Sag Generator Research Articles

An End-to-End Deep Learning Method for Voltage Sag Classification

Power quality disturbances (PQD) have a negative impact on power quality-sensitive equipment, often resulting in great financial losses. To prevent these losses, besides detecting a PQD on time, it is important to classify it, so that appropriate recovery procedures are employed. The majority of research employs machine learning model PQD classifiers on manually extracted features from simulated or real-world signals. This paper presents an end-to-end approach that circumvents the manual feature extraction and uses signals generated from mathematical voltage sag type formulas. We developed a configurable voltage sag generator that was used to form training and validation datasets. Based on the synthetic three-phase voltage signals, we trained several end-to-end LSTM classifiers that classify voltage sags according to ABC classification. The best-performing model achieved an accuracy of over 90% in the real-world dataset.

Study of stability after low voltage ride-through caused by phase-locked loop of grid-side converter

In a power system with a high percentage of converter coupled generation, dynamic characteristics of the converter affects the stability of the whole power system. The interaction of the various control loops of the grid-side converter, e.g., the phase-locked loop and the DC link voltage control loop, dominates the various dynamic characteristics of the grid-side converter, including its low voltage ride-through ability. In this paper, the phase-locked loop is modeled and analyzed and a stability criterion for the converter, depending on the grid impedance, is obtained. According to this criterion, a common low voltage ride-through test device based on the shunt impedance voltage sag generator is analyzed. The results show that, and explain why, the test device cannot reproduce the characteristics of the practical grid, which is also verified by experiments using a controller-Hardware-in-the-loop system.

Low-Voltage Ride-Through Remote Testing Method for Offshore Wind Turbines

Grid-connected wind turbines (WTs) are required to have low-voltage ride-through (LVRT) capability. On-site LVRT test is a convincing certificating method. To tackle the limited accessibility and harsh conditions of on-site test for offshore WTs, this paper proposes a remote testing method, which places the testing device on shore to produce the specified fault voltages through a subsea cable to the WT. For further eliminating the effects of introduced cable on LVRT test, a stepwise voltage sag generation strategy is applied to suppress the overvoltage and maintain required voltage sags. First, the LVRT testing requirements and voltage sag specification need to be considered in a practical test are introduced. The stepwise generation strategy and its implementation procedure based on the designed testing device are presented. Second, the effects of submarine cable on the WT-side voltage are analyzed under different generation stages of voltage sags. Next, the testing device’s impedance configuration method, based on the derived residual voltage expression, is given to generate the required steady-state voltage sags. Finally, simulation results indicate that with the proposed method, the effects of cable can be eliminated and the required grid faults can be emulated for remote LVRT test.

Ride through testing of variable speed drive due to voltage sag types (types I, II and III)

Variable speed drives (VSDs) are widely used in various applications mainly in process industry need constant rotational speed. It is developed from power electronic components thus saving energy in its operation. Unfortunately it is susceptible against power quality problem for example voltage sags. The VSD may be disruption or drop out when it is supplied by voltage sags and it is determined by sag characteristics. This study is to investigate effect of voltage sags Types I, II and III on VSD through laboratory testing. The voltage sags characteristics are generated from voltage sag generator (Shaffner 2100 EMC). The effects are presented in susceptibility curves in disruption and drop out conditions. The curves resulted are evaluated by standard curve recommended. Test results show that voltage sag Type I cause the VSD disruption only, whereas two types sag other result in the VSD disruption and also drop out. Evaluation results explain a few test points are in operation area for disruption condition whereas test points for dropping out far below the threshold recommended. Hence the VSD has good quality to voltage sags.

Implementation of Fault Ride-Through Techniques of Grid-Connected Inverter for Distributed Energy Resources With Adaptive Low-Pass Notch PLL

The amount of distributed energy resources (DERs) has constantly increased worldwide. As the power ratings of DERs have become considerably high, the grid code requirements are necessary to secure reliable power generation and transmission for the public electric network. In order to follow grid codes of the various countries and optimize the function of grid-connected inverters for DERs, a robust phase-locked loop (PLL) is essential for extracting the grid phase information accurately, when the grid voltage is polluted by harmonics and unbalanced. This paper proposes fault ride-through techniques based on a low-pass notch (LPN)-PLL. The LPN-PLL has not only fast and smooth transient responses to a sudden transition of the grid voltage but also has robustness to the distorted and unbalanced grid conditions. Therefore, the stable performance in the grid fault conditions is expected without the system trip. Furthermore, a universal voltage sag generator for the various grid codes with six parameters is proposed for the verification of low voltage ride-through (LVRT) performance. Experimental verifications are presented to show the LVRT performance based on the LPN-PLL with a three-phase grid-connected inverter (10 kV·A) and a prototype of the voltage sag generator (10 kV·A).

A Novel SPLL and Voltage Sag Detection Based on LES Filters and Improved Instantaneous Symmetrical Components Method

The software phase-locked loop and the voltage sag detection algorithm are the two key factors to evaluate the performance of a dynamic voltage restorer, whose dynamic response is usually impacted by phase jump, voltage unbalance, and harmonics of the grid voltage. This paper proposes a novel algorithm based on the combination of least error squares filters and an improved instantaneous symmetrical components method. Hence, a detailed theoretical procedure is first presented. Then, the simulation model is built in MATLAB/SINMULINK. To verify its effectiveness, a series of comparison and analysis have been carried out. Also, a 10-kV/2-MVA prototype is developed with a voltage sag generator platform. Finally, experiments have been done and the results show that the novel algorithm has an improved dynamic response compared with the traditional methods.

