A critical and comprehensive review on power quality disturbance detection and classification

This paper proposes a fast repetitive control (FRC) scheme with harmonic correction loops for the three-phase three-wire shunt active power filter (APF) applied in weak power grid. The FRC scheme consists of a repetitive control loop which is designed in the synchronous rotational frame and a fractional delay (FD) filter for approximating the FD caused by the fixed sampling rate. It can significantly improve the dynamic performance for the harmonic compensation. In weak grid situation, the grid frequency, voltage and then harmonic currents would vary rapidly with disturbances. A cumulative error cancellation loop is introduced into the FRC to improve the harmonic detection accuracy when grid frequency drifts. The harmonic correction loops are proposed to correct the harmonic references with selected orders when they vary rapidly with the grid voltage. With such loops, the compensation precision of the shunt APF can be highly improved. Simulation and experiment results verified the effectiveness of the proposed scheme.

Fast Repetitive Control With Harmonic Correction Loops for Shunt Active Power Filter Applied in Weak Grid

Power systems based on centralized production are facing two limitations: the lack of fossil fuels and the need to reduce pollution; Therefore, the importance of distributed generation resources (DGs) has increased by connecting renewable energy systems to the network. With the increasing penetration of renewable energies in the network, power quality challenges in low voltage and medium voltage distribution systems have become one of the main fields of studies. Since most of the renewable energy systems are connected to the network with the help of electronic power converters devices and the main purpose of these converters is to connect DGs to the network in compliance with power quality standards; Therefore, if the switching frequency of inverters is not implemented properly, major power quality problems will be created. On the other hand, the reduction in power quality causes acute problems in power networks, which include lack of proper performance, reduction in useful life and efficiency of electrical and electronic devices in the network, creation of series and parallel resonance in some harmonics due to the presence of inductors and the capacitor, and as a result, more distortion in the voltage of the distribution network. This paper actually provides a road-map for researchers to investigate power quality issues. In other words, the mentioned cases show the importance of research and providing the solutions to improving power quality in distribution networks. 

An Overview on Power Quality Issues and Control Strategies for Distribution Networks With the Presence of Distributed Generation Resources

This paper proposes an improved reference current generation and digital deadbeat current controller for single-phase shunt active power filters. The main advantages of the suggested control technique are simplicity, fast dynamics, low computational burden, high accuracy, and direct digital implementation. A straightforward modelling of system and design procedure is described in this paper. The stability analysis of the current control system, especially under parameter uncertainties, is studied. Also, a comprehensive comparison between the proposed technique and the conventional deadbeat controller is provided. In order to generate the reference compensating current, a second order generalized integrator-based PQ technique is used and the effect of integrator discretization in terms of dynamic response, accuracy and real-time computational burden is investigated. Simulation and experimental results on a real prototype system under steady-state and transients are reported to demonstrate the validity of theoretical analyses.

/pdf/an-improved-reference-current-generation-and-digital-2law7xmic9.pdf

An Improved Reference Current Generation and Digital Deadbeat Controller for Single-Phase Shunt Active Power Filters

In this paper, a novel ANOVA Kernel Kalman Filter (AKKF)-based adaptive control algorithm is introduced which is used for accurate harmonics support during operation of grid-integrated solar energy conversion system (SECS). For grid integrated SECS, a single-phase two-stage topology is considered, where local loads are attached on common point of interconnection (CPI), and a battery is attached on DC link. The AKKF is the improved form of Kalman Filter (KF), where the ANOVA Kernel (AK) trick is hybridized to improve the estimation accuracy of the KF. The objective of proposed control technique is to use this solar power to fulfil the load requirement. After satisfying the load requirement, the rest of solar power is fed to the grid. However, when the solar power is not available (in nighttime), then the system operates as Distribution Static Compensator (DSTATCOM), which provides reactive power support to the grid. The performance of the developed control technique is validated through experimentation on a developed prototype. During testing, adverse grid conditions, solar insolation variation, and load unbalance conditions are considered for satisfying the motive of the developed control technique.

