Partial Discharges in Electrical Machines for the More Electric Aircraft—Part I: A Comprehensive Modeling Tool for the Characterization of Electric Drives Based on Fast Switching Semiconductors

Abstract

The arrival on the market of new power devices based on wide bandgap semiconductors has raised a relevant interest due to their superior properties compared to conventional technologies. On the other hand, these devices are inherently characterized by high rates of voltage changes over time, which may result in reliability challenges in electric drives adopting them. In fact, dangerous voltage overshoots at the motor terminals and uneven voltage distributions within the machine windings may occur. These phenomena can trigger a high insulation stress and partial discharges and, as a consequence, they may concur to the premature failure of the dielectric materials. This paper proposes a flexible and comprehensive modelling approach for the accurate analysis and estimation of both voltage overshoots and voltage distributions in a typical converter-cable-motor system intended for more electric aircraft applications. The modelling results are validated against experimental measurements carried out on a physical prototype comprising a wide bandgapbased converter, a connecting cable and an electrical machine stator. The findings are then used in the companion papers (part II and part III) to investigate the dependence of partial discharge phenomena on these voltage waveforms, highlight reliability challenges in modern 270 V DC bus voltage drives for the more electric aircraft and discuss solutions.

Segmented Hairpin Topology for Reduced Losses at High-Frequency Operations

“…The constant terms A1 and A2 involved in (7) are found through the boundary conditions ( 9) and (10), where h is the height of the considered layer (see Fig. 3).…”

“…(email:eraldo.preci2@nottingham.edu.cn;ezzmd2@exmail.nottingham.ac.uk;ezzdg2@exmail.nottingham.ac.uk;Giampao lo.Buticchi@nottingham.edu.cn; eezcg@exmail.nottingham.ac.uk) S. Nuzzo and D. Barater are with Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Modena 41125, Italy. (e-mail: stefano.nuzzo@unimore.it; davide.barater@unimore.it ) and windings as well as higher stresses on coil insulations, thus efficiency and reliability are compromised [9], [10]. An evident example in this regard is represented by hairpin windings, whose full penetration in the transportation market is curbed by their inherently high ohmic losses at high frequency operations, where skin and proximity effects occur.…”

Hairpin Windings: An Opportunity for Next-Generation E-Motors in Transportation

“…WBG-based converters are enabling higher operating frequencies for machines. However, their inherently faster commutations and voltage gradients (dv/dt) may trigger voltage overshoots, uneven voltage distributions, partial discharges (PDs) and faster degradation of insulations [27], [28]. With a pure sinusoidal supply voltage, the voltage distribution is even, i.e.…”

“…proposed in [37] for low-voltage, random-wound machines. Basing on [27], a comprehensive model able to predict the voltage distribution within hairpin windings will be developed, where converter, cable and motor will be all taken into account. The model will target electrical stress within the winding and it will be tailored for the new winding structures envisioned above.…”

Reliability-Oriented Design of Inverter-Fed Low-Voltage Electrical Machines: Potential Solutions

“…V DC being the DC link voltage, K(t r ) is a function of the rise time and approaches one only for a very short rise time (<50 ns); OF has been mentioned before as shown in Figure 4, and a winding factor of 0.7 is adopted accounting for voltage distribution [58] and may be useful when the experiment and simulation are missing. In addition to the adoption of empirical factors, the high frequency (HF) model considering machine parameters can be used to predict both the EM terminal voltage [107][108][109][110][111][112][113][114][115] and turn/turn voltage [107,108,114,[116][117][118][119]. An example could be found in [108] as shown in Figure 9.…”