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Resonant inductive power transfer (RIPT) is an advanced wireless power transfer (WPT) technology that is emerging as a safe and practical solution for charging electric vehicles (EVs). Although dynamic wireless charging systems (DWCS) reduce the need for large batteries compared to static charging, their initial investment is high. This study presents an innovative approach to DWCS based on a multi-bar half-bridge inverter configuration. Each bar of the inverter independently powers a transmitting coil, which effectively reduces the overall system cost. The approach introduces variable frequency control technology (VFCT) into the half-bridge DWCS and utilizes SS and LCC-S compensation. The VFCT of this technology on DWCS is analyzed. In addition, the effect of square and rectangular coils on the proposed approach is investigated, and the effect of coil gap on the received power is analyzed. By studying a half-bridge multi-terminal DWCS and comprehensively evaluating the effects of gap and coil size, this study provides valuable information for optimizing RIPT technology for efficient and cost-effective EV charging.
Among the wireless power transfer (WPT) methods, resonant inductive power transfer (RIPT) uses magnetic coupling to transfer power across an air gap and is widely used in manufacturing, automation, biomedicine, material handling, and mobile and electric vehicle (EV) charging. 1,2 This EV charging method offers a practical, safe, weather-resistant, and vandal-proof solution that blends seamlessly into the outdoor environment. It enables safer wireless charging and supports a wide range of power needs, from high-power buses to low-power e-bikes. 3,4 A major challenge facing EVs is range, which traditionally requires bulky, expensive, and slow-charging batteries. Dynamic wireless power transfer (DWPT) addresses this issue by allowing EVs to charge while driving, reducing battery size and eliminating range limitations. 5 Dynamic Wireless Charging Systems (DWCS) charge EVs using magnetically coupled couplings embedded in designated road sections. Key considerations in developing this technology include reliability, complexity, and cost. The best solution is to create a low-cost, modular RIPT system that is easy to install and maintain. Future developments will focus on developing efficient and cost-effective large-scale RIPT roads for mobile EV charging6,7. DEWC systems are mainly divided into two types of transmitters: thin and segmented. Thin transmitters are cheaper due to the large area of a single coil and simpler power electronics, but suffer from high electromagnetic interference, exposure to external factors, high power losses, and low reliability. Segmented transmitters use multiple transmitters along a route, which solves some of the problems, but creates difficulties in achieving uniform power transfer and requires more power electronics, making the system more expensive8,9.
Different authors have proposed different approaches to the coil size and its effect on the speed. In a 2 kW charging system with a transmission range of 20 cm, the size of the receiving coil was 1 square meter. Zhang et al. investigated the effect of EV speed on the optimal length and found that the speed did not affect the optimal length when each charging pad charged one vehicle. The optimal size was determined to be 3 meters, determined by the average coupling coefficient criterion10. Buyya et al. used the calculations of the transmitted energy to calculate the primary coil length and the distance between the primary coils to ensure the float charge mode of EVs11. The length of the transmitter affects the overall reliability of the system12.
Proposed power electronics architecture for dynamic charging system: (a) dynamic charging system model, (b) multi-stage converter with SS, and (c) multi-stage converter with LCC-S compensation.
For systems with a receive coil length of less than 1 m², power transfer of 2 kW¹3 and 26.7 kW¹4 was achieved through a 20 cm air gap. The use of LCC-S compensation in both the transmitter and receiver reduces the input current. This paper presents a strategy for selecting the transmitter length in long-track DEWC systems that takes into account speed limitations and energy losses. Although a segmented transmitter solves some of the problems associated with increasing its length, it can make it difficult to achieve uniform transmit power distribution and lead to increased cost due to the increased number of power electronics components.
