Four-wire Active Power Filter Research Articles

A Novel Three-Dimensional Sigma–Delta Modulation for High-Switching-Frequency Three-Phase Four-Wire Active Power Filters

This article presents a new modulation technique called three-dimensional sigma–delta (3D-ΣΔ) modulation for high-frequency three-leg four-wire voltage source converters (VSCs) that use wide-bandgap (WBG) semiconductors. These WBG devices allow for the use of high switching frequencies with a greater efficiency than silicon devices. The proposed 3D-ΣΔ technique enables operation at a variable switching frequency, resulting in a significant reduction in switching losses compared to classical pulse-width modulation (PWM) techniques. Moreover, the 3D-ΣΔ technique uses a fast-processing 3D quantiser that simplifies implementation and considerably reduces computational costs. The behaviour of the 3D-ΣΔ modulation is analysed using MATLAB/Simulink and PLECS. The experimental results performed on an active power filter that uses silicon carbide (SiC) MOSFETs demonstrate an improvement in converter efficiency compared to the conventional SPWM technique. Additionally, the experimental results show how 3D-ΣΔ allows for the compensation of harmonics and homopolar currents, thereby balancing the electrical grid currents. The experiments also show that the proposed 3D-ΣΔ modulation outperforms an SPWM technique in terms of power quality, since the former achieves a larger reduction in the harmonic content of the power grid. In conclusion, the proposed modulation technique is an attractive option for improving the performance of four-wire converters in active power filter applications.

A Proposed Supercapacitor Integrated with an Active Power Filter for Improving the Performance of a Wind Generation System under Nonlinear Unbalanced Loading and Faults

This study proposes the integration of a supercapacitor (SC) with the DC link of a three-phase four-wire active power filter (APF) by using an interfaced three-level bidirectional buck-boost converter controlled by the fuzzy control approach. APF is a flexible alternating current transmission system (FACTS) device that enhances power quality in the electrical network by reducing the load current harmonics and compensating the reactive power. Regulating the DC voltage of the APF’s DC link and absorbing fluctuations in compensated reactive power during disturbances are the major objectives of the integration of an SC circuit to APF. The studied model is a wind farm of Gabal El-Zeit with a total capacity of 580 MW, connected to unbalanced nonlinear loads. The Gabal El-Zeit wind farm is divided into three projects with a capacity of 240 MW, 220 MW, and 120 MW. The model is simulated by the MATLAB/SIMULINK program, and the effectiveness of the proposed methodology is proved by applying different types of faults such as single-line-to-ground, double-line-to-ground, and three-line-to-ground faults. In addition, an additional SC circuit with a two-level converter is connected to the generators coupled to the wind turbines to enhance the performance of the wind farm during disturbances. The results show that SC-integrated APF can reduce the harmonic distortion and compensate the reactive power for high or low inductive loads. Also, it can regulate the DC voltage and absorb the fluctuations in the reactive power during faults. Finally, the performance and the stability of the overall electric system are improved.

An inductor design method based on multi-objective optimized algorithm for LCL-type shunt active power filter

The application of pulse width modulation (PWM) technology will produce a high-frequency switching ripple. Generally, it is considered to filter it with an LCL filter to ensure the compensation performance of the shunt active power filter. According to the system requirements for ripple current suppression and maximum current tracking capability, this paper first optimizes the design of the filter inductance in the LCL. Then, aiming at the shortcomings of the traditional inductor design process that is complicated and cumbersome, with repetitiveness and difficulty to obtain reliable analytical solutions, a 4-dimensional visualization based multi-objective optimized algorithm is proposed, and the ternary function expression between each design goal and known independent variables is first derived and established. And then, through the visual programming of the 4-dimensional data field, the optimal solution set that meets the multi-objective design requirements is directly given, which is intuitive, clear, simple, and practical. Finally, according to the algorithm results, the corresponding inductance was wound and applied to a 50kVA three-phase four-wire active power filter prototype. The experimental results verified the feasibility and effectiveness of the proposed design method.

Research on three-phase four-wire active power filter based on LCLCL coupling structure

In this paper, the main circuit topology of the three-phase four-wire active power filter (APF) and its harmonic current detection and control algorithm are studied. An active power filter system combining LCLCL filter and a three-phase H-bridge structure is proposed. This paper has applied harmonic detection algorithm based on an improved synchronous phase-locked loop (SRF-PLL) and recursive discrete Fourier transform (RDFT) while using triangular carrier modulation control based on PI adjustment to realize the harmonic compensation of the power filter to the grid current. The system has a notch effect on the harmonic at the switching frequency. It can detect the fundamental component and each harmonic component of the load current separately with a small amount of calculation, good real-time performance. Finally, a 5KVA single-phase APF prototype was built to test the superiority of the main circuit topology and the algorithm of current detection and control.

