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In a magnetic bearing system, the levitation coils or electromagnets must be driven by an amplifier in order to control their currents for levitation stability. This amplifier typically drives every coil individually with hard-switching H-bridges. However, the inherent high dv/dt of hard-switching in conjunction with the large parasitic capacitance of magnetic bearing coils typically results in high current spikes and severe ringing in the switching process, which may interfere with position sensors and system communication. Furthermore, driving each coil individually requires a large number of switches. In this brief, a switch sharing zero-voltage-switching (ZVS) multichannel switching amplifier topology is proposed, which not only reduces the number of switches needed when driving multiple coils, but also eliminates current spikes and reduces the switching loss of the magnetic bearing amplifier. The proposed topology is experimentally tested to validate expected benefits.

In inductive power transfer systems, impedance matching is critical in obtaining high efficiency. However, since the load impedance is subject to variations in most applications, especially wireless charging, maintaining impedance matching is a challenge. One valid solution is to maintain the equivalent load impedance at the optimal value against load variations by controlling a load-side power converter. Nonetheless, the system overall cost, size, and complexity can be increased. In this article, based on a proper selection between full-bridge and half-bridge modes of the inverter and rectifier, an operation mode selection method is proposed that can achieve semi-impedance-matching with large load variations. In general, with the proposed method, high overall efficiency can be obtained while neither additional power converters nor complicated control is required. A 1-kW prototype has been developed and the experimental results have verified the proposed method.

The power loop stray inductances of the silicon carbide (SiC) half-bridge power module (HBPM) must be included in the circuit simulation model to predict the power device switching characteristics and the power bus noise caused by the power converter. Instead of a full equivalent circuit model of the SiC HBPM, a simplified but accurate three-terminal equivalent circuit model is presented in this article. Based on the simplified model, a novel frequency-domain impedance measurement method based on the two-port network technique is proposed to extract the power loop inductances through direct measurement. By using the extracted power loop inductances of a 1.2-kV 300-A SiC HBPM, a three-terminal equivalent model of the HBPM is obtained, and its accuracy is validated by the finite element method and experiments.

Conventional critical conduction mode (CRM) control for many boost-derived power factor correction (PFC) circuits forms triangular inductor current. For three-level boost (TLB) converter, the conventional method is unattractive because losses increase but waveform quality remains unchanged, compared to other topologies. In order to obtain higher efficiency and improved waveform qualities, this article focuses on the distinctive structure of TLB and its inherent degree-of-freedom (DOF) in current-slope shaping. Based on the DOF, a new CRM control for TLB PFC is proposed and analyzed. Detailed design and digital implementation method are also provided. Different from conventional methods, the proposed CRM control divides each switching cycle into three parts including common on -time of two switches, additional on -time of one switch and common off -time. Accordingly, TLB inductor current is synthesized in quadrangular forms. The analyses and experimental results confirm that switching frequency and peak input current of TLB can be reduced by the proposed control. Due to the reductions, efficiency, total harmonic distortion, and quality of input current are improved with practically unchanged power factor.

Magnetic characteristics of a switched reluctance motor (SRM) determine the modeling accuracy, the performance of a position sensorless control, and the torque ripple reduction control. Due to double saliency structure and core saturation, the magnetic characteristics of SRM is dependent on both the rotor position and the winding current amplitude, which makes it difficult to measure the actual incremental inductance or flux linkage. This article presents the magnetic characteristics identification method. A quad current sampling technique is proposed to capture the derivative of the winding current at a specific rotor position and current amplitude. The flux linkage, co-energy, and torque are calculated from the obtained incremental inductance profile. The proposed method can be easily implemented on digital signal processor–based SRM drive without any extra circuit. The LCR meter and torque sensor measurements are provided to validate the proposed incremental inductance measurement method.

In this article, an optimal design procedure of shunt RC damped LCL filter is discussed. The proposed design procedure finds the minimum damping resistance to guarantee the stability of the grid-current controller without affecting the effectiveness of the filter. This minimum value is derived using the factorized filter input admittance and filter forward transadmittance. The proposed factorization procedure allows us to have an analytical expression of system poles and zeros. Moreover, the minimum damping resistor is determined upon the desired crossover frequency and the desired phase margin of the grid-current controller. After that, an objective function is assumed, and an optimization problem is formulated to minimize the physical size of the filter by minimizing the total capacitance and inductance and by minimizing the filter ripple content as well. Accordingly, the proposed objective function minimizes the filter physical size and filter power losses and, hence, enhances filter's efficiency. A prototype demonstrates and validates the proposed filter design and analysis experimentally.

