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EPE 2009 - Subtopic 15-4 - DS: 'Power Electronics for Power Systems'
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2009 - Conference > EPE 2009 - Topic 15: 'Transmission and Distribution of Electrical Energy' > EPE 2009 - Subtopic 15-4 - DS: 'Power Electronics for Power Systems'
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	A Comparative Analysis of p-PLL Algorithms for Single-Phase Utility Connected Systems   By Sergio SILVA, Alessandro GOEDTEL, Claudionor NASCIMENTO, LEONARDO CAMPANHOL, Denilson PAIÃO	[View]   [Download]
Abstract: This work presents a comparative analysis between four algorithms used to implement single-phase Phase-Locked Loop (PLL) systems, which are based on three-phase instantaneous active power theory. PLL systems have been used in applications involving power conditioning equipments, for instance, series, parallel and hybrid active power filters, uninterruptible power supply (UPS) systems, controlled PWM rectifiers, and others. However, the information of the utility voltage, such as phase-angle, frequency or amplitude, need to be obtained with quality and precision to guarantee the good performance of the power conditioning equipments. As the single-phase PLL systems will be studied into two-phase stationary reference frame, a fictitious quadrature voltage must be obtained using appropriated strategies. Simulation and experimental results are presented in order to evaluate the performance of the single-phase PLL algorithms under distorted conditions of the utility voltage.
	A Zero-Sequence Harmonic Blocking Design: Theoretical and Experimental Analysis   By Luís Carlos Origa DE OLIVEIRA, Weslei B. PERIN, Júlio Borges DE SOUZA, Rodrigo A. DE OLIVEIRA	[View]   [Download]
Abstract: The EPE 2009-team regrets to inform you that this full paper (or in case of invited lectures: presentation) was not uploaded before the deadline of our conference.
	Active Harmonic Filters and Balance Compensation on Electric Railway Systems using the Open Delta Transformer Connection   By Alexander BUENO, Jose ALLER, María GIMÉNEZ, José RESTREPO, Víctor GUZMAN	[View]   [Download]
Abstract: This work presents a filtering and unbalance compensation scheme for electric traction system with open delta transformers. The proposed method uses an active filter controlled with the instantaneous active and reactive power, to reduce the harmonic current distortion and the negative sequence obtained by the system under unbalanced operation in steady state. The scheme has been experimentally validated and the results show the controller advantages.
	Active Power Control Strategies for Inverter-Based Distributed Power Generation Adapted to Grid-Fault Ride-Through Requirements   By Fei WANG, Jorge DUARTE, Marcel HENDRIX	[View]   [Download]
Abstract: Distributed power generation is expected to deliver power into the grid without interruption during voltage dips. To improve system ride-through capabilities, a generalized active power control strategy is proposed for grid-interfacing inverters. Specifically, a current reference generation strategy based on symmetric-sequence components of unbalanced three-phase three-wire or four-wire systems is derived. It is shown that a single adjustable parameter can smoothly change the relative amplitudes of oscillating active and reactive power. This steering possibility enables grid-side inverters to optimally meet different requirements of coming standards. Simulations and experiments are carried out to validate the proposed strategy.
	An Unbalance Voltage Compensator Using a Fast On-Load Tap Changing Regulator   By Rodolfo ECHAVARRIA, Guadalupe ACOSTA, Ciro NUÑEZ	[View]   [Download]
Abstract: This paper presents a Fast On-Load Tap Changing Regulator used to correct unbalanced voltages. This regulator uses the semi natural commutation in order to improve the response. The proposed topology injects the voltage in only phase in order to balance the three phase system.
	Averaged large signal model of boost power factor corrector in boundary conduction mode   By Daniel KUEBRICH, Thomas DUERBAUM, Christian SCHILDBACH	[View]   [Download]
Abstract: A modeling approach of a power factor correction circuit operating in boundary conduction mode is presented. The PFC is controlled by a constant on-time of the switch. The effect of valley switching is simplified and taken into account as dead-time to generate a large signal model. On the basis a small signal model for the constant on-time controlled PFC voltage loop is derived. The large and small signal models are compared to measurements of the transfer function. For performing this low frequency transfer functions measurement a set-up using an oscilloscope and functional generator is described.
