Jürgen Häfner

Bio: Jürgen Häfner is an academic researcher from Technical University of Berlin. The author has contributed to research in topics: Active filter & AC power. The author has an hindex of 3, co-authored 5 publications receiving 605 citations.

Three-phase four-wire shunt active filter control strategies

Abstract: This paper describes a three-phase four-wire shunt active power filter using a conventional three-leg converter, without the need of power supply at DC bus Two approaches have been developed to control the active filter Both control strategies consider harmonics and zero sequence components in the voltage and current simultaneously The first one provides constant power and the second one sinusoidal current to the source, even under unbalanced voltage conditions Simulation results from a complete model of shunt active filter are presented to validate and compare the control strategies

A Shunt Active Power Filter Applied to High Voltage Distribution Lines

Abstract: The high requirement of rated power of an active power filter leads to high costs and limits the range of operation especially for high voltage applications. To overcome these problems, a combined system of a passive filter, using only one LC filter tuned to the lowest typical line current harmonic, and a shunt active power filter, sharing the filter capacitor to be decoupled from the fundamental line voltage, is proposed. These features strongly decrease the rated power of the active filter which is controlled only to suppress the harmonics of higher order and to eliminate resonance effects between the line impedance and the passive filter.

A Three-Phase Four-Wire Shunt Active Filter Employing a Conventional Three-Leg Converter

Abstract: A three-phase four-wire shunt active power filter using a conventional three-leg converter is presented. It needs no power supply at the d.c.-bus and the a.c.-neutral wire is directly connected to ...

Advanced power electronics for reducing mains pollution — active power filters and optimized utility interfaces

Abstract: Rapid advances in turn-off semiconductor elements offer new opportunities for reactive power compensation and reduction of harmonics in energy supply systems. Non-linear consumers and also solid state power electronic equipment like diode rectifiers and thyristor converters disturb the utility voltage waveform by injecting harmonic currents into the utility grid. Their need of reactive power results in higher line currents and thereby in an increase of the rated power of the supply system. Active power filters can be used to compensate the harmonic currents, to balance unbalanced systems and to provide reactive power to the load with small storage elements. Optimized utility interfaces are controlled to ensure sinusoidal input currents of the load with unity power factor. Both, the investigated active power filter as well as the optimized utility interface are based on a four-quadrant switch-mode voltage source inverter.

Fuzzy logic applied to compensation equipment in power electronics

Abstract: The reduction of mains pollution by advanced compensation equipment is one of the foremost topics in modern power electronics. Hybrid systems of active power filters and passive filters are pointed out to be an economical solution to reach this goal. The monitoring of the instantaneous powers of the line to detect the mains pollution influences the transient response of compensation equipment strongly. While in steady state the instantaneous powers are well defined, no clearly classification exists in case of transient load changes. The paper deals with the possibility to improve the dynamic performance of the power monitoring unit by fuzzy tuning and by this of the complete compensation equipment. SHUNT ACTIVE POWER FILTER Active power filters (APF) are able to compensate harmonic currents, to balance unsymmetrical three-phase systems and to provide reactive power to the load. In Fig. 1 the principle of an active shunt compensation of a general nonlinear load is given. Goal of a shunt active power filter is to shape the mains sided line current I s to be sinusoidal and in phase with the line voltage V s . Assuming a sinusoidal and symmetrical line voltage, the mains will then only provide the average part of the active power ~ of the load, while the APF delivers the instantaneous reactive power q and the alternating part of the active power of the load. The active power filter can be divided into two essential parts. A power monitoring unit (PMU) calculates online the instantaneous reference of the compensation current I~ depending on the instantaneous active and reactive power demand p + q of the load. A power electronic circuit is needed to inject the desired compensation current I c into the point of "Permission to make digital/hard copy of all or part of this material without fee is granted provided that copies are not made or distributed for profit or commercial advantage, the ACM copyright/server notice, the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery, Inc.(ACM). To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee." © 1996 ACM 0-89791-820-7 96 0002 3.50 619 common coupling at high power level. Three-phase fourquadrant switch-mode voltage source inverters QISI) are pointed out as suitable devices using high switching frequencies of several kHz. By applying an internal tolerance band current control method, the VSI will act as a controllable current source. Compensation of the instantaneous reactive power q = ~ + does theoretically not require any storage elements. Thus, no active source is needed at the DC side of the inverter, but a small rated DC capacitor as passive storage element is needed for obtaining the mode of operation of the inverter and for storing the short-term energy exchange represented by ~ . Fig. 1: Principle of an Active Shunt Compensation The instantaneous power theory introduced in [1] allows to relate the different powers to their physical meaning. With the help of a new (x-[~ two-dimensional-coordinate system for representing the voltages and currents by using the Clarke transformation (1) the instantaneous active and reactive power (2) are defined with: -4J[,,J (2> q.l-[-h3 vaJL'~J L~*qJ In general p and q can be split into average parts ~ , ~ and alternating part ~ , ~ . The~by p is equal to the conventional active power P and ~ cogesponds to the negative value of the conventional reactive power Q . The alternating parts i~ and are caused by harmonics of the load current together with the fundamental negative sequence component in case of unsymmetrical load conditions.

