Hybrid topology for multilevel power conversion
First Claim
1. A multilevel electric power converter, comprising:
- (a) a plurality of DC voltage sources providing DC source voltage levels, wherein a DC source voltage level provided by a one of the plurality of DC voltage sources is different from a DC source voltage level provided by another of the plurality of DC voltage sources;
(b) inverter switching devices connected to the DC voltage sources to form a plurality of inverters connected in series to an output of the power converter; and
(c) controller means for controlling the inverter switching devices to synthesize a multilevel inverter output voltage signal at the output of the power converter by selectively combining the DC source voltage levels provided by the DC voltage sources.
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Abstract
The present invention provides a multilevel electric power converter including a plurality of DC voltage sources providing different DC source voltage levels. The DC source voltage levels are preferably multiples of each other and may vary in a binary fashion or in a geometric progression with a factor of three to provide a large number of output voltage levels for a given number of inverter levels. The multilevel inverter is preferably implemented as a series connected set of H-bridge inverters, with each H-bridge inverter having an independent DC voltage source providing the desired DC source voltage level. A hybrid modulation strategy may be employed whereby the lowest voltage level inverter is modulated at a high frequency, e.g., by pulse width modulation, and higher voltage level inverters in the multilevel inverter are modulated to provide a low frequency stepped waveform. The combined high frequency pulse width modulated and low frequency stepped waveform has good spectral quality. A high voltage high quality waveform may be generated in this manner by taking advantage of the high voltage blocking capability of switching devices, such as GTO thyristors, in the high voltage inverters in the multilevel inverter, and the high frequency switching characteristics of switching devices, such as IGBTs, in the lowest voltage level inverter in the multilevel inverter. A multilevel inverter in accordance with the present invention may be employed in a single-phase or multi-phase applications.
175 Citations
31 Claims
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1. A multilevel electric power converter, comprising:
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(a) a plurality of DC voltage sources providing DC source voltage levels, wherein a DC source voltage level provided by a one of the plurality of DC voltage sources is different from a DC source voltage level provided by another of the plurality of DC voltage sources; (b) inverter switching devices connected to the DC voltage sources to form a plurality of inverters connected in series to an output of the power converter; and (c) controller means for controlling the inverter switching devices to synthesize a multilevel inverter output voltage signal at the output of the power converter by selectively combining the DC source voltage levels provided by the DC voltage sources. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A multilevel electric power converter, comprising:
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(a) a first inverter including a first DC voltage source providing a first DC source voltage level and first inverter switching devices connected across the first DC voltage source and responsive to first inverter switching device control signals; (b) a second inverter connected in series with the first inverter and including a second DC voltage source providing a second DC source voltage level and second inverter switching devices connected across the second DC voltage source and responsive to second inverter switching device control signals; (c) an output of the electric power converter connected to the first and second inverters; and (d) controller means for providing the first inverter switching device control signals and second inverter switching device control signals to control the first and second inverters to synthesize an AC voltage waveform on the output of the electric power converter, wherein the first inverter switching device control signals are provided at a frequency much higher than a fundamental frequency of the AC voltage waveform on the output of the electric power converter, and wherein the second inverter switching device control signals are provided to control the second inverter to produce a stepped waveform output signal. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for providing a multilevel electric power converter output voltage signal, comprising the steps of:
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(a) providing a plurality of DC voltage sources having DC source voltage levels, wherein a DC source voltage level provided by a one of the plurality of DC voltage sources is different from a DC source voltage level provided by another of the plurality of DC voltage sources; and (b) synthesizing a multilevel electric power converter output voltage signal having a peak voltage level higher than a largest of the plurality of DC source voltage levels by selectively combining the DC source voltage levels provided by the DC voltage sources. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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30. A method for controlling a multilevel electric power converter to synthesize an AC voltage waveform on an output thereof, wherein the electric power converter includes a first inverter having a first DC voltage source providing a first DC source voltage level and first inverter switching devices connected across the first DC voltage source and responsive to first inverter switching device control signals, a second inverter connected in series with the first inverter and having a second DC voltage source providing a second DC source voltage level and second inverter switching devices connected across the second DC voltage source and responsive to second inverter switching device control signals, wherein the output of the electric power converter is connected to the first and second inverters, comprising the steps of:
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(a) providing the first inverter switching device control signals at a frequency much higher than a fundamental frequency of the AC voltage waveform on the output of the electric power converter to produce a high frequency inverter output signal; and (b) providing the second inverter switching device control signals to control the second inverter to produce a stepped waveform output signal which is combined with the high frequency inverter output signal to produce the AC voltage waveform on the output of the electric power converter. - View Dependent Claims (31)
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Specification