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A 8:2:2 centre-tapped planar transformer with zero voltage gradient winding layout and b) the connection of PCBs.
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The use of LLC resonant converters has gained popularity in multiple applications that require high conversion efficiency and galvanic isolation. In particular, many applications like portable devices, flat TVs, and electric vehicle battery chargers require demanding slim-profile packaging and enforce the use of planar transformers (PTs) with low-h...
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At present, intermittent control is a main method to solve the problem of pumping output voltage with light load of LLC resonant converter, which can not only solve the problem of high pumping output voltage, but also, to a certain extent, improve the efficiency of light load to a certain extent when converter is operating. However, in extremely li...
Citations
... This significantly reduces additional losses due to skin and proximity effects, which strongly impact the performances of other technologies [3]. The copper losses can thus be maintained at acceptable levels, which explains why planar technology is now widely used in high switching frequency isolated converters (100 kHz to a few MHz) [4], [5], [6]. ...
Planar transformer technology provides a serious alternative to wound transformers for improving the efficiency and power density of isolated converters. The flat shape of its coil turns and the interleaving of its windings allow an excellent control of the skin and proximity effects. The major drawback of planar technology is the strong capacitive couplings between the windings. These couplings are detrimental to the increased switching frequency induced by the new wide-bandgap transistors, and to electromagnetic compatibility. Using fundamental equations, material properties and geometric dimensions, the present work proposes a semi-analytical electromagnetic model of planar transformers able to account for capacitive couplings. Compared with current models, it allows rapid estimation of all its sizing parameters : losses, leakage inductance, bandwidth and interwinding impedance. This novel model was experimentally validated over a wide frequency range (1 kHz up to 100 MHz) using transformers with both series and parallel connected windings.
... The windings are inherently thin; for instance, 2 oz copper with a thickness of 70 µm equals the skin depth of 1.2 MHz signals. Furthermore, interleaving methods can further reduce high-frequency winding losses and circumvent the inherent trade-offs in magnetic design [8], [9]. In prior art, many publications proposed high-frequency PCB-winding planar transformers for EV chargers [10]- [13]. ...
... The windings are inherently thin; for instance, 2 oz copper with a thickness of 70 µm equals the skin depth of 1.2 MHz signals. Furthermore, interleaving methods can further reduce high-frequency winding losses and circumvent the inherent trade-offs in magnetic design [8], [9]. In prior art, many publications proposed high-frequency PCB-winding planar transformers for EV chargers [10]- [13]. ...
As the growth in electric vehicle (EV) chargers continues to push research towards compact and efficient power converters, high-frequency magnetic designs become pivotal. However, they introduce new challenges related to excessive magnetic losses and adverse parasitic components. Using planar transformers with PCB windings can address these by offering good heat dissipation, low losses, and controlled parasitics. Furthermore, interleaved winding configurations can circumvent traditional design trade-offs. Therefore, this paper presents a planar transformer design using PCB windings with novel inter-leaving and design aspects to minimise the losses and parasitic components of the high-frequency transformer. It aims to achieve an optimal balance between the trade-offs whilst ensuring compatibility with the target converter's requirements and cooling system. The proposed anti-symmetrical interleaving achieves a drastic reduction of factor 8.6 in interwinding capacitance compared to conventional full-interleaving combined with low winding losses. The paper provides extensive comparison studies of different interleaving types, supported by thorough finite element simulations. The resulting design approach is applied to a 4 kW isolated dc-dc converter for level-1 EV charging. Finally, different prototypes are built and extensively characterised and validated for implementation in the EV charger. The resulting transformer features a gravimetric and volumetric power density of 15.1 kW/kg and 76.4 kW/l, respectively.
... Among the various DC-DC converter topologies, LLC resonant converters have recently been widely utilized as strong candidates for high power density OBCs owing to the absence of an output filter [11][12][13][14][15][16][17]. In order to maximize the advantages of LLC converters, special attention should be paid to reducing the size of high-frequency transformers, and this leads to the design and development of planar-type transformers [16][17][18][19][20][21][22]. A planar transformer can achieve a low-profile design because the windings can be implemented inside a printed circuit board (PCB). ...
... However, they inherently generate parasitic capacitance, which can cause output voltage distortion, increased loss, and electromagnetic interference (EMI) [23]. Therefore, previous planar transformer studies have focused on the minimizatio the parasitic capacitance via the PCB pattern arrangement [10,[18][19][20][21][22][23] and the control utilization of the parasitic capacitance [24][25][26]. Various core shapes and matrix config tions with fractional turns for current distribution have also been researched [22-30 addition, recent studies applying planar transformers to achieve a high OBC power sity have not addressed the optimal design of planar transformers [5,31,32]. ...
