초록 ▼

A sinusoidally weighted pulse width modulated switching signal may be developed, for operating an inverter to apply sinusoidal voltage to a single phase a-c induction motor, by comparing a triangular voltage waveform of fixed frequency with a variable frequency sine wave voltage, the switching signa

A sinusoidally weighted pulse width modulated switching signal may be developed, for operating an inverter to apply sinusoidal voltage to a single phase a-c induction motor, by comparing a triangular voltage waveform of fixed frequency with a variable frequency sine wave voltage, the switching signal varying between its high and low states whenever the triangular waveform and modulating sine wave intercept one another. A constant ratio of the amplitude of the sinusoidal motor voltage relative to the voltage\s frequency, and thus motor speed, may be obtained simply by translating the sinusoidal modulating waveform through a high pass filter before it is compared with the triangular wave. By setting the filter cut-off frequency above the operating frequency range (preferably from about 12 to 60 hertz) of the sine wave generator, the sine wave voltage will be attenuated by the filter in an amount inversely proportional to the sine wave frequency. In this way, the amplitude of the sine wave will vary in step with, and directly proportional to, frequency changes to achieve a constant motor voltage/frequency ratio.

대표청구항 ▼

A pulse width modulated inverter system for supplying single phase, adjustable amplitude and frequency sinusoidal voltage to a single phase a-c induction motor at a constant amplitude/frequency ratio, comprising: a triangular wave generator for developing a triangular voltage waveform of fixed frequ

A pulse width modulated inverter system for supplying single phase, adjustable amplitude and frequency sinusoidal voltage to a single phase a-c induction motor at a constant amplitude/frequency ratio, comprising: a triangular wave generator for developing a triangular voltage waveform of fixed frequency; a sine wave generator for developing a sinusoidal voltage waveform of variable frequency; a differential comparator coupled to said generators for producing, in response to the triangular voltage waveform and the sinusoidal voltage waveform, a sinusoidally weighted pulse width modulated switching signal; means responsive to said switching signal for applying to the single phase motor a sinusoidal voltage having an amplitude and frequency determined by the amplitude and frequency of the sine wave voltage received by said comparator; and a high pass filter effectively interposed between said sine wave generator and said comparator for adjusting the amplitude of the sine wave voltage applied to the comparator in response, and in direct proportion, to frequency variations of the sine wave, thereby to maintain a constant ratio between the amplitude and the frequency of the sinusoidal voltage applied to the motor.