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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]

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]

A dual-mode flyback inverter is proposed for photovoltaic power applications. The proposed dual-mode flyback inverter makes use of both discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations for more than 200 W power applications. However, it suffers from output current control problems such as low system gain during DCM and right-half-plain zero problem during CCM. To achieve accurate reference tracking, the authors propose to adopt the repetitive control scheme that increases the system gain at the fundamental and its harmonic frequencies of the grid. To reduce the burden from the conventional proportional-integral controller, the authors use the dual-mode nominal duty that helps the dual-mode flyback inverter generate the target output current while attenuating the effect of disturbances. To make the dualmode flyback inverter operate at the maximum power point (MPP), the authors use the incremental conductance method that offers smooth transition to the MPP. The experimental results show that the proposed flyback system implemented for 200 W dual-mode flyback inverter prototype achieves high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and high power capacity. [ABSTRACT FROM AUTHOR]