DC Modulation Research Articles

Internal Model-Based Disturbance Observer With Application to CVCF PWM Inverter

In constant-voltage constant-frequency (CVCF) pulsewidth modulation (PWM) dc–ac inverters, the lumped disturbance, including the parameter uncertainties, unmodeled dynamics, and nonlinear loads, will deteriorate the performance and cause high harmonic distortions, or even result in instability. Conventional disturbance observer (CDOB), in which a low-pass $Q$ filter is adopted to estimate the lumped disturbance, cannot completely eliminate the harmonics. While the conventional repetitive control (CRC) can attenuate the harmonics by using the error signal of previous period(s), that may result in slow transient response due to nonperiodic components in the tracking error during the transient state. In this paper, an internal model-based disturbance observer (IM-DOB) is proposed and has been applied in a CVCF PWM inverter to improve the control performance. In IM-DOB, a novel IM-based disturbance estimation observer is proposed to estimate the disturbance both in the low-frequency region and at harmonic frequencies, while compensation filters are introduced to enhance the robustness and stability. The IM-DOB scheme, which fuses the merit of CDOB and CRC, is actually a two-degree-of-freedom scheme. The stability analysis and a design case are also given. Comparative experiments are conducted to demonstrate the effectiveness of the proposed scheme.

Analysis and elimination of the return power of the pulse width modulation of the bidirectional full bridge DC–DC converter

In order to eliminate the circulation power bidirectional full bridge DC–DC converter, power analysis of circumfluence phenomenon exists traditional phase shifting control and dual phase shifting control, a kind of inductor current zero crossing control method is proposed, to completely eliminate the phenomenon of flow power. The operating principle of the inductor current zero crossing control is described and analyzed in detail, and the converter operating status is analyzed, establish the mathematical model of transmission power. The influence factors of the maximum transmission power of the forward and the reverse transmission values are discussed. Finally, the experimental results show that the inductor current zero crossing control is feasible.

Evaluation of the Built-in Voltage of a Au/n-GaAs Schottky Barrier Diode by Using Electroreflectance Spectroscopy

The built-in voltage (V bi ) of a Au/n-GaAs Schottky barrier diode was examined by using electroreflectance (ER) spectroscopy. The ER spectra were measured at various modulation voltages (v ac ) and dc bias voltages (V bias ). The interface electric fields (E i ) were obtained from the observed Franz-Keldysh oscillations (FKO) in the ER spectra. When v ac was increased, the amplitudes of the ER spectra varied linearly, but the line shapes of the ER spectra did not change. E i decreased from 19.3 × 104 V/cm to 4.39 × 104 V/cm with increasing V bias from −0.5 V to 0.6 V. From the relationship between V bias and E i 2 , the V bi and the carrier concentration (n) were found to be 0.70 V and 2.4 × 1016 cm −3, respectively.

Fault Diagnosis and Fault-Tolerant Control Operation of Nonisolated DC–DC Converters

This paper proposes a fault diagnosis and identification method for nonisolated dc–dc converters. The method can detect the fault, and identify the faulty switch and the switch fault type in less than one switching cycle. The main idea is to apply the derivative of the inductor current based on the modulation of the particular dc–dc converter to provide a predictive current emulator model. The measured inductor current and its corresponding predicted current are used to diagnose the switch fault. The method, implemented in a digital signal processor, is robust to common converter asymmetry such as load variations, input disturbances, etc. The proposed fault diagnosis method has been analyzed, tested, and validated for a boost converter.

An Intelligent Dual-Voltage Driving Method and Circuit For a Common Rail Injector for Heavy-Duty Diesel Engines

The control accuracies of the injection time and fuel quantity are the most important factors affecting the fuel economy and emissions of an engine equipped with a high-pressure common-rail fuel injection system. This paper presents an intelligent dual-voltage driving control that can simultaneously reduce the response time of the injector and improve the accuracy of the injected fuel quantity. The designed method employs a novel boost dc–dc circuit and does not require an additional independent dc–dc module that includes an inductor switch MOSFET and a controller. During the time interval between two continuous injections, the low-side MOSFET serves as a dc–dc switch, and the software in the controller controls the dual-voltage dc–dc, which uses the injector as a charging inductor of the dc–dc module. The operation principle of this intelligent driving circuit is described. Experimental results show that this method can not only significantly decrease the response time of the injector but also improve the stability of the fuel injection process.

