Low Current Stress Research Articles

Input Current Step-Doubling for Autotransformer-Based 12-Pulse Rectifier Using Two Auxiliary Diodes

To significantly decrease the input line current total harmonic distortion (THD) under simple circuit configuration conditions, this article propose an input current step doubling scheme for autotransformer-based 12-pulse rectifier using two auxiliary diodes. The auxiliary diodes are installed between the two retrofitted double-tap interphase reactors, and they inject specific square wave currents to increase the output current states of the rectification bridges. This modification extends the 12-step input line current to a 24-step input line current, and the near sinusoidal input line current with THD below 5% is obtained. As the proposed scheme only requires two low current stress (3.4% <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) auxiliary diodes, it achieves high-cost performance, is easy to implement and has a simple circuit configuration. A 2.2 kW simulation and experimental prototype is built to verify the theoretical analysis.

Comprehensive Analysis of Asymmetric Modulated Dual-Active-Bridge Converter and Its Hybrid Control Strategy

Dual active bridge (DAB) converter has been widely used in distributed power supply, new energy vehicles, energy storage systems, etc. Their modulation strategy is an important research direction. At present, the research on modulation strategy is basically symmetric phase shift, but it is not enough to generalize modulation strategy comprehensively. In this article, an asymmetric phase-shifting (APS) strategy is proposed to control the power flow by simultaneously adjusting the asymmetric duty cycle and the phase-shifting angle. With this modulation scheme, the current stress and cyclic power loss can be reduced by adjusting the modulation ratio of the inductor current waveform. As a result, the light-load efficiency can be improved compared with the conventional symmetric modulation scheme. The power characteristic, current stress, soft switching characteristic, and backflow power of this modulation strategy are analyzed and calculated comprehensively. Then, based on this asymmetric strategy, a hybrid modulation strategy that can achieve ZVS over the entire power range with low current stress, low return power, and minimum rms current at light load is proposed. Finally, a 100–50 V/300 W prototype is built to verify the analysis.

Common Ground Quasi-Z-Source Series DC–DC Converters Utilizing Negative Output Characteristics

This article presents a general method to obtain the improved common ground quasi-Z-source series dc–dc converters. Utilizing the negative output characteristic of the quasi-Z-source converter (QZSC), the output voltage of the improved converter is the sum of the input voltage and the output voltage of the original QZSC, which means that part of the energy is directly supplied by the input voltage source without passing through QZSC. Therefore, compared with the original QZSC, the proposed improved converter has advantages such as lower voltage stress, lower current stress, higher voltage gain, and higher efficiency. More importantly, all these improvements are obtained with no obvious drawback. No additional component is required, the input and output remain common ground, and if the input current of the original converter and the load current are continuous, the input current of the improved converter is also continuous. In order to prove the feasibility of the proposed method, first, the improved converters of three existing QZSCs are obtained. Then, the operation principle, parameter design, and comparison are introduced in sequence. Finally, the above analyses are verified by simulation and experiment results.

High step‐up active switched coupled inductor DC‐DC converter with voltage multiplier

AbstractHigh step‐up DC‐DC converters are commonly used in new energy applications such as DC microgrid, photovoltaic cell, and fuel cell. Thus, this article introduces a new nonisolated high step‐up DC‐DC converter based on active switched coupled inductor with a voltage multiplier cell. The proposed converter presents low current and voltage stress across the switches owing of the dual active switches structure. Besides that, by the voltage multiplier cell (one diode and one capacitor), the voltage gain of proposed converter is increased. In addition, it can be highlighted that the proposed converter has low component count, simplicity of operation in continuous and discontinuous conduction mode, and energy stored in the leakage inductor that is recycled in the capacitor of voltage multiplier cell. This article discussed the principle of operation, the ideal and nonideal voltage gain, external characteristic, voltage and current stress, design guidelines, and performance comparison with previous high step‐up converters. Finally, a prototype circuit with input power 300 W, input voltage 30 V, and output voltage 400 V was built in the laboratory to verify the theoretical evaluation, and the maximum achieved efficiency was 95.35% at nominal power 300 W.

