Vibration will normally not really move things at any speed along a true flat - you need some sense of 'down' and the size and shape of the pellets will affect exactly what slope you need. If need be you could have some sort of swan neck escalator/conveyor at the start or more than one part way along. But yes, it is usually solenoids driven with low frequency AC, either sinusoidal or square wave forms. 50Hz mains can be used for things like rice but larger particles move better at lower freqs.

It may be worth chatting to some of the chaps at somewhere like Cox and Plant  who do this for a living, if only to find out what the professional approach would be for the actual thing you are moving.

We used to used rotary vibrating hoppers to move 12KG steel billets onto a feeder chute to an induction heater. The kit basically comprised of a spiral chute mounted on rubber bushes and then onto a fixed steel chassis. 2 motors with bobweights were bolted either side tof the spiral assembly to 'shake' it. The weights could be adjusted to vary the feed speed depending upon billet weight.

We used to used rotary vibrating hoppers to move 12KG steel billets onto a feeder chute to an induction heater. The kit basically comprised of a spiral chute mounted on rubber bushes and then onto a fixed steel chassis. 2 motors with bobweights were bolted either side tof the spiral assembly to 'shake' it. The weights could be adjusted to vary the feed speed depending upon billet weight.