Design and analysis of a simultaneous wireless power and data transfer system across insulators for online monitoring devices on transmission lines

Abstract

To enhance the operational reliability of wireless power supply systems for transmission line monitoring devices and to facilitate bidirectional communication between the power transmitter and receiver, this study proposes a simultaneous wireless power and data transfer (SWPDT) scheme employing a multi-relay coil configuration. By exploiting the multi-resonant behavior inherent in high-order compensation topologies—specifically LCC and LCL structures—the proposed system realizes efficient co-transmission of energy and information. A comprehensive power transmission model, alongside an equivalent circuit model for data communication, is developed to capture the electromagnetic coupling and transmission dynamics within the multi-relay environment. The characteristics of both power and data channels are analytically examined, and the validity of the proposed methodology is substantiated through simulation studies. The results confirm that the system achieves robust power delivery while maintaining reliable data transmission, thereby offering a promising solution for deployment in high-voltage insulator string scenarios.

Keywords

wireless power transfer multi-relay coils simultaneous wireless power and data transfer high-voltage transmission lines

Introduction

With the advancement of smart grid technologies, online monitoring devices have been extensively deployed across high-voltage transmission lines and low-voltage towers, serving as vital components in maintaining the safety, stability, and efficiency of modern power systems.^1–3 Nevertheless, the dependability of their power supply has emerged as a critical constraint hindering their broader adoption within smart grid infrastructures. While conventional energy sources—such as photovoltaic modules and battery systems—have been introduced, they face inherent challenges when confronted with harsh environmental conditions, limited battery lifespan, and rising maintenance costs. Consequently, these traditional approaches are inadequate for meeting the rigorous reliability demands associated with smart grid monitoring applications.⁴

To address this challenge, the application of current transformer (CT) technology in high-voltage transmission lines has provided a novel approach to powering online monitoring devices.^5,6 By leveraging the continuous current flowing through transmission lines, stable power supply can be achieved.⁷ However, a critical technical challenge remains: how to efficiently transfer power wirelessly from the high-voltage side to the low-voltage side while maintaining insulation integrity. To overcome this issue, researchers have explored various wireless power transfer (WPT) technologies, including laser-based,⁸ ultrasonic,⁹ and microwave¹⁰ approaches, to break through the limitations of conventional power supply methods. However, these technologies often face challenges in engineering practice, such as high implementation complexity, excessive costs, and limited transmission efficiency.

In recent years, magnetically coupled resonant WPT technology has gained increasing attention as a promising solution to these challenges due to its advantages, including high transmission efficiency and strong adaptability. This technology effectively overcomes the limitations of conventional WPT methods in terms of transmission distance, efficiency, and stability, providing new possibilities for powering online monitoring devices.^11–13 However, several challenges persist in practical applications.

Since there is no direct physical connection between the energy transmission and reception sides, the system relies on wireless communication technologies to transmit control signals, monitor load conditions, and integrate sensor data. Traditional radio-frequency communication technologies often suffer from issues including large device size, high complexity, and susceptibility to electromagnetic interference (EMI) in high-voltage transmission line environments.^14–17 As a result, simultaneous wireless power and data transfer (SWPDT) has emerged as a research hotspot.^18–20

Conversely, maintaining a consistent and dependable power source for online monitoring equipment within the intricate and ever-changing conditions of power systems continues to present significant challenges. In the context of long-distance wireless energy transmission, the incorporation of multi-relay coil structures is recognized as a key enabler for enhancing transmission performance and coverage.^6,21 While multi-relay WPT systems can significantly enhance coil coupling strength and extend transmission distance, they also introduce new challenges, including an increased number of resonant components, high signal attenuation, and space constraints. These issues complicate the design of efficient and reliable energy-information parallel transmission methods suitable for multi-relay systems.

In response to the above challenges, this paper proposes a novel approach to achieve reliable cross-insulator energy and data transmission by exploiting the multi-resonant gain characteristics of high-order compensation topologies. The main contributions of this work are summarized as follows.

