Variable Duty Cycle Research Articles

Improved perturb and observe maximum peak power tracking for solar satellite systems

The aim of this work is to solve partial shading problem in solar panels to detect the global peak power point that can be used in satellite systems. This can be done by proposing a modified perturb and observe control algorithm depends on comparing all the local peak power points in photovoltaic system to detect the global one, by making initial estimation to the duty cycles of the corresponding local peak power then using perturb and observe to make fine tuning to reach the exact local peak points when oscillations happen. Also to detect the oscillations theory of operation of incremental conductance algorithm is used depending on the difference between incremental conductance and the instantaneous conductance values. The idea of operation is verified using boost converter applied in Matlab/Simulink showing good results. Also variable duty cycle is used to solve the problem of oscillations in output power.

A Three-Port Isolated Three-Phase Current-Fed DC–DC Converter Feasible to PV and Storage Energy System Connection on a DC Distribution Grid

This paper presents a three-port three-phase current-fed dc–dc converter with high-frequency isolation and bidirectional power flow. Port I is fed by a battery bank, port II employs a set of photovoltaic modules, and port III is connected to a dc link. The topology uses three single-phase H-bridge cells in the primary side and a three-phase H-bridge converter in the secondary one. High-frequency isolation is ensured by three single-phase transformers connected in an open delta-wye configuration. The theoretical analysis is performed considering the fundamental component of the voltage across the transformers. Maximum power point tracking, the battery current, and the power flow between the primary and secondary sides are controlled by the use of variable duty cycle technique in the primary side and the use of phase-shift technique between the primary and secondary bridges. In order to validate the study, experimental results of the proposed system considering the dc rated voltages as 48 V/96 V/380 V for Ports I/II/III, respectively, and rated power of 3.5 kW are carried out.

Ripple Vector Cancellation Modulation Strategy for Single-Phase Quasi-Z-Source Inverter

The double-frequency (2ω) power flows through the DC side of the single-phase quasi-Z-source inverter (QZSI) leads to the 2ω voltage ripple of capacitors and 2ω current ripple of inductors. This paper proposes a ripple vector cancellation modulation strategy (RVCMS) based on the thought of ripple vector cancellation. By analyzing the mechanism of ripple generation and transmission, we can obtain a variation of a shoot-through duty cycle to generate a compensated 2ω ripple used to cancel the 2ω current ripple of inductors caused by the 2ω ripple of DC link current, and the 2ω compensated variation of a shoot-through duty cycle with a specific amplitude and phase is added to the constant shoot-through duty cycle. Finally, simulation and experimental results demonstrate the correctness and effectiveness of the proposed modulation strategy for the single-phase QZSI.

Simulation and Experimentation of a Single Stage Boost Inverter

This paper presents simulation and experimental verification of a single stage DC to AC boost inverter for solar photovoltaic (SPV) applications. This topology integrates the boost converter inside the conventional h-bridge inverter topology. This eliminates the need for a separate boost converter. The whole system requires four basic switches of an h-bridge inverter for both boost and DC-AC conversion operation. Overall, the efficiency is improved because no additional switch is required for the boosting operation. The duty cycle variations are implemented using sinusoidal pulse width modulation (SPWM). The firing pulses for switches used in the h-bridge inverter are provided using Arduino-Uno platform. The principle of operation along with the simulation and experimental results are also presented.

Forming and Co-simulation of Square and Triangular Waveforms by Using System Generator

Nowadays Field Programmable Gate Arrays(FPGAs) are used to implement several processes in different areas such military defense, medical devices, automation, telecommunication, and image processing etc. Some of the advantages of FPGA are parallel and hardware processing. On the other hand programming FPGAs by classic design methodologies requires much effort. Therefore, design tools like System Generator can provide facilities about programming FPGAs. System Generator is a design tool from Xilinx to program the Xilinx FPGAs in MATLAB/Simulink graphic based editor. Also its block set is limited with respect to Simulink, has. In this study square, and triangular waveforms are built with the basic blocks of System Generator tool. These waveforms belong to basic sources for signal processing. Generally, they are used in power electronics especially for producing PWM, or sinus PWM. Also co-simulation can be done by using System Generator. Square waveform block, which is implemented, has variable amplitude, frequency, duty cycle, and offset values whereas triangular waveform has variable amplitude, frequency, and offset values. Triangular waveform has an error as 2 % due to data bus width.

