Multilevel Inverters (MLIs) are widely sought after in medium-voltage applications like electric ships, electric aircraft, and renewable energy integration due to excellent advantages like lower device stress, better power quality, and modularity. However, non-sinusoidal excitations from MLIs pose a serious problem to motor-insulation and lead to their premature breakdown. This paper investigates stress in medium-voltage motor insulation when the stator winding is excited by 3-, 5-, and 7-level multilevel inverter output waveforms. The effect of firing angle on insulation stress is also studied for each of the multilevel inverters. Results show that in addition to the number of output voltage levels, PWM wave shape is a critical factor which affects the insulation stress. Both these factors work together to impact the insulation health. A strong correlation is shown between the increase in the voltage root mean square (RMS) value and increase in dielectric stress when ignoring the dv/dt impact for a fixed DC input voltage and operating frequency of the inverter. Similarly, the dielectric stress in the stator insulation increased with an increase in firing angle for each of the MLIs. This paper shows a potential that both the RMSs can be optimized to reduce the insulation stress and improve the power quality of MLIs in medium voltage drives.

Since the introduction of mica paper and synthetic resin-based taping insulation for rotating-machines in 1950s, only evolutional improvements in their properties and processing have been made. Due to its challenging nature, much of recent insulation research has been focused on the aspect of reliability rather than performance enhancement. This paper presents the development and performance evaluation of a revolutionary nanostructured insulation in the manufacturing of large propulsion motors with game-changing torque density and payload efficiency for marine Next Generation Integrated Power System. It is demonstrated that nanostructured insulation based on 2D-platelet fillers could offer significant improvement over conventional insulation system in electrical, dielectric, thermal and mechanical properties. Optimal nanostructured insulation formation identified through a Design of Experiment study exhibits high thermal conductivity of $>0.8$ W/( $\text{m}\cdot \text{K}$ ), high breakdown strength of >40 kV/mm, low dielectric constant of less than 5.5 and low dielectric loss factor of less than 2.5% at 155°C. Voltage endurance tests on coupons with optimal formulation, in accordance with IEC 60343 standard, demonstrate satisfactory endurance life. Furthermore, a multi-physics finite-element-analysis model of the winding in a medium-voltage electric motor is established to perform electromagnetic and thermal analyses in ANSYS under various temperature boundary conditions. The study indicates a remarkable increase of 14% in torque handling capacity of a motor wound with proposed nanostructured insulation material when compared to an identical motor wound with conventional micaceous insulation.

A self-assembled two-dimensional montmorillonite nanocoating enables significantly enhanced corona resistance in the Kapton film.

Thermally conductive polymers are highly desired as electrical insulation materials in power-electronic and electrical machines toward high power density and payload efficiencies. This paper investigates the thermal conductivity of hybrid epoxy composites containing talc nanoclay, boron nitride (BN) clusters, and zinc oxide (ZnO) particles using the Design of Experiment (DoE) approach. A statistical model of the composite thermal conductivity based on the compositions of the components has been established with an R-squared of 98.17%. The effects of shapes, sizes, filler thermal conductivity, and the structured network of the fillers are discussed. The structured edge-connecting BN nanosheets endowed in nanostructured BN-clusters play a critical role in composite thermal conductivity enhancement. The thermal conductivity with the optimized formulation could reach 1.3 W m⁻¹ K⁻¹, which is 6× higher than that of neat epoxy resin, while maintaining superior dielectric properties. The results of DoE analysis can be widely applied to the design of polymer composites with optimal formulations.

Large voltage transients due to power electronic inverters are one of the major factors influencing the insulation lifetime. This paper studies the effect of square voltage transients and switching frequency on insulation breakdown time based on series of voltage endurance tests. A medium-voltage power-electronics inverter testbed is built to stress Polyimide films Kapton HN with square waveforms at different frequencies. The voltage endurance test data is used to develop behavioral aging models and identify the effect of voltage transients and switching frequencies on insulation breakdown time. Results show a new correlation between switching frequency, insulation thickness, and voltage stress that have not been covered in the literature before.

Large voltage transients and high frequencies from power electronic inverters are the major cause and concern for insulation failure within inverter-fed machines. This is especially true as more wide-bandgap devices and electric motor drives penetrate various applications, including renewable integration. To understand the impact of high-voltage and high-frequency of emerging power electronic inverters on insulation lifetime, a medium-voltage H-bridge inverter testbed was built to stress Kapton HN (Polyimide) films. These films of different thicknesses were subjected to voltage endurance tests at different inverter voltages and frequencies to evaluate their breakdown time. Three different machine learning regression algorithms – Linear, Random Forest and Support Vector Machine were employed on time to breakdown data to predict the insulation lifetime. Results show that Random Forest regression performs best and gives a reasonably accurate prediction of time to failure of Kapton HN film given its thickness at any inverter voltage and switching frequency tested. Additionally, a closed-form equation of insulation breakdown time is derived from the linear regression to predict breakdown time for various insulation thicknesses, under varying inverter voltage, and inverter switching frequency.