Four-leg Shunt Active Power Filter Research Articles

New Topology of a Hybrid, Three-Phase, Four-Wire Shunt Active Power Filter

With a view to reducing harmonic content in electrical power systems, and, consequently, improving power quality level, filters and other harmonic compensation devices are widely used. In the category of filters, they can be distinguished into two classes that are related to the operating mode, active or passive, both widely known and applied in electrical power grids and in the most diverse industry sectors. In this sense, taking into account the use of compensating devices in four-wire electrical systems feeding single-phase, non-linear loads, this paper presents a new hybrid arrangement of harmonic compensation that incorporates both active and passive filtering, which performs all functions concerning the harmonic compensation of a four-leg shunt active power filter. In this hybrid arrangement, the harmonic filtering of positive and negative sequence components is performed by a three-leg shunt active power filter, while the filtering of zero-sequence harmonics is attributed to the electromagnetic zero-sequence suppressor. The results, which confirm the effectiveness of the proposed hybrid arrangement, are proven through simulations and experimental tests in different operating scenarios, revealing a substantial improvement in the system’s power factor, as well as a reduction in harmonic distortions.

Self tunning filter for three levels four legs shunt active power filter with fuzzy logic controller

The low harmonic distortion and reduced switching losses are the advantages of using the multilevel inverter. For this purpose, the three-level inverter is used in this paper as a three-phase four-leg shunt active power filter (SAPF). The SAPF is used to eliminate the harmonic current to compensate the reactive power current, and to balance the load currents under an unbalanced non-linear load. A fuzzy logic controller and self-tuning filters (STF) are used to control the active power filter (APF) and generate the reference current. To demonstrate the validity of the proposed control strategy, we compared it with a conventional p − q theory, under distortion voltage conditions and unbalanced non-linear load. The Matlab-Simulink toolbox is used to implement the algorithm of Fuzzy logic control. The performance of the SAPF controller is found very effective and adequate as compared with the p − q theory.

A compound control strategy for LCL-based three phase four leg shunt active power filter

Conventional single inductor filter which is applied to three-phase four-leg shunt active power filter hardly meet the requirements for high frequency harmonic suppression. LCL filter has advantage both in high dynamic response and high frequency harmonic suppression. Repetitive control can realize accurate tracking of multi-harmonics signal. However, the design of corrector for repetitive control is mostly complicated. This paper proposes a topology of three-phase four-leg shunt active power filter based on LCL filter and improve its stability through capacitive current feedback. Compound control strategy which includes PI control and repetitive control is adopted to improve the compensation effect of harmonic current. Corrector for repetitive control has simple structure and is easy to design. The conventional PI control and compound control are compared and analyzed in detail. Moreover, the difference of property between LCL filter and single inductor filter is compared and analyzed. Simulation results show the correctness and effectiveness of the designed LCL filter and the proposed compound control strategy. The proposed method provides a reference for making three-phase four-leg shunt active power filter more practical.

Novel compound PWM strategy of a four-leg shunt active power filter

ABSTRACTThe currently used hysteresis method is of low control accuracy, and the PWM-based strategy fails to provide a high enough response speed; thus, there is always a trade-off between the performances of control accuracy and response speed for a four-leg shunt active power filter (APF) to cope with the large variation in the load harmonic profile. First, an improved SVPWM strategy is proposed in this paper; with the aim to increase the response speed of a four-leg APF by simplifying the implementation of current 3D-SVPWM methods, the principle and realisation of this strategy are explained in detail. Based on these works, a compound PWM algorithm that effectively integrates the improved SVPWM and a PI-based current hysteresis method is proposed to simultaneously guarantee a higher response speed and a higher control accuracy for a four-leg APF. The realisation and parameter tuning of the compound PWM are elaborated. The correctness and effectiveness of the improved SVPWM and the compound PWM strategy are verified by simulations using Matlab/Simulink software. Finally, experimental results on a four-leg APF implemented in a closed-loop real-time simulation platform are presented.

