Series Resonant Converter Research Articles

Transient Modulation for the Step-Load-Change Process in a Dual-Bridge Series Resonant Converter

A phase-shifted dual-bridge series resonant DC-DC converter (DBSRC) is a competitive candidate for applications of an energy storage system. At the request of a step-load-change command such as the start-up and power-level change, the converter may suffer from large-amplitude transient oscillations due to improper transient modulation. Furthermore, the DC bias current and overshoot current/voltage in the resonant tank and transformer caused by oscillations may result in transformer saturation and poor dynamic performance. To solve these problems, two fast transient modulation (FTM) methods are proposed in this paper. First, based on the steady-state analysis of the converter with phase-shift control, the current and voltage trajectory of the resonant capacitor can be obtained. Then, the detailed principles of two FTM methods are explained for achieving a smooth transition. Through the adjustment of the durations of the adjacent switching intervals temporarily, the transient trajectory can be predicted and is expected to match the destination trajectory within one switching period. Consequently, the proposed FTM methods enable the converter to move from one steady state to another instantly and the step-load-change transition can be an overshoot-free procedure. Finally, both simulation and experimental tests prove that the two modulation methods can effectively eliminate DC bias current and overshoot current/voltage in the DBSRC transient process and obtain a fast transient response.

Load Estimation for Induction Heating Cookers Based on Series RLC Natural Resonant Current

In domestic induction heating applications, cookware can be considered an equivalent load in a series resistor–inductor–capacitor resonant converter. Therefore, the electrical parameters of an equivalent circuit change according to the cookware material, size and the cookware position on the heating coil. This study proposes an online estimation method for detecting the cookware status, determining the material and estimating the equivalent heating resistance of cookware on an induction heating cooker (IHC) for power control. The proposed method could turn off the circuit in abnormal situations such as low equivalent heating coverage rate or non-ferromagnetic cookware and adjust the power in normal situations. In the method, a half-bridge series resonant converter (HBSRC) generates two test patterns with three resonant voltage pulses to detect cookware every 10 ms, only the current feedback information is needed to avoid the calculation loads and times necessary for complex signal operations in software. To verify the proposed method, a digital signal processor based HBSRC with 1000 W was constructed. The maximum errors between the estimated and measured resistance and inductance were 7.14% and 2.91%, respectively. Moreover, power control in emulated user operation reveal that the proposed method and control system can effectively estimate load online to detect cookware status and determine whether to turn off or vary the heating power for an IHC.

Analysis and Comparison of Series Resonant Converter With Embedded Filters for High Power Density DCX of Solid-State Transformer

A series resonant converter (SRC) operating as a DC transformer (DCX) is a candidate for the isolated bidirectional DC/DC converters of solid-state transformers (SSTs). However, the input/output current ripple of the SRC is relatively high, which requires bulky parallel capacitors and low-pass filters such as C/LC filters. These additional components reduce the power density. In addition, to operate an SRC as a DCX, a small resonant inductance is desired to reduce the voltage gain variation and achieve a faster transient response. To resolve these problems, a SRC with embedded filters is studied. Adding a clamping capacitor between split transformers not only significantly reduces current ripples and the harmonic components of the input/output currents but also connects resonant inductors in parallel to reduce the equivalent resonant inductance. In addition, dividing the resonant current into two split windings reduces the RMS current of the transformer. This paper presents a detailed analysis, a design methodology, and a comprehensive comparison with the conventional half-bridge CLLC converter with C/LC filters. 1-kW prototypes with a 600-V input voltage and 200-V output voltage demonstrate the superiority of the proposed converter; the second harmonic of the output current was significantly suppressed by 19.3 dB compared with that of the conventional converter with the same power density. The loss breakdown showed the proposed converter mitigated copper loss by 9.47% and eliminated the losses of the filter and DC-link capacitors. The prototype of the proposed converter had the highest efficiency of 95.4% at full-load among prototypes.

