In daily life, we often hear the term "DC variable frequency", such as DC motor fans, air conditioners, etc. Does DC motor have a frequency?
Some people refer to the automatic control variable frequency speed control system of brushless DC motors as "DC variable frequency", but DC electricity does not have the concept of frequency. However, this "DC variable frequency" is widely circulated. This so-called DC frequency conversion is how it comes about.
In the DC motor, only the input voltage is ostensibly controlled during speed regulation, but the automatic frequency conversion speed regulation system of the DC motor automatically controls the frequency according to the variable voltage. For the DC motor with excitation winding, the excitation can be controlled separately and the speed regulation range can be increased. However, if it is a DC motor with permanent magnet, the excitation control will be a bit troublesome and there will be demagnetization, There is no way to make the speed range comparable to that of a DC motor with an excitation winding. However, with the support of permanent magnets, those that use rare earth permanent magnets have very strong magnetism and do not require specialized excitation windings. DC motors will have a smaller volume, lighter weight, and higher efficiency.
DC frequency conversion can be understood from another perspective, which converts DC voltage into AC voltage with variable frequency. In the field of household air conditioning, I believe many people understand the concept of DC frequency conversion.