	COMPENSATION OF LOAD UNBALANCE, REACTIVE POWER AND HARMONIC DISTORTION BY COOPERATIVE OPERATION OF DISTRIBUTED COMPENSATORS   By Paolo TENTI, Paolo MATTAVELLI, Elisabetta TEDESCHI, Daniela TROMBETTI	[View]   [Download]
Abstract: Distribution grids are increasingly populated by a variety of renewable energy sources, which create new opportunities in terms of efficient use of energy and can also help to improve power quality. In fact, they are connected to the grid by means of Power Switching Interfaces (PSI) which are capable to control power flow and waveform of absorbed currents as well. They can therefore contribute to power balance and compensation of asymmetry and distortion together with other compensation units, e.g., passive filters, SVC (Static VAR Compensators) and APF (Active Power Filters). Of course, effective use of such distributed compensation capability requires cooperative operation of compensators and proper sharing of compensation duties. This paper shows that distributed compensation of load unbalance, reactive power and harmonic distortion can be achieved by a cooperative control approach. Energy efficiency and power quality can be managed as a whole at a system level, by taking full advantage of the distributed compensation capability.
	Construction and first result of a scaled transmission system with the Distributed Power Flow Controller (DPFC)   By Zhihui YUAN, Sjoerd DE HAAN, Braham FERREIRA	[View]   [Download]
Abstract: The Distributed Power Flow Controller (DPFC) is a new device within the family of FACTS devices. The DPFC has the same control capability as the UPFC, but with much lower cost and higher reliability. The paper presents the experimental results of the DPFC in a scaled simple power system. The objective of this DPFC experimental setup is to verify the principle of using 3rd harmonic to exchange active power between shunt and series converters. Several converters are made, and each is controlled by an individual DSP. It proves that the DPFC can independently control active and reactive power flow through the line.
	CONTROL STRATEGY FOR HYBRID POWER FILTER TO COMPENSATE UNBALANCED AND NON-LINEAR THREE-PHASE LOADS   By Salvador P. LITRAN, Patricio SALMERON, Jesús R. VAZQUEZ, Reyes S. HERRERA, Alejandro PÉREZ	[View]   [Download]
Abstract: A control algorithm is proposed for a three-phase hybrid power filter constituted by a series active filter and a shunt passive filter. The control strategy is based on the dual formulation of the vectorial theory of electrical power, so that the voltage waveform injected by the active filter is able to compensate the reactive power, to eliminate harmonics of the load current and to balance asymmetrical loads. An experimental prototype was developed and experimental results presented.
	Design and development of a supercapacitor-based microgrid dynamic support system   By Endika BILBAO, Haizea GAZTAÑAGA, Luis MIR, Ion ETXEBERRIA-OTADUI, Aitor MILO	[View]   [Download]
Abstract: This paper presents a supercapacitor-based dynamic support system for hybrid microgrids that guarantees the safe transition between operation modes (parallel / stand alone) and the correct dynamic power balance in stand-alone mode. The paper describes the design and development of the hardware and software components of a microgrid support system that has been implemented as a 7.8kW single phase prototype connected to a 125V-100Wh supercapacitor bank. The prototipe has been experimentally tested confirming the good performances observed in the preliminary simulation studies.
	Electromagnetic impact of underground HVDC cables   By Luca ZILBERTI, Oriano BOTTAUSCIO, Mario CHIAMPI, Michele PASTORELLI, Enrico PONS	[View]   [Download]
Abstract: This paper analyses the magnetic field emissions of a future HVDC transmission line for the interconnection between Italy and France, which will adopt underground cables laid along the Frejus highway. The current harmonics and the consequent magnetic field are estimated by combined use of different numerical models. The electromagnetic interferences with existing structures and the human exposure to magnetic fields have been analyzed and compliance with regulations limiting human exposure and technical Standards ensuring electromagnetic compatibility of appliances and devices has been assessed.