External Magnetic Field Minimization for the Integrated Magnetics in Series Resonant Converter

The resonant dc–dc converter is preferred for high-efficiency applications due to its less switching loss and better electromagnetic interference (EMI) characteristics. However, in a wide range of steady-state voltage gain applications, such as the on-board charger application, the wide output voltage range will lead to a bulky resonant inductor, which will decrease the power density. Magnetic integration of the inductor and transformer is an effective way to reduce the total magnetic volume. However, the traditional integrated magnetics of transformer and inductor will result in high magnetic field intensity in the external space nearby the integrated magnetic component. This external magnetic field will cause large eddy current losses in the neighboring metal heatsink and serious EMI issues. In order to deal with this problem, an integrated winding structure with a negligible external magnetic field is proposed in this article. By rebuilding the external winding segments with a better coupling coefficient, the external magnetic field intensity is canceled without efficiency and size sacrifices. Detailed analysis and design procedures of the proposed structure are presented. A 6.6-kW dc–dc prototype is built to verify the cancelation effect of the magnetic field intensity in the neighboring external space.

High-Performance Buck-Boost Partial Power Quasi-Z-Source Series Resonance Converter

Power converters are essential components of renewable energy systems. The converter efficiency decides the overall system efficiency. In a full power converter, its components process the whole input power, even if it is not mandatory. Partial power processing (PPP) is an exciting concept for improving overall system efficiency and reducing system cost and size. In PPP, the converter processes the amount of power needed to be processed. This work proposes a PPP based on the high-performance Quasi-Z-Source Series Resonance converter (QZSSRC). The proposed partial power converter belongs to the series input parallel output (SIPO) architecture. Previous publications in this area mainly consider converters with step-down voltage regulation, like the phase-shifted full-bridge converter. They underperform in this application due to operating at the maximum power when bucking the voltage the most. This paper studies two other types of dc-dc converters, buck-boost and boost, in SIPO partial power converters. Theoretical operation principles are corroborated with full experimental results given and analyzed. A 300 W prototype of the QZSSRC is used to convert the power of up to 2 kW in a PPP system with overall system efficiency values of over 99%.

Reliability Evaluation of Isolated Buck-Boost DC-DC Series Resonant Converter

This paper investigates the reliability of an isolated buck-boost DC-DC converter (IBBC) based on the configuration of a series resonant converter (SRC). Two approaches are employed to predict the IBBC reliability, which are based on the MIL-HDBK-217F handbook and FIDES guide. The latter approach can take into account how the failure rate of the converter components based on the physics of failure is influenced by a varying yearly mission profile. To do this, the thermal loading of each IBBC component is obtained, taking into account the photovoltaic (PV) mission profile of the solar irradiance and ambient temperature. In such a case, the PV module is operating at the maximum power point (MPP) and the IBBC transfers this power into the DC microgrid (MG). Second, the component-level failure rate is calculated with both reliability assessment approaches, to evaluate the converter-level failure rate. Therefore, the converter reliability can be defined while taking the serial reliability connection of the converter components into account. The reliability analysis is carried out using a cloud Python engine installed and running in a Google Colaboratory notebook. The results indicate that the primary semiconductors are the most vulnerable component in the IBBC. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B_{10}$</tex-math></inline-formula> lifetime of the case-study IBBC calculated using the MIL-HDBK-217F and FIDES approaches is 14.80 and 23.20 years, respectively. This indicates that, when compared to the methodology from the MIL-HDBK-217F handbook, the approach from the FIDES guide can provide a more accurate prediction for the IBBC lifespan considering the real field mission profile.

Modular Bidirectional Differential Converter With Series Parallel Connected Output for Ultra-Wide-Voltage Applications: Control, Module Shedding, and Fail-Safe Operation

In this article, a modular output series-parallel series resonant converter (SRC) differential buck converter is analyzed for high-power, ultra-wide-voltage applications such as battery formation systems and bench-type power supplies where a zero voltage discharging function is required. An independent control method in one module is proposed to increase the efficiency of the converter compared to the conventional complementary control method. In the modular output-series connection, higher efficiency can be achieved by shedding needless modules in the low voltage range. Module shedding and activating techniques are proposed to eliminate current and voltage transients during a mode change under any load condition without the use of additional bypass switches. In addition, when a fault occurs in one module, its effect on the other module is analyzed. A practical solution involving turn- off processes for fail-safe operation is proposed, which reduces current stress and voltage spikes on devices and effect among modules without depending on the external signal from the central controller and the communication delay. A prototype of a modular series-parallel SRC- differential buck converter is implemented to verify the proposed concept.