... The specifications of the resonant converter and planar transformer parame adopted in this study are summarized in Tables 1 and 2. Similar to general Litz wire tr formers, planar transformers first select the core size using the WaAc product of (1), w represents the transformer capacity. Therefore, previous planar transformer studies have focused on the minimization of the parasitic capacitance via the PCB pattern arrangement [10,[18][19][20][21][22][23] and the control and utilization of the parasitic capacitance [24][25][26]. Various core shapes and matrix configurations with fractional turns for current distribution have also been researched [22][23][24][25][26][27][28][29][30]. ...
This article presents a planar transformer design and optimization method for high power density on-board chargers (OBCs) utilized in electric vehicles (EVs). Owing to considerations of electrical safety, OBCs require an isolated converter, leading to a substantial increase in volume due to the inclusion of a transformer. To address this issue and achieve high power density, a planar transformer is used, and an optimized design method is proposed for pattern arrangement, width, and core shape. The feasibility of the design is verified through the development of a 3.3 kW OBC prototype. Consequently, when compared to conventional transformers, the design method in this article results in a 27% reduction in the transformer’s height and a 20% reduction in its overall volume. This reduction is advantageous for meeting the requirements of high power density OBCs.
... The following calculates the equivalent parasitic capacity, as described in [36][37][38][39]. The equation for determining the C stray is given by Equation (29), based on the equivalent circuit of six capacitors and the simplification to a single equivalent capacitance [38]. ...
This paper focuses on the study of the high frequency transformer incorporated in solid- state transformers, specifically on the development of the steps that enable the design of an optimized high frequency transformer and its equivalent model based on the desired characteristics. The impact of operating a transformer at high frequency and the respective solutions that allow this impact to be reduced are analyzed, alongside the numerous advantages that the utilization of these transformers has over traditional 50/60 Hz transformers. Furthermore, the power scheme of the solid-state transformer is outlined, focusing on the power converters, which are immediately before and after the high frequency transformer (HFT). We also investigate a control technique that allows for correct operation and the existence of power bidirectionality. In a novel approach, this paper demonstrates the systematic steps for designing an HFT according to the desired specifications of each given project, helping students and engineers achieve their objectives in power-electronic applications. Moreover, this paper aims at increasing the knowledge of this area of power electronics and facilitating the development of new topologies with high power density, which are very important to the integration of renewable power sources and other applications. Finally, a simulation is presented to validate a high frequency transformer and its control technique.
... The main features that make planar magnetics particularly attractive [4] for industrial applications include (i) low profiles, (ii) effective heat dissipation, (iii) ease of manufacturing, (iv) repeatability, (v) modularity, (vi) more straightforward implementation of winding interleaving, and (vii) predictable parasitics. As opposed to wire-wound magnetics, planar magnetics have some limitations, such as large interwinding capacitance [5], where there are methods to overcome these limitations. Compared to traditional transformers, planar magnetic devices are increasingly preferred due to their superior performances at higher frequencies used in power conversion applications. ...
... Thus, the operation frequency of these magnetics will be limited [24]. EMI and reduced efficiency are also caused by a high charge inrush current and highfrequency oscillations in the circuit [5]. It is also necessary to provide a reasonable amount of the switching current during the dead time in order to achieve zero-voltage switching for MOSFETs [25]. ...
Due to the need for highly efficient and compact power electronic converters to operate at higher frequencies, traditional wire-wound magnetics are not suitable. This paper provides a comprehensive review of planar magnetic technologies, discussing their advantages as well as associated disadvantages. An extensive review of the research literature is presented with the aim of suggesting models for planar magnetics. Several strategies are proposed to overcome the limitations of planar magnetics, including winding conduction loss, leakage inductance, and winding capacitance. The goal of this study is to provide engineers and researchers with a clear roadmap for designing planar magnetic devices.
... electric vehicle chargers), military applications and consumer electronics (e.g. cellphones and laptops) [2], [3]. Typically, to achieve a low profile converter designers tend to increase the operating frequency to shrink the size of magnetic components [4]- [6]. ...
... Although, increasing the operating frequency will decrease the size of conventional magnetic components (e.g. transformer and inductor) the switching losses might represent an important design limitation [3]. Therefore, the use of the planar core is gaining popularity, especially in the design of transformers for isolated DC-DC converters [7] [8]. ...
... Although the planar transformer shown in Fig. 1(a) is becoming more common in power electronics converter designs, their high-parasitic capacitances may cause severe problems for many applications [3]. The planar transformer parasitic includes winding resistances, leakage inductances and stray capacitances as shown in Fig.1(b) [3], [10], [11]. ...
... For the output capacitance C Q,eq of a single switch, Equation (27) can be substituted into Equation (25), yielding the following expression for C Q,eq (v): when 0 ⩽ v < V DS1 , ...
