Field Results on Developed Three-Phase Four-Wire Shunt Active Power Filters J. G. Pinto, Pedro Neves, D. Gonçalves, João L. Afonso Industrial Electronics Department University of Minho Guimarães, Portugal Email: {gpinto|pneves|dgoncalves|jla}@dei.uminho.pt Abstract-This paper presents three-phase four-wire Shunt Active Power Filters with ability to compensate current harmonics, power factor, and current unbalance. The power stage of the Active Power Filters is based on a two-level four-leg inverter. The switching technique is based on an optimized periodic sampling strategy, and the digital controller uses the Theory of Instantaneous Reactive Power (p-q Theory) expanded for three- phase four-wire systems. The presented Active Power Filters were successfully demonstrated in four different facilities. The presented experimental results show the performance of the Active Power Filters in operation with very different load profiles. I. INTRODUCTION The increasing use of rectifiers, thyristor power converters, arc furnaces, switching power supplies and other non linear loads is known to cause serious problems in electric power systems [1]. These problems can be partially solved with the use of passive filters, however, this kind of filtering cannot adapt to variations of the loads, and they also can produce undesired resonances [2]. One solution to avoid these problems is the Shunt Active Power Filter. These devices work as current sources, connected in parallel with the electric grid, and they are capable of providing the harmonics and the reactive power required by the loads [3]. Three-phase four-wire Shunt Active Power Filters are also capable of compensating unbalance and zero sequence currents, minimizing the neutral current [4]. In this way, the mains only supply the fundamental, balanced currents with a unitary power factor, avoiding voltage distortion and reducing power losses in the transmission lines. This paper appears in sequence of the work developed at the Energy and Power Electronics Laboratory of the University of Minho (Portugal), which had as main objective to develop prototypes of Shunt Active Power Filters to be used to demonstrate the applicability and advantages of this kind of devices in real facilities. With the help of low cost Power Quality Monitors (also developed at University of Minho [5]), various electrical power plants were monitorized. Based in the data collected with the monitorizations, four installations were chosen to exhibit the operation of the Active Power Filters. To show the major advantages and the ability of Active Power Filters to compensate any type of load disturbance, the selected facilities have very different characteristics. The first facility selected is in a large textile industry, and consists in a electrical switchboard that feeds a bulky machine for cloth whitening, comprising many variable speed drivers. The second chosen installation is the switchboard of a computational center. The third place consists in the electrical switchboard of a clinical analyses laboratory, in a hospital. The fourth site is the main electrical switchboard of a medical drugs distribution warehouse. A summary involving the major topics of this paper is described as follows. The developed Active Power Filters configuration, and a set of equations describing the control theory based on the Instantaneous Reactive Power theory for three-phase four-wire systems are presented in Section II. Aspects related to the construction of the Active Power Filter prototypes are detailed in Section III. In Section IV experimental results are presented and analyzed. Finally, conclusions and suggestions for further works are presented in Section V. II. ACTIVE POWER FILTER CONFIGURATION The power stage of the developed Shunt Active Power Filters is composed by a standard two-level, four-leg Voltage Source Inverter (VSI) that uses eight IGBTs and an electrolytic capacitor in the DC side. Fig. 1 shows the block diagram of the three-phase four-wire Shunt Active Power Filter. The inductors (L) are used to connect the inverter to the electric grid. The controller requires the three phase to neutral system voltages (v a , v b , v c ), the DC link voltage (V dc ), the four load currents (i La , i Lb , i Lc , i Ln ), and the four inverter currents (i fa , i fb , i fc , i fn ). When the Shunt Active Power Filter is connected, the source currents (i Sa , i Sb , i Sc ) become balanced and sinusoidal, and the neutral source current (i Sn ) becomes practically zero. The control strategy is based on the Theory of the Instantaneous Reactive Power (p-q theory) introduced by Akagi et al. [6] and expanded to three-phase four-wire systems by Aredes et al. [7]. It applies an algebraic transformation (Clarke transform) of the three-phase system voltages and load currents in the a-b-c coordinates to the Į-ȕ-0 coordinates. After the transformation, the p-q theory components are achieved by the expressions (1-3), where p is the instantaneous real power, q is the instantaneous imaginary power (by definition) and p 0 is the instantaneous zero- sequence power. 978-1-4244-4649-0/09/$25.00 ©2009 IEEE 480 J. G. Pinto, Pedro Neves, D. Gonçalves, João L. Afonso, “Field Results on Developed Three-Phase Four-Wire Shunt Active Power Filters”, IECON 2009 - The 35th Annual Conference of the IEEE Industrial Electronics Society, 3-5 November, Porto, Portugal.