Flicker Mitigation Research Articles

Study of Voltage Flicker Mitigation Using Emulated Electric Arc Furnace

Study of Voltage Flicker Mitigation Using Emulated Electric Arc Furnace

Stability analysis of selective inter-harmonic compensation approach for light flicker mitigation

Stability analysis of selective inter-harmonic compensation approach for light flicker mitigation

Stability analysis of selective inter-harmonic compensation approach for light flicker mitigation

Stability analysis of selective inter-harmonic compensation approach for light flicker mitigation

Integrated physical-layer secure visible light communication and positioning system based on polar codes

Visible light communication (VLC) with physical-layer security can provide information-theoretic security for the optical wireless channel based on the characteristics of the channel instead of encryption algorithms and secret keys at application layer. Since precise location information of communication parties is crucial for estimating channel states and designing secure communication schemes, this paper proposes an integrated visible light communication and positioning system which provides triple functionalities of high-accuracy indoor positioning, physical-layer secure visible light communication, and flicker mitigation illumination. A heterogeneous signal hybrid line coding scheme is proposed for the transmitter to converge the high-speed communication data signals and the low-speed positioning data signals, and a hybrid heterogeneous signal extraction scheme is proposed for the receiver to separate the hybrid heterogeneous signals with a high-bandwidth photodetector and a low-pass complementary metal-oxide-semiconductor (CMOS) image sensor. Based on the positioning information and the communication scheme, a polar codes-based forward error correction coding scheme is designed to achieve physical-layer security and transmission reliability simultaneously. Numerical results show that the proposed system can reach a secrecy code rate of 0.76 for a single-input single-output indoor VLC channel and a transmission efficiency of 0.38 without perceivable flicker. Experimental results show that the proposed system can achieve an average positioning accuracy of 3.35 cm and decrease the bit error rate of a legitimate receiver to a near error-free level (lower than 10−7) while keeping the bit error rate of an eavesdropper at 0.4887 (nearly 0.5) with a transmission data rate of 1 Mbps, resulting in near-zero suppression of the eavesdropped information and a high secrecy capacity of 0.9994.

A 3.0 µm Pixels and 1.5 µm Pixels Combined Complementary Metal-Oxide Semiconductor Image Sensor for High Dynamic Range Vision beyond 106 dB.

We propose a new concept image sensor suitable for viewing and sensing applications. This is a report of a CMOS image sensor with a pixel architecture consisting of a 1.5 μm pixel with four-floating-diffusions-shared pixel structures and a 3.0 μm pixel with an in-pixel capacitor. These pixels are four small quadrate pixels and one big square pixel, also called quadrate-square pixels. They are arranged in a staggered pitch array. The 1.5 μm pixel pitch allows for a resolution high enough to recognize distant road signs. The 3 μm pixel with intra-pixel capacitance provides two types of signal outputs: a low-noise signal with high conversion efficiency and a highly saturated signal output, resulting in a high dynamic range (HDR). Two types of signals with long exposure times are read out from the vertical pixel, and four types of signals are read out from the horizontal pixel. In addition, two signals with short exposure times are read out again from the square pixel. A total of eight different signals are read out. This allows two rows to be read out simultaneously while reducing motion blur. This architecture achieves both an HDR of 106 dB and LED flicker mitigation (LFM), as well as being motion-artifact-free and motion-blur-less. As a result, moving subjects can be accurately recognized and detected with good color reproducibility in any lighting environment. This allows a single sensor to deliver the performance required for viewing and sensing applications.

