**Wojciech Sleszynski 1, Artur Cichowski <sup>1</sup> and Piotr Mysiak 2,\***


Received: 27 October 2020; Accepted: 17 November 2020; Published: 19 November 2020

**Abstract:** The reported research aims at improving the quality of three-phase rectifier supply currents. An effective method consists of adding properly formed booster voltages to the fundamental supply voltages using a series active filter. In the proposed solution, the booster voltages are generated by three single-phase systems consisting of inverters, LC filters, and single-phase transformers. The application of LC couplings ensures low emission of disturbances, but may provoke compensator stability problems. The article presents the current control system for a series active filter designed to suppress the dominant harmonics in the supply currents of an 18-pulse rectifier, without interference into fundamental current components. A proportional control is proposed in combination with integral terms implemented in the orthogonal coordinate systems, which synchronically rotate with frequencies equal to those of the harmonic components to be eliminated. The use of complex gains in integral terms allows a simple phase correction of the output signals. A description is given of the method to determine controller parameters based on the mathematical model of the control object. Sample results of experimental tests performed in steady-state and transient conditions are included to illustrate the quality of performance of the series active filter as compared to the results recorded for the rectifier alone, and for the rectifier with additional line reactor. The applied control method of active filter significantly reduces harmonic distortion of the grid current, which is particularly advantageous at nonideal supply voltage and low loads.

**Keywords:** series active power filters; multipulse converters; power conditioning; coupled reactors
