DC Bias Research Articles

An Optimized PLL With Time Delay and Harmonic Suppression for Improved Position Estimation Accuracy of PMSM Based on Levenberg–Marquardt

This paper proposes an optimized phase-locked loop (OPLL) based on Levenberg-Marquardt (LM) to improve the estimation accuracy of the sliding mode observer (SMO) based position estimator. The position estimation suffers from dc bias caused by digital control delay, and harmonic caused by inverter nonlinearity and flux spatial harmonics. The OPLL is constructed with two parts to overcome the above negative effects. The delay phase is preliminarily calculated based on linear prediction, so as to compensate for the lag phase in the estimated back electromotive force (back-EMF); secondly, the objective function is built based on the reference and feedback position error, the former contains an unknown harmonic. The objective function can be minimized by the LM to solve for the harmonic amplitude, then the obtained harmonic is used to offset the harmonic components in the estimated position. Wherein, the required partial derivatives of the LM method can be deduced based on the transfer function of PLL and the delay-compensated back-EMF to achieve a stable update of harmonic amplitude. Finally, the corresponding comparative experiments in steady-state and dynamic conditions proved the superiority of the proposed method applied to permanent magnet synchronous motors.

Mode analysis and fault-tolerant method of open-circuit fault for a three-level dual active bridge DC-DC converter

The three-level dual-active-bridge (TL-DAB) DC-DC converter is a promising dc-dc converter for high-voltage and high-power systems. Open-circuit faults on power switches are crucial issues for the TL-DAB dc-dc converters, resulting in various performance degradations such as dc bias and divided capacitor voltage imbalance. The mode analysis after fault is necessary for fault detection and fault-tolerant control. Subsequently, fault-tolerant control is essential to reduce or overcome these issues. In the proposed fault-tolerant method, when the primary side inner switch or the secondary side switch breaks down, the gate-driving signal of the complementary switch is recommended to block and the effects can be removed. Finally, experiment results demonstrate that the issues caused by open-circuit faults can be reduced significantly with the proposed fault-tolerant method.

A 4:1 Switched Capacitor Converter With Low Flying Capacitors Voltage and High Efficiency

In this paper, a 4:1 switched capacitor converter (SCC) is derived. Compared with the Dickson 4:1 converter, the voltage of flying capacitors is lower and thus the effect of dc bias on multi-layer ceramic capacitor (MLCC) is reduced. With a limited number of MLCCs, the proposed converter achieves a higher efficiency, and it is suitable for the applications with limited volume such as mobile phone fast charging. A 20-V to 5-V prototype is built with 24 X7R MLCCs in 0805 package, and its efficiency is 1.7% higher than the Dickson 4:1 and 1.1% higher than the Series-parallel 4:1 at 16-A output current.

Impact-Ionization Switching of High-Voltage Thyristors Connected in Parallel

Thyristors triggered in the impact-ionization wave mode is a promising switching method in pulsed power technology. This triggering approach enhances the current capability of standard thyristors, allowing switching a current pulse with an amplitude of 200 kA and a current rise time rate-of-change (dI/dt) of 58 kA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> s. Thyristor wafer area can be considered as one of the factors that are limiting the peak current amplitude and dI/dt. Switching thyristors in parallel is a possible solution to overcome these limitations. However, no evidence was found in the literature for successful parallel switching of standard thyristors in the impact-ionization wave mode. In this research, the possibility of parallel switching of two standard thyristors rated for 2.2 kV with a wafer diameter of 32 mm was investigated. A Marx generator equipped with a peaking module was used to charge the thyristor equivalent capacitance (1 nF) up to double its static breakdown voltage with a voltage rise time rate-of-change (dV/dt) of more than 1 kV/ns, as required for impact-ionization triggering. The diagnostic system includes two wideband voltage probes (VPs) with a subnanosecond time response, which allows simultaneous measurement of a voltage drop across each thyristor connected in parallel. Two stages of thyristor operation were investigated: 1) a triggering stage, without energy switching, when a dc bias voltage is applied; and 2) a current flow stage, with energy switching, when an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$RLC$</tex-math> </inline-formula> discharge circuit is connected. In these experiments, thyristors change from blocking to conducting state within 400 ps, switching a current pulse with an amplitude of 11 kA and a dI/dt of 6 kA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> s (circuit limits). The current imbalance between the thyristors was less than 10%. To the best of the authors’ knowledge, it is the first time reported that high-voltage thyristors connected in parallel have been successfully triggered in the impact-ionization wave mode.

