Capacitive Power Transfer System Research Articles

Misalignment tolerance wireless power transfer system combining inductive and capacitive coupling

To resonate with the capacitive power transfer (CPT) system, inductors are usually needed, while additional capacitors are required for the inductive power transfer (IPT) system. To take advantage of the inductance of the IPT system, this study proposes a misalignment tolerance wireless power transfer system that employs the IPT coupler to compensate part of CPT's capacitance for railway applications. In the proposed system, two power transfer paths are formed by the IPT and CPT couplers. Additionally, the system merits a good anti-misalignment ability by carefully designing the parameters of the proposed system. In a well-alignment case, only the CPT coupler is utilised to transfer power. While in misalignment case, the IPT coupler is activated to transfer power to improve the misalignment tolerance. Besides, the transfer capability of the combined system can be improved when the misalignment happens. The system coupler, connection method and output power characteristics are presented in detail. Then, the general design procedure is provided with an example system at 1 kW. Experimental results show that the maximum variation of the output is 5.6% when misalignment is up to 250 mm (50%). While the power variation of the system involving single CPT can be as large as 52%.

Three-Phase Resonant Capacitive Power Transfer for Rotary Applications

This article proposes a three-phase resonant capacitive power transfer (RCPT) system for rotating applications requiring loose coupling. Existing plate designs for rotational CPT, such as the stacked four-plate and concentric structures, are found to exhibit imbalances that give rise to ground return or common-mode currents. These are particularly harmful at the high switching frequencies employed by compact and low-cost RCPT systems. Inherently balanced multiphase electrode designs are proposed to address this at the expense of permitting some coupling variation over rotation. Simulations show that three or more phases are required to avoid coupling nulls. While four or more phases may be preferred for applications requiring very stable coupling, three-phase is found to be the most practical solution in the context of cost, complexity, and inductor size. The proposed electrode structure offers high balance, a competitive average coupling coefficient, and a low per-plate resonating inductance. A highly integrated 27.12-MHz RCPT system was designed and implemented to validate these findings while accounting for practical limitations, such as manufacturability and cost. Using primarily commercial-off-the-shelf components, the system transferred 50 W at 25 mm under full rotation with an end-to-end efficiency of 73%.

Capacitive Wireless Power Transfer with Multiple Transmitters: Efficiency Optimization

Wireless power transfer with multiple transmitters can have several advantages, including more robustness against misalignment and extending the mobility and range of the receiver(s). In this work, the efficiency maximization problem is analytically solved for a capacitive wireless power transfer system with multiple coupled transmitters and a single receiver. It is found that the system efficiency can be increased by adding more transmitters. Moreover, it is proven that the cross-coupling between the transmitters can be eliminated by adding shunt susceptances at the input ports. Optimal values for the input currents and receiver load are determined to achieve maximum efficiency. As well the optimal load, the optimal input currents and the maximum efficiency are independent on the cross-coupling. By impedance-matching the internal conductances of the generators, the maximum-efficiency solution also becomes the one that provides the maximum output power. Finally, by expressing each transmitter–receiver link with its kQ-product, the maximum system efficiency can be calculated. The analytical results are verified by circuital simulation.

Hybrid control of capacitive power transfer system for coupling capacitance variation

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.

Analysis and Design Capacitive Power Transfer (CPT) System for Low Application Using Class-E LCCL Inverter by Investigate Distance between Plates Capacitive.

This study presents the analysis and design of a Capacitive Power Transfer (CPT) system for low power application using a Class-E LCCL inverter based on varying the distance between capacitance plates. The Class-E LCCL inverter can produce a high-frequency alternate current and reduce the size of the capacitance plate to minimise power losses during energy transfer besides yielding low switching losses. In specific, the performance of the LCCL CPT system at 1 MHz operating frequency and 24 V DC supply voltage was analysed via simulation and experimental works. Finally, a prototype of the CPT system was successfully designed, producing 10 W output power through a capacitive plate size of 0.0327 m2 and a 0.1 cm air gap at 96.68% efficiency. Based on the performance of the LCCL CPT System design, an efficiency analysis of the LCCL CPT System was performed; the capacitance plate distance was varied from 1 cm to 20 cm and produced a change in total impedance calculation from 57.69+j198.42 Ohm to −2.05j Ohm. Meanwhile, efficiency decreased from 96.68% to 1.25% but power was still transmitted in that range. These findings could be beneficial for hazardous electrical environments, portable applications, consumer electronics, and medical implants.