Pseudo-dc-link inverters are promising due to the single-stage configuration. The inverters can be isolated by high-frequency transformers, which also provide the freedom of step-up/down through winding turns ratio. Conventionally, a pseudo-dc-link inverter is based upon a pulsewidth modulation converter like flyback converter, but the accompanying switching losses can degrade efficiency and overall system performance. Alternatively, resonant converters (e.g., series resonant converter) seem to fit the need as they typically display soft-switching characteristics. However, the relevant research results are scarce because of two main reasons: high resonant current and limited soft-switching range. To overcome the difficulties, a hybrid modulation method is proposed in this article for a pseudo-dc-link inverter based on series resonant converter. In high-line region, the inverter operates with variable-frequency modulation, which leads to zero-voltage switching and relatively low-resonant current. In low-line region, the inverter operates with a short-pulse density modulation so that switching losses are greatly curtailed without excessive resonant current. The merits in both regions together contribute toward the high efficiency of the inverter. This article presents the operational principle of the proposed modulation as well as a comparison with other modulation methods. In addition, a 400 V–230 V ac, 2-kW prototype was built to verify the proposed modulation and the peak efficiency reaches 98.0%.

Pad misalignments are almost inevitable in most inductive power transfer (IPT) systems. It tends to cause parameter variations and, thus, significantly affects the performance of the IPT system. In this article, a hybrid IPT system with misalignment tolerance using the quadruple-D quadrature pads (QDQPs) is proposed to tolerate the x , y , z , and diagonal misalignments with load-independent output voltage, simplifying or even canceling control schemes. Besides, the proposed approach can restrict the increase of the primary current when the secondary side moves out of the operating region. Moreover, a new parametric design method is presented according to the misalignment characteristics of QDQPs. The method can limit the output voltage fluctuation to a certain range, given a predetermined misalignment distance. A 3.5-kW prototype was built to verify the proposed hybrid IPT system. The primary and secondary coil sizes are 400 mm × 400 mm, and the air gap is 150 mm. Experimental results demonstrate that the proposed hybrid system can tolerate −150 to +150 mm x -misalignment, −150 to +150 mm y -misalignment, −20 to +35 mm z -misalignment, and −100 to +100 mm diagonal misalignment with load-independent output voltage. Within the predetermined misalignment range, the output voltage fluctuation is less than 5%.

This paper presents a bridgeless Cuk-derived single power conversion inverter with reduced number of power components, which has reactive-power capability. The secondary diode of the conventional unfolding-type Cuk inverter is integrated into one of the secondary-side switches in the bridgeless Cuk-derived configuration, which reduces the number of active-power components. A modulation technique is developed to provide a current path during reverse power flow; this technique enables operations under unity and nonunity power factors. A repetitive controller coupled with a linear feedback controller and a feed-forward controller are used to achieve accurate output current tracking under the harsh control environment. Driving the diode-integrated switch in synchronous rectification mode provides higher power conversion efficiency than that under diode-based secondary side rectification. Circuit operation and design guidelines of the bridgeless Cuk inverter are presented in detail. A 500-VA prototype inverter was fabricated to demonstrate the desirable performance of the bridgeless Cuk-derived inverter.

In the no-load condition, LLC converter usually fails to regulate its output voltage although it operates at a high switching frequency. Till now, it is hard to obtain the exact relationship between design parameters and the maximum switching frequency for no-load regulation capability. In this paper, a specific criterion for no-load regulation of LLC converter is provided, without using active components or other modulation schemes. By analyzing the macroscopic switching period and microscopic switching transition in the no-load condition, it is shown that not only the peaking resonant current during the switching transition, but also the resonant tank design affect the no-load regulation of the LLC converter, which affects the no-load regulation capability. Furthermore, the relationship among design parameters is analyzed and the design guideline is also provided to achieve no-load regulation at the specified maximum switching frequency. To verify the effectiveness of the proposed design, 400 V input and 50 V/200 W output prototype is built and tested.

In photovoltaic applications, many previous research works have focused on pulsewidth modulation (PWM) resonant converters in order to achieve a high efficiency with a wide input voltage range. Conventional approaches utilized symmetric boosting modulation at the secondary side rectifier to obtain a symmetric operation, and they utilized two boosting modes in a switching period. Among various rectifier structures, the voltage doubler structure has a strong advantage due to a small number of components. However, it suffers from serious hard switching losses in the secondary side rectifier. In this paper, a new converter with a novel asymmetrical modulation is proposed and verified. The strong point of the proposed converter is that it eliminates hard switching turn- on losses from the rectifier, while maintaining the minimized number of components. Although the proposed converter adopts an asymmetric modulation, the offset current on the transformer becomes zero inherently. Furthermore, a “forced half resonance” operation of the proposed converter keeps rms current stresses at the same level as conventional converter although it has a higher peak current. Accordingly, the proposed converter achieves a superior efficiency with the minimum number of components at 35–25 V input and 380 V/300 W output specification.

