Half-bridge Mode Research Articles

A Structure-Reconfigurable LLC Resonant Converter With Wide Gain Range

In this paper, a structure-reconfigurable LLC (SR-LLC) resonant converter is proposed for wide output voltage applications. The converter can operate in half-bridge mode or full-bridge mode by modulating the driving signal of the switches. Four operation modes with scaled voltage gains are obtained by the independent or combined operation of resonant tanks. Compared with the conventional full-bridge LLC converter, the voltage gain range is greatly extended without extra switches. The consistent resonance parameters of two tanks allow four operating modes to have the same resonant frequency, which facilitates the design of magnetic components. Moreover, zero-voltage switching (ZVS) of the primary-side MOSFETs can be achieved in all modes. A 3.3-kW prototype with 75 V-450 V output voltage is built to verify the feasibility and effectiveness of the proposed converter. The peak efficiency of the prototype is 97.3%, and the efficiency curve is smooth in the ultra-wide output voltage range.

A Reconfigurable Rectifier-Based Power Improving Method of Free-Standing Two-Coil Magnetic Field Energy Harvesters Over a Wide Load Range

Free-standing magnetic field energy harvesters (FSMFEHs) have promising potential in charging sensors used in electrical power grids. The output power of the FSMFEH is highly dependent on the load resistance. However, the load resistance of the sensors varies over a wide range during the operation process. Therefore, a crucial challenge for an FSMFEH system is to maintain high output power over a wide load range. In this article, an innovative reconfigurable rectifier-based FSMFEH system with two coils connected in parallel is proposed. First, a new structure of two identical coils in parallel is proposed in magnetic energy harvesting applications. Then, a reconfigurable rectifier with two operation modes is developed to incorporate the new coil structure. By switching between the full-bridge mode and the half-bridge mode according to the actual load demand, the proposed FSMFEH can maintain high output power over a wide load range. In addition, the mode transition can be easily achieved by shorting one of the diodes, leading to a simple and low-loss control. The effectiveness of the proposed FSMFEH system is verified based on a laboratory prototype. It is provided that the experimental result is consistent with the theoretical analysis. The output power can be maintained above 8.19mW within the 50Ω to 1500Ω range when the busbar current is 100A.

A Mode-Switching-Based Phase Shift Control for Optimized Efficiency and Wide ZVS Operations in Wireless Power Transfer Systems

This paper proposes a mode-switching based phase shift control (MS-PSC) for wireless power transfer (WPT) systems, which is able to achieve power regulation, load matching, and wide ZVS operations simultaneously without using additional dc-dc converters. Based on the mode transitions between the full-bridge, mixed-bridge, and half-bridge modes of both the inverter and the rectifier, the MS-PSC method guarantees a wide-range ZVS with minimized circulation of reactive power. Therefore, the system efficiency is improved over a wider power range compared to the conventional triple-phase-shift (TPS) control and the existing hybrid modulation control. The principles of different operating modes are analysed. Then, the implementation of the proposed MS-PSC method and the mode selection strategy are presented. Finally, the effectiveness of the proposed MS-PSC method is validated in a WPT prototype. Experimental results show that the proposed MS-PSC method can achieve a high overall efficiency in a wide power range. Compared with the conventional TPS control, the MS-PSC method further optimizes the efficiency in 10%-63% of the rated power, with efficiency improvements ranging from 1.5% to 6%. As a result, the system efficiency remains at 93.5%-96.1% in the power range of 1-10 kW, with the transformer coupling coefficient k=0.19.

Research on MMC Improved Sub-Module Topology With DC Fault Ride-Through and Negative Level Output Capability

Modular multilevel converter (MMC) is a modern and preferred topology among the voltage source converters (VSCs) in high voltage direct current (HVdc) transmission. However, the traditional half-bridge sub-module (SM) cannot block the dc fault current. Hence, the novel SM topology with dc fault ride-through capability is introduced. This article proposes an improved diode-clamp SM (IDCSM) structure. Based on the DCSM topology, the two capacitors’ connection in the IDCSM is modified to operate independently and generate output voltage levels of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- u_{c}$ </tex-math></inline-formula> , 0, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$u_{c}$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2u_{c}$ </tex-math></inline-formula> based on the additional switching devices. The IDCSM with dc fault ride-through and negative level output capability can increase the number of output levels and significantly reduce hardware cost. In addition, this article adopts an equivalent half-bridge modulation (EHBM) strategy that can modulate all the MMC SM topologies with the comparison algorithm, simplifying the complicated logic calculation process. Then the IDCSM power loss, cost, and dc fault ride-through characteristics are illustrated in detail. Finally, the simulation and experimental results verify the feasibility of the proposed IDCSM topology and EHBM.