Multiobjective Parameter Optimization of a Four-Plate Capacitive Power Transfer System

For a four-plate capacitive power transfer (CPT) system, the existing coupling and compensation design methods can only provide an approximate local parameter optimization solution, instead of a globally optimized solution. This article proposes an accurate calculation method for cross-coupling capacitance and a multiobjective optimization algorithm combining nondominated sorting and Kent map for an SS-type CPT system. Mathematical models of the cross-coupling capacitances and port capacitances are established based on a two-port capacitive coupling model of the four plates. Besides, the constraints considering the reasonable region of the parameter values are given. Taking the output power, efficiency, and total harmonic distortion (THD) as objective functions, with the power transfer distance, operating frequency, load resistance, and input voltage as decision variables, the Pareto-optimal fronts are obtained by the proposed algorithm. A group of global optimal parameters is chosen from the solution sets, and a simulation model and a prototype of the CPT system are constructed. The efficiency of 87.1% at 252.3-W output power has been achieved. The simulation and experimental results verified the feasibility and effectiveness of the proposed calculating method for the cross-coupling capacitance and optimization method.

Analysis and Design of Inductive and Capacitive Hybrid Wireless Power Transfer System for Railway Application

Inductive power transfer (IPT) and capacitive power transfer (CPT) are mainly two effective ways to achieve wireless power transfer (WPT). IPT system needs capacitor to compensate the system, while the CPT system requires inductor to tune the system. Therefore, IPT coupler can be used to compensate the CPT coupler and vice versa. In this article, an inductive and capacitive hybrid wireless power transfer (HWPT) system is proposed to improve the system coupler antimisalignment ability. The couplers of IPT and CPT are employed together to compensate each other and transfer power together. Superposition theory is used to analyze the system working principle in detail. With the analysis results, a scaled-down system is built to validate the performance of the proposed approach. Experimental results show that the proposed HWPT system can achieve 653 W output power with 87.7% dc–dc efficiency at the well-aligned condition, and the maximum variation of the output power is 8.3% with the coupler misalignment from 0 to 270 mm (halfwidth of the coupler), which agree well with the analysis results.

Efficiency comparison of capacitive wireless power transfer for different materials

<p>This paper describes the application of several types of materials to act as capacitive plates in a Capacitive Power Transfer (CPT) system. In general, the efficiency of CPT system is greatly influenced by the coupling capacitance which is varied by distances and permittivity values. Thus this paper intended to compare the performance of CPT system in terms of the output efficiency for several types of capacitive plates. To be specific, copper plate, zinc, and aluminium are used in this work to act as coupling plates to the CPT system. The CPT system in this work applied class E inverter as it has lowest switching losses among its competitors, i.e. class D and class F. The work is validated through experimental setup of CPT system in which copper material provides the best efficiency of the system.</p>

A Sleeve-Type Capacitive Power Transfer System With Different Coupling Arrangements for Rotary Application

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.

Optimum Receiver-Side Tuning Capacitance for Capacitive Wireless Power Transfer

This paper reveals the optimum capacitance value of a receiver-side inductor-capacitor (LC) network to achieve the highest efficiency in a capacitive power-transfer system. These findings break the usual convention of a capacitance value having to be chosen such that complete LC resonance happens at the operating frequency. Rather, our findings in this paper indicate that the capacitance value should be smaller than the value that forms the exact LC resonance. These analytical derivations showed that as the ratio of inductor impedance divided by plate impedance increased, the optimum Rx capacitance decreased. This optimum capacitance maximized the TX-to-RX transfer efficiency of a given set of system conditions, such as matching inductors and coupling plates.

The Development of Capacitive Power Transfer for Biomedical Implantable Devices

Wireless power transfer using electric and magnetic near-fields has been used in many applications widely, and biomedical implants being one of them. The most commonly used method for powering power wirelessly to biomedical implantable device is using inductive coupling between two mutually-coupled coils. In this paper, a consider new method will be proposed in transferring power for biomedical device which is based on capacitive coupling and known as capacitive power transfer (CPT) system. The main reasons of using this method are the low electromagnetic interference (EMI), can reduce power losses and the abilities to transfer power across metal barriers compared to inductive power transfer. To be specific, in this work, we have designed Class E circuit as an inverter to convert the 12VDC to AC with 1 MHz frequency. The prototype of the capacitive power transfer for implantable application has also been successfully developed with capacitive plate dimensions of 3cmx3cm width per length for receiver plate and 4cmx4cm for transmitter plate, respectively. 5mm thickness of beef separation between the plates is used in this paper. The design specification of this work is accordance to stimulator for peripheral nerve implantable device which only needs 100 mW of power to operate in the CPT system. Overall, the developed CPT system for the biomedical device is able to deliver 76mWatt with 41.43% efficiency. To enhance the efficiency, the impedance matching circuit has been proposed in this work and the prototype is now able to deliver 140mWatt power to the DC load, achieving zero voltage switching (ZVS) waveform and efficiency of 77.5%.