The increasing usage of LLC-type dc-dc converters in utility, automotive, and power distribution applications has led to a push for a further increase in the converter's operating load range and efficiency. The secondary-side rectifier remains one of the lossiest areas in the converter, alluring designers to synchronous rectification (SR). One method is drain-source SR for cyclically adaptive, closed loop SR. However, when utilized, a severe current oscillation can be observed. An increase in SR duty cycle results in an increase in conduction time of the SR channel over the body diode. This issue becomes increasingly prevalent due to the usage of wide band-gap MOSFETs with high reverse drops and low sensed signal strength. This results in a current oscillation effect, leading to inconsistent SR operation, output ripple, and high EMI. In this paper, the issue is root caused analyzed. A method of improving drain-source SR for light-load SR operation is proposed. The method is prototyped on an FPGA to alleviate the issue on a $600\text{-}V_{in}/ 340\text{-}V_{out}$ 2.5-kW LLC-DCX (DC transformer) power converter.

This paper presents modeling, control, and system design of three-level boost (TLB) rectifier based medium-voltage (MV) solid-state transformer (SST) for dc fast charger application. In order to operate at MV with 1.2-kV SiC devices, the target system is configured by input-series output-parallel (ISOP) multimodule structure. Each module adopts TLB to front-end rectifier and stacked half-bridge LLCs to back-end isolated dc–dc converters. Operation principles of TLB rectifier and LLC converters are analyzed to derive an equivalent model of the entire system. Based on the detailed derivation, this paper aims to achieve three performance criteria, including bus voltage regulation, input current regulation, and voltage balancing. Basic feedback control loops are designed to control TLB’s output voltage and input current in an average manner, based on the derived system model. Then, ideal TLB duty-ratios in both continuous/discontinuous conduction modes are analyzed and duty-ratio feedforward control is proposed to improve the low quality of input current due to inherent feedback control limitations. For voltage balancing, system design approaches are used in the SST prototype. With the proposed control and system design, a prototype of four-module-stacked TLB SST was built and tested up to 3.8-kVrms and 16-kW conditions.

LLC resonant converter can achieve zero voltage switching (ZVS) for primary-side devices and zero current switching (ZCS) for secondary-side rectifiers. However, the reverse recovery and junction capacitance ( Cj ) of secondary-side diode critically affect the ZVS condition of primary-side switches. The effect of Cj has been discussed in literature, but not the reverse recovery. In this paper, the reverse recovery charge ( Q rr) is converted to an equivalent capacitance $(C_{{\rm rr}\_{\rm eq}})$ for the study of primary-side ZVS performance. An accurate model during deadtime is derived and further applied to characterize ZVS performance with different reverse recovery charges in different regions. The concept of establishing parameter C total to consider both Cj and $C_{{\rm rr}\_{\rm eq}}$ is proposed to evaluate the effect of the secondary-side rectifiers. This concept provides the guideline for diode and synchronous rectification mosfet selection to ensure ZVS condition for LLC converters. To verify the concept and the derived model, a 200/400 V 400 W LLC resonant converter prototype operating from 200 to 700 kHz is built and its ZVS performances with different diodes are compared. Two issues caused by Q rr effect, including $V_{\rm ds}$ reverse charging and asymmetrical waveform during deadtime, are explained thoroughly as well.

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-power applications because of the zero-voltage switching (ZVS) of all switches and the small number of components. However, when it operates with an asymmetrical duty ratio, it has a large dc-offset current in the transformer, which increases the size and core loss of the transformer. Moreover, because the dc-offset current decreases ZVS energy for one of the half-bridge switches, it has low efficiency in a light load condition. In addition, because most of the output current is concentrated in high-voltage-rating diodes that have large forward voltage drops, large conduction loss occurs in the secondary rectifier. To solve these problems, a new AHB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the AHB converter, the proposed converter not only eliminates the dc-offset current in the transformer, but it also has equalized current stress in the rectifier diodes. As a result, the proposed converter achieves high efficiency in entire load condition, compared to an AHB converter with a full-bridge rectifier. The effectiveness and feasibility are verified with a 250–400 V input and 100 V/200 W output prototype.

