Phase-shift Modulation Research Articles

Modulated dilatometry as a tool for simultaneous study of vacancy formation and migration

Abstract A model is presented to derive both vacancy formation and migration characteristics from length change measurements upon modulated time-linear heating. The length variation with linear heating yields access to the equilibrium concentration of thermal vacancies. The modulation amplitude and the phase shift between modulated temperature and length change is determined by the ratio of equilibration rate and modulation frequency which yields access to the vacancy migration characteristics. The contribution from thermal lattice expansion is obtained from a reference measurement at high modulation frequencies. Compared to static isothermal equilibration measurements after temperature jumps, the processes are monitored under quasi-equilibrium conditions avoiding obstacles associated with fast temperature changes. Furthermore, in contrast to the static isothermal case where the equilibration rate is obtained from the time-exponential decay, its determination from the amplitude and phase shift of modulation offers higher precision. The method is suitable for materials with high thermal vacancy concentrations and low vacancy diffusivities, among which is the important class of intermetallic compounds with B2-structure.

High‐frequency harmonic suppression method for interleaved traction converters based on synchronous sampling

High-frequency resonance in traction power supply systems (TPSSs) is of great concern because of its potential to cause great damage to the safety and stable operation of railroad systems; it has been demonstrated that when a locomotive generates a harmonic current with the resonant frequency of the series impedance on the traction network, a large amount of high-frequency harmonic voltage is generated. This paper proposes a high-frequency harmonic suppression method based on synchronous sampled carrier phase-shift PWM modulation strategy (SSCPS-PWM), which has the advantage of not only considering the consistency of sampling the analogue signal by multiple controllers, but also further optimising the precise synchronization between multiple converter pulses. This method generates lower high-frequency harmonic content and is particularly suitable for the field of high-power, low switching frequency, multi-controller locomotive traction converters. The proposed method was simulated and compared with the traditional method for the harmonics injected by the locomotive, and a real railway line with a harsh power supply condition was selected and field tests were conducted in four sections by a 7200kW 6-axle electric locomotive. The test results showed that the proposed method effectively reduced the high-frequency harmonic current of the locomotive and reduced the high-frequency resonant overvoltage in the TPSS.

An isolated modular multi‐level AC/AC converter with high‐frequency link and pulse flip circuit for fractional frequency transmission system application

Based on the modular topology and the traditional voltage-sourced converter (VSC) model, this paper presents an isolated modular multi-level AC/AC converter with high-frequency (HF) link and pulse flip circuit for fractional frequency transmission system (FFTS) application. The proposed converter uses the HF transformer to realize electrical isolation, omitting the industrial frequency (IF) transformer with large volume and heavy weight. In the primary side of the HF transformer, the power transmission is realized by the rectifier and the inverter. In the secondary side of the HF transformer, the double H-bridges are used to realize the natural freewheeling of the leakage current, which solves the problem of voltage overshoot. On the basis of carrier phase-shifted pulse width modulation (CPS-PWM), an improved modulation strategy is proposed to realize the HF output voltage of the inverter. It has the advantages of easy expansion, no circulation current, good output voltage quality, low cost and no need of offshore converter station, so it has great potential in the field of offshore wind power grid connection. The working principle, natural freewheeling modes, modulation method and overall system control scheme of the proposed topology are introduced in detail, and the feasibility of the proposed topology is verified by simulation in MATLAB/Simulink environment and test through APPSIM platform.

High-Efficiency Omnidirectional Wireless Power Transfer System

To achieve omnidirectional wireless power transfer (WPT), it is crucial to tune the direction of the total magnetic field from the transmitter (Tx) coils toward the receiver coil (Rx) that can be placed at different positions with respect to Tx. Several methods, such as amplitude modulation, phase-shifting, and frequency modulation, have been proposed to vary the Tx currents, depending on the angular position of Rx, but complex sensing and feedback control systems are required. In this article, we propose an efficient omnidirectional WPT system that is capable of self-tuning the power flow without any feedback from the Rx-side. It only requires a simple Tx current switching rather than complex feedback control system for detecting the Rx position. The proposed system consists of three orthogonal transmitter–repeater (Tx-Rp) channels that deliver power to Rx. In this configuration, the Tx currents are proportional to the mutual coupling between the Rp and Rx in the same channel, which ensures the self-tuning of the optimal power flow through channels. Both theoretical and experimental studies are performed to validate the proposed method. The prototype of the proposed approach enables the Rx to harvest power with almost uniform high efficiency (about 90%) regardless of its angular position.

