A hybrid-vehicle control system for controlling a vehicle driveline having an engine, a transmission, a first motor/generator provided between the engine and the transmission, and a battery, the hybrid-vehicle control system comprising: - a first inverter, coupled to the first motor/generator; - a voltage adjusting circuit coupled to the first inverter and to the battery, the voltage adjusting circuit being configurable to electrically connect the battery and the first inverter, to electrically disconnect the battery and the first inverter, and to adjust a voltage supplied from the first inverter to the battery for charging the battery; and - a controller, coupled to at least the first inverter, the voltage adjusting circuit, the battery, the transmission, the controller being configured to issue signals to shift the transmission to a target shift position during a gear shift operation according to a driving force requested by a driver, to control generation of electrical power by the first motor/generator during the gear shift operation so that the engine is controlled to a rotation speed corresponding to the target shift position of the transmission, and to calculate a requested output voltage of the first motor/generator from power generated by the first motor/generator during the gear shift operation; wherein: - when the requested output voltage becomes greater than or equal to a predetermined voltage during the gear shift operation, the controller is configured to control the voltage adjusting circuit to electrically disconnect the battery from the first inverter to raise a terminal voltage of the first inverter to the predetermined voltage, and to adjust the voltage supplied from the first inverter to the battery to a second voltage, and - the controller is configured to at least one of - control the engine to decrease a torque produced by the engine when the terminal voltage of the first inverter becomes higher than or equal to a predetermined first limit voltage during the gear shift operation; and - perform engine torque control for decreasing the torque of the engine when a switching frequency of the semiconductor switching element of a step-down chopper circuit comprised in the voltage adjusting circuit exceeds a predetermined frequency. - a first inverter, coupled to the first motor/generator; - a voltage adjusting circuit coupled to the first inverter and to the battery, the voltage adjusting circuit being configurable to electrically connect the battery and the first inverter, to electrically disconnect the battery and the first inverter, and to adjust a voltage supplied from the first inverter to the battery for charging the battery; and - a controller, coupled to at least the first inverter, the voltage adjusting circuit, the battery, the transmission, the controller being configured to issue signals to shift the transmission to a target shift position during a gear shift operation according to a driving force requested by a driver, to control generation of electrical power by the first motor/generator during the gear shift operation so that the engine is controlled to a rotation speed corresponding to the target shift position of the transmission, and to calculate a requested output voltage of the first motor/generator from power generated by the first motor/generator during the gear shift operation; - when the requested output voltage becomes greater than or equal to a predetermined voltage during the gear shift operation, the controller is configured to control the voltage adjusting circuit to electrically disconnect the battery from the first inverter to raise a terminal voltage of the first inverter to the predetermined voltage, and to adjust the voltage supplied from the first inverter to the battery to a second voltage, and - the controller is configured to at least one of - control the engine to decrease a torque produced by the engine when the terminal voltage of the first inverter becomes higher than or equal to a predetermined first limit voltage during the gear shift operation; and - perform engine torque control for decreasing the torque of the engine when a switching frequency of the semiconductor switching element of a step-down chopper circuit comprised in the voltage adjusting circuit exceeds a predetermined frequency. - control the engine to decrease a torque produced by the engine when the terminal voltage of the first inverter becomes higher than or equal to a predetermined first limit voltage during the gear shift operation; and - perform engine torque control for decreasing the torque of the engine when a switching frequency of the semiconductor switching element of a step-down chopper circuit comprised in the voltage adjusting circuit exceeds a predetermined frequency.