The inverter that requires isolation typically consists of an isolated dc-dc and a pulse-width-modulated dc-ac stages. However, the component counts, control complexity, efficiency and power density tend to be suffered with such a two-stage configuration. In this paper, a single-stage soft-switching isolated inverter based on MHz LLC converter is introduced with a novel hybrid modulation method, which operates under full-bridge and half-bridge variable frequency conditions for high- and low-line outputs, respectively. A rectified sine wave can be generated at the output of LLC converter and isolated through a high-frequency transformer for additional voltage gains. A lossless line frequency unfolder circuit is added afterwards to convert the rectified sine wave to ac sine output. The optimization method for the resonant tank is also proposed to achieve even lower voltage gains at high frequency to improve the output ac waveform quality. Compared to the traditional two-stage method, this single-stage solution makes the circuit simpler, and the bulky dc bus capacitor can be saved. To verify the circuit design and the proposed hybrid modulation method, a GaN based 380 V dc – 600 V ac , 1.2 kW prototype is built and tested. Under the full load condition, the measured total harmonic distortion of output voltage is 2.67% with 98.30% efficiency for the overall inverter.

This paper introduces a hybrid binary cascaded multilevel inverter (BCMLI) that allows the supply voltage of the lowest level to be a floating capacitor and thus reducing the need of multiple separated sources. Multiple such BCMLIs can be cascaded to increase the number of levels. This paper extends the configuration with two of 3-cell hybrid BCMLI modules cascading to achieve 29 voltage levels. A utility-scale hybrid BCMLI was designed and built using a single-source as the input and LLC converters to produce the 2-kV, 11.2-kW step-like output with 15 voltage levels. Two of such units were further cascaded to produce the 4-kV, 22.4-kW step-like output with 29 voltage levels. The circuit and control have been designed and simulated, and the hardware prototype has been built and tested. The total harmonic distortion was measured at 3.5% under the full-load condition. The LLC stage is a gallium nitride based converter operating at 1 MHz for an ultra-compact design. As the only loss is on the LLC stage, and high-voltage side is nearly lossless, the overall system efficiency exceeds 98.8%.

LLC resonant converter is widely used for isolated dc-dc power conversion applications due to its soft switching characteristics and simple structure. With the help of wide bandgap (WBG) devices, the switching frequency can be pushed to MHz range and the transformer loss becomes a more critical factor for the efficiency of the whole LLC converter. The high frequency effects, such as skin effect, proximity effect and fringing effect, make the transformer design even more challenging. Many research have been performed to evaluate core loss and copper loss from calculation, simulation or direct measurement in specific tester circuits. However, they are different from real circuit conditions. In this paper, the design principles and optimization considerations for the transformer in MHz LLC converter are presented. An accurate test-based method for core loss and copper loss estimation is proposed. Based on the proposed method, several optimization considerations are provided. To verify the optimized transformer design and its loss prediction method, a GaN based 1 MHz/2.8 kW LLC converter prototype is built, which can achieve 99.04% peak efficiency.

A single-inductor dual-supply dc–dc converter with bidirectional energy flow is proposed for the Internet-of-Things applications. This paper combines two dc–dc converters into one by sharing a single inductor, and it is capable of storing energy and powering output load by using the bidirectional inductor current. Besides, the voltage of the energy storage element is continuously monitored in the proposed converter, which eliminates the possibility of overcharging. Furthermore, the variations on the output voltage are typically negligible when the input voltage changes. In addition, a novel two-step startup procedure that does not require any on-chip/off-chip startup auxiliary circuit is proposed, which can significantly reduce the chip area. The proposed converter is fabricated by a 0.18- $\mu \text{m}$ CMOS mixed-signal process. The voltage range of the storing element is 1.2–1.4 V, and the maximal output power of the proposed converter is 18 mW with its output voltage setting at 1.8 V.

In this paper, a highly efficient isolated resonant converter with a novel modulation method is proposed for delivering power from photovoltaic (PV) modules to the dc microgrid. The proposed modulation method allows the converter to boost low input voltages and regulate a wide input voltage range. The converter design is based on a series resonant converter (SRC) that operates at the resonant frequency to achieve highest efficiency under nominal input voltage condition. Under shadowed or low irradiance conditions of PV panels, the converter will operate with the proposed “double-pulse duty cycle” modulation method to step up the voltage for the dc microgrid connection. With the proposed modulation method, the output switches serve for both synchronous rectification and voltage boost function. This method enables a higher voltage boost ratio than the SRC without adding additional switches while operating at the resonant frequency. A 300-W hardware prototype with gallium-nitride devices is built to verify the performance of the proposed converter and modulation method. The converter achieved a peak efficiency of 98.9% and a California Energy Commission weighted efficiency of 98.7% under nominal input voltage condition.

