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Apart from the load variation, the coupling misalignment of a capacitive power transfer (CPT) system can change the resonant frequency, which results in the variation of the output voltage/current. This paper proposes a dual-loop control CPT system aiming at reducing the effect of the coupling misalignment and load variation. Based on the modeling of the LC-LC compensated CPT system, the constant-current (CC) and constant-voltage (CV) frequencies are derived. Then the frequency splitting and frequency bifurcation are illustrated. The frequency tuning is realized by tracking the input and output voltage rather than the input voltage and current. This method is helpful for tracking CV frequency accurately, and it can avoid the system operating at other resonant frequencies caused by frequency bifurcations. Based on the proposed control method, a 250W experimental prototype with 20mm transmission distance is built. The CPT system can always operate in the load-independent CC/CV mode and the output voltage/current can be controlled to the target value with 2% error, when the load resistance and coupling misalignment vary from 5 to 50 ohms, 0 to 100mm x-misalignment, and 0 to 20mm z-misalignment.

To simplify the analysis process of the multirelay magnetic coupling wireless power transfer system, a novel analysis method based on the quadratic eigenvalue problem (QEP) has been proposed. The second-order underlying equation of the system is given. The eigensolution represents the inherent properties of the entire system and provides important and useful information. The analytical solutions of currents induced in each coil are expressed in terms of the eigensolution of the corresponding QEP. Real parts and imaginary parts of the eigenvalues represent attenuation coefficients and system resonance frequencies, respectively. The effect of the load resistance on the eigenvalues is studied. It is found that the attenuation coefficient of an eigenvalue increases as the load resistance increases so that it can be ignored. The relationships between eigenvalues and some key frequencies are discussed, such as system resonance frequencies, zero-phase angular frequencies, and constant voltage/current frequencies. The results show that fixed zero-phase angular frequencies and constant current frequencies are equal to the imaginary parts of the eigenvalues with load resistance is equal to zero, and the constant voltage frequencies are equal to the imaginary parts of the complex eigenvalues in a strong damping stage. Finally, experimental results verify the theoretical analysis.

This paper proposes a novel capacitive power transfer (CPT) system with switchable compensation for achieving constant current (CC) or constant voltage (CV) output against load and coupling capacitance variations. Meanwhile, a parameter design method is proposed to ensure a low input impedance angle at constant operation modes. Mathematical models of voltage and current gains are established, which are used to analyze the CC and CV operation modes of the proposed CPT system. Two relays are adopted in receiver to reconfigure the compensation network to switch the CC mode and CV mode. The communication between the transmitter and receiver is not needed, and complex control is not required either for changing two operation modes. An experimental setup with 2A output current in CC mode and 96 V output voltage in CV mode is constructed. Experimental results show that the maximum variation of the output current is 4.0% in CC mode, and the maximum variation of the output voltage is 5.0% in CV mode, when the load resistance and coupling capacitance vary from 24 to 72 ohms, and 500 to 1000 pF, respectively. Experimental results verify the CC/CV output and the effectiveness of the proposed parameter design method.

In order to solve the problem that the output voltage of bilateral LC -compensated capacitive power transfer (CPT) system varies with the variation of load and equivalent coupling capacitance, this article presented a parameter design method that maintained the output voltage constant and guaranteed a high power factor. The mathematical model of the bilateral LC -compensated CPT system was established. The characteristic of the primary and secondary LC -compensated network was analyzed, and then, the conditions remaining a constant output voltage with varying load and coupling capacitance were determined. The relationship between the power factor and the load versus equivalent coupling capacitance was given. With the proposed parameter design method, a 100-W bilateral LC -compensated CPT experimental setup was constructed. The output voltage changes from 55.0 to 58.7 V and the power factor varies from 0.902 to 0.977 when the load and coupling capacitance vary from 30.2 to $70.8~\Omega $ and from 310 to 1490 pF , respectively. Both the simulation and experimental results have verified the characteristic of constant output voltage and the effectiveness of the proposed parameter design method.

Focusing on the output voltage reduction caused by variation of the equivalent coupling capacitance in capacitive power transfer (CPT) system, this paper proposes a hybrid control strategy to achieve constant output voltage with the variation. The hybrid automata model is introduced for the cascaded CPT system considering the characteristics of higher order, nonlinear, multi-mode, continuous time and discrete states. The control process of the system is transformed into a selection of boundary transition conditions, which simplify the controller design and implementation. Then, a hybrid automata model of the system is established based on the theory of hybrid system, and the boundary transition of each mode of the system is given. The simulation and experimental results show that the proposed hybrid control strategy can keep the output voltage constant when the coupling capacitance of CPT system varies in a certain range.

