Switching Frequency Improvement of a High Speed on/off Valve Based on Pre-excitation Control Algorithm

The high-speed on/off valve(HSV)serves as the fundamental component responsible for generating discrete fluids within digital hydraulic systems.As the switching frequency of the HSV increases,the properties of the generated discrete fluid approach those of continuous fluids.Therefore,a higher frequency response characteristic of HSV is the key to ensure the control accuracy of digital hydraulic systems.However,the current research mainly focuses on its dynamic performance,but neglect its FRC.This paper presents a theoretical analysis demonstrating that the FRC of the HSV can be enhanced by minimizing its switching time.The maximum switching frequency(MSF)is mainly determined by opening dynamic performance when HSV operates with low switching duty ratio(SDR),whereas the closing dynamic performance limits the MSF when HSV operates with high SDR.Building upon these findings,the pre-excitation control algorithm(PECA)is proposed to reduce the switching time of the HSV,and consequently enhance its FRC.Experimental results demonstrate that PECA shortens the opening delay time of HSV by 1.12 ms,the closing delay time by 2.54 ms,and the closing moving time by 0.47 ms in comparison to the existing advanced control algorithms.As a result,a larger MSF of 417 Hz and a wider controllable SDR range from 20%to 70%were achieved at a switching frequency of 250 Hz.Thus,the proposed PFCA in this paper has been verified as an effective and promising approach for enhancing the control performance of digital hydraulic systems.

Effect of Acupuncture Cooperated with Low-frequency Repetitive Transcranial Magnetic Stimulation on Chronic Insomnia： A Randomized Clinical Trial

The effect of acupuncture cooperated with low-frequency repetitive transcranial magnetic stimulation （rTMS） on chronic insomnia was explored. Seventy-eight patients with chronic insomnia were randomly allocated into two groups： treatment group and control group. In the treatment group, the patients received acupuncture combined with rTMS treatment, and those in the control group were given acupuncture cooperated with sham rTMS treatment, 3 days per week for 4 weeks. Before and after treatment, the primary outcomes including the scores on Insomnia Severity Index （ISI） and Pittsburgh Sleep Quality Index （PSQI） and the secondary outcomes including total sleep time （TST）, sleep onset latency （SOL）, wake after sleep onset （WASO）, sleep efficiency （SE%） recorded by sleeping diary and actigraphy were observed in both groups. Seventy-five participants finished the study （38 in treatment group and 37 in control group respectively）. After treatment, the scores in the two groups were improved significantly, more significantly in the treatment group than in the control group. It can be inferred that acupuncture cooperated with rTMS can effectively improve sleep quality, enhance the quality of life of patients and has less side effects.

High efficiency sub-nanosecond electro-optical Q-switched laser operating at kilohertz repetition frequency

Based on a theoretical model of Q-switched laser with the influences of the driving signal sent to the Pockels cell and the doping concentration of the gain medium taken into account,a method of achieving high energy sub-nanosecond Q-switched lasers is proposed and verified in experiment.When a Nd:YVO4 crystal with a doping concentration of 0.7 at.%is used as a gain medium and a driving signal with the optimal high-level voltage is applied to the Pockels cell,a stable single-transverse-mode electro-optical Q-switched laser with a pulse width of 0.77 ns and a pulse energy of 1.04 mJ operating at the pulse repetition frequency of 1 kHz is achieved.The precise tuning of the pulse width is also demonstrated.

Effect of ultra-low frequency repetitive transcranial magnetic stimulation on dysphagia in elderly patients with acute cerebral infarction and quality of life

