Elsevier

ISA Transactions

Volume 107, December 2020, Pages 350-359
ISA Transactions

Practice article
Robust control of series active power filters for power quality enhancement in distribution grids: Simulation and experimental validation

https://doi.org/10.1016/j.isatra.2020.07.024Get rights and content

Highlights

  • Improvement of power quality using single-phase series active power filter.

  • Design of Backstepping sliding mode and ANFIS controllers for the series active power filter.

  • Experimental validation of the proposed controllers on a low voltage active power filter circuit.

Abstract

This paper presents a simulation study and an experimental implementation of a single-phase Series Active Power Filter (SAPF) for the mitigation of harmonics in the load voltage. The aim is to regulate the injection voltage of the SAPF to compensate the grid voltage via the injection transformer in addition to maintaining the load voltage stable. The control strategies investigated in this work include Backstepping Sliding Mode Control (BSMC) and a neuro-fuzzy controller based on ANFIS (Adaptive Neuro-Fuzzy Inference System) l. The proposed control strategies for the single-phase SAPF are initially evaluated in simulations under MATLAB/Simulink and then validated on a laboratory-scale hardware experimental set up consisting of a source and a single-phase SAPF. A comparative study of these controllers with respect to their performance and robustness in mitigating power quality against voltage disturbances and harmonics is presented. Both simulation and experimental results have demonstrated that ANFIS-based controller was able to achieve superior performance and a lower total harmonic distortion (THD) as compared to the other control methods.

Introduction

In recent years, power quality issues have become a vital concern for both the utility and end-users. This is due to the widespread use of nonlinear loads and modern power electronics devices in various domestic and industrial applications, such as electrical motor drives, power supplies, induction heating, electronic lighting, etc., [1], [2], [3]. These electronic and solid-state-based devices generate current harmonics which are injected into the distribution network and cause voltage disturbances at different points of the network.

Electric equipment connected at these points is directly affected by these harmonics and negative effects, notably a distortion in the voltage, may appear instantaneously or occur later. Harmonics can also cause overheating of electric cables as well as a disruption in the operation of certain electrical equipment or even cause a complete shutdown of certain machinery [4], [5]. The limits on harmonics levels were established by IEC61000 standards, and IEEE Std. 519-1992 [6].

Passive filters are traditionally used to mitigate harmonic distortion and have long been employed in the industrial and utility sectors [7]. However, passive filtering has several drawbacks including the lack of adaptation during variations of the load and network impedance. Furthermore, passive filters may cause resonance with network and in some cases this latter, when excited, can cause large harmonics in the voltage and current of the filter capacitor and the network [8], [9], [10]. Unlike passive filters, modern Active Power Filters (APFs) are power electronic-based devices which offer superior filtering performance and have faster transient response. They can compensate for current and voltage harmonics, reactive power and provide voltage control in the distribution network [11]. APFs are basically classified into two types: Shunt, parallel and series APFs. Shunt active filters are connected in parallel and inject into the network a current that is equal in amplitude to the harmonic current to be suppressed but with opposite phase. Series active filters, on the other hand, are connected in series with the network voltage via a matching transformer and behave like a voltage generator which imposes a harmonic voltage such that, when added to network voltage, produce a sinusoidal-like voltage waveform at the connection point [12], [13]. SAPF can compensate for voltage disturbances acting on the load side [14].

The aim of this work was to propose robust control strategies to improve the performance of the SAPF for the mitigation of harmonics in the presence of nonlinear loads in the network. Backstepping Sliding Mode Control (BSMC) is a switching type of control which can cope with nonlinearities, parameter uncertainties and disturbances and therefore can be considered as a suitable candidate for this application. ANFIS offers the desired robustness and learning ability to enhance the performance of the SAPF in dealing harmonics and can operate under various operating conditions.

This paper presents an analysis, a simulation study, and an experimental validation of three controllers for a SAPF to mitigate voltage disturbances and improve the power quality in the distribution network.

The remaining of the paper is organized as follows: Section 2 introduces the basic circuits of the SAPF and derives the control methods proposed in this work including Backstepping Sliding Mode Controller (BSMC) and an Adaptive Neuro-Fuzzy Inference System (ANFIS)-based controller. Section 3 presents the simulation results and discussions. In Section 4, the experimental prototype of the SAPF is described and the experimental results are presented under different voltage disturbance conditions. Finally, Section 5 summarizes the conclusions of this paper.

Section snippets

Modeling of the SAPF system

The overall structure of the SAPF is represented by the converter circuit depicted in Fig. 1. Kirchhoff’s voltage law gives [15]: vt=RfiL+LfdiLdt+VinjVinj=1Cficdt where vt is the output inverter voltage, Vinj is the SAPF output voltage, Vdc represents the voltage of the DC link, iL and iC are the currents flowing the inductor and capacitor filter respectively, Lf,Cf are the inductance and capacitance of the filter, Rf represent the inductor equivalent series resistance.

Taking Laplace of (1),

Proposed control strategies for the single-phase SAPF

Fig. 2 depicts the basic control scheme of the SAPF. The control scheme is based on a closed-loop control which regulates the injected voltage of the SAPF via an IGBT Voltage Source Inverter (VSI) driven by a Pulse Width Modulation (PWM) control strategy [16], [17].

Two control strategies are implemented in this work namely BSMC and ANFIS. The aim of these controllers is to regulate the injected voltage of the single-phase SAPF.

Simulation results

This section presents the simulations that have been undertaken to evaluate the performance of the BSMC and ANFIS-based control for the single-phase SAPF to reduce harmonics in the network. The parameters values employed in the model are listed in Table B.1 of Appendix B.

The single-phase SAPF model is implemented in MATLAB/Simulink. A detailed description of the Simulink models of the SAPF and BSMC control are given in Fig. C.1 and Fig. C.2 respectively (Appendix C). The proposed SAPF is

Experimental evaluation and results

This section presents the hardware used to design the experimental set-up of the SAPF and its auxiliary circuits. Fig. 10 shows the laboratory prototype of the system of the single-phase SAPF designed in this work for the mitigation of harmonics. The single-phase SAPF consists of the following components:

  • An injection/booster transformer for injecting voltage during abnormal condition.

  • A 20 kVA three-phase IGBT Inverter SKM 100 GB 123 D, rated 1200 V and 90 A and one anti-parallel diode. The

Conclusion

This paper presented a simulation study and a real-time validation of a single-phase SAPF (Series Active Power Filter) with two different control schemes based on Back-Stepping Sliding Mode Control (BSMC) and neuro-fuzzy control based on ANFIS (Adaptive Neuro-Fuzzy Inference System). The SAPF was able to effectively compensate the voltage harmonics to satisfy the international IEEE standards (IEEE 519-1992 and IEEE 1159-1995). The two control strategies have been compared under various fault

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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