A rational frequency tracking method for phase-shift PWM inverter using minimum admittance point in high-intensity ultrasonic power control

Optimal control for an above-knee prosthesis with two degrees of freedom

In order to ensure that the underwater acoustic communication device can output a stable signal during operation, avoid the transducer's resonance frequency drift caused by various environmental factors which can cause communication failure. This paper focuses on the transducer frequency detection technology. According to the piezoelectric effect, the vibration feedback of the transducer at different frequencies is collected by the PVDF sensor. The relationship between the frequency and the feedback signal of the sensor is obtained, and the feasibility of detecting the transducer's resonant frequency by the vibration sensor is verified. According to this characteristic, a self-check circuit of the resonant frequency is designed, which can adjust the power frequency to the optimal operating frequency and effectively improve the reliability of underwater acoustic signal transmission.

The speed of continuous improvement of technology, and the development speed of modern power technology widely used in power supply in social applications. However, scientists have been unable to solve problems, such as those that tend to arise under normal working conditions with work capacity. Frequency offset phenomenon, how to design transducer impedance matching circuit, and how to realize automatic frequency tracking, etc. Aiming at these problems, this paper studies how to achieve impedance matching by analyzing the equivalent circuit of the transducer. By comparing the impedance matching methods, a series matching circuit is used for impedance matching. The methods and methods of traditional frequency tracking control are analyzed, and the variable-step frequency tracking method is finally determined. On the basis of theoretical analysis, a 3000W ultrasonic power supply prototype is built. The correctness of hardware circuit design and software compilation is verified by experiments, and the automatic frequency tracking effect is observed. The feasibility of the method proposed in this paper is verified based on the analysis of experimental data.

We developed a multi (or mixed) mode excitation type piezoelectric motor that uses a rectangular bar type piezoelectric multilayer stator as the vibrating element. The stator has a first longitudinal vibration mode in a direction of longest length and second flexural mode in a direction of thickness. During operation of the motor, these two modes are coupled so at the two end surfaces, elliptical motions are generated. The elliptical motion at one end of the stator is transferred to a moving element through frictional contact. This paper introduces structure and operating principal of the piezoelectric multilayer stator. An equivalent circuitry model for the free stator and a frequency tracking method to operate the motor at its optimum operating frequency are also proposed. The frequency tracking method not only finds the best operating frequency, it also tracks the frequency variations from sample to sample and operating frequency shift due to temperature change.

This paper investigates optimal trajectory tracking for air-to-surface missiles using bank-to-turn steering and equipped with Doppler-beam-sharpening seekers. The seeker generates a radar image of the terrain that is continually updated in flight. The guidance problem for this type of sensor is complex, because constraints must be imposed on the flight path of the missile to ensure that the seeker can obtain adequate crossrange resolution for target recognition and aim-point selection. Terminal position, incidence, and angle constraints are also imposed in the guidance problem. An offline optimal trajectory can be obtained through trajectory optimization techniques that have been presented in previous papers. The focus of this work is on following the precomputed optimal trajectories. The method presented uses a linear quadratic regulator to calculate closed-loop in-flight controls. We also investigate the effectiveness of a preview term based on the prediction of the future trajectory from the current state. Preview control is an optimal tracking method that uses future trajectory samples within a preview window to improve the tracking accuracy. A set of preview gains is computed and is used in addition to the regulator gains. Over the last 2 km of flight, an impact-angle guidance law that minimizes the miss distance and impact-angle error is used to achieve the terminal constraints. The guidance scheme is evaluated for tracking offline Doppler-beam-sharpening trajectories in the presence of modeling errors, sensor noise, and disturbances.

