This paper presents a nonlinear closed-loop control combined with an integral time-delay feedback control of an infinitely variable transmission (IVT) to adjust its speed ratios with respect to variable input speeds that are induced by variable tidal speeds. A speed ratio closed-loop control for the IVT system involves a forward speed controller and a crank-length controller for different operating conditions of a tidal current energy converter (TCEC). The time-delay feedback control is designed to reduce speed fluctuations of output speeds of the IVT to track a desired output speed. Experimental investigation for tidal current energy applications was carried out to test validity of the time-delay feedback control of the IVT system. Rotation speeds of the TCEC based on measured variable tidal current data are used as control inputs for control experiments of the IVT system. An instrumented rotation speed measurement system of the IVT system is deployed so that quantities needed for the time-delay control variable can be measured. Experimental results of variable tidal speeds show that speed ratios of the IVT with the proposed control strategy can achieve excellent tracking responses for the desired constant output speed and reduce speed fluctuations of output speeds of the IVT.