A high-fidelity MEMS microphone with a polymer membrane that can detect infra-sounds

This study proposes a polymer MEMS microphone that operates through electromechanical amplitude modulation. We have developed a highly optimized MEMS structure with a flexible polymer material, resulting in a miniaturized and flexible device with excellent acoustic performance. The stiffness and damping characteristics of the polymer diaphragm are analyzed and it shows that the polymer material would be suitable for microphone applications. An equivalent circuit model is also developed for design purposes, so that the device could be properly designed using it and fabricated by in-house polymer thin film processes. The fabricated device is tested using a DC bias scheme to reach its signal-to-noise ratio (SNR) of 65 dBA within a bandwidth of 10 to 10,000 Hz, which is comparable to existing high-end commercial silicon MEMS microphones. We would then extend the frequency bands of linear detection down to the infrasound range by using electromechanical amplitude modulation. This operation scheme can also provide the microphone with no need for metal packaging. Its feasibility is confirmed theoretically by numerical simulations including electromechanical amplitude modulation and experimentally by implementing it at the PCB level. In addition, this approach enables the sensor stronger to the environmental noise so that metal shielding could be omitted.

A miniature tunable quadrature shadow oscillator with orthogonal control

This article presents a new design of a quadrature shadow oscillator. The oscillator is realized using one input and two outputs of a second-order filter cell together with external amplifiers in a feedback configuration. The oscillation characteristics are controlled via the external gain without disturbing the internal filter cell, following the concept of the shadow oscillator. The proposed circuit configuration is simple with a small component-count. It consists of, two voltage-different transconductance amplifiers (VDTAs) along with a couple of passive elements. The frequency of oscillation (FO) and the condition of oscillation (CO) are controlled orthogonally via the dc bias current and external gain. Moreover, with the addition of the external gain, the frequency range of oscillation can be further extended. The proposed work is verified by computer simulation with the use of 180 nm complementary metal–oxide–semiconductor (CMOS) model parameters. The simulation gives satisfactory results of two sinusoidal output signals in quadrature with some small total harmonic distortions (THD). In addition, a circuit experiment is performed using the commercial operational transconductance amplifiers LM13700 as the active components. The circuit experiment also demonstrates satisfactory outcome which confirms the validity of the proposed circuit.

Estimation of iron losses in Terfenol-D for variable DC-biased and AC excitation conditions

Giant magnetostrictive material (GMM) is well known for its hysteresis behaviors related to multiple influencing factors, such as bias magnetic field and excitation level. This feature greatly challenges the loss prediction of giant magnetostrictive transducers. The existing loss prediction models need further improvement to cover the sensitive magnetic properties of GMM. In this paper, the variations of the iron losses with the operation conditions are interpreted by the variations of the Jiles–Atherton model parameters, and a concise parameter identification procedure with great generalizability is proposed. The iron losses of Terfenol-D under variable excitation levels and the DC biases are further investigated. With the proposed procedure, the introduced eight additional modification parameters for the original Jiles–Atherton model are easy to obtain, and merely a few hysteresis loops of Terfenol-D are involved. An experimental setup is established for further demonstration. Comparisons between the measured and calculated results indicate the effectiveness of the proposed approach. Throughout the bias-excitation space within the frequency range under investigation, the iron losses can be precisely estimated with an acceptable error of less than 5%.

Modeling magnetostriction of grain-oriented sheet steels based on magnetization process and domain motion

Grain-oriented (GO) sheet steels are preferred for magnetic cores in large power transformers because of their low core loss and high permeability. However, GO sheet steels exhibit more complex magnetostriction than non-oriented (NO) materials, causing undesirable vibrations and acoustic noises in the transformer core, especially under certain operating conditions, such as DC bias and magnetic saturation. This paper proposes a magnetostriction model of GO sheet steels based on an improved understanding of the magnetization process and domain motion. Incorporating the positive and negative magnetostriction components attributed to domain wall motion and rotation, the proposed model can accurately reproduce the butterfly loops in a wide range of magnetization along the rolling direction (RD) of GO material. Its effectiveness and accuracy are verified by the experimental measurements.

