ABSTRACT:
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.
KEYWORDS:
1.
Photovoltaic
System
2.
Maximum Power Point Tracking (MPPT)
3.
Neutral Point
Clamped (NPC) Inverter
4.
Phase-Locked
Loop (PLL)
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure 1. Block diagram of the NPC
converter control system.
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).
CONCLUSION:
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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