	EXPERIMENTAL EVALUATION OF A SIMPLE ROBUST CONTROL FOR ACTIVE POWER FILTERING UNDER UNFAVOURABLE CONDITIONS   By JEAN-PAUL GAUBERT, ABDELMADJID CHAOUI	[View]   [Download]
Abstract: This paper deals with shunt active power filtering for power quality improvement under unfavourable non-linear load and source conditions. A simple hybrid control strategy is used, based on a numerical Integrator Proportional (IP) DC bus controller combined with a Phase-locked loop (P.L.L.) output to generate reference currents. A second analogue current controller is developed to insure- three phase sinusoidal synchronised waveforms of the main currents. The experimental evaluation of the robustness control is verified using 20 KVA Shunt Active Power Filter (SAPF) not only for transient conditions (step load, switch-on of SAPF) but also for the worst case of unbalanced loads (break phase) and source voltages. Several experimental results are presented and discussed to prove the robustness and the excellent performance of the proposed technique.
	FACTS location using Genetic Algorithm to increase energy efficiency in distribution networks   By Paola PEZZINI	[View]   [Download]
Abstract: The article presents a genetic algorithm (GA) application to find the best location and reactive power injection of a FACTS device in a power system. The GA is employed to increase the energy efficiency of the system, assumed as fitness function, considering that only the best individuals of a population are selected to create new possible solutions and these are meant to improve the energy efficiency of the system; the node and the reactive power values are considered as the elements needed to maximize the fitness function. Simulations are performed on a 33 bus test power system employing two different Matlab programs created by the authors to run the power flow and the location of the device. The power flow program performs a voltage limits check. Results show the evolution and the increase of the energy efficiency in the system.
	Harmonic voltage control with a STATCOM   By Beat RONNER	[View]   [Download]
Abstract: Harmonic current control with converters is widely practiced, e.g. compensation of harmonics generated by a load. Control of harmonic grid voltage components is much more difficult due to the fact that the grid impedance for harmonic frequencies changes in a wide range, which changes the behavior of the control loop significantly. This paper shows how a STATCOM is used to reduce voltage harmonics in a high-voltage grid. Two methods to control harmonic grid voltage components together with simulation and measurement results are presented.
	IMPLEMENTATION OF THREE-PHASE HYBRID TRANSFORMER USING MATRIX CHOPPER   By Jacek KANIEWSKI, Zbigniew FEDYCZAK, Marius KLYTTA, Miroslaw LUKIEWSKI, Pawel SZCZESNIAK	[View]   [Download]
Abstract: This paper deals with the implementation of a new solution for a three-phase AC transformer with electromagnetic and electric coupling (hybrid coupling). The electromagnetic coupling is realized by means of the conventional three-phase transformer (TR) with two secondary windings in each phase. The electrical coupling is realized by means of a matrix chopper (MC), which is supplied from auxiliary secondary windings of the transformer. This paper presents an operational description of the proposed solution and simulation and experimental test results collected together with theoretical analysis results.
	Influence of relaxation process on supercapacitor time response   By nicolas BERTRAND, OLIVIER BRIAT, JEAN-MICHEL VINASSA, EL HASSANE EL BROUJI	[View]   [Download]
Abstract: This paper deals with the fractional order modelling of the supercapacitor voltage response for a given current profile. The model is obtained using the porous electrode theory applied on the supercapacitor case. In order to simplify the complexity of the model, it is assumed that there is no diffusion process in the electrolyte. These assumption leads to neglect the supercapacitor self-discharge. So, we intend to combine both frequency and time identification methods. The differences on the obtained results show the importance of the experimental protocol. A numeric approach leads to estimate the supercapacitor initial state influence on the voltage response of a same model. An experiment is done on a 2000F/2.7V element to validate the assumption done and the result allows estimating the current sign dependency of the capacitance.
	Inverter-less flywheel applications for voltage sags and blackouts compensation   By Shuhei KATO, Takumi TSUJINO, Miao-Miao CHENG, Hideo SUMITANI, Ryuichi SHIMADA	[View]   [Download]
Abstract: Using a flywheel and a squirrel-cage induction motor, this paper proposes two inverter-less applications for electrical power quality improvement by compromising a little frequency fluctuations; (1) a voltage sag compensator using a capacitor self-excited induction generator without semiconductor power converters, (2) blackout delay system for industrial robots safety shutdown. In the first section, the original points are the proposal of an attractive configuration without the converters, design considerations of the stored energy in the flywheel system, and experimental validation of the design guides by a 10-kW class system. In the second section, the key point is the usefulness of the inverter-less system for industrial robots. Field tests of blackout for a real industrial robot (30 kVA) protection are reported. The flywheel system is found to work well and provides a backup for the robot.