To meet the needs of low-cost dynamic RIPT systems, various power electronics topologies have been proposed. The system should maintain high efficiency under varying loads and integrate one independent full-bridge converter into the transmitter. For this purpose, a multi-bridge converter is proposed, in which the switching bridge arm uses two bridge arms as a full bridge. 16. The disadvantage of the multi-bridge converter is that the effect of one bridge arm of two transmitters in this scheme is defective. One bridge arm of the multi-bridge converter is used as a half-bridge converter to drive a separate transmitter coil, which further reduces the cost of the system. 17, 18. In the literature 19, a coupler array controlled by a push-pull converter is proposed. Such an array is difficult to control the coupling coefficient, and it does not greatly limit the power transfer capabilities. A similar converter system proposes a dynamic multi-directional half-bridge conversion system for low-power applications, but with lower efficiency. Figure 1 shows a model of the dynamic charging system.
The proposed DWPT system topology takes into account the effects of series-series (SS) and LCC-S resonant compensation topologies20,21. A significant difference can be observed when the system is operated near the zero phase angle (ZPA) frequency. At this frequency, SS compensation behaves as a constant current source on the secondary side, while LCC-S compensation behaves as a constant voltage source on the secondary side22,23. This difference in system behavior is due to the different resonant compensation topologies on the primary side. SS compensation is generally poorly suited for DWCS using standard control methods, primarily due to the significant increase in primary current with mismatch. A key limitation of the SS topology is the lack of inherent current regulation on the primary side, making it very sensitive to mutual inductance changes caused by vehicle motion or lateral mismatch. As a result, even a small deviation from perfect alignment can result in a significant increase in primary current, requiring the use of higher-rated components or the implementation of complex control strategies to limit it. In contrast, the LCC-S compensating topology naturally regulates primary current through its impedance-shaping circuit. This feature provides more stable and predictable current behavior under various misalignment conditions, making the LCC-S a more suitable and reliable choice for dynamic wireless charging environments while reducing the reliance on bulky hardware and complex control mechanisms.
This study compares and analyzes the different system characteristics between SS compensation and LCC-S compensation under the same system conditions for the proposed half-bridge DWCS with VFCT24. By controlling the voltage gain with variable frequency, this method makes SS compensation suitable for dynamic charging systems. In dynamic charging of EVs, soft switching losses are inevitable, which leads to continuously changing switching losses. For DEWCs, power can be supplied directly to the motor and supplied from the battery only when the road traction is insufficient25. To prevent battery damage, it is necessary to control the changes in bus voltage caused by load switching or magnetic coupling. Maintaining the bus voltage at the rated level of the battery is necessary for effective voltage control26. Various methods have been proposed for this purpose.
The output voltage and transmission efficiency can be optimized by using DC/DC converters on the secondary side, but they operate under harsh switching conditions, which reduces the system efficiency27. Impedance matching techniques can also improve the efficiency. Alternatively, controlling the primary current using asymmetric pulse-width modulation (APWM) can regulate the voltage, but it has start-up problems28. APWM is simpler to design and implement, but it requires a wide input control signal range and cannot guarantee zero-voltage switching (ZVS) under large load changes29. Recently, dynamic regulators have been proposed to overcome the limitations of fixed-frequency WPT systems. These regulators allow the primary source to operate at a constant frequency while minimizing losses by continuously adjusting the capacitance in the resonant circuit30. However, this approach increases the complexity. To address these problems, a variable-frequency WPT system with LCL-S compensation31 has been proposed. This technology aims to improve the throughput and overall efficiency of the system by controlling both the frequency and duty cycle. By dynamically adjusting these parameters, the system can operate efficiently over a wide range and achieve zero voltage switching (ZVS) under large load variations32. This variable frequency switching approach has been successfully applied to both static and dynamic charging systems using a bridge converter, demonstrating its effectiveness in improving the performance of wireless power transfer (WPT) technology.
This paper presents a 1 kW power flow control system based on a multi-section converter and discusses the application of VFCT technology. The simulation results were verified using MATLAB and ANSYS Maxwell. In addition, a laboratory prototype was built to demonstrate the practical feasibility. This paper presents a cost-effective power flow control method using a multi-section high-frequency converter configuration to reduce power consumption, reduce the number of stimulation mechanisms, and ensure sufficient battery charging through a sensor network.
A new DWPT system is proposed using VFCT, which is a multi-branch half-bridge configuration in which each branch of the inverter independently drives the transmitting coil, thereby improving the efficiency and reducing the cost of the system.