To address the challenge of quickly tuning the resonance frequency of ultrasonic transducers in real-time after manufacturing, this paper proposes integrating Terfenol-D into the horn of a piezoelectric ultrasonic transducer. In practical applications, the transducer is mechanically excited by a piezoelectric vibrator connected to an alternating current power supply, while the Terfenol-D is surrounded by a coil connected to a direct current power supply. By utilizing the delta-E (ΔE) effect of Terfenol-D, the modulus of the material changes in response to variations in the surrounding magnetic field, enabling real-time online adjustment of the resonance frequency. The resonance frequency and amplification coefficient of the transducer were analyzed using the transfer matrix method. Then, an impedance analyzer was employed to measure changes in the transducer's impedance and resonance frequency under different electric currents. Experimental results demonstrate that the resonance frequency of the transducer increases with increasing electric current. The developed piezoelectric ultrasonic transducer, featuring Terfenol-D embedded in the horn, achieves rapid and real-time resonance frequency adjustment within a specific range. This innovation provides a novel solution for complex ultrasonic application scenarios requiring frequent transducer replacements.

Standard cells of the saturated type and ordinary H-pattern are capable of delivering a current of 1 μA continuously for a period of several months, a current of 10 μA for several weeks, and larger currents for shorter periods without undergoing any permanent loss of accuracy. While the current is flowing the voltage across the terminals of the cell is less than the e.m.f. as normally measured in the steady state by an amount which consists mainly of the resistive potential-drop, but which includes also a component ΔV depending on the chemical changes at the electrodes associated with the generation of the current. This latter component is, in general, greater the larger the current, and increases with the time of flow. When the current is stopped the voltage rises to a value which is short of the steady-state e.m.f. by an amount ΔE, which is smaller than ΔV but of the same order. If the cell is left undisturbed on open circuit ΔE gradually diminishes until the steady state e.m.f. is again reached, the time required for complete recovery depending on the magnitude and duration of the preceding current-flow. Values of these quantities for typical cells under a wide variety of conditions are given, with the object of providing a guide to the voltage-stability and working life that may be expected of cells operated within this range of conditions.

The minimum duration of treatment periods and the optimal multidrug therapy for human immunodeficiency virus (HIV) type 1 infection are considered. We formulate an optimal tracking problem, attempting to drive the states of the model to a "healthy" steady state in which the viral load is low and the immune response is strong. We study an optimal time frame as well as HIV therapeutic strategies by analyzing the free terminal time optimal tracking control problem. The minimum duration of treatment periods and the optimal multidrug therapy are found by solving the corresponding optimality systems with the additional transversality condition for the terminal time. We demonstrate by numerical simulations that the optimal dynamic multidrug therapy can lead to the long-term control of HIV by the strong immune response after discontinuation of therapy.

The modified positive position feedback controller, an active vibration control method that uses collocated piezoelectric actuator actuators and sensors, is developed using an adaptive controller. The adaptive mechanism consists of two main parts: 1) Frequency adaptation mechanism, and 2) Adaptive controller. Frequency adaptation only tracks the frequency of vibrations using Fast Fourier Transforms. The obtained frequency is then fed to MPPF compensators and the adaptive controller. This provides a unique feature for MPPF, by extending its domain of capabilities from controlling tonal vibrations to broad band disturbances. The adaptive controller mechanism consists of a reference model that is of the same order as the MPPF system and its compensators. The adaptive law provides the additional control force that is needed for controlling frequency changes caused by broad band vibrations. The experimental results show that the frequency tracking method that is derived has worked quite well. The results also indicate that the MPPF can provide significant vibration reduction on a cantilever beam that is used throughout the experiments.

In the context of the global green and low-carbon transformation, microgrids containing renewable energy have been widely developed. At present, renewable energy generation has the disadvantages of instability and low energy density. In addition, the high proportion of electric vehicles (EVs) connected to the state grid will cause different degrees of disturbance to its safe operation. Therefore, a coordinated operation strategy of EV and photovoltaic (PV)-energy-storage charging stations induced by dynamic electricity price considering carbon reduction benefit is proposed. On the power generation side, a dual-axis PV tracking control method with "fixed frequency + variable frequency" control is proposed. One day is used as a period to divide the time segments, and the same time segment uses the fixed frequency tracking method, while different time segments use the variable frequency tracking method to improve the power generation efficiency. On the electricity consumption side, a dynamic electricity price strategy is adopted, using the minimum carbon reduction cost as the reward function, optimizing the dynamic electricity price under the minimum carbon reduction cost using the deep deterministic policy gradient (DDPG) algorithm to promote the shifting of EV charging load to the effective hours of PV generation. In conclusion, the simulation analysis is carried out in Zibo City, and the generation capacity of the proposed tracking method on the power generation side is improved by about 32% compared with the fixed PV generation capacity. Compared with the time-of-use electricity price, the optimized dynamic electricity price under the minimum carbon reduction cost can better promote the load transfer and photoelectric consumption of EVs and reduce the carbon reduction cost.

