Search

Under inverter operating conditions, significant loss is incurred by the insulated gate bipolar transistor (IGBT) (referred to as T2 tube) in the lower part of the half-bridge submodule. The reduction of loss is beneficial for the improvement of equipment operation reliability. At the same time, the suppression of capacitor ripple voltage has the advantage for reducing capacitor demand and enhancing power density. However, attention is not given by existing optimization control strategies to the contradiction between loss distribution optimization and capacitor ripple voltage, making it difficult to balance equipment operation reliability and power density. Therefore, a comprehensive optimization method that combines the reduction of T2 transistor losses and the suppression of capacitor voltage ripple is proposed in this article. Firstly, the inherent contradiction between reducing the on-state loss of the T2 transistor and suppressing capacitor voltage ripple is explained by analyzing the impact path of charge on device loss and capacitor ripple voltage. Then, by introducing a penalty function, a comprehensive objective function is established that takes into account T2 transistor losses and capacitor voltage ripple. Subsequently, using the active bypass strategy as an example, a comprehensive optimization method based on the injection of second harmonic current and third harmonic voltage is proposed by analyzing the impact of the second harmonic current and third harmonic voltage injection on T2 transistor loss and capacitor voltage ripple. Finally, a simulation model is built in MATLAB/Simulink and PLECS for verification. The simulation results suggest that the reliability and power density of the device increase by the comprehensive optimization method, considering both T2 transistor losses and capacitor voltage ripple.

Power losses on the upper and bottom insulated gate bipolar transistors (IGBTs) in half bridge sub-modules (HBSMs) are uneven when hybrid modular multilevel converters (MMCs) work as inverters. The loss of the bottom IGBT in HBSM is much higher than any other device, which results in the high thermal stress and failure rate. To address this problem, a device power loss distribution optimization method is proposed in this paper. Firstly, device power losses are calculated, and the distribution characteristic is analyzed. Secondly, the influence of sub-module capacitor voltage on the device power loss is analyzed, and it is found that the loss of the bottom IGBT can be reduced for a low sub-module capacitor voltage. Thirdly, through combining third harmonic voltage injection and the differential distribution of the arm output voltage reference, a loss distribution optimization method based on low sub-module capacitor voltage is proposed. Finally, the simulation and experiment results verify that the proposed method can improve the uneven device loss distribution of hybrid MMC and the operation reliability of the converter.

Pre-chamber jet ignition is a key technology for future high-efficiency natural gas (NG) engines. It can achieve fast and stable combustion through excellent ignition performance. However, there are still some challenges, such as high combustion instability near the lean burn limit and the narrow engine operating range. Therefore, this paper investigates the combustion instability of a pre-chamber NG engine under ultra-diluted conditions by experimental method. At two engine loads, experiments are carried out with different jet ignition intensity schemes to study the effect of jet ignition intensity on the cyclic combustion variations. Then, the combustion instability characteristics of the pre-chamber NG engine are studied by cyclic variation analysis and phase space reconstruction. The results show that with the increase in the jet ignition intensity, the cyclic combustion variations decrease, and the cyclic variation coefficient of the indicated mean effective pressure decreases to below 2%. The lean burn limit of the pre-chamber natural gas engine is extended to an excess air ratio of 2.0. The operation instability of the pre-chamber NG engine is mainly due to cyclic variations in the ignition and combustion process. The nonlinear dynamic analysis shows that the combustion process in the lean burn pre-chamber NG engine behaves with chaotic characteristics under the operating conditions of low jet ignition intensity. As the jet ignition intensity increases, the combustion stability is improved and the cycle-to-cycle variations change from fairly deterministic to more stochastic behavior. The chaotic characteristics of the combustion process become weaker. In conclusion, it is of great importance to generate stable and high ignition intensity jets for reducing combustion instability and improving combustion efficiency in lean burn pre-chamber NG engines. [ABSTRACT FROM AUTHOR]

