Powertrain modularity

This paper outlines the main innovations of the EM-TECH and HighScape projects, targeting a wide range of vehicle applications, including passenger cars and commercial vehicles. Specifically, EM-TECH deals with: i) modular designs of on-board axial flux machines (AFMs) for reducing the implementation costs of scalable centralised powertrains for electric axle (e-Axle) solutions; ii) in-wheel motors (IWMs) integrated with electric gearing, for expanding the high efficiency region of electric corner (e-Corner) powertrains; and iii) the use of permanent magnets deriving from recycling processes to improve sustainability. In parallel, HighScape targets the physical and functional integration of the PE of WBG based traction inverters, onboard chargers, DC/DC converters, and electric drives for auxiliaries and actuators.

This document provides a comprehensive report on the activities related to the experimental validation of lab-scale power converter prototypes. It includes an analysis of the current standards for power converter testing, drawing on publicly available sources and the expertise of RHODaS partners.

The document also proposes a detailed test plan for High Power Converters (HPC), which are based on Low Power Converter modules. This plan encompasses electrical tests for both Low Voltage (LV) and High Voltage (HV) parts, as well as environmental, mechanical, and safety tests. Additionally, the document reports on laboratory tests to verify basic parameters of Low Power Converters (LPC), such as efficiency, distortion, and Common Mode Voltage (CMV).

The analysis highlights the absence of comprehensive standards for inverter testing, necessitating the search for relevant documents from various testing fields. Due to the high voltage levels considered in the DC/AC converter, of at least 1000 VDC Bus, it is necessary the adaptation of research methodologies in cases where direct references are lacking. This process requires substantial knowledge and experience in test systems and application of standards.

The conclusions drawn from these activities are expected to support future design, optimization and recommendations, focusing on further improvements in power converters and the use of standards specifically adapted for them in automotive applications.

Permanent magnet synchronous machines (PMSMs) are still the first choice for use in electric vehicles, due to their unparalleledefficiency and power density. However, they suffer from an inherently limited speed range. As field weakening or the addition of amechanical gearbox deteriorates the efficiency of the drive, it is suggested in this paper to equip the drive with reconfigurationswitches, giving rise to a so-called e-gear. The switches—which are implemented by means of mechanical relays—allow to change the winding connection of the electric machine from a series to a parallel connection and hence to double its efficient speed range.Simulations and experimental results on a 4-kW axial-flux PMSM confirm the feasibility of the concept and prove that the reconfiguration can be conducted in less than 35 ms.

In this document the insulation system of the HEFT motor is discussed. In particular, the following
points will be explained: Evaluation of voltage stresses; Definition of target partial discharge inception voltages (PDIV); Reference insulation system; Characterization of slot molding resins; Assessment of phase-to-phase insulation system; Assessment of phase-to-ground insulation system; Assessment of turn-to-turn insulation system; Chemical compatibility. 

Climate change has created an increased need for innovation in various sectors, including the automotive industry. Many corporations are striving to fulfil this need by developing and producing electric cars. However, the production process remains inefficient and environmentally harmful. The EU-funded HEFT project will reverse this trend by introducing a revolutionary synchronous motor for electric cars, which will be recyclable, cost-efficient and require fewer materials while producing fewer emissions and creating novel European circular economies. 

HEFT Project proposes a set of innovation challenges on electric synchronous motor configuration based on SiC inverters (direct cooling of rotor and stator, advance insulation for high voltage, multibarrier rotor topology, wave windings) and advanced materials (advanced GBD magnets, epoxy for magnet fixation, composite for motor housing, insulation resin). These innovations will result in a high-efficient and low-cost solution that will be validated on 2 motor topologies.

In this document it details the work carried out in the HEFT project with regards to the objective of improving SiC-based drive control to reduce powertrain losses and improve EV range. The following issues will be covered:
1. Online variable switching frequency control strategy to optimize drive operation and reduce inverter and motor losses.
2. Optimal flux operation point to increase motor efficiency.
3. Improved powertrain thermal management strategy.
 

All these control aspects will be used in both A+B segment motor and C+D+E segment motor, as control strategy is the same for both motors that will be designed in HEFT project (only some parameters’ tunning need to be modified). Therefore, as use case, A+B segment motor has been selected, because this motor has already been designed. However, some preliminary results regarding C+D+E segment motor are also shown in this deliverable (this motor is still under development) to show that the proposed control strategy is valid for any IPMSM.

The Dual Active Bridge Converter topology is widely recognized for its high power density in high-power applications, enabling soft switching and achieving high efficiencies in both buck and boost operation modes. However, under conventional phase-shift modulation, operation at light or no load results in hard-switching and high effective currents, leading to increased overall losses, one of its main drawbacks. These issues have been primarily addressed by implementing complex modulation strategies, leveraging from the multiple degrees of freedom in the control of the converter power, particularly the inner and outer shift angles of its bridges. Contrary to the traditional approach, this work proposes the modulation of the series inductance of the DAB converter by implementing a switched inductor, aiming for a simplified modulation strategy. The proposed method effectively achieves zero current under no-load conditions and significantly reduces effective currents at light loads compared to the traditional phase-shift modulation approach. Although an in-depth comparison with other modulation schemes is required, this work represents a stepping stone in the analysis of the topology and the comprehension of its trade-offs.

The study of multilevel dual-active-bridge (DAB) converters has garnered significant attention in recent years thanks to their advantages with respect to the conventional two-level (2L) DAB; namely, its greater performance and its capability to operate at higher voltage. The analysis of the converter high-frequency inductor current (𝑖LiL) is crucial, for instance, to compute its root mean square (RMS) value, required to estimate the conduction losses in the converter. The mathematical expression of 𝑖LiL is piecewise and multiple variations, i.e., modes, exist depending on the modulation parameter values. This increases the complexity of converter performance analytical study. Thus, a more practical and generalizable expression of 𝑖LiL current is desirable. This paper proposes novel compact analytic expressions for the instantaneous and RMS inductor current in the 2L-NL DAB converter, leveraging binary functions to define the piecewise intervals and to identify the mode as a function of the modulation parameter values. The proposed method paves the way for more simple and computationally efficient DAB performance optimization software tools that allow exploring any given converter structures and modulation strategies.

Multilevelπ π-type and ANPC converters without flying capacitors and clamping diodes are emerging candidates for industrial applications due to their simple structure, less number of devices, and better harmonic performance. However, the voltage balancing difficulty is the key issue of these topologies similar to diode-clamped topology under conventional PWM methods. The unbalance of capacitors voltages may affect the system integrity and stability, and may degrade harmonic performance. To sort out this issue, a simplified virtual vector PWM method to balance the dc-link capacitors voltage of four-level three-phase π -type and ANPC converters is presented in this paper. Simulation results show how easily and efficiently the proposed method can control the voltage of the capacitors for different modulation index values under balanced and unbalanced loads.

This deliverable reports the selection of the optimum power devices for implementing the SCAPE high-voltage switching cells, after a literature review and commercial availability check. In addition to suitable electrical characteristics, the selection of candidates considered the suitability and availability of bare-die components for their subsequent chip embedding process. Two SiC MOSFET references have been selected and samples have been obtained for an initial test campaign (GeneSiC G4R12MT07. 750V – 12 mΩ and Wolfspeed CPM3-0650-0015A. 650V – 15 mΩ). For the development of the low-voltage switching cells of the auxiliary SCAPE converters, GaN HEMTs from EPC will be selected. The deliverable also includes a prospective and literature review about power device emerging technologies.