This paper proposes an extended state observer (ESO)‐based second‐order sliding mode control (SMC) for dynamic voltage restorers (DVRs). Unlike the conventional first‐order SMC and some second‐order ...SMC (SOSMC) methods that suffer from chattering, the proposed control method can alleviate chattering and achieve finite‐time convergence. Chattering suppression (i.e. eliminating discontinuities) is achieved via continuous control input which is also used to generate the pulse width modulation signals. However, while removing the discontinuities in the control input, the performance of the control method is degraded when it is subjected to disturbances. Therefore, an active disturbance rejection (ADR) based on an ESO is proposed to enhance the performance. In addition, an advanced single‐phase phase‐locked loop (PLL) using linear observer and quasi‐type‐1 PLL is also proposed. The effectiveness of the proposed method is verified through simulation and experimental results which are compared with the results of the existing SMC methods applied to DVR.
This figure highlights the considered dynamic voltage restorers (DVR) topology. How the proposed DVR protects the sensitive load can be found in this figure.
In this paper, an alternative control method is proposed to improve the harmonic suppression efficiency of the active power filter in a distorted and an unbalanced power system to compensate for the ...perturbations caused by the unbalanced non-linear loads. The proposed method uses a self-tuning filter (STF) to process the grid voltage in order to provide a uniform reference voltage to obtain the correct angular position of the phase locked loop. Moreover, the required compensation currents are obtained by implementing another STF in the transformed set of currents in order to separate the fundamental and the harmonic currents. This allows the calculation of a precise reference current for the unbalanced, the non-linear and the variable load conditions. The proposed control method gives an adequate compensating current reference even for a non-ideal voltage and unbalanced current conditions. The real-time control of the filter under the distorted and the unbalanced power system is developed in an RT-LAB real-time platform. The results obtained in the software-in-the-loop configuration are presented to verify the effectiveness of the proposed control technique.
In the case of undistorted and balanced grid voltages, low ratio shunt active power filters (APFs) can give unity power factors and achieve current harmonic cancellation. However, this is not ...possible when source voltages are distorted and unbalanced. In this study, the cost-effective hybrid active power filter (HAPF) topology for satisfying the requirements of harmonic current suppression and non-active power compensation for industry is presented. An effective strategy is developed to observe the effect of the placement of power capacitors and LC filters with the shunt APF. A new method for alleviating the negative effects of a nonideal grid voltage is proposed that uses a self-tuning filter algorithm with instantaneous reactive power theory. The real-time control of the studied system was achieved with a field-programmable gate array (FPGA) architecture, which was developed using the OPAL-RT system. The performance result of the proposed HAPF system is tested and presented under nonideal supply voltage conditions.
A grid-synchronization-based fundamental frequency positive-sequence (FFPS) and negative-sequence (FFNS) amplitudes estimation technique is proposed for unbalanced and distorted grid. In this ...technique, the sequence amplitudes are extracted by extracting the phase-angle of the FFPS and FFNS components. The extracted phase-angles have DC and double frequency AC components. The AC component is filtered out by using a Moving Average Filter (MAF) of appropriate window length. From the extracted phase-angle, the unknown frequency can be estimated by using a suitable controller. A frequency-fixed equidistant samples-based pre-loop filter is also applied to eliminate the effect of measurement offset. The proposed technique has a very simple structure and is easy to tune. Small-signal modeling-based stability analysis and gain tuning procedure are also provided. The proposed technique strikes a good balance between fast convergence and disturbance rejection capability. Comparative numerical simulation and experimental results with similar other techniques demonstrate the suitability and performance enhancement by the proposed technique.
This article introduces a new configuration for grid synchronization to detect the positive-sequence component of the voltage under unbalanced and distorted conditions. The proposed configuration is ...based on the frequency-locked loop technique and combines a self-tuning filter with a conventional second-order generalized integrator. The introduced structure is able to produce two orthogonal output signals for detecting grid voltage information. More importantly, it behaves as a high-order filter to completely remove harmonic components and still reserves benefits from the previous second-order generalized integrator methods. The grid magnitude and frequency are identified accurately and then provided to the active power filter for proper operations. Simulation and experimental results are presented to verify the concept of the introduced method. In addition, the performances of the proposed and conventional configurations are compared to recognize the significant improvements and effectiveness in the new method.
Abstract-A single-phase active power filter is presented for small-scale, single-phase loads based on the second-order generalized integrator control method is presented in this article. The proposed ...system does not require voltage sensors on the AC and/or DC side. Only two current sensors are used to measure load and converter currents. Consequently, a proportional-integral regulator is not used, and there is no need for additional calculations for the determination of the grid-current amplitude. To obtain the correct reference grid current, the distorted load current is first processed by using the second-order generalized integrator algorithm, which does not require voltage information. A step-by-step performance study, in a real-time environment, shows that the proposed control technique is able to generate the proper compensating reference current for small-scale non-linear loads. As a result, the total harmonic distortion of the grid current is reduced from 25.33 to 3.80%, which meets the recommended IEEE 519-1992 Standard.
In this study, a control method is proposed to improve the harmonic suppression efficiency of the single-phase active power filter in a distorted power system to suppress current harmonics and ...reactive power. The proposed method uses the self-tuning filter (STF) algorithm to process single-phase grid voltage in order to provide a uniform reference grid current, which increases the efficiency of the system. The results of the simulation study are presented to verify the effectiveness of the proposed control technique in this study.
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