LLC Resonant Converter Modulations for Reduced Junction Temperatures in Half-Bridge Mode and Transformer Flux in the On-the-Fly Morphing Thereto

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters are typically unsuitable to be applied for wide voltage-transfer ratio applications. With a full-bridge inverter, however, they can be operated in a variety of different modulation modes to extend the operating range. Most notably, by permanently turning <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> one switch and turning <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> the other switch of the same bridge leg, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> can be operated in half-bridge mode reducing the gain by a factor of two. In this modulation, however, the switch that is permanently turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> is stressed by the complete resonant current while exhibiting no switching losses. This article proves that the frequency-doubler modulation can better balance the losses among all switches and should be the preferred mode of operation favored over the conventional half-bridge modulation. This article analyzes the beneficial loss distribution and proposes an on-the-fly morphing modulation to the frequency-doubler modulation and reverse. Furthermore, the morphing magnetizing current offset of the morphing is analyzed to show that the offset can be influenced by the design of the magnetizing inductance and through the morphing modulation itself. Finally, an improved morphing modulation is presented showing that the morphing flux offset can be reduced substantially. Experimental measurement results on a 1.8 kW prototype show that by employing the frequency-doubler modulation, the maximum inverter temperature can be reduced by about 20 K and that the maximum transformer flux deviation during morphing can be reduced significantly on average by 78%. Both results enable the use of switches with a lower on-state resistance and the application of transformers with a smaller core cross-section.

A Hybrid Extended Phase Shift Modulation Strategy for DAB Converter With DC Blocking Capacitor to Extend ZVS Range and Reduce RMS Current

This article is aimed at enlarging the zero-voltage switching (ZVS) range and reducing current stress for the dual-active-bridge (DAB) converter with dc blocking capacitors (DCBCs). A hybrid extended phase shift modulation strategy (HEPSMS) is proposed, which makes the converter switch between the full-bridge mode and the half-bridge mode to obtain multivoltage matching operation points. Thus, the root mean square (rms) current and the burden of achieving full load range ZVS are reduced. In addition, the voltage–second of the leakage inductor is controlled to achieve equivalent voltage matching under wide voltage output, thereby simplifying the control law and achieving full load range ZVS under a wide voltage range. The operation principle, ZVS range, and rms current are analyzed and compared with the conventional modulation method. Finally, a 1-kW experimental prototype with a 200-V input and a 100–400-V output was built to verify the feasibility and effectiveness of the proposed method.

A Step-Up Reconfigurable Multimode LLC Converter Module With Extended High-Efficiency Range for Wide Voltage Gain Application in Medium Voltage DC Grid Systems

In this article, a newmodular multimode reconfigurable step-up resonant converter that is capable of extending very high efficiency from full load to reduced load conditions is proposed for wide voltage gain application in medium voltage dc (MVdc) grid system. The proposed converter module is able to switch from a hybrid control scheme that consists of variable frequency and phase shift control to pulsewidth modulation (PWM) control in the auxiliary switch of the output voltage quadrupler (VQ). In addition, the input bridge can also be reconfigured to a half-bridge mode to suit high input voltage range while utilizing a hybrid control technique that consists of variable frequency and asymmetrical PWM control. With the proposed approach, the converter module is able to achieve constant output voltage regulation without requiring a wide spectrum of switching frequency or phase shift control. Hence, close-to resonance operation with very high efficiency can be maintained for a wide range of input voltage and loading conditions. Soft switching operations are always guaranteed for all the primary side switches, the output diodes and the auxiliary switch in the VQ. The steady-state and dynamic performance of the proposed modular multimode step-up converter are validated through simulation results on a silicon carbide (SiC) based 360 V–1 kV/16 kV, 80-kW system and experimental results on a proof-of-concept 150–400 V/6.6 kV, 10-kW SiC laboratory prototype. Results confirmed that the efficiency is maintained between 97.8% and 99.1% from full load to at least 20% load condition for the specified input voltage range.

