This paper proposes a nonlinear control strategy for a hybrid PV-battery system insuring frequency and voltage support of the power system. The hybrid system includes a PV panel and battery connected to three-phase DC-AC inverter via DC-DC boost converter and bidirectional DC-DC boost converter. A synchronous generator represents the power grid. The voltage regulators control DC-DC boost converter and DC-AC inverter while the frequency regulator controls the bidirectional DC-DC boost converter. A conventional MPPT is used to adjust the reference for nonlinear PV voltage regulator. The voltage regulator is designed based on multi-input multi-output exact feedback linearization technique. It consists of a module that uses the terminal voltage deviation to generate q-axis voltage component. A module that maintains the DC-link voltage is also added to generate d-axis voltage component as well. The proposed frequency regulator includes a module that changes the reference signal of a battery current control module when the frequency deviation is significant. The battery current regulator is designed based on partial input-output feedback linearization strategy. The proposed control system is evaluated in simulation. The results reveal that with the proposed control scheme, the PV-battery generator reacts like a conventional synchronous generator when the grid frequency changes considerably.