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.

The paper presents a proposal of the multi-pulse AC/DC converter for providing supply for multilevel inverters and considerably reducing the line current distortion factor. It can be applied as a suitable source of DC voltage and is convenient to supply such inverters that need three or more voltage terminals to supply all sections of the inverter. The converter in question works as a multi-pulse rectifier supplying a three-level NPC (Neutral Point Clamped) inverter. The load introduced by the inverter is simulated as an impedance depended on a selected inverter state. All possible states are determined by using a set of three digits: 0, 1, 2. The sourcing converter is constructed from diode bridge rectifiers connected in parallel as well as the system of magnetically coupled reactors. The reactors are used to shift subsequent line voltages so that they create a multiphase voltage system supplying component rectifiers. The article presents two alternative rectifiers: A 12-pulse diode rectifier using one magnetically coupled reactor unit 3CRλ, and a 24-pulse one using three 3CRλ units. Simulation and experimental tests have been executed and selected results included. Conclusion and discussion are added.

This paper describes a mathematical model of the AC/DC converter. The analytic expressions define fundamental physical variables of the converter and their relations: phase current and voltage, shift angle between these quantities, power factor, and supply voltage U_D. The mains voltage is defined as a digitalized sine wave while the current’s wave takes the form of a line segment defined in an appropriate time interval. The model permits the description of two modes of operation: inverter and rectifier. The assumed control method of the converter depends on the successive switching of selected vectors. They are qualified according to the principle of the lowest error between the reference and measured phase current value. The control method is realized by using hysteresis algorithms. Five different algorithm solutions and comparative results are implemented. Several examples of current, voltage, and vectors taken during the simulation and experimental works are executed.

This paper presents a passive concentrator for single-phase inverters with a three-phase output, which uses magnetically coupled reactors. Due to the development of renewable energy systems, the proposed systems may enable the easier integration of converters in the form of inverters with the power system. Two variants of cooperation of the concentrator with single-phase voltage inverters were considered. The first variant proposed a system topology in which three single-phase full-bridge inverters were connected to the concentrator, while the other variant proposed six half-bridge inverters. A control system of the inverters that does not use PWM was developed. A common star point was created for the supply voltages in the form of a capacitive divider covering all the inverters. An analysis of the concentrator system was presented, taking into account the cooperation with inverters. The overall power of the TDSλ system was defined and the relationship for its determination was given. Simulation studies were described, presenting the obtained voltage and current waveforms. The impact of changing the supply voltage of the inverters on the operation of the concentrator and the shape of the output voltages was assessed. The proposed systems allow you to connect 3 or 6 single-phase inverters. The use of magnetically coupled reactors enables the use of a magnetic system of lower power and size. The described concentrators enable the generation of multi-level three-phase output voltage with a low THD content.

The paper presents a proposal of the multi-pulse AC/DC converter providing supply for multilevel inverters. The presented solution can be applied to three-level NPC inverters. The converter is constructed from diode bridge rectifiers connected parallel as well as the system of coupled reactors. The reactors are used to shift subsequent line voltages so that they create a multiphase voltage system supplying component rectifiers. This design permits to block higher current harmonics what leads to considerable reduction of the current distortion factor and to improving the compatibility of the system.

W pracy przedstawiono pasywny koncentrator dla falowników jednofazowych z wyjściem trójfazowym, który wykorzystuje dławiki sprzężone magnetycznie. Rozważono dwa warianty współpracy koncentratora z jednofazowymi falownikami napięcia. W pierwszym wariancie zaproponowano topologię układu, w której do koncentratora podłączono trzy jednofazowe falowniki pełnomostowe, natomiast w drugim wariancie sześć falowników półmostkowych. Opracowano system sterowania falownikami nie wykorzystujący modulacji PWM. Dla napięć zasilających utworzono wspólny punkt gwiazdowy w postaci dzielnika pojemnościowego obejmującego wszystkie falowniki. Opisano badania symulacyjne, w których przedstawiono uzyskane przebiegi napięć i prądów oraz oceniono wpływ zmiany napięcia zasilania falowników na pracę koncentratora i kształt napięć wyjściowych.