Electrochemical transformation of platinum spheres into nanocubes and nanocubebipyramids

An electrochemical procedure (capping-agent free) to produce nanocrystalline platinum surfaces is developed by applying modulated AC and DC potentials to platinum wires in acid media. Platinum nanospheres grow after a DC potential has been applied for a long period, followed by hydrogen evolution reduction. The nanospheres can be further converted into nanocubes using high-frequency symmetric square wave potentials, or into cubebipyramids by subjecting the resulting spheres and cubes to cathodic hydrogen evolution at potentials between −3.0 and −0.5V in sulfuric acid. The cubebipyramids exhibit strong catalytic activity towards carbon monoxide oxidation, which can be explained by the formation of 2(111)×(100) stepped planes.

Tumor-derived high-mobility group box 1 and thymic stromal lymphopoietin are involved in modulating dendritic cells to activate T regulatory cells in a mouse model.

High-mobility group box 1 (HMGB1) is involved in the tumor-associated activation of regulatory T cells (Treg), but the mechanisms remain unknown. In a mouse tumor model, silencing HMGB1 in tumor cells or inhibiting tumor-derived HMGB1 not only dampened the capacity of tumor cells to produce thymic stromal lymphopoietin (TSLP), but also aborted the tumor-associated modulation of Treg-activating DC. Tumor-derived HMGB1 triggered the production of TSLP by tumor cells. Importantly, both tumor-derived HMGB1 and TSLP were necessary for modulating DC to activate Treg in a TSLP receptor (TSLPR)-dependent manner. In the therapeutic model, intratumorally inhibiting tumor-derived HMGB1 (causing downstream loss of TSLP production) attenuated Treg activation, unleashed tumor-specific CD8 T cell responses, and elicited CD8α+/CD103+DC- and T cell-dependent antitumor activity. These results suggest a new pathway for the activation of Treg involving in tumor-derived HMGB1 and TSLP, and have important implications for incorporating HMGB1 inhibitors into cancer immunotherapy.

Soft switching passive snubber cell for family of PWM DC–DC converters

In this paper, a novel soft switching passive snubber cell for family of isolated/non-isolated pulse width modulation DC–DC converter is proposed. In this proposed converter, the switch is turned on with zero current switching (ZCS) and is turned off with zero voltage switching (ZVS). Besides, the main diode is turned on and off with ZVS and ZCS, respectively. In addition, the reverse recovery losses of main diode are minimized. The auxiliary diodes in the snubber cell are operated with soft switching. The proposed converter has a simple structure, low cost and ease of application. The detailed theoretical analysis of new converter is made, and a 200-W laboratory prototype is implemented. The theoretical analysis is confirmed with the experimental results. Finally, the proposed passive snubber cell is applied to family of other isolated/non-isolated DC–DC converter in order to provide soft switching.

Utility Direct Interfaced Charger/Discharger Employing Unified Voltage Balance Control for Cascaded H-Bridge Units and Decentralized Control for CF-DAB Modules

A bidirectional high-frequency isolated ac–dc converter for utility direct interfaced electric vehicle charger with vehicle-to-grid (V2G) capability is presented in this paper. This type of charger can achieve the direct utility interface with medium voltage input. It is composed of multilevel cascaded H-bridge ac–dc converter as the first stage and modular current-fed dual active bridge dc–dc converters as the second stage. For the cascaded H-bridge converter, a unified control to balance the cascaded H-bridge dc voltages is proposed for both charging and discharging modes. For the second dc–dc isolation stage, the current-fed dual active bridge converter is used in facing of the wide conversion gain in battery charging application and also to reduce the charging current ripple. Meanwhile, to improve the system flexibility and reliability, decentralized control is utilized for individual current-fed dual active bridge converters in view of the battery charging profile. The proposed method along with the presented topology can achieve voltage balance in spite of the power flow direction, simplification of the controller for the dc–dc modules and can also bear unbalanced power flow. The simulation and experimental results have been presented to show the effectiveness of the proposed control.

