A low cost square fed delta modulator suitable for three phase FHP AC drives

Delta modulation offers a number of unique advantages in static PWM inverter applications in variable speed AC drives such as inherent constant volts per hertz control for a preset frequency range, smooth transition between the constant volts per hertz and constant volts modes of operation and severe attenuation of low order harmonics from the load voltage. In FHP drive range the control circuit cost is significant when compared with the total inverter cost. The main objective of this paper is to reduce the drive cost still maintaining the adequate performance for such drives. The scheme proposed here is square fed delta modulation technique which operates at predetermined switching frequency, simplifying the output filter design. Most of the advantages of conventional delta modulation technique are maintained with reduction in cost. This reduction is significant at low power ratings. The FHP drive employing this modulation technique and permanent magnet synchronous motor has potential in energy saving applications. The scheme is suitable for any AC motor and will favor the trend of using V/F control from energy cost point of view in even common applications. The analysis, simulation and experimental results for square fed delta modulator are presented in this paper.