Pockels Effect at the Interface between Water and Ti Electrode

The Pockels coefficient of interfacial water between bulk water and a Ti electrode was estimated from the electroreflectance spectra (ΔR/R) to be r13≈−150 pm/V as the maximum value of magnitude, which is comparable in magnitude to the largest coefficient for electrode interfacial water, i.e., 200 pm/V for interfacial water on a transparent oxide electrode. This Pockels signal increased by a factor of about ±3 by applying a DC bias voltage of ±1 V. The reflectance (R) of the Ti electrode had a dip structure in the UV region (3.5–4.5 eV) due to the interference of a 14 nm thick surface oxide film, and the ΔR/R spectra in aqueous electrolyte solution showed a large reflectance change in the UV region with a dispersive shape due to the contribution of the TiO2 film. The reproducibility of the electroreflectance experiment was high, suggesting that the surface oxide film contributes to the large Pockels effect of interfacial water and the robustness of the electrode.

High-sensitivity transition-edge-sensed bolometers: Improved speed and characterization with AC and DC bias

We report on efforts to improve the speed of low-G far-infrared transition-edged-sensed bolometers. We use a fabrication process that does not require any dry etch steps to reduce heat capacity on the suspended device and measure a reduction in the detector time constant. However, we also measure an increase in the temperature-normalized thermal conductance (G) and a corresponding increase in the noise-equivalent power (NEP). We employ a new near-IR photon-noise technique using a near-IR laser to calibrate the frequency-domain multiplexed AC system and compare the results to a well-understood DC circuit. We measure an NEP white noise level of 0.8 aW/rtHz with a 1/f knee below 0.1 Hz and a time constant of 3.2 ms.

Emergence of field-induced memory effect in spin ices

Out-of-equilibrium investigation of strongly correlated materials deciphers the hidden equilibrium properties. Herein, we have investigated the out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7 spin ices. Our experimental findings reveal the emergence of magnetic field-induced anomalous hysteresis observed solely in temperature-and magnetic field-dependent AC susceptibility measurements. The observed memory effect (anomalous thermomagnetic hysteresis) exhibits a strong dependence on both thermal and non-thermal driving variables. Owing to the non-collinear spin structure, the applied DC bias magnetic field produces quenched disorder sites in the cooperative Ising spin matrix and suppresses the spin–phonon coupling. These quench disorders create a dynamic spin correlation, having slow spin relaxation and quick decay time, which additionally contribute to AC susceptibility. The initial conditions and measurement protocol decide the magnitude and sign of this dynamical term contributing to AC susceptibility. It is being suggested that such out-of-equilibrium properties arise from the combined influences of geometric frustration, disorder, and the cooperative nature of spin dynamics exhibited by these materials.

An Improved Dual Second-Order Generalized Integrator Phased-Locked Loop Strategy for an Inverter of Flexible High-Voltage Direct Current Transmission Systems under Nonideal Grid Conditions

High-voltage flexible power systems, with their intrinsic characteristics, play an increasingly important role in electronic power systems. Synchronization between the inverter and the grid needs to be achieved by a phase-locked loop (PLL), the performance of which determines the quality of power transmission. This paper proposes a PLL adapted to extremely harsh grid conditions. Firstly, the traditional synchronous reference frame PLL and the dual second-order generalized integrator (DSOGI-PLL) are analyzed, and the errors in phase-locking and the shortcomings of these two methods in the presence of DC components in the grid are pointed out. Secondly, based on the harmonic grid voltage, a repetitive control internal model is introduced by DSOGI to realize the real-time tracking and regulation of the harmonic signals in order to suppress the harmonic voltage disturbance. In addition, a DC bias elimination and frequency adaptive method is proposed to solve the problems of DC bias and grid voltage frequency fluctuation in order to achieve adaptive tracking of the grid phase. Finally, the superiority of the proposed strategy is verified through simulations and experiments.