Three-Port Series-Resonant DC/DC Converter for Automotive Charging Applications

In the energy distribution grid of electric vehicles (EVs), multiple different voltage potentials need to be interconnected, to allow arbitrary power flow between the various energy sources and the different electrical loads. However, between the different potentials, galvanic isolation is absolutely necessary, either due to safety reasons and/or due to different grounding schemes. This paper presents an isolated three-port DC/DC converter topology, which, in combination with an upstream PFC rectifier, can be used as combined EV charger for interconnecting the single-phase AC mains, the high-voltage (HV) battery and the low-voltage (LV) bus in EVs. The proposed topology comprises two synergetically controlled and magnetically coupled converter parts, namely, a series-resonant converter between the PFC-sided DC-link capacitor and the HV battery, as well as a phase-shifted full-bridge circuit equivalent in the LV port, and is mainly characterized by simplicity in terms of control and circuit complexity. For this converter, a simple soft switching modulation scheme is proposed and comprehensively analyzed, in consideration of all parasitic components of a real converter implementation. Based on this analysis, the design of a 3.6 kW, 500 V/500 V/15 V prototype is discussed, striving for the highest possible power density and as low as possible manufacturing costs, by using PCB-integrated windings for all magnetic components. The hardware demonstrator achieves a measured full-load efficiency in charge mode of 96.5% for nominal operating conditions and a power density of 16.4 kWL−1.

Current-Fed LC Series Resonant Converter With Load-Independent Voltage-Gain Characteristics for Wide Voltage Range Applications

This article proposes a current-fed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant converter, which integrates a two-phase interleaved boost circuit with a full-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant converter. All switches can achieve zero voltage switching (ZVS) under full load range without utilizing a magnetizing inductor or an auxiliary inductor, and synchronous rectification (SR) can be realized without SR driving detection. With the proposed modulation, the resonant current is discontinuous without circulating current. Moreover, the voltage gain of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant conversion is fixed, which is independent of load; therefore, the design of voltage regulation range and related parameters can be simplified. The integrated boost circuit works in the critical current mode to achieve ZVS for all the switches. Meanwhile, digital adaptive frequency modulation is presented to ensure ZVS realization and to minimize the boost inductor current ripple. The working characteristics and design considerations for the key parameters of the proposed modulation are also presented in detail in this article. Finally, a 600-W prototype with 27–54 V input and 360 V output is built, and experimental results validate the effectiveness and the advantages of the proposed solution.

Improved topology of three-phase series resonant DC-DC boost converter with variable frequency control

This paper proposes an improved topology of the three-phase series resonant DC-DC Boost converter with variable frequency control. The DC output voltage can be properly regulated at a constant value from no-load condition to full-load condition by adjusting the switching frequency. This is feasible with the three series resonant circuits coupled to the three-phase inverter. The leakage and mutual inductances of the step-up transformer are used implicitly in the series resonant circuits. Therefore, the proposed converter, when matched to the traditional three-phase inter-leaved LLC converters, requires fewer transformers, passive components, and switching devices. Furthermore, it offers better efficiency and size reduction. The proposed SRC converter also relies on the transformer’s magnetizing inductance to ensure zero voltage switching (ZVS) for all the switches within the considered range of the operating frequency. The deployed variable frequency controller shows a good level of stability at the considered loading conditions. The output voltage-to-input voltage ratio is steadily regulated at 6:1, irrespective of the load variation, by varying the switching frequency. The experimental validation of the theoretical findings proceeded on a low power scaled-down laboratory prototype. From the achieved results, the performance of the proposed converter (in terms of its effectiveness) was validated.

