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A system and method for efficiently capturing electrical energy from a variable-speed generator are disclosed. The system includes a matrix converter using full-bridge, multilevel switch cells, in which semiconductor devices are clamped to a known constant DC voltage of a capacitor. The multilevel m

A system and method for efficiently capturing electrical energy from a variable-speed generator are disclosed. The system includes a matrix converter using full-bridge, multilevel switch cells, in which semiconductor devices are clamped to a known constant DC voltage of a capacitor. The multilevel matrix converter is capable of generating multilevel voltage wave waveform of arbitrary magnitude and frequencies. The matrix converter can be controlled by using space vector modulation.

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1. A switch cell, that is used in a switch branch of a matrix converter, that generates a multilevel output voltage signal from a multiphase ac electrical input signal having a first set of voltages, frequencies and phases, said output voltage signal being applied to an output leg of said matrix con

1. A switch cell, that is used in a switch branch of a matrix converter, that generates a multilevel output voltage signal from a multiphase ac electrical input signal having a first set of voltages, frequencies and phases, said output voltage signal being applied to an output leg of said matrix converter to generate a multiphase ac electrical output signal having different voltages, frequencies and phases, said switch comprising:four inverter arms, each of said four inverter arms comprising a diode having a positive pole and a negative pole, and a transistor having a gate, an emitter and a collector, said emitter connected to said negative pole of said diode and said collector connected to said positive pole of said diode, a first of said four inverter arms being connected to a positive node of said full bridge inverter and to an input leg of said plurality of input legs, a second of said four inverter arms being connected to said positive node of said full bridge inverter and to an output leg of said plurality of output legs, a third of said four inverter arms being connected to a negative node of said full bridge inverter and to said input leg, and a fourth of said four inverter arms being connected to said negative node of said full bridge inverter and to said output leg; a capacitor that is connected between said positive node of said full bridge inverter and said negative node of said full bridge inverter, that is charged to a dc voltage from said multiphase ac electrical input signal to produce said multilevel output voltage signal. 2. The switch cell of claim 1 wherein said multiphase ac electrical input signal is generated by a variable speed wind turbine.3. A matrix converter for converting a multiphase ac electrical input signal to a multiphase ac electrical output signal comprising:a switch matrix that connects a plurality of input legs of said matrix converter to a plurality of output legs of said matrix converter via switch branches; a plurality of multilevel switch cells that generate a multilevel output voltage signal that is applied to said plurality of output legs of said matrix converter to substantially match the phase, frequency and output voltage level of said multiphase ac electrical output signal, said plurality of multilevel switch cells having a full bridge inverter with a capacitor connected between positive and negative nodes of said inverter, to produce said multilevel output voltage signal in response to said control signals; a controller that generates said control signals by determining desired reference vectors for said multilevel output voltage signal and modulating between space vectors adjacent said desired reference vectors. 4. The matrix converter of claim 3 wherein said multiphase ac electrical input signal is generated by a variable speed wind turbine.5. The matrix converter of claim 3 wherein said plurality of multilevel switch cells are serially connected in each of said switch branches so that the output voltage of said multilevel output voltage signal that is generated by said plurality of multilevel switch cells is reduced in magnitude.6. The matrix converter of claim 3 wherein said full bridge inverter further comprises:four inverter arms, each of said four inverter arms comprising a diode having a positive pole and a negative pole, and a transistor having a gate, an emitter and a collector, said emitter connected to said negative pole of said diode and said collector connected to said positive pole of said diode; a first of said four inverter arms being connected to a positive node of said full bridge inverter and to an input leg of said plurality of input legs, a second of said four inverter arms being connected to said positive node of said full bridge inverter and to an output leg of said plurality of output legs, a third of said four inverter arms being connected to a negative node of said full bridge inverter and to said input leg, and a fourth of said four inverter arms being connected to said negative node of said full bridge inverter and to said output leg; a capacitor that is connected between said positive node of said full bridge inverter and said negative node of said full bridge inverter, that is charged to a dc voltage from said multiphase ac electrical input signal to produce said multilevel output voltage signal. 7. A matrix converter for converting a multiphase ac electrical input signal having a first set of voltage levels, frequencies, and phases to a multiphase ac electrical output signal having different voltage levels, frequencies, and phases, comprising:a plurality of input legs of said matrix converter that conduct said multiphase ac electrical input signal to said matrix converter; a plurality of output legs of said matrix converter that conduct said multiphase ac electrical output signal from said matrix converter; a series connected inductor disposed in each of said plurality of input legs of said matrix converter that filter said multiphase ac electrical input signal; a series connected inductor disposed in each of said plurality of output legs of said matrix converter that filter said multiphase ac electrical output signal; and a switch matrix that connects each of said plurality of input legs to each of said plurality of output legs via a plurality of switch branches, said switch matrix comprising: a plurality of multilevel switch cells that generate a multilevel output voltage signal, from said multiphase ac electrical input signal, that is applied to said plurality of output legs of said matrix converter to substantially match said phase and said output voltage level of said ac electrical output signal on said plurality of output legs of said matrix converter, said multilevel switch cells being serially connected in each of said switch branches so that the output voltage of said multilevel output voltage signal that is generated by said plurality of multilevel switch cells