This paper presents a sleeve-type capacitive power transfer (CPT) system for contactless rotary applications. Sleeve-type capacitive couplers with different coupling arrangements between primary and secondary metal sleeves are proposed in this research, which lead to different coupling characteristics with positive, zero, and negative coupling coefficients. The effect of coupling coefficient variations caused by both the power transfer distance and the ratio between the overlapping length and the height of outer sleeves is analyzed. Combining the sleeve-type coupler, the CPT system is developed with a double-sided LC-compensated network and half-bridge inverter. For the CPT systems with positive and negative coupling coefficients, parameter design methods are presented to determine system parameters to achieve zero phase angle (ZPA) condition under the same output power. Then overall system performances of the CPT systems with local maximum positive and local minimum negative coupling coefficients are analyzed and compared by simulation in MATLAB/Simulink and Maxwell. Finally, an experimental prototype is constructed, which has demonstrated a power efficiency of 85.3% at 100.8 W. Simulation and experimental results show that the CPT system with local minimum negative coupling coefficient has clear advantages in increasing transfer distance, reducing voltage on sleeves, suppressing fringing electric field, and improving power density.

For the wireless power supply of on-line monitoring equipment for HVTL (high voltage transmission lines), a multi-relay WPT (Wireless Power Transfer) system with double-sided LCC resonant network is proposed to improve the system output power and constant voltage output characteristic. In order to reduce the influence of frequency splitting on system output characteristic, three working modes are analyzed. A numerical simulation analysis has been carried out to prove that the working modes proposed can improve the system’s constant voltage output capability.

This paper proposes an LCL-L compensated capacitive power transfer (CPT) system with a four-plate compact capacitive coupler to achieve load adaptation. The coupling principle of four plates is explained, and the formulas between the cross-coupling capacitances and port capacitances are deduced by establishing a two-port capacitive network model of the coupler. The resonant frequency is designed to be unchanged whether the pick-up is removed or moved back to simplify system control. The model of the coupler and AC impedance model of CPT system are established, and the parameter design method is given. Finally, the feasibility and effectiveness of the proposed topology and its parameter design method are verified by simulation and experimental results.

For most capacitive power transfer applications, a reliable signal transfer link between the primary side and the secondary side plays an essential role. The parameters design of the system has a key effect on the operating performance, however, the existing parameter design method can only get an acceptable solution, instead of a globally optimal solution. This study has proposed a general and global optimal parameter design method based on the constraint multi-objective algorithm. The mathematical models of the power and signal channels as long as the power noise is established and all the objective functions are given according to the models. Besides, the constraints considering the reasonable region of the parameter values and the limitation of the voltage and current on the elements are given. Then the multi-objective optimisation problem with the objective functions and constraints are solved by the non-dominated sorting genetic algorithm II, and the proper global optimal parameters are selected from the Pareto set. Finally, a simulation model and an experimental setup with 180 W power and 200 kbps signal transfer capability are constructed, and the results verified the effectiveness and correctness of this method.

When wirelessly supplying electric power to movable devices using capacitive power transfer (CPT) technology, the sudden move in and move out of the pickup will cause a sudden change to the system structure. As a result, the current and voltage of the inverter may increase dramatically, which may destroy the semiconductor switches or other circuit components, and the system may consume a lot of power after the pickup is removed. To address the issues, this paper proposes an F-type compensated CPT system based on the characteristics of the inductor–capacitor–inductor resonant network. A steady-state model of the proposed CPT system is established, and a set of design equations is provided. The feasibility and validity of the proposed topology and its parameter design method have been verified by the simulation and experimental results. It has demonstrated experimentally that the CPT prototype can be self-protected and automatically enter standby mode after the pickup is removed, and restore to deliver the required power (>25 W) to the load at a high power efficiency (>80%) after the pickup is moved back to the primary circuit, which are the inherent features of the proposed system rather than relying on any additional detection and control.

This paper proposes a method to transfer power across a metal barrier wirelessly by combined capacitive and inductive coupling. At the primary side of the power transfer system a two plate coupling interface is designed to allow for a current flow in the metal barrier, which generates a magnetic field for transferring power via an inductive coil at the secondary side. The current distribution in the metal barrier is analyzed by taking the skin effect into consideration, based on which the magnetic field distribution around the metal surfaces is determined. A three-dimensional (3-D) model is established using a computer simulation technology (CST) package to simulate the magnetic field distribution, which gives consistent results compared to theoretical analysis. Finally, a wireless power transfer system is constructed, and practical measurements show that the magnetic flux density near the edges of the metal barrier is higher than that in the middle region. The output power around the edge is also higher although it is more sensitive to the variation of the distance and positioning of the receiving coil. It has demonstrated that more than 11 W of power can be transferred across an aluminum plate with a thickness of 2 mm when the power pickup is placed at an edge of the plate along the current path.