With the availability of wide bandgap devices, the power converters can now potentially operate at megahertz (MHz) or higher frequencies while achieving ultrahigh efficiency. Such a high-frequency switching is particularly important for isolated converters to reduce the size of the passive components, achieve high power-density, and reduce costs. However, unlike the conventional kilohertz switching, in MHz switching, the parasitic components will significantly affect the circuit operation. These effects are compounded by high-ratio step-up or step-down isolated converters because the parasitic capacitances/inductances are squared times the turns’ ratio of the transformer when reflecting from high-voltage (HV) to low-voltage (LV) side to LV/HV side. In this paper, a high-step-up series resonant converter is used as a design example to explore the effects of parasitic inductances induced from the LV side and parasitic capacitances induced from the HV side on the circuit operation under MHz switching conditions. Afterward, the printed circuit board (PCB) layout and the planar transformer are optimized through the finite-element method to minimize the parasitic effects. Finally, a 1-MHz, 38-V/380-V, 300-W resonant converter prototypes are built and compared to verify the design optimization.

LLC resonant converter is one of the promising converter topologies due to its simple structure and high efficiency. However, when LLC resonant converter is designed considering a hold-up time requirement, it has definite drawbacks such as large conduction and turn-off losses due to large circulating current. To solve this problem, various resonant converters with boost capability have been investigated. Although these methods improved overall performance, they still suffer from a large number of switching components. In this paper, a new LLC resonant converter with boost capability is introduced and verified. The advantage of the proposed converter is a small number of components while achieving the hold-up time capability. Furthermore, it achieves zero average transformer current despite its asymmetric operation. A prototype has been built and tested with 400–250-V input and 200-V/200-W output specification.

A 12-pulse converter has been commonly used for a large-scale power generating system. The arrangement of a delta–delta (Δ–Δ) and a delta–wye (Δ–Y) phase-shift transformer pair in series with the voltage source eliminates undesirable harmonics from nonlinear loads. Recently, a novel front-end for a multi-generator power system was proposed, which utilizes a single Y–Δ transformer to shunt between the two 30° phase-shifted generator outputs and results in the comparable harmonic elimination performance to the conventional 12-pulse rectifier. The shunt-type Y–Δ transformer front-end achieves more than 75% transformer size reduction, making it extremely attractive to large-scale industrial and shipboard applications. However, the exact 30° phase shift between the two rotating generators can drift in a practical system, especially under dynamic conditions. The harmonic performance under the non-ideal 30° phase-shift condition can deteriorate with the Y–Δ shunt-type front-end. To understand the impact of non-ideal phase-shifted generator sources, this paper derives the mathematical models through the use of an equivalent circuit, a square-wave analysis, and the phasor representation to show the harmonic cancellation principle and verifies the results with the computer simulation.

This paper presents a single-phase differential-type photovoltaic inverter named single inductor dual buck-boost inverter (SIDBBI) based on improved half-cycle PWM (HPWM). Conventional DBBI (CDBBI) is a good option for photovoltaic application due to step-up/down ability for varying inputs. However, inherent high inductor current and corresponding increments of inductor size and device ratings have made it less attractive than other topologies. This paper proposes an HPWM scheme with active clamping switches to reduce inductor voltage swing, highly induced current and component stresses by eliminating output voltages offsets. Under the proposed modulation, component voltage stresses in CDBBI can be reduced by zero offset, and there arises a chance to integrate half-utilized inductors, main switches and complementary diodes of two modules into one set, which is the proposed SIDBBI topology. 500 W prototypes of the conventional/proposed inverters have been built for verifications and comparison. Detailed analysis and experimental results under the proposed HPWM show that the size of SIDBBI can be reduced by 40.4% than CDBBI, maintaining comparable efficiency over 96% and wide input coverage by step-up/down ability. Comparative results address that SIDBBI is competitive in terms of component counts, stresses and losses, compared with various kinds of buck-boost inverter topologies.

This paper proposes a modified bridge switch-type flux-coupling nonsuperconducting fault current limiter (BSFC-NSFCL) for suppressing the fault current and voltage sag. A flux-coupling reactor and a bidirectional bridge switch are combined to perform the functions of steady-state line current sharing and fault current suppression. The modified BSFC-NSFCL mainly utilizes the magnetic flux cancellation effect to make the limiter behave as a short circuit on the circuit during normal operation. Hence, there is almost no impact on the power system when the limiter is used. When a fault event occurs, the bridge switch turns off immediately, and then, the magnetic flux cancellation effect disappears. Thus, the impedance of primary coil inserts into the circuit to restrict the fault current and voltage sag phenomena. Once the fault is removed, the bridge switch turns on again, and the BSFC-NSFCL recovers to the normal operation. The modified NSFCL is more cost-effective and easy to be implemented than the flux-coupling superconducting fault current limiter. Theoretical analysis for the BSFC-NSFCL has been fully developed and proven by MATLAB software. Finally, the analytical, simulated, and experimental results have been carried out to verify the feasibility and performance of the proposed BSFC-NSFCL.

