Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure throug...Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation(LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.展开更多
In this study,we explored a one-step direct synthesis of NH3 under mild experimental conditions utilizing pulse-modulated microwave plasma technology at atmospheric pressure.At a substantial gas flow rate,a microwave ...In this study,we explored a one-step direct synthesis of NH3 under mild experimental conditions utilizing pulse-modulated microwave plasma technology at atmospheric pressure.At a substantial gas flow rate,a microwave plasma jet was formed and the microwave-assisted ammonia synthesis can be realized.Impacts of various parameters including the gas flow rate,gas component,microwave absorbed power,pulse modulation frequency,and pulse duty cycle on ammonia synthesis were systematically investigated.To indicate the reaction path of ammonia synthesis,the distributions of both the gas temperature and active species were also studied using optical emission spectra technology.It is found that a considerable amount of ammonia was directly synthesized without involvement of any catalysts,the highest ammonia production rate and energy efficiency(EE),up to 2.93μmol·min^(-1) and 6.64×10^(-2)g·(k W·h)^(-1),respectively,were achieved under low microwave power of 84.42 W.The duty cycle has obvious influences on the synthesis efficiency,compared to a duty cycle of 80%,the ammonia synthesis rate,EE and nitrogen conversion decreased by about 22%at a duty cycle of 100%.This finding underscores the significance of incorporating pulse modulation in the microwave discharge process for ammonia synthesis.Furthermore,it was found that vibrational excitation of microwave plasma has a significant driving effect on ammonia synthesis.展开更多
Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effe...Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effects, similar to the thermal action of conventional hyperthermia combined with ionizing radiation (radiotherapy). The electric field and the radiofrequency current produced both the thermal and nonthermal processes. The thermal effects produce the elevated temperature as a thermal background to optimize the nonthermal impacts. The low frequency amplitude modulation ensures accurate targeting and promotes immunogenic cell death to develop the tumor specific memory T cells disrupting the malignant cells by immune surveillance. This process (abscopal effect) works like a vaccination. The low frequency amplitude modulation is combined in the new method with the high power pulses for short time, increasing the tumor distortion ability of the electric field. The new modulation combination has much deeper penetration triplicating the active thickness of the effective treatment. The short pulse absorption increases the safety and decreases the thermal toxicity of the treatment, making the treatment safer. The increased power allows for reduced treatment time with the prescribed dose.展开更多
A designed visual geometry group(VGG)-based convolutional neural network(CNN)model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direc...A designed visual geometry group(VGG)-based convolutional neural network(CNN)model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direct detection channel performance using eye diagram measurements.Experimental results show that the proposed technique can achieve a high accuracy in jointly monitoring modulation format,probabilistic shaping,roll-off factor,baud rate,optical signal-to-noise ratio,and chromatic dispersion.The designed VGG-based CNN model outperforms the other four traditional machine-learning methods in different scenarios.Furthermore,the multitask learning model combined with MobileNet CNN is designed to improve the flexibility of the network.Compared with the designed VGG-based CNN,the MobileNet-based MTL does not need to train all the classes,and it can simultaneously monitor single parameter or multiple parameters without sacrificing accuracy,indicating great potential in various monitoring scenarios.展开更多
A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the ...A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the circuit is described and analyzed. The circuit is realized in 0.6μm CMOS process,and the simulation results testify to the possibility of sub-retinal implantation.展开更多
A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation （GPCM）, which is suitable for the area where the work conditi...A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation （GPCM）, which is suitable for the area where the work condition is poor and a large flow rate is required. It is difficult to control the GPCM system because the system is discrete. With consideration of the stability and speediness of the GPCM position servo control system, a control strategy is developed through the theoretical and ex-perimental analyses. The control strategy integrates the merits of Bang-Bang control, PID control and fuzzy control. With this hybrid control strategy, the electro hydraulic control system has good per-formances, and the servo control is carried out with GPCM through on-off valves.展开更多
The discharge operation regime of pulse modulated atmospheric radio frequency （RF） glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequenc...The discharge operation regime of pulse modulated atmospheric radio frequency （RF） glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha（s）- gamma（γ） mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 kHz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.展开更多
A novel concept of collision avoidance single-photon light detection and ranging（LIDAR） for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for r...A novel concept of collision avoidance single-photon light detection and ranging（LIDAR） for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for robust anti-crosstalk purposes. Besides, single-photon detectors（SPD） and time correlated single photon counting techniques are adapted, to sense the ultra-low power used for the consideration of compact structure and eye safety. Parameters including pulse rate, discrimination threshold, and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite ultra-low transmitting power.展开更多
This paper gives a spectrum expression which is simple and has a clear physical conception for pulse frequency modulation signal, and has been confirmed by an experiment simultaneously.
