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This paper proposes a universal Shore-to-Ship Charging (S2SC) concept for multi-vessel onshore power supply and charging of onboard batteries. One of the main challenges of existing S2SC systems is the lack of interoperability between shore-side charging systems and onboard power system configurations. To address this issue, the proposed S2SC concept is designed to provide charging to multiple ships with various onboard configurations and vessel missions. To reduce the impacts of grid outage events and grid capacity limitations on the charging performance, an On-Shore Battery (OSB) unit is considered. This OSB is connected directly to a common dc bus, without a dedicated OSB converter to ensure a cost-effective solution. Furthermore, the power converters are designated to serve multiple functions while forming an integrated configuration. This can enable increased utilization of the infrastructure. Moreover, a charging management system is introduced as a high-level controller to deliver stable, controllable, and prioritized shore power to multiple vessels. This high-level controller regulates the OSB power and State-of-Charge (SoC) while ensuring the charging service during grid outages and limited grid capacity conditions. As a proof of concept, the complete model of a S2SC designed for supplying four different vessels is simulated and the control performance is validated via a series of case studies.

This article identifies the critical conditions of bifurcation and frequency splitting phenomena in inductive power transfer (IPT) systems used for battery charging, considering a constant voltage load (CVL) model. While prior studies covered these phenomena for IPT systems with constant resistance loads, their application to battery-loaded systems is limited due to the variation of equivalent load resistance with the operating frequency. By using the CVL model and analyzing the output power peak points, this article calculates the critical conditions for the frequency splitting phenomenon. This enables determining the power's monotonic range and peak in the frequency-control system. Moreover, by analyzing the monotonicity of the system's input impedance angle, the critical condition for bifurcation can be identified for determining the operating region that achieves zero-voltage switching or designing zero-phase angle IPT systems. To avoid bifurcation and achieve zero-voltage switching across the entire operational range, boundary conditions for frequency detuning design in systems with resistance or voltage loads are identified. The proposed analysis is validated through experimental measurements, and an example illustrating the impact of critical conditions on IPT system design for battery charging is provided.

In this work we address the modeling of multi-port subsystems with unknown inner dynamics by utilizing vector fitting to identify state-space models for performing eigenvalue-based analysis. Vector fitting is used to characterize frequency responses obtained from frequency domain analysis, for example, from Fourier transformation of time domain data. The intended use is for interconnection with other models in system stability analysis, where the use of compact state-space models is desirable. Typically, vector fitting of a multiple-input/multiple-output (MIMO) system leads to a large state-space model where each column (input) is fitted by a common pole set using a predefined model order. An alternative vector fitting process based on a pole collapsing scheme is proposed which can find suitable poles for a more compact state-space model. Additionally, a method for simpler, more automated order determination is introduced. The use of the presented approach for obtaining a fully compacted model (without pole repetitions) is examined and compared against a previously proposed method based on singular value decomposition. Application to an example system representing a 2-level power electronic converter demonstrates that the proposed method gives a model with improved accuracy of eigenvalue identification and model compaction, while retaining the essential information in terms of system dynamic behavior.

A method for improving the power reference tracking capability of Virtual Synchronous Machines (VSM) by phase angle feed-forward (PAFF) control is proposed in this article. The presented implementation includes compensation for the ac power flow dynamics and can be applied to any VSM-based control relying on a virtual swing equation. Fast and accurate power reference tracking is achieved independently from the emulated inertia time constant, and without influencing the grid synchronization mechanism of the VSM. Therefore, the grid forming capability of the VSM and the inertial response to grid frequency variations are not influenced by the proposed PAFF control. The effectiveness of the derived feed-forward terms is first validated with a simplified VSM scheme. The performance is also thoroughly evaluated for a detailed VSM implementation including closed loop current control and a virtual impedance. This includes operation with different grid impedance values and studies of the sensitivity of the PAFF function with respect to parameter variations in the VSM control or deviations from the assumed grid impedance. Experimental results with a 50 kVA converter controlled as a VSM are presented as verification of the improvement in power reference tracking capability.

This letter proposes a conditional pulse density modulation (PDM) method for inductive power transfer (IPT) systems, which can automatically adapt the generated output patterns to effectively suppress current/power ripples. The proposed conditional PDM introduces a sending current limitation as an additional condition to skip pulses, which modifies the output patterns generated by conventional delta-sigma-based PDM. Thus, the PDM pulse pattern is continuously adapted to attenuate any excited current/power oscillations. The presented modulator is simple to implement and well-suited for IPT systems with poorly damped constant voltage load characteristics. Simulations and experiments demonstrate the effectiveness of the proposed modulation method.