Method and apparatus for pulse-width modulation of a variable-frequency drive

A method for operating a hydraulic pump system with pulse-width modulation PWM of a variable-frequency drive VFD, comprising:

• for each sector of a space vector graph for the PWM of the VFD, identifying at least two possible clamping phases during displacement switching between a flow control mode and a pressure control mode in the hydraulic pump system comprising an electric motor and a hydraulic pump;
• comparing currents in multiple clamping phases in at least one PWM cycle by receiving current measurements from current sensors in the hydraulic pump system installed at respective clamping phases and comparing the current measurements of the respective clamping phases;
• in the sector of the space vector graph corresponding to the PWM cycle, determining the possible clamping phase with the maximum current in the at least two possible clamping phases;
• clamping the determined possible clamping phase with the maximum current, wherein a switch state of the possible clamping phase with the maximum current remains unchanged and only switch states of the other clamping phases change;
• obtaining a real-time current magnitude to detect the displacement switching, wherein the steps of comparison, determination and clamping are performed only in large current conditions in which the real-time current magnitude is larger than a threshold during the displacement switching, the threshold designated to ensure that the method is performed only when the current is larger than the threshold;
• and
• operating the hydraulic pump system by the PWM of the VFD by automatically eliminating switching actions in phases with current values larger than the threshold.