Complex sentence: At high power levels, DC motors are almost always cooled using forced n DC motors are often controlled by power electronics systems which adjust the voltage by "chopping" the DC current into on and off cycles which have an effective lower voltage.
Split into simpler sentences: At high power levels, DC motors are almost always cooled using forced air. Modern DC motors are often controlled by power electronics systems which adjust the voltage by "chopping" the DC current into on and off cycles which have an effective lower voltage.