Patent ID: 7344787

Claim:
A multi-stage compressor system that compresses air supplied to a cathode of a fuel cell system, comprising: a first stage compressor that compresses inlet air to provide a first pressurized air stream at a first pressure; a second stage compressor comprising: a compression unit that compresses said first pressurized air stream to a second pressurized air stream at a second pressure; and a drive unit that drives said compression unit using expansion energy of an exhaust stream of said fuel cell; a first heat exchanger that enables heat transfer between said second pressurized air stream and said exhaust stream to heat said exhaust stream: and a bypass valve having an open state, a closed state and a partially open state, wherein when in said closed state said first pressurized stream flows to said second stage compressor, when in said open state said first pressurized stream bypasses said second stage compressor and when in said partially open state a portion of said first pressurized stream bypasses said second stage compressor.