Study on the design and switching dynamics of hysteresis current controlled four‐leg voltage source inverter for load compensation

In a variable switching frequency control scheme, it is challenging to design the voltage source inverter (VSI) parameters without knowing the maximum and minimum switching frequencies. The switching frequency variation depends on the system parameters. Therefore, the expression for frequency variation in one inverter topology does not hold in other topologies. The design of hysteresis current controlled four-leg shunt active power filter (APF) requires the switching dynamics analysis to ensure satisfactory performance of the inverter. In this study, a detailed analysis on the switching dynamics of hysteresis current controlled four-leg VSI and design of various inverter components for compensating unbalanced and non-linear loads are presented. The results obtained from these analyses can be used in any applications involving hysteresis current controlled four-leg VSI. These results are supported by detailed simulation studies conducted on a three-phase four-leg shunt APF system using Matlab/Simulink. The theoretical studies and design of passive components are also verified by conducting experiments on a prototype of four-leg shunt APF developed in the laboratory.

Backstepping control of three-phase three-level four-leg shunt active power filter

In this paper, backstepping control for three-level four-leg shunt active power filter (SAPF) system is proposed. The adopted filtering topology requires both a three-dimensional space vector modulation (3DSVM) for controlling the three-level four-leg inverter as well as DC voltage and filter currents control. The regulation of the DC voltage and filter currents is accomplished by backstepping controllers. The voltage-balancing control of two split DC capacitors of the three-level four-leg SAPF is achieved using three-level three-dimensional space vector modulation equipped by a balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. The simulation results show the effectiveness of the proposed filtering system in terms of the compensation of the harmonics and the zero sequence current and the operation at unity power factor.

Unified Digital Phase-Locked Loop With Multiple Complex Resonators for Both Single- and Three-Phase Grid Synchronization

Grid synchronization is one of the critical techniques used in grid-connected systems, such as distributed generation, energy storage, and harmonic compensation equipment. To acquire efficient grid-connection or harmonic compensation performance, the accurate and real-time information of phase, frequency and amplitude is required, especially when the grid voltage contains disturbed or other unexpected components. According to different application fields, two kinds of phase-locking structures exist—single- and three-phase phase-locked loop (PLL), which are not cross compatible. In this paper, a novel unified digital PLL with multiple complex resonators for both single- and three-phase systems is proposed. First, single-phase and three-phase voltage signal is transformed uniformly to a similar complex form that consists of positive and negative sequence components rotating in counterclockwise and clockwise directions, respectively. Then, synchronous rotating frame PLL with a generalized prefilter is introduced. The proposed filtering structure consists of multiple complex resonators that can filter out harmonic frequency components and maintain fundamental positive sequence components accurately. Furthermore, a simplified structure of the complex resonator for single-phase system and an operation method for resonant factor are introduced. Finally, the validity and effectiveness of the proposed method are proven by the simulated and experimental results of a three-phase four-leg shunt active power filter.

Adaptive Backstepping Control of Three-Phase Four-Wire Shunt Active Power Filters for Energy Quality improvement

The increasing use of nonlinear loads entails serious electrical energy quality problem in power grids. In this paper, the energy quality issue is dealt with by using three-phase four-leg shunt active power filters (SAPFs). A new model that describes the whole controlled system including the SAPF and associated nonlinear and unbalanced loads is developed. The model also accounts for the electrical grid line impedance. The control objective is threefold: to make up for the harmonics and the reactive currents absorbed by the loads; to cancel the neutral current; and to regulate the inverter DC capacitor voltage. Based on the new model, a nonlinear controller is designed, using the backstepping technique. Moreover, the controller is made adaptive for compensating the uncertainty on the switching loss power. The performances of the proposed adaptive controller are formally analysed using tools from the Lyapunov stability and averaging theory, and their supremacy with respect to standard control solutions is illustrated through simulation.

