1. A medium-voltage drive system, comprising:a medium-voltage drive comprising at least one cabinet and a plurality of power devices disposed in the cabinet;
a heat sink disposed in the cabinet and coupled to the plurality of power devices, wherein the heat sink comprises a liquid-cooled or two-phase heat sink having a coolant system that circulates coolant through the heat sink to cool the power devices;
at least one fan for moving air to cool the power devices, wherein the fan is positioned to move air directly over the heat sink to cool the power devices;
at least one space heater disposed in the cabinet;
at least one ambient sensor for detecting a temperature of ambient air;
at least one device sensor for detecting a temperature of the power devices;
at least one variable frequency drive (VFD) coupled to the at least one fan for varying the speed of the fan; and
a controller communicatively coupled to the ambient sensor, the device sensor, the VFD, and the at least one space heater, wherein the controller is configured to output control signals to adjust the fan speed and the heater power level of the at least one space heater based on feedback received from the ambient sensor and the device sensor, wherein the controller is configured to reduce the speed of the fan in response to the ambient temperature or the device temperature lowering below a threshold, thereby maintaining a viscosity of the coolant within a predetermined range by reducing the speed of the fan.