Active power filters: a review

Abstract: There has been considerable interest in the development and applications of active filters because of the increasing concern over power quality, at both distribution and consumer levels, and the need to control reactive power and voltage stability at transmission levels. The existing approaches are classified and assessed to provide a framework of references for both researchers in this field and for generators, suppliers and consumers of electrical power who are, or may be, concerned about the problems associated with power quality and are considering installing active filters for their particular sets of problems.

An improved control algorithm of shunt active filter for voltage regulation, harmonic elimination, power-factor correction, and balancing of nonlinear loads

Abstract: This paper deals with an implementation of a new control algorithm for a three-phase shunt active filter to regulate load terminal voltage, eliminate harmonics, correct supply power-factor, and balance the nonlinear unbalanced loads. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a DC bus capacitor is used as an active filter (AF). The control algorithm of the AF uses two closed loop PI controllers. The DC bus voltage of the AF and three-phase supply voltages are used as feedback signals in the PI controllers. The control algorithm of the AF provides three-phase reference supply currents. A carrier wave pulse width modulation (PWM) current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBTs of the AF. Test results are presented and discussed to demonstrate the voltage regulation, harmonic elimination, power-factor correction and load balancing capabilities of the AF system.

An universal active power line conditioner

Abstract: The power circuit of a general active power line conditioner (APLC) is based on series and shunt power converters that share a single DC link. In the present paper, a generic control concept for these series and shunt converters is proposed. It is based on the instantaneous real and imaginary power theory. In fact, the resulting equipment deals with the custom power and FACTS concepts. This equipment incorporates not only the compensation functions at the fundamental frequency like a unified power flow controller (UPFC), but also provides active harmonic mitigation capabilities. For these reasons, the compensator proposed here is called the universal active power line conditioner (UPLC). Simulation and experimental results are presented to confirm that the new approach has better performance than those obtained by controllers based on traditional concepts of active and reactive power.

Multiobjective Battery Storage to Improve PV Integration in Residential Distribution Grids

Abstract: This paper investigates the potential of using battery energy storage systems in the public low-voltage distribution grid, to defer upgrades needed to increase the penetration of photovoltaics (PV). A multiobjective optimization method is proposed to visualize the trade-offs between three objective functions: voltage regulation, peak power reduction, and annual cost. The method is applied to a near-future scenario, based on a real residential feeder. The results provide insight into the dimensioning and the required specifications of the battery and the inverter. It is found that an inverter without batteries already achieves part of the objectives. Therefore, the added value of batteries to an inverter is discussed. Furthermore, a comparison between lithium-ion and lead-acid battery technologies is presented.

Improved Active Power Filter Performance for Renewable Power Generation Systems

Abstract: An active power filter implemented with a four-leg voltage-source inverter using a predictive control scheme is presented. The use of a four-leg voltage-source inverter allows the compensation of current harmonic components, as well as unbalanced current generated by single-phase nonlinear loads. A detailed yet simple mathematical model of the active power filter, including the effect of the equivalent power system impedance, is derived and used to design the predictive control algorithm. The compensation performance of the proposed active power filter and the associated control scheme under steady state and transient operating conditions is demonstrated through simulations and experimental results.