A PV Power Conditioning System Using Nonregenerative Single-Sourced Trinary Asymmetric Multilevel Inverter With Hybrid Control Scheme and Reduced Leakage Current

A power conditioning system (PCS) using multiple module-integrated converters and a single sourced 27-level asymmetric cascaded H-bridge multilevel inverter (MLI) without regeneration for photovoltaic (PV) applications is proposed. A newly suggested hybrid-switching closed-loop strategy is proposed to enable the use of a 27-level inverter in PV systems. The suggested hybrid-switching strategy implements fundamental line-frequency switching in the main H-bridge to ensure a high efficiency and low leakage current operation. Furthermore, high-frequency switching is used in the auxiliary H-bridge cells to achieve a higher bandwidth control loop. A cost-effective unidirectional single-ended 1-kW dc–dc module based on a boost coupled inductor and charge-pump circuits is proposed to achieve a single PV source per module for a multistring configuration. To couple the unidirectional converters with the central inverter, a jumping element in the hybrid switching strategy is introduced to enable an optimal nonregenerative operation. The proposed PCS with the control scheme is analyzed and verified using hardware results in a grid connected mode of operation.

A High Step-up PWM DC-DC Converter With Coupled-Inductor and Resonant Switched-Capacitor

In this paper, a novel high step-up pulse width modulation dc–dc converter integrating coupled-inductor and switched-capacitor (SC) techniques is presented. The proposed converter consists of a synchronous rectification Boost unit and multiple coupled-inductor-SC units. Its structure can therefore be easily extended for ultrahigh voltage gain. The diodes employed in the proposed converter can operate under soft-switching condition by utilizing leakage inductance of the coupled inductor. Low-voltage-rated transistors can be used to improve the efficiency as the voltage stress on the main switches of the proposed converter is reduced. The feasibility of the proposed converter is experimentally demonstrated by a 200 W prototype converter.

Model Validation of PWM DC–DC Converters

This paper presents hybrid automaton modeling, comparative model validation, and formal verification of stability through reachability analysis of pulse width modulation (PWM) dc–dc converters. Conformance degree provides a measure of closeness between the proposed hybrid automata models and experimental data. Nondeterminism due to variations in circuit parameters is modeled using interval matrices. In direct contrast to the unsound and computationally-intensive Monte Carlo simulation, reachability analysis is introduced to overapproximate the set of reachable states and ensure stable operation of PWM dc–dc converters. Using a 200 W experimental prototype of a buck converter, hybrid automata models of open-loop, and hysteresis-controlled converters are first validated against experimental data using their conformance degrees. Next, converter stability is formally verified through reachability analysis and informally validated using Monte Carlo simulations and experimental results.

Design and Implementation of a Wide-Area Damping Controller Using High Voltage DC Modulation and Synchrophasor Feedback

This paper describes the design strategy and testing results of a control system to improve damping of inter-area oscillations in the western North American Power System (wNAPS) in order to maintain dynamic stability of the grid. Extensive simulation studies and actual test results on the wNAPS demonstrate significant improvements in damping of inter-area oscillations of most concern without reducing damping of peripheral oscillations. The design strategy of the control system features three novel attributes: (1) The feedback law for the control system is constructed using real-time measurements acquired from Phasor Measurement Units (PMUs) located throughout the power grid. (2) Control actuation is delivered by the modulation of real power flow through a High Voltage Direct Current (HVDC) transmission line. (3) A supervisory system, integrated into the control system is in charge of determining damping effectiveness, maintaining failsafe operation, and ensuring that no harm is done to the grid.

