This paper presents a single-stage three-level Neutral Point Clamped (NPC) inverter for connection to the electrical power grid, with integrated Maximum Power Point Tracking (MPPT) algorithm to extract the maximum power available from solar photovoltaic (PV) panels. This single-stage topology is more compact than the traditional topology, it was chosen because with the proper control strategy. It is suitable to connect the PV panels to the power grid.
The paper describes the design of a 5 kW NPC inverter for the interface of PV panels with the power grid, presenting the circuit parameters and the description of the control algorithms. A phase locked loop control is used to connect the inverter into the grid. Then, a proposed DC Link voltage control to regulate the input voltage of the inverter. Although an MPPT algorithm was used to optimize the energy extraction and the system efficiency. Inverter Output Current control to produce an output current (current injected in the power grid) with low Total Harmonic Distortion (THD) implemented in a DSP. Simulation and experimental results verify the correct operation of the proposed system, even with fluctuations in the solar radiation.
- Photovoltaic System
- Maximum Power Point Tracking (MPPT)
- Neutral Point Clamped (NPC) Inverter
- Phase-Locked Loop (PLL)
Figure 1. Block diagram of the NPC converter control system.
EXPECTED SIMULATION RESULTS:
Figure 2. Block diagram of the E-PLL.
Figure 3. Startup of the proposed system with maximum solar radiation: (a)
PV current (ipanels); (b) PV panels voltage (vpanels);
(c) PV panels power (ppanels).
Figure 4. Operation with fluctuations in the solar radiation, from1000 W/m² to
800 W/m² and to 600 W/m: (a) Maximum theoretical power (pmax); (b)
Extracted power PV panels (ppanels); (c) Inverter output current (iout).
Figure 5. Reference current (iref *) and current injected into the power grid (iout).
Figure 6. Power grid voltage (vgrid) and inverter output current (iout).
Figure 7. Voltages in the two capacitors of the DC-link (vc1, vc2).
This paper presents the design, simulation and experimental results of a 5 kW single-stage three-level Neutral Point Clamped (NPC) inverter for connection to the electrical power grid, with integrated Maximum Power Point Tracking (MPPT) algorithm to extract the maximum available power from solar photovoltaic (PV) panels. It also describes the design of the PLL controller, used to track the fundamental power grid voltage in order to synchronize the NPC inverter with the power grid, and to generate a reference for the inverter output current (which consists in the injected power grid current).
All the controllers have been implemented using C code, validated by simulation in PSIM, and executed in a DSP. Experimental results indicate that the current injected in the power grid follows the reference, and that the voltages in the two DC-link capacitors are kept balanced. It is shown that the proposed system is able to always extract the maximum power available from the solar PV panels, even when there are solar radiation fluctuations.
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