United Technologies Corporation

International Fuel Cells, LLC

Other

Kenneth Lipman

Alexander H Levy

Douglas G Young

A method for defining a pulse width modulation (PWM) waveform pattern to control the switching bridges in a power inverter system to produce a low harmonic content output voltage signal includes assigning a waiting factor to each harmonic produced by the switching bridges in the power inverter system. Harmonics reduced by the power inverter system are identified and other harmonics are selected to be reduced. The selected harmonics are represented one-for-one by a corresponding set of equations and the equations are solved by each of the switch points in the PWM waveform pattern. A program for finding the switch points is also presented.

Method for defining pulse width modulation (PWM) waveform patterns to

A current balancing structure in which an alternating current output is produced by alternately connecting a DC potential to an output voltage bus through the switching action of a paralleled array of semiconductor devices forces equal current to flow through each device. During switching intervals, some semiconductor devices may 'turn-on' or 'turn-off' faster than others thus possibly forcing any conductive devices to carry a much higher current than when all the devices are conducting. Diodes protect the conductive devices by providing alternative circuit path to a DC reference potential voltage bus when one device becomes non-conductive before another paralleled device.

Current balancing structure for semiconductor switching devices

A method for reducing the signal harmonics of the output fundamental signals of a three-phase inverter systems made up of an N number of inverter bridges achieves harmonic signal reduction by combining the outputs of immediately adjacent bridges separated by 60.degree./N relative to one another and then summing the combined sum signal with the outputs of the next immediately adjacent bridge.

Harmonic reduction for multi-bridge converters

A method and apparatus is disclosed for generating thyristor gating signals for a force commutated inverter in order to produce variable frequency pulse-width modulated output waveforms with the appropriate percent fundamental voltage content for reactive power control and with the correct phase relationship to the utility line for real power control. A signal processor in conjunction with a memory is used to store individual patterns for generating a wide variety of PWM waveforms at different frequencies over the entire modulation range so as to provide the designer with the flexibility to select the most advantageous harmonic cancellation for each operating point. An embodiment of the invention .disclosed uses three microprocessors to generate the PWM waveforms and a fourth microprocessor to synhcronize the other three and produce the required phase shift. The principles disclosed apply to inverters used and controlled in parallel with a grid of real and reactive control signal commands and also those used independently by means of voltage magnitude commands.

Switching an inverter with stored signal sequences

A novel electrical inverter includes a source of direct current (DC) signals, a plurality, N, of addressable electrical switching devices where N does not equal two configured in parallel to receive signals from the DC source. The electrical switching devices generate a plurality of output signals phased relative to one another. An output transformer has a plurality of parallel configured input inverter winding sets for receiving and transforming a respective one of the phased electrical switching device output signals, and a plurality of serially configured output winding sets providing three phased fundamental signals as the sum of the transformed signals. The inverter is characterized by an auxiliary excitation circuit having a plurality of low voltage AC signal sources each configured with auxiliary winding sets and a series reactor and each for providing excitation signals to a plurality auxiliary winding sets each configured in parallel with and identical to a respective one of said output transformer input winding sets.

Auxiliary excitation circuit for phased transformers

A novel inverter circuit having symmetrical gate turnoff thyristors (GTO) includes reactive circuit elements for recovering stored energy. The circuit is characterized by a center tapped transformer configured without tightly coupled anti-parallel diodes, thereby allowing for the presentation of reverse voltages to each GTO.

Inverter circuit utilizing the reverse voltage capabilities of

A method and apparatus is disclosed for operating a fuel cell 14 which produces electrical energy in combination with an electrochemical cell 12 which uses electrical energy to produce a chemical product. The electrolysis cell produces an oxidant for use in the fuel cell and is linked with the fuel cell by a direct current converter which allows the fuel cell to operate between an upper voltage limit and a lower voltage limit and the electrochemical cell to operate at a voltage which is independent of the fuel cell voltage. In one embodiment, the electrochemical cell produces a fuel and an oxidant for the fuel cell as well as a saleable chemical product such as sodium hydroxide.

