The arcing-involved pulsating coagulation mode with both active and blank periods is essential for modern electrosurgery. This paper begins with a comprehensive introduction to such a pulsating mode, followed by its implementation challenges. Then, an industrial-scale low-speed microcontroller unit (MCU), TMS320F28379D, is utilized to exemplify the proposed output sampling and data-transferring strategy on a gallium nitride (GaN)-based high-frequency inverter that enables coagulation mode with interweaved active periods and blank periods. The inverter prototype fills the active period with 390 kHz sinusoids of amplitude ranging from hundreds to thousands of Volts, while maintaining null outputs during blank periods. The strategy of sampling the above-mentioned sinusoidal outputs, coupled with their data transfer facilitated by direct memory access (DMA), is also articulated for subsequential power computation. Besides that, a novel nonfixed duty cycle approach, featuring an alterable number of sinusoids as the active period, is proposed and integrated into the GaN-based inverter to enhance mode safety. Finally, the power tracking performance of the mode is evaluated initially on resistive load, secondarily on resistive plus capacitive load (R-C), and thirdly on fresh biotissue with the appearance of electrical arcing. The existing necessity of the null blank periods is examined at the end of the paper.

Multilevel converters have enabled various applications that are not possible with conventional two-level converters. Many of these applications, however, need a high output bandwidth, often approaching the switching rate limit of the transistors, with high quality, e.g., to actively stabilize and dampen a DC grid or specifically excite certain molecules or neural circuits in medical applications. A high bandwidth approaching the switching rate challenges existing modulation methods: carrier-based switching modulation is fine at low frequencies but experiences interaction between the carrier and the signal at the upper end of the spectrum; fundamental-frequency switching, such as nearest-level modulation (NLM), perform well at high frequencies but cause intolerable distortion for low frequency contents. We propose a hybrid modulation concept that can combine any methods from these two classes. It passes the error of a fundamental frequency method through a filtered switching modulator to combine the high output quality of the latter with the high bandwidth of the former. We optimize the filter to avoid under-modulation of the signal with the carrier of the modulator and to achieve the minimum overall distortion throughout a wide output bandwidth. We demonstrate the performance experimentally with a cascaded-bridge converter and compare it with the best prior arts. This technique ensures a usable output bandwidth up to 100% of the switching rate and maintains a total distortion level below 3%.

Well-selected power with accurate delivery is of importance in electrosurgery to generate proper temperature at the cutting site, and thus, reduce undesired collateral tissue damages. Conventional electrosurgery generator (ESG) targets tracking a preset power, manually set by surgeons per their experience before the surgery, with high accurate delivery. It is possible that this fixed power setting is not at the optimal point and, thus, increases the possibility of added-collateral biomedical tissue damage. To eliminate the potential negative impact of the fixed and ill-suited power setting, a real-time feedback control scheme is outlined in this article to adjust the preset power of the ESG to create an adaptive power reference, which is then tracked using an experimental high-frequency inverter (HFI) that enables electrosurgery with a fundamental (sinusoidal) output frequency of 390 kHz. Subsequently, experiments using the gallium nitride (GaN)-based HFI are carried out to demonstrate the efficacy of the new variable-power approach over the conventional fixed power approach in terms of collateral tissue damage reduction.

This paper presents a multi-resonant-frequency (MRF) filter for a high-frequency inverter (HFI) used in electrosurgery. The fundamental (sinusoidal) output frequency of the HFI is 390 kHz and is the same as the switching frequency of the HFI. The MRF is designed to extract the fundamental frequency of the tri-state bipolar waveform, generated by the HFI operating with phase-shift control. The structure and operation of the MRF are outlined. An experimental 300 W GaN-FET-based HFI prototype is developed to validate the feasibility of the proposed MRF under closed-loop control.

In order to apply power electronics systems to applications such as superconducting systems under cryogenic temperatures, it is necessary to investigate the characteristics of different parts in the power electronics systems. This paper reviews the influence of cryogenic temperature on power semiconductor devices including Si and wide bandgap switches, integrated circuits, passive components, interconnection and dielectric materials, and some typical cryogenic converter systems. Also, the basic theories and principles are given to explain the trends for different aspects of cryogenically cooled converters. Based on the review, Si active power devices, bulk CMOS based integrated circuits, nanocrystalline and amorphous magnetic cores, NP0 ceramic and film capacitors, thin/metal film and wirewound resistors are the components suitable for cryogenic operation. Pb-rich PbSn solder or In solder, classic PCB material, most insulation papers and epoxy encapsulant are good interconnection and dielectric parts for cryogenic temperatures.