Isolated High-Frequency Link PFC Rectifier With High Step-Down Factor and Reduced Energy Circulation

This article presents an isolated single-stage ac–dc high-frequency link full-bridge cycloconverter (HFLC) with high conversion ratio. Despite certain advantages, such topologies generally suffer from transformer leakage inductance problems and lack of effective modulation methods, particularly in the ac–dc operation mode. In this study, for the input current regulation with the power factor correction of the HFLC, a novel phase-shift modulation method is used. It allows soft-switched turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> of the dc-side transistors and zero current switching of the ac-side matrix switches without additional circuits or topology modifications. The introduced time-varying regulation of the peak current can be easily implemented; as a result, merely minor energy circulation occurs. Moreover, two of the ac-side transistors operate with fundamental frequency. Design constraints of the concept are analyzed and discussed. For verification, a 1.2-kW 230 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</sub> to 48 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> experimental prototype is used.

Design and Performance Analysis of Hybrid Multidimensional OAM-DM-WDM-OFDM-PON System with High-Capacity and Long-Distance Transmission

Orbital angular momentum (OAM) with mutually orthogonal advantage attribute to break through the high capacity and long-reach transmission limited in the classical passive optical network (PON). Employing Laguerre Gaussian (LG) mode as the orthogonal OAM excitation, a more dimensional multiplexing PON system is proposed to creatively hybridize OAM division multiplexing (OAM-DM) based on wavelength division multiplexing (WDM) and orthogonal frequency division multiplexing (OFDM). By utilizing the compatibility of OAM-DM and WDM, data of 40 Gbit/s OFDM signals is successfully transmitted in 80 km multimode fiber (MMF) with low crosstalk. Within this hybrid system, the effects of different wavelengths and different modes on the bit error rate (BER) are discussed at varying transmission distances. Moreover, the performance of several subsystems carrying quadrature phase-shift keying (QPSK), on-off keying (OOK), and OFDM modulation signals is also compared at a BER less than 3.8×10−3. It is observed that the proposed OAM-DM-WDM-OFDM-PON system has favorable performance, which is a reasonable solution for large-capacity PON architecture.

Design and Fabrication of an Isolated Two-Stage AC–DC Power Supply with a 99.50% PF and ZVS for High-Power Density Industrial Applications

Power quality in terms of power factor (PF), efficiency, and total harmonic distortions (THDs) is an important consideration in power supplies designed for 5G telecom servers. This paper presents a different magnetic parts design and manufacturing techniques of power supplies, design and selection criteria of switching elements as well as the optimal design of control loops based on small-signal stability modeling and an appropriate stability criterion. The designed telecom power supply consists of the power factor correction (PFC) stage to increase the input power factor and the isolated phase-shift pulse width modulation (PWM) zero-voltage switching (ZVS) DC–DC converter stage to regulate the supply voltage to the specified load value while maintaining a high conversion efficiency. A two-stage outdoor telecom power supply with a power rating of 2 kW was designed and fabricated on a printed circuit board (PCB). The distinct two-stage power components of the power supply were subjected to loss analysis. Furthermore, PSIM simulation and experiments were used to demonstrate the total harmonic distortions (THDs), voltage ripples, power efficiency, and PF performance of the supply current for the proposed power supply under various operating situations. This work produces an industrial high power density power supply with a high PF, low THD and high conversion efficiency which is suitable for telecom power server applications.

Output Current Ripple and Efficiency Optimal Control Method for Multi-Phase Interleaved LLC Resonant Converter

The interleaving technique is required for LLC resonant converters to achieve high power levels, handle higher input/output currents, and reduce output current ripple. However, the high system efficiency and the low output current ripple for the multi-phase LLC resonant converter cannot be achieved at the same time at low and medium power levels. Most methods try to keep the multi-phase LLC resonant converter in load-sharing mode regardless of the power level, which will result in low system efficiency at low and medium power levels. In this paper, an output current ripple and efficiency optimal control method with finite load distribution schemes is proposed for the multi-phase LLC resonant converter to balance the efficiency and output current ripple. The optimal control method improves the efficiency as much as possible while keeping output current ripple low. According to the calculation of output current ripple and efficiency, the optimal load distribution scheme is selected. The pulse-frequency modulation (PFM) and phase-shift modulation (PSM) hybrid control is applied to regulate the load of each phase. An analysis is provided, and a 540-W three-phase interleaved LLC resonant converter is built to verify the superiority.

