Very high efficiency uninterruptible power supply
View Patent ↗The invention is an electrical power conversion topology. The preferred embodiment is as a three-phase, on-line Uninterruptible Power Supply (UPS). The desired AC output voltage waveform is formed on each output line or phase of the UPS, using pulse modulation techniques and a smoothing output filter inductor. A semiconductor switching matrix is used to switch the power converter side of each output filter inductor between three voltage potentials, a positive battery potential, a negative battery potential and a third intermediate and varying AC potential synchronized with the desired output voltage. The invention potentially provides the same performance as that of a multi-level inverter topology approaching an infinite number of DC levels.
1. An on-line uninterruptible power supply for supplying power to an external AC load comprising; a positive DC source, a negative DC source, an AC source, an inductor and an arrangement of semiconductor switches, wherein each of said positive DC source, said negative DC source, said AC source and said external AC load have first and second terminals, wherein the second terminal of each of said positive DC source, said negative DC source, said AC source and said external AC load are coupled to an arbitrary neutral point, wherein DC source adjectives positive and negative refer to DC voltage potentials with respect to said arbitrary neutral point and wherein said arrangement of semiconductor switches provide a means for selectively coupling the first terminal of each of said positive DC source, said negative DC source or said AC source to a first terminal of said inductor and wherein a second terminal of said inductor is coupled to first terminal of said external AC load.
2. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 1 wherein said arrangement of semiconductor switches is capable high frequency pulse width modulation.
3. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 1 wherein said arrangement of semiconductor switches comprises a semiconductor bi-directional AC switch, wherein said semiconductor bi-directional AC switch is a means for discriminating between the direction of current from said AC voltage source input to selectively couple either current in one direction, current with a positive sense, or the opposite direction, current with a negative sense, into said first terminal of the inductor.
4. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 1 wherein; (i) selective coupling of said first terminal of positive DC source or of said first terminal of said negative DC source to said first terminal of the inductor increases or decreases the stored energy in the inductor and (ii) selective coupling said AC source to said first terminal of the inductor maintains the stored energy in the inductor.
5. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 1 wherein a desired voltage is regulated across the external AC load.
6. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 1 wherein said DC sources comprise energy storage batteries, capacitors or a combination of energy storage batteries and capacitors coupled in parallel.
7. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 6 further comprising an input rectifier to charge said energy storage batteries from an electrical power grid.
8. The on-line uninterruptible power supply for supplying power to an external AC load according to claim 1 wherein said AC source is an electrical power grid.
9. A method of providing AC power from an uninterruptible power supply wherein said uninterruptible power supply sources power from an AC source, a positive DC source and a negative DC source to supply power to an AC load wherein the AC source, the positive DC source and the negative DC source are selectively switched at high frequencies using an arrangement of semiconductor switches and pulse or switch-mode modulation to supply an AC current through an inductor and to the AC load wherein one of said AC source, positive DC source and negative DC source may be selected to source or sink current at any instant and wherein a selection of the positive DC source is used to source a positive load current, wherein a selection of the negative DC source is used to source a negative load current and wherein a selection of the AC source is used to clamp a desired low voltage across said inductor, with any of the sources providing the AC load current for a portion of a high frequency pulse or switch-mode modulated switching cycle.