This paper comprehensively reviews several techniques that address the static and dynamic voltage balancing of series-connected MOSFETs. The effectiveness of these techniques was validated through simulations and experiments. Dynamic voltage-balancing techniques include gate signal delay adjustment methods, passive snubbers, passive clamping circuits, and hybrid solutions. Based on the experimental results, the advantages and disadvantages of each technique are investigated. Combining the gate-balancing core method with an RC snubber, which has proven both technically and commercially attractive, provides a robust solution. If the components are sorted and binned, voltage-balancing techniques may not be necessary, further enhancing the commercial viability of series-connected MOSFETs. An investigation of gate driver topologies yields one crucial conclusion: magnetically isolated gate drivers offer a simple and cost-effective solution for high-frequency (HF) applications (2.5–50 kHz) above 8 kV with an increased number of series devices. Below 8 kV, it is advantageous to move the isolation barrier from the gate drive IC to an optocoupler and isolated supply, allowing for a simple design with commercially available components.@en

Closed-form solutions are presented for calculating the reflection coefficient with corresponding uncertainty of metrology-grade 3.5 mm air-dielectric coaxial transmission lines for use as reference standards in S-parameter measurements up to 33 GHz. The closed-form solutions allow the calculation of the sensitivity coefficients required for calculating the propagation of uncertainties from the material and mechanical parameters of the transmission line toward its reflection coefficient uncertainties. The presented uncertainty framework evaluates every uncertainty source’s contribution, with uncertainties in reflection coefficient ranging from 1 · 10⁻³ up to 6 · 10⁻³. The approach is validated up to 33 GHz via a comprehensive measurement comparison of the reflection coefficient parameter for three 3.5 mm transmission lines with 16, 60, and 150 mm lengths. The values obtained by the proposed model agree well within the measurement uncertainties with known traceable calibration results of the transmission lines.

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In the future, series-connected SiC MOSFETs will become widely used in power-electronic-based medium and high voltage (HV) applications such as modular multilevel converters (MMCs). Balanced voltage sharing among the SiC MOSFET string is hard to be achieved due to possible deviation on MOSFET switching delay. In this paper, two types of gate signal delay adjustment methods (gate balancing core and improved RC snubber method) are presented to solve the unbalanced voltage sharing caused by MOSFET turn-off delay differences. The methods are validated with laboratory experiments performed on low-voltage prototypes and a performance comparison of these two approaches is given. Both methods significantly improve the drain-source voltage sharing, but the gate balancing core method is most suitable for HV and high-frequency applications.@en

The addition of RF interferometers to vector network analyzer (VNA) test benches has allowed for realization of low-noise high-frequency measurements of extreme impedance devices. However, when employing correction techniques such as the short-open-load method, the RF response of the interferometer hardware introduces measurement inaccuracies due to unwanted load-dependent inconsistencies. This letter presents a novel VNA calibration method that enables both low-noise and accurate small-signal characterization of highly mismatched devices. The proposed solution is experimentally validated in the 10-18-GHz band, confirming a 23-fold improvement in measurement resolution with absolute accuracy across the entire Γ range of the VNA. The accuracy of the new calibration process is verified via comparison with traceable reference standards supported by state-of-the-art uncertainties.@en

A method is presented for automated probing of on-wafer devices for measurements at millimetre-wave frequencies. The proposed method automatically detects the contact between the measurement probe and on-wafer device, based on the evaluation of variation in the input reflection coefficient. It is shown that, using this automated technique, about five times better measurement repeatability is achieved in millimetre-wave device characterisation.

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This paper analyzes and accurately models the complex noise behavior of vector network analyzers (VNAs) when measuring large-mismatch devices and subsequently shows how the VNA measurement noise performance is enhanced through implementation of a high-speed, broadband, active RF interferometer module. The presented VNA noise model provides a solid framework, benchmarked by measurement data, to analyze existing RF interferometer approaches. The performance improvement of the proposed interferometer implementation is then benchmarked in terms of magnitude and phase stability of the renormalized impedance level. A test bench employing the novel add-on RF interferometer module is presented and demonstrated to achieve high-speed cancellation of the scattered wave over a broad frequency band. The first experiment shows ultralow noise in a 1-18 GHz broadband measurement of co-planar waveguide 0.5-Ω and 5-k Ω impedance standards. Employing the proposed hardware setup improves the noise uncertainty for the 5-k Ω impedance standard by a factor of 8 and 20 at 1 and 18 GHz, respectively. In the second experiment, a factor of 2 height-resolution enhancement is achieved in a scanning microwave microscope when the RF interferometer module is added to the instrument.

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Methods for traceable characterization and uncertainty evaluation of planar I-port CPW short-open-Ioad (SOL) devices are developed. The agreement of modelling and verification measurement results greatly supports the application of the proposed parameterization models and used FEM-based EM modelling of CPW structures for traceable characterization of planar CPW-based SOL devices in the frequency range between a few kHz up to 50 GHz.

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The installation of phasor measurement units (PMUs) by Enduris, one of the distribution network operators in the Netherlands to monitor their 50 kV ring distribution grid has resulted in increased observability of the power flows and voltages. However, with the increased observability, there is a need to analyse the distribution grid based on the data generated by the PMU monitoring system. This study provides steady-state and dynamic analysis of the 50 kV Enduris ring distribution grid in terms of voltage and power flow behaviour based on the real-time data acquired from the PMUs. First, the Enduris 50 kV distribution grid under study is modelled in PowerFactory software. This model is subsequently used for analysis of the distribution grid behaviour for two contingencies. The contingencies are actual grid events observed by the PMUs, and using this data, the contingencies are simulated and analysed. The analysis results of each contingency are compared with the data from the PMU monitoring system.

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This paper presents a comparison between two different approaches to fault location both with and without utilising transmission line parameters. Firstly, an impedance-based parameter-dependent algorithm, derived by using modal transformation theory and fast Fourier transform is presented. The methodology is able to locate the fault whether it is on an overhead line or on an underground power cable. The second algorithm is a parameter-free fault location method that uses time synchronised data. Here, the unknown fault location is determined from voltage and current phasors, synchronously measured at both line terminals. This approach to fault location avoids the requirement for prior knowledge of line parameters, which is advantageous as line parameters are not always known precisely. This paper presents the results of algorithm testing through the use of ATPDraw simulations and MATLAB. The results were validated through laboratory experiments. The results of the line parameter-free model are compared with those from the parameter-dependent model. Both algorithms were tested for single line to ground faults.@en