In this paper, a sliding-mode control (SMC) strategy is proposed for three-phase grid-tied LCL-filtered voltage source inverters in the natural frame. The SMC in the natural frame is based on controlling the sliding surface functions of phase-legs a and b. The sliding surface function of phase-leg c is obtained from the sliding surface functions of phase-legs a and b. This eliminates the need for sensing capacitor voltage and grid current of phase-leg c. The capacitor voltage references are generated by the proportional-resonant (PR) controllers which result in zero steady-state error in the grid current. The feasibility and performance of the proposed SMC strategy is investigated under steady-state, transient, unbalanced, and distorted grid conditions. Experimental results taken from a 9.8 kW system are provided to demonstrate the validity of the proposed SMC strategy.