Integrated closed loop control method and apparatus for combined uninterruptible power supply and generator system

Abstract

The present invention provides a method, computer program product, and apparatus and control system and method for providing substantially uninterrupted power to a load. The apparatus includes a control system coupled with an electrical power storage subsystem and a electrical power generator. The control system is configured to provide a plurality of modes of operation including at least a static compensator (STATCOM) mode, an uninterruptible power supply (UPS) mode and a generator mode (gen set), and to control transitions between each of the plurality of modes. In one embodiment, the control system is an integrated closed loop control system that includes a current control system and a voltage control system. The apparatus is capable of operating at least two of the plurality of modes simultaneously, including ramping the gen set mode up and simultaneously ramping the UPS mode down as the gen set mode is ramped down.

Description

FIELD OF THE INVENTION This invention pertains generally to control systems, and more particularly to control systems allowing plug-and-play integration of modules in a power conditioning system. BACKGROUND There are different devices known in the art for improving power quality and reliability of grid or utility line power supplied to sensitive loads. Three of these include, a static compensator (STATCOM), an on-line uninterruptible power supply (UPS), and an off-line UPS. A UPS may also be operated in cooperation with a power generator or gen set, for long term interruptions. FIG. 1A illustrates a typical STATCOM 100 in which a Voltage Source Converter (VSC) 102 is connected to an AC system 104 supplying a load 106 through a shunt-connected transformer 107. A capacitor 109 is connected to the DC terminals 108 of the VSC 102 and is usually an integral part of the VSC 102. The VSC 102 controls the line voltage by injecting or absorbing reactive power. A STATCOM aids in controlling...

AI Technical Summary

Benefits of technology

The invention provides an apparatus and method of providing uninterruptible power supply (UPS) capability or operating mode utilizing a voltage source converter (VSC), a source of stored energy, and / or generation together with an integrated cooperative control system. The invention provides for superior performance characteristics over a conventional uninterruptible power supply (UPS), and may be used for both critical loads or for stabilizing critical components in the electrical transmission and distribution grid. Method and apparatus performance improvement and optimization or near-optimization is achieved in both system hardware that provides the uninterruptible power supply and other component choice and operation. In particular, the invention makes it possible to fully utilize a voltage source converter (VSC) for the converter component of a conventional UPS to provide the UPS mode of operation without requiring all of the hardware and control of conventional UPS systems. Furthermore, with a VSC deployed, the inventive control method and apparatus enable a UPS to simultaneously control a load voltage while supplying load power, by independently injecting or absorbing both active and reactive power. Moreover, VSC functionality is preserved during transitions from one mode of operation to another, and during operation of an optionally connected generator set.

Thus, the inventive method and apparatus result in superior performance over conventional systems and methods, by operating the UPS as a static compensator (STATCOM) throughout the entire event duration, whether short or long term, to respond to the load's reactive power requirements. Embodiments of the novel method and apparatus, further, perform dynamic load leveling by providing or absorbing active power, improving and usually optimizing dynamic behavior under island conditions (where the load is isolated from the power grid and may sharply vary over short time periods), and optimizing or nearly optimizing behavior during transitions including load pick up by the UPS, hand off between the UPS and gen set, and re-synchronization to the grid. The inventive method may advantageously be implemented as a computer program and computer program product executing on or in a general or special purpose computer having a processor for executing computer instructions and a coupled memory for storing data, instructions, and commands.

Problems solved by technology

While a STATCOM has relatively low operation costs, a STATCOM does not provide active power and therefore fails to operate under short circuit conditions or other conditions where active power provision is required or desired.

Further, a STATCOM has a limited ability to correct voltage fluctuations due to grid faults or switching events.

The on-line UPS 110 requires double conversion resulting in relatively low efficiency and high operation costs.

Typically, the gen set has a long response time to dynamic voltage (or current) variations and a large overload capability.

The drawback of this operation principle is that the good dynamic behavior of the UPS (that is, rapid response to reactive or active power variations in the load and stabilization of frequency), especially during generator operation, cannot be used or achieved because there is no common control unit available.

Frequency deviations (typically approximately 10% of rated frequency, or about ±6 Hz for 60 Hz operation or ±5 Hz for 50 Hz operation) lasting several seconds may cause trouble or even damage to frequency dependent loads like computer screens, TV sets and other such devices.

However, in conventional UPS plus gen set systems, the full functional advantages of using a four-quadrant voltage source converter (VSC) during transfer to and subsequent operation of the gen set are not realized at least since the individual UPS and gen set controls are not cooperated.

Conventional control systems do not provide system designers as much incentive or flexibility to choose the VSC for the converter (see FIG. 2) since the VSC's full capabilities are not engaged by the available conventional control system technology.

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