Hybrid Active Filter Research Articles

A multi-band shunt hybrid active filter with reduced sensor count

A Shunt Hybrid Active Filter (SHAF) is an attractive option for realizing low-cost harmonic compensation solutions. This paper proposes a SHAF with multiple harmonic compensation capability using a single Voltage Source Inverter and reduced sensor count. This strategy is apt for harmonic filtering solutions where low cost is the exclusive priority. In this paper, a new estimation approach is proposed to obviate requirement of a large number of sensors. Multiple Synchronous Reference Frames (MSRF) and low pass filters are used to measure 5th and 7th harmonic components separately from load as well as filter currents. Individual current controllers are designed for the 5th and 7th harmonic currents. Control is realized in the synchronously rotating, orthogonal (dq) reference frame. Performance of the controller is validated through simulation, using realistic plant and controller models. Experimental results are provided to corroborate the analytical and simulation results.

Filter based non-invasive control of chaos in Buck converter

A non-invasive method for controlling chaos in the voltage-mode Buck converter is proposed by using a hybrid active filter based feedback controller in this Letter. The harmonic balance method is applied to obtaining the bifurcation-point equations of the controlled system. Hence, a stability-boundary diagram is constructed, through which the control parameters are chosen correctly. The results of simulation and experiment are given after all.

A New Method of Compensating Harmonic Currents for Wind Power Generation Systems with the Soft Starter Using a Hybrid Active Filter

This paper proposes a new method of compensating harmonic currents for wind power generation systems with the soft starter using a hybrid active filter. The hybrid active filter consists of single-tuned LC and small-rated active filters. The single-tuned LC filter absorbs the harmonic current while behaving as a phase-leading capacitor for the fundamental component. The small-rated active filter improves the compensation characteristics of the passive filter under the soft start of the constant-speed wind turbine. The required rating of the active filter can be reduced because the active filter does not supply the fundamental reactive current. The basic principle of the proposed compensation method is discussed, and then confirmed by digital computer simulation using PSCAD/EMTDC. Simulation results demonstrate that the waveform of the source current becomes sinusoidal under the soft start. The required rating of the active filter is about 8.5% of the induction generator rating. A new calculation method of THD with the detrending algorithm is proposed for the transient state. The THD of the source current is about 7.3% using the hybrid active filter.

Voltage-Balancing Control of a Three-Level PWM Converter in a Transformerless Hybrid Active Filter

This paper focuses on voltage-balancing control suitable for a three-level diode-clamped PWM converter used in a hybrid active filter. A three-phase downscaled system including a 400-V, 15-kW three-phase diode rectifier with a capacitive load as a harmonic-producing load is designed, constructed, and tested to verify the filtering performance of the hybrid filter and the voltage-balancing control performance of the three-level PWM converter. Experimental results, along with theoretical analysis, verify that the voltage-balancing control proposed in this paper works properly in all the operating regions from full-load to no-load conditions.

Analysis of Insertion Loss and Impedance Compatibility of Hybrid EMI Filter Based on Equivalent Circuit Model

The hybrid active electromagnetic interference filter (HAEF) is considered one of the best options for improving power quality for a number of considerations. A systematic classification and identification of HAEF configurations is given, including their insertion losses, impedance compatibilities, potential applications, and comparative features. It is aimed at providing a broad perspective on the status of HAEF technology to researchers and application engineers dealing with EMI issues. The basis of discussion is an equivalent circuit model that includes all possible combinations of active and passive elements and matches these to the desirable attributes. The evaluation indicates those topologies that are known and those topologies that are relatively new.

Letter to the Editor: Optimal Sizing of the Passive Filter's Elements in Hybrid Active Filters

Active filters are an up-to-date solution to power quality problems. These filters allow the compensation of current harmonics and unbalance, together with power factor correction, and can be a much better solution than the conventional approach (capacitors for power factor correction and passive filters to compensate for current harmonics). Active filters could have wide application for controlling harmonic currents from nonlinear loads. In this letter, a method is presented for finding the optimum values of the capacitor and inductor for the passive filter used with the proposed hybrid active filter to minimize the converter rating and comparing these results with the conventional active filter.

Theory (Instantaneous Power Theory and Applications to Power Conditioning; Akagi, H. et al; 2007) [Book Review

This new book presents a deep review of various power theories and shows how the instantaneous active and reactive power theory provides an important basic knowledge for understanding and designing active filters for power conditioning. The book consists of six chapters covering the following topics and more: instantaneous power theory; shunt active filters; hybrid and series active filters; and combined series and shunt power conditioners. The book is easy to read and each chapter ends with a summary and list of references. The book perfectly fills the gap on the power electronics book market. It is an extremely attractive reference book for research and development engineers who are interested in design of modern active power filters and conditioners as well as flexible ac transmission systems. It can also be recommended for advanced senior-level courses as well as for undergraduate courses.

