Frequency response based behavioral modeling verification for three phase AC-DC converter

In modern distributed energy systems (DES), focus is shifting from the conventional centralized approach towards distributed architectures. However, modeling and analysis of these systems is more complex, as it involves the interface of multiple energy sources with many different type of loads through power electronics converters. The integration of power electronics converters allows distributed renewable energy sources to become part of modern electronics power distribution systems (EPDS). It will also facilitate the ongoing research towards DC-based DES which is mostly composed of commercial DC-DC converters whose internal structure and parameters are unknown. For the system level analysis, the behavioral modeling technique is the only choice. Since most power electronics converters are non-linear systems and linear models can’t model their dynamics to a desired level of accuracy, hence non-linear modeling is required for accurate modeling. The non-linear modeling approach presented here aims to develop behavioral models that can predict the response of the system over the entire operating range. In this work, either a lookup table or a polytopic structure-based modeling technique is used. The technique is further applied to cascade and parallel connected converters, being two DES scenarios. First the procedure is verified via application to switching models in a simulation and then validated for commercial converters via experiments. The results show that the developed behavioral models accurately predict both the transient and steady state response.

A novel and cost-effective model for cloud energy storage based on a dual storage setup in active distribution grid with resilience consideration

The Frequency Response Analysis (FRA) is an efficient tool to diagnosis mechanical defects in transformer windings. After measurement of frequency responses, they must be compared to find any defects in the winding. The lack of clarity in the interpretation of measured frequency responses is the main problem of this method. This paper tries to solve this problem via a dimensional reduction of frequency response traces by Principal Component Analysis (PCA) to diagnose any short circuits in the winding. The precise location of the fault in the transformer winding is considered to be the main index, the effectiveness of which is presented by the results. Based on the approved transformer model, a dimensionality reduction method and feature selection are implemented to transformer's frequency response traces to map it from its main high-dimensional vector space to a lower dimensional one. It was shown that frequency response traces of Turn-to-Turn faults were separated from each other and the exact location of each fault was determined.

• Transient events can trigger internal resonances in transformer windings. • First-mode resonance can cause severe overvoltages in transformer windings. • Frequency response-based modeling captures winding dynamics without design details. • The method enables post-fault analysis assessing transformer resonance frequencies. This paper presents a black-box modeling approach for evaluating internal resonances in high-voltage windings of power transformers. The proposed method relies on frequency response measurements, specifically admittance and voltage transfer functions, over a frequency range of 20 Hz to 1 MHz. First, the black-box modeling methodology is presented, followed by a discussion of the frequency response measurements performed in a high-voltage laboratory environment using a Sweep Frequency Response Analysis (sFRA) instrument. Based on these measurements, Y-matrix and H-matrix models were developed and validated in both frequency and time domains. The analysis revealed critical resonance frequencies, especially the first-mode resonance, which cause significant overvoltages that pose a risk to the integrity of the winding’s insulation. These results highlight the importance of considering internal resonances during the design phase of power transformers to mitigate the risk of dielectric failure. Furthermore, the technique proves especially valuable for post-failure analysis, as it enables the investigation of resonance frequencies in a failed transformer or similarly designed unit, providing insight into whether these resonances contributed to the failure event in the operational power grid.

Frequency response has received a lot of attention in recent years at the national level, which culminated in the development and approval of North American Electricity Reliability Corporation (NERC) BAL-003-1 Frequency Response and Frequency Bias Setting Reliability Standard. This report is prepared to describe the details of the work conducted by Pacific Northwest National Laboratory (PNNL) in collaboration with the Bonneville Power Administration and Western Electricity Coordinating Council (WECC) Joint Synchronized Information Subcommittee (JSIS) to develop a frequency response analysis tool (FRAT). The document provides the details on the methodology and main features of the FRAT. The tool manages the database of under-frequency events and calculates the frequency response baseline. Frequency response calculations are consistent with frequency response measure (FRM) in NERC BAL-003-1 for an interconnection and balancing authority. The FRAT can use both phasor measurement unit (PMU) data, where available, and supervisory control and data acquisition (SCADA) data. The tool is also capable of automatically generating NERC Frequency Response Survey (FRS) forms required by BAL-003-1 Standard.

In recent efforts of making aircraft more energy efficient, aircraft-industries are moving towards More Electric Aircraft (MEA). MEA offers several benefits compared to a conventional aircraft system including improved power transmission efficiency, reduced fuel consumption, lesser weight and reduced environmental impact. One of the enabling technologies for MEA is power electronic converter which is required to convert and condition the generated electric power for different aircraft loads (Rosero et al., IEEE Aerosp Electron Syst Mag, 22:3–9, 2007) [1], (Wheeler and Bozhko, IEEE Electrif Mag, 2:6–12, 2014) [2], (Sarlioglu and Morris, IEEE Trans Transp Electrif 1:54–64, 2015) [3].

We present a study on a retarding effect that generally occurs in a frequency response measurement, which is induced by a time delay of the signal transition in a sweep frequency measurement. The retarding effect brings on frequency shift and amplitude attenuation to the frequency response that cannot be ignored in a precise measurement. Simulation and experimental results indicate that the frequency shift increases with the rise in the time constant TC and the frequency sweep speed Fstep/Tdwell. A compensation methodology for eliminating the response errors induced by the retarding effect and regaining the real frequency response of an object is proposed.

The identification of power apparatus parameters to be specified in transient models from frequency response tests is a well established practice. There has been, in addition, a significant effort in the development of fitting procedures that could derive the parameters from frequency response curves. This paper summarizes the present status of electrical parameter determination for synchronous machines and transformers from frequency response measurements. The document discusses power apparatus models, test setups, and fitting procedures.

