An inflatable cargo dunnage bag comprises an inflatable bladder, a first inner bag, and a second outer bag, wherein the inner and outer bags are fabricated from polywoven thermoplastic material so as to render the dunnage bag light in weight and moisture resistant whereby the dunnage bag can be used in the maritime industry. The system includes: an electric-power converter; a three-phase ac rotating machine; and a four-core non-coaxial cable, having a ground line and three-phase electric-power supplying lines, connecting the electric-power converter to the three-phase ac rotating machine. The switching controller may include a period counter to measure times between threshold crossings, and a delay counter to trigger a delayed state transition for the transistor bridge.