ANOVA Kernel Kalman Filter for Multi-Objective Grid Integrated Solar Photovoltaic-Distribution Static Compensator

Among the various selective harmonic current controllers, the traditional repetitive-based discrete Fourier transform controller (DFTRC) is increasingly favored thanks to its unique merits of excellent selectivity and simplicity. However, the traditional approach suffers from disadvantages like slow dynamic responses, defective control structure, and sensitivity to frequency fluctuation. In order to alleviate aforementioned shortcomings, an enhanced discrete Fourier transform-based controller is proposed. The proposed controller is based on the generalized discrete Fourier transform to improve the overall control performances of dynamic responses, structure flexibility, and control robustness. The proposed controller provides individual positive-feedback path and gain coefficient for each harmonic component. Therefore, it not only maintains the advantage of excellent selectivity but also realizes the individual control parameters tuning for each harmonic frequency, which is impossible in traditional DFTRC owing to the congenital defects of control structure. In addition, a correction function is embedded in the forward path to provide the overall phase compensation and correct the plant for better characteristic. The Lagrange interpolation method is adopted to realize the fractional-order delay and its adaption to frequency variations with fixed sampling frequency. Detailed mathematical model along with optimized design principle is given to make full use of the advantages of the enhanced control structure. Extensive experimental results validate the effectiveness of the theoretical analysis and the improvement achieved by the proposed controller.

Enhanced DFT-Based Controller for Selective Harmonic Compensation in Active Power Filters

Traditional Discrete Fourier Transform(DFT)-based repetitive controller is widely used in active power filters(APF) thanks to its unique merits such as excellent selectivity and simplicity. However, the structure of the only one feedback path results in the same steps of leading angles for all harmonic frequencies. Since the phase response may not be proportional to frequency and the gain of the plant varies with frequency, identical leading angles and gain coefficients can't compensate the phase lag and the gain attenuation effectively at different harmonics. All those facts imply constraints to obtain the best stability margins and performance. The proposed controller provides feedback path and gain coefficient for each harmonic according to the characteristics of the plant respectively. In addition, the correction term is embedded in the forward channel to provide overall phase compensation and correct the plant for better characteristics. As a result, the novel control structure incorporated in sliding DFT can improve the performance greatly. Detailed design consideration is given with focus on stability analysis and transient behavior of the APF. Experimental results validate the effectiveness of the theoretical analysis.

Analysis and design of enhanced DFT-based controller for selective harmonic compensation in active power filters

The invention provides a current control algorithm applicable to selective harmonic compensation of an active power filter and belongs to the field of power quality control. The active power filter isconnected in parallel between a power grid and a nonlinear load for concentrated harmonic compensation; the control part of the active power filter comprises a grid side current control outer loop, acurrent control inner loop and a direct current side voltage control outer loop. The current control algorithm applicable to selective harmonic compensation of the active power filter is applied to closed-loop control over grid side harmonic current. The current control algorithm applicable to selective harmonic compensation of the active power filter is composed of n harmonic current control units, wherein n is a positive integer, and every harmonic current control unit is composed of three parts including harmonic extraction, positive feedback digital time delay and forward gain; by introducing phase lead compensation into a positive feedback loop and gain adjusting coefficients into a forward channel and adding in a correcting function for amplitude and phase correction, the current control algorithm applicable to selective harmonic compensation of the active power filter is excellent in dynamic response and control robustness.

Current control algorithm applicable to selective harmonic compensation of active power filter

Selective harmonic extraction plays an important role in power quality assessment, harmonic compensation, and so on. Among the various methods, discrete Fourier transform (DFT)-based algorithms has found wide and popular applications due to advantages like simplicity and excellent selectively filtering properties. However, DFT suffers from disadvantages like slow dynamics and sensitivity to frequency variations. In order to alleviate these drawbacks, an improved and extended DFT—generalized DFT (GDFT) is proposed. It is revealed in this paper that the conventional DFT can be viewed as a comb filter connected in series with complex resonators, and DFT relies on the mechanism of pole-zero cancellation for harmonic extraction. More importantly, the key reason behind the DFT slow transient responses is the large delay introduced by the comb filter. Therefore, this paper proposed to reconfigure the comb filter according to specific harmonic patterns of the input signal for improving the dynamic responses and system flexibility. The proposed GDFT not only maintains the advantages of simplicity and selectively filtering properties but also features fast transients, around 0.3 fundamental cycle for typical applications, which is much shorter than the one-cycle settling time of the conventional DFT. A phase-locked-loop block is also incorporated into the harmonic-detection system to deal with possibly large frequency variations in practical applications. Extensive tests are provided to validate effectiveness of the proposed method.

Fast and Flexible Selective Harmonic Extraction Methods Based on the Generalized Discrete Fourier Transform

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Papers

Enhanced DFT-Based Controller for Selective Harmonic Compensation in Active Power Filters

Analysis and design of enhanced DFT-based controller for selective harmonic compensation in active power filters

Current control algorithm applicable to selective harmonic compensation of active power filter

Fast and Flexible Selective Harmonic Extraction Methods Based on the Generalized Discrete Fourier Transform