(1) An LCL compensation topology is employed in the relay coils to generate multiple resonant gain peaks, enabling the standardization of coil design and supporting both power and data transmission within a unified channel.

(2) A phase-locked loop (PLL)-based strategy is introduced to convert the high-frequency current of the power channel into a data carrier signal, eliminating the need for an additional carrier generator. This approach reduces hardware complexity and minimizes data transmission errors caused by high-frequency EMI.

(3) Two dedicated coil configurations are designed to minimize the physical volume of the relay coils and avoid magnetic cross-coupling within each relay unit, thereby enhancing transmission efficiency and communication reliability.

The remainder of this paper is organized as follows: Section 2 presents the system’s main components, Section 3 develops the power transmission circuit model, Section 4 establishes the equivalent circuit model for data transmission, Section 5 provides simulation validation of the proposed system, and Section 6 concludes the paper.

System overview

This paper analyzes the SWPDT in a multi-relay WPT system. Figure 1 presents the equivalent circuit diagram of the proposed SWPDT system. In the forward data transmission process, the data carrier is generated by a PLL circuit, eliminating the need for an additional information source. Due to the system’s symmetrical structure, reverse data transmission can also be achieved by incorporating an additional information source at the receiver side, following the same operating principle as forward transmission. Therefore, the reverse transmission process is not elaborated further in this paper.

In Figure 1, U_dc represents the system’s DC input voltage source, while S₁-S₄ are four MOSFETs forming a full-bridge inverter to generate the high-frequency AC signal for power transmission. On the transmitter side, the compensation inductor L_m, compensation capacitor C_m, and resonant capacitor C₁ form an LCC compensation topology, with L₁ serving as the transmitting coil. In the relay coupling mechanism, the coils L₂ and L₃, along with the resonant capacitor C₂, form an LCL compensation topology. On the receiver side, the receiving coil L_n, together with the resonant capacitor C_n, compensation capacitor C_s, and compensation inductor Ls, constitutes an LCC compensation topology. Additionally, D₁–D₄ represent four diodes, forming a full-bridge rectifier. C₀ serves as a filter capacitor, while the DC voltage regulation circuit is not explicitly shown in this paper. The load resistance is represented by R_L. In the theoretical analysis, the system’s power transmission characteristics are evaluated using an equivalent resistance R_eq and an equivalent AC input voltage U_in, where R_eq satisfies (1) and U_in satisfies (2).

R_{e q} = \frac{8}{π^{2}} R_{L}

(1)

U_{i n} = \frac{2 \sqrt{2}}{π} U_{d c}

(2)

Figure 2 presents the structural diagram of the relay coil arrangement within the proposed SWPDT system. Each relay unit comprises a circular coil (denoted as L_r12 and L_r21) and a double-D (DD) coil (represented as L_r11 and L_r22). Together with their corresponding resonant capacitors, the self-inductance of these coils forms an LCL-type resonant structure. The relay coils are configured in an alternating sequence. Specifically, if the DD coil is located on the left and the circular coil on the right in Relay Coil 1, then their positions are interchanged in Relay Coil 2, and this alternating pattern continues throughout the relay chain. This alternating arrangement ensures that electromagnetic energy is transmitted between coils of the same type during system operation, thereby improving energy transfer efficiency and reducing unwanted interference. The parameter d represents the spacing between adjacent relay coils.

The relay coil structure is specifically engineered to eliminate electromagnetic coupling between the DD coil and the circular coil within the same relay unit. As depicted in Figure 3, the magnetic field distribution between these two coil types demonstrates their mutual electromagnetic isolation.

As shown in Figure 3, the DD coil and the circular coil exhibit orthogonal magnetic field distributions, resulting in negligible mutual coupling between them. The magnetic field excited by the DD coil induces a minimal voltage in the circular coil. This physical configuration enables effective decoupling between the two coils, thereby preventing transmission failures of energy and information caused by cross-coupling effects.