Objective:To investigate the clinical effect of ultra-low frequency repetitive transcranial magnetic stimulation on dysphagia in elderly patients with acute cerebral infarction and its impact on quality of life.Methods:60 elderly patients with dysphagia caused by acute cerebral infarction were randomly divided into rTMS group and control group,30 cases in each group.Both groups received routine drug therapy and swallowing function training.rTMS group was additionally treated by ultra-low frequency(10mHZ)repetitive transcranial magnetic stimulation for 14 days.The changes of NIHSS score andADL score and NSE serum level and Wa Tian drinking water experiment and Fujishima Ichiro dysphagia scale score and SWAL-QOL score and SF-36 score were observed between the two groups before and after treatment.The clinical effect was evaluated by Wa Tian drinking water experiment.Results:After treatment,The clinical effective rate in rTMS group was significantly higher compared with that in the control group(P<0.05),NIHSS score and serum NSE level were significantly lower compared with the control group(P<0.05),ADL score and Fujishima Ichiro dysphagia score and SWAL-QOL score and SF-36 scores were significantly higher compared with the control group(P<0.05).After treatment,SF-36 total score(or SWAL-QOL Score)was negatively correlated with NSE serum level and NIHSS score,which was positively correlated with ADL score and Fujishima Ichiro dysphagia scale score score.Conclusion:Ultra-low frequency rTMS therapy can reduce NSE level,effectively improve dysphagia in elderly patients with acute cerebral infarction and significantly improve the elderly patients'life quality.

Cactus-Shaped Frequency Reconfigurable Antenna for Sub 10 GHz Wireless Applications

This paper presents,a novel cactus shaped frequency reconfigurable antenna for sub 10 GHz wireless applications.PIN diode is utilized as an electrical switch to achieve reconfigurability,enabling operation in four different frequency ranges.In the switch ON state mode,the antenna supports 2177-3431 and 6301-8467 MHz ranges.Alternatively,the antenna resonates within 2329-3431 and 4951-6718 MHz while in the OFF state mode.Radiation efficiency values,ranging from 68%to 84%,and gain values,ranging from 1.6 to 4 dB,in the operating frequency bands.the proposed antenna satisfy the practical requirements and expectations.The overall planner dimensions of the proposed antenna model is 40×21 mm^(2).Moreover,the measurement results from the prototype support the simulation results.Based on the frequency ranges supported by the antenna,it can be used for multiple wireless standards and services,including Worldwide interoperability and Microwave Access(WiMAX),Wireless Fidelity(Wi-Fi),Bluetooth,Long Term Evolution(LTE)and satellite communications.This increases its applicability for use in mobile terminals.

Degradation and breakdown behaviors of SGTs under repetitive unclamped inductive switching avalanche stress

The repetitive unclamped inductive switching(UIS)avalanche stress is conducted to investigate the degradation and breakdown behaviors of conventional shield gate trench MOSFET(C-SGT)and P-ring SGT MOSFETs(P-SGT).It is found that the static and dynamic parameters of both devices show different degrees of degradation.Combining experimental and simulation results,the hot holes trapped into the Si/SiO_(2) interface and the increase of crystal lattice temperature should be responsible for the degradation and breakdown behaviors.Moreover,under repetitive UIS avalanche stress,the reliability of P-SGT overcomes that of C-SGT,benefitting from the decreasing of the impact ionization rate at bottom of field oxide caused by the existence of P-ring.

High-power High-efficient and Simplified High-frequency Switching Power Supply for Electrolytic Plating

针对大功率电解电镀开关电源的输入整流级引起的无功和谐波等电能质量问题,研究了一种基于高效PWM整流的高频开关电源。该电源前级整流器仅用4个开关管来进行PWM整流,后级采用半桥逆变器进行高频变换,显著减少了开关数量。针对三相四开关PWM整流器,推导一种基于开关模型的无差拍控制方法,该方法可实现系统的快速、无差整流。针对多台开关电源的并联均流问题,提出一种基于虚拟阻抗的自均流控制方法,可实现多台电源的均流稳定运行。通过仿真与实验验证了所提结构和控制方法的正确性。

A fractional frequency divider based on phase switching and negative feedback delta-sigma modulator for MMMS applications

A fractional frequency divider based on phase switching and negative feedback delta-sigma modulator(NF-DSM) is presented. The phase switching circuit, realized by switching 8 signals generated by a divider-by-4 circuit, is adopted to reduce the frequency division step. The NF-DSM, which can obtain smooth output spectra, is proposed to generate the fractional part of the division ratio, moreover, the integer part of the division ratio is realized by a divider-by-2/3 circuit chain. Fabricated in TSMC 0.18 μm RF CMOS technology, the fractional frequency divider achieves a measured operation frequency from 0.5 GHz to 8 GHz. With a 1.8 V supply voltage, the maximum current consumption of the whole divider is 17.5 mA, and the chip area is 0.58 mm^2, including the pads.

