Electronic Transformer Research Articles

Research on Electromagnetic Interference of Smart Device Acquisition Unit under GIS Disconnector Operation

With the continuous improvement of substation voltage level and the wide use of GAS insulated SWITCHGEAR (GIS), switching overvoltage, especially the very fast transient overvoltage (VFTO) caused by disconnector operation, has attracted more and more attention. According to the demonstration project of a new generation intelligent substation with the highest voltage grade (330kV) in operation in China, analysing the physical process of VFTO generation and propagation in high voltage substation by combining simulation calculation with test detection. Taking the electronic current transformer of intelligent secondary equipment as an example, its exploitation is established. We got the output signal waveform of the acquisition unit port under the action of VFTO by the high frequency transient model of the unit. By comparing the distribution parameters and the measured signal waveforms, the high frequency characteristics of the acquisition unit of the electronic current transformer under the action of VFTO are reflected. The results show that the EMI of the acquisition unit of electronic current transformer is in the form of pulse group. The amplitude of EMI is about 900V and the stable impact frequency is about 50 kHz. The impact frequency directly related to the arc reburning frequency.

Model Predictive Control With Power Self-Balancing of the Output Parallel DAB DC–DC Converters in Power Electronic Traction Transformer

This paper focuses on the output parallel dual-active-bridge (DAB) dc–dc converters in power electronic traction transformers. A model predictive control with current-stress-optimized (MPC-CSO) scheme based on dual-phase-shift (DPS) control is proposed to improve the dynamic performance, balance the transmission power, and realize the current-stress optimization. The dynamic behavior of output voltage in the next horizon is predicted accurately under the input voltage fluctuation and load disturbance conditions by developing the prediction model. In addition, the proposed MPC-CSO scheme can track the output voltage with the desired value directly with no overshoot during the start-up process. Combining the MPC and CSO scheme, the fast dynamic response and high-efficiency performance of DAB converters can be achieved simultaneously, and the transmission power of each DAB cell can be self-balanced. Finally, three control schemes consisting of traditional voltage closed-loop control with single phase shift, traditional CSO control with DPS, and MPC-CSO with DPS schemes are compared in a scale-down three DAB dc–dc converter cells experimental prototype by using TMS320F28335+FPGA_6SLX45 as core controller. Extensive experimental results have verified the excellent performance of the proposed MPC-CSO scheme and associated analysis in this paper.

Multirate Digital Signal Processing and Noise Suppression for Dual Active Bridge DC–DC Converters in a Power Electronic Traction Transformer

Power electronic traction transformer (PETT) is a single-phase ac–dc conversional system, which is made up of a cascaded H-bridge converter and output-parallel dc–dc converters, such as dual active bridge dc–dc (DAB) converters. As the voltage fluctuation of the dc output voltage of DAB converters is very small and the gain cross-over frequency of the open-loop transfer function of DAB converters is generally high, the DAB closed-loop control system is very sensitive to the influence of noises. The typical noises include the equivalent noise due to the conflict of controller interrupts, the noise due to the mismatch of sampling frequency and switching frequency (which is denoted as switching noise), the noise due to the second-order voltage ripple in the dc input side, the noise due to the quantization process of the analog-to-digital converter (which is denoted as quantization noise), and the noise due to the measuring error of transducers and conditioning circuits (which is denoted as measurement noise). The generation mechanism of these noises and their impacts on the DAB converters are analyzed. On the basis, the corresponding noise suppression schemes are presented, especially for the switching noise, quantization noise, and measurement noise. Besides, the mathematical models toward the sampling and the phase-shift modulation under multirate circumstance are derived, and the multirate digital control strategy of the PETT is proposed. Finally, based on a five-cell PETT laboratory prototype with a rated power of 30 kW, further research is carried out and the experiment results all verify the effectiveness of the proposed algorithms.

Power flow control scheme for multiport power electronics transformers

Development of power electronics transformers (PETs) has made dc distribution and hybrid ac/dc systems a competitive solution for future network expansion. This study focuses on the functions of a multiport PET interfacing medium-voltage and low-voltage networks. A comprehensive power flow control scheme based on a globalised multiport transmission model of the PET and droop control is derived. This allows for a coordinated energy exchange between the ports of the PET, which enables autonomous operation. Simulations of the proposed approach in a hybrid ac/dc distribution network with different levels of distributed generation and loads verify the effectiveness of the method.