Distribution Matching for Dimming Control in Visible-Light Region-of-Interest Signaling

We propose a two-level dimmer based on binary distribution matching where a low-rate signal controls the output probability distribution of a high-rate bit sequence, which can be used in region-of-interest (RoI) signaling applications. To reduce the rate loss of the dimmer, we propose the extended multiset-partition distribution matching (EMPDM) algorithm with a novel binary-tree-structure implementation. In addition, we introduce 4p-EMPDM, a compact version of EMPDM, which has a typical composition (TC) and four leading composition pairs (CPs). The codebook of 4p-EMPDM includes only run-length-aware codewords, which reduces the maximum run-length of the transmitted bit sequence by 4.27 times. Hence, it guarantees flicker mitigation for visible-light RoI signaling systems at 6 kHz without using any run-length limited code (non-RLL). Using experimental data collected from the low-rate RoI signaling prototype, we introduced a threshold range where both intensity and area information of the received training symbols can be exploited to optimize the shaping ratios of the 4p-EMPDM dimmer. Because of the non-RLL feature, the proposed system can support soft-decision forward-error-correction (FEC) decoding to improve reliability. Our system outperforms related systems based on hybrid modulation schemes in terms of spectral efficiency, bit rate, and minimum required optical clock rate.

A Novel Combined Double Binary Turbo Coding and Color Shift Keying Technique for Flicker Mitigation in Multi Carrier Visible Light Communications

Although radio frequency (RF) systems have been developed at a level that can operate almost within theoretical limits in terms of spectral efficiency due to increasing demands, the RF spectrum allocated for wireless mobile communication has started to fill up rapidly and become insufficient. Visible light communication (VLC), one of the optical wireless communication systems, stands out as a promising technology that can be an alternative to RF technology in some application areas and can help meet the demands by playing a complementary role in some application areas. However, VLC systems face the flickering problem. In this study, it is proposed to combine the double binary Turbo coding (DBTC) technique with color shift keying (CSK) modulation, which does not have a flickering problem, as a solution to the flicker problem of VLC systems. The proposed combined DBTC-CSK method is tested on optical OFDM systems from multi-carrier wireless communication systems. Monte-Carlo simulations are performed to verify the performance of the proposed DBTC-CSK-OFDM system in terms of bit-error-rate (BER) over AWGN channel, single-path optical LOS channel and multi-path optical channel. According to the simulation results it is observed that, DBTC-CSK-OFDM system has better BER performance than that of RS–CC coded CSK-OFDM and un-coded CSK-OFDM systems, providing 5.5 dB and 14 dB SNR gain at multi-path optical channel environments, respectively.

Constant Weight Polar Coded Orthogonal Space-Time Block Codes for Dimmable Indoor MIMO-VLC Systems

The concatenation of constant weight polar code (CWPC) with orthogonal space-time block code (OSTBC), known as CWPC-OSTBC scheme is proposed for the indoor multiple-input multiple output visible light communication (MIMO-VLC) systems in this letter. The CWPC helps to mitigate against flickering, provides desired dimming targets, and coding gain while the OSTBC achieves MIMO diversity gain. Flicker mitigation and dimming control are obtained based on the modified Knuth balancing method with enhanced prefix coding. This method does not utilise lookup table and thus, it is practicable in the real-time. Numerical results are presented to discuss the channel capacity and bit-error-rate (BER) performance of the proposed CWPC-OSTBC scheme considering different parameters. The results show that increasing the transmission antennas of the OSTBC system provides diversity gains. More so, the CWPC-OSTBC scheme yields an improved coding gain compared to polar code without balancing and other state-of-the-art methods.

An approach for light flicker mitigation through reduced capacity STATCOM

An approach for light flicker mitigation through reduced capacity STATCOM

Automotive 3 μm HDR Image Sensor With LFM and Distance Functionality

We described a 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> super-exposure pixel 1.3-MP CMOS image sensor for automotive application that provided for up to 140 dB high dynamic range (HDR) coverage with multiexposure operation, as well as effective HDR with LED flicker mitigation (LFM) operation. At junction temperatures in excess of +100 °C, total signal-to-noise transitions were kept at or above 30 dB due to further development of the pixel pulsed gate operation and process optimization. Pulsed LFM operation provided for capturing flickering lights of any brightness. Two-photodiode pixel architecture in combination with single microlens covering the pixel also enabled distance extraction along with a color image using in-pixel phase detect.

