A Filterless Single-Phase AC-AC Converter Based on Coupled Inductors with Safe-Commutation Strategy and Continuous Input Current



A novel single phase ac-ac converter with no LC input/output filters is presented in this paper. The proposed converter has all the advantages of the previous single phase impedance source ac-ac converters; it can operate in buck/boost and in-phase/out-of phase with the input voltage, that makes it appropriate for voltage sags/swells compensator without any dc storage. A coupled transformer based on T-structure is utilized to give an opportunity to access desired output voltage with various duty cycles. In this topology snubber circuit is not required, because a safe commutation strategy enables to eliminate voltage and current spikes produced by short-circuit path. In addition, the converter performs in continuous current mode, so there is no inrush current. Also, the characteristic which the output voltage reverses or maintains phase angle with the input voltage is supported well, because the input and output share the same ground. Eventually, circuit analysis, operating principles and simulation results in MATLAB/SIMULINK are presented to verify the performance of the converter.


  1. Continuous input current
  2. T-source
  3. Safe commutaion strategy
  4. Ground sharing
  5. Dynamic voltage restorer (DVR)




Fig. 1. Filterless single-phase T-source ac-ac converter



Fig. 2. Simulation results of the proposed converter in boost in-phase mode at D = 0.9, R=10 Ω and n = 2, input/output voltage, c2 voltage, output current, input current.

Fig. 3. Simulation result of the proposed converter in boost in-phase mode at D = 0.9, R=20 Ω and n = 2, output current waveform

Fig. 4. Simulation results of the proposed converter in boost in-phase mode at D = 0.9, R=10 Ω and n = 3, input/output voltage, output current, input current

Fig. 5. Simulation results of the proposed converter in buck out-of-phase mode at D = 0.2, R=10 Ω and n = 2, input/output voltage, output current


In this study, a single phase T-source ac-ac converter has been introduced. The novel topology operates in continuous current mode and low THD, with no filters in input and output. With consider of this point, some privileges rise up such as declining in size and reducing in cost of the converter. Also, output voltage enables to reverse or sustain the phase angle relevant to input voltage greatly, because of the common ground. In addition, a safe commutation strategy is usedto prevent appearance of voltage spikes and current spikes, so it leads to the converter could be designed without any snubber circuits in bidirectional switches. The presence of a coupled transformer based on T- structure in the topology gives this permission to converter that operates in a wider range of duty cycles control. Furthermore, by using of T-source in this topology, desirable voltage gain has been obtained in small conducting duration, which leads to increase efficiency and decrease losses considerably. Moreover, this converter can be applied for DVR devices with utilizing buck-boost feature to compensate various voltage sags and voltage swells. Eventually, accuracy performance and theoretical results of the converter have been verified with consequences of the simulation.


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