Film bulk acoustic resonators with 400 MHz ultrawide-range tunability using crystalline PZT thin film

Tunable and switchable film bulk acoustic resonators (FBARs) have great application potential owing to their much-increased flexibility in radiofrequency (RF) circuits. Here, we report on the design and fabrication of a tunable and switchable FBAR based on a thin crystalline lead zirconate titanate (PZT, Pb[Zr0.6Ti0.4]O3) film. The FBAR device has a resonant frequency of 2.42 GHz with a high effective electromechanical coupling coefficient keff2 of 30%. The frequency tunable range of the device is up to 400 MHz (2.11–2.51 GHz, 16.6%) with a DC bias voltage of less than 12 V, and the device can also be switched off when the polarization intensity in the PZT film is zero. Through the investigation, a relationship between the ferroelectric nature of PZT material and the wide tuning range of FBAR is established, providing a theoretical and experimental guideline for further development.

Magnetic Flux Bias Compensation Based on Voltage Injection Method With an Auxiliary DC/DC Converter

DC bias will make the transformer core saturated, causing local overheating and insulation materials aging. Therefore, it is great of significance to study the suppression of DC bias in transformers. In this paper, a magnetic compensation scheme of DC bias based on a hybrid transformer (HT) integrated an auxiliary DC/DC converter is proposed. Firstly, a compensation mechanism is established by designing a novel HT topology structure, which lays the magnetic circuit foundation of DC bias compensation. Secondly, the mathematical model of transformer DC bias is established, and the DC compensation amount of HT is derived. A transient simulation model of three-phase HT is established by the finite element model, and the situation of the DC bias before and after the compensation is analyzed. Finally, the platform of the DC bias compensation scheme is built. The full compensation experiment of DC bias is simulated by two parallel HT. The experimental results show the DC bias compensation effect is obvious, the distortion of excitation current, temperature rise and flux density distribution drop obviously, which verifies the correctness of the scheme proposed in this paper. It provides a reference for solving the problem of DC bias.

Analysis of Low Phase Noise Graphene Oscillation Characteristics Under DC Bias in Phase-Locked Loop

In this paper, the oscillation characteristics of multilayer graphene are verified and analyzed by simulating and fabricating a multilayer graphene oscillator with low phase noise. Graphene has strong nonlinearity. Biasing can change the in-band conductivity of graphene. With electromagnetic excitation and DC bias circuit, multilayer graphene can be approximated as a series-parallel connection of multiple discrete element resistors and inductors, which can be used to make resonant circuits. In this paper, we first analyze the principle of bias voltage to change the surface conductivity of graphene, and establish a multilayer graphene Symbolically Defined Devices (G-SDD) simulation model based on the surface conductivity. When the G-SDD model is applied to the oscillator simulation circuit, the simulation results obtained are basically consistent with the experimental results. The multilayer graphene oscillator has an oscillation frequency of about 650 MHz, an output power of 6.48dBm, and a phase noise of -116.40dBc/Hz@1MHz. By comparison with other recent literature the better phase noise characteristics of this design are further highlighted.

A Simple and Fast Start-Up Strategy for Dual-Active-Bridge Converters With DC Bias Suppression

High power dual active bridge (DAB) converters are widely adopted in DC and hybrid AC/DC micro-grids, for which <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fast start-up dynamics</i> of DAB converters is a key requirement. Conventional start-up methods usually require complex operation stages, and a time-consuming parameter-tuning process, resulting in slow dynamics. In this work, we propose a new simple and optimal start-up method for DAB converters. Major contributions lie in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">three-folds</i> . (i) We theoretically analyze the transmission power and the peak inductor current of extended phase-shift modulation. (ii) A new Lagrange Multiplier method is proposed to solve the optimal phase-shift ratios of the underlying control problem, resulting in very fast control dynamics at maximum power transmission, fully respecting the system permissible current limit. (iii) An effective and simple strategy by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">solely</i> manipulating the gate signals in the first switching period is newly proposed to eliminate the magnetic bias. The proposed method avoids complex parameter-tuning procedures. Experimental results demonstrate the effectiveness of the proposed method. Results confirm that with the proposed solution a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">much faster</i> start-up process with a controllable inductor current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">without</i> DC bias is achieved, in comparison with the recently reported start-up methods.

