A controller for a multi-level converter regulates the DC midpoint voltage of the multi-level converter by accounting, for the effect non-redundant switch states have on the DC midpoint current. Application in the synthesis of 1234yf. There is further disclosed a communication system and communication protocol in which when the i-th data is not normally received, retry is inhibited only for a predetermined time to prevent the retry from unnecessarily occurring between a destination node slow in receiving process and a source node fast in transmitting process. As a result, a staircase waveform having 2n positive and negative stairs is generated while unnecessary harmonic wave components in the proximity of the sine wave signal by which the analog input signal is multiplied can be reduced. A length of a section of the suture between the anchor element and the annular body is chosen in that after said anchor element has moved through said annular body, a resulting new loop lies circumferentially and tightly around a strand-shaped tissue section to be fixed at said bone. In the higher speed gears, power is carried by the planet gear carrier directly to the differential cage, bypassing the speed reduction, torque multiplication and gear mesh losses of the planetary gear set.