A Transformerless Hybrid Filter Using a Three-Level Diode-Clamped PWM Converter

This paper deals with a transformerless hybrid active filter integrated into a medium-voltage three-phase diode rectifier used as the front end of an adjustable-speed motor drive. The hybrid filter is formed by a single LC filter tuned to the 7th-harmonic frequency per phase and a small-rated active filter based on a three-phase three-level diode-clamped PWM converter. A three-phase downscaled system rated at 400V and 15kW is designed, constructed, and tested to verify the filtering performance of the hybrid filter. Experimental results show that the current THD (total harmonic distortion) gets less than 5%, and that the voltage-balancing control proposed in this paper works properly even in transient states.

Design and Performance of a Transformerless Shunt Hybrid Active Filter for Installation on a 6.6-kV Power Distribution System

This paper presents the analysis and design of a shunt hybrid active filter for harmonic damping in a 6.6-kV power distribution system. This hybrid filter has been proposed and tested experimentally with a 200-V, 20-kW laboratory system, showing good damping performance. Another possible solution for harmonic damping is to install a shunt pure active filter at the end of a feeder. However, the pure filter is too costly and bulky to be installed in a 6.6-kV system. This paper discusses the design criteria for a hybrid filter intended for installation on a 6.6-kV power distribution system. Detailed comparisons between the pure filter and the hybrid filter are also included as a foundation for the design of the hybrid filter. The performed design confirms the feasibility of installation of the hybrid filter on a 6.6-kV power distribution system.

Active Harmonic Filters

Unlike traditional passive harmonic filters, modern active harmonic filters have the following multiple functions: harmonic filtering, damping,isolation and termination, reactive-power control for power factor correction and voltage regulation, load balancing, voltage-flicker reduction, and/or their combinations. Significant cost reductions in both power semiconductor devices and signal processing devices have inspired manufactures to put active filters on the market. This paper deals with general pure active filters for power conditioning, and specific hybrid active filters for harmonic filtering of three-phase diode rectifiers.

A 6.6-kV Transformerless Shunt Hybrid Active Filter for Installation on a Power Distribution System

This paper presents a fully-digital-controlled shunt hybrid filter for damping of harmonic propagation in power distribution systems. The harmonic propagation is caused by resonance between line inductances and power capacitors installed for power factor correction. A possible solution to damping out harmonic propagation is based on installation of a shunt pure active filter at the end of a feeder. This paper proposes a shunt hybrid active filter characterized by series connection of a seventh-tuned LC filter per phase and a small-rated three-phase active filter. Like the pure filter, the hybrid filter is connected to the end bus of a feeder. The capacitor of the LC filter imposes a high impedance to the fundamental frequency, so that the fundamental voltage appears across the capacitor. This unique feature allows us to directly connect the hybrid filter to the 6.6-kV power line without step-down transformers. Furthermore, the capacitor used in this hybrid filter is lighter, cheaper and smaller than the transformer used in the pure filter. Theoretical analysis, along with experimental results obtained from a 200-V, 20-kW laboratory system, verifies the viability and effectiveness of the proposed hybrid filter.

Delivering clean and pure power

There are two approaches to the mitigation of power quality problems. The first approach is called load conditioning, which ensures that the equipment is made less sensitive to power disturbances, allowing the operation even under significant voltage distortion. The other solution is to install line-conditioning systems that suppress or counteract the power system disturbances. Among the different new technical options available to improve power quality, active power filters have proved to be an important and flexible alternative to compensate for current and voltage disturbances in power distribution systems. Power filter topologies are discussed including shunt active filter, series active filters, series-shunt active filters, and hybrid active filters. New topologies using multilevel inverters are also discussed.

Analysis and design of a multiple-loop control system for a hybrid active filter

This paper investigates the control of a hybrid active filter consisting of a single tuned resonant branch and an active element. This filter is capable of suppressing multiple harmonics using a multiple-loop control system. Linear continuous-time models are first developed in the dq reference frame. This results in a two-input/two-output system with cross coupling. The continuous model is discretized and the design of a multiple-loop discrete-time controller is examined. Wideband current feedback loops are shown to affect the coupling between the d- and q-axis controllers and provide a resistance-like damping effect. Variations in stability with processing delay times are examined. Finally, this work is extended to include narrowband harmonic specific controls. The results of the control study are confirmed by simulation and experimental results.