A family of compensation topologies for capacitive power transfer converters for wireless electric vehicle charger

A large scale of electric vehicles can ideally maintain the stability of renewable power supply by acting as storage buffers for alleviating the intermittence in the integration of renewable energy sources for constructing a low-carbon energy system. However, the inconvenient conductive charging becomes a barrier in the popularization of electric vehicles. Wireless power transfer technology is in the spotlight because of the flexibility and convenience in powering electric vehicles. Recently, the Capacitive Power Transfer has received extensive attention due to simple coupler structure, rotatable coupler, and negligible heating of the metal foreign object. In the capacitive-based wireless charging system, the higher-order compensation topology is essential to enhance power transfer capability limited by the small coupling capacitance. However, with the increase of the resonant elements, the form of the resonant network becomes diverse. Currently, the researches focus on the characteristics of specific symmetrical compensation topologies. This paper presents a family of compensation topologies for the Capacitive Power Transfer system to achieve constant-voltage or constant-current output. A design procedure is summarized to construct the resonant networks, so as to design the compensation parameters. Considering the coupling capacitor variations caused by parking position deviation, a parameter tuning method is proposed to realize primary zero-voltage switching by adjusting the parameter of the double-sided inductor-capacitor-inductor-capacitor compensation topology. Experiments show that the prototype achieves constant-current output and zero-voltage switching when the coupling capacitance varies. The system efficiency reaches 93.57% at 1.5 kW input power with the input and output voltage around 250 V.

A New Design Approach to Mitigating the Effect of Parasitics in Capacitive Wireless Power Transfer Systems for Electric Vehicle Charging

This paper introduces a new design approach to mitigate the effect of parasitic capacitances and achieve high performance in large air-gap capacitive wireless power transfer (WPT) systems for electric vehicle (EV) charging. In a capacitive WPT system for EVs, the vehicle chassis and roadway introduce multiple parasitic capacitances that can overwhelm the coupling capacitance and severely degrade power transfer and efficiency. The proposed approach addresses this challenge by employing split-inductor matching networks, which allow the complex network of parasitic capacitances to be simplified into an equivalent four-capacitance model. The shunt capacitances of this model are directly utilized as the matching network capacitors, hence, absorbing the parasitic capacitances and eliminating the need for discrete high-voltage capacitors. A systematic procedure is developed to accurately measure the equivalent capacitances of the model, enabling the system’s performance to be reliably predicted. The proposed approach is used to design two 6.78–MHz 12-cm air-gap prototype capacitive WPT systems with capacitor-free matching networks. The first system transfers up to 590 W using 150-cm2 square coupling plates and achieves an efficiency of 88.4%. The second prototype system transfers up to 1217 W using 118-cm2 circular coupling plates, achieving a power transfer density of 51.6 kW/m2. The measured output power profiles of the two systems match well with their predicted counterparts, validating the proposed design approach.

Unified Load-Independent ZPA Analysis and Design in CC and CV Modes of Higher Order Resonant Circuits for WPT Systems

This article proposes a general unified methodology for arbitrary higher order resonant circuits. With the proposed methodology, the equivalent circuits and the general resonant methods of the higher order resonant circuit are presented to realize the load-independent constant current (CC) and constant voltage (CV) outputs at two different load-independent zero phase angle (ZPA) frequencies. In addition, the corresponding regularized mathematical models of the constant output current and voltage and the purely resistive input impedances in CC and CV output modes are derived. All compensation topologies in both inductive and capacitive power transfer (CPT) systems have the essence of higher order resonant circuits. It means that the proposed methodology can be applied to investigate the load-independent output and input characteristics of any inductive power transfer (IPT) and CPT topologies. A 3.3-kW LCC -series-compensated IPT system for electric vehicles (EVs) was designed and manufactured to verify the theoretical analysis. The system operating frequencies in both the CC output with ZPA and the CV output with ZPA are in compliance with the SAE J2954 standard.

Optimization of Capacitive Wireless Power Transfer System for Maximum Efficiency

Optimal inductance and capacitance values of a receiver (Rx) LC matching network are proposed in order to maximize the efficiency of capacitive wireless power transfer (CWPT). To maximize the overall Tx-to-load efficiency, a general polynomial equation is proposed that gives an optimum Rx inductance and capacitance value under the given constraints of inductor losses, load impedance, and coupling capacitance. It is found that the efficiency is maximized when the Rx input resistance is approximately equal to the impedance of the coupling capacitance. It is also shown that Tx inductance and capacitance values should be chosen based on the trade-off between efficiency and Tx amplifier operation. The proposed method is applied to wireless charging of an Unmanned Aerial Vehicle (UAV) because the small Rx plate of CWPT can easily be mounted on a UAV. The fabricated system delivers 45 W with overall efficiency of 78.2% across wide lateral misalignments even with a small Rx plate at 6.78 MHz.

