Voltage Sag Detection Method Research Articles

A novel voltage sag detection method for analyzing charging quality of electric vehicle

Electric car charging quality is severely impacted by voltage sag in the distribution network. Voltage sag events frequently occur in conjunction with other power quality disturbances, which leads to signal waveform distortion, making it difficult to identify voltage sag characteristics in composite power quality disturbance signals. The voltage sag amplitude, phase angle jump, and duration are all accurately detected in the composite power quality disturbance signal thanks to the method's two-stage waveform decomposition model, which eliminates the interference of the transition segment by pinpointing the beginning and ending points of the voltage sag using DQ transform. Moreover, the designed simulation experiments further verify that our proposed method outperforms other mainstream approaches, and it can be well used to effectively detect voltage sags of different causes under various signals that disturb the composite power quality, with an average accuracy rate of over 98.86 %.

A fast voltage sag detection method based on second order generalized integrator and delay transform method

Voltage sag is an important problem that causes power quality degradation, and the premise of solving the problem of voltage sag is to detect the depth of voltage sag accurately and quickly. Based on the past research on voltage sag detection, this paper proposes a voltage sag detection method that combines second order generalized integrator and delay transform method. Use the second order generalized integrator as the phase-locked loop and filter to extract the grid voltage phase angle and grid voltage fundamental wave, and then construct the quadrature component of the grid voltage fundamental wave by delaying a small angle. Square and square root calculation to quickly obtain voltage sag information. At the same time, the voltage sag information is used as the control signal of the second order generalized integrator to solve the problem of long response time of the second order generalized integrator. In this way, the interference of harmonics, zero-sequence and negative-sequence voltages on sag detection is excluded, and the rapidity of sag detection is ensured. Simulation and experiments show that the method can accurately and quickly determine the voltage sag depth.

A Novel Voltage Sag Detection Method Based on a Selective Harmonic Extraction Algorithm for Nonideal Grid Conditions

Voltage sag detection is utilized to capture the sag occurrence moment and calculate the sag depth of power grid voltage in real time, so as to generate reference voltage for controlling voltage interactive equipment such as dynamic voltage restorers (DVRs). However, the traditional voltage sag detection methods based on synchronously rotating frames (SRFs) are unable to acquire high-precision sag information under nonideal grid conditions such as unbalance or harmonic interference. In order to enhance the immunity of the sag detection, a method based on a selective harmonic extraction algorithm (SHEA) is proposed in this paper. Firstly, the state-space model of SHEA is established using discrete orthogonal basis to decouple and separate the signal of target frequency and the signal of interference frequency. The controllability, stability and convergence of SHEA are analyzed theoretically and serve as the criteria for parameter tuning. Moreover, a gain compensator (GC) is used to improve the low and middle frequency gains of the voltage sag detection method based on SHEA so that the dynamic response speed for sag judgment can be optimized quantitatively. The simulation results indicate that the proposed voltage sag detection method has good dynamic and steady-state performance under nonideal power grid conditions such as unbalanced sag, frequency drift, phase variation and harmonic interference.

Three-phase unbalanced voltage sag detection method based on morphological filtering

In dynamic voltage restorer (DVR), accurate and fast voltage sag detection method is the key. However, in the case of three-phase imbalance, the traditional voltage sag detection method still has shortcomings in real-time and accuracy. Therefore, a voltage sag detection method based on morphological filter is proposed. That is, based on the commonly used dq transformation method, the morphological filter is used to replace the Butterworth low-pass filter to suppress the second harmonic generated by the negative sequence component after dq transformation in the case of three-phase imbalance, reduce the system delay and improve the real-time and accuracy of the detection method. The morphological filter is designed, and the appropriate structural elements and morphological transformation algorithm are selected. The results show that the morphological filter has good filtering effect and small delay, and can better meet the detection requirements of DVR.

An Improved Detection Algorithm of Three-phase Unbalanced Voltage Sag Detection Method for Improving Power Supply Reliability

With the popularization of high-power power electronic switching equipment and the technical update of electrical equipment, voltage sags have become a major problem affecting power quality, which seriously affects the reliability of power supply in power systems. In the case where the voltage sags failure cannot be avoided, rapid and accurate detection of the voltage sag has become a key technology for improving the reliability of the power supply of the power system. Based on the symmetrical component method, an improved detection algorithm for three-phase unbalanced voltage sag is proposed in this paper, which can significantly improve the detection speed and the reliability of power supply. The method firstly constructs the virtual orthogonal signal of the grid voltage and uses the symmetric component method to realize the fast and accurate extraction of the positive and negative sequence components of the grid voltage fundamental. In addition, an improved method for constructing virtual orthogonal signals is proposed in this paper, which effectively improves the accuracy of the constructed orthogonal signals. Finally, the feasibility and priority of the improved detection method have been verified by MATLAB/Simulink.

