Interoperability in HVDC systems could be supported with open upper-level control and protection (C&P) software, while hardware-near C&P functions stay black-boxed and proprietary. Methodologies like model-based systems engineering and graph theory can assist in defining the boundary between open and closed software. Most likely, partially open C&P software in HVDC is not hindered by legislation, but has to be addressed in contractual agreements. Also, a new responsibility matrix for testing is proposed.

Interconnecting power converters (IPCs) are the main elements enabling the interconnection of multiple high-voltage alternating current (HVac) and high-voltage direct current (HVdc) subgrids. To ensure stable operation of the resulting hybrid ac/dc systems, grid-following (GFL) and grid-forming (GFM) controls need to be carefully assigned to individual IPC terminals when using common IPC controls. In contrast, dual-port GFM control imposes a stable voltage on the ac and dc terminals and can be deployed on all IPCs regardless of the network configuration. In this work, we use hybrid ac/dc admittance models, eigenvalue sensitivities, and case studies to analyze and quantify the underlying properties of ac-GFM control, ac-GFL, and dual-port GFM control. Compared to common ac-GFM and ac-GFL controls, dual-port GFM control: 1) renders IPCs dissipative over a much wider range of frequencies and operating points; 2) significantly reduces the sensitivity of IPC small-signal dynamics to operating point changes; and 3) exhibits an improved dynamic response to severe contingencies. Finally, the results are illustrated and validated in an experimental scaled-down point-to-point HVdc system.

Grid-forming converters can emulate the behavior of a synchronous generator through frequency droop control. The stability of grid-forming modular multilevel converters can be studied via the impedance-based stability criterion. This paper presents an ac-side impedance model of a grid-forming modular multilevel converter which includes a complete grid-forming control structure. The impact of different control schemes and parameters on the closed-loop output impedance of the converter is thoroughly analyzed and the learnings have been used in mitigating undesired control interactions with the grid. The results are verified through simulations in time- and frequency-domains along with experiments on a down-scaled laboratory prototype.

Double-sided cooled (DSC) power semiconductor modules have garnered increased interest over the past decade due to their ability to offer an additional path for heat removal, facilitating higher power density operation while reducing junction temperatures and thermal stresses. Nevertheless, when operating at similar junction temperatures, DSC modules might exhibit elevated thermo-mechanical stress compared to single-sided cooled (SSC) modules. This increase can be attributed to restricted vertical movement within the DSC modules. Furthermore, the integration of various spacers within the DSC modules, which enable bond wire connections to gate terminals, can significantly influence both the thermal performance and induced thermo-mechanical stresses. Depending on the materials used in the spacer, the thermal performance and thermo-mechanical stresses inside the module can vary. In this study, we have first analysed the thermal performance of the DSC power modules employing different spacers. Following that, we have also performed thermo-mechanical analysis in different solder layers. Finally, fatigue analysis is done to demonstrate the weakest solder layer inside the package.

This paper evaluates traction inverters for heavy-duty electric vehicles, focusing on key criteria such as raised power ratings with improved efficiency and power densities. Boosted voltage and current levels are required to achieve higher power levels and provide megawatt charging system solutions, which results in the need to utilize new semiconductors and topologies. In this study, 3-Level neutral point clamped (3L- NPC) and 2-Level 6-phase (2L-6Ph) voltage source inverters (VSIs) are evaluated and compared to conventional 2-Level 3-phase (2L-3Ph). The comparison uses figure-of-merit parameters and a virtual prototyping method based on several performance indices, such as efficiency, power density, output harmonic quality, and reliability. Then, efficiency maps are acquired to find out the sweet operating points, minimizing losses. Results show that the 3L-NPC VSI system provides a higher switching frequency, which also shrinks the size of the passive elements and cooling system. Although the 3L-NPC inverter requires additional power switches and isolated gate drivers, its estimated performance outweighs such reliability and cost-dependent issues. Therefore, this study concludes that multi-level inverter topologies hold promise for high-voltage, high-power traction drives.

