Diode clamp five-level converter modulation method
The traditional converter has a high voltage change rate and common-mode voltage, and the waveform harmonic content is large, which makes the design of the output filter complicated. Among them, diode clamp five-level inverter has appeared in various researches. Figure 1 shows the bridge arm structure of a diode-clamped five-level converter. where the voltage divider capacitance C1=C2=C3=C4, so UC1=UC2=UC3=UC4; Each bridge arm has 8 switching devices VT1~VT8 in series, and every 4 switching devices are in the same state of conduction or shutdown, among which (VT1, VT5), (VT2, VT6), (VT3, VT7), (VT4, VT8) are complementary switching pairs, that is, when one of the switches is turned on, the other must be turned off; Vice versa.
Figure 1 Bridge arm structure of a diode clamp five-level converter
The relationship between the output voltage of the five-level converter and the switching state is shown in the following table:
The diode clamping five-level converter uses four sawtooth carriers with the same frequency fc and the same peak-to-peak Uc for each phase compared to a sine wave with a frequency fm and an amplitude of Um. This is shown in Figure 2. At the moment when the sine wave and the sawtooth wave intersect, if the amplitude of the modulated wave is greater than the amplitude of a certain sawtooth wave, the corresponding switching device is turned on; Otherwise, the device is turned off.
Simulink simulation of a diode clamp five-level converter
In Simulink, the following diode clamp five-level converter circuit is built:
Through the above modulation method, the output line voltage waveform of the module obtained is as follows:
The resulting filtered pre-phase voltage and filtered line voltage are shown in the figure below: