Simple Sensorless Active Damping Solution for Three-Phase PWM Rectifier with LCL Filter Mariusz Malinowski * , Marian .P. Kazmierkowski ** , Wojciech Szczygiel, Warsaw University of Technology, Institute of Control & Industrial Electronics, Warsaw, Poland * malin@isep.pw.edu.pl , ** mpk@isep.pw.edu.pl , Steffen Bernet Technical University of Berlin, Institute of Energy and Automation Technology, Berlin, Germany Steffen.Bernet@TU-Berlin.de Abstract—Three-phase PWM (active) rectifiers are connected to the line power through inductance or LCL filter. LCL filter is more effective (better attenuates switching harmonics), however such solution causes stability problems. In order to assure stable operation either a damping resistor or active damping algorithm has to be used. However, extra resistor causes additional losses and active damping algorithm usually needs extra sensors. Therefore, this paper shows simulation and experimental results of a simple AC voltage sensorless active damping solution suitable for industrial application. Index Terms — Active damping, control of three-phase PWM rectifier, LCL filter. List of Symbols x - complex vector f - frequency t –time p, q – instantaneous active and reactive power u(V), i –voltage and current R, C, L – resistance, capacitance and inductance D – duty cycles of pulse width modulator S – switching states of converter Subscripts and Superscripts ..a, ..b, ..c - phases of three-phase system ..d, ..q - direct and quadrature component ..α, ..β, - alpha, beta components and zero sequence component ..* – estimated ..res – resonance ..sw – switching ..S – PWM converter ..L, ..C – inductor, capacitor ..ref – reference ..dc – dc link I. INTRODUCTION Main part of electrical energy is converted by power electronic devices e.g. diode and thyristor rectifiers, what became problem due to nonlinear characteristic of those systems. It brings undesired effects as: electromagnetic interferences as well as increased losses in transmission lines and transformers. Moreover, harmonics generated by converters are limited by standards (IEEE 519-1992, IEC 61000-3-2 / IEC 61000-3-4). One of solution to avoid mentioned problem is application of more expensive and more complicated PWM (active) rectifier, which has advantages as: bidirectional power flow, nearly sinusoidal input current and regulation of input power factor to unity. Reduction of the current harmonics around switching frequency and multiplication of switching frequency is important point to get high performance PWM rectifier, which fulfills standards (IEEE 519-1992, IEC 61000-3-2 / IEC 61000-3-4). Large value of input inductance allow achieving this goal, however, it reduces dynamics and operation range of PWM rectifier [7]. Therefore, simple inductance is substituted by, third order low-pass LCL filter [2, 8] (Fig. 1). In this solution the current ripple attenuation is very effective even for small inductance size, because capacitor impedance is inversely proportional to frequency of current. Nevertheless, LCL can brings even undesired resonance effect (stability problems), caused by zero impedance for some higher order harmonics of current. Unstable system can be stabilized using a damping resistor, so called passive damping. This solution despite of advantages such as simplicity and reliability, due to which it is widely used in industry, has several drawbacks: increase of losses, decrease of efficiency. Therefore, nowadays a tendency to replace passive with active damping (AD) may be observed. AD is implemented by modification of control algorithm which stabilizes the system without increasing losses. Basic idea may be explained easily in frequency domain (Fig. 2). Addition of active damping algorithm introduces a negative peak, that compensates for the positive one caused by presence of LCL filter [2]. AD solutions presented in the past have some drawbacks from practical (industrial) point of view. A method proposed by Pekik Argo Dahono, based on a so-called ‘Virtual Resistor’ [6] requires extra capacitor current sensor. Next, method proposed by V. Blasko et al. based on lead-lag element needs feedback from filter-capacitor voltage [5]. The method proposed by Marco Liserre et al. in [4] has no additional sensors, but genetic algorithm used to tune system, complicates final control algorithm. Fig.1 Equivalent circuit of three-phase PWM rectifier with LCL filter 987 0-7803-9252-3/05/$20.00 ©2005 IEEE Authorized licensed use limited to: UNIVERSIDADE FEDERAL DE MINAS GERAIS. Downloaded on February 8, 2009 at 18:04 from IEEE Xplore. Restrictions apply.