A Hybrid Modulation Control for Wireless Power Transfer Systems to Improve Efficiency Under Light-Load Conditions

Traditional wireless power transfer (WPT) systems usually adopt the triple-phase-shift control method to maintain a constant output voltage, track the maximum system efficiency point (MEPT), and achieve zero-voltage-switching (ZVS) operation for various applications. However, these three targets are achieved at the cost of high reactive power on both primary and secondary sides, especially under light-load conditions, leading to low efficiency. This has become one of the challenges that hinder a further deployment of WPT technologies in practice. To address this vital problem, in this article, how the reactive power lowers the system efficiency is revealed based on a mathematical model established. Then, a hybrid modulation control strategy based on a proper selection between the full-bridge and half-bridge modes of the inverter and active rectifier is developed. An experimental prototype is constructed to verify the effectiveness of the proposed control method. Experimental results show that the proposed method can reduce the reactive power, maintain a constant output voltage, and realize the MEPT and ZVS operation, with high efficiencies up to 94.29% in a wide load range.

A Hybrid Mode Control Strategy for LCC–LCC- Compensated WPT System With Wide ZVS Operation

In this article, an efficiency-oriented control strategy is proposed for LCC–LCC-compensated wireless power transfer (WPT) system to achieve zero-voltage-switching (ZVS) operation over a wide current regulation range, in which full-bridge (FB) and half-bridge (HB) modes are combined and switchable based on requirements from load. The harmonic-considered time-domain models for FB and HB modes are first built to calculate current through the switches at the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> moment accurately. Then, focused on the constant voltage charge stage with variable output current, the ZVS boundaries are identified in HB and FB modes as the preferable control trajectories, which determines the desired current output with joint considerations of frequency, phase-shift angle, and duty ratio. Next, a least squares optimization method is introduced to fit the theoretical control trajectories into a smooth curve that is practical for implementation on microcontrollers. Finally, a 4.4-kW WPT prototype is built to verify the feasibility and validity of the proposed control strategy. Results show that a high system efficiency can be achieved over a wide output current range, with an efficiency of 94.68% even at 20% rated power.

Interleaved Single-Stage LLC Converter Design Utilizing Half- and Full-Bridge Configurations for Wide Voltage Transfer Ratio Applications

Automotive on-board dc-dc converters are required to operate over a wide input and output voltage range depending on the state of charge of the input and the output battery. Conventionally, the unidirectional power transfer between these batteries is enabled by a two-stage converter concept. A first-stage nonisolated dc-dc converter regulates the input voltage of the galvanically isolated second-stage dc-dc converter such that the second-stage converter operates in its optimum operating point. This article presents a single-stage interleaved LLC resonant converter of 3.6 kW for this purpose. While LLC converters are usually not suitable to cover such a wide voltage range (the input voltage between 240 and 420 V and the output voltage between 8 and 16 V), this LLC converter is operated in a full-bridge mode for large gains and in a half-bridge mode for low gains. For intermediate gains and loads, the LLC employs the phase-shift mode. To operate the interleaved LLCs at equal switching frequencies enabling output current ripple cancellation to reduce the output capacitor, again, the phase-shift mode is utilized to balance the power transfer during the full-bridge mode while the asymmetrical duty-cycle mode is proposed for power balancing during the half-bridge mode. This article analyzes the converter design for these modes of operation and provides a comprehensive design procedure allowing the designer to simultaneously analyze all stress values for various resonant tank designs. A 3.6-kW prototype employing Si superjunction MOSFETs achieves a power density of 2.1 kW/L. The maximum efficiency reaches 96.5%, while for most operating points, it is kept well above 90%. The experimental measurement results validate the analysis and show that phase-shift operation and asymmetrical duty-cycle modulation can be utilized for power balancing for full-bridge and half-bridge configurations, respectively, such that a much smaller output capacitor can be employed.