In the proposed SWPDT system, all coils—including transmitting, relay, and receiving units—are wound with Litz wire to mitigate the effects of parasitic AC resistance. To streamline the theoretical analysis, losses arising from coil resistance, resonant capacitor dissipation, and switching device resistance are omitted. Furthermore, owing to the specific coil arrangement depicted in Figure 2, mutual inductance between non-adjacent coils is assumed to be negligible.

Power transmission channel analysis

When power transfer is taking place, the data transmission channel remains idle, resulting in the presence of only the high-frequency current at within the coil network. As a result, the circuit in Figure 1 can be further reduced to the simplified equivalent model illustrated in Figure 4.

Z_s is the equivalent impedance at the receiving end and expressed as:

Z_{s} = j ω_{p} L_{n} + \frac{R_{e q} + j ω_{p} L_{s}}{1 - ω_{p}^{2} L_{s} C_{s} + j ω_{p} C_{s} R_{e q}} + \frac{1}{j ω_{p} C_{n}}

(3)

As an illustrative case, a five-coil configuration—comprising three intermediate relay coils—is considered, with its corresponding equivalent circuit presented in Figure 5. For analytical simplification, it is assumed that all relay coils share the same self-inductance, and the mutual inductance between each pair of adjacent coils is uniform, that is,

L_{r 11} = L_{r 12} = L_{r 21} = L_{r 22} = L_{r 31} = L_{r 32} = L_{r}

(4)

M_{r 12} = M_{r 23} = M_{r}

(5)

Therefore, the resonant capacitors satisfy the following relationship:

C_{r 1} = C_{r 2} = C_{r 3} = C_{r}

(6)

In Figure 5, Z_{r_s} represents the reflected impedance of the receiving end on the relay coil, which can be expressed as:

Z_{r_s} = \frac{{(ω_{p} M_{s})}^{2}}{Z_{s}}

(7)

where M_s represents the mutual inductance between the receiving end and relay coil 3. Thus, in Figure 5, Z_rcan be expressed as:

Z_{r} = j ω_{p} L_{r} + \frac{(j ω_{p} L_{r} + σ_{1})}{j ω_{p} C_{r} (j ω_{p} L_{r} + \frac{1}{j ω_{p} C_{r}} + σ_{1})}

(8)

σ_{1} = \frac{M_{r}^{2} ω_{p}^{2}}{j ω_{p} L_{r} + \frac{(j ω_{p} L_{r} + σ_{2})}{j ω_{p} C_{r} (j ω_{p} L_{r} + \frac{1}{j ω_{p} C_{r}} + σ_{2})}}

(9)

σ_{2} = \frac{ω_{p}^{2} M_{r}^{2}}{j ω_{p} L_{r} + \frac{(Z_{r_s} + j ω_{p} L_{r})}{j ω_{p} C_{r} (Z_{r_s} + j ω_{p} L_{r} - \frac{1}{j ω_{p} C_{r}})}}

(10)

Further, the input impedance of the system, Z_in, can be derived as:

Z_{i n} = j ω_{p} L_{m} + \frac{(\frac{M_{i n}^{2} ω_{p}^{2}}{Z_{r}} + j ω_{p} L_{1} + \frac{1}{j ω_{p} C_{1}})}{j ω_{p} C_{m} (\frac{M^{2} ω_{p}^{2}}{Z_{r}} + j ω_{p} L_{1} + \frac{1}{j ω_{p} C_{1}} + \frac{1}{j ω_{p} C_{m}})}

(11)

where M_in represents the mutual inductance between the transmitting coil and the first relay coil.

To ensure that the proposed SWPDT system exhibits excellent power transmission characteristics, Table 1 lists the key parameter values used in the following analysis. For computational simplicity, numerical methods are employed to solve for the system’s transmitted power and efficiency, with the results presented in Figure 6.

Table 1.

Key parameters used in the analysis.