The Hybrid Power Electronic Transformer (HPET) has been proposed as an efficient and economical solution to some of the problems caused by Distributed Energy Resources and new types of loads in existing AC distribution systems. Despite this, the HPET has some limitations on the control it can exert due to its fractionally-rated Power Electronic Converter. Various HPET topologies with different capabilities have been proposed, being necessary to investigate the system benefits that they might provide in possible future scenarios. Adequate HPET models are needed in order to conduct such system-level studies, which are still not covered in the current literature. Consequently, this article presents a methodology to develop power flow models of HPET that facilitate the quantification of controllability requirements for voltage, active power and reactive power. A particular HPET topology composed of a three-phase three-winding Low-Frequency Transformer coupled with a Back-to-Back converter is modeled as an example. The losses in the Back-to-Back converter are represented through efficiency curves that are assigned individually to the two modules. The model performance is illustrated through various power flow simulations that independently quantify voltage regulation and reactive power compensation capabilities for different power ratings of the Power Electronic Converter. In addition, a set of daily simulations were conducted with the HPET supplying a real distribution network modeled in OpenDSS. The results show the HPET losses to be around 1.3 times higher than the conventional transformer losses over the course of the day. The proposed methodology offers enough flexibility to investigate different HPET features, such as power ratings of the Power Electronic Converter, losses, and various strategies for the controlled variables. The contribution of this work is to provide a useful tool that can not only assess and quantify some of the system-level benefits that the HPET can provide, but also allow a network-tailored design of HPETs. The presented model along with the simulation platform were made publicly available.

This paper discusses on the applicability of three methods namely n-ladder network, multi-conductor transmission line (MTL) and hybrid MTL to model the transformer winding frequency response. These methods have been used to model an actual transformer winding with end-to-end short circuit configuration. The corresponding model parameters are calculated based on winding construction and geometrical information. The frequency response curves obtained from different models are compared with the measured frequency response. Based on the obtained results, the suitability of considered techniques for modelling the end-to-end short circuit winding configuration is discussed.

An automated process for equalizing an audio system and an apparatus for implementing the process. An audio system includes a microphone unit, for receiving the sound waves radiated from a plurality of speakers, acoustic measuring circuitry, for calculating frequency response measurements; a memory, for storing characteristic data of the loudspeaker units and further for storing the frequency response measurements; and equalization calculation circuitry, for calculating an equalization pattern responsive to the digital data and responsive to the characteristic data of the plurality of loudspeaker units. Also described is an automated equalizing system including a acoustic measuring circuitry including a microphone for measuring frequency response at a plurality of locations; a memory, for storing the frequency responses at the plurality of locations; and equalization calculation circuitry, for calculating, from the frequency responses, an optimized equalization pattern.

An energy systems engineering approach for the design and operation of microgrids in residential applications

Nowadays the availability of computational models of nonlinear dynamic components is becoming a key requirement for the analysis and design of complex systems. The complexity of many components, however, as well as the lack of information on their internal structure often prevent from the development of traditional physical models. This scenario raise the interest for behavioral models, which are models obtained from the observation of the external behavior of components. In this thesis we focus on the development of behavioral models for the assessment of Signal Integrity (SI) and ElecroMagnetic Compatibility (EMC) effects on fast digital circuits. Such an assessment, that is mainly achieved by simulating the evolution of signals sent on interconnects by digital integrated circuits (ICs), requires e±cient and accurate models of IC ports driving and loading the interconnects themselves. The required models must allow the simulation of large realistic problems and must performs at an accuracy level useful to the prediction of sensitive effects, like crosstalk and radiation. Behavioral models meet such requirements and are establishing as the best tools for the description of IC ports. We analyze possible behavioral modeling methods for IC ports and concentrate on behavioral modeling via black-box identification. It amounts to the selection of a suitable parametric model and to the estimation of its parameters from measured transient responses. The selection of a suitable class of parametric models leads to Radial Basis Function (RBF) representations, that offer many advantages in the modeling of systems with strong nonlinear nature and multiple inputs. We developed a simplified RBF model that can be obtained from measured port voltage and current. The estimation of such model is simple and relies on a robust algorithm. In order to test the effectiveness of the proposed approach and its feasibility, we apply it to the modeling of several virtual devices and to an actualdevice of interest. The obtained models perform at a fairly good accuracy and effciency levels and turn out to be weakly sensitive to driven loads and measurement setup. Besides, since the model structure is selected by the estimation process itself, all the relevant physical effects relating input and output signals (e.g., substrate or packaging effects) are automatically taken into account

Vibration-based construction and extraction of structural damage feature index

We investigated the frequency response of a polarimetric fiber vibration sensor based on a polarization diversified loop structure according to the length of polarization-maintaining photonic crystal fiber (PM-PCF) used as a sensor head. The fiber vibration sensor was fabricated using a polarization beam splitter, PM-PCF, and two waveplates, that is, a quarter-wave plate and a half-wave plate. For intensity-based vibration measurement, a laser diode and a photodetector were utilized for the realization of the sensor system. The single-frequency vibration was applied to the sensor head by using a piezoelectric transducer. Over a frequency range of 1-3000 Hz, the frequency response of the fabricated sensor was observed for three kinds of sensor head lengths of 6.2, 8.4, and 12.2 cm. In measured frequency responses, a resonance peak appeared at 140 Hz irrespective of the PM-PCF length, but cut-off frequencies were measured as ~538, ~386, and ~228 Hz for PM-PCF lengths of 6.2, 8.4, and 12.2 cm, respectively. The phase shift per unit strain and the minimum detectable strain perturbation were measured as ~0.291 mrad/με and ~0.392 nε/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at 2000 Hz for 6.2-cm-long PM-PCF, respectively.