Study on detection method of distorted voltage sag in distribution network under the background of incorporating new energy

An advanced voltage sag detection method and compensation technique can improve the power quality of the distribution network to a entirely new level. A high performance voltage sag detection method demands fast response and good accuracy, even detecting distorted grid voltage sag caused by new energy accessing to distribution network. The voltage sag detection method, based on sliding window iterative discrete fourier transfer (DFT) algorithm, has excellent filtering ability but long detection time. On the other hand, the voltage sag detection method, based on nonrecursive DFT algorithm, has short detection time but poor filtering ability. Aiming to meet the requirements of fast response and good accuracy, this paper proposed a voltage sag detection method based on improved nonrecursive DFT algorithm. By means of disturbance filter, which is combined with several notch filters and a low-pass filter, the filter characteristic of nonrecursive DFT algorithm has been improved, and the detection delay time is reduced. The proposed algorithm can guarantee shorter detection time and higher detection accuracy.

Fast and precise voltage sag detection method for dynamic voltage restorer (DVR) application

Voltage sag detection method has a significant impact on the performance of dynamic voltage restorer (DVR). This paper proposes a fundamental voltage amplitude detection method which is applicable in both single/three-phase systems for DVR applications. Advantages of the proposed method include application in distorted power grid without any low-pass filter, precise and reliable detection, simple computation and implementation without using a phased locked loop and lookup table. The proposed method has been simulated and implemented experimentally and tested under various conditions considering all possible cases such as different amounts of voltage sag depth (VSD), different amounts of point-on-wave (POW) at which voltage sag occurs, harmonic distortion, line frequency variation, and phase jump (PJ). A detailed procedure to design the threshold band for comparator is presented. According to the achieved results and detailed analysis, maximum ripple of the calculated fundamental voltage amplitude is ±0.3% in normal condition of line frequency and ±1% in the case of ±1Hz variation of 60Hz line frequency. In addition, the error between the actual fundamental voltage amplitude and the calculated one is almost zero in normal condition of line frequency and maximum of ±0.25% in the case of line frequency variation with excessive-harmonic distortion. Furthermore, detection time (DT) of the proposed method is analyzed in detail for different amounts of VSD, POW and PJ. The best and worst detection time of the proposed method were measured 1 and 8.8ms, respectively. Finally, the proposed method has been compared with other methods available in the literature.

Voltage Sag Detection through Wavelet Energy Coefficient

 Abstract—In this work, a new voltage sag detection method based on wavelet transform is developed. Voltage sag detection algorithms, so far have provided their efficiency and computational ability. Several windowing techniques take long durations for disturbance detection. Due to increasing power quality standards new high quality performance disturbance detection techniques are necessary to obtain high power quality standard. Also research has been carried out for the last decade to isolate voltage sag detection form other voltage disturbances. In this paper a novel approach of wavelet transform has been carried out to detect voltage sag duration and magnitude. Results show that, the new approach provides very accurate and satisfactory voltage sag detection.

A new approach to voltage sag detection based on wavelet transform

In this work, a new voltage sag detection method based on wavelet transform is developed. Voltage sag detection algorithms, so far have proved their efficiency and computational ability. Using several windowing techniques take long computational times for disturbance detection. Also researchers have been working on separating voltage sags from other voltage disturbances for the last decade. Due to increasing power quality standards new high performance disturbance detection algorithms are necessary to obtain high power quality standards. For this purpose, the wavelet technique is used for detecting voltage sag duration and magnitude. The developed voltage sag detection algorithm is implemented with high speed microcontroller. Test results show that, the new approach provides very accurate and satisfactory voltage sag detection.

Development of a voltage sag detection method for nonutility generation systems

This paper deals with a new detection method based on three-phase vector operation for voltage sag. The detection method is applicable to a protection system using a high-speed interruption system which protects distributed generators and critical loads in a customer's facility. The algorithm and merits of this method are explained in detail. The detection characteristics are then analyzed using the ATP (Alternative Transients Program) and are confirmed using a real-time digital simulator, and it is shown that the method is useful for detecting voltage sag. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(4): 34–41, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20117

Voltage Sag Detection Technique for a Dynamic Voltage Restorer

Dynamic voltage restorers (DVRs) are used to protect sensitive loads from the effects of voltage sags on the distribution feeder. This paper presents and verifies a novel voltage sag detection technique for use in conjunction with the main control system of a DVR. In all cases it is necessary for the DVR control system to not only detect the start and end of a voltage sag but also to determine the sag depth and any associated phase shift. The DVR, which is placed in series with a sensitive load, must be able to respond quickly to a voltage sag if end users of sensitive equipment are to experience no voltage sags. A problem arises when fast evaluation of the sag depth and phase shift is required, as this information is normally embedded within the core of a main DVR control scheme and is not readily available to either users monitoring the state of the grid or parallel controllers. Previous research presented an additional controller, which required phase and sag depth information to manipulate the injection voltage vector returned by the main controller in order to prevent the DVR injection transformers from saturating. Typical standard information tracking or detection methods such as the Fourier transform or phase-locked loop (PLL) are too slow in returning this information, when either applied to the injection voltage vector, or to the supply voltages directly. As a result of this the voltage sag detection method in this paper proposes a new matrix method, which is able to compute the phase shift and voltage reduction of the supply voltage much quicker than the Fourier transform or a PLL. The paper also illustrates that the matrix method returns results that can be directly interpreted, whereas other methods such as the wavelet transform return results that can be difficult to interpret.