Phase-Shift Control With Unified PWM/PFM for Improved Transient Response in a Bidirectional Dual-Active-Bridge DC/DC Converter

Determining how to efficiently obtain superior transient response under both unidirectional power-changing and power-reversing operations in a bidirectional dual-active-bridge (DAB) dc/dc converter is a challenging problem. The traditional direct phase-shifting scheme would induce a transient dc current bias in the high-frequency link of the DAB, and therefore lead to some adverse issues, such as magnetic saturation and increased current stress. In addition, the ac transient can propagate to the dc terminates and give rise to a worse transient response in a closed-loop control system. In this study, a fast phase-shift control is proposed which can execute all the possible power changes in a unified manner. By properly operating the primary bridge with pulsewidth modulation (PWM) and the secondary bridge with pulse frequency modulation (PFM), the DAB converter can complete the phase-shifting operation fast without a dc current bias in the ac link. A closed-loop control based on the hybrid PWM/PFM is further designed to regulate the primary dc current with improved transient performance. Since both PWM and PFM are standard, the whole control algorithm can be implemented efficiently in practical applications. Experimental results are provided to show that the power of the DAB converter can be governed bidirectionally with the proposed phase-shift control. The dc terminal current can be changed to both polarities with fast transient and no apparent overshoot or oscillation.

TiO2-UV detection under different types of acids and rinsing process for films preparation

Titanium dioxide (TiO2) films were prepared by the sol–gel method under different types of acids. Effect of hydrochloric acid (HCl), nitric acid (HNO3) and nature-based solutions (NBS) under ultraviolet (UV) detection of films were investigated. Films were coated by dip coating on glass substrate. Moreover, TiO2 films were compared properties on water rinsing (Ri) and without rinsing (WRi) processes. The phase structure of prepared samples was characterized by means of X-ray powder diffraction (XRD). The results confirm that films were highly crystalline anatase TiO2 and free from other phases of titanium dioxide. For the optical property, the transmittance (%T) observed sharp rise in the violet-ultraviolet transition region and a maximum transmittance of ~80%. Photocurrents were measured under UV intensity of 260 mWcm–2 and DC bias voltage of -20 – 20 volts (V). The results observed that currents increased as bias voltage increased. Current - Voltage (I-V) curves observed different slopes under the different of acids and rinsing process. The photocurrent of TiO2-NBS-Ri was greater than TiO2-HCl-WRi and TiO2-HNO3-WRi of 10 and 20 times; respectively. These findings suggest that the significant effect of the acid and rinsing process on crystalline, morphological, optical, and electrical properties of nanostructured TiO2 films would be useful for applying the device in UV photoelectric detection.

Open-Circuit Fault Diagnosis and Tolerant Method of Multiport Triple Active-Bridge DC-DC Converter

The triple active-bridge (TAB) DC-DC converter, as a representative multiport converter, is widely used in DC distribution system. The open-circuit fault (OCF) of TAB seriously threatens the system safety operation. In this article, an OCF diagnosis and tolerant method is proposed for TAB converter to reduce the impact of OCF. The fault mode of TAB converter is first analyzed. Based on the analysis, an fault diagnosis method using the average value of bridge arm midpoint voltage and inductance current is proposed. To eliminate the DC bias and over-current caused by OCF, the symmetrical topology is constructed by modulation reconfiguration, and corresponding fault-tolerant operation strategies are proposed for OCF at different locations. When the OCF occurs on the bipolar DC bus side, the fault bus is cut off, while ensuring the power transmission between the monopolar bus and the critical load. When the OCF occurs on the critical load side, the bipolar DC bus could still supply its power. Based on the above strategy, the power transmission capability under OCF is guaranteed and the reliability of TAB converter is improved. Finally, the OCF diagnosis and fault-tolerant operation methods are verified through comparative numerical simulation and experimental results.

A Polar-Coordinate-Multisignal-Flux-Observer-Based PMSM Non-PLL Sensorless Control

In this letter, a polar-coordinate-multi-signal- flux-observer (PCMFO) is proposed for PMSM sensorless control. PCMFO is constructed in polar coordinate and uses the orthogonality relations between αβ-axis active flux. It permits estimating the rotor position and the flux simultaneously, instead of obtaining the active flux first and then the rotor position, so the phase-locked loop (PLL) is not necessary. Furthermore, PCMFO consists of paralleled multiple observers which respectively estimate the dc bias, fundamental wave and harmonics, thus eliminating the influence of these interfering signals on flux estimation. The theoretical analysis indicates PCMFO can reduce the system order, and suppress the estimation error caused by rotor speed varying and discretization. Then the PMSM sensorless control is constructed based on it. The experimental results verify the superiority of this method.