Improved Deadbeat Predictive Current Control of Dual Three-Phase Variable-Flux PMSM Drives With Composite Disturbance Observer

The dual three-phase variable-flux permanent-magnet synchronous motors (VF-PMSM) have received more attention in the variable-speed drive applications since they have advantages of high-efficiency in flux-tuning ability, low current stresses in phase legs and high fault-tolerant capability. The magnetization-state of the permanent magnets in VF-PMSM can be manipulated by the larger <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current pulse. However, the accompanied issues of parameter variation and inherent model uncertainty in magnetization manipulation of VF-PMSM increase the difficulty in parameter tuning for conventional proportional-integral controller, which deteriorates the control performance in current loop. To achieve the high performance of current tracking, an improved deadbeat predictive current control (DPCC) with composite disturbance observer has been proposed for dual three-phase VF-PMSM in this article. In the proposed composite disturbance observer, the generalized proportional--integral observer (GPIO) is employed for tracking the time-varying disturbance, and the sliding-mode observer is designed to reduce the settling time caused by the high-order GPIO for the improvement of the system dynamics. The analysis about the bandwidth-parameterized method has been presented for tuning the coefficients of the composite observer. The experimental results are presented to verify the validity of the proposed DPCC with composite disturbance observer for dual three-phase VF-PMSM drives under model uncertainty and different operating conditions.

Multiphase Low Stresses High Step-Up DC–DC Converter With Self-Balancing Capacitor Voltages and Self-Averaging Inductor Currents

Voltage gain ratio is a key limitation faced by nonisolated dc–dc converters in practical applications. Low voltage and current stresses, small volume, simple sampling control circuit, low cost, suitability for high power, scalability, and modularization are optimization trends of the dc–dc converter design. To improve the above-mentioned performance, a multiphase high step-up dc–dc converter is proposed, with advantages of high voltage gain, low switching voltage stresses, low switching current stresses, low capacitor voltage stresses, low output voltage ripple, capacitor voltages self-balancing feature, inductor currents self-averaging feature, ease of extension, and being able to be modularized. The topology derivation, comparisons with other high step-up converters, the operating principle, characteristics, and mathematical models of the proposed converter are studied in detail. Finally, a laboratory prototype of the proposed dc–dc converter operating from 400 to 800 W is built and implemented with input being 24 V and output being 400 V. The experimental results verify the feasibility and superiority of the proposed converter. The proposed multiphase high step-up converter is suitable for the applications, such as fuel cells, electric vehicles, energy storage systems, photovoltaic systems, and microgrids.

Use of Boost Power Stage for Static Voltage Gain Improvement of a Non-isolated Continuous Input Current Three-Level DC-DC Converter

The work presented in this paper describes the steady state analysis of a non-isolated and continuous conduction mode (CCM) operated three-level DC-DC converter with input boost power stage for achieving high static voltage gain. The proposed converter configuration is a double boost DC-DC conversion scheme. A boost power module consisting of a power switch, an inductor, a pre-charge diode, and a diode rectifier is introduced as the input stage in the conventional three-level DC-DC converter configuration to obtain the DC-DC converter topology suggested in this research work. The role of the input boost power stage is to extend the voltage gain of the conventional three-level boost converter. The proposed topology employs two power switches in addition to a boost power switch with simple control strategy so that the switching losses are reduced. The switches are subjected to low voltage and current stresses. The suggested non-isolated converter is operated under continuous inductor current mode in open loop configuration. The converter configuration has been simulated in MATLAB / SIMULINK platform. The input boost power stage receives a voltage of 24 V from a DC source. With low duty ratio (= 0.8) of the power switches, a DC voltage of around 208 V is obtained at the load end. The passive components of the converter are so designed that the filtering requirements on the DC output voltage and current waveforms are reduced. The voltage gain of the proposed converter is compared with that of the three-level boost converter without input boost power stage. The various modes of operation of the suggested converter are discussed with relevant equivalent circuits. The proposed system is validated using a developed hardware prototype model of 100 W converter with a low cost KA3525A PWM controller. Both simulation and prototype model results demonstrate that the proposed converter suits high voltage gain applications.

