Enrico Santi

An assessment of wide bandgap semiconductors for power devices

An advantage for some wide bandgap materials, that is often overlooked, is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for packaging technology. It is shown that the optimal choice for uni-polar devices is clearly GaN. It is further shown that the future optimal choice for bipolar devices is C (diamond) owing to the large bandgap, high thermal conductivity, and large electron and hole mobilities. A new expression relating the critical electric field for breakdown in abrupt junctions to the material bandgap energy is derived and is further used to derive new expressions for specific on-resistance in power semiconductor devices. These new expressions are compared to the previous literature and the efficacy of specific power devices, such as heterojunction MOSFETs, using GaN are discussed.

Comprehensive Review of Stability Criteria for DC Power Distribution Systems

Power-electronics-based dc power distribution systems, consisting of several interconnected feedback-controlled switching converters, suffer from potential degradation of stability and dynamic performance caused by negative incremental impedances due to the presence of constant power loads. For this reason, the stability analysis of these systems is a significant design consideration. This paper reviews all the major stability criteria for dc distribution systems that have been developed so far: the Middlebrook Criterion, the Gain Margin and Phase Margin Criterion, the Opposing Argument Criterion, the Energy Source Analysis Consortium (ESAC) Criterion, and the Three-Step Impedance Criterion. In particular, the paper discusses, for each criterion, the artificial conservativeness characteristics in the design of dc distribution systems, and the formulation of design specifications that ensure system stability. Moreover, the Passivity-Based Stability Criterion is discussed, which has been recently proposed as an alternative stability criterion. While all prior stability criteria are based on forbidden regions for the polar plot of the so-called minor loop gain, which is an impedance ratio, the proposed criterion is based on imposing passivity of the overall bus impedance. A meaningful simulation example is presented to illustrate the main characteristics of the reviewed stability criteria.

A multilanguage environment for interactive simulation and development controls for power electronics

Virtual prototyping of complex systems presents interesting challenges, especially with regard to systems in which different languages are used to represent different parts. We describe here one approach to solving such a problem. In particular, we describe how to integrate the virtual test bed (VTB) solver engine with the Simulink solver. This produces a rich environment for virtual prototyping of power electronic applications due to the inherent mixture of circuital and control problems. The integration is conducted within the context of the resistive companion approach. We present here the theoretical foundation of the approach, and also suggest the generality and extensibility to other solver engines such as SPICE. The theory is then enriched with some examples that illustrate the approach including the use of the VTB high-level graphic user interface.

A fuel cell based domestic uninterruptible power supply

The design process for a fuel-cell-based inverter system for domestic use is discussed. The peculiar characteristics of the fuel cell stack energy source require the use of a battery for buffering. The fuel cell characteristics and the battery requirements for this application are discussed. A large number of different possible solutions are examined. The proposed solution uses an active filter and a battery to compensate for the slow dynamics of the fuel cell.

Two-step parameter extraction procedure with formal optimization for physics-based circuit simulator IGBT and p-i-n diode models

A practical and accurate parameter extraction method is presented for the Fourier-based-solution physics-based insulated gate bipolar transistor (IGBT) and power diode models. The goal is to obtain a model accurate enough to allow switching loss prediction under a variety of operating conditions. In the first step of the extraction procedure, only one simple clamped inductive load test is needed for the extraction of the six parameters required for the diode model and of the 12 and 15 parameters required for the nonpunch-through (NPT) and punch-through (PT) IGBT models, respectively. The second part of the extraction procedure is an automated formal optimization step that refines the parameter estimation. Validation with experimental results from various structures of IGBT demonstrates the accuracy of the proposed IGBT and diode models and the robustness of the parameter extraction method.

Rapid prototyping of digital controls for power electronics

The process for designing digital controls for power electronics is typically quite convoluted and affords many opportunities for errors to occur. We present here a new and complete method for rapid prototyping of digital controls that allows rapid realization of new designs. The approach uses a collection of tools that include both software (the virtual test bed (VTB) and Matlab/Simulink) and hardware (dSpace DSP). An example application of the methodology completes the discussion.

