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A passive current sharing method for paralleled LLC resonant converters is proposed in this article, and the current sharing effect of paralleled common capacitor LLC resonant converter is analyzed. The passive current sharing method is achieved by adding coupled impedance between the LLC resonant converters, and the coupled impedance can be inductive, capacitive, infinitely small, and infinitely large. Among them, it is traditional paralleled LLC resonant converter without current sharing ability when the coupled impedance is infinitely large. First, the mathematical model of paralleled common capacitor LLC resonant converter with coupled impedance is built based on fundamental harmonic analysis. Second, according to the mathematic model, the current sharing effect of the paralleled common capacitor LLC resonant converter of different coupled impedance under different parameter difference is analyzed, it is easy to see the current sharing effect is improved after the couple impedance is added, and in general, inductive coupled impedance has a better current sharing effect for paralleled common capacitor LLC resonant converter. Last, the theoretical analysis results are verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

A passive current sharing method for a two-phase common inductor LLC resonant converter is proposed in this article, and the relative mathematical analysis of current sharing error is carried out. The concept of a common inductor comes from the introduction of coupled impedance, where the resonant inductors of two phases are connected, which means that the separated two phases are coupled by an additional impedance. Obviously, there are four cases of coupled impedance, which are infinite impedance, infinitely small impedance, inductive impedance, and capacitive impedance, and they are all analyzed in the article. In addition, for different inductor and capacitor parameter differences, the two-phase common inductor LLC resonant converter has different current sharing characteristics, and there is an optimal solution for different coupled impedance for each difference. However, under each parameter difference, when the coupled index g is a negative number, there is generally a better current sharing effect. At last, simulation and experimental results have proved the correctness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

The single-phase five-level transformerless inverters have been gradually applied in photovoltaic grid-connected systems due to low voltage stress and excellent waveform quality. However, they also suffer from serious leakage current as conventional three-level inverters. In order to reduce the leakage current, a single-phase five-level transformerless inverter is proposed in this article. The proposed inverter guarantees that the common-mode (CM) voltage is clamped to a half of the dc-link voltage when outputting ±Vdc/2 and zero voltage levels. Consequently, the high-frequency CM voltage is avoided and the leakage current is suppressed. The voltage stresses of eight switches and two flying capacitors are only Vdc/4, thus the system investment cost and total losses are reduced. The conduction and switching losses are analyzed in detail and a comparison with some existing topologies is also made. Finally, simulations and experiment are carried out based on a 1-kW prototype. The results show that the proposed single-phase five-level inverter can obtain both excellent differential-mode and CM performance. [ABSTRACT FROM AUTHOR]

In data center and telecommunication power supplies, the front-end dc–dc stage is required to operate with a wide input voltage range to provide hold-up time when ac input fails. Conventional LLC converter serving as the dc–dc stage is not suitable for this requirement, as the normal operation efficiency (at 400 V input) will be penalized once the converter is designed to achieve high peak gain (wide input voltage range). This paper examined the operation of the LCLC converter and revealed that the LCLC converter could be essentially equivalent to a set of LLC converters with different magnetizing inductors that are automatically adjusted for different input voltages. In nominal 400 V input operation, the LCLC converter behaves like an LLC converter with large magnetizing inductor, thus the resonant current is small. In the hold-up period, when the input voltage reduces, the equivalent magnetizing inductor will reduce together with switching frequency reducing, thus the converter achieves high peak gain. In this paper, a new design methodology is also proposed to achieve optimal utilization of the two resonant capacitors for high power application. To verify the effectiveness of the LCLC converter for hold-up operation, comprehensive analysis has been conducted; a detailed step by step design example based on capacitor voltage stress is introduced; an experimental LCLC prototype optimized at 400 V, with input voltage range of 250–400 V and 12 V/500 W as output has been presented. [ABSTRACT FROM AUTHOR]

In high-power applications, parallel operation is required to improve both efficiency and reliability. In an LLC converter, it is difficult to achieve parallel operation due to the gain sensitivity to component tolerance. This paper proposes a new structure of a common resonant capacitor for a multiphase LLC converter, which can achieve very good current-sharing performance with no additional components or control. To evaluate the current-sharing performance, a new first harmonic approximation (FHA) model is built in this paper to analyze the LLC converter with coupled resonant tanks. Both FHA analysis and powersim (PSIM) simulation results demonstrate the load-sharing improvement of the proposed common capacitor LLC resonant converter over the conventional two-phase LLC converter. The current-sharing performance from the FHA analysis and the PSIM simulation are compared, and the error of the FHA analysis is evaluated and explained. A 600 W two-phase LLC converter prototype based on the proposed method is also built to verify the feasibility. Excellent current-sharing performance (6% resonant current sharing error at a wide load range) has been achieved. [ABSTRACT FROM PUBLISHER]