This paper proposes an optimal signal processing based UAV tracking algorithm considering noise and cyber attacks in sensory measurements. After representing the UAV dynamics into a state-space form, the UAV embedded IoT sensors and IoT gateways are used to obtain measurements at the control center. The prediction and correction based optimal Kalman filtering algorithm is proposed to know the UAV states such as velocity and pitch angle. Extensive numerical results show that the proposed algorithm can properly track the UAV states within 0.9-0.45 sec.

In order to realize the low-voltage and low-power dissipation designing of digital circuits, minimum energy point tracking (MEPT) based on adaptive voltage scaling (AVS) circuit is proposed in this paper. With process, voltage and temperature and frequency variance, the supply voltage of digital circuits is decreased dramatically by AVS, and equals to minimum voltage point (MVP), and advantageously in reducing dynamic energy consumption. Based on the MVP, in order to effectively decrease energy consumption of digital circuits, minimum energy point (MEP) of digital circuits is searched via comparing energy dissipation under different supply voltage by MEPT. Therefore, the supply voltage and energy consumption of digital circuits are decreased dramatically by the proposed novel circuit. The proposed circuit has been implemented and fabricated in a standard 0.18 μm CMOS process. The experimental results show that, when operating frequency of load keeps 1.319 MHz, the MVP and MEP of load are 425 and 450 mV, respectively. For operation frequency 5.334 MHz, the MEP changes from 625 to 550 mV with the degree of activity of load difference. Comparing with the traditional fixed voltage circuits, the maximum saving 91% of dynamic energy is realized by the proposed circuit.

A discussion is given of the merits of a pulse-superposition method for determining ultrasonic-wave velocities in single crystals as a function of pressure and temperature. For this method [H. J. McSkimin, J. Acoust. Soc. Am. 33, 12 (1961)], the wave frequency is continuously matched to the resonance frequency of the crystal transducer in order to minimize the effect of coupling to the transducer. Ratios of velocities can be determined to within one part in ten thousand. Illustrative data are shown for crystal quartz in the pressure range 14.5 to 30 000 psi at both 25.0° and −195.8°C.

The dielectric and acoustic losses in oriented PVF2 have been measured from 0.1 MHz to 100 MHz and from 1.5 MHz to 39 MHz, respectively, in the direction perpendicular to the stretching direction at room temperature. A broad absorption peak located at around 5 MHz is observed in each case. The locations of these absorption peaks are of great disadvantage for ultrasonic transducer fabrication. The longitudinal acoustic velocity in the direction perpendicular to the stretching direction is also measured from 1.5 MHz to 39 MHz at room temperature. It is found that the velocity increases monotonically in this frequency range. As a result, the resonance frequency of a PVF2 transducer will be affected proportionally.

In order to evaluate the `resonance intensities' and resonance frequencies of piezoelectric transducers driven `partially', two mathematical methods are considered: One is the evaluation of `speed of divergence' at the resonance of Mason's equivalent circuit which is applied appropriately using the conventional concept of a distributed-parameter circuit, and the other is a superposition of complex dynamical variable η to form complex infinite geometric series in which |η|2 corresponds to the stored energy in the transducer and in which the way of superposition reflects the electrical and mechanical boundary conditions of the transducer. The resonance intensity is related to the effective power at the resonance. The `partial drive' can induce resonance modes other than a set of odd-degree modes, with various resonance intensities due to a nondissipative cause, on appropriate boundary conditions. The calculation results of the two methods agree with each other satisfactorily, and thus suggest the physical reasonableness of both methods.