Capacitor voltage feedforward decoupling control based on third harmonic injection modulation for five-level active neut
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ORIGINAL ARTICLE
Capacitor voltage feedforward decoupling control based on third harmonic injection modulation for five‑level active neutral point clamped converter Ziling Nie1 · Weiwei Ye1 · Junjie Zhu1 · Jie Xu1 Received: 6 January 2020 / Revised: 12 August 2020 / Accepted: 23 August 2020 / Published online: 17 September 2020 © The Korean Institute of Power Electronics 2020
Abstract 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. Keywords 5L-ANPC converter · Third harmonic injection · Feedforward compensation · Decoupling control · Capacitor voltage balance
1 Introduction The 5L-ANPC three-phase converter is proposed in 2005 [1–3]. Compared with other similar five-level converters, the 5L-ANPC converter is more convenient for capacitor voltage control and has fewer passive devices and higher system efficiency [4, 5]. It has broad prospects for application in medium-voltage drive, photovoltaic generation, and medium-voltage DC grid [6–9]. Traditional modulation algorithms include SPWM and SVPWM. SPWM is divided into level-shifted PWM * Weiwei Ye [email protected] 1
National Key Laboratory of Science and Technology on Vessel Integrated Power System, Naval University of Engineering, Wuhan, China
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(LS-PWM) and phase-shifted PWM (PS-PWM). In PSPWM for the 5L-ANPC converter, only two 180° phaseshifted carrier waves are needed [10–13]. Redundant switching states are used to control the FC voltages. However, the neutral-point current will be changed in several redundant swit
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