This paper proposes a fast soft-starting method based on phase-shift control strategy for electric vehicle dynamic wireless charging (EV-DWC) system. Firstly, the AC impedance model of the EV-DWC system is established based on the double-sided LCC compensation network. The overshoot suppression method for the output current of the inverter is presented. Then the control method combining phase-shift and fuzzy PID of full-bridge inverter is adopted to achieve fast dynamic response of the system. Finally, an experimental prototype of the EV-DWC system with the output power of 15kw is built, which archives 5ms settling time of the output current of the inverter. The simulation and experimental results proves the feasibility and effectiveness of the proposed method.

In order to improve the power transmission capacity of wireless charging system, a dual-transmitter wireless power transfer (DT-WPT) system with a repeater is presented in this paper. On this basis, in order to avoid the cancellation of the power injected by dual transmitters into the repeater, a method to keep the synchronization of the output voltage phases of the dual primary inverters is proposed in this paper. The method is achieved by adding a current-phase detection module in the system and it does not need communication between the two transmitting units.

To make the pickup coil and its compensation network more compact and efficient, an integration method is proposed to make the traditional bulky compensation inductance integrated into the center of the pickup coil in a form of planar coil. The mutual inductances among the primary coil, the pickup coil and the integrated compensation coil are investigated with finite element analysis method. Then the equivalent circuit is analyzed and the power transfer characteristics of the system are further investigated. It has been shown that the influence of the integrated coil can be ignored and the system keeps the constant current characteristics of the primary coil current and the equivalent load current. Finally, a 10kW prototype system is built up. The experimental results have verified the validity of the proposed integration method. The system is tested to be able to output 9.3kW with an efficiency of 93%.

In order to increase the signal transmission speed and reduce the interference between power transmission and signal transmission in Capacitive Power Transfer (CPT) system, this paper proposes a high-speed signal transmission method based on partial power channel by using orthogonal frequency division multiplexing (OFDM) modulation and demodulation technology. The circuit model of the system is established, and mathematical expressions of power interference voltage and signal voltage are deduced. The parameter design method of the CPT system is presented to reduce the interference and improve the speed of signal transmission without reducing power transmission capacity. The system experimental setup achieves signal transmission speed of 80Mbps with little interference to power transmission, which verifies the validity of the proposed method.

In this paper, the power flow mechanism of a typical Capacitive Power Transfer (CPT) system is studied by analysing the electric field, magnetic field, and Poynting vector, to determine the power distribution as well as the average power flow to the load. It is found that the average power from the source flows along the wires on the transmitting side and passes the external areas of the coupling plates mainly along the channel between the two coupling pairs (instead of going through the air gaps in between), then converges along the wires before reaching the load. The average power calculated by integrating the real part of the Poynting vector across a defined power flow plane at the receiving end is consistent with CST (Computer Simulation Technology) simulation, circuit analysis, and practical measurements of the CPT system. Although the power density described by Poynting vector changes with the separation distance between the two coupling pairs, the total average power keeps approximately constant because the power flow area changes accordingly. Compared to the traditional lumped circuit analysis, the Poynting vector analysis shows the power distribution around the coupling plates in relation to their physical configuration. This research reveals the power flow mechanism and distribution in a CPT system from field point of view, which is useful to gain deeper understanding of the CPT system beyond the traditional circuit theory and would also be helpful to improve practical system design in the future.

An important feature of an inductive power transfer (IPT) system is its power transfer efficiency and capability can be significantly affected by the load and the magnetic coupling variations. Therefore, identifying the load and the mutual inductance is essential to improve the system performance. This paper proposes a load and mutual inductance identification method for IPT systems with parallel-compensated power pickups based only on the information detected from the primary side. The proposed method can be implemented for primary resonant circuits whether they are series or parallel tuned, or with a hybrid compensation, such as an LCL configuration. An identification model is established according to the steady-state characteristics of the system. Identification results are obtained based on mathematical derivations and analyses. The proposed identification method is realized without any extra communication or control, and both the simulation and experimental results have verified its feasibility.

A new parallel transmission method of power and data is proposed for peer-to-peer wireless power transfer (WPT) systems. Essentially, data are modulated and transferred via high-frequency electric field generated by the parasitic capacitances of the coupling coils and the metal shield plates, while power is transferred through relatively low-frequency magnetic field generated by the coupling coils. Coupling structure and operation principle are illustrated and analyzed. Besides, the signal to noisy ratio performance is studied and optimized. With the proposed method, a 40 W prototype is built and the data transmission rate reaches 230 kbps. Experimental results have verified that the proposed method is valid and has the advantages of good flexibility and large spatial position offset redundancy. Because the method does not do any modification on the main circuit of the WPT system, it also has advantages of low cost and easy to implement.