PWM control for power converter system utilizing pulse dropping at minimum pulse widths

Claim 1

An apparatus for controlling a power converter system including a power converter circuit having a plurality of power semiconductor elements and pulse generator means for producing pulses which control conduction of said semiconductor elements so as to cause said power converter circuit to produce an output of a predetermine pattern, said apparatus comprising: means for repeatedly executing at a selected time interval an event calculation process for determining active ones of said semiconductor elements which should be rendered conductive in an instant period of time interval until execution of the next event calculation process and a conductive time for which each of said active semiconductor elements should be conductive based on at least one input determined according to the predetermined pattern of the output of said power converter circuit applied thereto; means for comparing said conductive time of each of said active semiconductor elements with a predetermined first value of the conductive time; means for correcting the conductive time of any of said active semiconductor elements, when the conductive time is less than said first value, to a selected one of zero and a predetermined second value not less than said first value which is selected depending on a history of the conductive times of said active semiconductor elements determined in previous event calculation processes; and means for determining a pulse width of the pulse to be produced by said pulse generator means for controlling the conduction of each of said active semiconductor elements in correspondence with the conductive time determined for said active semiconductor element, when said conductive time is not less than said first value, and in correspondence with the corrected conductive time for said active semiconductor element, when the conductive time before correction is less than said first value.

Claim 2

An apparatus for controlling a power converter system including a power converter circuit having a plurality of power semiconductor elements and pulse generator means for producing pulses which control conduction of said semiconductor elements so as to cause said power converter circuit to produce an output of a predetermine pattern, said apparatus comprising: means for repeatedly executing at a selected time interval an event calculation process for determining active ones of said semiconductor elements which should be rendered conductive in an instant period of time interval until execution of the next event calculation process and a conductive time for which each of said active semiconductor elements should be conductive based on at least one input determined according to the predetermined pattern of the output of said power converter circuit applied thereto; means for comparing said conductive time of each of said active semiconductor elements with a predetermined first value of the conductive time; means for correcting the conductive time of any of said active semiconductor elements, when the conductive time is less than said first value, to a selected one of zero and a predetermined second value not less than said first value which is selected depending on a history of the conductive times of said active semiconductor elements determined in previous event calculation processes; and means for determining a pulse width of the pulse to be produced by said pulse generator means for controlling the conduction of each of said active semiconductor elements in correspondence with the conductive time determined for said active semiconductor element, when said conductive time is not less than said first value, and in correspondence with the corrected conductive time for said active semiconductor element, when the conductive time before correction is less than said first value.