The invention provides a capacitor assembly, comprising an annular capacitor board and a tubular capacitor connected with the annular capacitor board in a communicating manner by a capacitor pin, and the annular capacitor board and the tubular capacitor are both provided with hollow cavities through which a shaftway rod can pass. As the capacitor assembly is tubular, the capacitor assembly has a compact structure, the occupied area is reduced, the outside dimension of a frequency converter is reduced, the frequency converter can conveniently stretch into the shaftway with round cross section, the interference of the shaftway wall to the frequency converter of the capacitor assembly is avoided, and the application of the frequency converter in the mine equipment can be realized. The invention further provides the frequency converter, comprising a tubular shell capable of being arranged in the shaftway, an inner barrel sheathed in the tubular shell and capable of enabling the shaftway rod to pass through, and a main frequency converter body arranged in a cavity between the tubular shell and the inner barrel, wherein the main frequency converter body comprises a driving board and the capacitor assembly. The application of the frequency converter in the main equipment is realized and the lengths of a control cable and a driving cable are reduced.