Antonio Griffo

Derivation and Scaling of AC Copper Loss in Thermal Modeling of Electrical Machines

Accurate prediction of temperature-dependent ac winding loss effects is crucial in the design of electrical machinery. Average ac winding loss as a function of operating frequency is commonly characterized by the ratio of the equivalent ac and dc resistances (Rac/Rdc). However, as the ac and dc components of the winding loss scale differently with temperature, a single value of Rac/Rdc derived for one temperature can be inadequate when used in thermal modeling. In this paper, methods of deriving the Rac/Rdc ratio, together with scaling techniques of the ac winding loss accounting for thermal effects, are discussed. As an alternative to computationally intensive 3-D finite-element analysis, an experimental approach based on tests on full-scale stator assemblies is proposed. A previously proposed scaling technique of the ac winding loss is discussed and developed further. The proposed techniques of deriving the ac winding loss accounting for temperature variation are illustrated using both theoretical analysis and experimental data.

Design study of a three-phase brushless exciter for aircraft starter/generator

This paper presents a design study of a 3-phase AC main exciter (ME) for an aircraft starter-generator. A computationally efficient methodology for optimizing the design of the ME is presented. The optimisation is carried out using coupled two-dimensional (2D) magnetostatic finite element solver and particle swarm optimisation procedure (PSO). The ME design is then analysed using 3D FE to account for the end-winding effects, and the results are fed into a lumped-parameter circuit model of the ME. The circuit model allows for the operating modes of the ME being analysed in a computationally efficient manner also accounting for non-linearities. The theoretical findings are experimentally validated on a prototype generator.

Sensorless starting of a wound-field synchronous starter/generator for aerospace applications

The present paper describes an angle and speed estimation algorithm suitable for the control of a wound-field synchronous starter/generator (S/G) without position sensors for aircraft engine starting applications. The proposed control strategy is based on the injection of a high-frequency voltage signal and the subsequent demodulation of the resulting high-frequency stator current components. The coupling due to high-speed operation that degrades the estimation accuracy of similar algorithms based on signal injection is taken into account. Modeling of the machine response to a high-frequency voltage signal injected into the estimated d-axis is presented, also considering the influence of damping circuits both on the d- and q-axis. Local asymptotic stability of the proposed observer is also demonstrated. Through extensive experimental results, the proposed control technique is shown capable of guaranteeing full-torque sensorless operation at zero speed and sustained operation up to engine ignition speed.

Design and Characterization of a Three-Phase Brushless Exciter for Aircraft Starter/Generator

This paper evaluates a three-phase ac main exciter (ME) for a wound-field synchronous aircraft starter-generator capable of operating in both starting and generating modes. The research has been based around a 225-kVA generator utilizing the existing single-phase ME hardware. Initially, a reconfiguration of the existing single-phase unit into a three-phase one has been carried out. Subsequently, an optimization of the ME stator has been performed. The hardware evaluations have been performed in parallel to the development of design methodologies suitable for future starter/generator design. The three-phase ac ME design needs to satisfy the required current output at both start and generate modes with minimum input voltampere rating of the inverter required to drive the ME. The MEs output capabilities have been predicted in all operating conditions using a computationally efficient combination of 3-D finite-element models together with a lumped-parameter circuit approach. The theoretical findings from the analyses have been validated on a prototype ME, confirming that the three-phase ac ME is capable of generating the required current output in both operating modes. The developed modeling system allowed for the identification of the MEs optimal operating points with regard to the minimum input apparent power (in voltamperes) at the required output power and a methodology for the accurate and computationally efficient evaluation of future starter/generator designs.

Large signal stability analysis of DC power systems with constant power loads

This paper presents a detailed analysis of the dynamic behaviour under large disturbances of a high voltage DC electric power system representative of the power distribution networks which are commonly being proposed for future ldquomore electricrdquo vehicles. Numerical simulations are undertaken to analyze the region of asymptotic stability of the system under different operating conditions. Analytical derivations based on the use of the Brayton-Moser Mixed Potential are employed along with Lyapunov stability theorems to determine an analytical estimation of the stability region.

