DC Converter with Wide Soft Switching Operation, Wide Input Voltage and Low Current Ripple

LLC converters are attractive with their ability of enable to achieve soft switching, but there is a trade-off between voltage gain and efficiency in wide voltage regulation range applications. In this paper, a novel hybrid LLC and full-bridge (FB) converter is proposed for wide voltage gain applications. The converter consists of a half bridge (HB) LLC resonant converter and a switch-off current-clamp FB converter connected in parallel. The turn-off current of the LLC converter over the entire range is significantly reduced through the clamping operation of the FB converter. Consequently, all primary-side switches of LLC converter achieve zero-voltage switching-on (ZVS) and low-current switching-off (LCS), while secondary-side diodes achieve zero-current switching-off (ZCS), leading to a substantial reduction in switching losses. Furthermore, a smooth transition variable-frequency plus phase-shift control strategy is proposed to achieve wide-range of voltage regulation. The proposed control has three operation modes: variable-frequency with a shift angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> is 0 mode, phase-shift mode, and variable-frequency with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula>. These modes cover the low, medium, and high voltage gain ranges, respectively. A 7.5 kW-rated experimental prototype is designed to convert a 400 V input to a 150-750 V wide output. The prototype demonstrates a peak efficiency of 98.04% and maintains an efficiency of over 93.8% from 30% load to full load across the 150-750 V output range.

This work has adopted the concept of asymmetric inductor magnetization to develop a new quadratic converter with the advantages like a wide range quadratic voltage gain and low source current ripple. In addition, the proposed high quadratic converter has achieved reduced voltage stress due to the presence of switched capacitor cell at the output side. Initially, the operation of the converter and steady-state analysis, including efficiency calculations, are explained. In addition, the design and selection of converter components are presented along with a small-signal analysis. Further, a comprehensive comparison with recent high quadratic gain converters is presented. The comparison is made with regard to the total component count, voltage conversion ratio, effectiveness index, electric stress, current ripple, switching device power (SDP) rating, and input current ripple factor. Furthermore, the 150 W laboratory prototype is used to verify the performance of the proposed converter in terms of operation, dynamic response, and efficiency, and the corresponding experimental findings are reported. The wide range voltage gain, low current ripple, and low electric stress features of the proposed converter highlight its superiority in fuel cell electric vehicle applications.

In this study, a parallel inductor-inductor-capacitor (LLC) resonant converter series-connected on the primary side and parallel-connected on the secondary side is presented for server power supply systems. Based on series resonant behaviour, the power metal-oxide-semiconductor field-effect transistors are turned on at zero voltage switching and the rectifier diodes are turned off at zero current switching. Thus, the switching losses on the power semiconductors are reduced. In the proposed converter, the primary windings of the two LLC converters are connected in series. Thus, the two converters have the same primary currents to ensure that they can supply the balance load current. On the output side, two LLC converters are connected in parallel to share the load current and to reduce the current stress on the secondary windings and the rectifier diodes. In this article, the principle of operation, steady-state analysis and design considerations of the proposed converter are provided and discussed. Experiments with a laboratory prototype with a 24 V/21 A output for server power supply were performed to verify the effectiveness of the proposed converter.

A parallel LLC resonant converter with series-connected in primary side and parallel-connected in secondary side is presented for server power supply systems. Based on the series resonant behavior, the power MOSFETs are turned on at zero voltage switching (ZVS) and the rectifier diodes are turned off at zero current switching (ZCS). Thus the switching losses on power semiconductors are reduced. In the proposed converter, the primary windings of two LLC converters are connected in series. Thus two converters have the same primary currents to ensure that two converters can supply the balance load current. In the output side of two LLC converters are connected in parallel to share the load current and to reduce the current stresses on the secondary windings and the rectifier diodes. In this paper, the principle of operation, steady state analysis and design consideration of the proposed converter are provided and discussed. Experiments with a laboratory prototype with 24V/21A output for server power supply were provided to verify the effectiveness of the proposed converter.

In this article, we propose a current-fed bidirectional resonant converter that has minimal switching loss over a wide voltage gain range. The proposed bidirectional resonant converter employs a double current-fed structure at the low-voltage side and an active voltage doubler with a bidirectional switch at the high-voltage side.The converter operates as a pulsewidth-modulation (PWM) double current-fed resonant converter in the forward mode and a PWM half-bridge resonant converter in the backward mode. By incorporating a bidirectional switch across center nodes of the active voltage doubler, the converter achieves almost zero-voltage switching at the turn-off instant, thereby, incurring little switching loss at all active switches. The proposed topology exhibits a high conversion ratio with low transformer turns-ratio and a low current ripple at the low-voltage side. The operating principles and theoretical derivations of the converter are discussed in detail. The performance of the proposed bidirectional converter are verified using a prototype that has 48-72-V low voltage, 380-V high voltage, and 1-kW output power.