An Effective Charger for Plug-In Hybrid Electric Vehicles (PHEV) with an Enhanced PFC Rectifier and ZVS-ZCS DC/DC High-Frequency Converter

A plug-in hybrid electric vehicles (PHEV) charger adapter consists of an AC/DC power factor correction (PFC) circuit accompanied by a full-bridge isolated DC/DC converter. This paper introduces an efficient two-stage charger topology with an improved PFC rectifier as front-end and a high-frequency zero voltage switching (ZVS). Current switching (ZCS) DC/DC converter is the second part. The front-end converter is chosen as bridgeless interleaved (BLIL) boost converter, as it provides the advantages like lessened input current ripple, capacitor voltage ripple, and electromagnetic interference. Resettable integrator (RI) control technique is employed for PFC and DC voltage regulation. The controller achieves nonlinear switching converter control and makes it more resilient with the faster transient response and input noise rejection. The second stage incorporates a resonant circuit, which helps in achieving ZVS/ZCS for inverter switches and rectifier diodes. PI controller with phase shift modulator is used for second-stage converter. It improves the overall efficacy of the charger by lowering the switching losses, lowering the voltage stress on the power semiconductor devices, and reversing recovery losses of the diodes. The simulations and experimental results infer that the overall charging efficiency increases to 96.5%, which is 3% higher than the conventional two-stage approach using the interleaved converter.

A Novel Bidirectional Five-Level Multimode CLLC Resonant Converter

In order to widen voltage gain of bidirectional on-board charger to meet requirements of electric vehicle with different voltage levels, a novel bidirectional five-level multimode <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant converter is proposed by combining the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant tank module (RTM) with the five-level cascaded neutral-point clamp active bridge which is composed of two three-level neutral-point clamp (3L-NPC) bridge arms. Furthermore, the converter can, respectively, establish three voltage gain modes of high, medium, and low to effectively widen voltage gain adjustment capabilities through the fixed-frequency plus phase-shift hybrid modulation independently adopted in each 3L-NPC bridge arm, while soft-switching is realized by phase control between resonant current and input voltage of RTM. Meanwhile, the key parameters of RTM would be symmetrically designed to make bidirectional power transmission characteristics, which become consistent based on soft-switching and monotonic voltage gain control. Finally, according to the simulation platform and experimental prototype, it can be shown that the practical voltage gain is close to the theoretical design gain and converter has good dynamic performances after realizing soft-switching in each mode.

Efficiency Improvement of Dual-Receiver WPT Systems Based on Partial Power Processing Control

In wireless power transfer (WPT) system for light electric vehicles (LEVs), adopting dual receivers on the receiver side is an available way to offer a high-current power supply. In this article, the partial power processing (PPP) control method is proposed for optimizing the power loss of the dual-receiver WPT system. With the PPP control method, only one of the active rectifiers will be regulated by the variable angle phase-shift (VAPS) modulation to adjust the required power under different load power demands and misalignment situations. As a result, the switching loss of the two active rectifiers, which accounts for a considerable part of the overall power loss with a high operating frequency, can be dramatically reduced. At last, 24 V-50 A-1200 W LEV wireless charging experimental setup to verify the effectiveness of the proposed PPP control method. Compared with the conventional power distribution method based on impedance matching with VAPS, the proposed PPP control method can increase the efficiency by 6%–7% with misalignment situations, achieving the overall efficiency as high as >92% at the heavy load.

Phase Current Reconstruction Error Suppression Method for Single DC-Link Shunt PMSM Drives at Low-Speed Region

The extensive application of vector phase shift modulation method in permanent magnet synchronous motor drive systems with single dc-link current sensor results in obvious current ripple in the low-speed region. The patterns of these ripples vary greatly in different sectors, leading to nonnegligible phase current reconstruction errors. In this article, an estimation of the local average current change rate (ELAC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R) based reconstruction error suppression method within the switching cycle is proposed to resolve this problem. By comparing the actual and the ideal sampling points, the increase of current ripple and the reconstruction error caused by the combination of the vector phase shift and the single current sensor sampling in the low-speed region are modelled and analyzed. Then according to equivalent modelling of the current ripple between the ideal and the actual sampling points, the more accurate phase current information can be quickly obtained based on the sampling value. The compensation process is significantly simplified and the computation burden of the processor is reduced. Experimental results show that the performance of current reconstruction can be improved effectively with less harmonic content with the proposed method.