This paper investigates the dependence of the supercapacitor Peukert constant on its terminal voltage, aging condition, and operating temperature. Recent studies show that the charge delivered by a supercapacitor during a constant current discharge process increases when the discharge current decreases if the discharge current is above a certain threshold, i.e., Peukert's law applies. By conducting extensive experiments using three supercapacitor samples with different rated capacitances from different manufacturers, this paper reveals that the Peukert constant increases when the initial voltage of the constant current discharge process is lower, the supercapacitor is more heavily aged, or the operating temperature is lower. The physical mechanisms accounting for the Peukert constant dependence are illustrated by analyzing an ladder circuit model. When the supercapacitor terminal voltage is higher, the aging condition is lighter, or the operating temperature is higher, more charge is stored in the supercapacitor. Consequently, when the same discharge current is applied, the discharge time is longer and the branch capacitors are more deeply discharged. Therefore, the relaxation effects of the slow branches are reduced and the supercapacitor behaves more like a single capacitor rather than a distributed capacitor network, which ultimately leads to a lower Peukert constant.

Wireless energy harvesting devices convert received AC energy into DC voltages suitable to power the back-end functionality of the devices. The low energy available to the devices require high AC-DC conversion efficiency in order for enough power to be delivered to the load. This paper presents a model to characterize loss through charge pump cells in wireless energy harvesting devices. The proposed model includes the time-domain effects of the input radio-frequency (RF) energy wave and provides additional insight into how clock and switch parameters along with architecture considerations can be used to improve the efficiency of AC-DC conversion. Results are verified using simulation in a 0.18-m CMOS technology. We show the impact of threshold voltage on reverse conduction and the limitations on increasing transistor switch sizes to support high current loads. Design examples use the presented model to optimize design parameters to decrease loss in the charge pump. We compare the performance between sine-wave and square-wave clocked charge pumps to show the trade-off between charge pump loss and clock generation power consumption. Furthermore, the benefits of easily computing architectural changes is demonstrated using the proposed model showing how the calculated equivalent resistance can be used to determine the benefits of mixed-mode clocking.

This paper investigates the effects of three aspects of the supercapacitor physics on its charge capacity: porous electrode structure, charge redistribution, and self-discharge. The relationship between the delivered charge and the discharge current is examined for both the upper and lower bounds of the utilized charge capacity, which refers to the amount of charge delivered during a constant current discharge process. In the upper bound case, Peukert's law applies when the discharge current is above a certain threshold and does not apply anymore if the discharge current is below the threshold. In the lower bound case, if the discharge current is above the threshold, the delivered charge increases when the discharge current decreases although the increase rate is lower compared to that in the upper bound case. The individual and combined effects of supercapacitor physics are studied. The porous electrode structure and the charge redistribution process result in an increase in the delivered charge when a smaller discharge current is applied. The impact of self-discharge is negligible when the discharge current is relatively large. If the discharge current is sufficiently small, self-discharge results in a significant energy loss and consequently a drop in the delivered charge.

This paper investigates the impact of charge redistribution on supercapacitor charge capacity by experimentally estimating the charge capacity bounds. An analysis of a physics-based ladder circuit model for supercapacitors reveals the theoretical bounds and provides guidelines for designing experiments to estimate the bounds. The upper bound corresponds to a long time constant voltage charging process and the lower bound is established using a charging process with the largest possible current. Bounds of two types of supercapacitor charge capacity are estimated: the total charge stored in the supercapacitor that can be released during multiple discharging processes and the utilized charge delivered during one discharging action. The relationship between the utilized charge capacity and the discharge current is examined and different patterns are observed depending on the supercapacitor state of charge (SOC). For a fully charged supercapacitor, the utilized capacity increases when the discharge current decreases. For a supercapaictor partially charged by a relatively large current, the utilized capacity is dependent on both the discharge current and the supercapacitor operation voltage range. The difference between the bounds is significant for both types of charge capacity. These observations provide guidelines for optimizing the supercapacitor charging and discharging policies for different applications.

A multiscale electrothermal simulation approach is presented to optimize the design of a hybrid switch soft-switching inverter using a library of dynamic electrothermal component models parameterized in terms of electrical, structural, and material properties. Individual device area, snubber capacitor, and gate drive timing are used to minimize the total loss of the soft-switching inverter module subject to the design constraints including total device area and minimum on-time consideration. The proposed multiscale electrothermal simulation approach allows for a large number of parametric studies involving multiple design variables to be considered, drastically reducing simulation time. The optimized design is then compared and contrasted with an already existing design from the Virginia Tech Freedom Car Project using the generation II module. It will be shown that the proposed approach improves the baseline design by 16% in loss and reduces the cooling requirements by 42%. Validation of the electrical and thermal device models against measured data is also provided.