Symbol	Value	Symbol	Value
U _dc	24 V	C_m, C_s	26.39 nF
L_m, L_s	24 μH	C₁, C_n	24.36 nF
M _r	5 μH	L _r	50 μH (0.3 Ω)
L ₁	50 μH (0.3 Ω)	L _n	50 μH (0.3 Ω)
M _in	5 μH	C _r	12.67 nF

As shown in Figure 6(a), the output power of the proposed system exhibits a multi-peak response with respect to both frequency and load resistance. Under a fixed input voltage, several resonant peaks appear at different frequencies, with their positions slightly shifting depending on the load impedance. The simulation results indicate that there exists an optimal combination of operating frequency and equivalent load that maximizes output power.

Figure 6(b) presents the corresponding transmission efficiency under the same conditions. Similar to the output power, the efficiency also shows a multi-peak behavior with frequency, but it tends to decrease as the equivalent load resistance increases. Considering both power transfer and efficiency, the operating point of 275 kHz and a 10 Ω equivalent load is selected to achieve a balanced and efficient system performance.

Information transmission analysis

Compared to amplitude shift keying (ASK) and phase shift keying (PSK), frequency shift keying (FSK) enables SWPDT more effectively without affecting power transmission. As described in Section 2, the proposed system supports bidirectional information transmission, making it well-suited for signal processing applications in high-voltage transmission lines. To enhance system reliability in high-voltage electromagnetic environments and to minimize interference on switching devices and signal sources, a PLL is selected as the frequency conversion scheme. The PLL achieves high-precision frequency conversion by locking the phase of the input signal and dynamically adjusting the output frequency.

This study focuses on the forward transmission process as a representative case, given the analogous transmission mechanisms shared by the information and power channels; thus, detailed discussion of the reverse process is omitted. In the context of information transfer, the voltage gain of the system plays a critical role in determining the accuracy of signal demodulation and is therefore regarded as a key performance indicator of the information channel.

Based on the parameters listed in Table 1, Figure 7 illustrates the system voltage gain as a function of operating frequency under varying compensation inductances (L_m and L_s). As observed in Figure 7(a), the voltage gain curve exhibits four distinct peak points, indicating the presence of multiple resonant modes. One of these peaks can be selected as the information transmission frequency (f_d). Taking the simulation results in Figure 7(a) as an example, an information frequency of 295 kHz is selected to ensure a sufficient frequency offset from the power transmission frequency, thereby facilitating effective signal demodulation. At this frequency, the information channel demonstrates strong frequency stability against variations in the compensation inductance. Such a frequency selection helps maintain high information transmission performance even under system parameter deviations. Figure 7(b) illustrates the variation of the information channel output voltage U_{d_out} under different equivalent load impedances R_eq. As the load impedance increases, the output voltage rises rapidly and gradually saturates around 6.4 V when Req exceeds approximately 100 Ω. This indicates that the system exhibits higher output capability under high impedance loads and reduced sensitivity to load variations, demonstrating good load adaptability.

In summary, the operating principle of the PLL circuit is as follows: The input signal, a 275 kHz square wave, is generated by the inverter circuit in the power transmission channel. After being fed into the PLL system, the output signal’s phase and frequency are adjusted through a feedback mechanism, ultimately stabilizing at 295 kHz as the information carrier frequency.

To ensure system stability, key PLL parameters, such as loop bandwidth, damping factor, and phase comparator, are carefully tuned to minimize steady-state errors and enhance locking performance. The voltage-controlled oscillator (VCO) generates the required output frequency based on the PLL’s control voltage.

A switching transistor is used to modulate the data signal, toggling between ON and OFF states to represent logic “0” and “1.” On the receiver side, the transmitted information undergoes demodulation through a band-pass filter (BPF), envelope detector (ED), low-pass filter (LPF), and comparator.

Figure 8 presents the information channel transmission results of the proposed system. Channel 1 represents the original data. Channel 2 shows the information voltage waveform across the receiving resistor. Channel 3 displays the voltage waveform after the BPF. Channel 4 presents the waveform after the ED. As observed in Figure 8, the system successfully achieves an information transmission rate of 10 kbps.