Total Suppression of High-Frequency Transient Oscillations in Dual-Active-Bridge Series-Resonant Converter by Trajectory-Switching Modulation

Dual-active-bridge series-resonant converter (DABSRC) is increasingly used in many emerging power electronics applications requiring fast dynamic responses. However, under conventional transient phase-shift modulation strategy, DABSRC generally suffers from large-amplitude transient oscillations when its phase-shift angle is changed abruptly by a high-gain controller. These oscillations occur at the beat frequency, which results from the interaction between the switching-frequency and resonant-frequency components in the series-resonant tank during transient states. Besides incurring high voltage and current stresses on the power-stage devices, these transient oscillations also span many switching cycles between the original and new steady states and cause perturbations to the output voltage of DABSRC, thereby degrading its dynamic performance and output voltage quality. To mitigate these problems, a new transient modulation strategy, known as trajectory-switching modulation (TSM), is proposed for achieving an accurate and computationally efficient trajectory planning of the resonant voltages and currents of DABSRC during transient states, and its basic operation is to govern the transient switching patterns of the gating signals according to a simple set of closed-form equations. The proposed TSM strategy can guarantee convergence to the next new steady state within about one switching cycle and avoid needing costly sensors and complex computation for implementation, and it is inherently compatible with high-gain controllers for realizing oscillation-free fast dynamic responses.

Research on Reactive Power Optimization Control of a Series-Resonant Dual-Active-Bridge Converter

In order to meet the demands of the bidirectional transmission of electric vehicle charger power, a series-resonant dual-active-bridge (DAB) converter is investigated in this paper. Firstly, the active and reactive power and zero voltage switching (ZVS) conditions of the full-bridge arm under extended phase-shift modulation, dual phase-shift modulation and triple phase-shift modulation are analyzed. Secondly, with the minimum reactive power as the optimization objective, the extended phase shift (EPS) is finally selected as the modulation method after comparing the minimum reactive power under various modulation methods when the normalized value of active power is varied in the range of 0–1. By constructing the objective function and determining the constraints, an off-line reactive power–minimization control strategy is proposed to achieve the ZVS of the full-bridge arm and, finally, the feasibility of the proposed control strategy is verified by simulation and experiment.

Optimal Dual Active Bridge DC-DC Converter Operation with Minimal Reactive Power for Battery Electric Vehicles Using Model Predictive Control

The dual active bridge DC-DC converter is a promising power converter used in several applications. Much research has been focusing on the study of such a converter from different angles. In this paper, an optimal design of the DAB converter is proposed to provide minimal reactive power in addition to reduced weight and size for the converter magnetic components in order to assure the DC-DC conversion stage of battery electric vehicles’ powertrains. Two modes of operation are considered in order to fulfill such a requirement and minimize reactive power of the converter (circulating current/conduction losses): an optimal extended phase shift (EPS) modulation along with an optimal triangular phase shift (TrgPS) modulation. The operation of the DAB converter under the two modes is being driven using a model predictive controller. Simulation results using MATLAB/Simulink presented in the paper show that the operation of the DAB converter for such an application is optimal when operating under optimal TrgPS modulation. In addition to the aforementioned features, it also solves many other concerns, such as transient load fluctuation and input voltage disturbance effects, and provides ease of control.

Research on oil exploration seismic Rayleigh wave imaging based on multi-channel analysis of surface waves and genetic-damped least squares joint inversion

Rayleigh waves in oil exploration seismic records usually have strong energy and are considered as noise, but Rayleigh waves also carry information about subsurface. In this paper, we process Rayleigh waves from a set of oil seismic data to detect underground structures of shear-wave velocity (vs) using multi-channel analysis of surface waves (MASW). Fundamental mode and higher order mode dispersion curves of the Rayleigh wave were automatically extracted by a modified phase shift method. We then use the genetic and damped least squares (DLS) joint inversion algorithm to inverse the dispersion curves and obtain a one-dimensional (1D) vs structure under each shot gather. Finally, all 1D vs structures were combined to create a 3.2 km long two-dimensional (2D) section, revealing a stratum structure down to 80 m depth. The results show that MASW technology successfully improves the use of oil seismic data, the automatic dispersion extraction method based on modified phase shift improves the efficiency of data processing, and the joint inversion algorithm reduces the dependence of the Rayleigh wave dispersion inversion on initial model.