A Sharing-Branch Modular Multilevel DC Transformer With Wide Voltage Range Regulation for DC Distribution Grids

As the key equipment in dc distribution grids, dc transformer (DCT) suffers from low power density caused by a large number of submodules (SMs). Hence, this article proposes a novel DCT for the interconnection of medium-voltage dc (MVdc) and low-voltage dc (LVdc) distribution grids, which adopts a series-connected half-bridge SM branch (SSB) on MV-side to achieve low voltage stress of devices and reduce the number of SMs. Quasi square wave modulation strategy and phase-shifted control are employed to realize bidirectional power transmission control and zero-voltage switching (ZVS) for all switches. Furthermore, in order to ensure low current stress and ZVS within wide voltage range, a certain number of SMs are constantly inserted or bypassed to achieve voltage matching. Besides, smooth transition control strategy is employed to avoid current spikes caused by abruptly bypassing or inserting SMs. Based on the theoretical analysis, design consideration and control strategy are elaborated. Finally, a 500&#x00A0;kW&#x002F;6&#x2013;12&#x00A0;kV&#x002F;750&#x00A0;V simulation model and a 2&#x00A0;kW prototype are built to verify the proposed DCT.

Nonisolated high step‐up DC‐DC interleaved SEPIC converter based on voltage multiplier cells

AbstractThis work presents a nonisolated high step‐up single‐ended primary inductance converter (SEPIC) topology for high‐power, high‐current applications. The converter operation is based on the interleaving principle, and the active switches are driven by gating signals phase shifted by 180°, whereas automatic current sharing is achieved owing to an autotransformer with unity turns ratio. It is possible to extend the voltage gain employing voltage multiplier cells (VMCs) composed of diodes and capacitors. Prominent advantages of the structure include low current and voltage stresses on the semiconductors, inherent modularity, better thermal distribution, and reduced dimensions of the filter elements. A comprehensive theoretical analysis is derived, from which a 1‐kW prototype is designed and thoroughly evaluated.

A new single-stage single-switch isolated AC–DC PFC topology with high duty cycle and low current stress and high efficiency

A new single-stage single-switch isolated AC–DC PFC topology with high duty cycle and low current stress and high efficiency

An Optimized DPS Control for Dual-Active-Bridge Converters to Secure Full-Load-Range ZVS With Low Current Stress

It is a challenge for dual-active-bridge (DAB) converters to take a good balance between full-load-range zero-voltage switching (ZVS) and control complexity with a wide voltage range. Dual-phase-shift (DPS) control can extend the ZVS range greatly compared with single-phase-shift (SPS) control, and it has fewer control variables with reduced operation modes compared with triple-phase-shift (TPS) control. However, with conventional DPS control, at least a pair of switches will be operated under hard switching within a large power range, which severely reduces the efficiency, especially at the high switching frequency. To solve this problem, based on the Lagrange multiplier method (LMM), an optimized DPS control utilizing magnetizing current is proposed. In this article, the magnetizing inductance is designed to create the possibility of full-load-range ZVS achievement for all power switches. Based on ZVS analysis considering switch junction capacitors and power characteristics analysis, a power control law premised on full-load-range ZVS achievement is proposed to achieve low current stress. Finally, the effectiveness of the proposed solution is verified by experimental results obtained with a 500-W, 250-kHz gallium–nitride (GaN)-based prototype.