Design and Implementation of Fpga Based Digital Switching Controller for Dc-Dc Converters Used In System- On- A-Chip Applications

DC-DC converters are electronic devices that are used to change DC electrical power efficiently from one voltage level to another. This paper proposes a new Digital Pulse Width Modulator (DPWM) which generates variable duty cycle PWM pulse and it can be used as switching controller for DC-DC converters used in battery powered portable electronic and mobile devices. DPWM utilizes the advantage of Digital Clock Manager (DCM) present in FPGA to multiply the clock frequency to eliminate the clock skew. The proposed DPWM uses the four bit gray counter and one hot encoder with SR flip flop to generate the PWM pulse whose duty cycle can be varied according to the control signal. To verify the results DPWM was implemented in SPARTAN 3A.

An Enhanced Multiple Harmonics Analysis Method for Wireless Power Transfer Systems

First harmonic analysis (FHA) is arguably the most widely used analytical technique for wireless power transfer (WPT) circuits due to its simplicity. Although FHA can provide closed-form solutions, the existence of rectifier diode forward voltage drop and higher order harmonics, especially the second and third harmonics at variable duty cycle operation, can significantly deteriorate its accuracy. This paper presents an accurate and efficient method called enhanced multiple harmonic analysis (eMHA) for the optimal design and optimal control of WPT systems. The eMHA method considers the nature of nonlinear rectification networks under nonsinusoidal current and reexamines the concept of the equivalent load. As a result, the rectified WPT system is transformed into a series of linear systems with complex load impedances. The steady-state electric quantities can be then explicitly calculated. This enables eMHA to seamlessly work with numerical optimization algorithms to facilitate the automated design and optimization of WPT systems. An example of optimal design and optimal control of a 10 W WPT system is demonstrated. The results obtained by eMHA and FHA are also compared. A prototype of the designed circuit was constructed. The accuracy and effectiveness of eMHA are verified by experimental measurements. This paper is accompanied by a MATLAB-based analytical tool with a graphical user interface demonstrating the effects of circuit variables on electrical quantities and waveforms.

Study of duty cycle influence on the band gap energy of TiO2/P coatings obtained by PEO process

Plasma Electrolytic Oxidation (PEO) processing was used to produce ceramic coatings of TiO2/P, on commercially pure titanium sheets varying the energy per cycle supplied by the power source. Specifically, this work was focused on evaluating the influence of the variations of the duty cycle on the band gap energy of the obtained TiO2/P coatings. The coatings were produced in a base electrolyte composed of Na3PO4 and NaOH. The PEO processing was carried out using a constant voltage of 356 V, a pulse frequency of 2000 Hz and duty cycle variations of 1%, 10%, 30% and 50% with a total processing time of 7 min per sample. X-ray Diffraction (XRD), Raman Spectroscopy (RS), Atomic Force Microscopy (AFM), and Infrared Spectroscopy (IRS) were used to characterize the structural phases of the coatings, the surface morphology, and the concentration of phosphate, respectively. According to the analysis carried out by AFM, as the duty cycle increases, the roughness increases and the pores surrounded by nodular regions begin to appear in the discharge channel during oxidation. XRD showed an amorphization of the anatase phase as the duty cycle increases, which is considered a stable intermediate state between anatase and rutile. From RS, the band corresponding to the rutile structure was evident for the sample with 50% of the duty cycle. Finally, diffuse reflectance spectroscopy revealed that increases in the duty cycle from 10% to 50%, induced a change in the band energy of the coatings from 3.29 to 3.02 eV.

Abstract 2171: Activatable nanodelivery of high payload gemcitabine augments therapeutic efficacy in murine breast and pancreatic cancer models