	Investigation of six-pulse three-phase converters in unsymmetrical operation   By Manuel WEILAND, Bernhard FOERST, Gerhard HEROLD	[View]   [Download]
Abstract: Power converters operated in unsymmetrical three phase electrical systems will generally work asymmetrically. This introduces disadvantages for the operation of the electrical power system, such as non characteristic harmonics in voltage and current. In this paper, a method is presented to control the behavior of electrical equipment based on line commutated current converters using unsymmetrical firing angles. Thereby the operation of the essentially non linear system is described as sectional continuous linear problem. For its solution an approach with differential equations in the range of space phasors is used. On the basis of a six pulse line commutated current converter it is shown to be possible to optimize the unsymmetrical operation with respect to certain quality criteria.
	Investigation of the Dynamic Control of a Converter Topology Interfacing an Energy Storage with the dc Link of a VSC   By Hailian XIE, Lennart ÄNGQUIST, Hans-Peter NEE	[View]   [Download]
Abstract: Integration of energy storage (ES) into a static synchronous compensator (StatCom) makes it possible for the StatCom to provide a certain amount of active power as well as reactive power support. The possible benefit of the additional active power support of a StatCom can be power oscillation damping capability, mitigation of phase-jump related disturbances, etc. Direct connection of an ES device to the dc link of the VSC incurs high voltage rating of the VSC due to the considerable voltage swing associated with the ES device. In order to reduce the total cost, a dual thyristor converter topology has been proposed as the interface between the ES and the dc link of the voltage Source Converter. In this paper, the dynamics of the proposed system are investigated. Control strategies are proposed and verified by simulations with PSCAD/EMTDC. A comparison is made between two control methods.
	LVDC DISTRIBUTION SYSTEM PROTECTION – SOLUTIONS, IMPLEMENTATION AND MEASUREMENTS   By Pasi SALONEN, Pasi NUUTINEN, Jarmo PARTANEN, Pertti SILVENTOINEN	[View]   [Download]
Abstract: An LVDC (low voltage DC) distribution system is a promising technology to be used in future smart distribution system having high level cost-efficiency and reliability. Protection of an LVDC distribution system differs from the traditional 20/0.4 kV AC distribution network; direct current and IT network complicates the customer-end protection. This paper describes practical protection solutions for the LVDC network and presents an LVDC system laboratory prototype in which experimental testing is performed.
	Lyapunov Based Nonlinear Control of TCSC system   By Abdelkrim BENCHAIB	[View]   [Download]
Abstract: This paper presents a nonlinear controller for TCSC system. The controller based on nonlinear model, is derived using Lyapunov technique. Based on the work of [1], we will propose a new controller that has better performances. Stability analysis as well as simulation results will show the effectiveness of the proposed method.
	Optimal Design of High Performance Repetitive Controller for Shunt Active Filters Using Strength Pareto Multi-Objective Optimization Approach   By Seyed Mohammadreza RAFIEI, lEONARDO LIMONGI, GIOVANNI GRIVA, RADU BOJOI	[View]   [Download]
Abstract: In this paper an algorithm for optimal design of active power filters using Strength Pareto multi-objective optimization approach is proposed. Some parameters of the repetitive current controller together with the inverter’s DC bus voltage have been considered as design variables. Different optimizing pairs of objective functions including THD of the line currents and the transient response of the filter have been considered and discussed. The proposed methodology gives a wider horizon to the controller design task for active power filters. The simulation and experimental results prove the effectiveness of the proposed design methodology.
	Optimisation of the modular multilevel converters performance using the second harmonic of the module current   By Andreja RASIC, Gerhard HEROLD	[View]   [Download]
Abstract: The EPE 2009-team regrets to inform you that this full paper (or in case of invited lectures: presentation) was not uploaded before the deadline of our conference.
	Reactive Power and Harmonic Currents Compensation in Traction Systems using Active Power Filter with DFT-based Current Reference Generator   By Tomáš KOMRSKA, Jan ZAK, Zdenek PEROUTKA	[View]   [Download]
Abstract: This contribution deals with a shunt-type active power filter designed mainly for railway applications (50-Hz and 16.7-Hz electrification systems) which is able to compensate undesired harmonic currents as well as reactive power. Its control algorithm employs an optimized DFT-based fundamental current and voltage estimator generating an accurate control reference signal. The APF configuration, the current reference generator and the APF control algorithm are discussed in detail in this paper. Theoretical conclusions are verified beside simulations also by experiments on designed laboratory prototype of rated power of 5.75 kVA.
