An FPGA Based Digital Controller for AC Loads Utilizing Half and Full Wave Cycle Control

Voltage control for AC loads can be performed by controlling phase and cycles of AC voltages reaching load end. Cycle control tends to be more beneficial, as it reduces the amount of harmonic frequency in the circuit compared to phase control circuit. When a wave is passed in cycle control circuit, then either an entire half cycle or a complete full cycle is passed, hence eliminating the sharp change in the wave which is typical in phase control, causing harmonic frequency in the circuit. Cycle control is the most convenient process to control the output voltage for reducing RFI and this is the very approach that has been utilized in designing this project. This project utilized a voltage comparator to generate a digitized AC voltage and an SCR (Silicon Controlled Rectifier) to supply the required AC cycles to the load. The central controller was a digital controller, implemented in a Xilinx Spartan 2 FPGA. The digital controller utilized a Finite State Machine (FSM) that took in digital AC signal and the desired percentage of load voltage. With this information it passed a certain number of half or full cycles to the load, at the same time ensuring that, number of these AC cycles satisfied users percentage requirement. The digital controller was modeled in VHDL (Hardware Description Language), synthesized with XST tool, placed and routed in a Xilinx Spartan2 FPGA (xc2S50 – pq208) in Xilinx ISE 9.1i WebPack design environment. The placed and routed designed was implemented in the Pegasus FPGA board from Digilent containing the above mentioned FPGA. The simulations and the outputs of the implemented hardware accorded with the expected outputs.