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We propose a new duty-ratio feedforward controller for the flyback inverter with a synchronous rectifier (SR) circuit. For grid-connected photovoltaic power systems, the power factor (PF) of the output current must be high under most of the load conditions. To improve the PF of the flyback inverter even under light load, we propose a compensation method for the output capacitor current. The proposed method improves the displacement factor as well as the distortion factor, so the flyback inverter with the SR circuit has high power quality. By means of the SR circuit, the flyback inverter can operate in reverse when the negative current is required. The derivation of the proposed method is presented based on time-domain analysis. We also provide the boundary of the region where the proposed scheme should be adopted. The effectiveness of the proposed method is demonstrated in experiments with a 120-W rated power prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a repetitive controller with phase-lead compensation for an unfolding-type Cuk continuous conduction mode (CCM) inverter operating in the CCM. The Cuk CCM inverter features medium power capacity, step up/down ability, and low input/output current ripples, so it is well suited to distributed power generation systems. To achieve accurate tracking of the reference output current, we make the use of the repetitive controller coupled with a conventional proportional-integral controller and a nominal duty ratio. In developing the proposed controller, we use the average model of the Cuk CCM inverter in the grid-connected case. The two right-half plane (RHP) zeros in the transfer function of the Cuk CCM inverter cause phase lag of the closed-loop system; to compensate for the phase lag, we implement a phase-lead compensation algorithm in the repetitive control scheme. We also provide detailed and practical design guidelines of the control parameters to develop a stable Cuk CCM inverter. Experimental tests using a 500-W Cuk CCM inverter demonstrate the desirable performance of the proposed control approach. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a Lyapunov-function-based controller for the flyback converter operating in the continuous conduction mode (CCM). The controller consists of a duty-ratio feedforward control unit and a Lyapunov-function-based feedback control unit. The duty-ratio feedforward signal is used to reduce the burden from the Lyapunov feedback controller. The control system guarantees global exponential stability of the closed-loop system and, hence, offers fast transient response under large-signal perturbations. In constructing the controller, we use the average model of the flyback CCM converter taking the parasitic components into account. Numerical simulations confirmed its superior performance, and experimental tests validated the proposed control approach. [ABSTRACT FROM PUBLISHER]

We propose a downsampled iterative learning controller (ILC) for a flyback inverter operating in continuous conduction mode (CCM). The flyback CCM inverter features step-up/-down ability, small number of circuit components, and high conversion efficiency, so it is well suited to the distributed renewable energy systems. But the conventional proportional-integral (PI) controller for the flyback CCM inverter shows poor steady-state response because the inverter itself suffers from time-varying grid-voltage disturbances and its transfer function has a right-half plane zero. The ILC itself achieves acceptable steady-state response of the flyback CCM inverter but can excite large overshoot in the iteration domain; this overshoot may destroy the solid state devices in the power circuit. To overcome this problem, we use a downsampled ILC technique that guarantees monotonic convergence of tracking error. The proposed ILC is computationally simple and easy to implement. Numerical simulations and experimental tests validate the proposed control approach. [ABSTRACT FROM PUBLISHER]

This paper proposes an iterative learning control (ILC) scheme for a dual-mode flyback inverter operating in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). In dealing with more than 200-W power applications, the dual-mode flyback inverter takes advantage of both DCM and CCM operations. However, it is difficult to control the output current because the system gain is quite low in DCM and the system transfer function has a right-half plane zero in CCM. To overcome the problems occurring in DCM and CCM operations, we propose an ILC scheme with multiple phase-lead compensation. The ILC is proposed to achieve accurate reference tracking and to reject periodic disturbances. The multiple phase-lead compensation technique is then employed to compensate for the effect of different system dynamics. As a theoretical result, we derive the asymptotic stability of the closed-loop system. We also performed the numerical simulations and experimental tests to validate the proposed control approach. [ABSTRACT FROM AUTHOR]

Adaptive beamforming methods for ultrasound imaging have been studied to improve image resolution and contrast. The most common approach is the minimum variance (MV) beamformer which minimizes the power of the beamformed output while maintaining the response from the direction of interest constant. The method achieves higher resolution and better contrast than the delay-and-sum (DAS) beamformer, but it suffers from high computational cost. This cost is mainly due to the computation of the spatial covariance matrix and its inverse, which requires O(L^3) computations, where L denotes the subarray size. In this study, we propose a computationally efficient MV beamformer based on QR decomposition. The idea behind our approach is to transform the spatial covariance matrix to be a scalar matrix \sigma \mathbfI and we subsequently obtain the apodization weights and the beamformed output without computing the matrix inverse. To do that, QR decomposition algorithm is used and also can be executed at low cost, and therefore, the computational complexity is reduced to O(L^2). In addition, our approach is mathematically equivalent to the conventional MV beamformer, thereby showing the equivalent performances. The simulation and experimental results support the validity of our approach. [ABSTRACT FROM PUBLISHER]

This paper presents an enhanced time-delay controller (TDC) for the position control of an autonomous underwater vehicle (AUV) under disturbances. A conventional TDC performs well when the involved data acquisition rate is fast. However, in AUV control applications that use a Doppler velocity log (DVL) navigation system, we cannot keep the data acquisition rate sufficiently fast because a DVL sensor generally supplies data at a slow acquisition rate, which degrades the performance of the TDC. To overcome this problem, we propose an integral sliding-mode controller to be supplemented to the conventional TDC to improve the control precision even if the DVL navigation system is in operation. The proposed controller is computationally simple and robust to unmodeled dynamics and disturbances. We performed computer simulations and experiments with the Cyclops AUV to demonstrate the validity of the proposed controller. [ABSTRACT FROM PUBLISHER]