	Repetitive control for a dynamic voltage restorer for power-quality improvement   By Pedro RONCERO SÁNCHEZ, Enrique ACHA, J.L. ORTEGA-CALDERÓN, Vicente FELIU-BATLLE, AURELIO GARCIA-CERRADA	[View]   [Download]
Abstract: This paper presents a control system based on a repetitive controller to compensate key power-quality disturbances, namely voltage sags, harmonic voltages and voltage imbalances, using a Dynamic Voltage Restorer (DVR). The control scheme deals with all three disturbances simultaneously within a specified bandwidth. The control structure contains a feed-forward term to improve the transient response and a feedback term to ensure zero error in steady-state. PSCAD/EMTDC has been used to carry out all modelling aspects of the repetitive controller and test system. Simulation results show that the control approach performs effectively and yields excellent voltage regulation. Further work is required towards a digital implementation of the controller.
	Sampled Energy Control of a Single\_Phase Shunt Active Power Filter Synthesising a Resistive Load   By Robert WATSON	[View]   [Download]
Abstract: Shunt Active Power Filters (APF’s) are becoming an important consideration for installations where a large number of non-linear loads are responsible for failure to comply with standards for harmonic distortion of the current waveform. This paper is concerned with a control strategy for a voltage-fed shunt APF. A control system is proposed that uses two sampled difference-energy components to achieve good dynamic performance to changing loads. The system uses a current error driven discrete proportional hysterisis method to inject harmonic and reactive correction currents into the load so as to remove these components from the source current. Another feature of this system is that the source current remains proportional to the source voltage so that the combined load/APF appears purely resistive.
	Shore supply for train maintenance Using a PWM inverter in bi-directional mode   By Johnny BOU SAADA	[View]   [Download]
Abstract: In the absence of an overhead line in maintenance workshops, there is a requirement to power the train from a shore supply in order to provide a DC Bus for the train inverters and battery chargers during maintenance activities. In this paper we describe a new way to supply the DC Bus, using the industrial 3 phase voltage supply, without any extra active components. With this method we respect all of the harmonic rejection criteria to the grid, while maintaining a very high power factor.
	Storage Systems Design Approach for Power Conditioning in Wind Parks   By Constantinos SOURKOUNIS	[View]   [Download]
Abstract: For technical and economical reasons, the stochastic fluctuation of wind energy density significantly limits the amount of feedable energy from wind energy converters in regions with good wind conditions. From the technical point of view the fluctuating energy offer from the wind reduces the energy quality in electrical grids. This results in voltage and frequency variations in isolated grids. Depending on the installed wind energy converter undesired high harmonics are spread throughout the connected grid. The attenuation of the mains pollution from wind energy converters or wind parks are of essential importance for a wide spread utilization of wind energy, so that it can noteworthy contribute to the energy supply. An obvious approach is the installation of dynamic energy storage systems. Thereby short term wind caused power fluctuations as well as load changes can be absorbed or smoothed on location. The necessary storage capacity is calculated by the frequency distribution of the wind gusts energy content.
	Tapping wind turbines to HVDC lines   By Inigo MARTINEZ DE ALEGRIA, Jose Luis MARTIN, Haritza CAMBLONG, Jon ANDREU, Pedro IBANEZ	[View]   [Download]
Abstract: Connection of winfarms to the main grid through an HVDC transmission system has many technological advantages that can help increase the amount of wind power connected in a system. The high cost of the power converters in HVDC systems is the main drawback that is holding back the use of HVDC in wind farms. HVDC systems are usually Point to Point connections but multi point connections of wind farms to a common HVDC cable can reduce the cost of new windframs. An alternative to conventional HVDC connection of wind farms to reduce the cost of the HVDC system is presented. The wind turbines may be directly connected to the HVDC line and the need for the costly Offshore HVDC VSC converter station is overridden.
