Ultrasonic wireless power transfer (UWPT) has been a promising technology to recharge the sensor batteries that locate in enclosed metal containers. An accurate and comprehensive analytical model is the key enabling tool for designing the UWPT system. In this article, a novel equivalent circuit model has been proposed for a typical UWPT system with two symmetric piezoelectric transducers bounding onto an aluminum plate coaxially. The proposed model is a two-port network equivalent circuit that can be described by T parameters. By considering the losses of the UWPT system, the accuracy of this model has been enhanced in comparison with the widely used equivalent circuit model, which ignores its losses. The experimental results show that the average error of output power decreases about 6.4 times in the proposed model compared to the existing model. Moreover, the proposed model is tested under various working conditions to validate the enhanced accuracy.

Uniform steady-state and small-signal circuit models for pulsewidth-modulated dc-dc converters operated in discontinuous conduction mode are presented. The models are developed using a new approach that accurately accounts for nonlinearity of current waveform due to component parasitic resistances. The uniform model structure for a set of dc-dc converters is transformed by substituting the practical inductor with an equivalent inductor in series connection with the output capacitor. The resulting models are used to derive the uniform expressions of voltage transfer ratio, efficiency, and various transfer functions. The proposed models can be considered as an alternative to the previously established techniques, and are shown to be fairly accurate in steady-state and small-signal representations through detailed simulations and experimental tests.

A new digital control technique is proposed to improve the speed of both load current and source voltage transient responses for dc-dc converters operating in continuous conduction mode (CCM). The key structure of the proposed control technique is a combination of a limiting integral loop and related arithmetic operations to produce the desired switching sequence during transient condition. The limiting integral loop is built as a novel structure for capacitor charge balance operation. In contrast to previous approaches, the proposed control technique is valid for three basic converters: 1) buck; 2) boost; and 3) buck-boost. Moreover, since the transient period is forced to be an integer multiple of the switching cycle, the advantage of fixed switching frequency is inherently provided. Simulation and experimental results from a noninverting synchronous buck-boost converter prototype are given to validate the effectiveness of the proposed solution.

In this paper, a new direct torque control strategy for induction machine based on indirect matrix converter is introduced and investigated. In the inverter stage, the classical direct torque control method is employed. In the rectifier stage, the outputs of flux and torque hysteresis comparators, generated based on the request signals for flux and torque, are used to produce the switching signals for the switches directly and without any need for an additional control unit. In this method, the input current is nearly sinusoidal and the input displacement angle is adjustable. Moreover, zero current switching can be implemented in the rectifier stage through inserting short periods of zero voltage vector in the inverter stage. Using this control strategy, the advantages of indirect matrix converter and direct torque control method are combined. Steady-state and transient behaviors of the system are simulated using PSIM simulation package and simulation results are used to verify the effectiveness of the proposed strategy and support the analytical results

This paper investigates the fault-tolerant tracking control problem of high-speed trains (HSTs) subject to unknown model parameters with unavailable uncertainties, unmeasurable additional disturbance, and unpredictable actuator faults constrained by actuator saturation. An adaptive passive fault-tolerant tracking control strategy based on variable-gain proportion-integral-derivative (PID)-type sliding mode surface is proposed to handle the problem. Unknown model parameters, gains of the PID-type sliding mode surface, and upper bounds of the lumped system uncertainty which includes additional disturbance, modeling uncertainties, and uncertainties resulting from actuator faults, are estimated online by adaptive technology. The input saturation (actuator output saturation) constraint is handled by introducing an auxiliary signal. The proposed controller can compensate for the effects of the lumped uncertainty and the actuator faults effectively. Moreover, the controller is model-independent, which means it requires no prior knowledge of model parameters and upper bounds of the lumped uncertainty, and does not depend upon fault detection and diagnosis module. The asymptotic stability of the closed-loop train system is demonstrated by Lyapunov theory. Good fault-tolerant tracking capacity, effective anti-actuator saturation ability, and strong robustness of the proposed controller are verified via numerical simulation.