control strategy for hybrid power filter to compensate unbalanced
10
Control strategy for hybrid power filter to compensate unbalanced and non-linear, three-phase loads S. P. Litrán, P. Salmerón, J. R. Vázquez, R. S. Herrera, A. Pérez ESCUELA POLITÉCNICA SUPERIOR. UNIVERSITY OF HUELVA Electrical Engineering Department, Ctra. de Palos de la Frontera s/n Palos de la Frontera, Huelva, Spain Tel.: +034– 959 21 75 85 Fax: +034 – 959 21 73 04 E-Mail: [email protected]; [email protected]; [email protected]; reyes.sanchez@[email protected]; [email protected]URL: http://www.uhu.es Acknowledgements This work is part of the projects "A new technique to reduce the harmonic distortion in electrical systems by means of equipment of active compensation", ref. DPI2004-03501, sponsored by the “Comisión Interministerial de Ciencia y Tecnología, CICYT, del Ministerio de Ciencia y Tecnología” of Spain, and “Design and implementation of a new equipment of active compensation with series connection for the improvement of the electrical waveform quality”, ref. P06-TEP-02354, sponsored by the “Consejería de Innovación, Ciencia y Empresa de la Junta de Andalucía”, Spain. Keywords Active power filters, harmonics, instantaneous reactive power, power quality, hybrid filters 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. Introduction Many social and economic activities depend on electrical energy quality and its efficiency. Both industrial and commercial users are interested in guaranteeing the signal quality which feed their electric systems, therefore, the mitigation of the current harmonics or voltage harmonics generate by the load is necessary. Traditionally, a passive LC power filter is used to eliminate current harmonics when it is connected in parallel with the load [1]. This compensation equipment has some drawbacks [2-4], because of which, the passive filter cannot provide a complete solution. Shunt active power filter, series active power filter and combined systems with passive filter and active filter have been proposed to improve the behavior of passive filters [5-16]. A configuration with an active filter connected in series to the source and passive filter in parallel to the load (Fig. 1) is analyzed in this work [11-14]. In this topology, the shunt passive filter suppresses the prevalent harmonics currents produced by the load, while the active filter connected in series with the source acts as a “harmonic isolator” between the source and the load, besides it compensates the reactive power and balances asymmetrical loads. The used control strategy is based on the instantaneous power theory [17-20]. The active power filter designed consists of a three-phase PWM (pulse With Modulation) voltage source inverter (VSI), which is connected in series with the ac source impedance and load, through three single phase CONTROL STRATEGY FOR HYBRID POWER FILTER TO COMPENSATE UNBALANCED AND NON-LINEAR THREE-PHASE LOADS LITRAN Salvador P. EPE 2009 - Barcelona ISBN: 9789075815009 P.1