Modeling and Verification of the State Space Equation for an Isolated Series Resonant Converter

Modeling and Verification of the State Space Equation for an Isolated Series Resonant Converter

Comparison of Control Techniques for Series Resonant Converter

There are many different derivatives of the variable and fixed frequency switching control techniques used in the control of load resonant converters. In this study; among these techniques frequency modulation (FM), phase shift modulation (PSM) and pulse density modulation (PDM) are applied separately to series resonant converter (SRC). The techniques are examined and compared in many respects. An experimental setup was built, which consists of a 400W converter (with the input voltage of 200 V and the output voltage of 36V), a control circuit and a resistive load to verify the theoretical studies. The converter is controlled by FM, PSM and PDM separately for 120 kHz basic operating frequency and different output currents. The experimental results are compared in terms of efficiency, output voltage ripple, soft switching, switch voltage and ease of application and hardware. The comparison results are presented. It is observed that FM has better performance than the other two techniques in many aspects.

Improved hybrid fixed-frequency modulation strategy for series resonant converters for wide range applications

Improved hybrid fixed-frequency modulation strategy for series resonant converters for wide range applications

Nonlinear Implementable Control of a Dual Active Bridge Series Resonant Converter

This article presents a novel control strategy for a dual active bridge series resonant converter. The strategy seeks to ensure the stability of the converter over its entire dynamic range while enhances the transient response. Both properties allow the use of the converter in new applications, where fast dynamics are required, surpassing the performance of existing feedback loops. Starting from the generalized averaged model of the converter, we propose a nonlinear control strategy by means of Lyapunov's stability theory. After that, we derive a series of modifications in order to implement the strategy in a microcontroller or a DSP, including a sensorless method to tackle the lack of measurements of certain variables and an adaptive control law to deal with uncertain parameters in the model. The strategy is evaluated in simulations and experiments, employing a commercial converter, and comparing the results with other control policies.

Interleaved LLC half-bridge series resonant converter with integrated transformer

ABSTRACT High efficiency and simple structure are the main reasons for the widespread use of LLC converters. Nowadays, the application of LLC converters is still in development. In general, increasing the power level to use a parallel converter is quite popular. However, this method uses a separate transformer, which will lead to an obvious decrease in power density. Moreover, the separate transformer will also cause current imbalance due to the error of the magnetic material characteristic. Therefore, this study proposes an integrated transformer for a conventional interleaved LLC converter. This proposed structure can effectively increase the power density and decrease the problem of current imbalance. The operating principle of the interleaved LLC converter and an analysis of the integrated transformer are presented. Finally, experimental results are recorded for a prototype converter. The specifications are as follows: DC input voltage is 380 VDC, output voltage is 12 VDC, maximum output current is 50 A, output power is 600 W, and maximum conversion efficiency is approximately 95.5%.

Current Sharing Control of an Interleaved Three-Phase Series-Resonant Converter with Phase Shift Modulation

Recently, three-phase series-resonant converters (SRCs) have been proposed for high power applications. Three-phase SRCs can achieve zero-voltage-switching (ZVS) of the primary power switches and regulate the output voltage by pulse-frequency modulation. The interleaving technique is also a conventional method for DC-DC converters to achieve a high power level, reducing the output voltage ripples due to operating out of phase at the same frequency between the two converters. However, an interleaved three-phase SRC cannot easily synchronize switching instants between the two modules due to the component tolerances of circuits. In the proposed control method, phase shift modulation (PSM) is used to solve the output current imbalance caused by component tolerances. The power switches of the converter can also maintain synchronizing switching instants between the two modules. Therefore, the lower output voltage ripple can be achieved. A detailed analysis and design of this new control method for interleaved three-phase SRCs are described. Finally, prototype converters with a 2.4 kW total output were built and successfully tested to verify the feasibility of the current sharing modulation.