Optimal allocation of energy storage systems, wind turbines and photovoltaic systems in distribution network considering flicker mitigation

Renewable energies have introduced themselves as efficient resources for power production but their integration into power grid makes some challenges during operation. One of these challenges is the negative impact of wind turbines (WTs) on power quality. Flicker produced by WTs is one of the most important parameters which significantly affects power quality of distribution networks. In this paper, to mitigate flicker produced by WTs, distribution network planning problem is solved by considering power quality issue. For this aim, in the objective function, in addition to power losses and energy storage system (ESS) cost, flicker emission and voltage deviation are also minimized. Due to the complexity of the planning problem, crow search algorithm with differential operator (CSAd) is proposed to optimally site and size WTs and ESSs. In CSAd, new solutions are generated by using the information of high-quality solutions. To investigate the impact of various factors on the network performance, the planning problem is solved at different scenarios: (1) Siting and sizing ESSs, (2) Siting ESSs, WTs and PVs as well as sizing ESSs and (3) Siting ESSs, WTs and PVs as well as sizing ESSs and WTs. Simulation results show that optimal siting and sizing of ESSs and WTs can considerably improve the distribution network parameters in terms of power losses and flicker emission. Moreover, the proposed approach produces more accurate and robust results than the other studied methods.

A Novel Smart Charging Method to Mitigate Voltage Fluctuation at Fast Charging Stations

The research presented in this paper focuses on the impact of fast charging stations (FCSs) on voltage quality. When the operation of FCSs causes a voltage fluctuation and light flicker, the FCSs may be disconnected, as per the utility general standard practice, which results in financial loss represented by FCS downtime. FCS downtime can be avoided by mitigating voltage fluctuation and light flicker. Flicker mitigation devices that are available in the market are characterized by their high total annual equivalent costs. As an alternative, a novel smart charging method is proposed in this study in order to mitigate both voltage fluctuation and light flicker, whereby customers can select one of three charging services available in fast chargers: premium, regular, or economic charging power. The charging power is selected according to customer priority in relation to time and cost, which offers more flexibility than those currently available in the literature. For instance, the premium power can be selected if the time is more valuable to the customer at the time of arrival at the FCS; in contrast, the regular or economic power are utilized if the cost is more valuable than the time. The results reveal that when an FCS charges a vehicle by an uncontrolled charging method, the FCS violates the flicker tolerance especially when demand for its service is increased by 20% and beyond. In contrast, the flicker limit is not violated when vehicles are charged from an FCS as per the proposed smart charging approach, even when the penetration on the FCS is increased by 50%. The proposed smart charging method offers a compromise solution to satisfy several stakeholders with different interests. Thus, the system operator equipment, FCS investors, nearby customers, and owners of electric vehicles will not be impacted by integrating the FCSs into the distribution networks.

A review of IEEE P2020 flicker metrics

In this paper, we review the LED flicker metrics as defined by the IEEE P2020 working group. The goal of these metrics is to quantify the flicker behaviour of a camera system, to enable engineers to quantify flicker mitigation, and to identify and explore challenging flicker use cases and system limitations. In brief, Flicker Modulation Index quantifies the modulation of a flickering light source, and is particularly useful for quantifying banding effects in rolling shutter cameras. Flicker Detection Index quantifies the ability of a camera system to distinguish a flickering light source from the background signal level. Modulation Mitigation Probably quantifies the ability of a camera system to mitigate modulation of a flickering light source. This paper explores various use cases of flicker, how the IEEE P2020 metrics can be used to quantify camera system performance in these use cases, and discusses measurement and reporting considerations for lab based flicker assessment.