Exploration of Power Device Reliability using Compact Device Models and Fast Electro-Thermal Simulation

This paper presents the application of compact insulated gate bipolar transistor and p-i-n diode models, including features such as local lifetime control and field-stop technology, to the full electrothermal system simulation of a hybrid electric vehicle converter using a lookup table of device losses. The vehicle converter is simulated with an urban driving cycle (the federal urban driving schedule), which is used to generate transient device temperature profiles. A methodology is also described to explore the converter reliability using the temperature profile, with rainflow cycle counting techniques from material fatigue analysis. The effects of ambient temperature, driving style, and converter design on converter reliability are also investigated.

New Developments in Gallium Nitride and the Impact on Power Electronics

Wide bandgap III-nitride semiconductor materials possess superior material properties as compared to silicon, GaAs and other III-V compound materials. Recent achievements in gallium nitride (GaN) technology for optoelectronics have resulted in ultra-bright blue light emitting diodes and lasers, ultraviolet emitters, and solar-blind optical detectors. In the electronic area, drastic improvement of microwave device performance has been achieved, yielding record high power densities of 20-30 W/mm. Novel applications of these materials in high-power electronics for switching, energy conversion and control are just emerging. This paper provides an overview of the state-of-the-art III-nitride wide bandgap technologies and it explores power electronic applications while illustrating the enormous potential that GaN based devices have for overcoming the major challenges of power electronics in the 21st century. The paper discusses the unique material and device properties of GaN-based semiconductors that make them promising for high-power, high-temperature applications. These include high electron mobility and saturation velocity, high sheet carrier concentration at heterojunction interfaces, high breakdown voltages, and low thermal impedance (when grown over SiC or bulk AIN substrates). The chemical inertness and radiation hardness of nitrides are other key properties. As applied to power electronics, the Ill-Nitride technology allows for high-power switching with sub-microsecond and nano-second switching times. The paper will present the innovations that further improve the performance of high-power DC-DC converters, switches and other building blocks. These include novel insulated gate HFET design that significantly expands the allowable input voltage amplitude, further increases the device peak currents, and most importantly, tremendously improves the large-signal stability and reliability. Insulated gate switching devices have been shown to operate at up to 300 degC with no noticeable parameter degradation. Novel monolithic integrated circuits of high-power switches and DC-DC converters and their performance parameters will be presented. The paper also discusses the major challenges associated with modern GaN technology and work in progress to overcome them

Transient Electrothermal Simulation of Power Semiconductor Devices

In this paper, a new thermal model based on the Fourier series solution of heat conduction equation has been introduced in detail. 1-D and 2-D Fourier series thermal models have been programmed in MATLAB/Simulink. Compared with the traditional finite-difference thermal model and equivalent RC thermal network, the new thermal model can provide high simulation speed with high accuracy, which has been proved to be more favorable in dynamic thermal characterization on power semiconductor switches. The complete electrothermal simulation models of insulated gate bipolar transistor (IGBT) and power diodes under inductive load switching condition have been successfully implemented in MATLAB/Simulink. The experimental results on IGBT and power diodes with clamped inductive load switching tests have verified the new electrothermal simulation model. The advantage of Fourier series thermal model over widely used equivalent RC thermal network in dynamic thermal characterization has also been validated by the measured junction temperature.

Synergetic synthesis of DC-DC boost converter controllers: theory and experimental analysis

This paper describes a new approach to the synthesis of controllers for power converters based on the theory of synergetic control. The controller synthesis procedure is completely analytical, and is based on fully nonlinear models of the converter. Synergetic controllers provide asymptotic stability with respect to the required operating modes, invariance to load variations, and robustness to variation of converter parameters. With respect to their dynamic characteristics, synergetic controllers are superior to the existing types of PI controllers. We present here the theory of the approach, a synthesis example for a boost converter, simulation results, and experimental results.