Markovian switching model and non‐linear DC modulation control of AC/DC power system

Since the power system is actually a continuous-discrete hybrid system jointly driven by continuous time and random discrete events, a Markovian switching model of AC/DC power system is established to reflect the operating state of the system. Based on the model, a novel non-linear DC modulation control with time-delay compensation is derived to improve the transient rotor-angle stability of the entire AC/DC power system. The main contributions are: (i) the external events are described as Markovian jumps in system model parameters to reflect the random discrete characteristic of system operating. Meanwhile, the Markovian state transition rates are replaced by the outage rates and repair rates, which avoids expensive computation when the numbers of system operating modes are large; (ii) The time delays are regarded as a kind of bounded disturbance depending on system state and input. By a robust compensation control, the negative influence of time delay disturbance can be eliminated. Simulation performed on a dual-infeed AC/DC system shows the effectiveness of the proposed method in improving the transient stability of the power system.

Fast switch fault diagnosis for PWM DC–DC low power converters

In this paper, a fast switching fault diagnostic scheme is proposed for low‐power pulse width modulation (PWM) DC–DC converters operating in different conduction modes. The outstanding feature of the proposed scheme is that no additional sensing circuits are needed. This is achieved by using the differential of output ripple voltage and the switch gate driver signal for diagnosis. Since the output voltage has to be normally measured for control purposes and the PWM signals are known to the controller, no additional sensors are needed in the proposed scheme. Moreover, based on the real‐time output voltage measurement and switch gate driver signal, the characteristics of switch open‐ and short‐circuit faults can be rapidly extracted, specifically, in less than one switching cycle. Besides, the fault detection scheme can be implemented by a low‐cost logical hardware circuit, which can be integrated into the control unit. The fault diagnosis principle, design considerations, and implementation of the detection scheme are discussed in this paper. Experimental results show that the fault detection system can detect the switching fault in four‐tenths of the switching period. Besides, the proposed method can be used in the applications where the output voltage ripple rate is more than 4%, which covers most situations. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Photonic microwave multi-band frequency conversion based on a DP-QPSK modulator for satellite communication

We propose and demonstrate a simple, flexible and stably operated multi-band frequency conversion approach based on a dual-polarization quadrature phase shift keying modulator (DP-QPSK). The modulator incorporating two dual parallel Mach–Zehnder modulators (DPMZMs) which perform as OFC generator and +1st carrier suppressed single sideband generator, respectively, to achieve the purpose of frequency conversion. The theoretical analysis indicates that by properly adjusting six DC bias points in the integrated modulator and two modulation indices, a frequency of received RF signal can be directly converted into different frequencies that cover different bands simultaneously. The simulation results verified the possibility. For example, the received C band frequency of 3.8 GHz can be converted into X, Ku, K and Ka bands. An X band frequency of 9.6 GHz can be down-converted to C band and up-converted to Ku, K, Ka band. In addition, the simulation also focuses on how the adjustable parameters (such as DC bias points and modulation index) influence the conversion results. It demonstrates stable conversion efficiency against the DC drafting.

ZVT‐PWM DC–DC boost converter with active snubber cell

In this study, a novel zero voltage transition pulse width modulation (ZVT-PWM) DC–DC boost converter with an active snubber cell is proposed. All of the semiconductor devices in the converter turn on and off with soft switching (SS). The main feature of the proposed converter is the absence of extra current or voltage stress on the main switch and main diode. There is also no extra voltage stress on the auxiliary switch and the auxiliary diodes. The main switch turns on with ZVT and turns off with zero voltage switching. The auxiliary switch turns on with zero current switching and turns off with zero current transition. The proposed converter smoothly operates under light-load conditions. Having a simple structure at low cost is the main advantage of the proposed converter. This study also realises the theoretical analysis of the proposed converter. The experimental results, the operating stages and the key waveforms of the proposed converter, are given in detail for 500 W and 100 kHz switching frequency. Moreover, it is shown that the overall efficiency reaches a value of 97.8% at nominal output power. The proposed SS topology can be used in applications with the battery power source and low-voltage DC-link.