Vector control schemes have recently been used to drive linear induction motors(LIM)in high-performance applications.This trend promotes the development of precise and efficient control schemes for individual motors.T...Vector control schemes have recently been used to drive linear induction motors(LIM)in high-performance applications.This trend promotes the development of precise and efficient control schemes for individual motors.This research aims to present a novel framework for speed and thrust force control of LIM using space vector pulse width modulation(SVPWM)inverters.The framework under consideration is developed in four stages.To begin,MATLAB Simulink was used to develop a detailed mathematical and electromechanical dynamicmodel.The research presents a modified SVPWM inverter control scheme.By tuning the proportional-integral(PI)controller with a transfer function,optimized values for the PI controller are derived.All the subsystems mentioned above are integrated to create a robust simulation of the LIM’s precise speed and thrust force control scheme.The reference speed values were chosen to evaluate the performance of the respective system,and the developed system’s response was verified using various data sets.For the low-speed range,a reference value of 10m/s is used,while a reference value of 100 m/s is used for the high-speed range.The speed output response indicates that themotor reached reference speed in amatter of seconds,as the delay time is between 8 and 10 s.The maximum amplitude of thrust achieved is less than 400N,demonstrating the controller’s capability to control a high-speed LIM with minimal thrust ripple.Due to the controlled speed range,the developed system is highly recommended for low-speed and high-speed and heavy-duty traction applications.展开更多
Traditional chaotic pulse position modulation(CPPM)system has many drawbacks.It introduces delay into the feedback loop,which will lead to divergence of chaotic map easily.The wrong decision of data will cause error p...Traditional chaotic pulse position modulation(CPPM)system has many drawbacks.It introduces delay into the feedback loop,which will lead to divergence of chaotic map easily.The wrong decision of data will cause error propagation.Mismatch of parameters and synchronization error between the receiver and transmitter will arouse high bit error rate.To solve these problems,a demodulation algorithm of CPPM based on particle filtering is proposed.According to the mathematical model of the system,it tracks the real signal by online separation in demodulation.Simulation results show that the proposed method can track the true signal better than the traditional CPPM scheme.What's more,it has good synchronization robustness,reduced error propagation by wrong decision and low bit error rate.展开更多
The state space average model and the large signal models of Pulse Skip Modulation （PSM） mode are given in this paper. Farther more, based on these models and simulations of PSM converter circuits, the analysis of t...The state space average model and the large signal models of Pulse Skip Modulation （PSM） mode are given in this paper. Farther more, based on these models and simulations of PSM converter circuits, the analysis of the characteristics of PSM converter is described in this paper, of which include efficiency, frequency spectrum analysis, output voltage ripple, response speed and interference rejection capability. Compared with PWM control mode, PSM converter has high efficiency, especially with fight loads, quick response, good interference rejection and good EMC characteristic. Improved PSM slightly, it could be a kind of good independent regulating mode during the whole operating process for a DC-DC converter. Finally, some experimental results are also presented in this paper.展开更多
This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The propos...This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The proposed SUPWM scheme can achieve an output voltage of(2N+1)(where N is the number of submodules in each arm)levels,which is the same as that of the carrier-phase-shifted PWM(CPSPWM)scheme.Meanwhile,the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC.Moreover,the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers.The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.展开更多
