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This paper examines an improved dual-battery energy storage scheme designed to achieve wind power dispatchability. The capacity of the battery energy storage system is greatly reduced by allowing direct power flow from wind turbine generator to the grid via a dc bus, as the two batteries interchange their charging and discharging roles at specific time. The method to determine the optimal capacity of the energy storage system is given, and is based on the characteristics of the battery and long-term wind power profile. Numerical examples show the validity of the proposed schemes.

Active ripple current reduction method is proposed for isolated DC/AC dual active bridge (DAB) converter to reduce the double grid frequency ripple in the DC current. Unlike those active methods that require extra switches to construct separate ripple reduction circuit, in this method, one or two branches of LC ripple steering circuits are used along with existing full bridge switches in a multiplexing manner. For the purpose of the ripple elimination, unsymmetrical phase shift modulation and duty cycle regulation methods are proposed and applied to both legs of the converter on the primary side of DAB converter. Also a current sharing (CS) scheme is presented to balance the current on both LC ripple steering circuits.

The improvement of misalignment tolerance is a key challenge for the optimization of wireless power transfer (WPT) systems. WPT coil design plays an imperative role in improving the misalignment tolerance. However, misalignment tolerance needs to be considered along with the dynamics of the receiving coil. This paper presents a coil optimization method to improve misalignment tolerance according to the receiver positioning behavior. A novel figure-of-merit (FOM) is introduced by incorporating maximum efficiency and the probability of alignment (PA). A case study for parameter optimization of circular spiral coils is presented with the use of the proposed FOM.

Low-frequency switching strategies are considered as an effective way of achieving efficient performance in multilevel inverters. Selective harmonic elimination (SHE) is a modulation technique of this category which gives a superior outcome suppressing low-order detrimental harmonics. Limited number of decision variables offered by SHE in the corresponding nonlinear equations hinders obtaining quality waveforms. Current research is targeted on two distinct objectives for CHB inverters. First objective is to obtain a quality output signal. The second one is accomplishing a realistic solution with compromised voltage quality where a broad operating range becomes mathematically challenging. These aims are achievable by deploying additional degree of freedom in the equation set. In other words, the introduction of floating voltage levels contributes to effectively doubling the number of variables. The enhancement of output waveforms is presented through several illustrations and comparisons. Subsequent laboratory implementation validates the proposal and confirms its feasibility.

Battery modelling is a significant component of advanced Battery Management Systems (BMSs). The full electrochemical model of a battery can represent high precision battery behavior during its operation. However, the high computational requirement to solve the coupled nonlinear partial differential equations (PDEs) that define these models limits their applicability in an online BMS, especially for a battery pack containing hundreds of cells. Therefore, a reduced SPM-Three parameter model is proposed in this paper to efficiently model a lithium ion cell with high accuracy in a specific range of cell operation. The reduced model is implemented in a Simulink block for developing an advanced battery modelling tool that can be applied to a wide variety of battery applications.

Arc faults in a PV system are difficult to study using models developed for conventional power sources mainly due to non-linear behavior of PV current and its dependence on external factors such as irradiance, shading and maximum power tracking controls. This paper presents a unique model derived from fundamentals of Mayr and Cassie arc models and introducing a hyperbolic tangent function to approximate arc current at near zero gap. Arc impedance widely changes with heat dissipated through arcs periphery. Unique feature of the proposed model is that it takes into account this change of impedance with time which could be used to analyze arcs with changing lengths due to movements of current carrying elements. A test bench has been built with adjustable gap between two electrodes to conduct experiments. Both experimental results and simulation outcomes are presented to verify the proposed model.

