This paper introduces a novel analytical model for the accurate inductance calculation of rounded rectangular coils in wireless power transfer systems (WPTSs). Comprehensive analysis is conducted for the rounded rectangular coil and a new parametric model is proposed to precisely define its structure. A new inductance calculation model is proposed for the rounded rectangular coils based on Neumann's formula and the obtained parametric structure model. The Geometric Mean Distance method is introduced to reduce the complexity and difficulty of self-inductance modeling. The image current method is adopted to achieve accurate inductance modeling for rounded rectangular coils with ferrite plates. Finally, the accuracy of the proposed analytical model is validated and compared with two other traditional methods. It turns out that the proposed models can achieve high calculation accuracy in self-inductance and mutual inductance calculation. The proposed model exhibits the merits of high accuracy and fast calculation speed which makes it promising for future coil designing and optimization.

The circular coil is extensively employed in different wireless power transfer (WPT) applications due to its simple structure and satisfactory magnetic coupling capabilities. Different analytical models have been proposed to calculate the inductance of circular coils and some of them have achieved relatively high accuracies for coreless circular coils. However, the influence of ferrite plates is not fully considered in these studies, thus limiting their application potential. Therefore, a new analytical model and practical calculation method of circular coil's inductance are proposed in this paper. First, the parametric structure model for circular coils is derived, and the analytical inductance model is proposed based on Neumann's Formula. Second, the image current method is adopted to calculate the inductances of circular coils when ferrite plates are added to WPT systems. Then, a new Feedforward Neural Netweork (FNN) model is designed and trained to improve the computation accuracy of the proposed analytical inductance model for different circular coils in WPT systems. The proposed model exhibits exceptional precision and stability, which makes it promising in coil designing and optimization for diverse applications.

Despite the widespread use of resonant converters in various applications, their analysis and design still necessitate a solid comprehension of the converter's operating principle and nonlinear behavior, which can be a significant manpower burden. To alleviate this issue and free us from repetitive work, this paper proposes a zero-knowledge artificial neural network (ZANN)-based waveform and critical parameter calculator for resonant converters. A normalized resonant network is employed to generate adequate data for training the ZANN. The ZANN can identify the essential characteristics of different resonant networks based on the configuration of hyperparameters. The accuracy of the calculator is verified using a 3-kW 480-V CLLC prototype. The results show that the accuracy of the root-mean-square (RMS) values is less than 5%, while the accuracy for the peak values is less than 20%.

The CLLC resonant converters are widely used in data center, battery chargers, electrical vehicles due to its high efficiency and high power density. The voltage gain characteristic of CLLC resonant converters plays an important role in both operation analysis and design optimization. This paper presents a precise and fast backpropagation neural network (BPNN)-based voltage gain model of CLLC that considers two degrees of freedom (2DOFs), the switching frequency$\boldsymbol{f}_{\mathbf{s}}$and duty ratio$\boldsymbol{d}$, in all operation conditions. The effectiveness of the model is verified by a 3-kW 480-V CLLC prototype. The voltage gain error is reduced by 95% compared to the conventional fundamental harmonic approximation (FHA) method, and the calculation burden is reduced by 99% compared to the time-domain method.

The high switching frequency of wireless power transfer systems makes soft switching important due to switching losses. In the current literature, numerous solutions have been proposed for maintaining soft switching within the entire operating range. However, this study shows that variable frequency control can cause loss of zero voltage switching (ZVS) during system transients, even if soft switching during steady-state operation is ensured. The causes of this phenomena are analyzed thoroughly and two approaches to address such issue are discussed. Firstly, a limitation on the changing rate of the frequency can alleviate the issue. Secondly, phase advance control could also be possible, although this approach requires further studies. Results from both simulations and laboratory experiments are presented to verify the analysis and the control method proposed to avoid losing ZVS during transient conditions.

