This article investigates the peak-to-peak output voltage ripple for the four-switch buck+boost (FSBB) converter under four-segment inductor current mode zero-voltage switching (ZVS) modulation strategies in a comprehensive way. Based on the operating mode of the FSBB converter and the relative magnitudes of the output current and inductor current at the switching instants, four distinct cases were analyzed, with corresponding voltage ripple expressions derived for each. The analysis presented in this article provides theoretical guidance for the selection of output capacitor size of the FSBB converter under ZVS modulation strategies. In addition, the introduced analytical method was also used to evaluate and compare the output voltage ripple under three state-of-the-art ZVS modulation schemes. To validate the theoretical analysis, two sets of simulations were conducted. Finally, a laboratory FSBB converter prototype was also built and tested for the validation purpose with an input voltage of 150 V, output voltage of 200 V, and operating power of 1.2 kW.

Charging electric vehicles (EV) via wireless power transfer (WPT) has emerged as a novel charging concept in recent years. In this thesis, a WPT charging system featuring LCC-S compensation and a back-end four-switch buck+boost (FSBB) converter was chosen as the research object. The main research content of this thesis is divided into two parts. The first part delves into the FSBB converter. Comprehensive and detailed analysis on the soft-switching modulation strategy on this converter was investigated and presented. The second part focuses on accurate modeling of electrical stresses and current distortion phenomenon for compensation topologies.

The double-sided LCC (DLCC) compensation has been widely used in inductive power transfer (IPT) systems because it has a load-independent current source output directly proportional to the coils’ coupling, which makes it inherently safe against misalignment. The input current of the DLCC typically has high harmonic distortion due to the low-pass filter characteristic of the input LC components. Consequently, predicting the inverter’s turn-off current through circuit modeling using the first-harmonic approximation (FHA) would result in a significant estimation error. However, an accurate computation is essential to determine whether the inverter’s zero-voltage switching (ZVS) turn-on is achieved. This paper defines an analytical model that effectively predicts the inverter turn-off current point for any operating condition, i.e., when the diode rectifier operates in continuous and discontinuous conduction modes. It has been found that the inverter turn-off current depends on the loading condition. Therefore, the proposed method is based on modeling the equivalent load as the rectifier together with the battery. Experimental verification has been conducted using two IPT systems with nominal power levels of 3.7 kW and 7.7 kW.

This article presents an optimal multivariable control (OMC) strategy for the LCC-LCC compensated wireless power transfer systems. To mitigate reactive power and achieve higher efficiency, the proposed OMC method incorporates dual-side hybrid modulation and primary-side switch-controlled-capacitor (SCC) tuning into the triple-phase-shift (TPS) control. First, the impact of hybrid modulation and SCC tuning on the system characteristics is investigated. The inverter and rectifier zero-voltage-switching (ZVS) conditions are then analyzed to achieve dual-side ZVS with minimal reactive power. Furthermore, a multivariable optimization problem is established based on the power loss analysis. The solution to this problem provides optimal control variables that minimize the overall system loss. Through collaborative modulation and control of the inverter, rectifier, and SCC, the proposed method reduces the rms values of the currents and lowers the turn-off currents for the converters. As a result, this approach improves efficiency in both light- and heavy-load conditions, enabling wide output regulation and full-range efficiency optimization simultaneously. Finally, the proposed method is benchmarked with the existing TPS method. Experimental results demonstrate that the proposed method achieves higher dc-to-dc efficiency in the power range of 0.2-2.2 kW, with a maximum efficiency improvement of up to 6.3%.

Triangular current mode (TCM) zero-voltage switching (ZVS) modulation method is widely adopted in power electronic converters to achieve acceptable efficiency in high switching frequency operations. For bidirectional dc-dc converters, in order to realize ZVS turn-on, a reverse inductor current can be utilized for this purpose through variable frequency control. In this article, this reverse switched current is revisited considering the parasitic resistances presented in the mosfet switches and the inductor for three common types of dc-dc converters, i.e., buck, boost, and buck-boost converters, which study was normally neglected in the previous research. Universal closed-form equations of the modified duty cycle and switched current are derived, which can be utilized to calculate the reverse current under different operating conditions. It is found that the parasitic resistances can have a negative impact on the switched current value, and this may lead to an unexpected loss of ZVS turn-on. A laboratory prototype of a four-switch buck+boost converter featuring TCM-ZVS buck, boost, and buck-boost operation capability was built to investigate and verify the proposed concepts. The operating voltage and power range are from 100 V to 400 V, and 300 W to 1 kW, respectively.

