129 CHAPTER 6 CONCLUSION AND SCOPE FOR FUTURE RESEARCH 6.1 CONCLUSION The different control techniques like Phase Opposition Disposition, Alternate Phase Opposition Disposition, Third Harmonic Injection Pulse Width Modulation and Sine Pulse Width Modulation for five level cascaded multilevel inverter are simulated and compared. A novel modulation technique is proposed for multilevel voltage source inverter and simulated in the MATLAB/SIMULINK environment and its performance parameters are analyzed for different levels of multilevel inverter. The output parameters like output percentage THD, percentage THDV and percentage THDI are analyzed. All the modulation techniques yield more or less the same output fundamental component only but the lower order harmonic distortion levels will differ with techniques for the various modulation indexes. At lower modulation indexes, the percentage THD levels are higher and it is not preferred for the practical applications. At higher modulation indexes the Super Imposed Carrier based inverter contains the output THD of thirty five percent, POD based inverter contains twenty three percent and the proposed SVPWM yields the better output with THD of less than ten percent. With SVPWM the load draws comparatively a smaller load current compared to other techniques. The output waveforms of the voltage and load current are also approximated sine wave. 130 The cascaded multilevel inverter for different levels are modeled in the MATLAB/SIMULINK environment. The cascaded inverter is the best choice when compared to other multilevel topologies due to the absence of the input voltage unbalance and freewheeling diodes. In the cascaded multilevel inverter configuration the output percentage THD reaches zero as the level of the inverter reaches infinity but it is not a feasible solution for practical realization and hence the level of inverter is limited to five level and the output percentage THD is controlled with the implementation of the proposed SVPWM technique in the modern FPGA digital processor. The code for the proposed hardware is generated in the system generator environment and downloaded to the XC3S400 FPGA processor. The three phase five level cascaded multilevel inverter power circuit and the protection circuit for the same is constructed, tested and integrated with the digital processor. The integrated module is tested for the lower voltage and the voltage shall be increased to the desired value. The three phase output voltages are analyzed and patterns are compared with the simulation outputs. The output is connected to the three phase AC induction motor and the output waveforms are analyzed with the FLUKE make power quality analyzer. The waveforms were captured and they are coinciding with the simulated values. The three phase voltage of 400 Volts AC is obtained across the output terminals for the DC input of 432 Volts. The harmonics table is also obtained for the different load conditions of the three phase induction motor. The third order output THDV for the 50Hz output supply voltage of 397V is 4.3% for all the phases and 5.1% for neutral. The fifth order output THDV for the 50Hz output supply voltage of 397V is 0.6% for all the phases 131 and 4.8% for neutral. The seventh order output THDV for the 50Hz output supply voltage of 397V is in the range of 0.1 to 0.3% for all the phases and 2.7% for neutral. Similarly the third order output THDI for the 50Hz output is 4.3% for all the phases and 4.5% for neutral with the three phase output load current of 2.25Amperes. The fifth order output THDI for the 50Hz output supply is in between 1.5 and 2.8% for all the phases and 8.7% for neutral with the load currents of 2.25Amperes in each phase. The seventh order output THDI for the 50Hz frequency is in between 1.5 and 1.8% for all the phases and 8.9% for neutral with the load currents of 2.25Amperes in all the phases. The implementation of the proposed technique reduces the THD value significantly. The evaluated THD values very much satisfying the limits prescribed by the different standards for THD. The evaluated hardware results conform to the standards meant for power quality in addition to other advantages. 6.2 SCOPE FOR FUTURE RESEARCH The control technique for multilevel power converters can be further simplified and generalized to different levels and other class of power converters and inverters. The levels of multilevel configuration can be increased and further improvements in terms of performance and power quality issues can be broadly studied and could be implemented with hardware circuits. The same cascaded multilevel inverter configuration can be installed for other applications like SVC system and performance can be studied for larger AC systems. The proposed system can be designed for larger electrical drives and parameters can be monitored and varied 132 dynamically with high speed network interconnections. Hence the power quality problems in power distribution can be controlled or completely eliminated. The effect of EMI is not dealt in this thesis which can be studied in detail for specific techniques with latest equipment. The quality of the power supplied to the consumers and electrical utilities should adhere to the stringent norms prescribed for the power quality. In order to ensure the same power quality at all levels of consumer usage, the dedicated low cost integrated chips for these kinds of applications could be developed and manufactured in large scale. This makes the technology easily accessible to common man.