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This paper presents a division-summation (D-Σ) digital controlled three-phase four-leg voltage source inverter with load impedance estimation for uninterruptible power supply applications. The D-Σ digital control developed for current tracking can accommodate wide filter inductance variation, which has been successfully adopted in grid-tied applications. This paper proposes a load impedance estimation...
This study presents design of D-Σ digital controlled hybrid-frequency inverters with LCL filter for grid-connected applications. Hybrid-frequency inverters consist of inverters with different frequencies and power ratings connected in parallel. The lower frequency inverter has higher power rating, while the higher frequency inverter has lower one. The inverters are controlled to cancel out low-frequency...
Resonant frequency of an LCL filter in grid-connected inverters decreases with increase in inductive grid impedance. It is also affected by drop in magnetic permeability of filter inductor with increase in current. This resonant frequency variation affects grid-voltage harmonic rejection and compromises stability. Hence, an improved resonant frequency based LCL filter design method is presented in...
The natural swinging filter inductance due to core's magnetic permeability can affect control stability. Conventional control methods generally adopt larger cores to avoid this issue. Division-Summation (D-Σ) digital control, on the other hand deals with the problem by including this filter inductance variation in the control law. It allows the use of much smaller core than conventional control methods...
A division-summation (D-Σ) digital control can track sinusoidal reference current in four operation modes: grid-connection, rectification, PF leading and PF lagging mode. It can overcome the limitation of abc to α-β-γ frame transformation and cover wide filter inductance variation. However, the switching sequences for the four modes are different from each other, increasing complexity of firmware...
This paper presents a division-summation (D-Σ) digital control for a three-phase transformerless bi-directional photovoltaic inverter with wide inductance variation, which can eliminate the leakage ground currents due to panel parasitic capacitance. The bi-directional inverter fulfilling grid connection and rectification with power factor correction has been implemented in the laboratory. The proposed...
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