A pump assembly (1) includes a pump unit (2), an electrical drive motor (203) for driving the pump unit (2), and a control unit (201) for controlling the drive motor (203). The control unit (201) includes a frequency converter (209), a voltage converter (207) and a controller (211). The voltage converter (207) is configured to provide an input voltage (Uin) to the frequency converter (209). The input voltage (Uin) is adjustable within a voltage range between a minimum input voltage (Umin) and a maximum input voltage (Umax). The controller (211) is configured to determine an actual power consumption of at least one of the drive motor (203), the frequency converter (209) and the voltage converter (207) during operation of the pump unit (2). The controller (211) is further configured to tune the input voltage (Uin) depending on the determined actual power consumption during operation of the pump unit (2).