This paper presents a new design and implementation of a three-phase multilevel inverter (MLI) for distributed power generation system using low frequency modulation and sinusoidal pulse width modulation (SPWM) as well. It is a modular type and it can be extended for extra number of output voltage levels by adding additional modular stages. The impact of the proposed topology is its proficiency to maximize the number of voltage levels using a reduced number of isolated dc voltage sources and electronic switches. Moreover, this paper proposes a significant factor (FC/L), which is developed to define the number of the required components per pole voltage level.
A detailed comparison based on (FC/L) is provided in order to categorize the different topologies of the MLIs addressed in the literature. In addition, a prototype has been developed and tested for various modulation indexes to verify the control technique and performance of the topology. Experimental results show a well-matching and good similarity with the simulation results.
- Low frequency modulation
- Multi-level inverter
- Multi-level inverter comparison factor
- Sinusoidal pulse-width modulation (SPWM)
- Symmetrical DC power sources
Fig. 1. Proposed three-phase MLI topology.
EXPECTED SIMULATION RESULTS:
Fig. 2. Output line-to-line voltages ( VAB,VBC , and VCA ) with low frequency (50 Hz) modulation technique. (a) Simulation.
Fig. 3. Output phase voltages ( VAN,VBN , and VCN ) with low frequency modulation technique. (a) Simulation.
Fig. 4. Inverter outputs with R-L load (VAB ,VAN , and IAN) with low frequency modulation technique. (a) Simulation.
Fig. 5. Pole voltages for scheme I, mi =0.95 and fs=2.5kHz. (a) Simulation.
Fig. 6. Line-to-line voltages for scheme I, mi =0.95 and fs=2.5kHz . (a) Simulation.
Fig. 7. Phase voltages for scheme I, mi =0.95 and fs=2.5kHz . (a) Simulation.
Fig. 8. Pole voltages for scheme II, mi =0.95 and fs=2.5kHz . (a) Simulation.
Fig. 9. Line-to-line voltages for scheme II, mi =0.95 and fs=2.5kHz . (a) Simulation.
Fig. 10. Phase voltages for scheme II, mi =0.95 and fs=2.5kHz. (a) Simulation.
Fig. 11. Line-to-line voltage and phase voltage at for scheme I, mi =0.95 and fs=2.5kHz . (a) Simulation.
Fig. 12. Line-to-line voltage and phase voltage for scheme II, mi =0.95 and fs=2.5kHz . (a) Simulation.
Fig. 13. Inverter output voltages: (a) three phase line-to-line voltages ( VAB, VBC, and VCA ), (b) line-to-line voltage, phase voltage and the phase current under R-L load.
A new modular multilevel inverter topology using two modulation control techniques is presented. The proposed has several advantages compared with existing topologies. A lower number of components count such as isolated dc-power supplies, switching devices, electrolyte capacitors, and power diodes are required. So it exhibits the merits of high efficiency, lower cost, simplified control algorithm, smaller inverter’s foot print and increased the overall system reliability. Due to the modularity of the presented topology, it can be extended to higher stages number leads to a good performance issues such as low, low, and low and eliminating the output filter will be obtained.
Beside the low frequency modulation, two schemes are successfully applied to control the suggested . This paper also suggests a significant factor, which defines the required components to generate one voltage level across the output pole terminals. The issue related to the cost of each used component is out of scope of this paper. The system simulation model and its control algorithm are developed using PSIM and MATLAB software package tools to validate the proposed topology. A laboratory prototype has been developed and tested for various modulation indexes to verify the control techniques and performance of the topology, the similarity between the simulation and obtained experimental results was confirmed.
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