Input Filter for a Power Electronics Transformer in a Railway Traction Application

The need for lighter and smaller railway traction drives and recent advances in power semiconductor technology have resulted in a new energy conversion paradigm, one without the classical heavy and bulky line-frequency transformer. Several multilevel topologies have been introduced over the past years, all having in common the use of medium-frequency (MF) energy conversion to reduce the weight and volume of the magnetic components. This paper is concerned with the design of the input filter for an MF traction converter, focusing on a solution that minimizes the filter's overall mass. Two filter topologies are investigated, namely a single-pole filter (inductor) and a passively damped $LCL$ filter. The paper first describes the requirements to be fulfilled, establishes the spectrum to consider for the design, and proposes a method to determine the initial parameters of the filter's components. The results show that an $LCL$ -type filter achieves considerable weight savings in comparison to the single-pole solution.

Benefit analysis of using multi‐port and multi‐function power electronic transformer connecting hybrid AC/DC power grids

This study proposes a generalised configuration of the multi-port and multi-function power electronic transformer (MPMF-PET) based mixed AC/DC power grids, and the equivalent circuit and mathematical model of the MPMF-PET are established. To illustrate the benefits of using MPMF-PET to improve the integration and power control ability of a distributed energy resource in an existing distribution network, an iterating evaluation algorithm is proposed for system power flow calculations. Case studies are carried out on a real distribution system modified with MPMF-PET. Results show that the performance of the hybrid AC/DC distribution system is increased by MPMF-PET through proper control and optimal operation, which realised the renewable energy in the AC system to power the DC system and increased the renewable energy acceptance.

A Short-Time Transition and Cost Saving Redundancy Scheme for Medium-Voltage Three-Phase Cascaded H-Bridge Electronic Power Transformer

Reliability is one of the major concerns when the electronic power transformer (EPT) is employed in the field, and redundancy is a common approach to improve the reliability. For hot and cold redundancy schemes, the redundancy performance will be degraded due to the small number of power modules (PMs) when the EPT is employed in the medium-voltage power grid. For the three-phase EPT, at least three redundant PMs are needed (one redundant PM per phase), which leads to a high redundancy cost. In this paper, a novel redundancy scheme is proposed. The proposed scheme can accomplish the faulty PM replacement process within tens of microseconds with nearly no transition. And only one PM and a set of switches are needed for the three-phase redundancy, which can effectively save the redundancy cost. The proposed scheme is analyzed and supported by simulations and experimental results.

An LLC-LC Type Bidirectional Control Strategy for an LLC Resonant Converter in Power Electronic Traction Transformer

An LLC-LC type bidirectional control strategy for an LLC resonant converter is proposed in this paper. It can achieve bidirectional power flow automatically without any power flow detection procedures. Meanwhile, the soft-switching can be always guaranteed all the time. In order to adapt to the proposed control strategy, a no-load-point-based design method is put forward in this paper, which can rapidly obtain optimal parameters of an LLC resonant converter. What is more, by using the proposed control strategy, the starting characteristic in no-load condition can be improved, output voltage rising and current surge risk can be avoided. Finally, an experimental platform of power electronic traction transformer power cell (consisting of a single-phase rectifier and a bidirectional LLC resonant converter) is built to verify the validity of the proposed control strategy.

State prediction of electronic voltage transformer based on Q-ARMA

As an ideal substitute for traditional electronmagnetic transformers, electronic voltage transformers are widely used in smart grids. Its problem at present is the poor long-term stability of the error, which has caused some hidden danger to the safety, stability and economic of the power grid. The regular off-line calibration method is not conducive to the timely detection of the error state for electronic voltage transformer. A method of error state prediction based on Q -ARMA is proposed in this article. The measurement data of the three-phase electronic voltage transformer are collected, and the error state of the electronic voltage transformer is mapped to the Q statistic under the constraints of the electrical physical relationship by using the principal component analysis method. The influence of grid fluctuation on the prediction of error states is eliminated by this method. The ARMA prediction model of Q statistics is established, and the experiments show that this method can accurately predict the trend of the error state of electronic voltage transformer.