Inductance optimisation method of a four-wire shunt APF based on unified mathematical model

ABSTRACTLeg inductors which connect a shunt Active Power Filter (APF) to power network play a crucial role in guaranteeing desired performances of the APF. Optimal tuning of the inductances is still a tricky problem that has not yet been tackled systematically and theoretically. This paper proposes a novel inductance optimisation method that is universally applicable to four-wire shunt APFs with arbitrary topologies and PWM strategies. Based on the unified mathematic model, indexes used to quantitatively evaluate the abilities of a four-wire APF in compensating phase harmonic currents and depressing neutral line current are formally formulated. The upper and lower value constraints of the inductances are derived by comprehensively taking into account the characteristics of load harmonic profile and PWM strategy. Inductances are further optimised in the feasible value ranges with concern of several engineering application issues. Simulation and lab experiment results are provided to verify the validity and effectiveness of the proposed method.

Improved control strategy of TFAPF in active distribution networks

In order to solve the deterioration of power quality caused by power electronic devices in active distribution networks, it is necessary to improve the three-phase four-wire active power filters (TFAPF) control strategy. This study adopts the non-harmonic detection and proposes an improved control strategy of TFAPF based on the multi-model principle. Firstly, the mathematical model of TFAPF in the stationary coordinate system is established by replacing the network side current and the DC bus voltage directly as the state variables. Secondly, TFAPF in active distribution networks requires the power fluctuation and fast dynamic response, the proposed control strategy of TFAPF in the stationary coordinate system is applied, namely proportional integral, vector resonant and repetitive control composite controller as the current loop controller of TFAPF with a fast dynamic response, high accuracy and small amount of calculation, provide guarantee for the power quality in active distribution networks. Finally, the feasibility of the proposed control strategy is verified by simulation.

A Simplified PWM Strategy for Three-Level Converters on Three-Phase Four-Wire Active Power Filter

Presently, the neutral-point potential offset is an inherent problem for three-level converters on three-phase four-wire active power filters. The conventional three-dimensional space vector pulse width modulation (3-D-SVPWM) strategy is adopted as a normal solution to the problem, but the selection of space vector sectors for four-wire converter is both abstract and complicated in practice. This paper proposes a new PWM strategy accordingly to simplify the selection process and the calculation of duration. Compared to the conventional 3D-SVPWM, the proposed method locates the sector of optimal vector directly with the polarity of three-phase reference voltage. Then, by applying voltage–second balance rule, it can perform a fast calculation of the duration and generate PWM signals to control the switching devices’ on/off. As an approach to correct the imbalance dc-link capacitor voltage, this strategy reconstructs the switching sequence. A portion of state O duration is disassembled into states P and N to suppress the neutral-point potential offset. The proposed strategy is validated with a range of experiments. The results indicate that this simplified PWM strategy can effectively reduce the computational burden, and also the dc-link capacitor voltage is well controlled.

Modeling, Simulation and Control Design of a PWM Three-Phase Four-Wire Shunt Active Power Filter for a 60 kW Industrial Load

Electric Power Quality remains a major concern for energy suppliers and consumers. One of the major reasons that contribute to the worsening of power quality is the existence of current harmonics in the power network caused by nonlinear electric loads. A common solution to eliminate such harmonics is the application of Active Power Filters (APF). In this paper, experimental measurements of the current were conducted on a power line that belongs to Electricité du Liban (EDL); feeding a three-phase large industrial load. Two control schemes for a shunt three-phase four-wire APF are developed: one is based on the use of hysteresis current controller to compensate the current distortion and the reactive power, the other consists of multiple loops PI controllers that ensure voltage regulation at the DC side of the filter and current wave shaping at the AC side. The latter control scheme is based on a small–signal averaged model of the converter, computed in the (dq0) synchronous frame. The simulations are performed using Matlab/Simulink tools. Results show an important reduction of the Total Harmonic Distortion (THD) and significant improvement of the power factor for both methods. Also, a comparison between the obtained results shows that the second control scheme is better than the first one on the level of harmonics reduction.

DC-Link Voltage Balance Control in Three-phase Four-wire Active Power Filters

The three-phase four-wire shunt active power filter (APF) is an effective method to solve the harmonic problem in three-phase four-wire power systems. In addition, it has two possible topologies, a four-leg inverter and a three-leg inverter with a split-capacitor. There are some studies investigating DC-link voltage control in three-phase four-wire APFs. However, when compared to the four-leg inverter topology, maintaining the balance between the DC-link upper and lower capacitor voltages becomes a unique problem in the three-leg inverter with a split-capacitor topology, and previous studies seldom pay attention to this fact. In this paper, the influence of the balance between the two DC-link voltages on the compensation performance, and the influence of the voltage balance controller on the compensation performance, are analyzed. To achieve the balance between the two DC-link capacitor voltages, and to avoid the adverse effect the voltage balance controller has on the APF compensation performance, a new DC-link voltage balance control strategy for the three-phase four-wire split-capacitor APF is proposed. Representative simulation and experimental results are presented to verify the analysis and the proposed DC-link voltage balance control strategy.

