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Variable frequency DC/AC converter with EMI reduction

This paper presents a way of generating a variable frequency sinusoidal signal in conjunction to the developed spread spectrum frequency modulation technique that is used to suppress the EMI caused by high switching frequencies. These are implemented through Verilog Hardware Descriptive Language (Verilog HDL) and synthesized on Altera DE2-70 FPGA board using Quartus tool chain to satisfy the low cost requirement and flexibility which are verified through (1) Modelsim simulations, (2) Debussy simulations and by (3) actual digital to analog conversion using DAC7541. For experimental validation, series of measurements are done on the output of the inverter prototype driven by the generated SPWM signal. Measurement results at the output SPWM show that the applied technique may have caused an increase in THD by 0.092% 0.039% and 0.087% at frequencies 50 Hz, 60 Hz and 70 Hz respectively, but it has significantly reduced the EMI peak with at least 12.8 dB.