Fast Sensor-Less Voltage Balancing and Capacitor Size Reduction in PUC5 Converter Using Novel Modulation Method

ABSTRACT:

 This paper proposes a novel sensor-less switching method based on logic gates for five-level packed U-cell (PUC5) converter. It comprises only two level-shifted triangular carriers and logic gates. Hence, the number of triangular carriers is halved and the switching states table is eliminated, which cause remarkable reduction in complexity of the proposed modulation method. Moreover, employing the proposed sensor-less switching method leads to decrease in the PUC5 capacitor value by factor of carrier ratio, fast self-balancing of the PUC5 capacitor voltage, and halving the output LC filter inductor and capacitor values in stand-alone mode as well as the grid link inductor value in grid connected mode. In addition, the PUC5 converter start-up transient time is considerably decreased and the first switching harmonic cluster frequency is doubled, which lead to notable improvement of steady-state and dynamic performance of the PUC5 converter. The proposed sensor-less switching method has been implemented in both stand-alone and grid-connected operating modes of PUC5 converter. Provided simulation and experimental results verify the feasibility and effectiveness of the proposed sensor-less switching method as well as its improved dynamic and steady state performances in both stand-alone and grid-connected modes.

KEYWORDS:

 

1.      Capacitor size reduction

2.      Logic gate based modulation method

3.      Multilevel inverter

4.      Packed U-cell (PUC)

5.      Sensor-less control

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:  

In this paper, a novel sensor-less switching method based on logic gates was proposed for PUC5 converter. It comprises only two level shifted triangular carriers and logic form equations and does not have switching states table. Hence, the proposed method does not compel complex calculations and can be easily implemented on low-cost microcontrollers. By utilizing the proposed sensor-less modulation method, the charging and discharging of capacitor is balanced in each switching period, which causes fast self-balancing of the PUC5 capacitor voltage. Moreover, employing the proposed sensor-less switching method leads to decrease the PUC5 capacitor value by factor of carrier ratio ( 0 SW C F R F = ), and halving the output LC filter inductor and capacitor sizes in stand-alone mode as well as the grid link inductor size in gridconnected mode. In addition, the PUC5 converter start-up transient time is considerably decreased and the first switching harmonic cluster frequency is doubled, which lead to notable improvement of steady-state and dynamic performance of PUC5 converter. The proposed sensor-less switching method has been evaluated for both stand-alone and grid-connected modes. An external current controller has been used to control the injected active and reactive power to the grid. Provided simulation and experimental results for stand-alone and gridconnected gridconnected modes verify the feasibility and effectiveness of the proposed sensor-less switching method as well as its improved dynamic and steady state performance.

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