LLC resonant converter is popular for dc-dc converter designs due to its simple topology, galvanic isolation and soft switching capability. Therefore, lots of researches have been performed for LLC converter design and optimization to pursue high efficiency and high power density with high switching frequency. However, relevant research about the analysis and ZVS model for LLC converter with light load condition under MHz switching is scarce. In this paper, detailed analysis for MHz GaN based LLC converter is provided with light load. Moreover, a simple and accurate ZVS model is proposed, which can help determine fully ZVS condition for primary side devices. To verify the analysis and the proposed ZVS model, a 1 MHz/300 W (10% load) GaN based LLC converter prototype is built and tested.

For wide gain range applications with LLC resonant converter, variable frequency modulation is widely used to achieve different output voltage. The first harmonics approximation (FHA) is one of the most popular adopted methods to calculate voltage gain with different switching frequency. However, it is not accurate when the switching frequency is far away from the resonant frequency and the diode effect on voltage gain makes FHA deviate from the actual results even more. Several models have been proposed to solve the drawback of FHA method that only first harmonic of the resonant current is examined. Few of them takes the diode effect on voltage gain into consideration. In this paper, detailed analysis of diode effect on voltage gain is presented and based on the analysis, an accurate voltage gain model for LLC converter is proposed. To verify the proposed model, a 1.6 kW GaN based LLC converter prototype is built and tested at 700 kHz and 1 MHz.

Since the last decade day by day, there is a revolution in an existing power grid network due to an increase in demand for the convenient electric power supply required for the smart component in the power grid network. So this is a time for the power grid to become smart in accordance with all components which are actively participated in his network which is nothing but Smart Grid network. A different component in a Smart grid network required variable AC/DC power supply at the different amplitudes and different frequencies. Power electronics converters are required to meet all these requirements. Solid State Transformer (SST) is one of the key components in a smart grid network. This paper presents the Bidirectional Soft Switched Solid-State Transformer for a Smart Grid Network. A proposed circuit presents in this paper used a LCLC type resonant network to achieved soft switching action. An analysis of the resonant network and it's effect on the performance indices are presents in this paper. A front end bidirectional boost rectifier is used in a proposed circuit to achieved bidirectional power flow feature and desired voltage gain at the output. A proposed circuit is designed for power level 10KW and is simulated in a PSIM/Simulink co-environment. The results were obtained at an input voltage of Three-phase 440V, 50 Hz, and provide the output of 800V, 12.5A and is verified for desired features in the proposed converter.

In unidirectional LLC converters, synchronous rectification (SR) is a technique that can be implemented to minimize the conduction loss of the secondary-side LLC rectifier. In drain-source voltage-sensed SR, a premature turn off issue can be observed due to parasitics present in the drain-source voltage sensing loop. In this digest, a novel use of multilevel gate drivers (MLGDs) and digitally adaptive control for multilevel turn-off can be implemented to mitigate parasitic effects, boost efficiency and the applicable load range of drain-source SR. Multilevel gate driving boosts the sensed SR signal strength, extending the total SR conduction period. This driver can be combined with an adaptive delay block to maximize efficiency. Because the increased drain-source signal integrity is increased at the turn-off moment, this also prevents an oscillation issue at light loads. Overall rectifier efficiency is increased over a traditional gate driver or non-adaptive MLGD due to a reduction in parallel diode conduction from tuning the transition point. The concept of the adaptive multilevel gate driver is proposed, explained, and simulated in this paper. A discrete multilevel gate driver is built and an adaptive delay block designed in a FPGA and tested on a LLC-DCX resonant converter for proof of concept.

This paper focuses on the LLC resonant converter working in the zero-voltage-switching (ZVS) region where the switching frequency (f s ) is larger than the resonant frequency (f r ). The secondary side devices critically affect both the normal operation and deadtime operation of the LLC converter. The effect of diode junction capacitance (C j ) and reverse recovery on the ZVS condition during deadtime has been discussed in the literature, but their effect on the waveform during normal operation has not. In this paper, a detailed description and analysis of deadtime operation with Silicon and Silicon Carbide (SiC) diodes are provided firstly and an accurate model for their effect on the following normal operation is derived based on the deadtime analysis. From the derived model, an improved ZVS condition for f s > f r region is presented, which can also provide the guideline for the selection of secondary side devices. To verify the proposed analysis and model, a 694 kHz/100 W GaN based LLC converter prototype with different secondary side devices is built and tested.