The linear and nonlinear characteristics of time-resolved photoluminescence （PL） of n-type bulk semiconductor GaAs modulated with terahertz （THz） pulse are studied by using an ensemble Monte Carlo （EMC） method. ...The linear and nonlinear characteristics of time-resolved photoluminescence （PL） of n-type bulk semiconductor GaAs modulated with terahertz （THz） pulse are studied by using an ensemble Monte Carlo （EMC） method. In this paper the center energy valley （Г valley） electron concentration changes with the pulse delay time, sampling time and the outfield are mainly discussed. The results show that the sampling time and the THz field should exceed certain thresholds to effectively excite photoluminescence quenching （PLQ）. Adopting a direct current （DC） field makes the sampling time threshold shortened and the linear range of THz field-modulation PL expanded. Moreover, controlling the sampling time and the outfield intensity can improve the linear quality： with forward time, the larger outfield is used; with backward time, the smaller outfield is used. This study can provide a theoretical basis of THz field linear modulation in a larger range for new light emitting devices.展开更多
By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinu- soidal pulse width modulation （BSPWM） and unipolar double-frequency sinusoidal pulse width modulati...By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinu- soidal pulse width modulation （BSPWM） and unipolar double-frequency sinusoidal pulse width modulation （UDFSPWM） respectively, the performances of the two modulation strategies are analyzed in detail. The circuit parameters, used in this paper, are fixed. When the systems, modulated by BSPWM and UDFSPWM, have the same switching frequency, the stabil- ity boundaries of the two systems are the same. However, when the equivalent switching frequencies of the two systems are the same, the BSPWM modulated system is more stable than the UDFSPWM modulated system. In addition, a convenient method of establishing the discrete-time model of piecewise smooth system is presented. Finally, the analytical results are confirmed by circuit simulations and experimental measurements.展开更多
In order to compensate for the deficiency of Sine Pulse Width Modulation（SPWM）, on the base of analyzing the principle of space w tot pulse width modulation and being compared with SPWM, the method of solving workin...In order to compensate for the deficiency of Sine Pulse Width Modulation（SPWM）, on the base of analyzing the principle of space w tot pulse width modulation and being compared with SPWM, the method of solving working time of adjacent vector and the method of generate space voltage vector were introduced. The experiment to the inverter which consists of IGBT proves that SVPWM centrol algorithm can reduce harmonic effectively, it is beneficial to enhancing the utilization rate of voltage source inverter direct current power supply.展开更多
From Maxwell＇s equations and Post＇s formalism, a generalized chiral nonlinear Schr6dinger equation （CNLSE） is obtained for the nonlinear chiral fiber. This equation governs light transmission through a dispersive ...From Maxwell＇s equations and Post＇s formalism, a generalized chiral nonlinear Schr6dinger equation （CNLSE） is obtained for the nonlinear chiral fiber. This equation governs light transmission through a dispersive nonlinear chiral fiber with joint action of chirality in linear and nonlinear ways. The generalized CNLSE shows a modu- lation of chirality to the effect of attenuation and nonlinearity compared with the case for a conventional fiber. Simulations based on the split-step beam propagation method reveal the role of nonlinearity with cooperation to chirality playing in the pulse evolution. By adjusting its strength the role of chirality in forming solitons is demonstrated for a given circularly polarized component. The application of nonlinear optical rotation is also discussed in an all-optical switch.展开更多
In this paper, the performance of various Pulse Position Modulation (PPM) schemes has been analysed for PIN and APD receivers in the presence of atmospheric turbulence. It is observed that the performance of the APD r...In this paper, the performance of various Pulse Position Modulation (PPM) schemes has been analysed for PIN and APD receivers in the presence of atmospheric turbulence. It is observed that the performance of the APD receiver is always better than that of the PIN receiver as expected. Among the various modulation schemes, the performance of Differential Amplitude PPM (DAPPM) scheme with more number of amplitude levels is better than that of the other schemes for the same single level peak amplitude. Further, the optimum gain of APD receiver does not change substantially for different modulation schemes and turbulent conditions.展开更多
基金supported by the program for National Natural Science Foundation of China (Nos. 52174173, 52274188, and 52104190)the Joint Funds of the National Natural Science Foundation of China (No. U24A2091)+1 种基金The Natural Science Foundation of Henan Polytechnic University (No. B2021-2)Double FirstClass Initiative of Safety and Energy Engineering (Henan Polytechnic University) (Nos. AQ20240703 and AQ20230304)。
文摘Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation(LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.