The impact of SS and LCC-S compensation on the proposed DWCS is evaluated, and the impact of transmitter length and segment gap on the output power is analyzed.
The effect of VFCT on SS and LCC-S compensation in a dynamic charging system is analyzed for square and rectangular coil configurations.
This paper is divided into several sections, which are described below. Section 2 is devoted to the simulation of the proposed system, covering aspects such as coil design, routing, and circuit design. Section 3 describes the simulation and experimental setup of the proposed system. Section 4 analyzes the simulation and experimental results, and provides acknowledgements and conclusions.
In DWPT systems, the choice of inverter topology has a significant impact on the cost, complexity, and reliability of the system. Traditional full-bridge inverters use two bridge legs (four switches) per coil, which provides high modularity and excellent fault isolation since each coil operates independently. However, this approach increases the component count and costs. To address this issue, multi-leg common-bridge and common-bridge inverters reduce the number of switches by using a single bridge leg between coils, requiring N + 1 bridge legs for N coils. This, however, creates problems with control synchronization and thermal management, and can also reduce reliability. As a more balanced alternative, the multi-leg half-bridge inverter topology offers an attractive solution, requiring only N bridge legs to connect N coils, with each bridge leg acting as an individual resonant half-bridge inverter. A three-coil system requires only six switches, significantly reducing the hardware complexity and cost. In addition, it simplifies heat distribution and provides acceptable fault tolerance, making it particularly suitable for dynamic applications such as charging electric vehicles while driving.
Schematic diagram of a half-bridge resonant inverter with (a) SS compensation, (b) LCC-S compensation, (c) SS equivalent circuit, (d) LCC-S equivalent circuit, and (d) control circuit.
Figure 2 shows the proposed circuit configuration for single-arm operation. Figure 2(a) shows a single arm with SS compensation, while Figure 2(c) shows the LCC-S compensation. Their equivalent circuits are shown in Figures 2(b) and 2(c), respectively. In the SS compensation, CPa and Cs are the series compensations associated with the primary and secondary windings, respectively. Each arm of the converter acts as a half-bridge converter. These half-bridge converters respectively drive the transmitting coil and collectively feed multiple coils in the road system. The entire WPT system is controlled by a half-bridge inverter operating at variable frequency (fO). The half-bridge inverter consists of two switches S1 and S2, which are alternately turned on and off with a delay (td) between switches. On the secondary side, the DWPT system also uses a high-bridge rectifier circuit with high-frequency diodes to convert the high-frequency AC to DC.
Here ωO represents the resonant frequency and Rac (AC equivalent resistance/RA) at the input side of the rectifier is expressed as,
To achieve efficient resonant wireless power transmission, the series compensation capacitor should be selected so that it resonates with the self-inductance of the coil at a certain frequency (resonant frequency), thereby improving the power transfer between the transmitting and receiving coils. The series compensation capacitor can be:
This diagram (Figure 2) allows us to represent the WPT system in matrix form, following Kirchhoff’s voltage law,
Where LP and LS are the self-inductance of the primary and secondary coils, respectively. CPa=CPb=CPc=CPn is the series compensation capacitor of the primary winding. CS is the secondary compensation capacitor of the series compensation, which is similar to the SS and LCC-S compensation capacitors. The self-inductance, the primary winding filter inductance, the primary winding filter capacitance, and the series capacitance of the LCC-S compensation system with the arm “n” can be expressed as follows: LPa=Lp.a.=Lpb=Lpc. =Lpn, Lpfa=Lpfb=Lpfc…=Lpfn, Cpfa=Cpfb=Cpfc. = Cpfn and Cp.a.=Cpb=Cpc…. =Cpn.
Thus, the two key characteristics of an IPT system are the input impedance angle and the voltage conversion ratio.
