Abstract: This paper describes a new approach of generating driving signals for three phases inverters. The Pulse Position Modulations are used instead standard Pulse Width Modulation signals as driving signals. The simplicity and reliability in driving power switchers in inverters are the results of described approach. The Field Programmable Gate Array (FPGA) as high frequency PWM inverter controller is suitable for using in this approach. Presented controller has three basic blokes: numerically controlled oscillator, amplitude modulator and PWM timer. Direct Digital Synthesis (DDS) of PWM signal using sine lookup table provides three pairs of center based, dead time adjusted driving signals. PWM signal has duty cycles in the range 0.5\% to 99.5\% with 8-bit resolution at switching frequency up to 100 kHz. All three parameters of the output waveform: frequency, phase and amplitude are defined and controlled by digital words. Controller has serial data interface to the host processor and as a peripheral block minimizes the conventional software overhead in generating the PWM waveforms. In the stand-alone mode of operation, two-chip solution, which includes FPGA and A/D converter, is applied as a control block in the three phase fixed frequency DC/AC converter.
Key words: Three phases inverter, pulse width modulation, pulse position modulation, FPGA, digital synthesis.