Dual feedback loop DC-to-AC converter

A DC-to-AC converter for supplying a regulated AC to a load at a predetermined frequency from a DC power source, comprising:

• a. a DC-to-DC converter connected to the DC power source, including means for producing a high frequency AC that is transformed and rectified to provide a controlled intermediate DC voltage that can differ from the DC voltage of the DC power source;
• b. a capacitor bank for storing energy of the intermediate DC voltage provided by the DC-to-DC converter, this stored energy being used to meet short-term peak power demands of the load;
• c. a DC-to-AC inverter connected to the capacitor bank and operative to convert the intermediate DC voltage across the capacitor bank to an AC output signal having quasi-sine wave shaped positive and negative pulses during each period thereof;
• d. a current transformer for producing a current signal indicative of the current in the DC-to-DC converter;
• e. a voltage monitoring circuit for producing an error signal as a function of the difference between the intermediate DC voltage across the capacitor bank and a reference voltage, wherein the voltage monitoring means include integrator means for integrating the intermediate DC voltage across the capacitor bank with a short time constant, if the intermediate DC voltage is less than a predetermined minimum value and otherwise, with a long time constant, thereby producing an integrated signal for comparison with the reference voltage;
• and
• f. pulse width control means, connected to receive the current signal and the error signal, for producing a variable pulse width signal that regulates the intermediate DC voltage produced by the DC-to-DC converter in response to both the current signal and the error signal, thereby regulating the AC output signal from the DC-to-AC inverter.

A method for converting DC to AC and regulating the voltage level of an AC signal supplied to a variable load, comprising the steps of:

• a. variably controlling power supplied from a DC source to obtain an intermediate DC voltage signal by converting a DC power signal from the DC source to a high frequency AC signal, transforming the high frequency AC signal to an AC voltage, and rectifying the AC voltage to a DC voltage that can differ from that of the DC source;
• b. storing energy in a capacitor substantially at a predetermined DC voltage level;
• c. inverting the intermediate DC voltage signal, producing an AC output signal;
• d. monitoring a DC supplied to charge the capacitor to the predetermined DC voltage level, producing a current signal indicative of a magnitude of that DC;
• e. monitoring the intermediate DC voltage signal across the capacitor, producing an error signal indicative of the difference between that voltage and the predetermined DC voltage level;
• f. regulating the intermediate DC voltage signal in response to the current signal and the error signal, by controlling the power supplied by the DC source, thereby regulating the AC output.

A direct current (DC) to alternating current (AC) converter, comprising:

• a. DC-to-DC converter means, connected to a source of DC voltage, for producing an intermediate DC voltage signal, the DC-to-DC converter means including a DC-to-AC converter, a rectifier, and a power transformer connected to supply AC from the DC-to-AC converter to the rectifier that produces the intermediate DC voltage signal;
• b. a capacitor connected to receive the intermediate DC voltage signal and operative to store energy from that signal;
• c. DC-to-AC inverter means, connected to the capacitor, for inverting the intermediate DC voltage signal, thereby forming an AC output signal that can be used to power a load;
• d. current monitoring means that includes a transformer connected to monitor the AC that the power transformer supplies to the rectifier, wherein the current monitoring means produces a current signal indicative of the magnitude of that AC;
• e. voltage monitoring means for monitoring the intermediate DC voltage signal across the capacitor and producing an error signal corresponding to the difference between the intermediate DC voltage signal and a predetermined DC voltage;
• and
• f. control means, connected to receive the current signal and the error signal, for regulating the voltage of the intermediate DC voltage signal, and thus the AC output signal supplied to the load by the DC-to-AC inverter means, in response to the current signal and the error signal.

A method for converting DC to AC and regulating the voltage level of an AC signal supplied to a variable load, comprising the steps of:

• a. variably controlling power supplied from a DC source to obtain an intermediate DC voltage signal;
• b. storing energy in a capacitor substantially at a predetermined DC voltage level;
• c. inverting the intermediate DC voltage signal, producing an AC output signal;
• d. monitoring a DC supplied to charge the capacitor, producing a current signal indicative of a magnitude of that DC;
• e. monitoring the intermediate DC voltage signal across the capacitor to produce an error signal indicative of the difference between that voltage and the predetermined DC voltage level;
• f. integrating the error signal selectively using either a short time constant or a long time constant producing an integrated error signal, the long time constant being used unless the intermediate DC voltage signal across the capacitor is less than a predetermined minimum;
• and
• g. controlling the power supplied by the DC source in response to the current signal and the integrated error signal, thereby indirectly regulating the AC output.