Francesca Grazian

This work presents an efficiency-oriented modulation and morphing strategy for a three-phase three-level dual active bridge converter operating across both 800 V and 400 V electric vehicle battery systems. By reconfiguring the converter into a single-phase dual active bridge or a hybrid half-bridge/full-bridge structure at light-load, the proposed approach reduces current-invariant losses. A unified dual phase-shift framework is formulated to analytically model power flow and peak-current minimization across all three-level modulation variants, inner phase shift, duty-cycle control, and T-type zero-level modulation, demonstrating that all combinations produce equivalent voltage and current waveforms. Simulation efficiency maps are generated for all valid primary/secondary modulation pairs and indicate that inner and duty-cycle modulation achieve the highest efficiency across the full operating window. Hardware-in-the-loop experiments confirm stable three-phase-to-single-phase morphing and accurate power tracking between reference and measured power profiles for both voltage levels. The results validate that the proposed morphing strategy enables wide-range, auxiliary-free light-load operation suitable for next-generation EV charging architectures.

This paper presents a hybrid modulation (HM) scheme to facilitate secondary-side control in wireless power transfer (WPT) systems. To achieve broad power regulation in WPT systems, the conventional pulse width modulation (PWM) exhibits a significant efficiency drop under light loads, while the existing pulse density modulations (PDMs) lead to considerable current and voltage ripples. To address this issue, an optimal discrete PDM (D-PDM) is proposed for active rectifier modulation. By symmetrically and uniformly distributing pulses, the proposed optimal D-PDM eliminates even-subharmonics in rectifier input voltage, thereby reducing the current distortions and output voltage ripple while removing the capacitor DC blocking voltages. Moreover, the pulse width regulation is incorporated into the optimal D-PDM, enabling continuous output tuning and further minimizing subharmonics in the voltage. Based on a WPT prototype, the proposed HM is benchmarked with the existing PWM and PDMs. Experimental results show that the proposed HM significantly mitigates current and voltage ripples while facilitating continuous tuning when compared with the existing PDMs. Additionally, when compared to the PWM, the proposed HM demonstrates notable efficiency improvements within the 10%-60% power range, achieving a maximum efficiency enhancement of up to 5.5%.

This paper presents a parameter recognition based impedance tuning method for the impedance mismatch caused by capacitance drift and coil misalignment in series-series (SS)-compensated wireless power transfer (WPT) systems. First, a parameter recognition method is proposed to identify the unknown parameters of the resonant circuits by only measuring the RMS values of the coil currents. No phase detection circuits and auxiliary measurement coils are required. Furthermore, according to the recognized parameters, the reactance on both sides are minimized simultaneously by regulating the system frequency and the phase shift angles of the active rectifier. Compared with the existing methods, the proposed parameter recognition method adopts a dynamic frequency approaching strategy to avoid severe system detuning due to the bifurcation phenomenon. Moreover, based on the recognized parameters, the proposed impedance tuning method can simultaneously cope with the parameter deviations caused by capacitance drift and coil misalignment on both sides without using extra circuits and switches. Experimental results show that the unknown parameters of the resonant circuits are recognized accurately, with the average relative errors all less than 3%. Additionally, by implementing the impedance tuning method, the dc to dc efficiency of the WPT prototype is improved by 4.3%-15% in the experiments.

Light-duty electric vehicles (EVs) typically have a rated voltage of either 400V or 800V. Especially when considering public parking infrastructures or owners with multiple EVs, e.g., car rental companies, EV wireless chargers must efficiently deliver electric power to both battery options. For this purpose, this paper proposes an advanced and compact version of the previously defined voltage/current doubler (V/I-D) converter, here comprising two coupled series-compensated bipolar pads (BPPs). The presented system can efficiently charge EVs with both battery voltage classes at the same power level without affecting the current rating of the converter’s circuit components. The control scheme is implemented at the power source side in terms of switching frequency and input voltage, and only passive semiconductor devices are employed on board the EV. The equivalent circuit is analyzed, focusing on the BPPs’ undesired cross-coupling and its effect on the power transfer. Methods to compensate for the cross-coupling are proposed regarding the BPP design and operating strategy. At 7.2kW and aligned BPPs, the DC-to-DC efficiency of 96.34% and 96.53% have been measured at 400V and 800V, respectively. The proposed method has been experimentally validated at different misalignment profiles while considering battery voltages 300V-400V and 600V-800V, which proves that the V/I-D converter is a universal charging solution for EV batteries.

The lithium-ion battery of an electric vehicle (EV) is typically rated at either 400 or 800 V. When considering public parking infrastructures, EV wireless chargers must efficiently deliver electric power to both battery options. This can be normally achieved by regulating the output voltage through a dc–dc converter at the cost of higher onboard circuit complexity and lower overall efficiency. This article proposes a wireless charging system that maintains a high power transfer efficiency when charging EVs with either 400- or 800-V nominal battery voltage at the same power level. The control scheme is implemented at the power source side, and only passive semiconductor devices are employed on board the EV. The presented system, called voltage/current doubler (V/I-D), comprises two sets of series-compensated coupled coils, each of them connected to a dedicated H-bridge converter. The equivalent circuit has been analyzed while explaining the parameters' selection. The analytical power transfer efficiency has been compared to the one resulting from the conventional one-to-one coil system at 7.2 kW. For the same power level, the dc-to-dc efficiency of 97.11% and 97.52% have been measured at 400-V and 800-V voltage output, respectively. Finally, the functionality of the V/I-D converter has been proved at both the even and uneven misalignments of the two sets of coupled coils.