RF power silicon-on-glass VDMOSFETs

Applicability of vertical double-diffused MOSFETs for future base station power amplifiers has been demonstrated by characterizing the first devices fabricated in a substrate transfer silicon-on-glass technology. For a gate length of 0.8 /spl mu/m and gate width of 350 /spl mu/m, the measured f/sub T//f/sub max/ is 6/10 GHz, and the breakdown voltage approaches 100 V. The devices feature an output power of 12 dBm at the 1-dB compression point, excellent linearity (IM3/IM5 of -50/ -70 dBc at 10-dB backoff) and high power gain (14 dB) at 2 GHz, and are the first vertical DMOSFETs suitable for 2-GHz power applications. Excellent heat sinking and no significant degradation of the quiescent current due to hot-carrier injection ensure thermal stability and good long-term reliability of the fabricated devices.

Compensation of Inverter Nonlinear Distortion Effects for Signal-Injection-Based Sensorless Control

A simple analytical technique, which uses readily available datasheet parameters, is developed to model the low-current switching characteristics of insulated-gate bipolar transistors (IGBTs). Simulation and experimental results obtained using three differently rated inverters are presented to demonstrate the accuracy of the technique. The model is applied to compensate the nonlinear distortion, introduced by IGBT switching action in a three-phase inverter, of high-frequency injected voltage and current signals used in sensorless control of a permanent-magnet brushless ac machine. Experimental results show that the compensation technique improves rotor position estimation by up to 20° electrical.

Input Admittance Characteristics of Permanent Magnet Brushless AC Motor Drive Systems

This paper analyzes the input admittance/impedance characteristics of a permanent-magnet brushless AC motor drive system, taking account of the influence of both current and speed control loops as well as the motor and inverter losses. It is shown that, if voltage feedforward compensation is not employed, the input admittance of the drive system differs significantly from that of an ideal constant power load, and is influenced by the speed and current control loop bandwidths. It is also shown that, when the drive is connected to a DC supply via an LRC filter, the magnitude of the input admittance at the filter resonant frequency has a crucial effect on system stability margin.

Two-Leg Three-Phase Inverter Control for STATCOM and SSSC Applications

Flexible ac transmission systems (FACTS) devices are attracting an increasing interest both in power system academic research and in electric utilities for their capabilities to improve steady-state performance as well as system stability. Several converter topologies for FACTS applications have been proposed in the recent literature, even if those based upon voltage source inverters (VSI) seem to be more attractive due to their intrinsic capability to rapidly respond to network changes such as perturbations subsequent to a fault and their property of being immune to resonance problem. In this paper, a new topology for inverter-based FACTS is proposed. This configuration, employing a two-leg three-phase inverter is employed for both series and parallel-connected reactive power compensators. The converter utilizes a modular topology for allowing a satisfaction of electronic components rating. A control strategy based on variable structure control technique with sliding mode is employed to track appropriate reference quantities. Design and control, as well as good tracking performances, are also verified through numerical simulations.

A High-Fidelity and Computationally Efficient Electrothermally Coupled Model for Interior Permanent-Magnet Machines in Electric Vehicle Traction Applications

Accurate temperature predictions for permanentmagnet machines are essential to prevent irreversible demagnetization and undesirable reduction in lifetime. This paper proposes a high-fidelity and computationally efficient electrothermally coupled model for interior permanent-magnet machines (IPMs) in electric vehicle (EV) traction applications. First, a high-fidelity IPM model accounting magnetic saturation, spatial harmonics, iron loss, and temperature effects is presented. The temperature effects on both the dand q-axis flux-linkages and the torque in the proposed model are quantified. The IPM model with due account of temperature effect is integrated with a state-space lumped parameter thermal model to establish a high-fidelity and computationally efficient electrothermally coupled model for IPMs. Both the steady-state and driving cycle operations are simulated with the proposed model and the results are compared to those predicted by the machine model without considering temperature effect as well as by the machine model which only accounts for the temperature effect on the winding resistance. Considerable temperature differences between those predicted by the proposed model and those predicted by the latter two models are observed. Experimental validation of the proposed model is performed with a 10-kW IPM prototype machine operating in generating mode.