Silicon carbide (SiC)-based metal-oxide-semiconductor field-effect transistors (MOSFETs) hold promising application prospects in future high-capacity high-power converters due to their excellent electrothermal characteristics. However, as nascent power electronic devices, their long-term operational reliability lacks sufficient field data. The power cycling test is an important experimental method to assess packaging-related reliability. In order to obtain data closest to actual working conditions, forward power cycling is utilized to carry out SiC MOSFET degradation experiments. Due to the wide bandgap characteristics of SiC MOSFETs, the short-term drift of the threshold voltage is much more serious than that of silicon (Si)-based devices. Therefore, an offline threshold voltage measurement circuit is implemented during power cycling tests to minimize errors arising from this short-term drift. Different characterizations are performed based on power cycling tests, focused on measuring the on-state resistance, thermal impedance, and threshold voltage of the devices. The findings reveal that the primary failure mode under forward power cycling tests, with a maximum junction temperature of 130 degrees C, is bond-wire degradation. Conversely, the solder layer and gate oxide exhibit minimal degradation tendencies under these conditions.

The HVDC industry is moving towards multivendor HVDC systems, with multiterminal systems under planning in many parts of the world, and the desire for DC-side system expansion included in many functional requirements. Today’s typical collaborative design methods are not suitable to meet the challenges of these future multivendor systems, which will increasingly require sharing of information about elements of the system (e.g., converter control, protection, …) as well as interdisciplinary decision-making on coordination of devices and the overall system functionality. One method to enable more effective system development in such an environment is Systems Engineering or Model-Based Systems Engineering (MBSE). There are numerous ways in which to use Systems Engineering to enable HVDC system specification, design, and implementation according to the needs of the application. This paper discusses the possible future needs of HVDC systems, and considers different ways in which Systems Engineering can be used to perform more effective specification and design in a multivendor context. The work is one outcome of CIGRE WG B4.85 (‘Interoperability in HVDC systems based on partially open-source software’). The use of MBSE in existing HVDC systems is first discussed, identifying that some manufacturers use Systems Engineering tools extensively for HVDC project design and development, but there is currently no framework or method for sharing models externally. Several case studies are then examined, discussing possible methodologies and benefits of using Systems Engineering for grid-level design, converter control definition, functional division, and grid-level control and protection definition. The high-level challenges and outlook for future widespread application of MBSE are then discussed, highlighting the need for additional technical harmonisation in the field as well as more efforts towards collaboration mechanisms to enable sharing of information that is becoming essential for effective multivendor system design and expansion.

Commercialization of SiC MOSFETs and electrification of the automotive sector has resulted in the accelerated development of power semiconductor devices. To take the most advantage of the SiC properties and make the power semiconductor modules automotive graded, the power module packaging technologies are developing at a rapid pace. New materials are being introduced and more innovative ways are being investigated to operate the SiC die at high temperatures while maintaining high reliability. Silver (Ag) sinter, due to its superior properties, has been introduced as a state-of-the-art die-attaching technology, while different ways are being investigated to either eliminate the aluminium (Al) bondwires or replace them with copper (Cu) counterparts. In this study, we will use the Finite Element (FE) method to investigate the impact of different packaging aspects like using copper foil and Ag sinter on thermal and mechanical performance of the power module. We will also investigate the effect of different packaging on power module reliability.

Solder layers, used as bonding material inside the power module to attach the semiconductor die on Direct Bond Copper (DBC) substrate and DBC substrate on baseplate, are one of the regions most prone to failure. The failure usually occurs in the form of solder cracks and depends on various operating conditions, such as-maximum temperature, temperature swing, and heating time. The cracks generated inside the solder layers can eventually result in its delamination. Power modules are usually power cycled to estimate the failure sites and mechanisms. However, the failure mechanisms can vary depending on the frequency, amplitude, and range of the temperature in the Power Cycling Tests (PCT). In this study, we have used the Finite Element Method (FEM) in COMSOL Multiphysics to analyse the impact of the PCT on both die attach, and baseplate attach solder layers. Additionally, the effect of the degree of asymmetry in the die position on the reliability of both the solder layers are analysed. The FEA (Finite Element Analysis) results are analysed to have a better understanding about the aspects impacting the lifetime of the power module.

Incorporation of inverter-based resources is progressively increasing in modern power systems. The absence of inherent physical inertia in converter-based systems has resulted in a decrease in the total inertia of the grid. Grid-forming control of voltage source converters emulates the workings of a conventional synchronous generator through frequency droop control, allowing the converter to provide inertial support while contributing to the support of grid voltage. This paper presents a dc-side impedance model of a grid-forming modular multilevel converter. A control interaction between a grid-forming and a grid-following converter in a back-to-back structure is investigated and a stabilizing compensator is proposed.