We report a stable, high-power, continuous-wave (cw) optical parametric oscillator (OPO) pumped at 1064nm by a commercial Nd:YVO4 solid-state laser. The oscillator is singly resonant, based on an angle-polished MgO-doped periodically poled LiNbO3 (MgO:PPLN) in a four-mirror ring cavity. Maximum output idler up to 2.15 W is achieved at 3069.1 nm with 9.8 W of pump power, corresponding to a pump-to-idler conversion efficiency of 21.9%. The device exhibits excellent power stability better than 0.19% rms over 30 minutes, which is related to the reduced intracavity residual reflections and thermal self-locking effect.