Wireless charging must be highly efficient throughout the entire battery charging profile to compete in the electric vehicle (EV) industry. Thus, optimum load matching is commonly used: it operates at the equivalent load that maximizes the efficiency, which depends on the coil’s alignment. In this paper, the optimum load is made independent of the coils’ position by changing the system’s resonant frequency through switch-control capacitors (SCCs). This eliminates the need for load-side voltage control. The output current follows the battery voltage rise during the battery charging cycle to always match the optimum load, which can be achieved by regulating the input voltage via the power factor correction converter. This method is called here constant optimum load (COL). Two SCC topologies have been implemented in a 3.7kW hardware demonstrator. The one implementing the half-wave modulation achieves higher efficiency than the one employing full-wave modulation, with 96.30% at 3.2kW and aligned coils. When misalignment occurs, the half-wave modulation technique results in higher efficiency than the conventional-fixed compensation, where the efficiency is lower by up to 0.68% at partial load. Based on these results, the proposed COL method is proved suitable for 3.7kW EV-static wireless charging achieving one of the highest peak efficiencies listed in today’s literature for the same power class.

Due to the urgent desire for a fast, convenient, and efficient battery charging technology for electric vehicle (EV) users, extensive research has been conducted into the design of high-power inductive power transfer (IPT) systems. However, there are few studies that formulate the design as a multiobjective optimization (MOO) research question considering both the aligned and misaligned performances and validate the optimal results in a full-scale prototype. This article presents a comprehensive MOO design guideline for highly efficient IPT systems and demonstrates it by a highly efficient 20-kW IPT system with the dc–dc efficiency of 97.2% at the aligned condition and 94.1% at 150-mm lateral misalignment. This achievement is a leading power conversion efficiency metric compared to IPT EV charging systems disseminated in today’s literature. Herein, a general analytical method is proposed to compare the performances of different compensation circuits in terms of the maximum efficiency, voltage/current stresses, and misalignment tolerance. An MOO method is proposed to find the optimal design of the charging pads, taking the aligned/misaligned efficiency and area/gravimetric power density as the objectives. Finally, a prototype is built according to the MOO results. The charging pad dimension and total weight, including the housing material, are 516*552*60 mm ³ /25 kg for the transmitter and 514*562*60 mm ³ /21 kg for the receiver. Correspondingly, the gravimetric, volumetric, and area power density are 0.435 kW/kg, 581 kW/m ³ , and 69.1 kW/m ² , respectively. The measured efficiency agrees with the anticipated value derived from the given analytical models.

In wireless charging systems, the H-bridge converter's switching frequency is set close to the system's natural resonance for achieving optimized zero voltage switching (ZVS). Variations to the system's natural resonance are commonly tracked by following the changes in the resonant current's zero-crossings. The main implementation challenge is accounting for the time delay between the real monitored current and the final resulting switches' commutations. This becomes critical at high switching frequencies, particularly when the magnetic coupling and load vary widely. This paper proposes an auto-resonant detection method that continuously ensures optimized ZVS turn-on with the minimal circulating current over the coupling and loading operable range. The suggested implementation provides two split variable references for the resonant frequency detection, which adaptatively compensate for the propagation delay based on the resonant current slope. The auto-resonant scheme is benchmarked against the commonly employed method with fixed current detection references. The results highlight the auto-resonant strategy's advantages, namely extended operable range, wider ZVS turn-on region, ease start-up, and improved DC-to-DC efficiency. The auto-resonant functionality is verified experimentally with a 200W low-voltage e-bike wireless charger. Finally, the benefits of the presented method are analytically explored for high-power applications by considering the H-bridge semiconductor losses of a state-of-art 50kW wireless charging system.

If electric vehicles have to be truly sustainable, it is essential to charge them from sustainable sources of electricity, such as solar or wind energy. In this paper, the design of solar powered e-bike charging station that provides AC, DC and wireless charging of e-bikes is investigated. The charging station has integrated battery storage that enables for both grid-connected and off-grid operation. The DC charging uses the DC power from the photovoltaic panels directly for charging the e-bike battery without the use of an AC charging adapter. For the wireless charging, the e-bike can be charged through inductive power transfer via the bike kickstand (receiver) and a specially designed tile (transmitter) at the charging station, which provides maximum convenience to the user.

In inductive power transfer applications that use resonant compensation networks, the commonly employed H-bridge inverter should be kept operating in soft-switching to ensure high power efficiency and low irradiated electromagnetic noise. To achieve so, the zero-crossing detection circuit for the resonant current or voltage must be fast and accurate in any operating condition. This paper researches the concept of an auto-resonant control for the typical H-bridge resonant converter used in wireless charging systems. In the method proposed here, the reference levels for the zero-crossing detection of the inverter’s current are automatically adapted depending on the slope of the current itself at the zero-crossing. In this way, it is possible to compensate for the circuit delay even in the presence of parameters’ variation and to ensure that the soft-switching is always maintained. The functionality of this control method is proven first mathematically, and then with circuit simulations. The core steps for the implementation are described with the support of functional blocks. Finally, the system start-up strategy is explained, which uses an auxiliary timed oscillator to modulate the inverter with a fixed 50% duty cycle at a higher frequency than the nominal. This guarantees that the start-up is in the inductive region and, thus, the zero-voltage switching turn-on. Once the detection circuits sense the current flow, the oscillator is automatically disabled, and the nominal power transfer starts.