To maximize the economic benefits, the PV system in general operates on the so called maximum power point tracking (MPPT) mode. However, in certain occasions (e.g., in a microgrid or in a weak system), the PV cannot always operate on the MPPT mode but on the dispatchable mode for some time, due to the top priority of the system stability. To this end, a Newton quadratic interpolation based control strategy for the PV system is presented in this paper. With this novel strategy, the PV system can work on the dispatchable mode to flexibly adjust the active power output in some range, and it will automatically switch to the MPPT mode if necessary. The proposed control strategy is verified by simulation. (6 pages)