The Simplified Control of Three-Phase Four-Leg Shunt Active Power Filter for Harmonics Mitigation, Load Balancing and Reactive Power Compensation

In this paper, the simplified control of three-phase four-leg shunt active power filter for harmonics mitigation, load balancing and reactive power compensation is proposed. In order to calculate the harmonics, current imbalance and reactive power, the load currents are detected and transformed to dq0 variables. By using the low-pass filter, the fundamental active power current can be separated from the d-axis current. Therefore, the commanded active power filter currents are consist of d-axis harmonic currents, q-axis and 0-axis currents. These components are regulated by the PI controller with feedforward utility voltage via the four-leg space vector inverter. Moreover, the design guidelines of space vector phase-locked loop (PLL), current controllers and DC-bus voltage controller are also presented. Validity of the proposed control schemes is confirmed by the simulation.

Hybrid direct power/current control using feedback linearization of three-level four-leg voltage source shunt active power filter

This paper proposes a hybrid direct power/current control-three dimensional space vector modulation combined with feedback linearization control for three-phase three-level four-leg shunt active power filter (SAPF). The four-leg SAPF ensures full compensation of harmonic phase currents, harmonic neutral current, reactive power and unbalanced nonlinear load currents. It also regulates its self-sustaining DC bus voltage. The voltage-balancing control of two split DC capacitors of the three-level four-leg SAPF is achieved using three-level three dimensional space vector modulation with balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. Complete simulation of the resultant active filtering system validates the efficiency of the proposed nonlinear control method. Compared to the traditional control, the use of feedback linearization control allows to exhibit excellent transient response during balanced and unbalanced load, and grid voltage.

An improved deadbeat control algorithm for three-phase four-leg shunt active power filter

ABSTRACTConsidering the influence of the alternating current side resistor, this paper completes the mathematical model for the three-phase four-leg active power filter and deduces the discrete model of the deadbeat control. A novel delay compensation method is proposed to improve the deadbeat control algorithm. Comparing with the algorithm without delay compensation, the proposed algorithm can effectively reduce the delays caused by digital computing and pulse width modulation output. This is achieved by increasing thë sampling and processing frequency without estimating the actual values. The predictive algorithms are also analysed in this paper. For the improved algorithm, the simulation and experimental results show that the total harmonic distortion values of three-phase source currents become lower and the neutral current becomes smaller than the algorithm without delay compensation. Therefore the proposed algorithm can solve the harmonic and unbalancing problems effectively.

Adaptive non-linear control of three-phase four-wire Shunt active power filters for unbalanced and nonlinear loads.

The problem of controlling three-phase, four-leg shunt active power filters (SAPF) is addressed in presence of nonlinear and/or unbalanced loads. A new control model for four-leg SAPF, taking into account for the electrical grid line impedance, is developed. The control objective is threefold: (i) compensating for the current harmonics and the reactive power absorbed by the nonlinear load; (ii) annulations of neutral line current (iii) regulating the inverter DC capacitor voltage. To this end, based on the new model, a nonlinear controller is developed, using the Lyapunov technical design. It is therefore able to ensure good performances over a wide range variation of the load current. Moreover, the controller is made adaptive for compensating the uncertainty on the switching loss power. The performances of the proposed adaptive controller are formally analyzed using tools from the Lyapunov stability and averaging theory. The supremacy of the proposed controller with respect to standard control solutions is illustrated through simulation

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.

A Novel Fuzzy—Adaptive Hysteresis Controller Based Three Phase Four Wire-Four Leg Shunt Active Filter for Harmonic and Reactive Power Compensation

This paper presents a fuzzy logic based three phase four wire four-leg shunt active power filter to suppress harmonic currents. Modified instantaneous p-q theory is adopted for calculating the compensating current. Fuzzy-adaptive hysteresis band technique is applied for the current control to derive the switching signals for the voltage source inverter. A fuzzy logic controller is developed to control the voltage of the DC capacitor. Computer simulations are carried out on a sample power system to demonstrate the suitability of the proposed control strategy, for harmonic reduction under three different conditions namely, ideal, unbalance, unbalance and distorted source voltage conditions. The proposed control strategy is found to be effective to reduce the harmonics and compensate reactive power and neutral current and balance load currents under ideal and non-ideal source voltage conditions.