Evaluation of stability and robustness of poly-Si resistors with different dopant concentrations

The stability and robustness of lightly and highly doped poly-Si resistors were evaluated. These resistors exhibited distinct electrical resistance properties and temperature dependences, which can be explained through the grain and grain boundary conduction mechanisms. The resistance shift saturated under the low current stress condition, but continued to increase under the high current stress condition. A novel carrier trapping density model was proposed to explain this behavior. A generalized free energy model that considered stress temperature and stress current dependences was proposed to account for the stability lifetime of a poly-Si resistor based on the resistance shift criterion. Robustness evaluation with transmission line pulse test revealed that the breakdown current exhibited a pulse width dependence which was further explained by a thermal-conduction energy model.

Double stage converter with low current stress for low to high voltage conversion in nanogrid

A low to high voltage conversion technique has been proposed in this paper using double stages of switched inductors for nanogrid applications. The proposed converter topology utilizes fewer components, achieves high voltage gain at a small value duty ratio, and has high efficiency. Moreover, the proposed converter provides a reduced switch current stress to obtain a stable constant boosted DC voltage. Therefore, it requires low-current rating switches and hence leads to cost reduction. Additionally, the load and the source end are connected to the same ground. The principle of operation, theoretical waveforms in Continuous Conduction Mode (CCM), and Discontinuous Conduction Mode (DCM) with steady-state analysis are discussed. A detailed discussion about the effect of non-idealities on the high voltage conversion, the design of components, and a comparison of the performance characteristics such as the number of components, Voltage Gain in CCM, switch current stress, normalized switch voltage stress, and efficiency of the proposed converter topology with other converters are presented. The experimental results of the 500W laboratory prototype are also shown to validate the operation of the proposed converter.

A Modified Switched-Coupled-Inductor Quasi-Z-Source Inverter

This article proposes a modified switched-coupled-inductor quasi-Z-source inverter, which is characterized by a continuous input current, low dc-link voltage overshoot, and high efficiency. The bootstrap capacitor in this improved module enhances the boost capability of the inverter at a low shoot-through duty cycle D. Thanks to the distinct positions of the third and fourth windings N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sub> and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">24</sub> of the multiwinding coupled-inductor in the proposed inverter, these windings have low current stress during shoot-through state and no current flow at nonshoot-through state. The work environment of the coupled-inductor is optimized, and the inverter efficiency is substantially improved due to its low copper loss. This article studies the operating modes, analyzes the voltage and current stresses of different components, and studies their energy consumption in detail. Finally, the feasibility of the proposed inverter is validated via a 1-kW prototype developed in the laboratory and the test results are consistent with the theoretical analysis.

Unified multimode modelling, stability analysis, and reinforced sliding‐mode design of high‐order buck/boost DC–DC converters for DC energy systems

Unified modelling, analysis, and reinforced sliding-mode design of a high-order buck/boost converter are proposed for DC energy systems. The high voltage gain with low current stress on the converter’s circuit components will noticeably improve its performance in DC energy systems. The mathematical model of this multimode converter is established by deploying the averaging state-space modelling approach and a duty-ratio constraint-deriving method. According to the unified multimode model, a reinforced sliding-mode controller is proposed for this converter, and the sliding surface is designed using the estimated load information. A complete stability analysis of the reinforced sliding-mode regulated converter system is also carried out. In addition, a hardware-based comparison study involving the proposed controller and an existing robust sliding-mode controller is provided to validate the effectiveness of the unified workflow involving modelling, analysis, and regulation design.

Modelling, analysis, and implementation of a switched‐inductor based DC/DC converter with reduced switch current stress

This paper proposes a technique for switch current stress reduction in a Switched Inductor DC-DC Boost Converter (SIBC). The proposed technique comes up with a low-cost design, high voltage conversion ratio with a less duty cycle value, and lower current stress without increasing the component count. This topology is basically a transformer-less design where one diode of the traditional switched inductor configuration has been replaced with a switch, which is in parallel with the existing switch, resulting in a design that can incorporate active switches with a low current rating, since the total input current is equally shared by them. The detailed modes of operation in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) and steady-state analysis, the non-idealities’ effect on voltage gain, design approach, and a comparative study with other DC-DC converters for some significant performance characteristics are provided. The experimental validations for the performance and working of the 500 W designed prototype are presented.

