Abstract
In this paper, a grid-connected photovoltaic (PV) generation system is proposed with the purpose of providing support to low-voltage grids, namely through the elimination or attenuation of the grid imbalances. This compensation must consider the load types, which can be either linear or non-linear, and whether the reactive power and current harmonics generated by the non-linear loads need to be compensated in addition to the unbalanced active power. This must be well considered, since the compensation of all aspects requires oversized PV inverters. Thus, the different unbalanced compensation schemes are addressed. Several schemes for the generation of the inverter current references taking into consideration the compensation and load type are presented. For this PV generation system, a dual four-leg, two-level inverter is proposed. It provides full unbalanced compensation owing to the fourth leg of the inverter and also extends the AC voltage, which is important when this compensation is required. To control this inverter, a control scheme for the inverter that considers several compensation factors is proposed. A vector voltage modulator associated with the controller is another aspect that is addressed in the paper. This modulator considers the balance between the DC voltages of the inverters. Several compensation schemes are verified through computational tests. The results validate the effectiveness of the proposed PV generation system.
Highlights
The PV generation system was connected to a low-voltage grid with 230/400 VRMS
The proposed multilevel inverter consists of two four-leg, two-level inverters that are connected to a three-phase transformer with an open-end winding arrangement
For the control of the multilevel inverter AC currents and to balance the DC buses, a control scheme based on a voltage PI compensator, sliding mode current controller and vectorial voltage modulator was developed
Summary
One of the renewable energy sources that plays an important role is solar energy, when harnessed using photovoltaic (PV) generators. These energy generators have shown enormous growth in recent years [1]. Besides acting in the conversion from DC to AC and control of the system in grid-connected applications, the inverter can be an active grid participant. In such cases, it must be designed to support the optimized operation of the electric grid by providing ancillary services. One of the ancillary services that is starting to be considered is the compensation of the grid-unbalanced loads [3]
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