is reduced in magnitude, said plurality of multilevel switch cells comprising: a full bridge inverter that generates said multilevel output voltage signal in response to control signals, said full bridge inverter having four inverter arms, each of said four inverter arms comprising a diode having a positive pole and a negative pole, and a transistor having a gate, an emitter and a collector, said emitter connected to said negative pole of said diode and said collector connected to said positive pole c)f said diode, a first of said four inverter arms being connected to a positive node of said full bridge inverter and to an input leg of said plurality of input legs, a second of said four inverter arms being connected to said positive node of said full bridge inverter and to an output leg of said plurality of output legs, a third of said four inverter arms being connected to a negative node of said full bridge inverter and to said input leg, and a fourth of said four inverter arms being connected to said negative node of said full bridge inverter and to said output leg; and a capacitor, that is connected between said positive node of said full bridge inverter and said negative node of said full bridge inverter, that is charged to a dc voltage from said multiphase ac electrical input signal to produce said multilevel output voltage signal; a controller that generates said control signals by determining a desired reference vector for said multilevel output voltage signal and modulating between space vectors adjacent said desired reference vector. 8. The matrix converter of claim 7 wherein said multiphase ac electrical input signal is generated by a variable speed wind turbine.9. A method of converting a multiphase ac electrical input signal having a first set of voltages, frequencies and phases to a multiphase ac electrical output signal having different voltages, frequencies and phases comprising:applying said multiphase ac electrical input signal to a plurality of input legs of a matrix converter; connecting said plurality of input legs of said matrix converter to a plurality of output legs of said matrix converter via a plurality of switch branches; generating a multilevel output voltage signal from said multiphase ac electrical input signal using at least one multilevel switch cell in each of said switch branches, said switch cells generating said multilevel output voltage signal using a full bridge inverter with a capacitor connected between positive and negative nodes of said inverter, to produce said multilevel output voltage signal in response to control signals; and generating said control signals by determining a desired reference vector for a desired output voltage of said multilevel output voltage signal and modulating between space vectors adjacent said desired reference vector. 10. The method of claim 9 wherein said process of generating said multilevel output voltage signal comprises using a full bridge inverter having four inverter arms, each of said four inverter arms comprising a diode having a positive pole and a negative pole, and a transistor having a gate, an emitter and a collector, said emitter connected to said negative pole of said diode and said collector connected to said positive pole of said diode, a first of said four inverter arms being connected to a positive node of said full bridge inverter and to an input leg of said plurality of input legs, a second of said four inverter arms being connected to said positive node of said full bridge inverter and to an output leg of said plurality of output legs, a third of said four inverter arms being connected to a negative node of said full bridge inverter and to said input leg, and a fourth of said four inverter arms being connected to said negative node of said full bridge inverter and to said output leg; anda capacitor, that is connected between said positive node of said full bridge inverter and said negative node of said full bridge inverter, that is charged to a dc voltage from said multiphase ac electrical input signal to produce said multilevel output voltage signal generated by each of said plurality of multilevel switch cells. 11. The method of claim 9 wherein said process of generating a multilevel output signal comprises using a plurality of serially connected multilevel switch cells in each of said switch branches to reduce the magnitude of said multilevel output voltage signal on each of said serially connected multilevel switch cells.12. A method of converting a multiphase ac electrical input signal to a multiphase ac electrical output signal comprising:applying said multiphase ac electrical input signal to a plurality of input legs of a matrix converter; filtering said multiphase ac electrical input signal with a series connected inductor disposed in each of said plurality of input legs; connecting said plurality of input legs to a plurality of output legs of said matrix converter via a plurality of switch branches using a switch matrix; generating a multilevel output voltage signal from said multiphase ac electrical input signal using a plurality of serially connected multilevel switch cells in each of said switch branches to reduce the magnitude of said multilevel output voltage signal on each of said multilevel switch cells, said switch cells generating said multilevel output voltage signal using a full bridge inverter that generates said multilevel output voltage signal in response to control signals, said full bridge inverter having four inverter arms, each of said four inverter arms comprising a diode having a positive pole and a negative pole, and a transistor having a gate, an emitter and a collector, said emitter connected to said negative pole of said diode and said collector connected to said positive pole of said diode, a first of said four inverter arms being connected to a positive node of said full bridge inverter and to an input leg of said plurality of input legs, a second of said four inverter arms being connected to said positive node of said full bridge inverter and to an output leg of said plurality of output legs, a third of said four inverter arms being connected to a negative node of said full bridge inverter and to said input leg, and a fourth of said four inverter arms being connected to said negative node of said full bridge inverter and to said output leg, and a capacitor connected between said positive node of said full bridge inverter and said negative node of said full bridge inverter that is charged to a dc voltage from said multiphase ac electrical input signal to produce said multilevel output voltage on each of said plurality of multilevel switch cells that is applied to said plurality of output legs; generating said control signals by determining desired reference vectors for said multilevel output voltage signal and modulating between space vectors adjacent said desired reference vectors; filtering said multilevel output voltage of each of said plurality of multilevel switch cells using a series connected inductor in each of said plurality of output legs to produce said multiphase ac electrical output signal.