Photovoltaic (PV) systems with integrated energy storage units traditionally have been complex and required multiple DC-DC converters. In this paper, a novel multiport isolated LLC resonant converter and a modified maximum power point tracking (MMPPT) control method are introduced to reduce complexity. The proposed topology is designed to operate under a wide input voltage range and contains an integrated bidirectional pulse width modulation (PWM) converter and a LLC resonant converter. Frequency modulation control is implemented for regulating the output voltage of the whole system while the PWM converter is controlled by the MMPPT which generates the battery current reference and PI controller. MATLAB/Simulink was used to demonstrate the feasibility of the topology.

A new class of hybrid soft-switching dc-dc converters combining a half-bridge LLC converter and a full-bridge phase-shift modulated converter is proposed for electric vehicle (EV) on-board charger applications. The hybridization allows the converter operating under soft-switching condition in a wide input and output voltage range and from true zero to full load condition. It not only eliminates possible MOSFET damage due to hard-switching under high-voltage low-current condition, but also minimizes the duty cycle loss and circulating current induced conduction loss. The entire on-board charger consists of a power factor correction (PFC) stage and a hybrid dc-dc converter. Both conventional boost and bridgeless PFC converters were implemented to incorporate the proposed hybrid dc-dc converter for a 6.6 kW on-board charger. Hardware prototypes have been designed, fabricated and tested to verify the validity and performance of the proposed circuit. Experimental results show that the proposed topology is attractive for EV onboard charger applications as the design has demonstrated a peak efficiency of 98.4% for the dc-dc stage and 96.1% for the entire on-board charger. The prototype on-board charger has been installed in an EV for field testing.

The inductor inductor capacitor (LLC) resonant topology has become more popular for deployment in high power density and high-efficiency power converter applications due to its ability to maintain zero voltage switching (ZVS) over a wider input voltage range. Due to their ease of operation and acceptable accuracy, frequency domain-related analytical methods using fundamental harmonic approximation (FHA) have been frequently utilized for resonant converters. However, when the switching frequency is far from the resonant frequency, the circuit currents contain a large number of harmonics, which cannot be ignored. Therefore, the FHA is incapable of guiding the design when the LLC converter is used to operate in a wide input voltage range applications due to its inaccuracy. As a result, a precise LLC converter model is needed. Time domain analysis is a precise analytical approach for obtaining converter attributes, which supports in the optimal sizing of LLC converters. This work strives to give a precise and an approximation-free time domain analysis for the exact modeling of high-frequency resonant converters. A complete mathematical analysis for an LLC resonant converter operating in discontinuous conduction mode (DCM)—i.e., the boost mode of operation below resonance—is presented in this paper. The proposed technique can confirm that the converter operates in PO mode throughout its working range; in addition, for primary MOSFET switches, it guarantees the ZVS and zero current switching (ZCS) for the secondary rectifier. As a function of frequency, load, and other circuit parameters, closed-form solutions are developed for the converter’s tank root mean square (RMS) current, peak stress, tank capacitor voltage, voltage gain, and zero voltage switching angle. Finally, an 8 KW LLC resonant converter is built in the hardware-in-loop (HIL) testing method on RT-LAB OP-5700 to endorse the theoretical study.

This paper proposes a new zero-current switching (ZCS) pulse width modulation (PWM) switch cell that has no additional conduction loss of the main switch. In this cell, the main switch and the auxiliary switch turn on and turn off under zero current condition. The diodes commutate softly and the reverse recovery problems are alleviated. The conduction loss and the current stress of the main switch are minimized, since the resonating current for the soft switching does not flow through the main switch. Based on the proposed ZCS PWM switch cell, a new family of DC to DC PWM power converters is derived. The new family of ZCS PWM converters is suitable for the high power applications employing IGBTs. Among the new family of DC to DC PWM converters, a boost converter was taken as an example and has been analyzed. Design guidelines with a design example are described and verified by experimental results from the 2.5 kW prototype boost converter operating at 40 kHz.

