Abstract
This paper proposes discontinuous pulse width modulation (DPWM) for a grid-connected inverter system using an LCL-filter which consists of two inductors and a capacitor that is connected in parallel per phase. The modulation signal is discontinuously changed, and the harmonic voltages are generated in the wide frequency range at the output terminal of the inverter when the conventional DPWM is used. If these harmonic voltages are present in the resonance frequency band by an LCL-filter, then the resonance problem of the grid current occurs. To suppress the resonance problem, the proposed DPWM injects the sixth harmonic to the modulation signal. Therefore, in the improved DPWM, harmonic voltages at the output terminal of the inverter are sufficiently reduced because the discontinuous change of the modulation signal disappears. The proposed DPWM method is verified by a Powersim (PSIM) simulation (Powersim Inc., Rockville, MD, USA) and experiments with a 3-kW neutral-point clamped (NPC)-type grid-connected inverter system.
Highlights
There has been growing interest in renewable energy because of the depletion of natural resources and increasing environmental pollution from the use of fossil fuels and nuclear energy [1,2,3].For these reasons, the use of grid-connected inverter systems for renewable energy sources has become an important topic [4,5]
discontinuous pulse width modulation (DPWM), harmonic voltages at the output terminal of the inverter are sufficiently reduced because the discontinuous change of the modulation signal disappears
In the DPWM, many harmonic voltages are generated in the wide frequency range at the output terminal of the inverter
Summary
There has been growing interest in renewable energy because of the depletion of natural resources and increasing environmental pollution from the use of fossil fuels and nuclear energy [1,2,3]. To control the grid current sinusoidal waveform, the grid-connected filter is essentially required The aim of this filter is to attenuate the harmonic components in the switching frequency band. In the DPWM, many harmonic voltages are generated in the wide frequency range at the output terminal of the inverter. If these harmonic voltages are in the resonance frequency band, the grid current oscillates [14]. This problem adversely affects the quality of the current and increases the total harmonic distortion (THD). The proposed method injects the sixth harmonic to the modulation signal to reduce the harmonic voltages at the output terminal of the inverter. The proposed algorithm is verified by PSIM simulations and experiments using a 3-kW neutral-point clamped (NPC)-type grid-connected inverter system
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