... However, in practical applications, the equivalent capacitance of the transformer is significant in analyzing soft-switching conditions for LLC resonant converters when the equivalent capacitance of the transformer is sufficiently large and comparable to the output capacitances of the switching devices. In this section, the equivalent capacitance of the transformer is calculated with a six-capacitor model [27]. ...
... As stated in refs. [27,28], the general transformer is a twoport structure from the magnetostatic perspective, and the transformer can be considered a three-port structure from the electrostatic standpoint after considering the influence of the interwinding capacitance between the primary side and secondary side. From this three-port structure, the six-capacitor model of the transformer can be obtained, as shown in Figure 5(a). ...
In this paper, an improved time‐domain analytical method for LLC resonant converters is proposed. Unlike traditional time‐domain analytical methods, the resonant current in the dead time is derived by considering the equivalent capacitances of the switching devices and the transformer. The equivalent output capacitance of the primary‐side switch is calculated by using a two‐segment fitting approach. The equivalent capacitance of the transformer is calculated by using the six‐capacitor model. The current increment method is used to calculate the initial value of the magnetizing current and to determine the numerical calculation conditions for the proposed time‐domain expressions. Finally, the dead time ranges for zero‐voltage switching of the converter are derived based on the improved time‐domain method. Experiments were carried out with a 10 kW LLC resonant converter. The lower limit of the dead time calculated with the proposed method is closer to the experimental results than the values of two conventional methods.
... Unidirectional onboard chargers are also easy to design, relatively chip, and it is simple to control, which suits the industry requirements. A well-known unidirectional resonant converter is LLC, which contains two inductors and one capacitor as a resonant tank; in order to reduce the size of converters, leakage inductance can be integrated, as [11] explains planar transformers; however, it has its benefits and drawbacks. The gain-frequency characteristic of the LLC tank is one of the most sufficient characteristics among others. ...
EVs have gained significant attention due to their independence from fossil fuels, as well as their ability to reduce greenhouse gas emissions. In this paper, a bidirectional CLLC resonant converter for EV charger applications is proposed, in which the voltage stresses of its power switches are reduced to half of its input voltage while it can transfer high power values. A detailed analysis of the converter operating principle and characteristics are provided in this paper. Several factors contribute to achieving high efficiency by using the proposed resonant converter, including zero-voltage switching (ZVS) on its primary side and zero-current switching (ZCS) on its secondary side, in both forward and reversed operation modes. An asymmetric CLLC configuration is used, which has one less inductance than the well-known symmetrical CLLC topology; hence, it is more compact and convenient for design and control, but its features are almost similar to the conventional symmetric bidirectional CLLC converter ones. Performance of the proposed converter has been verified through simulations conducted in PSpice/OrCAD.
... Various approaches have been adopted to address this problem. In [18], transformer parasitic capacitive elements were evaluated and reduced by the winding arrangement, which is difficult to use in high-voltage applications. In [19], the authors experimentally evaluated the concept of reducing transformer capacitive parasitic elements with a layered integrated rectifier by separating stored energy in the electric field AC and DC components to reduce transformer capacitive parasitic elements. ...
... These parasitic effects narrow down the operating limits of the LLC resonant circuit and disturb the soft-switching conditions of the power elements and thereby affect the operation of the converter [1,9,18]. causes a high primary charge, distortion of the current and voltage waveforms on the primary side, and loss of ZVS in the primary-side switches, particularly when >1 under light-load conditions. Figure 3 shows the DC gain curve for the design load and frequency range including different value of while the quality factor varies. ...
... These parasitic effects narrow down the operating limits of the LLC resonant circuit and disturb the soft-switching conditions of the power elements and thereby affect the operation of the converter [1,9,18]. C stray causes a high primary charge, distortion of the current and voltage waveforms on the primary side, and loss of ZVS in the primary-side switches, particularly when f n > 1 under light-load conditions. ...
The inductor–inductor–capacitor (LLC) resonant converter is a suitable topology for wide output voltage and load range applications with limited circuit parameters. One of the most significant design boundaries of an LLC resonant converter in high-voltage applications is the parasitic capacitance effect of the main circuit components, particularly the transformer and junction capacitances of the secondary rectifier network. Parasitic capacitance effects are much higher in high-voltage applications than in low-voltage applications. Therefore, the use of an LLC resonant converter is limited to high-voltage applications. This study proposes to reduce the capacitive effects of high-voltage transformers and rectification networks with a multi-winding transformer with an integrated rectifier design and to use it in high-voltage applications with the advantages of the LLC resonant converter. For the proposed prototype, comparative experimental measurements were conducted using a conventional scheme. The measurements validate the reliability of the LLC converter for high-voltage applications, improving the output regulation performance while significantly reducing parasitic capacitances.