Effects of different frequencies of repetitive transcranial magnetic stimulation on the recovery of upper limb motor dysfunction in patients with subacute cerebral infarction

Studies have confirmed that low-frequency repetitive transcranial magnetic stimulation can decrease the activity of cortical neurons, and high-frequency repetitive transcranial magnetic stimulation can increase the excitability of cortical neurons. However, there are few studies concerning the use of different frequencies of repetitive transcranial magnetic stimulation on the recovery of upper-limb motor function after cerebral infarction. We hypothesized that different frequencies of repetitive transcranial magnetic stimulation in patients with cerebral infarction would produce different effects on the recovery of upper-limb motor function. This study enrolled 127 patients with upper-limb dysfunction during the subacute phase of cerebral infarction. These patients were randomly assigned to three groups. The low-frequency group comprised 42 patients who were treated with 1 Hz repetitive transcranial magnetic stimulation on the contralateral hemisphere primary motor cortex （M1）. The high-frequency group comprised 43 patients who were treated with 10 Hz repetitive transcranial magnetic stimulation on ipsilateral M1. Finally, the sham group comprised 42 patients who were treated with 10 Hz of false stimulation on ipsilateral M1. A total of 135 seconds of stimulation was applied in the sham group and high-frequency group. At 2 weeks after treatment, cortical latency of motor-evoked potentials and central motor conduction time were significantly lower compared with before treatment. Moreover, motor function scores were significantly improved. The above indices for the low- and high-frequency groups were significantly different compared with the sham group. However, there was no significant difference between the low- and high-frequency groups. The results show that low- and high-frequency repetitive transcranial magnetic stimulation can similarly improve upper-limb motor function in patients with cerebral infarction.

A Novel Technique for Detection of Time Delay Switch Attack on Load Frequency Control

In this paper, we focus on the estimation of time delays caused by adversaries in the sensing loop (SL). Based on the literature review, time delay switch (TDS) attacks could make any control system, in particular a power control system, unstable. Therefore, future smart grids will have to use advanced methods to provide better situational awareness of power grid states keeping smart grids reliable and safe from TDS attacks. Here, we introduce a simple method for preventing time delay switch attack on networked control systems. The method relies on an estimator that will estimate and track time delays introduced by an adversary. Knowing the maximum tolerable time delay of the plant’s optimal controller for which the plant remains stable, a time-delay detector issues an alarm signal when the estimated time delay is larger than the minimum one and directs the system to alarm state. In an alarm state, the plant operates under the control of an emergency controller that is local to the plant and remains in this mode until the networked control system state is restored. This method is an inexpensive and simple way to guarantee that an industrial control system remains stable and secure.

Model predictive control of three-level active front-end converter with low switching frequency

In medium voltage-high power(MV-HP)applications,the high switching frequency of power converter will result in unnecessary energy losses,which directly affect efficiency.To resolve this issue,a novel finite control set-model predictive control(FCS-MPC)with low switching frequency for three-level neutral point clamped-active front-end converters(NPC-AFEs)is proposed.With this approach,the prediction model of three-level NPC-AFEs is established inα-βreference frame,and the control objective of low average switching frequency is introduced into a cost function.The proposed method not only achieves the desired control performance under low switching frequency,but also performs the efficient operation for the three-level NPC-AFEs.The simulation results are provided to verify the effectiveness of proposed control scheme.

Dependence of Switching Current Distribution of a Current-Biased Josephson Junction on Microwave Frequency

We investigate the distribution of the switching current of a current-biased Josephson junction （CBJJ） and its dependence on the microwave frequency using two theoretical methods, one of which is the quantum trajectory method and the other is the master equation method. Both the methods show that the distribution of the switching current of CBJJ will exhibit double peaks in a certain range of microwave frequency if proper microwave power is given, and the gap between the two peaks will increase with the microwave frequency. The obtained results can be used to identify the energy difference of the ground and first excited states in a Josephson junction for any bias current.

Frequency Switches at Transition Temperature in Voltage-Gated Ion Channel Dynamics of Neural Oscillators

Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltagegated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.

