Giorgio Pietrini

Closed-form approach for predicting overvoltage transients in cable-fed PWM motor drives for MEA

The More Electric Aircraft (MEA) concept has set tight constraints for power density and efficiency of electromechanical actuators in aircraft applications. In order to comply with these high power standards, new wide-bandgap (SiC and GaN) semiconductor devices may be exploited. Unfortunately, the extremely short switching times of these devices can easily trigger high frequency ringing voltage at motor terminal in cable-fed PWM motor drives due to pulse reflection. The resultant overvoltage stresses the insulation of stator windings decreasing the motors lifespan. The most common solutions involve bulky and heavy passive filters, not suitable for MEA design approach, so the overvoltage suppression remains an open question. This paper explores the influence of pulse rising (and falling) time to the magnitude of motor terminal overvoltage through a detailed closed-form analysis of the problem in order to support electrical drive design optimization.

Accurate modeling of ultra low-power ΣΔ modulator

This paper presents a behavioural model suitable for the simulation of low-power Sigma-Delta Modulators. Second-order effects affecting the settling behaviour of the switched-capacitor integrator was included, leading to improved accuracy. Due to the oversampling mode of the converter, transistor-level simulations are extremely time consuming. Accurate behavioural models are thus mandatory in the first design phase of the modulator, in particular when the involved analog blocks must be optimized for minimum power consumption at some converter resolution.

Multi-stress lifetime model of the winding insulation of electrical machines

In this paper, a novel multi-stress model which estimates the lifetime of the winding insulation relative to its duty cycle is proposed and investigated. With an adequate implementation of this model, then an electrical machine can be designed not only in terms of its performance requirements, but also considering the associated reliability and lifetime aspects. The determination of the model parameters is based on the results of accelerated thermo-mechanical ageing tests.

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.

Low-power 3 rd order ΣΔ modulator in CMOS 90-nm for sensor interface applications

The manuscript describes the design and implementation of a low-power, fully differential switched-capacitor ΣΔ modulator in STM 90-nm CMOS technology, for sensor interface applications. With the aid of an accurate behavioral model, the power consumption is minimized without sacrificing the effective resolution. Through the optimization of single-stage integrators, with feed-forward summation, and using a class-A OTA op-amp with local positive feedback, a total power consumption of 50-μW from a 1.2-V power supply is achieved. The modulator reaches a peak SNR of 94-dB and a noise floor of 8.6-μV-rms over a 250-Hz signal bandwidth. The proposed design is one of the first modulator implemented in a 90-nm CMOS and achieving a 16-bit effective resolution with a 1.5-pJ/conv. figure-of-merit.