Electricity: single generator systems – With flywheels or massive moving parts
Utility Patent
1999-05-12
2001-01-02
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
With flywheels or massive moving parts
C290S052000, C307S064000
Utility Patent
active
06169390
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to power transmission and distribution systems, and more particularly to a flywheel-microturbine system for providing long and short term backup power to a load.
BACKGROUND OF THE INVENTION
Microturbine Systems for Long Term Backup Power
Recent improvements in permanent magnet and other materials have led to the production of high speed permanent magnet generators that are especially suitable for use with microturbines. When connected to a microturbine, a high speed permanent magnet generator is typically operated as a motor for starting the microturbine. During this starting phase, an inverter supplies high frequency AC voltage to the generator's stator. After, the turbine has come up to speed, it provides power to a load (backup power) or directly to the power grid (grid-parallel operation), through a power electronics converter.
FIG. 1
schematically depicts a typical system incorporating a microturbine prime mover
10
, high speed generator
12
, and power electronics
14
for both starting and normal operation. During starting, either the power grid or some form of backup energy provides power to the DC bus. This energy flows through a high frequency inverter N
2
to operate the high speed generator
12
as a motor. When the turbine
10
comes up to some high speed, spark and fuel are applied. The turbine
10
then runs on its own, coming up to full operating speed.
The high speed generator
12
then provides power to the DC bus through a rectifier D
1
. Another inverter N
1
takes the energy coming into the DC bus and converts it to the power grid frequency and voltage (via a transformer T
1
, which is not always needed) to either drive a load or inject current into the power grid. Inverter N
1
may also be made to function as the starting inverter for applications where the device does not need to output power during the starting phase.
Flywheel Systems for Short Term Backup Power
A flywheel, in conjunction with power electronics, can function as an energy storage device for a power system. Typically, a flywheel is spun up to speed using a high frequency AC inverter. During discharge, the flywheel typically delivers energy through a rectifier to a DC bus.
FIG. 2
illustrates a typical system incorporating a flywheel
16
and the power electronics
14
′ needed to interface with the load or power grid. This diagram shows the electronics
14
′ in an on-line UPS layout; however, other topologies, such as off-line or line-interactive, are possible. During normal operation, the power grid provides power to the DC bus through rectifier D
1
. Power flows through the DC bus to inverter N
2
to spin the flywheel up to speed and to add energy as various loss mechanisms deplete the flywheel's total energy storage. Power also flows through the DC bus to inverter N
1
to power the load or add energy to the grid.
When the power grid fails, the flywheel discharges current through a rectifier D
2
to the DC bus. The rectifier may be built into inverter N
2
or be external to N
2
as shown. Inverter N
1
only needs to provide voltage at the frequency of the power grid, but it must be rated for full load power. Inverter N
2
must provide high frequency, but it only needs to be rated for a fraction of full load power—assuming that the flywheel spin-up speed is allowed to be much lower than the flywheel's discharge speed.
Power quality systems of the kind described above often incorporate short term backup systems and long term backup systems. The short term backup systems provide stored energy (via a flywheel, battery, capacitor, or the like) that is available at all times. The long term backup power systems generate power (e.g., with a diesel generator) that is available only after a delay on the order of a few seconds. The delay is a result of having to bring the generator's prime mover up to operating speed. When flywheel energy storage is used in combination with microturbine power generation, the overall system suffers because of typically long spin up delays in the microturbine. One solution to this problem is to use over-rated power electronics for spinning up the turbine, but this is very expensive. A goal of the present invention is to provide a system for decreasing the microturbine/high speed generator spin-up time without increasing the size and cost of the power electronics.
SUMMARY OF THE INVENTION
The present invention provides a power supply system for providing long and short term backup power to a load. A system in accordance with the invention comprises a microturbine system, a flywheel system, and a power electronics module. The microturbine system includes a microturbine attached to a first, high speed motor-generator that includes a first stator, and the flywheel system includes a flywheel attached to a second motor-generator. According to the invention, the microturbine system is started by coupling a high frequency AC voltage output of the flywheel system to the stator of the first motor-generator.
In a presently preferred embodiment of the invention, the connection of the high frequency AC voltage to the stator involves no intervening electronics. Moreover, the high frequency AC voltage is preferably in the range of from about 500 Hz to about 2 kHz. Further, the power electronics module preferably comprises an inverter capable of motoring both the flywheel and the microturbine.
Other aspects of the present invention are described below.
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ABB Power T&D Company Inc.
Ponomarenko Nicholas
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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