Inverter having constant frequency chopper synchronized to modulation frequency
AssigneeAllis-Chalmers Corporation
InventorFrederick A. Stich
Life of this patent
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Abstract
A static inverter has a chopper transistor between a unidirectional source and the inverter load current carrying semiconductor switches, time ratio controlling means including a constant frequency oscillator for modulating the chopper at the constant oscillator frequency and for regulating the width of pulses conducted by the chopper as a function of the magnitude of an analog command signal, means for modulating the inverter semiconductor switches at a frequency which is a function of the analog command signal to establish the inverter output frequency, and means for synchronizing the switching of the chopper to the inverter output frequency so that the chopper is reset at the beginning of each half cycle of inverter output frequency.
Claims10
A variable frequency, variable voltage power supply comprising, in combination,
- a static inverter adapted to be coupled to a unidirectional electric power source and including a plurality of load current carrying semiconductor switches,
- semiconductor chopper means in one polarity of said source between said source and said semiconductor switches without a filter between said chopper means and said switches,
- means for modulating said semiconductor switches at a selectively variable frequency to establish the output frequency of said inverter,
- means including a carrier constant frequency oscillator for time ratio controlling said chopper means at the carrier frequency of said oscillator, said carrier constant frequency being independent of said inverter output frequency and sufficiently high to permit elimination of a filter between said chopper means and said semiconductor switches, and
- means for synchronizing the switching of said chopper means to said inverter output frequency so that chopping is identical in the positive and negative half cycles of the inverter output waves.
A variable frequency, variable voltage supply comprising, in combination,
- an n-phase inverter adapted to be coupled to a unidirectional electric power source and having a load current carrying semiconductor switch in each output phase,
- chopper transistor means in one polarity of said source between said source and said semiconductor switches
- voltage controlled oscillator means for deriving a train of modulation frequency controlling pulses,
- an n-phase generator for deriving n phase reference waves displaced 360/n electrical degrees apart and synchronized to said modulation frequency controlling pulses and each of which is associated with one phase of said inverter,
- means for modulating said semiconductor switches in the respective phases of said inverter in accordance with the associated phase reference waves to establish the inverter fundamental output frequency,
- oscillator means for generating a train of carrier constant frequency, generally triangular ramp pulses,
- means for comparing said train of ramp pulses to a steady state signal to derive variable width signals at said carrier constant frequency,
- pulse width modulating means for switching said chopper transistor means in accordance with said variable width signals, said carrier constant frequency being independent of said modulation frequency and sufficiently high to permit elimination of a filter between said chopper transistor means and said semiconductor switches, and
- means for synchronizing the switching of said chopper transistor means to said phase reference waves so that said chopper transistor means is reset at the beginning of each half cycle of inverter fundamental output frequency and chopping is the same in the positive and negative half cycles of the inverter output waves.
Dependencies are inferred from the claim text.