基金supported by National Natural Science Foundation of China(Nos.52077026,51977023,52177126 and 12475253)the Fundamental Research Funds for the Central Universities(No.DUT23YG227)the Dalian Life&Health Guiding Project(No.2023ZXYG34)。
文摘In this study,we explored a one-step direct synthesis of NH3 under mild experimental conditions utilizing pulse-modulated microwave plasma technology at atmospheric pressure.At a substantial gas flow rate,a microwave plasma jet was formed and the microwave-assisted ammonia synthesis can be realized.Impacts of various parameters including the gas flow rate,gas component,microwave absorbed power,pulse modulation frequency,and pulse duty cycle on ammonia synthesis were systematically investigated.To indicate the reaction path of ammonia synthesis,the distributions of both the gas temperature and active species were also studied using optical emission spectra technology.It is found that a considerable amount of ammonia was directly synthesized without involvement of any catalysts,the highest ammonia production rate and energy efficiency(EE),up to 2.93μmol·min^(-1) and 6.64×10^(-2)g·(k W·h)^(-1),respectively,were achieved under low microwave power of 84.42 W.The duty cycle has obvious influences on the synthesis efficiency,compared to a duty cycle of 80%,the ammonia synthesis rate,EE and nitrogen conversion decreased by about 22%at a duty cycle of 100%.This finding underscores the significance of incorporating pulse modulation in the microwave discharge process for ammonia synthesis.Furthermore,it was found that vibrational excitation of microwave plasma has a significant driving effect on ammonia synthesis.
文摘Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effects, similar to the thermal action of conventional hyperthermia combined with ionizing radiation (radiotherapy). The electric field and the radiofrequency current produced both the thermal and nonthermal processes. The thermal effects produce the elevated temperature as a thermal background to optimize the nonthermal impacts. The low frequency amplitude modulation ensures accurate targeting and promotes immunogenic cell death to develop the tumor specific memory T cells disrupting the malignant cells by immune surveillance. This process (abscopal effect) works like a vaccination. The low frequency amplitude modulation is combined in the new method with the high power pulses for short time, increasing the tumor distortion ability of the electric field. The new modulation combination has much deeper penetration triplicating the active thickness of the effective treatment. The short pulse absorption increases the safety and decreases the thermal toxicity of the treatment, making the treatment safer. The increased power allows for reduced treatment time with the prescribed dose.
基金supported by the National Key Research and Development Program of China (Grant No.2019YFB1803700)the Key Technologies Research and Development Program of Tianjin (Grant No.20YFZCGX00440).
文摘A designed visual geometry group(VGG)-based convolutional neural network(CNN)model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direct detection channel performance using eye diagram measurements.Experimental results show that the proposed technique can achieve a high accuracy in jointly monitoring modulation format,probabilistic shaping,roll-off factor,baud rate,optical signal-to-noise ratio,and chromatic dispersion.The designed VGG-based CNN model outperforms the other four traditional machine-learning methods in different scenarios.Furthermore,the multitask learning model combined with MobileNet CNN is designed to improve the flexibility of the network.Compared with the designed VGG-based CNN,the MobileNet-based MTL does not need to train all the classes,and it can simultaneously monitor single parameter or multiple parameters without sacrificing accuracy,indicating great potential in various monitoring scenarios.
文摘A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the circuit is described and analyzed. The circuit is realized in 0.6μm CMOS process,and the simulation results testify to the possibility of sub-retinal implantation.
文摘A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation （GPCM）, which is suitable for the area where the work condition is poor and a large flow rate is required. It is difficult to control the GPCM system because the system is discrete. With consideration of the stability and speediness of the GPCM position servo control system, a control strategy is developed through the theoretical and ex-perimental analyses. The control strategy integrates the merits of Bang-Bang control, PID control and fuzzy control. With this hybrid control strategy, the electro hydraulic control system has good per-formances, and the servo control is carried out with GPCM through on-off valves.
