Abstract
Unbalanced loads cause the imbalance of the grid current and the resulting imbalance of the grid voltage when the imbalance rate of the grid current increases considerably. To cope with this problem flexibly at low cost, we modify the circuit structure from previously installed Δ-Y transformer 3-phase 3-leg inverter to split dc-link capacitor 3-leg inverter eliminating the transformer. And then we propose two kinds of compensation algorithms for balancing the grid current that can basically utilize a preinstalled control board. It is divided into reactive compensation, where dc-link of the inverter does not supply effective power to the grid but compensates for the imbalance of grid current, and effective compensation, where dc-link of the inverter supplies effective power to the grid for compensating the unbalanced grid current. We design an additional power calculator board to obtain power information, and apply it to a 10kW prototype, and then verify its validity through PSIM simulation and experiments.
Highlights
In 3-phase 3-wire structures, voltage imbalance cannot be avoidable as an unbalanced current when load imbalance occurs [1]–[8]
For split dc-link capacitor 3-leg inverter modifiable from the preinstalled -Y transformer 3-leg inverter and the control system, we propose two kinds of compensation algorithms that can improve the imbalance rate of the grid current using a power calculator
The split dc-link capacitor 3-leg inverter requires large capacitors to minimize voltage imbalance due to the unbalanced current flowing through the mid-point of the split dc link capacitors
Summary
In 3-phase 3-wire structures, voltage imbalance cannot be avoidable as an unbalanced current when load imbalance occurs [1]–[8]. The imbalance rate is increasing significantly due to various single-phase loads or nonlinear loads This can cause a number of problems on the load or the grid, such as a drop in the equipment’s output power and an increase in losses, due to excessive current flow to the neutral line [9]–[11]. Three single-phase H-bridges coupled to the loads with an isolation transformer was introduced for 4-wire active power filtering [15] It needs lower dc-link voltage, which is a half as compared to split dc-link capacitor 3-leg inverter. For split dc-link capacitor 3-leg inverter modifiable from the preinstalled -Y transformer 3-leg inverter and the control system, we propose two kinds of compensation algorithms that can improve the imbalance rate of the grid current using a power calculator. To verify the validity and performance of the proposed approach, we implement PSIM simulations and experiments based on 10kW prototype
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