Hydraulic systems with variable speed drives

A method of operating a hydraulic system comprising a variable speed drive coupled to a hydraulic pump, the method comprising:

• determining position of a hydraulic servo-control valve of the hydraulic system,
• wherein the hydraulic servo-control valve controls flow of hydraulic fluid from the hydraulic pump to a hydraulic actuator of the hydraulic system;
• and
• controlling speed of the variable speed drive,
• wherein the speed is controlled based on the position of the hydraulic servo-control valve,
• wherein controlling the speed of the variable speed drive controls amount of the hydraulic fluid pumped by the hydraulic pump,
• wherein controlling the speed of the variable speed drive comprises changing a current speed to a speed level corresponding to the position of the hydraulic servo-control valve, and
• wherein the speed level corresponding to the position of the hydraulic servo-control valve being fully closed is a maximum operating speed of the variable speed drive.

A hydraulic system comprising:

• a hydraulic actuator;
• a bypass line;
• a hydraulic servo-control valve operable to control a flow of hydraulic fluid between the hydraulic actuator and the bypass line;
• a hydraulic pump coupled to the hydraulic servo-control valve and operable to pump the hydraulic fluid to the hydraulic servo-control valve;
• a variable speed drive coupled to the hydraulic pump and operable to drive the hydraulic pump;
• and
• a system controller operable to control speed of the variable speed drive based on position of the hydraulic servo-control valve and to decrease the speed if the position of the hydraulic servo-control valve is less than 50% of a fully closed position.