The simulation results demonstrate that the PLL effectively converts the 275 kHz frequency to 295 kHz with high precision and stability. This frequency conversion method is not only theoretically feasible but also provides a reliable solution for practical applications, making it particularly suitable for systems requiring high-frequency accuracy.

The proposed method demonstrates the significant advantages of using a phase-locked loop for frequency conversion, showing great application potential in fields such as power electronics and signal processing. Unlike conventional approaches, the PLL-based frequency conversion eliminates the need for an additional information carrier source, thereby avoiding potential interference under high-voltage and strong electric field environments. This enhances information transmission accuracy and ensures stable system operation in high-voltage transmission line applications.

Figure 9 illustrates the design flow of the proposed system. First, the equivalent topology model of the multi-relay wireless power transfer system is established. Then, the resonant frequency of the power channel is selected, followed by the calculation of output power and transmission efficiency. If the results do not meet the specified power and efficiency requirements, the frequency parameters are adjusted iteratively for optimization. Once the power channel parameters are determined, the design process proceeds to the information channel. The operating frequency of the information channel is selected, and the corresponding transmission gain is calculated. If the gain does not meet the demodulation requirements, the frequency is re-adjusted until the performance criteria are satisfied. This process ensures the coordinated design of both power and information transmission paths within the system.

System simulation

Building upon the preceding theoretical analysis, this section presents simulation studies for both the power and information transmission channels. The simulations are conducted by modeling the respective resonant coupling circuits for energy and data transfer, and incorporating an information demodulation circuit to verify the analytical predictions. To improve the relevance and applicability of the results, a multi-relay wireless power transfer system comprising three relay coils is utilized as the simulation model.

In this section, the parameters are listed in Table 1, with the equivalent resistance R_eq set to 10 Ω. Figure 10 presents the information transmission results of the proposed system: Channel 1 represents the original data. Channel 2 shows the waveform after envelope detection. Channel 3 displays the waveform after low-pass filtering. Channel 4 illustrates the demodulated data.

As observed from Channel 1 and Channel 4, the proposed system successfully demodulates the received signal with high accuracy, recovering the original data effectively.

Figure 11 presents the waveform characteristics of the power transmission channel, where Channel 1 displays the inverter output voltage, Channel 2 shows the corresponding output current, Channel 3 represents the voltage across the load, and Channel 4 illustrates the load current. As shown in Figure 11, under the parameter conditions specified in Table 1, the proposed system achieves a transmitted power of 17.5 W with an overall efficiency of 24.3%.

Conclusion

Wireless power supply systems for online monitoring devices deployed on high-voltage transmission lines are required to exhibit exceptional reliability. In this work, a high-order compensation topology combining LCC and LCL configurations was employed to harness the advantages of multiple resonant points. By integrating phase-locked loop (PLL) technology, the system enables the concurrent injection of power and information into a shared coupling structure, thus realizing simultaneous wireless energy and data transmission. Simulation outcomes confirm the system’s ability to ensure stable power delivery alongside effective data communication. Furthermore, the use of two distinct coil types to construct the LCL resonant cavity supports standardized coil design, which promotes system miniaturization, improved integration, and enhanced reliability. Nevertheless, the presence of multiple compensation stages within the multi-relay WPT architecture introduces complexity to the information transmission path and leads to significant signal attenuation. As a result, the current system exhibits limited data transmission rates. To address this limitation and broaden its applicability to high-voltage transmission line monitoring scenarios, further refinement of system parameters is necessary to improve data throughput.

Footnotes

Acknowledgements

The authors acknowledge the Science and Technology Project of China Southern Power Grid Co., Ltd.: Research on energy harvesting from high-voltage transmission lines, wireless power transfer system design, and key technologies for modularization (GDKJXM20231222).

ORCID iD

Jianlong Liang

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Science and Technology Project of China Southern Power Grid Co., Ltd. (GDKJXM20231222).

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

References

Beibei

Qiqi

Jiang

, et al. A deep sensing system for monitoring the health status of transmission line equipment based on self-powered sensors. IEEE Sens J 2023; 23(18): 20834–20844.

