Minsung Kim

Time-Delay Controller Design for Position Control of Autonomous Underwater Vehicle Under Disturbances

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.

Discrete-Time Repetitive Control of Flyback CCM Inverter for PV Power Applications

In this paper, a discrete-time repetitive controller (RC) is proposed for a flyback inverter operating in continuous conduction mode (CCM), which has a simple structure, low cost, and high efficiency. Conventional controller results in poor control performance due to the effect of the right-half-plane zero in CCM operation. To achieve accurate tracking performance and disturbance rejection, the RC is developed and applied to the flyback inverter in CCM operation. In the RC scheme, a low-pass filter is used to allow tracking and rejection of periodic signals within a specified frequency range. A phase lead compensator is also used to compensate for the effect of the closed-loop system dynamics. The stability of the closed-loop system is derived, and the zero tracking error is achieved. Numerical simulations validated the proposed control approach, and experimental tests using a 200-W digitally controlled module-integrated converter prototype confirmed its feasibility.

Integral sliding mode controller for precise manoeuvring of autonomous underwater vehicle in the presence of unknown environmental disturbances

We propose an integral sliding mode controller (ISMC) to stabilse an autonomous underwater vehicle (AUV) which is subject to modelling errors and often suffers from unknown environmental disturbances. The ISMC is effective in compensating for the uncertainties in the hydrodynamic and hydrostatic parameters of the vehicle and rejecting the unpredictable disturbance effects due to ocean waves, tides and currents. The ISMC is comprised of an equivalent controller and a switching controller to suppress the parameter uncertainties and external disturbances, and its closed-loop system is exponentially stable. Numerical simulations were performed to validate the proposed control approach, and experimental tests using Cyclops AUV were carried out to demonstrate its practical feasibility.

Development of mooring-less robotic buoy system using wave powered renewable energy

For long-term operation, a wave-energy harvesting robotic buoy system that holds position automatically without anchoring line is proposed. We made a prototypes which consists of the propulsion system and power generation system. We adopted the Wave glider platform to hold the buoy position without mooring, and developed a flip-type self-rectifying wave turbine system (WTS). We developed modeling equations to describe the proposed system and simulated them using numerical software, then tested their station-keeping ability and energy-harvesting power in wave tank. Developed prototype patrolled within a 3-m diameter area, and the WTS generated 10.1 W of power. The station-keeping area was smaller than that of the existing mooring buoy, which means that the robotic buoy system can obtain precise and accurate observation data in the ocean without additional costs for mooring systems, and its wave-harvested energy can provide sufficient electric power to maintain the whole system.

Repetitive Controller With Phase-Lead Compensation for Cuk CCM Inverter

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.

Flyback CCM inverter for AC module applications: iterative learning control and convergence analysis

ABSTRACT This paper presents an iterative learning controller (ILC) for an interleaved flyback inverter operating in continuous conduction mode (CCM). The flyback CCM inverter features small output ripple current, high efficiency, and low cost, and hence it is well suited for photovoltaic power applications. However, it exhibits the non-minimum phase behaviour, because its transfer function from control duty to output current has the right-half-plane (RHP) zero. Moreover, the flyback CCM inverter suffers from the time-varying grid voltage disturbance. Thus, conventional control scheme results in inaccurate output tracking. To overcome these problems, the ILC is first developed and applied to the flyback inverter operating in CCM. The ILC makes use of both predictive and current learning terms which help the system output to converge to the reference trajectory. We take into account the nonlinear averaged model and use it to construct the proposed controller. It is proven that the system output globally converges to the reference trajectory in the absence of state disturbances, output noises, or initial state errors. Numerical simulations are performed to validate the proposed control scheme, and experiments using 400-W AC module prototype are carried out to demonstrate its practical feasibility.

Multi-body point absorber system without a mooring

In this paper, we propose a multi-body point absorber system which can harvest ocean wave energy without needing a mooring. The proposed multi-body point absorber system consists of two elements: a multi-body point absorber that extracts the power from the wave, and a Wave Glider that keeps the whole system within a prescribed area. We describe the concept of proposed system. We analyze the heave dynamics of the multi-body point absorber and performed numerical simulations to validate its feasibility.

Downsampled Iterative Learning Controller for Flyback CCM Inverter

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.