Ignoring the internal resistance of the coil, the input impedance angle (θin) and the conversion gain (Gv) of SS and LCC-S can be derived from the following formulas:
In this paper, the closed-loop PLL method is applied to the dynamic wireless charging system (DWCS) discussed in Section 34. The model diagram is shown in Figure 2(e). In the dynamic wireless charging system (DWC), maintaining continuous power transfer without noticeable drops is critical for efficient power transfer. To achieve this, sensors are strategically placed at the midpoint of each transmit (Tx) coil, ensuring smooth activation of the next coil before the current coil is deactivated, as shown in Figure 3. For example, when Tx1 is active, the sensor at its midpoint detects an approaching vehicle and pre-activates Tx2 before Tx1 is deactivated. A similar process occurs when the vehicle is moving forward, with Tx2 triggering Tx3, ensuring smooth power transfer. This overlapping activation approach eliminates power drops, reduces mismatch sensitivity, and minimizes switching losses, thereby improving the reliability and efficiency of the system.
In addition, variable frequency control is implemented using a digital phase-locked loop (PLL), which corrects the phase difference between the inverter output voltage and the secondary current by dynamically changing the switching frequency. The system starts at a nominal frequency of 85 kHz, and the inverter operates with a duty cycle of 49% to protect its switching branches. A zero-crossing detector (ZCD) detects the phase difference and corrects it using a proportional-integral (PI) controller to ensure stable operation. Safety mechanisms include predefined frequency limits and automatic return to the original frequency in the event of a fault or signal interruption. These frequency limits are determined based on previous dynamic charging analysis without the need for a phase-locked loop (VFC) and taking into account frequency division. The fast response of the digital PLL controller improves adaptability, making it ideal for high-speed dynamic EV charging systems, ensuring smooth and efficient energy transfer between multiple transmitting coils. SS compensation operating frequency tracking equation: 34,
During dynamic operation, the resonant frequency of the system changes due to changes in the coupling coefficient k caused by the coil mismatch. In traditional fixed-frequency systems, this leads to a mismatch between the operating frequency and the resonant frequency, which reduces the power transfer efficiency, increases reactive power, and causes output instability. In contrast, the variable frequency control technology (VFCT) proposed in this paper can dynamically adjust the operating frequency in real time based on the system feedback and continuously monitor the resonant point. This enables the system to maintain optimal power transfer conditions even when the coupling changes. Thus, VFCT ensures stable and efficient power transfer while minimizing reactive losses. VFCT is especially useful in systems using SS compensation because it helps suppress excessive primary current growth by maintaining operation at the resonant point.
In this paper, VFCT, which was originally applied to series compensation (SS), is also applied to LCC-S compensation.
This paper examines a distributed charging station (DWCS) system and evaluates the impact of square coils with different air gap distances. Although the deployment of such a system in a city depends on factors such as the location of major roads, traffic patterns, and density, this study demonstrates its design using a simplified single-lane charging station as an example.
Two types of roads are considered for the analysis: one with square coils, the other with rectangular ones. Both cases are evaluated at two transmission distances (TD): 0 cm and 12.5 cm. Both systems use square receiving coils. The arrangement of the coils, showing their shape and position, is shown in Figure 4. The aspect ratio of the rectangular coil is chosen to be 1:2.
Effect of frequency sweep on voltage resistance and input resistance/angle for SS and LCC-S compensation.
Table 1 provides a complete overview of the design and calculation parameters required for the DWCS operation. These parameters are validated by simulation using Ansys Maxwell and MATLAB software. The simulation results are illustrated for a WPT system with a rated power of 1 kW and a switching frequency of 85 kHz. The effects of load resistance and coupling coefficient on frequency change are analyzed to investigate the frequency splitting and bifurcation effects. Figures 5(a)–(b) show the effect of frequency change on Gv and θin of the proposed system where the SS load change compensation is shown. Figures 5(c)–(d) show the effect of frequency change on Gv and θin of the proposed system where the LCC-S load change compensation is shown. Figures 5(e)–(f) show the effect of frequency change on voltage gain and input phase angle of the proposed system where the SS coupling coefficient change compensation is shown. Figures 5(g)–(h) show the effect of frequency variation on Gv and θin of the proposed system, where LCC-S compensation is illustrated to change the coupling coefficient.