Reduced-rating Hybrid Active Power Filter Comprising Zero-sequence Transformer and Three-phase Three-wire Active Power Filter for Three-phase Four-wire Distribution System

A three-phase four-wire active power filter is proposed in this article that consists of a three-phase three-wire active power filter, zero-sequence transformer, and single-phase active power filter. The reference current for tracking the desired source current is based on the neural network (constraint anti-Hebbian rule algorithm). The three-phase three-wire active power filter compensates current harmonics and reactive power requirement of the non-linear load. A zero-sequence transformer and single-phase active power filter are used to mitigate the neutral current. The proposed hybrid scheme (three-phase four-wire active power filter) significantly reduces the volt–ampere rating of the active power filter and improves the performance under different utility voltage conditions. The simulation of the proposed three-phase four-wire active active power filter is carried out for different voltage conditions. Further, the MATLAB-simulated (The MathWorks, Natick, Massachusetts, USA) response of the three-phase four-wire active active power filter has been validated on a prototype of the three-phase four-wire active-active power filter. The experimental result obtained from the prototype verifies the effectiveness and viability of the proposed scheme.

Flexible active compensation based on load conformity factors applied to non‐sinusoidal and asymmetrical voltage conditions

This study proposes a flexible active power filter (APF) controller operating selectively to satisfy a set of desired load performance indices defined at the source side. The definition of such indices, and of the corresponding current references, is based on the orthogonal instantaneous current decomposition and conformity factors provided by the conservative power theory. This flexible approach can be applied to single- or three-phase APFs or other grid-tied converters, as those interfacing distributed generators in smart grids. The current controller is based on a modified hybrid P-type iterative learning controller which has shown good steady-state and dynamic performances. To validate the proposed approach, a three-phase four-wire APF connected to a non-linear and unbalanced load has been considered. Experimental results have been generated under ideal and non-ideal voltage sources, showing the effectiveness of the proposed flexible compensation scheme, even for weak grid scenarios.

Experimental Verification of Quasi Z-Source Inverter Based Hybrid Series Active Power Filter for Interconnection of PV into the Utility Grid

This paper proposes a Photovoltaic/Battery interfaced Quasi Z-source inverter based three-phase four-wire Hybrid Series Active Power Filter (HSAPF)to compensate the voltage and current related power quality problem in small distributed power system. The HSAPF consists of shunt passive filter and series active filterconsuming a battery. The shunt active filter mitigates the current harmonics generated by a nonlinear load. The series active filter mitigates the voltage sag/swell and load voltage harmonics, which consumes the power from Photovoltaic (PV) array with quasi Zsource inverter (qZSI). A new controller of qZSI based HSAPF uses two control schemes to boost the PV/Battery output voltage and achieve maximum power point tracking PV array. The simulation and experimental results are presented to validate the performance of proposed qZSI based HSAPF.

Self-Reconfiguration Property of a Mixed Signal Controller for Improving Power Quality Compensation During Light Loading

This paper proposes a FPAA-FPGA/DSP-based mixed signal controller that achieves superior performance when compared with conventional digital controllers in power quality compensation. This includes adaptive signal conditioning and programmability on-the-fly, higher flexibility, parallel computation capability, and easy implementation. In practical applications, the power quality compensator may suffer from poor compensation performance, particularly during light loading. The adaptive signal gain and programmable on-the-fly functions of the mixed signal controller are intended to improve the system compensation performance, which cannot be achieved by using conventional digital controllers alone. In this study, an approximate total harmonic distortion (ATHD) is proposed to determine the total harmonic distortion value more quickly, reducing the evaluation time of the power quality compensation system performance. With hysteresis pulse width modulations, when the hysteresis error margin is designed, the ATHD can be determined instantaneously. Finally, representative simulation and experimental results of a three-phase four-wire center-split hybrid active power filter are presented. These verify the validity and effectiveness of the proposed mixed signal controller in improving current quality compensation performance during light load conditions, compared with a conventional digital controller.

Control for the Three-Phase Four-Wire Four-Leg APF Based on SVPWM and Average Current Method

A novel control method is proposed for the three-phase four-wire four-leg active power filter (APF) to realize the accurate and real-time compensation of harmonic of power system, which combines space vector pulse width modulation (SVPWM) with triangle modulation strategy. Firstly, the basic principle of the APF is briefly described. Then the harmonic and reactive currents are derived by the instantaneous reactive power theory. Finally simulation and experiment are built to verify the validity and effectiveness of the proposed method. The simulation results show that the response time for compensation is about 0.025 sec and the total harmonic distortion (THD) of the source current of phaseAis reduced from 33.38% before compensation to 3.05% with APF.

