Dynamic Voltage Restorer Using Switching Cell Structured Multilevel AC-AC Converter

IEEE Transactions on Power Electronics, 2016


Dynamic voltage restorer (DVR) technology has become a mature power quality product. In high-power applications, DVR using a multilevel converter is commonly used. However, DVR using a multilevel direct pulse width modulation (PWM) ac-ac converter has not been well studied. This paper presents a new DVR topology using a cascaded multilevel direct PWM ac-ac converter. In the proposed scheme, the unit cell of the multilevel converter consists of a single-phase PWM ac-ac converter using switching cell (SC) structure with coupled inductors. Therefore, the multilevel converter can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed DVR. This improves the reliability of the DVR system. The output voltage levels of the multilevel converter increase with the number of cascaded unit cells, and a high ac output voltage is obtained by using low-voltage-rating switching devices. Furthermore, a phase-shifted PWM technique is applied to significantly reduce the size of the output filter inductor. A 1-kW prototype of single-phase DVR is developed, and its performance is experimentally verified. Finally, the simulation results are shown for a three-phase DVR system.



  1. Commutation problem
  2. coupled inductor
  3. direct PWM AC-AC converter
  4. dynamic voltage restorer (DVR)
  5. multilevel converter
  6. pulse width modulation (PWM)
  7. switching cell (SC)





Fig. 1. Three-phase DVR systems using VSI [2]. (a) DVR with energy storage. (b) DVR with no energy storage.




Fig. 2. Simulated waveforms of the three-phase DVR ( voa=vob=voc=220 Vrms,Po=3kW, )



In this paper, a new DVR system, employing the proposed cascaded multilevel direct PWM ac-ac converter, was presented. Compared with the conventional DVR topologies using the VSI, the proposed scheme has the advantages of fewer power stages, higher efficiency, and the elimination of bulky dc-link capacitor. In addition, unlike the existing DVR with the direct PWM ac-ac converter, the proposed DVR ensures stable operation because the proposed cascaded multilevel ac-ac converter has the following unique advantages over the conventional ac-ac converters.

  • It is immune to EMI noise because the switching devices are not damaged by the EMI noise’s misgating on- or off.
  • The commutation problem found in the conventional ac-ac converters can be effectively eliminated without using either dedicated soft commutation strategy or lossy RC snubber circuits.
  • It operates properly even with highly distorted input voltage, which is impossible with the conventional approach using soft commutation strategy.

Furthermore, the proposed multilevel ac-ac converter can obtain high ac output voltage with low-voltage-rating switching devices by cascading unit cells. The equivalent output frequency of the multilevel converter is increased by using a phase-shifted PWM technique, which reduces the size of the output LC filter. The performance of the proposed DVR is successfully verified by using a 1-kW prototype. Finally, a three-phase DVR system using the proposed scheme is verified through simulation.



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A Novel High StepUp DCDC Converter Based on Integrating Coupled Inductor and Switched-Capacitor Techniques for Renewable Energy Applications


In this paper, a novel high step-up dc/dc converter is presented for renewable energy applications. The suggested structure consists of a coupled inductor and two voltage multiplier cells, in order to obtain high step-up voltage gain. In addition, two capacitors are charged during the switch-off period, using the energy stored in the coupled inductor which increases the voltage transfer gain. The energy stored in the leakage inductance is recycled with the use of a passive clamp circuit. The voltage stress on the main power switch is also reduced in the proposed topology. Therefore, a main power switch with low resistance RDS(ON) can be used to reduce the conduction losses. The operation principle and the steady-state analyses are discussed thoroughly. To verify the performance of the presented converter, a 300-W laboratory prototype circuit is implemented. The results validate the theoretical analyses and the practicability of the presented high step-up converter.


Coupled inductor, DC/DC converters, High step-up, Switched capacitor.




Fig. 1. Circuit configuration of the presented high-step-up converter.


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Fig. 2. Simulation results under load 300 W.


This paper presents a new high-step-up dc/dc converter for renewable energy applications. The suggested converter is suitable for DG systems based on renewable energy sources, which require high-step-up voltage transfer gain. The energy stored in the leakage inductance is recycled to improve the performance of the presented converter. Furthermore, voltage stress on the main power switch is reduced. Therefore, a switch with a low on-state resistance can be chosen. The steady-state operation of the converter has been analyzed in detail. Also, the boundary condition has been obtained. Finally, a hardware prototype is implemented which converts the 40-V input voltage into 400-V output voltage. The results prove the feasibility of the presented converter.


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