Alessandro Soldati

Multistress Characterization of Fault Mechanisms in Aerospace Electric Actuators

The concept behind the more electric aircraft is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical, and bleed air/pneumatic systems, and pursue efficiency, reliability, and maintainability. This paper presents a specialized test rig whose main objective is to assess insulation lifespan modeling under various stress conditions, especially investigating the interaction between ageing factors. The test setup is able to reproduce a multitude of environmental and operational conditions at which electric drives and motors, used in aerospace applications, are subjected. It is thus possible to tailor the test cycle in order to mimic the working cycle of an electrical motor during real operation in aircraft application. The developed test-rig is aimed at projecting the technology readiness to higher levels of maturity in the context of electrical motors and drives for aerospace applications. Its other objective is to validate and support the development of a comprehensive insulation degradation model.

Frequency-based control of a micro-grid with multiple renewable energy sources

Stand-alone micro-grids need a proper management of the active power exchange. This work is focused on the parallel operation of multiple grid-connected converters in an island-grid system. The proposed solution features a master inverter which emulates the grid and multiple grid-connected converters operating in parallel. The current sharing and overload protection is achieved by small frequency variations of master inverters output, that are detected by the grid-connected converters. This mechanism exploits the behavior of the derating characteristics embedded in grid-connected inverters, that must reduce the output power if the grid frequency increases. In this case, standard grid-connected equipment can be used to realize micro-grids without the need of digital communication between the power units. Two possible scenarios are analyzed: low-power microgrid with master/slave converters, and low voltage grid fed by a Smart Transformer (ST) which performs the frequency control.

Multistress characterization of insulation aging mechanisms in aerospace electric actuators

The concept behind the More Electric Aircraft (MEA) is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical and the bleed air/pneumatic systems and pursue efficiency, reliability and maintainability. This paper presents a review of the main stress factors affecting the lifespan of insulation materials in aerospace applications. A special test bed is also proposed, to assess insulation lifespan modelling under various stress conditions, especially investigating the interaction between ageing factors. The test bed will allow to characterize insulation degradation under variable ambient and power supply parameters for simple models such as twisted pairs, up to coil form and complete machine operated at rated load. The proposed approach is based on the design of experiments (DOE). The results of the work that will be carried out will allow to identify the most influential factors affecting insulation lifetime and the interactions between them.

A voltage controlled power resistor circuit for active gate driving of wide-bandgap power devices

Wide-bandgap devices are under the spotlight of scientific research as they exhibit great performance in terms of efficiency and temperature operation. However, to fully exploit their characteristics, dedicated driving circuits are needed. High-power gate-insulated switching devices exhibit important input capacitance; when fast switching speeds are demanded, high-current pulses are needed to drive the gate terminal. This is particularly true for wide-bandgap devices, capable of lower transition times than conventional silicon devices. The proposed circuit is a voltage controlled resistor, which output can drive wide-bandgap devices. Design criteria, as well as simulation results, are presented.

Active thermal control by controlled shoot-through of power devices

Active Thermal Control (ATC) consists in driving power switches in a less efficient way when low load conditions are present. The resulting wasted power is used to self-heat the device, reducing amplitude and occurrence of thermal cycles and hence improving the reliability. This paper presents a novel way to control losses, and hence temperature, of both positive- and negative-current devices in half-bridge topologies at various load conditions. The goal is achieved by means of a controlled shoot-through of the half-bridge leg.

Comparing control topologies for wide-bandgap power-device drivers: A simulation study

Wide-bandgap power switches, based on SiC and GaN, are emerging on the semiconductor market. Standard resistor drivers are insufficient to exploit all the advantages of these new devices. Fine control over current and voltage waveforms during switching, equivalent on-state resistance and immunity to noisy environments, demand the development of dedicated drivers. This study aims at determining a suitable control topology for the gate (or base) terminal of the power device, in order to enact regulation of the switching waveforms and performances. Four different topologies, both open- and closed-loop are simulated, examined, and compared with the standard resistor driver.

Thermal stress mitigation by Active Thermal Control: Architectures, models and specific hardware

This work proposes an Active Thermal Control (ATC) of power switches. Leveraging on the fact that thermal stress has wide impact on the system reliability, controlling thermal transients is supposed to lengthen the lifetime of electronic conversion systems. Indeed in some environments, such as transportation, reliability and lifetime are still obstacles to widespread adoption of electric and electronic actuators, despite a general trend of electrification spreading in many different areas of interest. Active thermal control is attained leaving the electric parameters of load untouched, while acting dynamically on gate parameters (voltage and resistance), by means of a specifically designed gate driver. Two different control algorithms, sharing similar model and hardware, are presented: one is based on a linear controller, while the other relies on a model-predictive control (MPC) strategy. Simulation results of control schemes are presented, together with evaluation of the proposed loss models. Experimental proof of the ability of the proposed control to reduce thermal swing and related stress on the device is presented, too.

Wavelet-based prognostic-oriented temperature sensing with sigma-delta ADCs in power applications

Thermal stress is one of many possible failure causes of power electronics systems; thermal cycles are known to produce mechanical fatigue on power electronic devices, thus leading to their failure in time. Temperature swing can be somehow controlled, if some decrease in efficiency can be tolerated by the power system, changing gate driver parameters to heat up the device in low load conditions. This is known as Active Thermal Control (ATC). To implement ATC, the temperature information of devices is needed. Since this sensing is carried out near power conductors, switched at high frequency, strong disturbances will affect the reading. This paper proposes a new signal-conditioning scheme based on discrete wavelet transform (DWT) and compares it to some established filtering techniques to assess which is most suitable for the application. Hints about insulation of measuring equipment will be given, too. Moreover, the possibility offered by the algorithms to store long-time temperature information (through compression of incoming data) will be described, as large-span observation can help prognostic algorithms in forecasting the remaining useful life of the power apparatus.

Active thermal control for reliability improvement of MOS-gated power devices

This paper proposes an Active Thermal Control (ATC) method for MOS-gated power switches aimed at reducing temperature swing amplitude during operation. It leverages on the fact that thermal cycle amplitude of many actuation system components (such as power devices) has a large impact on the system reliability and lifetime. These figures can then be improved, which eases the adoption of electrification in markets, such as transportation, where they are still below target values. The proposed ATC method leaves electric load parameters untouched, while acting dynamically on gate parameters, namely voltage and resistance. A model-predictive control (MPC) strategy is used to determine the most suitable parameters to use. Simulations of the control scheme are presented first, to predict the potential benefits on temperature swing amplitude, and the consequent improvements in terms of device lifetime are inferred, using literature models. Then, experimental proof of concept is presented and discussed, together with its limitations and drawbacks.

Implementing discrete PID controllers: Benchmarking manual vs. Automatic generation of embedded code

PID controllers are fundamental in many control applications, thanks to their effectiveness, understanding from designers, tunability to different systems, overall performance. When coming to their embedded implementation, different approaches exist: manufacturer-provided libraries, user-defined editions, automatically generated code. This paper addresses these different choices and benchmarks their results, both in order to help designers in the judgment and make apprentices understand the practical consequences of key concepts as system discretization and frequency-domain description.