AC motor control method and its control apparatus
AssigneeKabushiki Kaisha Toshiba
InventorAkio Hirata
Life of this patent
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Abstract
A self-extinguishing element such as a gate turn-off thyristor (GTO) is used for each arm of the inverter. A capacitive load is connected to the output terminal of the inverter. In a region where the output frequency of the inverter is low, the self-extinguishing element is forcibly commutated. In a high-frequency region, where the output frequency of the inverter is higher than that in the low-frequency region, the capacitive load causes the self-extinguishing element to be load-commutated.
Claims8
A control method for variably controlling the speed of an AC motor serving as an inductive load, by use of a frequency converter which is formed of a rectifier, a DC reactor, and an inverter connected to a capacitive load, comprising the steps of:
- forcibly commutating switching elements constituting said inverter, when the output frequency of said inverter is below a predetermined value;
- and
- load-commutating said switching elements when the inverter output frequency is above said predetermined value and current supplied to said inductive and capacitive loads becomes a phase-advanced reactive current.
The control apparatus for variably controlling the speed of an AC motor serving as an inductive load, by use of a frequency converter which is formed of a rectifier, a DC reactor, and an inverter connected to a capacitive load, comprising:
- output-frequency detection means for detecting whether or not the output frequency of said inverter is higher than a predetermined value;
- forced-commutation means, coupled to said output-frequency detecting means, for forcibly commutating switching elements constituting said inverter when said output frequency is lower than said predetermined value;
- and
- load-commutation means, coupled to said output-frequency detection means, for load-commutating said switching elements when said output frequency is higher than the said predetermined value and a current supplied to said inductive and capacitive loads becomes a phase-advanced reactive current.
Dependencies are inferred from the claim text.