Novel multi‐level inverters with flyback high frequency link

A novel topological family of multi-level inverters with flyback high frequency link is proposed in this study. The inverters can transfer high DC voltage into regulated sinusoidal voltage with low total harmonic distortion (THD). The circuit configuration consists of high DC input voltage, DC-link capacitors, novel multi-level conversion unit, high frequency flyback transformer, cyclo-converter, output filter capacitor and AC load. This topological family includes diode-clamp type full-wave mode, hybrid-clamp half-bridge mode, multi-end mode and improved multi-end mode. To achieve reliable multi-level inversion and overcome DC-link capacitor voltages unbalance, multi-carrier modulation and DC-link capacitor voltage balancing strategy are presented. In addition, steady principle and AC small-signal model are analysed. Simulation and experimental results are given to prove that the novel flyback high frequency isolated multi-level inverters have the following advantages such as the high frequency electrical isolation, the bi-directional power flow, the two-stage power conversion (DC-high frequency AC (HFAC) - low frequency AC (LFAC)), the lower voltage stress of power switches and the low THD of output voltage.

An Operation Mode Selection Method of Dual-Side Bridge Converters for Efficiency Optimization in Inductive Power Transfer

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.

Double Voltage Rectification Modulation for Bidirectional DC/DC Resonant Converters for Wide Voltage Range Operation

It is difficult to achieve wide voltage range for full-bridge-based bidirectional resonant dc/dc converter due to the large resonant current caused by the small magnetizing inductance. A half-bridge modulation was proposed to extend the output voltage range by offering an additional step-down voltage step of 0.5 normalized gain. But in backward operation, the converter cannot provide the two-times step-up voltage gain to match the forward 0.5 step-down voltage gain, which disables the converter to truly work bidirectionally with large voltage range. This paper proposes a double voltage rectification (DVR) modulation on the rectification side to achieve twice the voltage gain for the backward direction to effectively widen the operation voltage range, which matches the ratio of the two dc port voltages where the half-bridge modulation is used in the forward direction. In the DVR modulation, the operation of the input-side resonant tank is the same as that of the conventional modulation. The switches on the input side still turn on with zero-voltage switching (ZVS), and the body diodes on the rectification side still turn off with zero-current switching. Moreover, the turning on and off of the mosfets on the rectification side are also ZVS, which causes no additional losses and guarantees high-frequency operation. The rotational operation of the rectification-side switches improves the thermal balance condition, enlarging the power capacity and improving the reliability of the converter. A smooth transition method between the two modulations is also proposed, which still guarantees ZVS turning on for the rectification-side switches. The symmetrical CLLLC resonant converter is taken as an example to illustrate the operation principle and features of the proposed modulation. And other bidirectional resonant converters for the DVR modulation are also presented. Finally, a 3-kW bidirectional CLLLC resonant converter prototype with 100-kHz resonant frequency is built to verify the proposed modulation.

A Structurally Reconfigurable Resonant Dual-Active-Bridge Converter and Modulation Method to Achieve Full-Range Soft-Switching and Enhanced Light-Load Efficiency

This paper proposes a reconfigurable dual-active-bridge (DAB) converter that is capable of switching between two converter structures for enhancing its performances at different output power levels. For 50%–100% load, the converter operates in full-bridge mode and achieves soft-switching in all switches independently of the input-to-output voltage ratio. Below 50% load, the converter is reconfigured to operate in half-bridge mode for reduced circulating current and improved light-load efficiency while maintaining the desired soft-switching characteristic of full-bridge mode. The achievement of soft-switching is aided by the use of a tuned $LCL$ resonant tank, which enables an accurate prediction of the phases of tank currents with respect to tank voltages, and therefore simplifies the realization of soft-switching. The effects of dead time are discussed and expressions for guiding the selection of appropriate dead time for ensuring soft-switching in practical implementation are derived. The proposed converter and the modulation scheme are experimentally verified with a 1.6-kW converter prototype, which demonstrates their merits in comparison with a nonreconfigurable, full-bridge DAB topology and conventional modulation schemes.