Abstract Gemcitabine (Gem) is the standard of treatment for metastatic pancreatic ductal adenocarcinoma (PDAC) and an effective anticancer drug for various solid tumors. However, clinical application of Gem chemotherapy is hampered by suboptimal delivery of the drug, mainly due to short circulation time and poor penetration of drug into the hypo-vascularized and dense fibrous stroma of PDAC. Here, we present a novel method to improve both loading and stability of Gem in temperature-sensitive liposomes (TSL). TSL have the potential to be locally activated by exposing tumor to ultrasound-mediated hyperthermia (USH) triggering release of large amounts of free drug in the tumor vasculature, which can then rapidly penetrate into the heated tumor. Gem was passively loaded into TSL composed of DPPC:DSPC:DSPE-PEG2k (80:15:5) in the presence of copper(II) gluconate and triethanolamine at final 0.12 mg-drug/mg-lipid. Formation of a CuGem complex improved drug loading and stability and reduced systemic toxicity. Mice with bilateral invasive neu deletion (NDL) tumors (4-5 mm) were treated with an i.v. administration of CuGem-TSL at 10 mg Gem/kg body weight. USH was employed to trigger the release of drug; one tumor in the bilateral tumor model was insonified with a peak ultrasound pressure of 1.1 MPa at a frequency of 1.5 MHz at 43°C for 5 min prior to and 30 min post drug injection with a variable duty cycle. We found that copper(II) gluconate possesses superior potential to solubilize Gem up to 150 mg/mL and augments passive drug loading. Upon loading Gem, formation of a complex with copper further improved drug loading and stability within TSL. By optimizing the lipid composition of the liposomal shell, we achieved high loading content of Gem at up to 12% by weight in TSL (CuGem-TSL), 4-fold greater than previously reported. Cryo electron microscopy confirmed the presence of liquid crystalline structures within CuGem-TSL, which was not observed in the absence of copper (Gem-TSL). The resulting high-content CuGem-TSL displayed a rapid release of Gem (80%) within 5 min at 42°C with only 25% release over 30 min at 37°C in the presence of serum. In vitro CuGem-TSL demonstrated equivalent toxicity to free Gem against both murine breast cancer and pancreatic cancer. One hour following intravenous administration, 75% of Gem was effectively retained in circulating TSL, whereas no drug was detected in mouse plasma with free drug administration. Three repeated administrations of CuGem-TSL combined with USH over a two-week treatment course suppressed tumor growth in NDL, model of murine breast cancer, with limited toxicity, enhancing survival when compared to treatment with free Gem alone. Additionally, in a more aggressive tumor model of murine pancreatic cancer (KrasLSL-G12D/+; Trp53LSL-R172H/+; Pdx-Cre, mT4 tumor source), CuGem-TSL with USH induced cell death and regions of apoptosis and necrosis. Citation Format: Samantha T. Tucci, Azadeh Kheirolomoom, Elizabeth S. Ingham, Lisa M. Mahakian, Sarah M. Tam, Josquin Foiret, Neil E. Hubbard, Alexander D. Borowsky, Mo Baikoghli, R. Holland Cheng, Katherine W. Ferrara. Activatable nanodelivery of high payload gemcitabine augments therapeutic efficacy in murine breast and pancreatic cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2171.

Abstract 3952: Localized nanodelivery combined with immunotherapy promotes curative anti-tumor responses in a murine breast cancer model

Abstract Optimal pairing of chemotherapy with immunotherapy can harness potential synergies and augment tumor immunity in solid tumors with low mutation burden by i) reducing tumor bulk, ii) releasing tumor antigen for cross-presentation and cross-priming, iii) releasing cancer-suppressive cytokines/chemokines, and iv) retaining circulating immune cell populations. Temperature-sensitive liposomes (TSL) have the potential to accomplish these goals as ultrasound (US) insonation or other treatment modalities can release the chemotherapy within bulky solid tumors in response to hyperthermia to maximize the local response and minimize off-target effects. Here we used Doxorubicin (Dox), stabilized within the core of TSL by forming a drug complex with copper (CuDox), to mediate immunogenic cell death (ICD) and release of type I interferons (IFNs). This activatable chemotherapy (CuDox-TSL+US) was combined with immunotherapy using CpG-ODN, a toll-like receptor 9 agonist, and a PD-1 antibody (αPD-1) for checkpoint blockade. We assessed the schedule and sequence of the chemo-immunotherapy protocol to maximize therapeutic outcome. CuDox-TSL were made of DPPC:MPPC:DSPE-PEG2k, 86:10:4 in the presence of copper (II) gluconate and triethanolamine at 0.2 mg-Dox/mg-lipid. Mice with bilateral invasive neu deletion (NDL) tumors (4 mm) were treated with an i.v. administration of CuDox-TSL at 6 mg Dox/kg body weight. One tumor was insonified with a peak ultrasound pressure of 1.1 MPa at a frequency of 1.5 MHz at 42°C for 5 min prior to and 20 min post drug injection with a variable duty cycle. Upon completion of US-hyperthermia, 100 µg of CpG-ODN 1826 was injected intratumorally to the insonified tumor. Three days later αPD-1 (200 µg, i.p.) was administrated. We found that Dox in combination with hyperthermia induced release of ICD markers and type I IFNs in cell culture of various murine cancer cell lines. Following intravenous administration of CuDox-TSL, ultrasonic activation of liposomes in the treated tumors promoted release and cross-presentation of a model tumor antigen by antigen-presenting cells in distant tumors. While a variety of chemo-immunotherapy protocols achieved a complete response in more than 50% of treated mice, the complete response rate was greatest (90%) when one week of immunotherapy priming preceded activatable chemotherapeutic administration. Repeated chemotherapeutic delivery, while effectively reducing viable tumor, also reduced efficacy and the fraction of viable CD8+ T-cells as indicated by flow cytometric analysis. Taken together, the results suggest that a single-dose administration of activatable chemotherapy after immune priming enhances survival in a murine model of breast cancer. In clinical practice, however, assessment of macrophage and T-cell populations over the course of treatment could help inform dose timing and number of treatment repetitions. Citation Format: Azadeh Kheirolomoom, Matthew T. Silvestrini, Elizabeth S. Ingham, Lisa M. Mahakian, Sarah M. Tam, Spencer K. Tumbale, Josquin Foiret, Neil E. Hubbard, Alexander D. Borowsky, William J. Murphy, Katherine W. Ferrara. Localized nanodelivery combined with immunotherapy promotes curative anti-tumor responses in a murine breast cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3952.