Zhe-Wen

Xu-Ping

Ning-Mu

, et al. Phi-OTDR based on - line monitoring of overhead power transmission line. J Lightwave Technol 2021; 39(15): 5163–5169.

Haocheng

Song

Yang

, et al. Advances in nanogenerators for electrical power system state sensing and monitoring. Nano Energy 2023; 115: 108738.

Zhou

Zilin

Chi-Kwan

, et al. A weather-independent and renewable power supply with wireless power transfer feature for powering online monitoring systems in smart grid. IEEE Trans Ind Electron 2023; 70(6): 6414–6424.

Niang

, et al. Wireless power transfer using domino-resonator for 110-kV power grid online monitoring equipment. IEEE Trans Power Electron 2020; 35(11): 11380–11390.

Cui

Lin

Dai

, et al. The design of a long-distance high-efficiency WPT for online monitoring equipment based on a new relay structure. Electr Eng 2022; 104(5): 3007–3014.

Wang

Chenjin

Cun

, et al. Start-up and saturation optimization of high-power energy harvester with compound topologies overhead AC transmission line. IEEE J Emerg Sel Top Power Electron 2020; 8(4): 3609–3617.

Zhang

Wen

Qingwen

, et al. Distributed laser charging: a wireless power transfer approach. IEEE Internet Things J 2018; 5(5): 3853–3864.

Chen

, et al. Considering losses to enhance circuit model accuracy of ultrasonic wireless power transfer system. IEEE Trans Ind Electron 2020; 67(10): 8788–8798.

10.

Zhu

Jin

, et al. Long-range wireless microwave power transmission: a review of recent progress. IEEE J Emerg Sel Top Power Electron 2021; 9(4): 4932–4946.

11.

Fang

Jialong

Hay

PBM

, et al. Quasi-static modeling and optimization of two-layer PCB resonators in wireless power transfer systems for 110-kV power grid online monitoring equipment. IEEE Trans Ind Electron 2022; 69(2): 1400–1410.

12.

Yan

Xie

Yong

, et al. A monitoring equipment charging system for HVTL based on domino-resonator WPT with constant current or constant voltage output. IEEE Trans Power Electron 2022; 37(3): 3668–3680.

13.

Hou

, et al. A multirelay wireless power transfer system with double-sided LCC compensation network for online monitoring equipment. IEEE J Emerg Sel Top Power Electron 2023; 11(1): 1262–1271.

14.

Deng

Tang

Sun

, et al. EMI suppression method for LCC-S MC-WPT systems by parameter optimization. IEEE Trans Power Electron 2024; 39(9): 11134–11147.

15.

Yousu

Sun

Liu

, et al. Simultaneous wireless power and data transfer: a comprehensive review. IEEE Trans Power Electron 2022; 37(3): 3650–3667.

16.

Junmei

Lou

Xie

, et al. Mitigating cross-technology interference through fast signal identification. IEEE Trans Veh Technol 2023; 72(2): 2521–2534.

17.

Haque

Ahmed

Kumar

. Comprehensive performance analysis of zigbee communication: an experimental approach with XBee S2C module. Sensors-Basel 2022; 22(9): 3245.

18.

Inmaculada Casaucao

Trivino

Zhengyu

. Simultaneous wireless power and data transfer for electric vehicle charging: a review. IEEE Transactions on Transportation Electrification 2024; 10(2): 4542–4570.

19.

Aydin

Javan-Khoshkholgh Amir . Simultaneous wireless power and data transfer : methods to design robust medical implants for gastrointestinal tract. IEEE J Electromagn RF Microw Med Biol 2022; 6(1): 3–15.

20.

Karimi

Alexandre

Catherine

. Wireless power and data transmission for implanted devices via inductive links : a systematic review. IEEE Sens J 2021; 21(6): 7145–7161.

21.

Hou

Wang

, et al. A dual-frequency dual-load multirelay magnetic coupling wireless power transfer system using shared power channel. IEEE Trans Power Electron 2022; 37(12): 15717–15727.