This paper presents a three-phase three-wire shunt active power filtering system based on two level voltage source inverter which is intended to compensate both current harmonic distortion and reactive power under nonideal voltage conditions. The concepts of the p-q theory are used to calculate the reference compensating current according to the compensation strategy. An improvement in an existing phase-locked loop circuit is proposed to handle the shape of the small amount of additional current needed to cover the power system losses. In the dc-voltage loop, an optimal set point value which minimizes the harmonic distortion of the supply current and depends on power to be compensated is also proposed. Digital signal processor based implementation of the whole control system is described with details on the developed experimental platform dSPACE DS1103 for rapid prototyping. Experimental results obtained from a 15 kVA laboratory setup verify the effectiveness of the active filtering system.

This study is focused on the topical issue of increasing the energy efficiency in DC railway systems, in the context of global concerns for reducing the CO₂ emissions by minimizing the energy consumption and energy loss. The main achievements in this complex issue are synthesized and discussed in a comprehensive review, emphasizing the implementation and application of the existing solutions on concrete case studies. Thus, all specific subtopics related to the energy efficiency are covered, starting with power quality conditioning and continuing with the recovery of braking energy, of which a large part is lost in the classic DC-traction substations. The solutions of onboard and wayside storage systems for the braking energy are discussed and compared, and practical examples are given. Then, the achievements in transforming the existing DC-traction substations in reversible substations with capabilities of power quality improvement are systematically reviewed by illustrating the main results of recent research on this topic. They include the equipment available on the market and solutions validated through implementations on experimental models. Through the results of this extensive review, useful reference and support are provided for the research and development focused on energy efficient traction systems.

This paper concentrates on the LCL filter with damping resistance intended to connect the shunt active power filter of an active dc-traction substation to the point of common coupling with the transmission grid. In order to find design conditions and conceive a design algorithm, attention is directed to the transfer functions related to currents and the associated frequency response. The mathematical foundation of the design method is based on meeting the requirements related to the significant attenuation of the high-frequency switching current, concurrently with the unalterated flow of the current that needs to be compensated by active filtering. It is pointed out that there are practical limitations and a compromise must be made between the two requirements. To quantify the extent to which the harmonics to be compensated are influenced by imposing the magnitude response at both highest harmonic frequency to be compensated and switching frequency, a performance indicator is defined. As an additional design criterion, the damping power losses are taken into consideration. The validity and effectiveness of the proposed method are proved by simulation results and experimental tests on a laboratory test bench at small scale reproducing the specific conditions of a dc-traction substation with six-pulse diode rectifier.

This paper is focused on the optimal design of the controllers in an active filtering and regeneration system for DC railway traction substation. The control algorithm of the system is based on the indirect current control method and uses two closed loops with PI controllers: an outer one for the DC voltage control and the other for the grid current control. In order to perform the energy regeneration function during the braking process, the filtering and regeneration system is connected to the power grid by a regeneration transformer. Thus, comparative with the direct coupling and direct current control technique, the transfer functions of the system are different. The DC voltage controller is tuned in accordance with the Modulus Optimum criterion and the grid current controller is tuned by the Symmetrical Optimum criterion. In order to verify the operation of the system and assess its performance, detailed computer simulation studies were conducted using the Matlab/Simulink package. The practical case of the 12-pulse parallel rectifier in the traction substation is taken into consideration. The simulation results are presented to prove the validity of the proposed procedure of the controllers' design.

This paper is concerned with the possibilities of transformation the DC traction substations with uncontrolled rectifiers into active substation, being able to ensure both the braking energy recovery and active filtering function. There are a lot of approaches on the management of regenerative braking energy, most of them based on energy storage systems or the concept of reversible substation. Few references refer to the addition of complementary functions, such as harmonic filtering, and involve the adoption of specific structures without further argumentation. In this paper, the intention is to analyze and find argumentations on the possibilities of coupling a three-phase active power filter based on voltage source inverter topology in the power structure of a DC traction substation. The most used types of uncontrolled rectifiers, i.e. the three-phase bridge scheme and both 12-pulse parallel and series structures are taken into consideration. Based on correlation between the DC-line and AC-line voltages, it is shown that the active power filter can be connected directly in the secondary of the existing traction transformer only in the case of 12-pulse series rectifier. A dedicated recovery transformer is required for the other two schemes of rectifiers and some considerations and results on the compensating power and correlation between the active filtering performance and the voltage in the recovery transformer primary are presented.

The paper is focused on the presentation of the different theories of powers and current decomposition methods in the compensating current calculation for three-phase three-wire shunt active filtering systems. The decomposition methods are grouped into two categories, depending on the type of coordinate system used in the processing measurements involved in calculations. The former is based on the phase coordinates system and includes: the theory of Fryze, the theory of Fryze-Buchholz-Depenbrock, the so-called generalized theories of instantaneous reactive and non-active powers, the Currents' Physical Components Theory (CPC) and the Conservative Power Theory (CPT). The latter refers to the orthogonal reference frame-based approaches such as the p-q theory and id-iq method. The applicability of each theoretical approach in the control of a shunt active power filter was analyzed. A summary highlighting the applicability under non-sinusoidal voltage and the main performance of each method is performed. Next, our platform for testing the control strategies of shunt power filters, based on DSP DS1103 system, is presented. An implementation on a dSpace 1103 DSP system of the theories presented above and some experimental results are given in the second part of the paper.