A frequency modulation scheme is proposed for a Capacitor-Inductor-Inductor-Capacitor (CLLC) Resonant Dual Active Bridge (RDAB) that relies on dynamic retuning of the resonant capacitors to the switching frequency as it is modulated. The proposed modulation scheme greatly reduces the circulating reactive currents in the High Frequency Link (HFL) by operating at a range of fixed discrete switching frequencies. A Triple Phase Shift (TPS) modulation scheme is used in between the discrete steps of switching frequencies and capacitances. In this paper, a mathematical analysis is presented of the RDAB and the proposed modulation scheme is compared to all of the existing modulation schemes. The CLLC RDAB is implemented in simulation and the simulation results demonstrate the effectiveness of the proposed modulation scheme at decreasing the circulating reactive currents, and therefore, greatly decreasing the conduction losses of the converter at light load, while maintaining its soft switching capability.

Three-phase cage induction machines, configured in two series-connected and one isolated (TSCAOI) configuration, have earlier been proposed for variable speed single-phase electricity generation. Although steady-state characteristics of TSCAOI generators have previously been investigated, both the nature of torque due to unbalanced operation and its impact on overall performance are yet to be analyzed. This paper therefore carries out a detailed investigation into the torque production of the generator, analyzing both the average and fluctuating components of the torque under various operating conditions. Theoretical torque-speed characteristics of a 3 kW 4-pole TSCAOI configured generator are presented in comparison to simulations, discussing its salient features and limitations.

Multi-port dc-ac and dc-dc converters are of great interest for applications where electricity is generated through a variety of energy sources and where energy storage systems are required. In this paper, a three-port, dc-dc-ac Solid State Transformer (SST) is presented that can control the magnitude and direction of power transfer between a battery, a dc bus and the ac grid. The proposed SST features a low magnetic component count, has high power density, high efficiency and provides galvanic isolation between all three ports. The presented topology is operated with a fixed switching frequency and is phase shift modulated. In this paper, a mathematical analysis of the proposed SST is presented along with its sensitivity to parameter variation. The requirements for soft switching is derived and it is demonstrated that the converter can soft switch over large input voltage variation. The modulation parameters are optimized so that the high frequency link currents are minimized while soft switching is maintained. Additionally, in the simulation results, the ac grid current is modulated so that no Power Factor Correction (PFC) circuitry is required.

Regularly sampled pulse width modulation (PWM) has been a mainstay of the power electronics community since the advent of digital controllers. In this form of PWM the modulating signal is sampled only at either the peaks and/or the troughs of the triangular carrier waveform, then held constant until the next sampling instant, which allows ample time for the calculation of switching instants. Unfortunately, it produces phase and amplitude distortion of the modulating signal that can be significant at low pulse numbers. In applications where the desired modulating signal is not known a priori, this phase delay can become a critical limitation. The analogue alternative to regular sampling is naturally sampled PWM, where the modulating signal is permitted to vary as a continuous waveform. This form of PWM does not apply any phase or amplitude distortion to the modulating signal. True natural sampling is, however, impossible to implement on the digital control platforms that are used in modern power electronics applications. In this paper, a type of hold circuit known as a First-Order Hold (FOH) circuit is used in conjunction with the technique known as resampled regular PWM to improve upon the limitations of regular sampling. It is found that this augmentation to the PWM strategy improves both the linearity and phase delay of the modulator as well as (for high pulse numbers) harmonic performance. The FOH circuit has an overshoot in its transfer function which should be avoidable if the modulating signal is sampled at a sufficiently high rate.

This paper presents a novel battery direct integration scheme for renewable energy systems. The idea is to replace ordinary capacitors of a three-level flying-capacitor inverter by three battery banks to alleviate power fluctuations in renewable generation. This approach eliminates the need for interfacing dc-dc converters and thus considerably improves the overall efficiency. However, the major problem with this approach is the uneven distribution of space vectors which is due to unavoidable unbalance in clamping voltages. A detailed analysis on the effects of this issue and a novel carrier based pulse width modulation method, which can generate undistorted currents even in the presence of unevenly distributed space vectors, are presented in this paper. A charge/discharge controller is also proposed for power sharing and state of charge balancing of battery banks. Simulation results are presented to verify the efficacy of the proposed system, modulation method and power sharing controller.