Objective. We aimed to examine the benefits of catheter ablation on left heart structure and function in patients with persistent atrial fibrillation (AF) accompanied by heart failure (HF) with preserved ejection fraction (HFpEF), in comparison with the benefits in patients with AF accompanied by HF with reduced ejection fraction (HFrEF) or patients with no HF. Methods. A total of 399 patients with nonvalvular persistent AF who underwent catheter ablation from 2015 to 2021 were retrospectively included sixty‐seven patients with recurrence of AF within 1 year were excluded, as well as 53 patients who failed to be followed up at (12 ± 1) months after the procedure. Finally, 279 patients who fulfilled the criteria were included and divided into these groups: the HFpEF group (left ventricular ejection fraction (LVEF) ≥50% and N‐Terminal Pro‐Brain Natriuretic Peptide (NT‐proBNP) ≥125 pg/ml or E/e′ ≥15, n = 116), HFrEF group (LVEF <50%, n = 48), and no HF group (NT‐proBNP <125 pg/ml, n = 115). The endpoints were changes in image‐based functional status from baseline to 1 year, including echocardiogram and speckle‐tracking echocardiography. Results. The left atrial structure of patients with HFpEF decreased significantly 1 year after catheter ablation (left atrial anteroposterior dimension: 41.48 ± 4.53 mm vs. 38.64 ± 4.40; left atrial mediolateral dimension: 41.99 ± 5.52 vs. 38.24 ± 4.63 mm; left atrial superoinferior dimension: 61.36 ± 6.73 vs. 56.44 ± 6.97 mm). The left atrial and left ventricular volumes were significantly reduced and the ejection fraction was increased in all three groups, with HFrEF patients benefiting more. In the speckle‐tracking echocardiography indexes, significant improvements were observed in left atrial strain (16.83 ± 6.91 vs. 28.05 ± 9.92), left atrial storage function (0.97 ± 0.38 vs. 1.49 ± 0.58), and left atrial pump function (−1.15 ± 0.55 vs. −1.68 ± 0.75) among HFpEF patients after 1 year, with no changes in left atrial conduit function (−1.55 ± 0.62 vs. −1.50 ± 0.54). In addition to the above improvements in left atrial structure and function, there was no significant improvement in left ventricular diastolic function in patients with HFpEF (E/e′, 14.11 ± 5.52 vs. 14.30 ± 7.25, P = 0.85). Conclusion. Catheter ablation is beneficial in restoring sinus rhythm in patients with persistent AF with coexisting HFpEF, significantly decreasing the left atrial size, improving left atrial storage function and left atrial pump function, and increasing left atrial and left ventricular ejection fraction. [ABSTRACT FROM AUTHOR]

Background: Recent studies suggested that the left bundle branch area pacing (LBBAP) has a better efficacy to reduce QRS duration and produce a lower pacing threshold than the conventional right ventricular outflow tract septal pacing (RVOP), which resulted in a better cardiac function and ventricular synchronization. However, whether the LBBAP has a better efficacy in improving left atrial structure, function in pace‐dependent patients compared with RVOP has not been well studied. Objective: The purpose of this study was to compare the atrial outcomes of pace‐dependent patients who received LBBAP or RVOP procedures. Methods and Results: A total of 72 patients (including II° AVB, high AVB, and III° AVB, excluding atrial fibrillation patients with atrioventricular block) consecutively enrolled in this single‐center prospective clinical study and randomly assigned to the RVOP group and the LBBP group with 36 patients. All patients were pace‐dependent. The changes in echocardiogram, speckle‐tracking echocardiography, brain natriuretic peptide (BNP), and 6‐min walking distance were documented and compared between two groups at baseline, 7 days, 1, 3, and 6 months after the implantation. There were no significant differences in baseline characteristics between the two groups. The results of the study were as following: (1) left atrial structure index: Our study indicated that there are no significant differences in left atrial anteroposterior dimension (LAAPD), left atrial superoinferior dimension, and left atrial mediolateral dimension between two groups. While the LAAPD in the LBBAP group was significantly reduced at 6 months after implantation ([38.22 ± 2.17] mm vs. [34.13 ± 1.59] mm, p <.05). (2) Left atrial strain index: We observed that the S% was significantly improved in both groups at 3 and 6 months after implantation but more prominent in the LBBAP group at 6 months (36.94 ± 11.67 vs. 25.87 ± 8.93, p =.01). SRs, SRe were improved in the RVOP group at 6 months after implantation but was further significantly increased in the LBBAP group. Similarly, the SRa in the LBBAP group was significantly better than the RVOP group after 6 months (−2.11 ± 0.75 vs. −2.51 ± 0.70, p =.04). (3) Left atrial ejection index: LAEF% in the LBBAP group was significantly improved compared with the RVOP group (60.02 ± 1.88 vs. 53.65 ± 2.45, p =.047) and baseline (60.02 ± 1.88 vs. 49.68 ± 2.75, p <.05) at 6 months after the surgery. (4) Left ventricular ejection index: The LVEF% in the LBBAP group was significantly increased than the RVOP group after 6 months (69.14 ± 4.99 vs. 64.60 ± 4.84, p =.01) and the BNP level was significantly lower in the LBBAP group compared with the RVOP group at 7 days, 1, 3, and 6 months after implantation (p <.05). (5) 6‐min walking distance: the 6‐min walking distance was significantly increased at 3 and 6 months after implantation compared with that before (p <.05) in both groups, but was more prominent in LBBAP groups ([483.03 ± 11.02] m vs. [431.09 ± 10.69] m,p <.05). Conclusion: Compared with the traditional RVOP, the LBBAP procedure increased left atrial myocardial stress as well as left atrial ejection in pace‐dependent patients at follow‐up to 6 months. [ABSTRACT FROM AUTHOR]

