Hydraulic Drive System for Electrically-Driven Hydraulic Work Machine

A hydraulic drive system for an electrically-driven hydraulic work machine including a first hydraulic pump, a plurality of actuators driven by hydraulic fluid supplied from the first hydraulic pump, a plurality of flow control valves that control directions and flow rates of the hydraulic fluids to be supplied to the plurality of actuators, a first electric motor that drives the first hydraulic pump, a first power storage device that supplies electric power to the first electric motor, and a first horsepower control device configured to decrease, when a delivery pressure of the first hydraulic pump increases, a delivery flow rate of the first hydraulic pump to control an absorption horsepower of the first hydraulic pump so as not to exceed a first allowable value,

• the hydraulic drive system comprising:
• a second hydraulic pump;
• a common hydraulic fluid supply line in which hydraulic fluids delivered from the first and second hydraulic pumps are merged and are supplied to the plurality of flow control valves;
• a second electric motor that drives the second hydraulic pump;
• a second power storage device that supplies electric power to the second electric motor;
• a second horsepower control device configured to decrease, when a delivery pressure of the second hydraulic pump increases, a delivery flow rate of the second hydraulic pump to control an absorption horsepower of the second hydraulic pump so as not to exceed a second allowable value;
• and
• a controller including a horsepower distribution control section configured to change at least one of the first and second allowable values of the first and second horsepower control devices such that a charge state of the first power storage device and a charge state of the second power storage device become equal to each other.