PWM-Controlled Series Resonant Converter for Universal Electric Vehicle Charger

This article presents a pulsewidth modulation (PWM) controlled series resonant converter (SRC) for a universal EV charger. This article focuses on the boost mode of a SRC. By adapting two PWM boost switches with a full bridge rectifier, it is possible for a SRC to cover a very wide range of gain with a high and flat efficiency curve. As the output voltage increases, the secondary side rectifier of the proposed converter gradually converts from a full bridge rectifier to a voltage doubler rectifier. Since the switching frequency is fixed to the resonant frequency in boost mode, the proposed converter naturally achieves “two peak efficiency points” with full bridge and voltage doubler rectifiers. Two peak efficiency points limit the efficiency drop over a wide range of gain, and that is the reason the proposed converter achieves a high and flat efficiency curve. The effectiveness of the proposed converter and control has been verified on an 800 V input and 200-950 V/3.3 kW output prototype.

A Cost-Reliability Trade-Off Fault-Tolerant Series-Resonant Converter Combining Redundancy and Reconstruction

Adding redundant converters or switches are two common strategies to achieve fault-tolerant operation of converters. The former one is straightforward but costly, while the latter one is cost-effective but with sacrifice on the reliability as it only works for switches’ failure. Aiming to achieve a good trade-off between cost and reliability, a novel fault-tolerant full-bridge series-resonant converter (FB-SRC) which only needs a redundant half-bridge SRC (HB-SRC) to gain fault tolerance for all fault-prone components is proposed in this article. The proposed converter can keep working normally when short-circuit fault or open-circuit fault happens on switches, diodes, or the output filter capacitor. After fault occurs, the redundant HB-SRC converter will combine the remaining healthy part of original FB-SRC to reconstruct an input-parallel and output-series dual HB-SRC, which can maintain the rated output power with reduced cost. In the article, component's reliability of SRC is first analyzed. Then, operation and performance analysis of the proposed fault-tolerant converter is introduced in detail. As the voltage/current stresses of components are almost the same during the prefault and postfault operation, the converter design is simple. Finally, experimental results of a 500 W prototype are also given to verify the effectiveness.

Isolated Soft Switching Current Fed Series LC Resonant DC-DC Convertor for Electrical Vehicle Application

The current fed series resonant converter for electrical vehicle application is offered in this paper. The converter is able to achieve ZVS for primary side semiconductor switches. In the overlap time of voltage and current at zero crossing series resonant tank circuit is gives short interval of resonant pulse. This resonant pulse provide natural voltage decrease for semiconductor switches and voltage pulse is zero earlier compare to current across switches and ZVS achieve for semiconductor switches. All devices turn off softly so dependency on snubber is decreased to clamp the voltage across the switches. Presented converter reduce the circulating current so switching losses is decreased and converter efficiency will improvise. The proposed converter is simulated in MATLAB Simulink environment to investigate and analyses the proposed converter.

Wide Range Series Resonant DC-DC Converter with a Reduced Component Count and Capacitor Voltage Stress for Distributed Generation

This paper proposes a galvanically isolated dc-dc converter that can regulate the input voltage in a wide range. It is based on the series resonance dc-dc converter (SRC) topology and a novel boost rectifier. The proposed topology has a smaller number of semiconductors than its SRC-based existing topologies employing an ac-switch in the boost rectifier. The proposed dc-dc converter comprises only two diodes and one switch at the output side, while the existing solutions use two switches and two diodes to step up the voltage. The proposed converter boosts the input voltage within a single boosting interval in the positive half-cycle of the switching period. In addition, the resonant current in the negative half-cycle is sinusoidal, which could enhance the converter efficiency. The resonant capacitor voltage is clamped at the level of the output voltage. Therefore, the voltage stress of the capacitor could significantly reduce at various input voltage and power levels. This makes it perfect for distributed generation applications such as photovoltaics with wide variations of input voltage and power. The converter operates at the fixed switching frequency close to the resonance frequency to obtain the maximum efficiency at the nominal input voltage. The zero-voltage switching (ZVS) feature is achieved in the primary semiconductors, while the diodes in the output-side rectifier turn off at nearly zero current switching. The mathematical model and design guidelines of the proposed converter are discussed in the paper. The experimental results confirmed the theoretical analysis based on a 300 W prototype. The maximum efficiency of the converter was 96.8% at the nominal input voltage, and the converter has achieved a wider input voltage regulation range than that with the boosting cell comprising an ac-switch.