Experimental Verification of Photovoltaic-based Three-phase Four-wire Series Hybrid Active Power Filter

—This article proposes a photovoltaic and battery interfaced series hybrid active power filter, which is comprised of a series active power filter and an inductor-capacitor (LC) shunt passive filter. The main benefits of the proposed system provide the compensation against the voltage harmonics, current harmonics, and voltage interruption for the whole day. A series active power filter demands a source of energy for compensating the voltage sag/swell. The proposed topology utilizes the green energy source with an energy storage unit to meet the DC-link voltage requirement of the series active power filter. The control strategy is based on the dual formulation of the compensation system principles with adaptive fuzzy logic controller. The simulation and experimental studies are carried out to validate the effectiveness of the proposed photovoltaic interfaced three-phase four-wire series hybrid active power filter.

Fuzzy Recursive Integral PI Control for Three-Phase Four-Wire Shunt Active Power Filter

This paper focuses on the current tracking control of three-phase four-wire active power filter (APF). The conventional PI control method usually causes a large deviation of the harmonic compensational current, and results in a slow response, which means that harmonic compensational performance under the conventional PI control is not ideal. In order to improve the compensation performance and the dynamic response speed of APF, the authors present a new control strategy by integrating the parameters online tuning of fuzzy adaptive with the recursive integral PI control algorithm. New algorithm takes full advantages of the characteristic of integrating the deviation of each sample-point of the recursive integral PI control and the adaptive merits of the parameters online tuning algorithm. The simulation experiments indicate that the control algorithm is feasible and can effectively improve the harmonic compensation performance of active power filter.

DC-Bus Voltage Control Strategy Based on Low-Pass Filter for Three-Phase Four-Wire APF

The DC-bus voltage control is critical for stable operation of the three-phase four-wire Active Power Filter. DC-bus stable voltage loop and balance voltage loop are established based on the small signal model. Considering the disadvantages of the traditional PI control, second-order low-pass filter is introduced into the proposed controller. Simulation and experimental results are conducted to validate the effectiveness of the proposed strategy.

Research on Active Power Filter Based on One-Cycle Control

One-cycle control (OCC) is a kind of nonlinear control technology. It is the most advanced reactive power compensation and harmonic suppression method. In the paper, a three-phase four-wire active power filter (APF) with one-cycle control is presented. This method does not need any measured quantities of three-phase input voltages and three-phase load currents, and also not need multipliers. The controller used has simple structure, which is composed of some integrators, flip-flops, comparators etc. The APF proposed has features of high precision and effective compensation. Through the theoretical analysis and the application by the OCC-APF, the results confirm that this approach can achieve the compensation in transient state and steady for the harmonic currents and reactive currents separately, and therefore, shows a good application prospect.

Control Method of the Three-Phase Four-Leg Shunt Active Power Filter

This paper presents a novel all-digital approach applied to three-phase four-wire active power filter (APF), which is made up of three-phase four-leg voltage source converters. The controller just detects the main current and DC side capacitor voltage. Calculation method of the switch duty cycle is deducted on the base of mathematics model formed. This controller has fewer measurement, higher robustness and simpler calculation as comparing to traditional controllers. Simulation verify that the APF with proposed controller can compensate the harmonics effectively.

Study on a novel approach to active power filter control using neural network-based harmonic identification scheme

This paper proposes an effective control scheme for three-phase three-wire (3P3W) active power filter using neural-based harmonic identification scheme. To achieve excellent steady state and dynamic response, the feedback control plus feed-forward control structures is utilized in the proposed control algorithms. The steady-state error minimization is achieved by the feedback loop, where the proportional integral regulators were adopted in d-axis and q-axis of the synchronous rotating reference frame synchronized with grid voltages by using the phase-locked loop. The adaptive linear combiners are utilized in the feed-forward loop, which serves the purpose of load disturbance rejection, and it significantly enhances dynamic performance of active power filter (APF). The modeling of the APF is based on the state-space modeling technique and the decoupled state-space model in synchronous d–q frame is also presented. Moreover, the mathematical formulation of the neural harmonic identification scheme and the selection of learning rate are discussed. It is found that the optimal learning rate is a compromise between the steady-state accuracy and the requirement of dynamic response. To verify the theoretical analysis, extensive simulation results are presented under both the balanced and unbalanced load conditions. The validity and effectiveness of the presented scheme is substantially confirmed by the simulation and experimental results, and it can be easily extended to applications of single-phase and three-phase four-wire APFs.