This paper investigates the impact of DC fault-limiting reactors (DCRs) on the dynamics of Modular Multilevel converter-based multi-terminal DC (MTDC) grids, with a particular focus on their damping and coupling characteristics. The first part examines the instability introduced by large DCR values using a simplified low-frequency model and a comprehensive small-signal analysis of a four-terminal meshed DC grid. A dedicated controller is proposed to stabilize the system and is compared with other mitigation measures, such as modifying the control mode and changing the power flow direction. The second part investigates the coupling effects of DCRs in DC grids, showing that the commonly assumed equivalent DC grid capacitance becomes invalid in the presence of DCRs. This leads to different conclusions regarding DC voltage support between stations, particularly during fast transient responses. All findings are validated through time-domain simulations of a four-terminal DC grid.
The performance-limiting electron and hole trapping centers in 4H-SiC PiN power diodes are determined by combined deep-level transient Fourier spectroscopy (DLTFS) experiments and technology computer-aided design (TCAD) simulations. Two electron traps E-1 (E-C - 0.19 eV) and E-2 (E-C - 0.67 eV) and three hole traps H-1 (E-V + 0.16 eV), H-2 (E-V + 0.3 eV), and H-3 (E-V + 0.63 eV) are detected by DLTFS. Since DLTFS measurements were limited to 400 K, a few deep-level defects could not be detected in our experiments. In addition to the traps identified by DLTFS, two deep levels commonly reported at elevated temperatures, E-3 (E-C - 1.65 eV) and H-4 (E-V + 1.43 eV), are integrated into the TCAD model to perform a reliable trapping analysis. The effects of electron traps, hole traps, and individual traps are evaluated by selectively excluding them from the simulation. Hole trapping is found to be more prominent than electron trapping in pristine (as-fabricated/untouched) diodes. Among the traps, shallow hole trap H-1 exhibits a strong impact in reducing the conduction current (followed by E-3) in pristine diodes. To explore the fundamental nature of each trap, the concentration (N-T) of an individual trap is increased to a higher value without changing the N-T of other defects. Subsequently, the diode characteristics are analyzed at higher N-T of the specific trap. The traps E-2 and E-3 significantly reduce the diode current at higher N-T. The deep acceptor E-2 is primarily responsible for the donor doping compensation in the n(-) drift layer.
The insertion of a dielectric barrier between the conductors in gas insulation can improve effectively the insulation performance in high voltage equipment such as MV gas insulated switchgear. The dielectric barrier increases the breakdown voltage because of two main reasons: increasing the shortest path, and allowing surface charge deposition to reduce the total electric field. The electric field measurement in such systems is a very important to understand the physical involved phenomena, however, it is so challenging. In this work, the electric field at the vicinity of the HV electrode is investigated experimentally and numerically in a needle-barrier-plane configuration under positive lightning impulse. The electric field is measured using a very compact and fully dielectric electrooptic probe. The results of the experimental measurements show a good agreement with the numerical simulations for both Ez and Er field components. The surface charge density having the same polarity as the applied voltage impacts mainly the vertical component of the electric field, while the space charge density generated by the PD activity impacts mainly the radial component of the electric field.
The global transition to renewable energy is transforming power systems, necessitating advanced transmission solutions to ensure reliability and resilience. High-voltage direct current (HVdc) systems, particularly multiterminal dc (MTdc) networks, are pivotal in integrating diverse renewable energy sources into hybrid ac/dc networks. These systems facilitate efficient power transfer over long distances and enable dynamic energy sharing across regions. However, the increasing penetration of inverter-based resources introduces complex control challenges that must be addressed to maintain grid stability and resilience.
The goal of this investigation is to validate the Inverse Power Model (IPM) – Arrhenius electro-thermal life model via the results of Accelerated Life Tests carried out at various voltages and temperatures on polypropylene-based blends developed in the NEWGEN project, to assess the endurance of this new insulation for HVDC cables to electro-thermal stress. The final aim is to select the best PP blends and space charge suppressing additives in the perspective of manufacturing prototypes of full-size HVDC cables. The present first part of the investigation focuses on a ternary PP blend put forward in a first stage. The second part of the investigation – a next paper – is devoted to a binary PP blend developed later, as such binary blend performed better from the manufacturing viewpoint. The values of Arrhenius parameter B obtained for the ternary blend are quite large, thus proving very good thermal endurance of the blend. Moreover, for both ternary and binary blends the values of life exponent of the IPM found in the first and second part of the investigation are also quite large; this result is a proof of the good voltage endurance of the PP blends. Failure times have exhibited a large scatter and a strong dependence on electric field and temperature - as expected - as well as a puzzling behavior of the life exponent versus temperature. As explained in Part 2, such behavior stems from the increase of the local field enhancement factor due to space charges as electric field and temperature rise.