Analysis, Design, and Implementation of a Zero-Voltage-Transition Interleaved Boost Converter

This study proposes a novel zero voltage transition (ZVT) pulse width modulation (PWM) DC–DC interleaved boost converter with an active snubber cell. All the semiconductor devices in the converter turn on and off with soft switching to reduce the switching power losses and improve the overall efficiency. Through the interleaved approach, the current stresses of the main devices and the ripple of the output voltage and input current are reduced. The main switches turn on with ZVT and turn off with zero voltage switching (ZVS). The auxiliary switch turns on with zero current switching (ZCS) and turns off with ZVS. In addition, the snubber cell does not create additional current or voltage stress on the main switches and main diodes. The proposed converter can smoothly achieve soft switching characteristics even under light load conditions. The theoretical analysis and operating stages of the proposed converter are made for the D > 50% and D < 50% modes. Finally, a prototype of the proposed converter is implemented, and the experimental results are given in detail for 500 W and 50 kHz. The overall efficiency of the proposed converter reached 95.5% at nominal output power.

Tolerogenic dendritic cells generated with dexamethasone and vitamin D3 regulate rheumatoid arthritis CD4+ T cells partly via transforming growth factor-β1.

Tolerogenic dendritic cells (tolDC) are a new immunotherapeutic tool for the treatment of rheumatoid arthritis (RA) and other autoimmune disorders. We have established a method to generate stable tolDC by pharmacological modulation of human monocyte-derived DC. These tolDC exert potent pro-tolerogenic actions on CD4+ T cells. Lack of interleukin (IL)-12p70 production is a key immunoregulatory attribute of tolDC but does not explain their action fully. Here we show that tolDC express transforming growth factor (TGF)-β1 at both mRNA and protein levels, and that expression of this immunoregulatory cytokine is significantly higher in tolDC than in mature monocyte-derived DC. By inhibiting TGF-β1 signalling we demonstrate that tolDC regulate CD4+ T cell responses in a manner that is at least partly dependent upon this cytokine. Crucially, we also show that while there is no significant difference in expression of TGF-βRII on CD4+ T cells from RA patients and healthy controls, RA patient CD4+ T cells are measurably less responsive to TGF-β1 than healthy control CD4+ T cells [reduced TGF-β-induced mothers against decapentaplegic homologue (Smad)2/3 phosphorylation, forkhead box protein 3 (FoxP3) expression and suppression of (IFN)-γ secretion]. However, CD4+ T cells from RA patients can, nonetheless, be regulated efficiently by tolDC in a TGF-β1-dependent manner. This work is important for the design and development of future studies investigating the potential use of tolDC as a novel immunotherapy for the treatment of RA.

IL-10–Modulated Human Dendritic Cells for Clinical Use: Identification of a Stable and Migratory Subset with Improved Tolerogenic Activity

Dendritic cells (DCs) are key regulators of protective immune responses and tolerance to (self-)Ags. Therefore, the scientific rationale for the use of tolerogenic DC therapy in the fields of allergies, autoimmunity, and transplantation medicine is strong. In this study, we analyzed the tolerogenic capacity of IL-10-modulated DC (IL-10DC) subpopulations to identify a DC subset that combines potent immunosuppressive activities with valuable immune properties for clinical implementation. IL-10DCs consist of two phenotypically distinct subpopulations: CD83highCCR7+ IL-10DCs and CD83lowCCR7- IL-10DCs. Suppressor assays with activated effector T cells revealed that CD4+ regulatory T cells generated by CD83high IL-10DCs (iTreg+) exhibited a significantly higher suppressive capacity compared with CD4+ regulatory T cells generated by CD83low IL-10DCs (iTreg-). In this context, iTreg+ displayed a more activated phenotype (proliferation, cytokine production) compared with iTreg- In contrast to CD83low IL-10DCs, CD83high IL-10DCs exerted a strong migratory capacity toward the secondary lymphoid organ chemokine CCL21 and retained a functionally stable phenotype under inflammatory conditions. In addition, CD83high IL-10DCs expressed significantly higher levels of surface and soluble CD25. Functional analysis demonstrated that IL-10DC-related soluble CD25 efficiently inhibited the proliferation of activated T cells and that blockade of CD25 function abolished the induction of regulatory T cells by IL-10DCs, indicating a critical role for IL-10DC-related CD25 in shifting the immune response toward an iTreg- controlled tolerance reaction. In conclusion, the selective use of the CD83high IL-10DC subset may result in a higher efficacy of tolerance induction in vivo and may support the development of novel DC vaccination strategies for transplantations, as well as for allergic and autoimmune diseases.