The output power of a single-phase inverter is insufficient for high-power applications, such as fast wireless chargers for electrical vehicles. A higher power level can be obtained via a multiphase parallel resonant inverter, which comes with a possible cost of the unbalance current problem. Coupled inductors with a cyclic cascade connection instead of a complex controller are employed to alleviate this problem. A blocking capacitor is introduced to stop the dc component of the circulating current. Equations for suppressing ability of circulating currents under the proposed topology with various numbers of parallel phases are derived. Main power loss components are analyzed and the reason why multiphase systems with a high output current have a higher efficiency is theoretically explained. A prototype of an inverter with six-phase half-bridge parallel topology is developed and built to verify the theoretical analysis. The prototype is used to supply an inductive power transfer system, which delivers power at a distance of 20 cm. When the receiving power of the 6.87 Ω load in the rectifier is 20 kW, one obtains a 95.6% efficiency measured as the power of the dc-load divided by that of dc-input at the inverter.

This paper introduces the design and implementation of a plug-in free online 3-D interactive laboratory based on networked control system laboratory (NCSLab) framework. The system relying only on HTML5 provides full supports for control engineering experimentation. The users are allowed to design their own control algorithms and apply them to the remote test rigs. Using the web-based interface, multiple widgets such as real-time charts, virtual gauges, and live images are available to customize the monitoring interfaces. To enhance the sense of immersion, 3-D animations which are synchronized with the remote experimental processes are also provided. The users can watch and interact with the remote experiments through the 3-D replicas. Various HTML5 based toolkits are integrated seamlessly under the NCSLab framework. NCSLab provides visualized services for the whole process of control experimentation including remote monitoring, tuning, configuration, and control algorithm implementation. As the network delay could disturb the 3-D representation, a communication scheme using web protocols is also implemented. The feedback from teaching shows the general acceptance and effectiveness of NCSLab is notably high. As most existing online laboratories adopt either native applications or plug-ins, the methodologies and technologies used in NCSLab could be insightful for other online laboratories toward web-based cross-platform systems.

In order to provide high and extendable power levels for inductive power transfer (IPT) system, a parallel multi-inverter system based on modular inverter is presented. Various power requirements can be implemented via adjustment of the number of paralleled inverters, which provide a high modularity. A master-slave scheme is employed for the switching-driver signals of parallel inverters, where one acts as a leader while others as followers. Despite of the master-slave scheme, the proposed circuit topology has natural robustness because of the equality in terms of the hardware configuration of each modular inverter. For proper parameters, the output phase (current lagging corresponding voltage) of an inverter is lower than the average of output phase of all inverters, when its output voltage lags behind others, and vice versa. Based on this approach, PI controllers are designed to implement phase synchronization for output voltages of all inverters. An IPT prototype supplied by the proposed parallel multi-inverter with 3 inverters was designed, built and tested. Experiments shown that the proposed parallel multi-inverter system has not only good circulating current suppression capacity, but also excellent performance of phase synchronization. The maximum DC-DC efficiency was 94% at a 35.1 kW receiving power. This paper is accompanied by a Matlab/Simulink file demonstrating phase synchronization control.

A multiphase inverter with phase-shifted control is proposed for the inductive power transfer (IPT) of EVs where the charging voltage can be regulated by adjusting the angle among the inverter phases. An equivalent circuit model is developed and linearized to analyze the system dynamic characteristics at its operating point. In terms of the high order model, a balanced model reduction method is used to remove the fast modes which are outside the desired system bandwidth and insignificant to controller design. In addition, the model is discretized and the communication delay of the feedback loop is considered in the discretized model. Based on this model, the parameters of a PI controller are designed to achieve the expected performance indexes. A 6.5 kW S-S compensation IPT system prototype with constant voltage control is built and tested to verify the control performance. The experimental results show that the charging voltage can be maintained constant within 6 ms and has no overshoot under disturbances, which verifies that the closed-loop system with PI controller operates properly and efficiently for IPT. Besides, the measured transmission efficiency of the system at a receiving power of 6.5 kW is 95.1%

This paper investigates control-oriented modeling of a class of wireless power transfer systems with a phase-shift controlled inverter. Two methods are studied: the conventional analytical modeling method which is based on physical laws, and the refined instrumental variable method which is based on sampled data. It shows that the former provides good physical insights into the system, and that the resulting models are accurate when the true circuit component parameters are known. However, poor results may be obtained if this condition is not satisfied. By contrast, the later provides a cheap solution for accurate modeling, which requires a set of sampled input-output data only and the resulting model can capture very well the dynamic behavior of the system within its operating range. To have virtues of both methods, it is therefore suggested to use them as a combination, that is, using the analytical method to determine the model order while using the data-driven method to estimate the model parameters. All results derived in this paper are verified by means of both numerical simulation and experimental validation.

A coil with a high quality factor Q is desired to obtain a high efficiency for inductive power transfer (IPT). Q is proportional to the coil inductance and operating frequency, while it is inversely proportional to the coil resistance, which increases with frequency. An optimized frequency exists to achieve the maximum efficiency. Eddy currents and resulting ac resistance in Litz-wire coils are attributed to magnetic field. Especially, the induction component of the ac resistance is approximately proportional to the squared magnetic field to which the coil is exposed to. FEA simulations are conducted and surface integral method is employed to determine the squared field. Additionally, the volume integral method is proposed to evaluate the overall effect of the field on the induction resistance. The optimized frequency for the maximum efficiency is obtained, using the squared field calculation and resulting ac resistance evaluation. Sample prototype coils are manufactured to verify the resistance analysis methods. An IPT system is built employing these coils. Experiments show that the IPT system achieves the highest efficiency at frequencies closed to the predicted optimized ones.