In DWCS, GV and θin are the key parameters that determine the stability and performance of the system. The behavior of these parameters changes depending on the operating frequency and load conditions. In the SS compensation topology, fO < fL or fO > fH, the voltage conversion gain GV remains almost constant even if the load Rac changes significantly. Near the ZPA frequency (fO is 85 kHz), GV increases with increasing RL and reaches a maximum value at the ZPA frequency. θin is zero at fO. When Rac is large, θin is negative at f < fO and positive at f > fO. In the LCC-S configuration, when Rac is large, GV increases with increasing frequency. However, when Rac is small, GV first increases and then decreases with increasing frequency. No matter how the load changes, GV is the same at fO. The input impedance angle θin is zero at fO, and when Rac is large, θin is positive for f < fO and negative for f > fO. In SS and LCC-S configurations, bifurcation occurs when Rac is small, resulting in two additional ZPA frequencies fL and fH in addition to fO. To achieve ZVS and ensure stable system operation, the system must operate in the positive phase angle region. Bifurcations usually occur when the coupling coefficient k is high or the load resistance is low. To avoid this, frequency control should be implemented. In DWCS, the coupling coefficient k is critical. Changes in the coupling coefficient affect the voltage gain and the input impedance angle, as do changes in the load resistance. Frequency splitting occurs when the frequency deviates from the nominal value and is aggravated by increasing load resistance. By understanding the behavior of the voltage conversion ratio and input impedance angle under different operating conditions, designers can optimize the performance and stability of the DWCS while ensuring ZVS operation and avoiding bifurcation issues.
As the vehicle speed increases, rapid changes in the mutual inductance between the transmitting and receiving coils lead to rapid fluctuations in the coupling coefficient (k), which may reduce the power transfer efficiency. To address this issue, our proposed approach combines adaptive modulation techniques with advanced coupling control algorithms (potentially enhanced by artificial intelligence or machine learning) to maintain stable power transfer even under highly dynamic conditions such as high-speed vehicle movement. Although the upper limit of the VFCT response speed to rapid inductance changes is not explicitly investigated in this paper, the system is primarily designed for semi-dynamic wireless charging where the vehicle speed is moderate and the coupling changes are not too abrupt. However, the flexible and intelligent control strategy of the VFCT opens up great potential for managing inductance changes at higher speeds. Although the impact of load changes has not been studied in detail, the VFCT exhibits inherent robustness by dynamically adjusting the operating frequency based on reflected impedance changes.
Two types of transmitting coils are selected for the proposed dynamic charging system. The simulation in ANSYS is performed for rectangular coils of different lengths. The dimensions of the first coil are 50 cm x 25 cm, and the second one is 25 cm x 25 cm. The dimensions of the receiving coil remain the same: 25 cm x 25 cm.
The Ansys parameters and experimental settings are shown in Table 2. In Figure 6, the magnetic flux density model generated by Ansys Maxwell shows the magnetic flux distribution inside the charging system. It can be seen that the magnetic flux density is uniformly distributed over the square coil. For the same coupling coefficients or distances, the magnetic flux density of the rectangular coil is smaller than that of the square coil. However, rectangular coils, especially those extended along the vehicle’s direction of travel (usually the longitudinal axis), have advantages in dynamic wireless charging applications. When the receiver coil passes the transmitter, its increased length increases the effective coupling time, thereby increasing the average output power over the entire travel time. However, for the rectangular coil, the magnetic flux density at its corners is higher than that at the center of the coil. This means that the coupling coefficient between the transmitter and receiver at the center of the rectangular coil is smaller than the coupling coefficient at the corners of the coil at the same distance. Figure 7 shows the magnetic flux distribution under dynamic conditions. Figure 7(a) shows the square coil model. Figure 7(b) shows the rectangular coil model.
