Development And Analysis Of Three Phase Nine Level Cascaded H-Bridge Multilevel Inverter Using Bipolar And Unipolar Switching Schemes

Nazmudi, Akmal Afiq (2015) Development And Analysis Of Three Phase Nine Level Cascaded H-Bridge Multilevel Inverter Using Bipolar And Unipolar Switching Schemes. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

Multilevel inverter is one of the popular devices used in high power medium- voltage (MV) drives. The multilevel inverter has a particular advantage of operation at high direct current (DC). The most significant advantage of multilevel inverter can generate output voltage with very low harmonic distortion and synthesis a staircase voltage waveform by having multiple voltage level. The MLI can solve the problem of high harmonic distortion that produce by the square wave or the conventional inverter that have been used widely in the power DC to alternative current (AC) conversion. The total harmonic distortion (THD) can cause the additional losses, overheating and overloading to the system. There are various topologies of Multilevel Inverter are introduced; however, the most common multilevel inverter topologies are Neutral Point Clamped (NPC) inverter and the Cascaded H-Bridge (CHB) inverter. In this project, the cascaded multilevel inverter is selected because the cascade multilevel is easy to implement compared to other topologies. The cascaded inverter is more reliable because the cascaded H-bridge multilevel inverter (CHB-MLI) does not require any clamping diode and flying capacitor. The performance of cascaded H-bridge inverter was analyzed and discussed by using bipolar and unipolar switching schemes. The performance of the cascaded multilevel inverter was evaluated in term of the total harmonic distortion for current (THDi) and voltage (THDv) connected to the R, RL and RC load. The simulation of the CHB-MLI was tested with manipulating several parameters such as the various numbers of carrier wave, various values of amplitude modulation ratio and the various values of the frequency modulated ratio. The RL load produce the lowest of THD compared to another load that has been tested. The RL load produces the lowest THDi which is 0.23% using unipolar switching scheme, with the 0.95 of amplitude modulation ratio (ma) and 500 of frequency modulation ratio (mf). The development of Hardware of Three Phase Nine- Level Cascade H-Bridge Multilevel Inverter (CHB-MLI) is conducted after the simulation result obtained. The hardware experiment is connected to only R and RL loads. The hardware experiment of the Three Phase Nine Level CHB-MLI is tested with manipulating several parameters such as various values of amplitude modulation ratio and the various values of the frequency modulated ratio. The lowest THD that produced in the hardware experiment is produced by the RL load with 1.09% of THDi. MATLAB simulink is used to model the CHB-MLI. Some of the result met the standard of IEEE 519 and for high value of harmonic, the additional of passive filter will reduce the THD.

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