Intensification of delignification of sawdust and subsequent enzymatic hydrolysis using ultrasound.

The current work investigates intensification of delignification of sawdust and subsequent enzymatic hydrolysis to produce reducing sugars with the use of ultrasound. Alkaline hydrolysis of sawdust was initially performed to remove lignin which hampers the rate of enzymatic hydrolysis. Effect of different parameters in the case of ultrasound (US) assisted and conventional processes such as alkali concentration (0.5-2.5 N), substrate loading (0.2-1.0% w/v) and temperature (40-80 °C) have been investigated. Optimized parameters obtained for US assisted process showed better trends as compared to conventional process with about 1.25 times higher yields and significant reduction in time by about 4 h. The process parameters for US assisted and conventional enzymatic hydrolysis to produce reducing sugars were also optimized by varying substrate loading (0.5-10% w/v), reaction temperature (30-70 °C) along with variation in US power (10-80 W) and US duty cycle (30-90%). US assisted enzymatic hydrolysis performed at 4% w/v substrate loading along with 50 W US power and 50% duty cycle at 50 °C resulted in 7.46 mg/mL of reducing sugars yield within 1 h while conventional stirring with 6% w/v substrate loading and 50 °C resulted in approximately same yield of reducing sugars within 3 h. The requirement of lower time for similar yields or in other words higher yield in same time clearly highlights the process intensification benefits due to the use of ultrasound. Overall it can be concluded from the study that US assisted processes resulted in efficient delignification along with higher yield of reducing sugars in lower treatment time as compared to conventional process.

A Novel Control DC-DC-AC Buck Converter for Single Phase Capacitor-Start-Run Induction Motor Drives

A novel control DC-DC-AC buck converter for single phase capacitor-start-run induction motor drives is presented in this paper. The objective is to minimize harmonic distortion in inverter output voltage supply to a Single Phase Induction Motor (SPIM). Here, the output of a variable duty cycle buck DC-DC converter is fed to an H-bridge inverter to generate a very close sinusoidal output voltage. Few power semiconductor switches are utilized to produce inverter output voltage with reduced harmonic distortion comparable with results achieved in multilevel inverters. The SPIM was analysed in the stationary d-q reference frame while the buck converter was operated in the Continuous Conduction Mode (CCM) to ensure that the output voltage vary exactly as the duty cycle. The simulation results show good starting transient characteristics for the SPIM and also stable operation under intermittent loading of 4 N-m. The average inverter output voltage of 157.4 V was achieved with Total Harmonic Distortion (THD) as low as 6.32%. This configuration is simple, cheap, and has reduced control complexity.