This paper presents implementation of triangular critical conduction mode (CRM) modulation scheme to three-level boost (TLB) converter and proposes a three-level CRM modulation scheme for the topology. Compared to conventional triangular method, the proposed one performs full-utilization of three-level capability and synthesizes quadrangular inductor current waveform. By adjusting a designable period of the proposed scheme in a switching cycle, several variables including operating frequency, inductor current peak and component rms currents can be decreased. As a result, converter efficiency can be improved and current stresses of circuit components can be mitigated. In this paper, details of TLB operation principle, analysis of the proposed scheme and effects of adjustable design parameter are provided. A 700-W TLB converter prototype has been set up in order to verify the effectiveness of proposed CRM modulation scheme.

Gallium Nitride (GaN) devices have shown greater potential in high switching frequency operation due to its much lower switching loss compared to Silicon devices. However, the faster switching speed makes it more difficult for device dynamic characterization because it is more sensitive to the parasitic components in the circuit and it requires better testing equipment. Double Pulse Test (DPT) is commonly used to characterize device dynamic performance and proper device drain current probing method is a must for accurate switching loss measurement. However, for GaN devices designed to have loop inductance within sub-nH range, any coaxial shunt to measure drain current will insert enough parasitic inductance to influence switching performance and impact measurement results. In this paper, a novel and simple method is proposed to accurately evaluate switching loss without shunt resistor in series with GaN device in a half bridge configuration, which is a common building block in power electronics circuits. A 130 W GaN based buck converter prototype is built to verify the proposed method.

This paper presents a dual-mode Cuk inverter for photovoltaic/thermoelectric power applications. A dual-mode Cuk inverter operates in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM), and has the advantages of low ripples of voltage and current at the input and output, medium power density, and step-up/step-down ability, but is difficult to control because DCM and CCM have distinct system dynamics. To overcome this control problem, we propose to use a repetitive controller (RC) with a multiple phase-lead compensator for the dual-mode Cuk inverter. If the RC is applied by itself, the distinct system dynamics may severely degrade its system performance. Thus, in the proposed RC, we mainly use a multiple phase-lead compensator to compensate for the different phase lags of the dual-mode Cuk inverter. To reduce the burden from the RC, we use the dual-mode nominal duty ratio as feedforward control input. We also analyze the boundary of operation modes in the dual-mode Cuk inverter, then provide detailed and practical guidelines to design the control parameters. Experimental results obtained on a 500-W digitally controlled module integrated converter prototype confirmed the effectiveness of the control approach.

In order to overcome the drawbacks of conventional bridgeless single-ended primary inductance converter (SEPIC) power factor correction (PFC) circuits, an improved bridgeless SEPIC PFC circuit is introduced by adding an additional output diode and an inductor. The undesired capacitive coupling loop and the circulating loss are removed. Thus, the high efficiency can be achieved. The operation principle and design consideration of the proposed converter are introduced in detail. Furthermore, a novel control method is employed to control the current continuous mode bridgeless SEPIC PFC circuit without input-voltage sensing. Meanwhile, the UCC28019-based modified hardware implementation circuit is designed and described. A 100-W prototype with 90–135 Vrms input line voltage and 60-V output voltage is built and tested. The corresponding experiment shows the validity of the proposed circuit topology and control strategy. A peak efficiency of 94% and power factor above 0.99 are achieved under 65-kHz switching frequency operation condition.

The series resonant dc-dc converters are mature technology used mostly in applications requiring constant dc voltage gain. They were recently enhanced by the application of the boost rectifiers. This approach showed new opportunities for input voltage regulation range extension. The given paper summarizes known operating modes and shows a way of significant input voltage range extension through the utilization of hybrid full-bridge switching cell. Two converter topologies are introduced in this paper. Possible operating modes are identified and summarized.

High frequency PCB windings magnetic is one of the key components in high power density and high efficiency MHz power converter. High frequency PCB windings magnetic losses are the main limitation for the whole converter efficiency and power density, while the PCB windings losses are the main part of the magnetic losses. Currently, the Dowell’s model is used for the layout of PCB windings. However, the Dowell’s model has its restrictions, namely, magnetic field is assumed to be distributed evenly in one direction. But the magnetic field around the windings are three-dimensional and unevenly. Therefore, further arrangement of PCB windings is proposed to minimize the PCB windings losses. Besides, the magnetic circuit is analogous to electrical circuit, and the magnetic core structure shape the footprint of the PCB winding, so different magnetic core structure can be proposed for the trade-off design among the high power density, high efficiency, and low temperature stress. Therefore, both PCB winding layout and magnetic core structure design are important for the optimization of high frequency magnetic components.

