A Low Switching Frequency High Bandwidth Current Control for Active Shunt Power Filter in Aircrafts Power Networks Milijana Odavic, Pericle Zanchetta, Mark Sumner University of Nottingham, Nottingham, UK eexmo1@nottingham.ac.uk, pericle.zanchetta@nottingham.ac.uk, mark.sumner@nottingham.ac.uk Abstract- A five-level active shunt power filter (ASF) structure with a predictive current controller is proposed in this paper for application in aircraft power systems with variable fundamental frequency (ranging from 360Hz to 800Hz). The tested ASF is capable of a high bandwidth current control with a low switching frequency being able to effectively track harmonic current reference signals up to 5.6 kHz. Analysis of the proposed ASF structure for the aircraft applications includes current tracking performance and harmonic spectrum of the output ASF voltage. A comparison of the proposed five-level topology is made with the two–level one. I. INTRODUCTION A tendency in the today aircraft industry is to achieve “more electrical aircrafts” to gain better efficiency and reduce the cost [1, 2]. The increased number of electrical loads on-board requires different power levels and therefore more power electronics converters, pushing for careful attention on the power quality issue in the aircraft power system. The use of active power filters (APF) in power systems represents the best solution, in terms of performance and effectiveness, for harmonic distortion elimination, power factor correction, balancing of loads, voltage regulation and flicker compensation [3]. The shunt APF, connected in parallel with the non-linear load, is commonly utilized to compensate for current disturbances while the series APF is utilized to compensate for voltage disturbances. The control structure of the active shunt filter (ASF) includes three key elements: the dc-link voltage control, the current control system and the method to determine the current references from the sensed currents of the harmonic producing load. The main focus of this paper is the performance of the ASF current control loop. In ASF applications, the reference for the current loop consists of harmonic components at frequency much higher than the fundamental (usually 5 th and 7 th in three-phase systems). In the specific case of this research work the ASF is employed for harmonic compensation in an aircraft power system with the fundamental frequency varying from 360 to 800 Hz. This makes the current controller design a quite challenging task since the main harmonics to cancel will be in the worst case scenario at 4 kHz and 5.6 kHz. A predictive controller [4], which incorporates a method for predicting variables two sample periods ahead of their appearance, is here employed allowing the control to work in the presence of microprocessor, and actuation delays. The proposed controller is a model-based controller and therefore the knowledge of system parameters is essential for satisfactory performance. Furthermore it introduces a minimal phase error by predicting the current reference two sampling instants ahead. This prediction is based on a polynomial extrapolation technique, designed using the Genetic Algorithm (GA) optimisation tool. Multilevel converters [5] are generally used to obtain high voltage capability, good power quality, good electromagnetic compatibility and low switching losses at the expense of to the larger number of switching devices and capacitor banks needed. Among these features the possibility of lower switching frequency operation is the most attractive for this work. The multilevel structure, chosen in this work for ASF applications in aircrafts, is a series connection of H-bridges per phase. This converter has a modular structure with a separate dc side of each module and balanced switch current. A five- level ASF structure is used in this work to obtain a low switching frequency with a high bandwidth current control loop for effective harmonics compensation in aircrafts power networks. The second section of the paper gives a small introduction about the aircraft power system specifications. The third section presents the five-level converter structure chosen for active power filtering application in aircrafts with an appropriate pulse width modulation. In the fourth and fifth sections, the overall control structure and current controller design are presented respectively. Verification of the proposed system performance is given through the simulation results in the sixth section. A few remarks concerning harmonic spectrum issues are indicated in the seventh section and finally the proposed five-level ASF structure is compared with the two-level one in the eight and last section. II. AIRCRAFT POWER SYSTEM In conventional aircrafts, the main power source to power the electrical subsystems, such as engine starting system, ignition system, passenger cabin service, lighting system etc., are aircraft engine driven AC generators [1, 2]. At present most