A passive-impedance-matching (PIM) technology is proposed to achieve automatic current sharing for multiphase resonant converters through matching the input impedance of each phase. The series inductors (or series capacitors) of each phase are connected in parallel to achieve a couple of virtual resistors including positive and negative resistors and variably series inductors (or capacitors). A virtual positive (or negative) resistor increases (or decreases) the input impedance of the respective phase, and the variably series inductors can also compensate the component tolerance such that the impedance of each phase is matched. The current-sharing performance of the common-inductor two-phase LLC resonant converter (as one example) is evaluated under the first-harmonic-approximation assumption. The virtual positive and negative resistors and variably virtual inductors are calculated. The proposed method can share the primary resonant current and the load current for all phases without any additional circuit and control strategy. The PIM technology is extended to other resonant converter topologies, including common-inductor or common-capacitor series-resonant converter, LCC, CLL resonant converter, etc. A 600-W 12-V common-inductor two-phase LLC resonant converter prototype is built to verify the feasibility and demonstrate advantages of PIM technology. [ABSTRACT FROM PUBLISHER]

In this paper, a new common inductor current sharing method is proposed for a multiphase LLC resonant converter for high-power applications. Automatic current sharing is achieved by using a common resonant inductor connecting the resonant inductors in each LLC phase in parallel. The current sharing performance of the proposed method is evaluated under first harmonic approximation (FHA) assumption. The proposed method can automatically share the primary resonant current and the load current for all phases without any additional circuit and control strategy. A 600-W two-phase LLC converter prototype based on the proposed method is built to verify the feasibility. Excellent current sharing performance (less than 0.5% current sharing error at full load) has been achieved. [ABSTRACT FROM PUBLISHER]

Diode–capacitor-based dc–dc converters provide a simple and low cost solution for high step-up voltage regulation in solar and fuel cell generation. Transient modeling analysis reveals their worse influence of nonlinear and nonminimum-phase system characteristic due to right-half-plane (RHP) zero, especially in high voltage gain application. However, the process of energy transfer for diode–capacitor-based dc–dc converter is different from basic dc–dc converter. Based on the unique feature, this paper proposes an improved main circuit structure with parallel connection of resistive–capacitive damping network across the intermediate capacitor to achieve good dynamic performance. By optimal parameter design according to Routh–Hurtwitz criterion, all the RHP zeros in the transfer function of control-to-output voltage are eliminated completely. Then, by the case of diode–capacitor-based boost converter, the adaptive PI controller is designed to deal with nonlinear characteristic of voltage gain. It gets good dynamic performance under wide range output voltage. All the theoretical findings and design approaches are verified by simulation and experiment results. The existing diode–capacitor-based high step-up dc–dc converters with slight main circuit modification are more promising in renewable energy application. [ABSTRACT FROM AUTHOR]

This paper proposed a new half-bridge (HB) LLC resonant converter family with pulse-width modulated (PWM) auxiliary switch (sLLC converter) for hold-up mode operation. The proposed sLLC converters could operate with synchronous rectifier, which is suitable for low-output voltage applications. In the proposed converters, an auxiliary switch is added at the primary side to provide charging path for the series resonant inductor. For nominal 400-V input, sLLC achieves same performance as conventional LLC converter, and all the good features such as soft switching are naturally retained. For slight input voltage fluctuation, frequency modulation is used to regulate the output voltage. When the input voltage reduces further, HB switches will operate at constant minimum frequency, and the auxiliary switch will operate in the PWM mode to energize the resonant inductor with the bus voltage directly during hold-up period. Thus, the converter achieves higher voltage gain, and the output voltage can be maintained at desired level. To verify the effectiveness of the proposed sLLC converter, operational principle and equivalent circuits will be carefully explained and analyzed in this paper. A 300-W prototype is built for 250–400-V input 12-V output application. [ABSTRACT FROM AUTHOR]

Nonlinear inductors have wide applications in dc/dc converters. The multiwindow multipermeability nonlinear inductor based on low-temperature co-fired ceramic (LTCC) technology has been proven to have a gradually changing wide-range inductance value curve while requiring no extra dc bias, which makes them suitable in various high-efficiency dc/dc converters. This paper focuses on the design of such a multiwindow multipermeability inductor based on an innovative module. Currently, the design of the LTCC inductors requires complicated simulation when coupling matrices among all the windows are taken into consideration. A simplified model for calculating the inductance value is proposed in this paper to reduce complexity. In the proposed model, the complicated inductance simulation is simplified to calculating inductance of three basic units in a nine-window inductor. By simulating the nine-window inductor, inductance of a rectangle-shaped inductor with any number of evenly distributed windows on it can be calculated. Based on the proposed model, the design guideline of the nonlinear inductor is also summarized. A 16-window two-permeability prototype is presented to demonstrate the design process according to the new model. The complete simulation and the test results are also provided to verify the model. The proposed model correlates with the simulation results very well. [ABSTRACT FROM PUBLISHER]