Frequency splitting phenomena are investigated systematically by circuit theory in a series-tuned contactless power transfer (CPT) system. First, in a symmetrical CPT system, the splitting equation is defined and the key frequency splitting characteristics are described by the trough and the ridge equations in a complete fashion. The even and the odd splitting frequencies are exactly two roots of the ridge equation; the splitting coupling is determined theoretically when the even and odd splitting frequencies merge together. Second, in an unsymmetrical CPT system, the idea of the trough and the ridge equation is exploited to find exactly the splitting coupling. Next, the relationship between frequency bifurcation and splitting is elucidated; and a zero-phase control method is suggested to track the splitting frequency when the coupling changes in the splitting region. Finally, the theoretical results are validated by a 10-W prototype with planar spiral coils.

An asymptotic coupled-mode theory (CMT) method is used to analyse the frequency splitting phenomena in contactless power transfer (CPT) systems. Theoretical analysis and experimental results show that the CMT method catches the key pitchfork characteristics of the frequency splitting phenomena, and a concise expression is derived to relate the splitting point to all key system parameters.

Rubber tyred gantry (RTG) cranes are an important piece of transport equipment in ship and rail container terminals. They have a diversified power demand, for example, peak powers of 292-kW driving, 178 kW regenerating, and 7-kW idle power. The high peak power demand determines the system prime mover (internal combustion engine) rating, which is highly over-rated for the crane average energy requirements. Such a variation in peak to idle power demand favors a hybrid power solution which, given appropriate design, can yield significant gains in fuel or energy usage and, importantly, reductions in local emissions, thus improving air-quality. In this study, a hybrid energy source for an RTG crane is presented. The hybrid energy source comprises of a lithium battery and a down-sized diesel-generator connected to the dc link through an active front end unit. While other systems have been previously proposed, the system presented here utilizes a smaller diesel-generator, thus reducing plant and fuel consumption. In addition, the battery connects directly to the dc link reducing system power electronics while improving battery response and efficiency. Experimental results from a full-size evaluation system are presented showing a 57% reduction of fuel consumption compared to a conventional RTG crane system.

Frequency splitting patterns in low‐order wireless power relay transfer systems are analysed by the coupled‐mode theory. In addition to the V‐type splitting pattern reported widely, two new patterns, I‐type and W‐type, are introduced. Specifically, it is found that a 0‐relay system shows a V‐type or I‐type splitting; a symmetrical 1‐relay system shows an I‐type or W‐type splitting; and a symmetrical 2‐relay system usually shows a V‐type or W‐type splitting. The criteria for different frequency splitting patterns are given, and the theoretical results are validated finally by 1‐relay and 2‐relay wireless power transfer experimental systems.

A control method that combines trajectory planning and backstepping is proposed for the antisway problem of underactuated overhead cranes under wind disturbance. First, a set of flat outputs is proposed so that the crane system dynamics can be represented by each order of flat outputs. Sufficient relevant constraints are given to ensure that the trolley can arrive at the desired position in a limited time under variable rope lengths, and that the swing angle can be suppressed when the payload is lifted or lowered during operation. The planned trajectory is obtained by solving for the optimal parameters of the flat output. Next, to reduce the deviation caused by wind disturbance on the actual control of the trajectory, a tracking controller is designed. Because the system output space and flat output space are differentiable homeomorphisms, the backstepping controller constructed based on the flat output can indirectly control the system output, which makes the backstepping method applicable to underactuated cranes. The simulation results show that the proposed method is effective and has strong robustness.

Underwater wireless power transfer (UWPT) is an important technique to power underwater devices while its frequency splitting phenomena are not fully elucidated. In this study, frequency splitting phenomena of a symmetrical planar two‐coil wireless power transfer (WPT) system resonated at 90 kHz are investigated in seawater and freshwater. A concise frequency splitting analysis of this WPT system in air based on circuit model is given first and then experimental data are reported to show there is little difference between power transfer in air, freshwater and seawater in the range of 40–140 kHz of this WPT system. Consequently, the frequency splitting analysis and observations in air are also applicable in freshwater and seawater. It is found a V‐type frequency splitting pattern exists in this WPT system under seawater and freshwater. Frequency shift is observed in this UWPT system in overcoupled region, and no frequency shift is observed in undercoupled region. In undercoupled region, in the low frequency zone of 40–90 kHz the load voltage characteristics in three media are identical; in the high‐frequency zone of 90–140 kHz, the load voltage in air is slightly larger than those in freshwater and seawater.