A single phase matrix down-converter for airport lighting regulation

Airport lighting systems employ single-phase current controlled regulators, that provide a constant, programmed current to a series string of loads. These consist of coupling transformers for each load, that will self saturate in case of an open load. Typical present technology uses phase control with ferroresonant transformers. These have the disadvantages of poor efficiency, large size, high cost and poor input current distortion. Lower cost alternatives have been marketed, replacing the ferroresonant transformer with a conventional transformer. This has reduced the cost and improved the efficiency, at the cost of an even worse level of input distortion. Another recent approach uses rectifier and PWM inverter technology. This approach has not met the cost requirements, and while improving the output current waveform, still has significant input current distortion due to the capacitor input single-phase rectifier section. A regulator based on a PWM matrix down-converter is described, which meets the project cost and efficiency requirements while providing sinusoidal input and output currents. Notable is the fact that this converter works equally well over a wide range of load power factors, with relatively simple control logic