Kabushiki Kaisha Toshiba

Shinji Tatara

Satoshi Miyazaki

Kosaku Ichikawa

Masami Okayasu

A neutral point clamped (NPC) inverter control system including a DC power source to output DC voltage having a neutral point, an NPC inverter to convert the DC voltage into AC voltage in three phases through a PWM control, a mode selecting unit to decide a first and a second PWM modes by comparing amplitude of voltage reference with a prescribed value that is defined by a minimum pulse width, a first voltage reference conversion means to add a prescribed bias value at which a polarity changes to positive/negative within a fixed period to secure the minimum pulse width to voltage references in respective phases in a first PWM mode, a second voltage reference conversion means to fix the voltage reference in one phase by a value that secures the minimum pulse width when voltage reference in one phase is smaller than a prescribed value that is defined by the minimum pulse width in a second PWM mode and correct voltage references of other two phases so as to make line voltage to a value corresponding to the voltage reference, and a modulation frequency change-over means to lower PWM control modulation frequency in the first PWM mode and to suppress power loss caused by switching in the first PWM mode.

Neutral point clamped (NPC) inverter control system

A method of controlling a cycloconverter, for supplying an AC power having a given frequency to a converter group having at least two cascade-connected converters and controlling a firing angle of each of the converters, thereby converting the AC power supplied to the converter group into an AC power having a predetermined frequency, includes the steps of controlling an output voltage from a converter in one stage of the converter group to obtain an AC output voltage including a synthetic voltage of an AC voltage having an amplitude equal to a difference between a maximum output voltage of the converter and a DC voltage and a predetermined DC voltage in accordance with the polarity of a reference voltage signal having a predetermined frequency, controlling an output voltage from a converter in the other stage of the converter to obtain an AC output voltage obtained by subtracting the output from of the converter in one stage from the reference voltage signal, and continuously varying a voltage value of the DC voltage in accordance with the frequency of the reference voltage signal.

Cycloconverter and the method of controlling the same

An electric power converter, in which a plurality of converters convert a first electric power having a first frequency into a second electric power having a second frequency, and the second electric power is supplied to a load such as an electric motor, and in which a correction controller changes a reference voltage to generate reference voltage signals to be supplied to the converters in order to shift firing phase angles of the converters, thereby preventing a generation of higher harmonics of integer orders of the first electric power.

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Tokyo, Japan

Shinji Tatara