5-level double converter with different DC divided link voltage

This paper proposes a 5-level double converter with dividing the DC link voltage in different ratio and new pulse width modulation (PWM) technique. The 5-level double converter has five potentials (P2, P1, NPP, N1, and N2) in the DC link and they can be obtained with splitting the DC link by four capacitors (Fig.1). The NPP potential corresponds to base potential and the value is zero. In the proposed method, the ratio of P2, P1, N1, and N2 potentials is 1:2:2:1 respectively whereas the conventional method is 1:1:1:1 respectively. For a DC link voltage Vdc, P2, P1, NPP, N1, and N2 potentials are Vdc/2, Vdc/3, zero, -Vdc/3, and -Vdc/2 respectively. Otherwise, those of the conventional method are Vdc/2, Vdc/4, zero, -Vdc/4, and -Vdc/2 respectively. In the conventional method, switching signals of the inverter are generated by a space vector modulation (SVM) method. However, this modulation technique is unsuitable for high modulation index region because switching patterns of the region are less than them of the other region. Otherwise in the proposed method, more switching patterns available, and can be reduced the laps of the switching patterns. Concretely, available switching patterns of the proposed method are 97 patterns whereas 61 patterns in the conventional method. Therefore, the harmonic reduction of the output voltage in the high modulation index region can be expected. Switching signals of the 5-level rectifier are generated by instantaneous-value-compared current control method with multi band hysteresis comparators (MHCs) to supply a DC power source for inverter. In case of the proposed method, the ratio of current error and potential axis is divided in the ratio of 1:2:2:1. We confirmed the performance of the 5-level double converter by simulation. Simulation results show that the 5-level potential is stability, input phase currents can be generated sinusoidal waveform, and harmonics reduction of output voltage is possible compared with the conventional method.