Prediction of wind farm reactive power fast variations by adaptive one-dimensional convolutional neural network

One of the prominent problems in wind farms is voltage flicker emission. To prevent flicker emission or mitigate the impact as best as possible, a static VAr compensator (SVC) is a great candidate both economically and technically. However, SVCs cannot completely compensate the fast-changing reactive power due to delays caused by the reactive power calculation unit and the triggering fire angle of the SVC. This paper proposes a predictive control system for SVCs, by merging an additional predictive control block into the conventional control system. It is constructed based on deep neural networks, namely adaptive one-dimensional convolutional neural network (1D-CNN). The training process is conducted based on the adaptive learning weights process to enhance the prediction accuracy and training computational complexity of the 1D-CNN. Numerical results on the actual dataset in a wind farm in Manjil, Iran, have verified the forecasting accuracy and flicker mitigation of the proposed controller.

Dimming controlled multi header pulse position modulation (MH-PPM) for visible light communication system

Abstract Visible light communication (VLC) has recently drawn more attention due to the existing light sources having a bandwidth that can deliver data transmission at higher bit rates. To maintain desired brightness levels along with reliable data transmission, VLC requires to control dimming levels. In this paper, a dimming control scheme based on pulse position modulation (PPM) is proposed, which constructs a dimming encoded frame per symbol of input data. The scheme utilizes multiple headers, which is selected depending on the dimming levels and the number of bits in a symbol of input data. The proposed scheme for the VLC system supports various dimming levels. The multi header PPM frame generation for input data K = 4 $K=4$ and dimming values α = 0.25, 0.375, and 0.5 is simulated using NI Labview. The proposed dimming scheme has an excellent short-run length property which is well under the maximum flickering time period and is thus capable of flicker mitigation. The slot error performance of the proposed dimming control scheme in a VLC system for varying dimming levels is simulated in Matlab. Simulation results show that the proposed scheme has excellent error performance for a low dimming value of α = 0.25. The experimental results are also carried out in the optisystem considering the practical measured parameters of the indoor environment for free space channel and simulating the VLC system for the proposed scheme. The simulation is carried for different data rates over varying link ranges and the experimental results show that the proposed scheme performs best when dimming value α = 0.25 and data rate 2 Gbps.

EKF-based TS fuzzy prediction for eliminating the extremely fast reactive power variations in Manjil wind farm

The inherent time-varying nature of the wind farm power causes undesired voltage flicker in the power network. In order to mitigate the flicker to enhance the performance of the wind power system with very fast dynamics, the static VAr compensator (SVC) is utilized. However, the SVC operates with some delays which negatively affects its performance. This persuades us to predict the reactive power of the wind farm to compensate for the real-world delay. The predicted reactive power is then utilized in the SVC. Therefore, this paper develops a novel fuzzy one-step-ahead prediction approach for the wind farm reactive power. The proposed fuzzy prediction uses a Takagi-Sugeno (TS) fuzzy representation whose unknown parameters are tuned online based on an extended Kalman filter (EKF). The wind farm is modeled as a time-varying current source which its amplitude and phase change every 0.01 s. A large set of the actual data of a wind farm in Manjil, Iran is gathered and directly utilized in the simulation process. Several flicker indices are calculated to evaluate the proposed prediction method. The obtained results show the performance enhancement and flicker mitigation of the suggested power scheme.

Non stationary‐ARMA flicker model for squirrel cage induction generators based wind farms

Time varying nature of the wind power is studied previously considering different time intervals from seconds to days. However for power quality problems such as flicker, a model which considers the extremely fast variations is essential. Here by using large number of actual records, a time-varying model is proposed which considers the extremely short-time variations of wind active and reactive powers. The wind farm is modelled as a current source with time varying amplitude and phase which change every 0.01 s. Autoregressive moving-average (ARMA) models are utilized to model the variations and ARMA coefficients are calculated for every record. Same to the actual behaviour, the proposed model is non-stationary as the ARMA order and coefficients are different at every run of the model. The proposed model is confirmed through utilizing several applications which need the power time series with extremely short sampling intervals. The following studies are performed by using the actual data and then the proposed model: power spectral density of active and reactive power variations, instantaneous flicker, short term flicker (Pst), estimating the Pst using the maximum value of the instantaneous flicker, estimation of cumulative Pst for multiple wind turbines, and the impact of SVC on flicker mitigation.