A novel cascaded transformer coupled multilevel inverter with reduced number of switches for high power applications

PurposeThe purpose of this paper is to design a cascaded Multilevel inverter with reduce number of switches for high power applications. This paper came up with an innovative three-phase multilevel inverter (MLI) topology, which is a cascaded structure based on classical three-legged voltage source inverter (VSI) bridges as an individual module. The prominent advantage of this topology is that it requires only one direct current (DC) link system. The main characteristic of it is that a higher number of voltage levels can be achieved with considerably a smaller number of semiconductor switches, which improves the reliability, power quality, cost and size of the system significantly.Design/methodology/approachThe individual modules are cascaded through three-phase transformers to provide higher voltage at the output with the higher number of voltage levels. In this work, the phase-shifted pulse width modulation technique is implemented to verify the result.FindingsThe proposed topology is compared with three-phase cascaded H-bridge MLI (CHB-MLI) and a modified CHB-MLI topology and found better in many aspects. The proposed MLI can produce a higher number of voltage levels with fewer semiconductor switches and associated triggering circuitry. As the device count in the proposed MLI is less compared to other MLI discussed, it tends to have less switching and conduction loss which increases the efficiency and reliability. As the number of level increases, the voltage profile and the total harmonic distortion of the proposed MLI improves.Originality/valueThis is a transformer-based modular cascaded MLI, which is based on classical VSI bridges. Here in this topology, a single module provides all three phases. So, a single string of cascaded modules is enough for three-phase multilevel voltage generation.

Bidirectional wireless power/data transfer via magnetic field

Recently, inductive power transfer (IPT) system has been used for wireless charging of electric vehicles (EVs). However, most of them only treat the issue of single directional wireless power transfer (WPT). This research proposes a novel bi-directional IPT (BD-IPT) scheme EVs, which can simultaneously transmit power/data via magnetic field when the mutual inductance changes. For power transmission, resonant inverters with phase-shift pulse width modulation (PSPWM) are used to generate carrier waves and alternating current. As for data transmission, a dedicated communication method with the accompanied protocol is proposed. Binary phase shift keying (BPSK) is used to simulate the two-quadrature amplitude modulation (QAM), which generates digital signals for data transmission without the need of extra communication links. Hamming codes are combined with single-error correction and double-error detection (SECDED) to ensure communication quality.

High-Frequency Oscillation of the Active-Bridge-Transformer-Based DC/DC Converter

The dual-active-bridge converter (DAB) has attracted tremendous attention in recent years. However, its EMI issues, especially the high-frequency oscillation (HFO) induced by the dv/dt and parasitic elements of the transformer, are significant challenges. The multi-active-bridge converter (MAB) based on the multi-winding transformer also faces similar problems, which are even more complicated. This article investigates the HFO of active-bridge-transformer-based DC/DC converters including DAB and MAB. Firstly, the general HFO model is studied using the analysis of the AC equivalent circuit considering the asymmetrical parameters. Ignoring the AC resistance in the circuit, the high-order model of the voltage oscillation could be reduced to a second-order system. Based on the simplified model, the oscillation voltage generated by an active bridge is analyzed in the time domain. Then, a universal active voltage-oscillation-suppression method-selected harmonic-elimination phase-shift (SHE PS) modulation method is proposed. The impacts of the system parameters on the method are also revealed. The experimental results show the excellent performance of the proposed active suppression method, with voltage spike amplitude (VSA) reductions of 92.1% and 77.8% for the DAB and MAB prototypes, respectively.

Reduction in Circulating Current With Improved Secondary Side Modulation in Isolated Current-Fed Half Bridge AC–DC Converter

Current-fed half bridge converter with bidirectional switches on ac side and a full bridge converter on dc side of a high frequency transformer is an optimal topology for single stage galvanically isolated ac-dc converter for onboard vehicle charging application. AC side switches are actively commutated to achieve zero current switching (ZCS) using single phase shift modulation (SPSM) and discontinuous current phase shift modulation (DCPSM). Furthermore, zero voltage turn-on (ZVS) is achieved for dc side switches. Compared to SPSM, DCPSM maintains a constant peak current in the converter throughout the grid cycle of ac mains voltage. However, constant peak current contributes to a high circulating current near the zero crossings of ac mains voltage and also at light load conditions.This paper proposes an improved discontinuous current phase shift modulation (IDCPSM) to increase the efficiency of the converter across different loading conditions. A dual control variable is adopted to actively reduce the circulating current while maintaining soft switching of both ac and dc side switches across the grid cycle of ac mains voltage. A 1.5 kW laboratory prototype has been developed to experimentally validate the analysis, design and improvement in performance for different loading conditions.