	UNCONTROLLED RECTIFIERS FOR HVDC CONNECTION OF LARGE OFF-SHORE WIND FARMS   By Ramon BLASCO-GIMENEZ, Salvador ANYO-VILLALBA, Johel RODRIGUEZ, Francisco MORANT, Soledad BERNAL	[View]   [Download]
Abstract: Modern wind turbines allow for tight control of terminal voltage, this is particularly true for synchronous generator (SG) based wind turbines. Therefore, an integrated design of wind turbine and HVDC link control can lead to a substantial simplification of the off-shore rectifier. This paper introduces an integrated control algorithm for line commutated thyristor (LCT) based HVDC transmission line whereby the off-shore rectifier tap changer is eliminated and a cheaper and more efficient uncontrolled rectifier is used instead of a LCT-based rectifier. The presented control strategy allows for good performance during steady state and transient operation, including on-shore fault ride-through operation.
	Use of Kalman Filters for Renewable Energy Sources Isolation Transformers Current Harmonics Compensation   By Hector BELTRAN SAN SEGUNDO, Emilio PEREZ , Carlos ARIÑO, Enrique BELENGUER, Nestor APARICIO, Jaime ZABALZA, José TORRELO, Salvador SUBIELA	[View]   [Download]
Abstract: This paper is focused on the analysis of a Kalman filter performance when introduced in the current control loop of a distributed generator connection inverter. The goal is to use this kind of filter to reduce the harmonic content of the currents injected by this equipment in their point of common coupling. The study has been performed by means of simulation, using Matlab-Simulink, and by implementing the filter on a DSP in our lab. Both, simulation and experimental results, clearly demonstrate that this kind of control system can improve the response produced by the inverters. The elimination of certain well-known noisy harmonics introduced by an element such as the isolation low voltage transformer has been in this way accomplished.
	Use of participation factors and parameter sensitivities in study and improvement of low-frequency stability between electrical rail vehicle and power supply   By Steinar DANIELSEN, Olav Bjarte FOSSO, Trond TOFTEVAAG	[View]   [Download]
Abstract: Dynamical phenomena like oscillations and instability in railway power systems have come into concern in the experts’ community the recent years. In several occasions, modern advanced electrical rail vehicles have been a source for low-frequency power oscillations leading to an unstable power system due to lack of damping, and as a consequence operational problems. Traditionally the dynamical behaviour of such a power-electronic based vehicle is studied by instantaneous-value time-domain simulations. In this paper, the entire single-phase railway power supply including the vehicle is modelled together in the time-invariant rotating reference frame. Such a reference-frame transformation is common for power-system analysis and allows utilization of linearization tools as eigenvalue analysis including participation factors and parameter sensitivity analysis. These tools are here used for study and improvement of the stability of the complex railway power system. The results from the linear analysis are compared to time simulations.
	Vector Control of a 1-Phase to 3-Phase Mains Supply Extender   By Veronica BIAGINI, Paolo BOLOGNESI, Pericle ZANCHETTA	[View]   [Download]
Abstract: Mainly due to historical and convenience reasons, for power levels up to several kVA electric utilities provide power distribution typically uses 1-phase a.c. feeders, despite a 3-phase supply would be technically preferable permitting for instance to use more efficient and compact induction motors, 3- phase rectifiers providing lower output ripple etc. This paper deals with a simple converter able to extend a 1-phase mains to a 3-phase standard supply source, featuring reversibility, good power quality at both input and output sides and a less complex structure than conventional solutions. The converter topology and operation principle are recalled, as well as its main theoretical characteristics and the control strategies previously analyzed. The opportunity to employ a vector control approach and a space vector modulator is then addressed, investigating the peculiar aspects correlated to the unconventional operation of the converter. Significant results referred to both steady-state and transient conditions, obtained by a simulation model purposely developed to investigate the actual performances of the examined system, are finally reported and commented.
	Voltage Source Active Power Filter with Small Inductors and Improved Efficiency   By Perttu PARKATTI, Heikki TUUSA, Hannu SARÉN, Kosti KUUSELA, Björkman MICHAEL	[View]   [Download]
Abstract: Power losses and voltage stresses are a problem in active filters. This paper proposes a voltage-source active filter (VSAF) with an LCLC-circuit which has lower voltage stresses, smaller power losses and smaller inductors than a conventional VSAF. The method is based on the series capacitor structure used to block the fundamental supply voltage component. The structure improves the efficiency of the active harmonic filtering and saves energy. Experimental results are presented in the paper. The results show that the power losses decreased significantly and very small inductors could also be used.