Analysis of Soft-Switched High Frequency AC-AC Converter for Induction Motor Drive

The systematic mathematical analysis of the high frequency soft-switched AC-AC converter is proposed for variable frequency induction machine load in this paper. Both PWM and square-wave modes of operation have been considered. The frequency relation and phase unbalance problem due to discrete time integral half-cycle switching has been discussed in the beginning. Then, generalized Fourier series have been derived for output voltage, output current and supply current in two modes.The analytical results help to understand tbe converter characteristics, design optimally a convertermachine system of arbitrary capacity considering the various trade-off parameters.

A Switching Method for a Model Reference Robust Control with Unknown High Frequency Gain Sign

The problem of controlling a single-input-single-output plant without prior knowledge of high frequency gain sign is addressed by using the model reference robust control approach.A switching method is proposed based on a monitoring function so that after a finite number of swi- tchings the tracking error converges to zero exponentially.Furthermore,it is shown that if some initial states of the closed-loop system are zero,only one switching is needed.

A NOVEL AERONAUTICAL STATIC INVERTER WITH HIGH FREQUENCY PULSE DC LINK

A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test.

A wideband low-phase-noise LC VCO for DRM/DAB frequency synthesizer

The wideband CMOS voltage-controlled oscillator（VCO）with low phase noise and low power consumption is presented for a DRM/DAB（digital radio mondiale and digital audio broadcasting）frequency synthesizer.In order to obtain a wide band and a large tuning range,a parallel switched capacitor bank is added in the LC tank.The proposed VCO is implemented in SMIC 0.18-μm RF CMOS technology and the chip area is 750 μm×560 μm,including the test buffer circuit and the pads.Measured results show that the tuning range is 44.6%;i.e.,the frequency turning range is from 2.27 to 3.57 GHz.The measured phase noise is-122.22 dBc/Hz at a 1 MHz offset from the carrier.The maximum power consumption of the core part is 6.16 mW at a 1.8 V power supply.

Velocity compensation methods for LPRF modulated frequency stepped-frequency(MFSF) radar

In the high speed target environment,there exists serious Doppler effect in the low pulse repetition frequency（LPRF） modulated frequency stepped frequency（MFSF） radar signal.The velocity range of the target is large and the velocity is high ambiguous,so the single method is difficult to satisfy the velocity measurement requirement.For this problem,a novel method is presented,it is a combination of cross-correlation inner frame velocity measurement and range-Doppler coupling velocity measurement.The cross-correlation inner frame method,overcoming the low Doppler tolerance of the cross-correlation between frames,can obtain the coarse velocity of the high speed target,and then the precision velocity can be obtained with the range-Doppler coupling method.The simulation results confirm the method is effective,and also it is well real-time and easy to the project application.

A 23.75-GHz frequency comb with two low-finesse filtering cavities in series for high resolution spectroscopy

A laser frequency comb with several tens GHz level is demonstrated,based on a Yb-doped femtosecond fiber laser and two low-finesse Fabry-Perot cavities（FPCs） in series.The original 250-MHz mode-line-spacing of the source comb is filtered to 4.75 GHz and 23.75 GHz,respectively.According to the multi-beam interferences theory of FPC,the side-mode suppression rate of FPC schemes is in good agreement with our own theoretical results from 27 dB of a single FPC to43 dB of paired FPCs.To maintain long-term stable operation and determine the absolute frequency mode number in the23.75-GHz comb,the Pound-Drever-Hall（PDH） locking technology is utilized.Such stable tens GHz frequency combs have important applications in calibrating astronomical spectrographs with high resolution.

Discharge Characteristics of SF_6 in a Non-Uniform Electric Field Under Repetitive Nanosecond Pulses

The characteristics of high pressure sulphur hexafluoride（SF6） discharges in a highly non-uniform electric field under repetitive nanosecond pulses are investigated in this paper.The influencing factors on discharge process,such as gas pressure,pulse repetition frequency（PRF）,and number of applied pulses,are analyzed.Experimental results show that the corona intensity weakens with the increase of gas pressure and strengthens with the increase of PRF or number of applied pulses.Spark discharge images suggest that a shorter and thicker discharge plasma channel will lead to a larger discharge current.The number of applied pulses to breakdown descends with the increase of PRF and ascends with the rise of gas pressure.The reduced electric field（E/p） decreases with the increase of PRF in all circumstances.The experimental results provide significant supplements to the dielectric characteristics of strongly electronegative gases under repetitive nanosecond pulses.