Simulation of Cascaded Multilevel inverter

In this chapter simulation process of cascaded multilevel inverter is described. Simulation of 1-ϕ Cascaded type multilevel inverter for stair case topology using MATLAB SIMULINK. A seven level inverter with three H-Bridges and input voltage ratio of three bridges is 1:1:1. Modulation index of the inverter is 0.8

Following block are used for simulation

Fig.10.1 Block used for simulation

Circuit connection in Simulink is shown in fig.10.2.

Fig.10.2 (a) Circuit connection

Fig.10.2 (b) H-Bridge connection

Controlling pulses for positive half cycle and negative half cycle are shown in fig.10.3 (a) and fig.10.3 (b) respectively. Pulse parameters of these pulses are shown in table 10.1 and table 10.2 respectively.

Fig.10.3 (a) Pulses for positive half cycle

Table 10.1 Pulse parameters for positive half cycle

Fig. 10.3(b) Pulses for negative half cycle

Table 10.2 Pulse parameters for negative half cycle

Fig.10.4 output voltage waveforms

Fig.10.5 THD of output waveforms

The THD of output voltage waveform is 10.475182. To remove further more harmonics we can add harmonic filter in the circuit. From fig 10.5 we can see that 13^th order and 17^th order harmonics are dominating harmonics so 15^th order harmonic filter can be added which can remove both 13^th and 17^th order harmonics and reduce THD.

A circuit diagram of multilevel inverter with harmonic filter is shown in fig.10.6

Fig.10.6 Circuit diagram with 15^th order filter

Fig.10.7 output of circuit with filter

Fig.10.8 THD of output waveforms

From fig.10.8 we can see that 13^th and 17^th order harmonics are totally eliminated and THD of the output waveform is 5.300176.

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