ABSTRACT:
The
Photo-voltaic (PV) tied Z-source Neutral-point clamped multilevel inverter
(Z-NPC-MLI) is used in solar grid connected applications due to its single
stage conversion and better performance. Though the Z source inverters
adaptation is accepted in grid connected technology, the need for suitable
controller and PWM scheme are necessary to meet out the performance such as
shoot through switching, neutral point balancing, and harmonic reduction. The
space vector pulse width modulation (SVPWM) strategy is a prominent modulation
technique for Z-source NPC-MLIs due to the flexibility to select the
appropriate voltage vector. Previous publications have shown the control of a
Z-source MLI using the SVPWM with and without modification of shoot through
switching. However, the current controller (CC) based SVPWM is not matured,
which is the most essential consideration for the grid connected inverter to
provide neutral point balancing, shoot through control for low harmonic
distortion and a high quality current. With all these aims, this paper presents
a PV tied Z-NPC-MLI grid connected system with a unique hysteresis current control
SVPWM (HSVM) strategy with neutral point (NP) balancing control and direct
current control in the inverter input side. Also, the proposed HSVM is assuring
the grid connection with high quality voltage and current waveforms. This CC
based SVPWM for Z-NPC MLI has been validated through simulation and FPGA based
experimental investigations. The results are confirmed the feasibility and
reliability of the proposed HSVM for the PV tie grid connected Z- Source
NPC-MLI.
KEYWORDS:
1. Z
source MLI
2. Neutral-point
clamped inverter
3. Space
vector PWM (SVPWM)
4. Hysteresis
current controller (HCC)
5. Neutral
point balancing
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Figure 1. PV Tied Grid Connected Three-Phase
Three-Level Z Source Npc-Mli.
EXPECTED SIMULATION RESULTS:
Figure 2. Simulation Results Of Pv Output.
Figure 3. Simulation Results Of Three Phase
Voltage And Current
Waveform
Of Z-Npc-Mli
Figure 4. Simulation Results Of Harmonics Spectra
For Z-Npc-Mli Atma D 0:9; (A) Voltage Harmonics Spectra,(B)Current Harmonics
Spectra.
Figure 5. Simulation Results Of Actual Load
Current And Reference Current When H Band Is Fixed At 5amps.
Figure 6. Simulation Results Of Z-Npc-Mli Voltage
Across Dc-Link Capacitors; (A) Conventional Svm Method, (B) Hsvm.
Figure 7. Simulation Results -Transient Response
Of Inverter Output Currents.
CONCLUSION:
In
this paper the three-level Z source NPC-MLI has investigated for PV tied grid
connected system. Further also developed the PV tied grid connected system with
hysteresis current control combined Z source SVPWM is known as HSVM is
developed. The proposed HSVM uses minimal ST compares to conventional Z source
SVPWM. In addition the proposed HSVM eliminates the low frequency oscillations
using suitable ST (Upper and Lower ST), with regular switching events, which
ensures the neutral point DC-link capacitors balancing along with current
control. The HSVM maintains the volt-second and inverter voltage boosting competence
irrespective of the angular location of the reference vector throughout the
inverter operation. A 2 kWp solar panels attached three-phase three-level IGBT
based Z-NPC- MLI grid connected system is established with Xilinx family FPGA
SPARTAN-6 controller. From the results, it shows that the performance of
proposed method is superior than compare to conventional Z source SVPWM in
terms of Neutral point fluctuation, current control capability and better harmonic
performance. This proposed HSVM method well suited for wind tied inverters,
industrial and Electrical vehicles motor applications.
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