The pursuit of battery charging technology for electric vehicle (EV) has led to extensive research on the inductive-based wireless power transfer (WPT) systems. In this paper, the compensation component (including coils) stresses will be studied in two commonly adopted compensation topologies, namely S-S and LCC-S compensations. Due to the peak voltage calculation inaccuracy for certain components based on conventional fundamental frequency analysis, an improved peak voltage calculation method is introduced in closed form, which is proved to be more accurate by both simulation and experiments.

This paper introduces variable-frequency zero voltage switching (ZVS) modulation strategy for the four-switch buck+boost converter with one operating pattern for the inductor current, i.e., three-segment inductor current modulation control. The proposed modulation scheme guarantees a smooth transition from step-up to step-down or from step-down to step-up operating modes without abrupt duty cycle or switching frequency change. Triangular current mode (TCM) ZVS control could be derived from this three-segment inductor current modulation strategy. Moreover, the controller design can be simplified compared with other multi-mode control methods. Experimental results were given to validate the modulation control strategy based on a 300−600 V input, 400 V output, 3.3 kW prototype.

This paper presents the semiconductor losses analytical equations in closed form for two-level voltage source converter, three-level neutral point clamped (NPC) and three-level T-Type PFC topologies in high power applications. The reverse parallel current conduction between the SiC MOSFETs channel and body diode is considered. A circuit simulation model is built in PLECS to estimate the semiconductor losses and to verify the accuracy of the developed analytical model. A calculation example of the semiconductor losses of a 200 kW three-phase rectifier is shown.

This article introduces a three-mode variable-frequency zero-voltage switching (ZVS) modulation method for the four-switch buck+boost converter. This method makes this circuit concept well suited for applications, such as wireless power charging of electric vehicles, where this circuit operates as a power buffer between the resonant converter and the battery with the function to implement the required charging profile. Herein, the buck+boost converter operation is subdivided into three operating regions according to the converter static voltage gain, i.e., buck-, buck-boost- and boost-type modes. A ZVS turn-on triangular current mode (TCM) control is adopted for buck-type and boost-type modes. In the buck-boost-type mode when the input-to-output voltage gain is close to unit, all the possible modulation cases are studied thoroughly based on the phase shift of the two half bridges in a full switching period. The selection of the most suitable modulation scheme is performed to minimize the rms value of the inductor current while taking into account the simplification of the practical implementation. Closed-form equations are derived, which makes it easy to implement in practice. The proposed strategy is described, analyzed, and finally verified through a 3 kW surface mounted device (SMD) silicon carbide (SiC) mosfet-based laboratory prototype with designed input voltage of 300-600 V and the typical output voltage of 400 V class battery. The efficiency from the measured results is remarkably high, i.e., between 99.2% and 99.6% in a power range from 1 to 3 kW. Finally, tests for the operating mode transitions demonstrated the feasibility of the proposed modulation method. The power density of this converter is 4.86 kW/L.

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 mm3/25 kg for the transmitter and 514∗562∗60 mm3/21 kg for the receiver. Correspondingly, the gravimetric, volumetric, and area power density are 0.435 kW/kg, 581 kW/m3, and 69.1 kW/m2, respectively. The measured efficiency agrees with the anticipated value derived from the given analytical models.

In a wireless charging system, a back-end DC/DC converter can be used after the coil rectification stage to match the battery charging requirements and to optimize the resonant converter operation. In this paper, a synchronous boost converter is selected according to suggested coil parameters from SAE J2954 standards on a WPT1 3.7 kW power class. This converter is analysed while cascaded to a resonant converter with series-series (S-S) compensation. The semiconductor and inductor losses under hard-switched continuous conduction mode (CCM) and triangular current mode (TCM) are calculated and compared. A benchmark study shows that both the TCM and CCM operations have similar performance of efficiency in constant current (CC) charging profile while TCM has a higher efficiency in the constant voltage (CV) charging profile of a Nissan Leaf EV battery.

SiC MOSFETs have become more and more popular in recent years. Apart from its superior performance, attentions should be paid to its driving method. In this paper, an improved transformer driving circuit is proposed which can provide an almost constant negative turn-off voltage within a wide dutycycle range. Both simulation and experimental results are given to verify the effectiveness of this method.