Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2000-11-02
2004-03-02
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S132000, C323S351000
Reexamination Certificate
active
06700804
ABSTRACT:
TECHNICAL FIELD
The invention relates to power conversion electronics.
BACKGROUND OF THE INVENTION
Alternating current (AC) has been almost universally adopted for utility power distribution and consequently is the standard form of electrical power for industrial, commercial, and domestic purposes. Independent of the source of energy used to generate the electricity (for example, hydroelectric, nuclear, solar, wind-power), AC must be provided at a fixed frequency of 60 Hz in North America (usually 50 Hz elsewhere) and phase-synchronized before being made available to the large power grid from which users obtain electricity.
Semiconductor-based power electronic converters are often used to conform electrical power generated from various power sources to the 60 Hz fixed frequency, phase-synchronized AC required by the grid.
Power compensation systems are often used to provide real and/or reactive power to a utility power system in response to voltage instabilities or fault conditions on the systems. In such power compensation systems, DC sources including batteries, capacitor banks, fuel cells, or superconducting magnetic energy storage (SMES) devices supply power to an inverter which converts the DC to AC before introduction to the utility grid. Unfortunately, the DC-AC rectification/inversion process wastes a portion of the generated power due primarily to the dissipation occurring within the large energy storage devices (e.g., inductors) and within the semiconductor devices themselves.
DC to AC power converters typically incorporate switching circuitry which receives a DC voltage and is controlled to generate a pulse width modulated (PWM) signal. This power signal is then provided to a filter network to provide an AC power signal. Typically, the DC signal is pulsed and applied to the primary windings of a transformer. This, in turn, generates a pulsed signal on the secondary windings of the transformer, where the amplitude of the secondary signal is varied in accordance with the ratio of primary to secondary transformer windings. A rectifier and capacitor are typically employed to smooth the pulsed secondary voltage into a AC voltage.
DC to DC converters are often used to convert a DC signal of a first amplitude into a DC signal of a second amplitude. One type of DC to DC converter is known as a “buck” converter and uses a switching device to pulse the DC power signal across a frequency dependant filter network, such as an inductive-capacitive (or LC) filter. The amplitude of the signal is directly proportional to the duty cycle of the pulsating signal driving the switching device. Typically, these switching devices are power transistors, relays, or any other form of electronic switching device.
SUMMARY OF THE INVENTION
The invention relates to power conversion circuitry operated to perform DC-AC, DC-DC, AC-DC, and AC-AC power conversion.
In one aspect of the invention, an integrated assembly includes a power converter module having an input bus bar, an output bus bar, an n-level inverter and driver circuitry adapted to control the n-level converter, in response to received control signals. The n-level converter switches between a pair of voltage levels selected from a set of n levels, where n is 3 or greater. The integrated assembly also includes a controller providing the control signals to the driver circuitry, and fiber optic lines connecting the driver circuitry of the n-level converter to the controller.
Embodiments of this aspect of the invention may include one or more of the following features. The n-level converter is capable of generating power levels in excess of 1 megawatt and preferably as high as 2.5 megawatts at 7.6 KV. The integrated assembly has a width of approximately 20 inches, a length of approximately 28 inches, and a height of approximately 23 inches. The n-level converter includes a printed circuit board (PCB). The n-level converter is an n-level inverter.
The integrated assembly includes a DC-DC converter which, in operation, receives a DC input voltage, generates a DC output voltage and provides the DC output voltage to the n-level inverter. The DC-DC converter includes controlled switching devices (e.g., power transistors), each receiving a portion of the DC input voltage and each having a voltage rating characteristic less than said DC input voltage. The sum of the voltage rating characteristics of each of the controlled switching devices is greater than the DC input voltage. The controlled switching devices include a first switching device and a second switching device, and the DC-DC converter includes a filter circuit connected between output terminals of the first and second switching devices. The filter circuit includes a capacitive device for providing the DC output voltage to a load, such as auxiliary electronic circuitry associated with the n-level converter. The integrated assembly includes a diode, positioned between the outputs of the first and second switching devices, for providing a discharge path for the capacitive device of the filter circuit.
The controller is adapted to selectively energize and deenergize said switching devices, a duty cycle of the switching devices controlling the amplitude of the DC output voltage. The controller, in operation, is configured to monitor the DC output voltage and adjust said duty cycle of the switching devices to maintain said DC output voltage at a predetermined level.
The controller includes protection circuitry, which in response to an indication of a fault condition of the integrated assembly provides a signal to the controller to terminate operation of the n-level power converter module. The fault condition may be an overvoltage, undervoltage, overcurrent, or an over-temperature condition. The protection circuitry includes a sensor, which monitors the output of the n-level power converter module and, in response to an overvoltage condition at an output of the n-level power converter module, provides the signal to the controller to terminate operation of the n-level power converter module. The sensor monitors the output current of the n-level power converter module. The integrated assembly also includes a cooling system including, for example, a heat sink.
Among other advantages, the n-level power converter module is used in a stand-alone configuration, integrated, for example, with a high power DC power source. In addition, the microcontroller for providing the intelligence required by the n-level converter module is part of (i.e., on-board) the integrated assembly. Because the “on-board” microcontroller can be programmed, the n-level converter module's functionality can be changed for use in different applications. Furthermore, the n-level inverter module is bi-directional. By “bi-directional” it is meant that electric power is allowed to flow in either direction through the n-level inverter. The power flowing out of the inverter can have different characteristics than the power flowing in; providing a method for conditioning the power. Thus, the microcontroller of the n-level inverter module can be programmed to perform AC-DC conversion (rectification), DC-DC conversion, DC-AC conversion (inversion), and AC-AC conversion. For example, in one application, the integrated assembly is used to condition power for a motor drive, while in another application, it is used as part of an uninterruptible power supply (UPS). The ability to use the same integrated assembly for different applications provides tremendous flexibility to the user. Although the various parts of the system (e.g., protection circuitry, switch sequencing) can operate relatively autonomously, the particular manner in which they operate can be changed to, suit a particular application.
Fiber optic lines provide high speed, noise immune communication of signals between components of the system; thus, transmission losses are reduced. Furthermore, because the n-level converter is constructed on a printed circuit board, the interconnection paths between components (e.g., high power switching devices) of the converter and drive c
American Superconductor Corporation
Fish & Richardson P.C.
Han Jessica
LandOfFree
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