10. Cycloconverter

Variable speed operation of rotating field machines requires a variable frequency supply. Nowadays, a variable frequency supply is usually realised by means of an inverter (see Chap. 11), which accomplishes this starting from a DC source (i.e. a DC battery or the rectified grid voltage). The cycloconverter offers another solution, however limited to rather low output frequencies. Nowadays, the cycloconverter is (or was) mainly used for high output power (and low output frequencies). In this chapter we review the operating principle, provide some examples of practical three-phase circuits and discuss the main control methods. Important aspects are the output voltage harmonic content and the input current harmonic content and reactive power requirements.