Method and apparatus for operating a fuel cell in combination with an

A method and apparatus is disclosed for operating a fuel cell 14 producing electrical energy in combination with an electrochemical cell 12 using electrical energy to produce a chemical product. The electrolysis cell produces hydrogen for use as a fuel in the fuel cell and is linked with the fuel cell by a direct current converter 16 which allows the fuel cell to operate between an upper voltage limit and a lower voltage limit. The direct current converter 16 employs a gated switch means, such as a thyristor 98, to intermittently pass electrical power from the fuel cell to the electrochemical cell such that the voltage drop across the direct current converter is equal to the difference in voltage between the fuel cell and the electrochemical electrolysis cell.

A method and apparatus is disclosed for operating a fuel cell 14 which produces electrical energy using hydrogen in combination with a chlorate electrolysis cell which uses electrical energy to produce a chlorate product and hydrogen. A regulator means employs a direct current converter 16 having a gated switch means, such as thyristor 98, to intermittently pass electrical power from the fuel cell to the chlorate electrolysis cell such that the voltage drop across the direct current converter is equal to the difference in voltage between the fuel cell and the electrolysis cell.

A method and apparatus is disclosed for operating a fuel cell 14 which produces electrical energy in combination with an electrochemical cell 12 which uses electrical energy to produce a chemical product. A direct current converter 16 intermittently passes electrical power from the fuel cell to the electrochemical cell to enable the fuel cell to operate at a desired voltage which is independent of the voltage for the electrochemical cell. This permits the fuel cell to operate within a schedule of desired operating voltages.

An individual commutation for use with an inverter includes two resonant loops one of which is connected to the main current path adjacent each of the main thyristors. Each resonant loop includes a series coupled commutation capacitor and inductor together with commutation thyristor which is enabled to provide a commutation pulse to extinguish the load current through conducting main thyristor for a sufficient period to allow transition to the nonconducting state.

Inverter with individual commutation circuit

A magnetic amplifier sensor for measuring the magnitude and polarity of a DC current flowing in a line includes a pair of saturable cores, each having a primary and secondary winding mounted thereon. The primary coils are connected in series and a portion of the DC current component to be measured is diverted to a shunt circuit which includes the primary windings. The secondary coils are connected to a push/pull type of AC source so that the flux levels in the cores operate in a drive/reset mode. A DC current in the primary winding causes a variation in the absolute magnitude of the flux levels of the two cores as a function of the time constant of the shunt circuit so that during the drive interval one core saturates before the other. After rectifying, a differential signal is formed which when integrated provides an output signal whose magnitude is indicative of the magnitude DC component of current in the shunt circuit and where polarity is indicative of the polarity of the DC component of current in the shunt circuit. A second embodiment of a magnetic amplifier sensor includes an additional winding on each of the saturable cores. A portion of the output signal is fed back to the two additional windings, which are connected in series, to provide the negative feedback for improving overall input-to-output linearity, and also for enhancing the response time of the amplifier sensor.

Dual core magnetic amplifier sensor

The RMS voltage of the output sine wave of a power inverter is regulated by pulse width modulation (PWM) of the rectangular waveform fundamental signal of the inverter bridge with a single sliding notch in each half cycle of the rectangular wave, each notch having a pulse width and position in the wave which is dependent on the required attenuation of the RMS value, and which may be varied, in a continuous manner, between a variable pulse width edge notch, a fixed pulse width notch which slides from an edge notch to a center notch position, and a variable pulse width center notch.

Sliding notch pulse width modulation (PWM)

All harmonics of an order less than (6.multidot.N-1) are cancelled from the fundamental signal presented in each output phase of a three-phase converter as the sum of corresponding phase angle fundamental signals from an N number of converter bridges, where N is a non-power of two.

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West Hartford, CT, United States of America

Kenneth Lipman