The duty cycle is based on operating temperature; in my experience. Super heavy duty wiring insulation has the best duty cycle; probably 80% to 90% of the time before the wiring gets too hot. Standard wiring I believe has a duty cycle around 50 percent of the time. The manufacturer of the equipment figures this out and places the information in the owners manual, usually. Of course what is in the manual is normally only a guideline. Or actually measuring the wiring temperature in the warmest location would be a substitute for what is in the manual; less or more duty cycle; whenever the max insulation temperature is reached in the warmest location in the wiring. And with heat, circuit breakers will trip and is a nearly foolproof method of not melting wiring. This info is in the National Electrical Code somewhere.
If you mean calculating dwelling times of a 3 phase inverter by space vector modulation, you may look into:
http://dx.doi.org/10.1109/UPEC.2006.367646
Sorry, I did not make myself clear. Duty cycle of motors or equipment is not something you calculate; too many variables; and unique to each piece of equipment. One reads the insulation temperature of the motor or other equipment while running in the warmest location until it gets to the maximum temperature allowed of the wire insulation. As listed in the National Electrical Code; wire insulation max temperatures are generally 90 deg C or 110 deg C and other temperatures I do not remember. The equipment manufacturer generally supplies the max cycle time of the equipment; when it reaches the max
wire insulation temperature; generally between 50% of the operating time to 90% of the operating time; and usually specifies the amount of cool down time before motor restart. Motors and equipment are regularly oversized to allow continuous operation. The equipment manual almost always specifies the the max allowed cycle time. If it does not, the equipment manufacturer is probably not reputable and not reliable; or they do not know what they are doing. Or, it is a one time, one use piece of equipment; dying at the end of its cycle; and needing wiring repair. Large electric motors are commonly rewound after several thousand hours of operation. Motor frames last nearly forever; wiring does not.
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