Research and design of integral circuit for electronic current transformer

Aiming at the problem of serious magnetic saturation, small dynamic range and difficult digital processing of traditional electromagnetic current transformers, an electronic current transformer design method based on digital integrators is proposed. It includes selection of integral algorithm, determination of sampling rate and resolution, and structure design. Using the calibration test platform for system testing and analysis, the ratio error is less than ± 0.5%, the phase angle error is less than ± 20’, and the entire system achieves the 0.2 class accuracy. The test results show that the electronic current transformer is stable, reliable and accurate, and can meet the practical application requirements.

Cloud energy management system for building-scale AC/DC hybrid microgrid

This paper proposes a Cloud Energy Management System (C-EMS) for the building-scale hybrid microgrid. The building-scale hybrid microgrid is composed of renewable energy generators, charging piles, dc and ac loads, a diesel generator, energy storage devices, and a power electronic transformer connected to the ac power grid. The C-EMS is in charging of them. With the management of C-EMS, for the power system, the building-scale hybrid microgrid can be considered as a four-quadrant controllable node, which means it can be controlled to either generate or consume reactive and active power to the power system. In addition, based on wireless communication, the C-EMS receives the command of cloud management centre and make the microgrid operate at the assigned power. Therefore, numerous C-EMS can be managed via the cloud manage centre, which improves the controllability of the power system. The proposed C-EMS has been verified by the simulations carried out in Matlab/Simulink.

Optimization Strategy of Reduction of Switching Times in Rectifier Stage Based on Power Electronic Transformer

The control strategies of conventional power electronic transformer are mostly double closed-loop control based on dq coordinate decomposition, and the control strategy is complex. Based on the analysis of the topology of single phase cascaded power electronic transformer, this paper takes the transformer primary rectifier as the typical object. According to the multilevel synthesis strategy, an improved ladder wave level control strategy is proposed and the quasi-proportional resonance is proposed. The simulation results show that the new control strategy can verify the proposed scheme by ensuring that the total voltage of the rectifier stage is maintained at a given value, the voltage of each module rectified voltage is approximately equal, and the switching frequency of the switching device is greatly reduced, and power factor of grid approaches 1.

Solid-State Transformer (S2T) of Single Phase Matrix Converter

<span lang="EN-US">Solid-State Transformer (S2T) also known as Power Electronic Transformer (PET) is applied in various industrial fields compared to the conventional transformer due to it flexible voltage transfer ratio, high power density, and low harmonic distortion. This paper presents the S2T of Single Phase Matrix Converter (SPMC) that acts as cyclo-converter. A 1kHz frequency was synthesized on the primary side of the transformer using Pulse Width Modulation (PWM) technique, whilst, the output converted by the SPMC that produces the 50Hz frequency. A part of AC to AC operation, the switching algorithm for safe-commutation technique is also presented to solve the commutation problem caused by the usage of inductive load. Minimization of size, losses and optimal efficiency are the advantages of this approach. The proposed model was simulated by using MATLAB/Simulink (MLS).</span>

Partial Discharge Analysis in High-Frequency Transformer Based on High-Frequency Current Transducer

High-frequency transformers are the core components of power electronic transformers (PET), whose insulation is deeply threatened by high voltage (HV) and high frequency (HF). The partial discharge (PD) test is an effective method to assess an electrical insulation system. A PD measurement platform applying different frequencies was set up in this manuscript. PD signals were acquired with a high-frequency current transducer (HFCT). For improving the signal-to-noise (SNR) ratio of PD pulses, empirical mode decomposition (EMD) was used to increase the SNR by 4 dB. PD characteristic parameters such as partial discharge inception voltage (PDIV) and PD phase, number, and magnitude were all analyzed as frequency dependent. High frequency led to high PDIV and a smaller discharge phase region. PD number and magnitude were first up and then down as the frequency increased. As a result, a suitable frequency for evaluating the insulation of high-frequency transformers is proposed at 8 kHz according to this work.