A Phase Angle Self-Synchronization Topology for Parallel Operations of Multi-Inverters in High Frequency AC Distribution

—High frequency ac (HFAC) power distribution system (PDS) has been known as the effective alternative of dc power distribution system (DC PDS) because of its excellent advantages such as high power density, high efficiency, fast dynamic response and fewer conversion stages. Multiple HFAC inverters are operated in parallel to satisfy the source side requirements like high power grade, safety margin and reliability. In order to eliminate circulation current caused by the amplitude and phase differences among the inverters, the amplitude and phase of individual inverter are required to be synchronous. However, parallel controls become extremely complicated as amplitude and phase are coupled together in full-bridge inverter with traditional phase-shift modulation. In this paper, a controllable half-bridge LCLC resonant inverter and dual-PWM modulation are presented with phase angle self-synchronization. Control strategy is given for voltage adjusting and phase-amplitude decoupling. Besides, the resonant network normalization parameters and control angle is summarized to ensure soft-switching. The simulation model and experimental prototype are implemented with the output frequency of 25 kHz. The experiment results and theoretical analysis agree well to verify the features of the proposed inverter.

A Bidirectional Resonant DC–DC Converter Suitable for Wide Voltage Gain Range

This paper proposes a new bidirectional resonant dc-dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc-dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype.

Torque Ripple Minimization in Direct Torque Control of Brushless DC Motor

This paper mainly proposes a direct torque control strategy to minimize torque ripple in brushless DC (BLDC) motor. BLDC motor has large current and torque ripple when one voltage vector applied in one cycle due to its low inductance. Hence, this paper proposed a hysteresis torque control with PWM mode to control the resultant torque. Moreover, when the direct torque control system is operating during the two-phase half-bridge <TEX>$120^{\circ}$</TEX> conduction mode, large torque ripple in commutation area appears every 120 electrical degree. Based on analyzing the root of torque ripple in detail, lookup tables of switching devices states for new half-bridge modulation mode in the positive and negative reference torque put forwarded. Finally, simulations by MATLAB software and experiment results from DSP are presented to verify the feasibility and effectiveness of the proposed strategy operating in four-quadrant operation.

Differential Buck DC–DC Chopper Mode Inverters With High-Frequency Link

A circuit configuration and a circuit topological family of differential buck dc-dc chopper mode inverter with high-frequency link are proposed in this paper. The circuit configuration, the topology family, the instantaneous output voltage and the capacitance current feedback control strategy, the steady principle characteristic, and the design criteria for the key circuit parameters are fully investigated in this paper. The circuit configuration is differentially composed of two identical isolated bidirectional buck dc-dc choppers with the same input and output LC filters. These two choppers generate unipolarity sinusoidal pulse width modulation voltage waveforms with positive and negative half low-frequency cycle separately. Each dc-dc chopper consists of high frequency inverter, high frequency transformer, and high frequency rectifier. The circuit topological family includes six circuit topologies, namely, one-transistor forward mode, push-pull mode, push-pull forward mode, two-transistor forward mode, half-bridge mode, and full-bridge mode. Taking one-transistor mode circuit topology as example, the prototype is designed and implemented. The results from the theoretical analysis and principle test indicate that the inverters have advantages of high frequency galvanic isolation, simple topology, bidirectional power flow, single-stage power conversion, high conversion efficiency, high-quality output voltage waveform, and strong adaptability to various loads.

Novel Current-Mode AC/AC Converters With High-Frequency AC Link

A novel circuit-topology family of the current-mode AC/AC converter with high-frequency AC link, based on a Flyback converter, is proposed. These circuit topologies, which can transfer one unregulated sinusoidal voltage with high total harmonic distortion (THD) into another regulated constant-frequency sinusoidal voltage with low THD, are composed of input cycloconverter, high-frequency storage transformer, and output cycloconverter. The circuit-topology family includes single four-quadrant power switch mode, push-pull mode, half-bridge mode, and full-bridge mode circuits. The single four-quadrant power switch mode and push-pull mode converters are suitable for low input voltage fields, but the half-bridge mode and full-bridge mode converters are suitable for high input voltage fields. The operational mode, steady principle, and transient voltage feedback control strategy of the kind of converter are investigated. The output characteristic curve, its relation to internal resistance, and the design criteria for the key circuit parameters are given. The theoretical analysis and the test result of the 500 VA 220 V 15% 50 HzAC/220 V 50 HzAC prototype have shown that the converters have advantages such as high-frequency galvanic isolation, simple topology, two-stage power conversion [low frequency alternating current (LFAC)/high frequency alternating current (HFAC)/LFAC], bidirectional power flow, high efficiency, high power density, low THD of the output voltage, strong adaptability to various loads, higher line power factor, low audio noise, etc.