After the simulation, the corresponding hardware configuration shown in Figure 8 was implemented. The proposed method uses a six-terminal high-pass filter (HPF). In this HPF, only three terminals are used to excite three transmit coils (square/rectangular shape). A Spartan 6 LX9 FPGA micro board supplies pulses to the system. Sensors are used to convert the pulses from one leg of the inverter to another. RI8TU-10,016 is used as a grid-side rectifier. Power transmission is realized by the transmit coil of the HPF consisting of six SiC power MOSFETs S1-S6 (three legs) (SCT2080KE). Then, the secondary-side high-frequency rectifier consisting of OnSemi-RURG30120 is used to convert AC to DC to power the equivalent load/battery.
To prevent short-circuiting of the switches on each branch, the signals of each pair should be in antiphase, and the delay time between the signals should be very short. The proposed DWCS is controlled by a field-programmable gate array (FPGA). The FPGA logic is implemented in VHDL language in Xilinx ISE software and is fully verified and functionally tested. As mentioned above, the dimensions of the two transmitting coils connected to the two branches are shown in Table 2. As mentioned above, the gap between the two transmitting coils is maintained at 0 cm and 12.5 cm. In the FPGA logic, a sensor is embedded in front of each transmitting coil, which is used as a trigger to track the position of the receiving coil on the wireless charging path.
The hardware results are shown below (from top to bottom): input voltage, input current of the primary resonant circuit, input voltage and input current of the bridge rectifier. (a) SS compensation fully aligned, (b) SS compensation 50%, (c) various SS compensation offsets, (d) LCC-S compensation fully aligned, (e) LCC-S compensation 50%, and (f) various LCC-S compensation offsets (results for Tx and Rx: square).
Figure 9 shows the output voltage and current of the half-bridge inverter together with the input voltage and current of the rectifier circuit when the Rx coil is fully aligned with the first Tx coil and there is 50% mismatch. Figures 9(a) and 9(b) show the output voltage and current of the inverter and the input voltage and current of the rectifier circuit in the fully aligned state of SS compensation and the 50% mismatch state, respectively. Vp-SS and Ip-SS represent the output voltage and current of the inverter, and Vs-SS and Is-SS represent the input voltage and current of the rectifier for SS compensation. Figures 9(d) and 9(e) represent the LCC-S compensation, where Vp-LS and Ip-LS represent the output voltage and current of the inverter, and Vs-LS and Is-LS represent the input voltage and current of the rectifier for LCC-S compensation. Considering these waveforms, LCC-S compensation provides lower voltage and current ripple compared to SS compensation system.
In order to improve the comparative study of SS and LCC-S, comparative experiments were conducted with the parameters shown in Table 1. Figures 9(c) and 9(f) show the changes in the amplitude of the input and output voltage of the magnetic coupling under different mismatch positions. Figure 9(c) shows the results with SS compensation. Figure 9(f) shows the LCC-S compensation. By observing these waveforms, we find that as the Rx coil moves away from the Tx coil and the mismatch with the coil decreases, the primary current Ip-SS increases with SS compensation. With LCC-S compensation, the primary current Ip-SS decreases. Figure 10(b) shows these changes in the inverter output current associated with the changes in SS mismatch and LCC-S compensation. Implementing SS compensation in a dynamic charging system requires components with a current rating 5-6 times higher than that of LCC-S compensation, or requires the implementation of control methods to limit the primary current; this adds complexity to the system. As the gap between the two transmit coils increases, the mismatch between the transmit and receive coils also increases, resulting in an increase in the primary side current. As a result, constant current systems require components (such as switches, inductors, and capacitors) with much higher current ratings, which increases cost and thermal load. In contrast, LCC-S compensation inherently limits the primary side current through its impedance shaping circuit, providing a more stable and predictable current behavior under mismatch conditions. This makes it more suitable for dynamic conditions and is recommended in dynamic charging systems compared to constant current compensation.
(a) Mismatch and coupling gain: the receive coil moves to Tx. (b) Change in mismatch current with SS and LCC-S compensation (results for Tx and Rx: squared). (c) Air gap and coupling gain at different air gap distances.