In this work, a medium and high power rating electric vehicle (EV) charger based on Vienna rectifier (VR) and half bridge resonant inductor-inductor-capacitor (LLC) converter, is presented. The two switch VR forms the front-end converter, and performs active power factor correction (PFC), by operating under continuous conduction mode (CCM). Moreover, its output voltage is regulated by an outer voltage control loop, in a two loop pulse width modulated (PWM) control. The EV battery is charged using constant voltage (CV) and constant current (CC) controller by a pulse frequency modulation (PFM) based half bridge LLC converter. The DC-DC conversion stage of this charger is soft switched due to zero voltage switching in LLC converter. Simulation results and its performance under steady state and dynamic conditions, are presented. Moreover, the power quality (PQ) and steady state results are verified and presented for a 5.6kW experimental prototype.

The drive to reduce the charging time and energy loss in electric vehicles (EVs) has led to increasing battery voltages to 800 V, 1000 V, 1.25 kV, and 1.5 kV, posing new challenges for designing EV fast chargers, especially for heavy-duty EVs. Two-stage converters, comprising isolated and regulated dc-dc stages, are emerging for their superior performance. This article proposes a novel two-stage bidirectional dc-dc converter with an extremely wide operating voltage range. The design features a dual-transformer reconfigurable three-leg converter (DTR3LC) in the first stage, an interleaved reconfigurable buck converter (IRBC) in the second stage, and four auxiliary switches for reconfiguration. These switches enable the secondary side of the DTR3LC to switch between parallel and series connections, which are then regulated by the IRBC, resulting in high efficiency and low current ripple across a wide voltage range. A 1-kW scaled-down laboratory experimental setup was developed and tested with an input voltage of 80 V to charge EV batteries ranging from 15 to 150 V, achieving a maximum efficiency of 95.32% at 150 V.

A number of soft-switching pulse-width-modulated (PWM) converter techniques have been proposed, aimed at combining the desirable features of both the conventional PWM and resonant converters while avoiding their respective limitations. In this paper, three classes of zero-voltage soft-switching PWM converters (namely the zero-voltage switched (ZVS) quasi-square-wave converters, ZVS-PWM converters, and zero-voltage-transition PWM converters) and two classes of zero-current soft-switching PWM converters (namely the zero-current-switched PWM converters and zero-current-transition PWM converters) are reviewed; their merits and limitations are assessed. Experimental results of several prototype of converters are presented to illustrate each class of converter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The search for a cost feasible, optimal design of LLC converter for wide input voltage range conditions is inhibited by errors in steady state values of peak gain, tank current, tank voltage, active power etc., due to various approximations in the analysis. This leads to erroneous selection of circuit parameters. The present work provides an exact, approximation free time domain mathematical model of LLC converter operating in transformer secondary current discontinuous mode (DCM) below resonance in boost mode. The proposed approach defines voltage gain as a function of relative switching frequency ω and t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> , which represents the rectifier diode to switch conduction ratio for DCM operation. Existing works have defined voltage gain as an explicit function of quality factor (Q) and ω. The current approach leads to accurate derivation of converter voltage gain, tank RMS current, tank capacitor voltage, zero voltage switching (ZVS) angle etc. Analytical expressions are validated with simulation studies using PSIM for various inductor ratio values. A final design is verified on an experimental prototype of 320W output LLC converter designed for an input range of 20-40V for solar PV applications.

This paper proposes an iterative design procedure for a high-power LLC resonant converter, taking part in a 60 kW modular DC/DC conversion stage for an electric vehicle (EV) ultra-fast battery charger. The basics of operation of the LLC converter are briefly recalled and the most relevant analytical expressions are reported. Due to the high-power requirement and the wide output battery voltage range (i.e. 250-1000 V), a modular design approach is adopted, leveraging the split input DC-link structure provided by a 3-level active front-end. A total of four modules, with at 15 kW nominal power and a 250-500 V output voltage regulation capability, are designed with a straightforward iterative procedure based on the first-harmonic approximation (FHA). Finally, the proposed methodology is verified experimentally on a 15 kW LLC converter prototype directly resulting from the design procedure.

In this paper keeping position and zero torque (KP-ZT) control of switched reluctance motor (SRM) drives is proposed to avoid any movement when used for charging reactor in electric vehicles. A sliding mode position control technique as an outer loop and zero torque control method as an inner loop are used to attain this. Whereas, power factor correction (PFC) and voltage regulation is achieved with buck type integrated SRM drive by conventional boost converter for wide input and output voltage range. In this two stage PFC topology, multi-phase SRM drive operates as a high power interleaved buck converter to reduce cost, size, weight, and volume of battery charger with high reliability, improved power quality and low battery current ripple. Then, In order to implement the proposed ZT control, an online method is proposed to calculate current reference in each phase with regarding to zero torque condition. Finally, Lagrange optimization method is used for copper loss minimization during battery charging and results are compared with the case of using an extra clutch to let the motor to move.