An improved SVC control for electric arc furnace voltage flicker mitigation

The work focuses on the possibilities of improving the Static Var Compensator (SVC) control system for more effective reduction of the flicker effect. The studied SVC control system consists of an open control loop, which provides a fast response to dynamic changes in Electric Arc Furnace (EAF) power, and a closed control loop, which provides precise control to ensure the required value of the power factor in the Point of Common Coupling (PCC). The improvement consists in the use of alternative techniques for signal processing of input control variables. The first alternative technique is the use of Second Order Generalized Integrator (SOGI), which is also used in other related applications. The second alternative technique is to use the flicker weighting function, which corresponds to the function used to measure the flicker effect using a standardized flicker meter. Experimental laboratory equipment and theoretical model in frequency domain was used to verify the properties of the proposed techniques. To simulate the dynamic behavior of EAF, data measured from real operation were used, which were implemented into an experiment using VSC. Analysis of measured data and data obtained from laboratory apparatus shows high similarity. The experiments were carried out in several variants to reflect the differences in the various stages of the production process in the EAF. For all variants, the resulting flicker effect was evaluated and the individual techniques were compared with each other and with the results of other works.

Filters Optimized Tuning for Wind Farms Reactive Power Calculation

Fast reactive power variation in wind farms creates flicker. Static VAR compensators (SVCs) are the most commonly used devices for flicker mitigation. The reactive power calculation unit is the main component in the control system of SVCs. This article deals with two new approaches for reactive power calculation. In both methods, the main parameters of a filter-based technique are optimized using a novel optimization approach. The first method has a non monotonic step response which is converted to a desirable monotonic response by the second method. This results in a better response to a time-varying reactive power. The problem formulation and definition of a new objective function are presented. A data pool is gathered from Manjil wind farm, Iran, for different conditions. This data pool is used in the objective function to derive the optimal setting. The performance of the proposed methods is assessed using this dataset and is compared with other techniques. Also, real-time implementation of the algorithm is evaluated using TMDSCNCD28335 as the processor. To do so, the reactive power variation in a wind generation unit is emulated in a prototype test bench and the algorithm is run in real-time by the processor during the system operation.

Deep Learning Forecaster-Based Controller for SVC: Wind Farm Flicker Mitigation

One of the major challenges in grid-connected wind farms is the flicker emission caused by the reactive power extremely short time variations. A general used solution is installing a static volt-ampere reactive (VAR) compensator (SVC) as the most cost-saving device, which still holds the risk of incomplete reactive power compensation subject to the operating delay time. To this end, an accurate extreme short-term reactive power forecasting structure is essential. Although there are many studies related to the forecasting of wind power in long, medium, and short terms, however, the extremely short-term reactive power prediction of the wind farms is only addressed in few studies. The main aim in this article is to develop a method based on the convolutional neural network (CNN) to directly learn nonstationary and complex features from the raw wind farm reactive power time series and to contribute a predictive controller to mitigate the voltage flicker through an SVC connected to the wind farm. However, high sensitivity of typical mean-squared-based loss functions might lead to considerable errors in the forecasting. To resolve this issue, a modified loss function is proposed to enhance the performance and, consequently, an improved CNN is presented. The evaluation of the proposed method is based on the actual recorded data of a wind farm in Manjil, Iran. The data are directly used in the modeling of the wind farm. A current source, which is based on the actual records its amplitude and phase angle change every 0.01 s, is utilized to model the wind farm. The numerical results in terms of flicker sensation and short-term flicker perceptibility (Pst) measurement are used to verify the performance of the proposed method through comparison with the wind farm performance without SVC and SVC with a common control system.