Figure 10(a) shows the coupling coefficient of a square transmitter coil and a rectangular transmitter coil with a square receiver coil as a function of misalignment. The receiver coil at the corner of the rectangular coil has a higher coupling coefficient than the receiver coil at the center of the coil with the same air gap. The square coil provides a longer transmission range than the rectangular coil with similar characteristics. The contact pads of the square coil have better tolerance to misalignment than the rectangular coil. Figure 10(c) shows the coupling coefficient as a function of air gap for square and rectangular transmitter systems. It can be seen from the figure that the square coil is better than the rectangular coil in terms of vertical misalignment.
In order to maintain a constant output power of charging, a self-oscillating WPT system was demonstrated to provide stable power in the split region. In the DWCS system, the k value between Tx and Rx changes when the coil moves from one transmitting coil to another. The maximum coupling coefficient is 0.3, and the nominal is 0.248. The coupling coefficient at the center of two adjacent transmitting coils depends on the size of the Tx and Rx coils and the distance between them. By using VFCT, the system automatically operates at the split frequency, rather than the resonant frequency, which ensures the stable operation of the proposed system.
Figure 11 shows the change in the coupling coefficient when switching the receiving coil from one transmitting coil (square/rectangular) to another transmitting coil (square/rectangular). When the gap between the two transmitters is 0 cm, the coupling coefficient at the center of the two transmitters is minimal and is about 0.1. Similarly, when the gap between the coils is 12.5 cm, the minimum coupling coefficient is 0.05. It is obvious that with an increase in the gap between the two transmitting coils, the minimum coupling coefficient also decreases. From these graphs, it is clear that at the peak moment, the coupling coefficient of the transmitting coil with the square coil is higher.
Power unevenness of a square road with and without VFT: (a) 12.5 cm with SS compensation, (b) 12.5 cm with LCC-S compensation, (c) 0 cm with SS compensation, and (d) 0 cm with LCC-S compensation.
Figure 12 shows the output power of the proposed square coil DWCS. The proposed method provides better average power than the traditional method. In the case of 12.5 cm gap and SS compensation, the average power increases from 490 W to 565 W. For LCC-S, the average power increases from 560 W to 575 W. In the case of 0 cm gap and SS compensation, the average power increases from 530 W to 565 W. For LCC-S, the average power increases from 650 W to 665 W. Since the gap between the coils is the effect of the proposed method, the effect of zero gap between adjacent coils is slightly smaller. Applying the proposed method to LCC-S compensation results in an increase in the rated power, but this increase is small compared to SS compensation.
Figure 13 shows the output power of the proposed DWCS for rectangular coils. The average power of the proposed VFT method is higher than that of the traditional method. For the case of 12.5 cm gap, with SS compensation, the power increases from 660 W to 670 W. For LCC-S, the power increases from 695 W to 700 W. For the case of 0 cm gap, with SS compensation, the average power increases from 720 W to 730 W. For LCC-S, the power increases from 740 W to 755 W. With the increase of the gap between the coils, the efficiency of the proposed method decreases slightly when the gap between adjacent coils is zero. With the recommended LCC-S compensation method, the rated power increases, but the increase is not so significant compared with SS compensation.
Output power of rectangular roads with and without VFT technology: (a) 12.5 cm with SS compensation, (b) 12.5 cm with LCC-S compensation, (c) 0 cm with SS compensation, and (d) 0 cm with LCC-S compensation.
Looking at the graph, the square coil configuration provides higher peak power when the receiving coil moves from one coil to another. However, when considering the number of coils N, the power fluctuations will be significant, which may affect the battery life of the system. It is well known that the power transfer between the transmitting coil and the dynamic system is maximum when the coils are perfectly aligned. On the contrary, when the receiving coil is located in the middle of the coil, the received power is significantly reduced. Figure 14 is a block diagram comparing the efficiency of a dynamic wireless charging system with a square and rectangular coil configuration. As shown in the figure, the peak efficiency of the rectangular coil may be slightly lower than that of the square coil due to its wider but less concentrated magnetic field distribution. However, in dynamic scenarios, rectangular coils are generally able to achieve higher average power transfer efficiency since the longer communication time provides more stable and consistent power transfer.
Post time: Jul-21-2025