Insulated Coupler Structure Design for the Long-Distance Freshwater Capacitive Power Transfer

This article proposes a long-distance capacitive power transfer (CPT) system in the freshwater environment. The theoretical model of the capacitive coupler is derived in the freshwater scenario, considering the impact of the insulation. The finite element analysis by high-frequency structure simulator (HFSS) is used to simulate the coupler structure. Compared with the system in air, the coupling capacitance in a freshwater system is less sensitive to the distance variation. The transfer distance is therefore significantly extended in the freshwater environment. Then, a prototype is implemented to validate the analysis, in which the plate length is 200 mm. In the freshwater testing, experiments show that the system achieves 219.6 W output power across a distance of 500 mm with the efficiency of 60.17%. When the misalignment is 100 mm, the variation of output power is within 3.3%, and the efficiency is still maintained at 54.9%. When the transfer distance is 350 mm, the system efficiency is 69.0%. Therefore, the experimental results validate that the proposed long-distance CPT system is achieved in the freshwater environment.

An Improved Design Methodology of the Double-Sided LC-Compensated CPT System Considering the Inductance Detuning

This paper proposes an improved design methodology of the double-sided LC -compensated capacitive power transfer (CPT) system considering the inductance detuning. Compared to the perfect-resonant scenario, this paper shows that the inductance detuning has the benefit to achieve the soft-switching condition for the CPT system, and the output current and internal voltage stresses can also be maintained within the desired range. The contributions of this paper are summarized in three parts. First, it analyzes the impacts of the inductance variations on the system frequency property, including the input current, output current, and internal capacitor voltage stresses. Second, it proposes three principles to detune the inductances as the methodology to design a CPT system. Third, a prototype is implemented, which achieves 368.5 W power transfer across a 400 mm × 400 mm × 4 mm glass layer with 91.8% dc–dc efficiency. Experimental results validate that the proposed design principles are satisfied, showing that the output current is within the desired range, the input soft-switching condition is achieved, and the internal voltage stresses are within the safety limit. Moreover, the efficiency and frequency properties are also validated by the experimental results, showing a wide power range of the high-efficiency operation (higher than 90%) and a wide frequency bandwidth of the soft-switching operation (from 0.96 to 1.12 MHz).

Single-bit modulator for wireless power transfer system

<p>This paper proposes a single-bit ADC system based Proportional and Integral (PI) controller to maintain a desired level of power transfer efficiency in Capacitive Power Transfer (CPT) systems. In this paper, a simple single-bit ADC system i.e., Single-Bit Modulator (SBM) is considered as an alternative to the commonly used multi-bit ADC systems. Unique features of employing SBM are 1) its ability to convert analog signals into single-bit signals and 2) its easy integrability in digital chips with linear variable differential transformers (LVDTs) such as FPGAs. A SBM based PI (SBM-PI) controller is designed to judicially interface with the single-bit output of SBM. The proposed (SBM-PI) controller guarantees less hardware resources, latency and regulates the output voltage to provide the desired power transfer efficiency. The behavior of SBM-PI controller is compared to that of a conventional multi-bit controller, with the results of both controllers being identical. The effectiveness of the proposed controller with SBM is further demonstrated using the experimental prototype of CPT by implementing a SBM-PI controller using $16$ MHz ATmega8 microcontroller. The experimental results from a laboratory prototype illustrate that SBM-PI controller successfully regulates the output voltage of CPT to control the power flow.</p>

Parameter Design Method With Constant Output Voltage Characteristic for Bilateral LC-Compensated CPT System

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.

Four-plate capacitive power transfer system with different grounding connections

In this paper, a four-plate capacitive power transfer (CPT) system with different grounding connections is studied by taking the mutual coupling between the plates and the ground into consideration. A 4 * 4 mutual capacitance matrix model including the ground capacitances is established to accurately describe the coupling relationship between the four plates and the ground. Based on the proposed model, eight grounding connections are identified for effective power transfer among fifteen theoretically possible combinations. The electric field distribution and system output performance of a typical CPT system with two pairs of parallel plates are simulated for different grounding connections. A practical coupling setup consisting of two pairs of vertically placed parallel 300 mm * 300 mm square aluminum plates is built to verify the modeling and analysis. Both simulation and experimental results show the measured output voltage under different grounding connections are in good agreement with the theoretical results. It has been found that the ground has minimal impact on power transfer when one pair of the coupled transmitter and receiver plates are grounded, and the highest voltage gain and the lowest leakage electric field are also achieved under this grounding connection. However, considering the practicality, grounding one transmitter plate is the most suitable connection.