introduced and a comprehensive review is provided for currently operating BESSs that are interconnected at the distribution level. Possible grid support functions of utility-scaled BESS are presented. This paper also presents the current electro-chemical based ESSs in the U.S. with different grid support functions. The V2G technology is introduced focusing on benefits for grid support. The state-of-the-art of GCI, BESS, and V2G technologies presents many opportunities and challenges that need to be addressed in the future.

Modeling three-phase grid-connected inverter system using complex vector in synchronous dq reference frame and analysis on the influence of tuning parameters of synchronous frame PI controller

This paper presents a mathematical modeling of three-phase grid-connected inverter system including output LCL filter and closed loop control using complex vector notation. The control scheme used is synchronous frame PI control on complex space vector of grid current in synchronous dq reference frame. Effect of controllers tuning parameters is investigated using complex vector root locus and complex vector frequency response function of closed loop system according to different tuning parameters. Control scheme and three-phase grid-connected inverter are simulated using MATLAB Simulink and SimPowerSystems™.

New configuration of multi-functional grid-connected inverter to improve both current-based and voltage-based power quality

In this paper, a new configuration of a multi-functional grid-connected inverter is proposed to improve both voltage-based and current-based power quality issue. By implementing bidirectional switches using semiconductor devices, a multi-functional grid-connected inverter can be connected in series or parallel to the grid and provides three modes of operation. This paper presents the control scheme of a multi-functional grid-connected inverter in each operating mode, the realization of bidirectional switches, and simulation results of the proposed multi-functional grid-connected inverter.