Tek Kademe Dönüştürücülü Güç Elektroniği Trafosu

Güç elektroniği trafoları (PET'ler), manyetik çekirdeği ve iletken sargıları oluşturmak için gerekli olan demir ve bakır miktarını azaltarak geleneksel dağıtım trafoların boyutunu ve maliyetini düşürme potansiyeline sahiptir. PET'ler orta ölçekli frekanslarda çalışarak trafo çekirdek boyutunu düşürmeyi gerçekleştirebilmektedir. Önerilen PET topolojisi diğer PET'ler ile kıyaslandığında PET'in hem maliyetini hem de fiziksel boyutunu azaltmayı sağlamayı hedeflemektedir. Son olarak, teorik analizin etkililiğini doğrulamak için kullanılan dönüştürücü için benzetim sonuçlar verilmiştir.

Evaluating the metering error of electronic transformers on-line based on VN-MWPCA

Electronic transformers are used to measure the voltage and current signals, which are used to sense the state of the transmission networks. The deterioration of their metering error will affect the stable operation of the power system. The traditional method of evaluating the metering error of electronic transformers is to compare them with the standard transformer. There are outstanding problems such as over inspection and under inspection of the traditional method, which cannot be used for evaluating the metering error for a large number of electronic transformers on-line in a long-term. In this article, the correlation between primary transmission networks is analyzed to establish a new evaluation standard without a standard transformer. The standard can be calculated as a characteristic statistics, by using the measured data based on the VN-MWPCA proposed. Then the metering error of electronic transformers is evaluated by analyzing the abnormal change of the statistics. The field application analysis shows that the method proposed can be used to evaluate the metering abnormal of a Class 0.2 electronic transformer on-line accurately.

Design an Efficient Power Electronics Transformer (PET) for the Improvement of Quality in Power

This paper consists of a new device called as Power Electronics transformer (PET) which has been recommended in paper so that it understands that voltage transformation, galvanic isolation, and enhancing force personal satisfaction for a just gadget. The PET gives a complete methodology for designing a transformer that uses Power electronic frameworks which comprises for primary coil and auxiliary coils of a transformer. A couple features to example, such-and fast voltage regulation, voltage list recompense what's more likewise revision for control figure could a chance to be united under PET. This paper indicates another thought of plotting An vitality electronic transformer. In the schema process, those AC/DC, DC/AC, AC/AC converters In addition secondary back transformers have been utilized. Grid converter similarly meets desires Likewise AC/AC converter on force electronic transformer. Those proposed drive electronic transformer performs perplexedly capacities to example, amendment regarding energy. Factors, elimination of swell and voltage sag, reduction of voltage flicker and fault situation protection capabilities. The recommended force electronic transformer need been shown using MATLAB/ SIMULINK Furthermore also change Previously, force characteristic with recommended perfect gas need been checked by the simulink outcomes.

Power Electronic Transformer Control Technology Based on DSP

Power Electronic Transformer Control Technology Based on DSP

Study on Structure and Control Strategy of Hybrid AC / DC Power Grid

Hybrid AC/DC power grid is the development direction and inevitable choice of the future power transmission and distribution network along with the high proportion penetration of distribution generation (DG). The design principle of hybrid AC/DC power grid structure is studied and a novel hybrid AC/DC power grid network structure which combined power electronic transformer (PET) with traditional transformer was proposed to reach the goal of flexible regulation under stable operating conditions. The corresponding control strategy of the proposed grid was designed based on the master-slave control and peer-to-peer control. The correctness of the proposed hybrid AC/DC power grid and the rationality of the control strategies are verified according to the simulation under the PSCAD/EMTDC simulation environment.

Research on the Influence of Sampling Frequency on Energy Measurement Precision of Electronic Instrument Transformer

Digital metering system, the electronic energy meter analog-to-digital conversion sampling function moved to the electronic instrument transformer, and electronic instrument transformer sampling frequency compared with the electronic energy meter is low, the sampling frequency will be insufficient in the analog-to-digital conversion process Introduce quantization error. In this paper, the measurement error model of electronic instrument transformer based on analog-to-digital conversion sampling principle is established, and the influence of sampling frequency on energy measurement error is quantitatively analyzed. The analysis shows that the accuracy of electronic instrument transformer measurement is related to oversampling rate.