Capacitor voltage feedforward decoupling control based on third harmonic injection modulation for five-level active neutral point clamped converter

摘要

For the five-level active neutral point clamped (5L-ANPC) converter, the coupling problem between the DC-link capacitor voltages and flying-capacitor (FC) voltages will increase the capacitor voltage fluctuations. The capacitor voltage fluctuations and current harmonics of the space vector pulse width modulation (SVPWM) are less than those of the sinusoidal pulse width modulation (SPWM), because the maximum linear modulation index of the SVPWM is higher than that of the SPWM. However, SVPWM has difficulty in realizing the decoupling control of the capacitor voltages, and the computation complexity of SVPWM is much higher than that of SPWM. This paper proposes a third harmonic injection modulation algorithm for the 5L-ANPC converter. The proposed algorithm injects the third harmonic into the modulation waves of SPWM, which makes the maximum linear modulation index of SPWM the same as that of SVPWM, to reduce the capacitor voltage fluctuations and current harmonics. The calculation of the third harmonic only requires a standard sorting algorithm and a simple linear operation; thus, it is easy to implement. Based on the third harmonic injection modulation algorithm, two variables are introduced to control the neutral point (NP) current and the FC current. And the two variables are used to feedforward compensate the modulation waves, realizing the decoupling control of the capacitor voltages. The proposed decoupling control method can further reduce the capacitor voltage fluctuations. Experimental results are presented to verify the validity of the proposed algorithm.