Fully Electronically Tunable and Easily Cascadable Square/Triangular Wave Generator with Duty Cycle Adjustment

A novel multiple-output dual-X current conveyor transconductance amplifier with buffer-based square/triangular wave generator is introduced in the paper. The proposed generator provides square wave in current mode and triangular wave in voltage mode. Outputs as square and triangular waves are available from terminals with appropriate impedance levels thereby making the proposed generator circuit easily cascadable in both current and voltage modes. The oscillation frequency and amplitude of output square wave are electronically and independently controllable. One more interesting feature of the proposed generator circuit is the adjustable duty cycle. The proposed circuit of square/triangular wave generator is verified through the HSPICE simulation results carried using 0.18[Formula: see text][Formula: see text]m CMOS technology. The simulation results show linear variation of duty cycle against external DC current over a range of 6.5–96%. The variation of square wave’s amplitude via bias current is found to be linear from 10[Formula: see text][Formula: see text]A to 80[Formula: see text][Formula: see text]A. Moreover, the proposed generator can operate very well up to 23.8[Formula: see text]MHz with nonlinearity less than 5%. The proposed generator circuit is also experimentally verified.

Research on Drive Control of Piezoelectric Injector

This article is based on PWM switching power supply technology, using high-performance SoC SCM ADμC841 as the main control unit and through the IGBT on-off control, the drive circuit of the piezoelectric injector is designed. The simulation model of the drive circuit is established by Matlab/Simulink. According to different current trends during charging and discharging, three current driving modes were simulated and analyzed. The test results show that the variable duty cycle based on current feedback uses an approximate trapezoidal current charging method, which not only has a faster charge-discharge speed, but also can effectively limit the maximum current, and has a stable charge and discharge process. Therefore, the variable duty ratio is the best driving method among the three driving methods.

Circuit Theoretic Considerations of LED Driving: Voltage-Source Versus Current-Source Driving

Light-emitting diodes (LEDs) are solid-state devices with specific $v$ – $i$ characteristics. In this paper, we study the basic requirement of the driving circuits and discuss the proper approach to drive LEDs in view of their characteristics. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of circuit duality principle for developing new current-source-mode (CSM) drivers that are less known but are theoretically more versatile compared to their conventional voltage-source-mode counterparts. The study highlights the effects of the choice of driving circuits in terms of the number and size of circuit components used, duty cycle variation, sensitivity of control, nonlinearity and control complexity of LED drivers. We propose a CSM single-inductor multiple-output (SIMO) converter, which demonstrates the advantage of having inductorless and easily controlled current-source drivers, and present a comparison of the CSM SIMO converter with the existing SIMO converters. We further illustrate that a high-voltage-step-down ratio can be naturally achieved by the CSM high-voltage-step-down converter without the use of transformers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidence supporting the major conclusions.

Quadratic Buck–Boost Converter With Zero Output Voltage Ripple at a Selectable Operating Point

We introduce a new dc–dc converter topology with the following features: first, quadratic voltage gain, which allows the converter to work over a wide voltage range with a minimal variation of duty cycle and without the use of extreme duty cycles; second, output voltage ripple mitigation, which can be accomplished with respect to a fixed but otherwise arbitrary duty cycle by proper selection of components and switching signals. Since the proposed converter can be designed to have zero output voltage ripple for the nominal gain (duty cycle), this allows the use of small values of capacitances. The underlying principles and steady-state equations in continuous conduction mode are presented in detail. Experimental tests are presented to validate the analysis.

Modeling of power supplies for power modulators with LTspice

This paper is showing simulations of power supplies for repetitive power modulators using LTspice. We are presenting power supplies with single-phase and three-phase AC input and the effects of the rectifier stages on AC input current waveforms in both cases. We are also presenting the resulting power factor including circuits for electronic power factor correction. LTspice models for electronic power factor correction using cycle-by-cycle switching as well as time-averaged models are presented. The time-averaged models replace the PWM (pulse width nodulation) switch with a transformer model with variable duty cycle. They are valid for a range of DC-DC converters. We are extending the time-averaged model for operation in continuous (CCM) and discontinuous (DCM) conduction mode and presenting results that show the fidelity of these models by comparison to cycle-by-cycle results. We are providing the detailed mathematical derivation for the DCM model expansion in the appendix. Time-averaged models do not have to keep track of thousands of steep switching transitions and can run orders of magnitude faster than cycle-by-cycle switch-mode models. Results using the time-averaged model are presented for a power supply with primary (wave-shaping) and cascaded secondary feedback control that regulates the output voltage of the converter.