A Four-Phase Current-Fed Push–Pull DAB Converter for Wide-Voltage-Range Applications

In this article, a four-phase current-fed push–pull dual active bridge converter is proposed for applications requiring high power and a wide-voltage range. In addition to the conventional advantages of a small filter inductor, a small clamp capacitor, and low current stress in the primary switches due to the effect of four-phase interleaving, the proposed converter has a low total rms current of switches when operating at a wide-voltage range compared with the existing two- and three-phase converters. Also, the proposed converter was shown to be capable of the complete ZVS turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-on</small> of all switches under a wide duty cycle range of 0.25–0.75 in both power-flow directions when small auxiliary inductors were added. A balanced four-phase transformer structure is proposed not only to cancel the dc-flux offset caused by the dc component of the primary winding current but also to reduce the core volume, footprint, and height of the transformer compared with the separated-core transformer. The experimental results from a 15-kW prototype are provided to validate the proposed concepts. The converter achieved a peak efficiency of 98% and maintained high efficiency when operated at a wide-voltage range.

Active Cross-Commutated (ACC) Buck Converter

To address the hard-switching issue of conventional buck converter and high-voltage/current stress issue of soft-switched converter like resonant cross-commutated buck converter, a new soft-switched dc–dc topology with two-phase operation is proposed in this article. The ac current generated from the floating half bridge of one phase is injected into the switching node of another phase to realize zero-voltage switching for all MOSFETs and zero-current switching for the low-side MOSFETs. This method is named as active cross-commutation (Acc). The benefits of AccBuck converter include soft switching, low-voltage stress of low-side switches, low current stress for all switches, and fixed switching frequency. The operation principles with and without parasitic output capacitance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</sub> ) are analyzed by using the state-plane method. Clamped diodes are added to reduce the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</sub> -related ringing. The analytical formula of voltage gain is derived, which is related to the duty ratio, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</sub> , inductance, load current, and switching frequency. A prototype was fabricated to demonstrate the proposed converter. During the fixed-duty-ratio operation, the converter achieves 97.8% peak efficiency and 1410 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density at 50 A output current, 54 V input, and 9 V output. The calculated load line and regulation capability are also verified experimentally.

A hybrid two‐stage modular DC–DC converter with zero‐voltage switching

AbstractConventional modular multilevel converters (MMCs) are widely used in high power applications due to their various astonishing advantages; however, they fail to achieve balanced capacitor voltage in DC operation. In this paper, a hybrid two‐stage modular DC–DC converter is proposed to solve the issue of unbalanced capacitor voltages. The proposed converter consists of a single‐phase half‐bridge MMC with half‐bridge submodules followed by a medium voltage valves‐based H‐bridge rectifier. The proposed converter is used in medium‐voltage applications such as feeding a DC‐load or interconnection between two DC grids of different voltage levels. The proposed configuration achieves successful DC–DC conversion with a low number of switches, a high conversion ratio with bidirectional power flow, low current stresses, soft switching across the second stage, and low switching losses. The operational concept and the control algorithm have been illustrated in detail. Finally, the effectiveness of the proposed DC–DC converter is evaluated based on simulation studies of MATLAB SIMULINK and a scaled‐down laboratory experimental test rig.

Hybrid High Voltage Gain Transformerless DC–DC Converter

In this article, a new hybrid transformerless high voltage gain dc–dc converter was created by merging a two-inductor boost converter with voltage multiplier and switched capacitor cells. The main advantages of the proposed converter are high voltage gain, simplicity of operation, high efficiency, lower voltage, and lower current stresses on the components. A 200 W, 37.4 V/400 V, 100 kHz prototype was implemented in the laboratory to evaluate the proposed converter, which reached a maximum efficiency of 98.24 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> .