LLC resonant converter is widely used due to its high efficiency and high power density capability. The design methodology for it has been addressed in many literatures. However, most of them focus on the step-down LLC converter due to its high-output current applications such as data center. In this paper, the optimal design methodology for high frequency GaN based step-up LLC converter for solid-state transformer application is discussed. An accurate model for deadtime operation is derived. From the model, the approach for device selection for both primary and secondary sides and the magnetizing inductance design to have zero-voltage-switching (ZVS) are presented. To verify the design methodology, LTSPICE simulation is performed. Besides, a 1 MHz 1.8 kW step-up LLC converter prototype is designed and tested. With the proposed design methods, the efficiency can achieve 98.75%.

Due to high efficiency and simple structure, LLC resonant converter is a promising topology for developing solid-state transformers. The heart of an LLC converter is the high frequency transformer that provides necessary insulation and step-up/down between primary and secondary sides. In addition, the efficiency of the transformer is a critical factor as it processes the entire power. This becomes even more challenging when circuit switching frequency is raised for shrinking passive component sizes, as skin effect and other non-ideal effects start to kick in. In solid-state transformer applications, size, efficiency and insulation have stringent specifications and meeting all requirements at once is not a simple task. Therefore, this paper presents multiple perspectives in terms of transformer design in an LLC converter and demonstrates with a 3-kW transformer capable of more than 15 kV insulation. Testing results show peak converter efficiency of 98.9% with transformer power density of 480 W/in3.

A trend for low-power conversion system is to integrate every component to a single chip. Magnetic component has been the key to determine the power density of the integrated switching power converter. In this paper, a hybrid resonant buck-type converter with an ultracompact custom-designed coupled inductor is presented for low-power integrated on-chip applications. This converter achieves zero-voltage switching for the high-side switch and near zero-voltage zero-current switching for low-side and auxiliary switches. The soft-switching condition allows the circuit operating at high switching frequencies. An ultracompact planar coupled inductor with a dimension of 5.25 mm × 1.95 mm × 3.86 mm is designed and customized for future integrated on-chip applications. The high-power density of this magnetics component is achieved by high switching frequency and optimized printed circuit board (PCB) windings design. A hardware prototype with 24 to 60-V input and 3.3 to 5-V, 3-A output operating at 2–3 MHz is presented to verify the circuit operation. The prototype achieves a peak efficiency of 90.7% using silicon devices at 2-MHz switching frequency.

Current control loop response in voltage source inverters impacts the quality of output current and output voltage waveforms. Parabolic current control provides a fast transient response with approximate-constant switching frequency, solving the frequency variation problem of hysteresis current control. This makes it a good candidate for the current control loop of voltage source inverters to achieve a good system performance. Yet, parabolic current control is often implemented with digital-to-analog converters, analog comparators, and field-programmable gate array circuits where increasing switching frequency pushes update speed and bandwidth requirements. Concurrently, even if the transient response of parabolic current control is fast, it can still take up several switching cycles converging to steady state. In order to solve both problems, a new current control strategy, motivated by the convergence analysis of parabolic current control but with a convergence process that takes just one switching operation, is proposed: single-step current control. Since single-step current control samples two data points in a switching cycle instead of using continuous parabolic carriers, it can be easily implemented in a digital microcontroller then high switching frequency can be achieved. The small signal model, dead-time compensation, and stability analysis are also studied in this paper. The convergence speed of the algorithm is verified with experimental hardware prototype and the transient performance of the designed voltage source inverter meets expectation.

This paper proposes an iterative learning control (ILC) scheme for a dual-mode flyback inverter operating in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). In dealing with more than 200-W power applications, the dual-mode flyback inverter takes advantage of both DCM and CCM operations. However, it is difficult to control the output current because the system gain is quite low in DCM and the system transfer function has a right-half plane zero in CCM. To overcome the problems occurring in DCM and CCM operations, we propose an ILC scheme with multiple phase-lead compensation. The ILC is proposed to achieve accurate reference tracking and to reject periodic disturbances. The multiple phase-lead compensation technique is then employed to compensate for the effect of different system dynamics. As a theoretical result, we derive the asymptotic stability of the closed-loop system. We also performed the numerical simulations and experimental tests to validate the proposed control approach.

In this study, the authors propose a feedback control method for energy storage systems for storing electrical energy and for load levelling. The proposed method uses both source and load power feedback, resulting in a fast response with respect to load levelling. To verify the proposed system, a power conditioning system based on the proposed feedback scheme was implemented and tested, in order to show the effectiveness of the scheme with respect to load levelling and energy harvesting. The system involved 60 of 50 W photovoltaic panels and a 20 Ah lithium polymer battery. An office was selected for testing, which was performed over an entire year. The authors obtained the operating profiles and determined the reduction in the daily total energy usage of the consumer as well as the standard deviation in load levelling.