EVALUACIÓN DE LA INMUNIDAD DE UN MOTOR DE INDUCCIÓN MONOFÁSICO FRENTE A HUECOS DE TENSIÓN

This paper shows a methodology for evaluating the immunity of a single-phase induction motor to voltage sags by simulations in Matlab/Simulink. For this, a model of a single-phase voltage sag generator was designed and algorithms were implemented, to obtain, model and improves the sensitivity curve of the induction motor with respect to the voltage drop. The implemented methodology is a simple guide to estimate the impact of voltage sags on induction motors. Additionally, the proposed method reduces the amount of voltage sags to which the motors are usually subjected in lab test using other methodologies.

A Novel Voltage Sag Generator for Grid-Connected PV System's Low Voltage Ride-Through Test

A novel voltage sag generator (VSG) is proposed for grid-connected photovoltaic (PV) systems low voltage ride-through (LVRT) test. The topology and parameters of the current-limiting reactor group, grounding reactor group and bi-directional thyristor valve of the VSG is designed to generator voltage sags with several sag depths and phase angles. Furthermore, for a 250kW grid-connected PV inverter modeled by real-time digital simulator (RTDS), LVRT simulations in different sag depths at different phase angles are done with the VSG. Simulation results show that the proposed VSG has reasonable design and can reveal adequately how the voltage sag depths and phase angles influent the LVRT results.

A Paralleled Integrated Control Device of Squirrel-Cage Induction Wind Generator LVRT

To minimize the influence of power grid with wind power generation resulted by voltage sags with short duration, a paralleled integrated control device of squirrel-cage induction wind generator LVRT (Low Voltage Ride Through) is proposed which adds paralleled module circuits to conventional wind generator. With closed-loop hysteresis current control based on instantaneous reactive power theory and rated voltage control, this device can achieve reactive power compensation in normal operation and voltage stability when voltage sags. Power produced by wind generator is consumed during the sag and wind power generation system is connected to grid all the time. Simulation models about the device were built based on PSCAD / EMTDC platform and the analysis verifies the device’s achievement of LVRT.

A Simple Sag Generator Using SSRs

Power line voltage sags are among the most frequent and costly power quality problems. Most equipment must be designed such that they can tolerate voltage sags (within limits defined according to some standards). Furthermore, some equipment must continue proper operation even under extreme sag conditions (critical loads); this property often may not be accommodated inside the device itself, and sag-compensating power conditioners have been developed for such purposes. While, in practice, voltage sags are not wanted, generating sags becomes necessary for the purpose of experimentally verifying the performances of the equipment (both the equipment under sag condition and the sag-compensating power conditioner) under sag conditions. In this paper, a simple and economical, yet highly performing, sag generator is developed, its design is discussed, and its feasibility is demonstrated by experiments. The proposed solid-state relay (a semiconductor power module of triac characteristics) and variable transformer (variac)-based sag generator is built for three-phase 10-kVA ratings, and balanced/imbalanced voltage sags are demonstrated in the laboratory. The performance under resistive, inductive, and nonlinear loads is evaluated, and finally, the utilization of the sag generator in the test of a series-active-filter-based power quality conditioner is demonstrated. The proposed approach provides a very simple, yet highly effective, solution for voltage sag generation.

Bag the sags - Embedded solutions to protect textile processes against voltage sags

This article describes the vulnerability of variable speed drives (VSD) to voltage sags on a theoretical basis. Then, three embedded mitigation methods are addressed in theory which protect textile processes against voltage sags, and practical measurements with a sag generator are shown. The use of embedded solutions such as kinetic buffering and boost convertor or an active front end will increase the voltage sag immunity of the process. Finally, two processes in the textile industry are described, and a brief cost-benefit analysis of the solutions is made. Experiments with a sag generator show that the voltage sag behaviour can be well described by theoretical models.

A three-phase sag generator for testing industrial equipment

A diesel powered three-phase standby 480 V, 15 kW, 60 Hz synchronous generator has been modified to give controlled three-phase voltage sags. These sags can be controlled in both depth and duration. A 486-based computer with a data acquisition system controls the generator and monitors the system under test. The custom software interface allows the user to select the depth and duration of the each sag. Typically, the user will select a series of sags in selectable increments down to a certain depth. The data acquisition system has both digital and analog inputs, so that data lines, AC and DC voltages and currents, contactors and relays, etc. can be monitored during the tests. The software interface enables the user to select allowable tolerance bands for the monitored signals. If one or more of the signals falls outside the allowable range, the test is suspended. The sag depth and duration that caused the equipment to "fail" the test is then recorded, After testing over a range of sag durations, a CBEMA-type curve is available for the system under test. The sag generator enables the user to systematically determine the sensitivity of the components of an installed process line. This will enable the user to determine cost-effective ride-through enhancement strategies or to test the effectiveness of currently installed equipment. Although this test generator is small, the basic concept can be scaled up to the 2 MVA range.

Power quality and factory automation

A case study involving monitoring power quality disturbances at a representative plant and identifying the disturbances that disrupt production is described. The sensitivities of representative electronic control equipment to the identified disturbances were measured and then projected to form a plant disturbance threshold. For the monitoring effort, six disturbance analyzers were installed at four voltage levels extending from the utility 40 kV station to 120 V control power in an individual machine tool. Voltage sags were the only disturbance to directly cause lost production and were the most common disturbance at 68% of the total number of events recorded. Two programmable logic controller (PLC) transfer lines and a computerized numerically controlled (CNC) lathe were tested with a sag generator to determine the sensitivities of the equipment. The most sensitive components required the voltage during a sag to drop to less than 80-86% of rated to malfunction, whereas the least sensitive required the voltage to drop below 30% of rated. From the test results, the calculated sag threshold at the utility feed to the plant to disrupt production was 87% of the nominal voltage for more than 8.3 ms. >