Capacitance reduction is of great significance for economical and high power density operation of modular multilevel converters (MMCs). This paper proposes a low-capacitance MMC for high voltage direct current (HVDC) applications. The average capacitor voltage reduction control (ACVRC) is employed to decrease the average capacitor voltage, so that a high capacitor voltage ripple can be accommodated without exceeding the peak value of capacitor voltage. The capacitance reduction under ACVRC is analyzed. To prevent the increase of the arm references and avoid the decline of the linear modulation region, an optimal third-order harmonic voltage injection (THVI) method is proposed. The average capacitor voltage and capacitance are designed under ACVRC and THVI. Besides, the existing circulating current control-based method can also be used to further reduce capacitance. Simulations are conducted, which verify the correctness of the analysis and the feasibility of proposed low-capacitance MMC.

This paper proposes a hysteresis ON-OFF control method for inductive power transfer (IPT) systems with low output ripples and fast transient responses. System power is regulated by skipping pulses, thus achieving zero voltage switching over the full operating range. Moreover, each switching state is determined by a hysteresis comparator operating on the measured power. This prevents the skipped pulses from exciting poorly damped oscillations. The dynamic behavior of IPT systems with the hysteresis ON-OFF control method is excellent because the controlled state of the system is directly adjusted in every half cycle. The effectiveness and feasibility of the proposed method are validated by simulations and experimental results from a small-scale laboratory prototype.

Fast and stochastic power fluctuations caused by renewable energy sources and flexible loads have significantly deteriorated the frequency performance of modern power systems. Power system frequency control aims to achieve real-time power balance between generations and loads. In practice, it is much more difficult to exactly acquire the values of unbalance power in both transmission and distribution systems, especially when there is a high penetration level of renewable energies. This paper explores a deep learning approach to identify active power fluctuations in real-time, which is based on a long short-term memory recurrent neural network. The developed method provides a more accurate and faster estimation of the value of power fluctuations from the real-time measured frequency signal. The identified power fluctuations can serve as control reference so that the system frequency can be better maintained by automatic generation control, as well as emerging frequency control elements, such as energy storage system. A detailed model of Singapore power system integrated with distributed energy storage systems is used to verify the proposed method and to compare with various classical methods. The simulation results clearly demonstrate the necessity for power fluctuation identification, and the advantages of the proposed method.

This paper presents a new concept of co-ordinated active power sharing between shunt and series converters of unified power quality conditioner (UPQC) for distributed generation applications. Normally, the UPQCs are used to mitigate both voltage and current power quality problems. However, these UPQCs are also used for delivering active power in addition to its power quality improvement by integrating distributed generation (DG) at the DC link of back to back connected converters. But, only the shunt converters are used to carry the whole active power from the DG sources and the series converters are used to handle only voltage related power quality problems. So, the shunt converter is loaded heavily and the series converter is kept idle in steady state cases. The more dependency on the shunt converter also reduces the reliability of the total system. This proposed control strategy is used to carry active power through both series converter and shunt converter even at the steady state conditions. The proposed method improves the utilization of the converters and also the reliability of the system. The effectiveness of the proposed control strategy is demonstrated by comparing with the conventional control algorithm, where only the shunt converter is used to carry active power. The proposed system is validated by performing hardware in loop (HIL) tests using OPAL-RT and dSPACE DS1103.

Three-phase three-wire shunt active power filters (APFs) usually employ very large electrolytic capacitors in the dc-link to mitigate utility side harmonics. These capacitors are however known to be bulky and of short operating lifetime, particularly for systems where high ripple currents exist. This paper presents the concept of dc-link compensator (DLC) that aims to decouple the harmonic power from the dc-link of APF. With proper system sizing and design, most of the harmonic power can be eliminated by this DLC circuit and very small electrolytic capacitors or even film type capacitors can be used instead. Moreover, DLC itself is constructed with small passive components and features very simple circuit configuration. Experimental results are provided to show its effectiveness.

This paper presents an efficiency improved single-phase power factor correction (PFC) converter with its target application to plug-in hybrid electric vehicle (PHEV) charging systems. The proposed PFC converter features sinusoidal input current, three-level output characteristic, and wide range of output DC voltage. Moreover, the involved DC/DC buck conversion stage may only need to convert partial input power rather than full scale of input power, and therefore the system overall efficiency can be much improved. Through proper control of the buck converter, it is also possible to mitigate the double-line frequency ripple power that is inherent in a single-phase AC/DC system. Both simulation and experimental results are presented to show the effectiveness of this converter.