The ideal skull defect repairing material should have good biocompatibility and mechanical properties, and contribute to osteogenesis. In this study, we designed and fabricated biodegradable, bioactive and mechanically robust porous scaffolds composed completely of biological materials. We used a gelatin–chitosan blend as the matrix, sodium phytate instead of toxic glutaraldehyde for cross-linking, and the pH-neutral bioactive glass (PSC) to improve biological activity and mechanical properties. The chitosan–gelatin–30%PSC/sodium phytate composite scaffold avoided the problems of high toxicity in conventional cross-linking agents with glutaraldehyde, the poor mechanical support of the pure chitosan or gelatin scaffold, and the mismatch of the degradation rate with bone repair, becoming a promising new candidate for skull defect repair. [ABSTRACT FROM AUTHOR]

The smart car is designed based on Freescale’s MC9S12XS128 and a linear CCD camera. The linear CCD collects the road information and sends it to MCU through the operational amplifier. The PID control algorithm, the proportional–integral–derivative control algorithm, is adopted synthetically to control the smart car. First, the smart car’s inclination and angular velocity are detect through the accelerometers and gyro sensors, then the PD control algorithm, the proportional–derivative control algorithm, is employed to make the smart car have the ability of two-wheeled self-balancing. Second, the speed of wheel obtained by the encoder is fed back to the MCU by way of pulse signal, then the PI control algorithm, the proportional–integral control algorithm, is employed to make the speed of smart car reach the set point in the shortest possible time and stabilize at the set point. Finally, the PD control algorithm is used to regulate the smart car’s turning angle to make the smart car respond quickly while the smart car is passing the curve path. The smart car can realize the self-balancing control of two wheels and track automatically the black and while lines to march.

In this paper, the Nyquist admittance ratio criterion was used to analyse the influencing factors on the stability of the system, such as the parameters of DC line, the intensity of interconnected AC power grid, the droop coefficient and etc. The theoretical analysis showed that the increase of the DC line resistance would decrease the system stability margin, while the increase of the DC line inductance had small effect on the system stability margin; the weaker the gird intensity was, the smaller the system stability margin was, while the larger the droop coefficient was, the larger the system stability margin was. In the case that AC and DC line parameters were the same, the system stability margin under Udc-Idc droop control mode was larger than that under Udc-P droop control mode. According to these influencing factors, suggestions were given to improve system damping and system stability through reducing the impedance of DC line, enhancing the interconnection of AC power grid and optimising the droop coefficient. Finally, a detailed simulation model was built with DIgSILENT simulation tool to verify the correctness of the above theoretical analysis by time-domain simulation results. [ABSTRACT FROM AUTHOR]

The penetration of wind power is increasing in distribution network for reducing reliance on fossil fuels and covering continuously increasing demand for energy. However, it is argued that the forecasting error of wind power cannot be avoided even using the best forecasting approach. Therefore, in this study, a mean‐variance‐skewness based expectation maximisation (MVSbEM) model has been proposed by maximisation of the mean and skewness while simultaneously minimisation of the variance to obtain the optimal trade‐off relationship between the profit and risk of distribution network planning (DNP) considering uncertain wind power integrated. In the MVSbEM model, the indexes of network loss, voltage deviation, and investment cost are concurrently taken into account under several kinds of actual operation constraints. In addition, the authors have made a full investigation on the MVSbEM by considering different forecasting errors, power factors of wind power, the different forecasting wind speeds, the number of wind turbines as well as the lines and substations upgrading. Furthermore, in order to reduce the computational burden, the Latin hypercube sampling method is used to sample uncertain wind speed. The feasibility and effectiveness of the MVSbEM model have been comprehensively evaluated on a modified IEEE 33‐bus system. [ABSTRACT FROM AUTHOR]