State feedback linearized model for phase-controlled series-parallel resonant converters

This paper proposes a linearized large-signal state space model for phase-controlled series-parallel resonant converter. The model combines multiple-frequency and average state-space modeling techniques to generate a universal model with DC state variables that are easier to control compared to the fast resonant tank dynamics. In order to perform linearization, the proposed model utilizes a state feedback scheme from output filter inductor current. The model also serves as a tool for large signal prediction/estimation of converter state variables. The model accuracy was verified by comparing with a detailed switching model of the converter built in MATLAB simulation environment

Comparing SiC MOSFET, IGBT and Si MOSFET in LV distribution inverters

Efficency, power quality and EMI are three crucial performance drivers in LVDC applications such as electrical supply, EV charging or DC aerospace. Recent developments in SiC MOSFETs and MMC for LVDC promise two significant improvements in LVDC inverter performance. However, the designer is left with many combinations of technology and inverter level to choose from. This paper aims to clarify this choice by identifying one optimum Si design and one optimum SiC design, using detailed loss calculations. An IGBT inverter is included as a baseline. Loss calculations estimate the effects of Si MOSFET switching loss and all parasitic interconnection loss. The validity of the loss estimations are verified using careful experiments on a Si MOSFET cell. Close agreement indicates that the modelling approach is valid for extension to many cells in series, and to the parallel connection of many devices. Despite the lower EMI inherent in MMC inverters, Si MOSFETs risk worse EMI, due to poor reverse recovery characteristic. Slowed device gate switching experimentally demonstrates the reduction in switching noise, promising very low EMI. This initial study has therefore identified two promising candidate SiC and Si MOSFET inverters which will be fully constructed in future work, in order to aid designers in choosing the optimum semiconductor technology and topology for LVDC inverters

Comparison between flying capacitor and modular multilevel inverter

The paper describes the operational principle of flying capacitor and modular multilevel inverters. The detailed discussions of dc link capacitors voltage balancing methods for both inverters are given in order to enable fair comparison. The causes of dc link capacitors voltage imbalance in flying capacitor multilevel inverter with more than three levels are highlighted. Computer simulation is used to compare the performance of both inverters under several operating conditions

Comparison between two VSC-HVDC transmission systems technologies : modular and neutral point clamped multilevel converter

The paper presents a detail comparison between two voltage source converter high voltage dc transmission systems, the first is based on neutral point-clamped (also known as HVDC-Light) and the second is based on innovative modular multilevel converter (known as HVDC-Plus). The comparison focuses on the reliability issues of both technologies such as fault ride-through capability and control flexibility. To address these issues, neutral point-clamped and three-level modular converters are considered in both stations of the dc transmission system, and several operating conditions are considered, including, symmetrical and asymmetrical faults. Computer simulation in Matlab-Simulink environment has been used to confirm the validity of the results

Modular input-parallel output-series DC/DC converter control with fault detection and redundancy

Large offshore wind farms require extensi ve sub-sea cables within the collection network. Present solutions are based aro und medium-voltage AC collection networks. Recent studies have highlighted the poten tial benefits of DC collection networks. However, achieving DC/DC conversion at th e required voltage and power levels presents a significant challenge for wind-tu rbine power electronics. This paper proposes an alternative DC collection network based around a modular DC/DC converter with input-parallel output-series (IPOS) connection. This modular topology can overcome the limitations imposed by semiconduct or voltage ratings and provides fault-tolerant operation. Small-signal analysis of the converter is presented to be used to facilitate controller design for the converter inpu t and output stages. A new master- slave control scheme and distributed voltage sharin g controllers are proposed that ensure power sharing under all operating conditions , including during failure of a master module. This control scheme achieves fault-t olerant operation by allowing the status of master module to be reallocated to any he althy module. The proposed control scheme is validated using simulation and experiment ation, considering active power sharing between modules with parameter mismatch

Efficient base driver circuit for silicon carbide bipolar junction transistors

The silicon carbide bipolar junction transistor needs large transient currents supplied into and out of its base terminal for rapid switching. To realise this, it is normally desirable to have a base driver circuit supply rail at a high voltage. However, the device also needs a steady base current to hold it in the on-state. Supplying this current from a highvoltage source is inefficient. A circuit is presented that applies high transient base-emitter voltages, but with low driver circuit power consumption

Compaction of Rods: Relaxation and Ordering in Vibrated, Anisotropic Granular Material

We report on experiments to measure the temporal and spatial evolution of packing arrangements of anisotropic, cylindrical granular material, using high-resolution capacitive monitoring. In these experiments, the particle configurations start from an initially disordered, low-packing-fraction state and under vertical vibrations evolve to a dense, highly ordered, nematic state in which the long particle axes align with the vertical tube walls. We find that the orientational ordering process is reflected in a characteristic, steep rise in the local packing fraction. At any given height inside the packing, the ordering is initiated at the container walls and proceeds inward. We explore the evolution of the local as well as the height-averaged packing fraction as a function of vibration parameters and compare our results to relaxation experiments conducted on spherically shaped granular materials.Comment: 9 pages incl. 7 figure

Patient characteristics, anaesthetic workload and techniques in the UK: an analysis from the 7th National Audit Project (NAP7) activity survey

Detailed contemporary knowledge of the characteristics of the surgical population, national anaesthetic workload, anaesthetic techniques and behaviours are essential to monitor productivity, inform policy and direct research themes. Every 3–4 years, the Royal College of Anaesthetists, as part of its National Audit Projects (NAP), performs a snapshot activity survey in all UK hospitals delivering anaesthesia, collecting patient-level encounter data from all cases under the care of an anaesthetist. During November 2021, as part of NAP7, anaesthetists recorded details of all cases undertaken over 4 days at their site through an online survey capturing anonymous patient characteristics and anaesthetic details. Of 416 hospital sites invited to participate, 352 (85%) completed the activity survey. From these, 24,177 reports were returned, of which 24,172 (99%) were included in the final dataset. The work patterns by day of the week, time of day and surgical specialty were similar to previous NAP activity surveys. However, in non-obstetric patients, between NAP5 (2013) and NAP7 (2021) activity surveys, the estimated median age of patients increased by 2.3 years from median (IQR) of 50.5 (28.4–69.1) to 52.8 (32.1–69.2) years. The median (IQR) BMI increased from 24.9 (21.5–29.5) to 26.7 (22.3–31.7) kg.m–2. The proportion of patients who scored as ASA physical status 1 decreased from 37% in NAP5 to 24% in NAP7. The use of total intravenous anaesthesia increased from 8% of general anaesthesia cases to 26% between NAP5 and NAP7. Some changes may reflect the impact of the COVID-19 pandemic on the anaesthetic population, though patients with confirmed COVID-19 accounted for only 149 (1%) cases. These data show a rising burden of age, obesity and comorbidity in patients requiring anaesthesia care, likely to impact UK peri-operative services significantly