Advanced Control Algorithm for Three-Phase Shunt Active Power Filter Using Sliding DFT

Abstract

This paper describes n digital control algorithm for a three-phase shunt active power filter (APF) using switching–sliding discrete Fourier transform (SSDFT). Traditionally, APF control algorithms use first harmonic detector circuits, which can be implemented using the SDFT algorithm. The classical SDFT algorithm is characterized by long-term stability issues, resulting from numerical errors. Many complex modifications to improve the stability of the SDFT algorithm have been proposed in the scientific literature. This article proposes a solution to the SDFT stability problem using the basic structure of the algorithm. The authors propose the use of the switching SDFT algorithm, where two original SDFT algorithms are implemented in parallel. Both algorithms are turned on alternately after a set period of time and reset to zero in order to reset numerical errors causing their unstable operation. Compared to the classical three-phase SDFT algorithm, the three-phase SSDFT requires only about 25% more arithmetic operations. The proposed approach has been validated using experimental tests and dramatically reduces the numerical errors. The control algorithm has been implemented using the TMS320F28379D microcontroller. The sampling method using only the internal A/D converter of a microcontroller is also presented. The article includes the experimental test results of the complete APF.

Overview of Signal Processing Problems in Power Electronic Control Circuits

“…Of course, it would be good if microcontrollers with six A/D converters were developed, allowing simultaneous measurement of three currents and three voltages in three-phase systems. However, even four converters allow the implementation of the three-phase active power filter (APF) control system [59]. The maximum error value of the amplitude of a sinusoidal signal can be calculated by the following formula [37]:…”

“…Typically, before the system is fully synchronized, slowly changing oscillations may occur. For example, for systems synchronized to the voltage frequency in the mains, you can consider abandoning such a system because, currently, the frequency of the mains voltage is very stable (about ±50 mHz) [59]. Figure 9c shows a block diagram of a digital control circuit that employs synchronization, utilizing a phase-locked loop (PLL) to generate an output signal whose phase is linked to the phase of an input signal.…”

“…Typically, before the system is fully synchronized, slowly changing oscillations may occur. For example, for systems synchronized to the voltage frequency in the mains, you can consider abandoning such a system because, currently, the frequency of the mains voltage is very stable (about ±50 mHz) [59].…”

Review of RoCoF Estimation Techniques for Low-Inertia Power Systems

“…Equation (8) implies that the measurement device that can track the dynamic voltage/current phase at a node of the power system, namely the synchrophasor, can be used to track the real-time local RoCoF with a proper algorithm; however, RoCoF estimation techniques face great challenges in accuracy and robustness. This section provides a comprehensive review of the existing real-time RoCoF tracking algorithms of synchrophasors, which can be divided into three main categories: (i) DFTbased [64][65][66][67][68][69][70][71][72][73][74][75][76], (ii) Kalman filter techniques [77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92], and (iii) other methods [93][94][95][96][97][98][99][100]. The details for each category are provided in the subsection.…”

A Frequency/Phase/Amplitude Estimator for Three-Phase Applications Operating at a Low Sampling Rate

“…However, a DFT-based frequency detector requires a high computational effort. This drawback can be alleviated by implementing the DFT method in a recursive form [14]. Nevertheless, some stability concerns regarding the recursive DFT have recently been reported [15].…”