Implementation of a Hybrid Filter with a Potential Application to Adjustable Speed Compressor Drives for Air Quality Control

This article presents a TMS320C31 DSP-based implementation of a hybrid active filter to compensate the harmonics of an R-C nonlinear load. A diode bridge rectifier with an R-C load is considered to represent variable-speed compressor load. The topology of a hybrid filter combines a shunt passive filter (PF) and a shunt active filter (AF). An inductor, placed in series with the line between the AF andthe PF, not only reduces the load harmonics but also creates a harmonics voltage source at the input of diode bridge rectifier. This harmonics voltage source makes the PF more effective and reduces its susceptibility to possible mistuning in the parameters. The PF is tuned to compensate 5th and 7th harmonics, while the AF compensates the rest of the harmonics of the load current. A PWM voltage source inverter (VSI) with an indirect current-controlled technique is used as an AF. The control algorithm of a shunt AF is based on a dc bus voltage feedback loop and load current feedforward loop. A proportional plus integral control is used on the self-supporting dc bus voltage of the shunt AF. It is demonstrated that an R-C nonlinear load draws current with higher peak value and needs a hybrid solution for the load current harmonics. Experimental verification of simulated results is carried out on a scaled-down prototype module of the hybrid filter.

Analysis and operation of hybrid active filter for harmonic elimination

Abstract This paper presents a hybrid active filter topology and its control to suppress the harmonic currents from entering the power source. The adopted hybrid active filter consists of one active filter and one passive filter connected in series. By controlling the equivalent output voltage of active filter, the harmonic currents generated by the nonlinear load are blocked and flowed into the passive filter. The power rating of the converter is reduced compared with the pure active filters to filter the harmonic currents. The harmonic current detecting approach and dc-link voltage regulation are proposed to obtain equivalent voltage of active filter. The effectiveness of the adopted topology and control scheme has been verified by the computer simulation and experimental results in a scaled-down laboratory prototype.

A Novel 3-Phase Hybrid Harmonic and Reactive Power Compensator

The application of shunt active filters for the harmonic and reactive power compensation in the high power range is mainly restricted because of their low efficiency and the high cost of inverters with high switching frequency. Moreover; the compensation effect is completely lost in case of internal fault in active filter. Hybrid active filters as the combination of a low power PWM inverter and passive filters have been researched and developed to overcome the limitations of shunt active filter. However, they do not have control over fundamental reactive power. This paper proposes a new hybrid active compensator for harmonic and fundamental reactive current compensation, which consists of two small-rated active filters and one bank of passive filters. Simulation and experimental results are presented to show the advantages of the proposed compensator topology.

Hybrid active filter for harmonically unbalanced three phase three wire railway traction loads

This paper investigates a hybrid active/passive topology and control strategy appropriate for removing harmonics caused by unbalanced nonlinear loads. Unbalanced loads such as railway traction loads may use static compensators to balance the fundamental frequency components. The harmonic currents produced by this combination are unlikely to be balanced. Purely passive structures are not sensitive to this harmonic imbalance, however some active structures are. Controllers aimed at balanced three phase loads using synchronous transformations will not remove all of the harmonic components. The controller presented in this paper uses harmonic sequence components to detect both balanced and unbalanced components and reduce both harmonic components to zero.

A hybrid active filter for damping of harmonic resonance in industrial power systems

A hybrid active filter for damping of harmonic resonance in industrial power systems

A Hybrid Active Filter for Damping of Harmonic Resonance in Industrial Power Systems

This paper proposes a hybrid active filter for the damping of harmonic resonance in industrial power systems. The hybrid filter consists of a small-rated active filter and a 5th-tuned passive filter. The active filter is characterized by detecting the 5th-harmonic current flowing into the passive filter. It is controlled in such a way as to behave as a negative or positive resistor by adjusting a feedback gain from a negative to positive value, and vice versa. The negative resistor presented by the active filter cancels a positive resistor inherent in the passive filter, so that the hybrid filter acts as an ideal passive filter with infinite quality factor. This significantly improves damping the harmonic resonance, compared with the passive filter used alone. Moreover, the active filter acts as a positive resistor to prevent an excessive harmonic current from flowing into the passive filter. Experimental results obtained from a 20-kW laboratory model verify the viability and effectiveness of the hybrid active filter proposed in this paper.

Control of square-wave inverters in high-power hybrid active filter systems

This paper presents a new control scheme for a hybrid parallel active filter (HPAF) system intended for high-power applications-up to 100 MW nonlinear loads-to meet IEEE 519 recommended harmonic standards. The active filter inverter is realized with small-rated (1%-2% of the load rating) square-wave inverters operating at the dominant harmonic frequencies. The proposed system achieves harmonic isolation at desired dominant harmonic frequencies, such as the fifth and seventh, even in the presence of supply voltage harmonic distortions. A novel method of active filter inverter DC-bus control, as proposed here, achieves power balancing by exchanging energy at the fundamental frequency and at the dominant harmonic frequency (such as the fifth). The proposed square-wave inverter-based HPAF system provides improved filtering characteristics as compared to the conventional passive filter and is expected to be cost effective for high-power nonlinear loads compared to the conventional passive filter or other active filtering solutions. The concept of harmonic isolation at dominant harmonic frequencies by square-wave inverters with the proposed control scheme is validated by simulation results.