基金supported by National Natural Science Foundation of China(Nos.11475043 and 11375042)
文摘The discharge operation regime of pulse modulated atmospheric radio frequency （RF） glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha（s）- gamma（γ） mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 kHz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.
基金Project supported by Tsinghua University Initiative Scientific Research Program,China(Grant No.2014z21035)
文摘A novel concept of collision avoidance single-photon light detection and ranging（LIDAR） for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for robust anti-crosstalk purposes. Besides, single-photon detectors（SPD） and time correlated single photon counting techniques are adapted, to sense the ultra-low power used for the consideration of compact structure and eye safety. Parameters including pulse rate, discrimination threshold, and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite ultra-low transmitting power.
文摘This paper gives a spectrum expression which is simple and has a clear physical conception for pulse frequency modulation signal, and has been confirmed by an experiment simultaneously.
基金The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through Large Groups Project under grant number(RGP.2/111/43).
文摘Vector control schemes have recently been used to drive linear induction motors(LIM)in high-performance applications.This trend promotes the development of precise and efficient control schemes for individual motors.This research aims to present a novel framework for speed and thrust force control of LIM using space vector pulse width modulation(SVPWM)inverters.The framework under consideration is developed in four stages.To begin,MATLAB Simulink was used to develop a detailed mathematical and electromechanical dynamicmodel.The research presents a modified SVPWM inverter control scheme.By tuning the proportional-integral(PI)controller with a transfer function,optimized values for the PI controller are derived.All the subsystems mentioned above are integrated to create a robust simulation of the LIM’s precise speed and thrust force control scheme.The reference speed values were chosen to evaluate the performance of the respective system,and the developed system’s response was verified using various data sets.For the low-speed range,a reference value of 10m/s is used,while a reference value of 100 m/s is used for the high-speed range.The speed output response indicates that themotor reached reference speed in amatter of seconds,as the delay time is between 8 and 10 s.The maximum amplitude of thrust achieved is less than 400N,demonstrating the controller’s capability to control a high-speed LIM with minimal thrust ripple.Due to the controlled speed range,the developed system is highly recommended for low-speed and high-speed and heavy-duty traction applications.
基金Supported by the National Natural Science Foundation of China(No.41074090)Henan Science and Technology Key Project(No.092102210360)+1 种基金Henan Provincial Department of Education Science ang Technology Key Project(No.13A510330)Doctorate Program of Henan Polytechnic University(No.B2009-27)
文摘Traditional chaotic pulse position modulation(CPPM)system has many drawbacks.It introduces delay into the feedback loop,which will lead to divergence of chaotic map easily.The wrong decision of data will cause error propagation.Mismatch of parameters and synchronization error between the receiver and transmitter will arouse high bit error rate.To solve these problems,a demodulation algorithm of CPPM based on particle filtering is proposed.According to the mathematical model of the system,it tracks the real signal by online separation in demodulation.Simulation results show that the proposed method can track the true signal better than the traditional CPPM scheme.What's more,it has good synchronization robustness,reduced error propagation by wrong decision and low bit error rate.
基金Supported by the National Natural Science Foundation of China (No.60436030)
文摘The state space average model and the large signal models of Pulse Skip Modulation （PSM） mode are given in this paper. Farther more, based on these models and simulations of PSM converter circuits, the analysis of the characteristics of PSM converter is described in this paper, of which include efficiency, frequency spectrum analysis, output voltage ripple, response speed and interference rejection capability. Compared with PWM control mode, PSM converter has high efficiency, especially with fight loads, quick response, good interference rejection and good EMC characteristic. Improved PSM slightly, it could be a kind of good independent regulating mode during the whole operating process for a DC-DC converter. Finally, some experimental results are also presented in this paper.
基金This work was supported in part by the National Natural Science Foundation of China under Grant 51707088,51607081the 5th-level talent introduction program of Kunming University of Science and Technology.