Low-intensity pulsed ultrasound modulates multi-frequency band phase synchronization between LFPs and EMG in mice

Objective. Low-intensity pulsed ultrasound stimulation (LIPUS) targeted to the mouse motor cortex can simultaneously induce local field potentials (LFPs) and electromyogram (EMG) responses. However, the functional coupling relationship between LFP and EMG signals has not been elucidated to date. This study aimed to investigate the phase synchronization between LFP and EMG signals induced by LIPUS over the mouse motor cortex. Approach. LIPUS at 500 kHz with varied sonication intensities and duty cycles (DCs), was delivered to the mouse motor cortex. LFPs of the motor cortex and EMG responses of the tail were simultaneously recorded during LIPUS. We then evaluated two control groups using the same experimental parameters, but changed the position of EMG recording to the hind leg and the ultrasound stimulus target to the primary visual cortex. The phase synchronization between LFPs and EMG signals was evaluated by performing a phase locking value (PLV) analysis in the time-frequency domain and was compared across specific frequency bands. Main results. The results showed that LIPUS increased the phase synchronization in a broad frequency band (5–150 Hz), and the maximum duration of the increased PLV was stable at approximately 200 ms. It is worth noting that the sonication parameters directly affected the time-frequency domain distribution of cortico-muscular synchronization. Specifically, significant alpha and beta synchronization appeared at 0.2 and 0.4 W cm−2 Isppa stimulation, while gamma synchronization occurred at 0.8 and 1.1 W cm−2 Isppa stimulation. The synchronization in all frequency bands apparently increased at 30% DC. Beta synchronization weakened when the DC was less than 30%. Furthermore, no significant phase synchronization was observed in the two control groups. Significance. Considering the close association between specific motor function and cortical-muscular synchronization in different frequency bands, we suggest that LIPUS over the motor cortex could selectively modulate motor function via different sonication parameters. Additionally, the phase synchronization between LFPs and EMG might be an invaluable index for assessing the ultrasonic effect on the motor system, which could be used in future clinical research to optimize ultrasound parameters. Thus, this study provides new insight into evaluating the neuromodulatory effects of ultrasound on motor function, thereby supporting the therapeutic application of ultrasound in neurological disorders characterized by motor deficits.

On the Feasibility of Tailoring Copper–Nickel Functionally Graded Materials Fabricated through Laser Metal Deposition

In this study, pulse-width modulation of laser power was identified as a feasible means for varying the chemical gradient in copper–nickel-graded materials. Graded material deposits of 70 wt. %. copper-30 wt. %. nickel on 100 wt. %. nickel and vice versa were deposited and characterized. The 70/30 copper–nickel weight ratio in the feedstock powder was achieved through blending elemental copper and 96 wt. %. Ni–Delero-22 alloy. At the dissimilar material interface over the course of four layers, the duty cycle of power was ramped down from a high value to optimized deposition conditions. This change was theorized to influence the remelting and deposition height, and by extension, vary the chemistry gradient. X-ray Energy Dispersive Spectroscopy (EDS) analysis showed significant differences in the span and nature of chemistry gradient with varying duty cycles. These observations were also supported by the variation in microhardness values across the interface. The influence of different chemistry gradients on the tensile performance was observed through mini-tensile testing, coupled with Digital Image Correlation (DIC). The strain fields from the DIC analysis showed variations in strain for different chemistry gradients. The strength measurements from these specimens were also different for different chemistry gradients. The site of failure was observed to always occur within the copper-rich region.

Optimized Modulation and Dynamic Control of a Three-Phase Dual Active Bridge Converter With Variable Duty Cycles

The three-phase dual active bridge (3p-DAB) converter is a promising topology for high power dc–dc conversion due to advantages of bidirectional power flow, inherent soft-switching capability, and reduced filter volume. This paper presents comprehensive analysis of the duty cycle control (DCC) for optimizing the performance of the 3p-DAB. Based on DCC, an optimized modulation strategy is proposed to minimize the conduction losses of the 3p-DAB in the whole load range. The proposed modulation strategy extends the soft-switching range of the 3p-DAB with large voltage variations simultaneously. It is established through loss analysis that the proposed modulation strategy boosts the efficiency of the 3p-DAB, especially at low loads. When the duty cycles change fast as a result of the abruptly changed transmission power, the transformer currents can become unbalanced, leading to the magnetic bias and oscillations in dc currents. This paper further proposes a fast transient current control (FTCC) method for the 3p-DAB with variable duty cycles. The FTCC enables the converter to transfer from one steady state to another within about one-third switching period, hence balancing the transformer currents rapidly and avoiding oscillations in dc currents. Finally, experimental results verify the outstanding performance of the proposed modulation strategy and FTCC method.