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.
- Z source MLI
- Neutral-point clamped inverter
- Space vector PWM (SVPWM)
- Hysteresis current controller (HCC)
- Neutral point balancing
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.
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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