文摘This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The proposed SUPWM scheme can achieve an output voltage of(2N+1)(where N is the number of submodules in each arm)levels,which is the same as that of the carrier-phase-shifted PWM(CPSPWM)scheme.Meanwhile,the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC.Moreover,the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers.The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.
基金supported by the National Natural Science Foundation of China(Grant Nos.11574105,61475054,61405063,and 61177095)the Hubei Science and Technology Agency Project,China(Grant No.2015BCE052)the Fundamental Research Funds for the Central Universities,China(Grant No.2017KFYXJJ029)
文摘The linear and nonlinear characteristics of time-resolved photoluminescence （PL） of n-type bulk semiconductor GaAs modulated with terahertz （THz） pulse are studied by using an ensemble Monte Carlo （EMC） method. In this paper the center energy valley （Г valley） electron concentration changes with the pulse delay time, sampling time and the outfield are mainly discussed. The results show that the sampling time and the THz field should exceed certain thresholds to effectively excite photoluminescence quenching （PLQ）. Adopting a direct current （DC） field makes the sampling time threshold shortened and the linear range of THz field-modulation PL expanded. Moreover, controlling the sampling time and the outfield intensity can improve the linear quality： with forward time, the larger outfield is used; with backward time, the smaller outfield is used. This study can provide a theoretical basis of THz field linear modulation in a larger range for new light emitting devices.
基金supported by the National Natural Science Foundation of China (Grant No. 51277146)the Foundation of Delta Science,Technologythe Education Development Program for Power Electronics (Grant No. DREG2011003)
文摘By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinu- soidal pulse width modulation （BSPWM） and unipolar double-frequency sinusoidal pulse width modulation （UDFSPWM） respectively, the performances of the two modulation strategies are analyzed in detail. The circuit parameters, used in this paper, are fixed. When the systems, modulated by BSPWM and UDFSPWM, have the same switching frequency, the stabil- ity boundaries of the two systems are the same. However, when the equivalent switching frequencies of the two systems are the same, the BSPWM modulated system is more stable than the UDFSPWM modulated system. In addition, a convenient method of establishing the discrete-time model of piecewise smooth system is presented. Finally, the analytical results are confirmed by circuit simulations and experimental measurements.
文摘In order to compensate for the deficiency of Sine Pulse Width Modulation（SPWM）, on the base of analyzing the principle of space w tot pulse width modulation and being compared with SPWM, the method of solving working time of adjacent vector and the method of generate space voltage vector were introduced. The experiment to the inverter which consists of IGBT proves that SVPWM centrol algorithm can reduce harmonic effectively, it is beneficial to enhancing the utilization rate of voltage source inverter direct current power supply.
基金Supported by the National Natural Science Foundation of China under Grant No 60977032the Program for Innovation Research of Science of Harbin Institute of Technology(PIRS-HIT)under Grant No T201407
文摘From Maxwell＇s equations and Post＇s formalism, a generalized chiral nonlinear Schr6dinger equation （CNLSE） is obtained for the nonlinear chiral fiber. This equation governs light transmission through a dispersive nonlinear chiral fiber with joint action of chirality in linear and nonlinear ways. The generalized CNLSE shows a modu- lation of chirality to the effect of attenuation and nonlinearity compared with the case for a conventional fiber. Simulations based on the split-step beam propagation method reveal the role of nonlinearity with cooperation to chirality playing in the pulse evolution. By adjusting its strength the role of chirality in forming solitons is demonstrated for a given circularly polarized component. The application of nonlinear optical rotation is also discussed in an all-optical switch.
文摘In this paper, the performance of various Pulse Position Modulation (PPM) schemes has been analysed for PIN and APD receivers in the presence of atmospheric turbulence. It is observed that the performance of the APD receiver is always better than that of the PIN receiver as expected. Among the various modulation schemes, the performance of Differential Amplitude PPM (DAPPM) scheme with more number of amplitude levels is better than that of the other schemes for the same single level peak amplitude. Further, the optimum gain of APD receiver does not change substantially for different modulation schemes and turbulent conditions.
