Electricity: single generator systems – Automatic control of generator or driving means
Reexamination Certificate
2002-12-31
2004-10-05
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
C322S007000, C322S016000, C322S028000, C290S04000F, C290S044000
Reexamination Certificate
active
06801019
ABSTRACT:
This invention relates to an AC power generating system in which an AC power output is produced by conversion from an intermediate DC output.
WO98/28832 discloses a generating set which comprises an engine/generator which provides a variable voltage electrical output, this output being rectified and fed to a DC to DC converter, the output DC voltage of the DC to DC converter being monitored by a control circuit and serving as an intermediate DC output which is fed to an inverter to generate an AC output which supplies an external load. The DC to DC converter decouples or isolates the intermediate DC output from the fluctuations in the current and/or voltage output of the generator so that the apparatus is able to accommodate substantial variations in the output of the generator while maintaining the intermediate DC output within desired operating parameters. The DC to DC converter also serves to decouple or isolate the generator from variations in the load. An energy storage device, for example a capacitor, is connected in parallel with the DC link and thereby provides a short term energy reserve when the load applied to the DC link voltage varies suddenly. This energy storage device may be supplemented by other similar devices with respective control systems. In some cases such supplementary energy storage devices may be excluded. Instead a load anticipation circuit may be introduced to cope with high impact or step loads.
The concept of power generation by such a generating set which automatically varies its speed to match load variations at any time is to operate the prime mover at an optimum speed, based on efficiency or fuel economy or low noise or any other desirable parameter, while providing the required engine kW output to satisfy the load demand and any losses in the system. To achieve this, the control circuit includes various electronic controllers which monitor and control the intermediate DC output or link voltage across a capacitor, through a voltage sensor and a feedback signal voltage.
The measurement and control circuit of the generating set disclosed in WO98/28832 monitors the generator output voltage and current together with the DC link voltage and operates through a feedback control loop to vary the speed of the engine so as maintain the DC link voltage constant and limit the generator output current to a level determined a current reference signal.
U.S. Pat. No. 5,563,802 discloses an integrated power system which includes an engine/generator power supply integrated with storage batteries to provide household-like AC power. For a small load demand, the storage batteries are used to provide electricity. For a large load demand, the engine/generator starts to supply electricity. The engine/generator also recharges the storage batteries if the load demand is smaller than the engine/generator maximum load capacity. For a larger load demand, both the engine/generator and the storage batteries supply electricity in parallel. The engine speed is variable for various loads. A pulse-width modulated signal is generated which monitors the DC voltage of the high voltage DC bus. This arrangement provides the variable engine speed system by speeding up or slowing down as the system power requirements change so as to maintain the voltage on the high voltage DC bus substantially constant. The bigger the load, the higher the engine speed that is required to produce the necessary power and keep a constant DC voltage.
U.S. Pat. No. 5,198,698 discloses an auxiliary power supply system including an internal combustion engine driving an alternator the output of which is rectified and supplied to DC bus lines across which a storage battery is connected. The DC bus lines may supply a consuming device such as an uninterruptible power supply or telecommunications system. The voltage across the bus lines is sensed and when the voltage drops below a selected value, indicating that the consuming device is drawing power from the battery beyond a desired limit, the engine is turned on for a period of time to warm it up, during which the power from the generator is not supplied to the DC bus lines. Thereafter, the generator supplies power to the DC bus lines to supply the consuming device and partially recharge the battery until the consuming device is no longer drawing power, after which the engine is shut off. The power supply system includes a controller which monitors the intervals of time between turn-ons of the engine and if a selected period of time is exceeded, the engine is started without supplying power from the generator to the DC bus lines to allow the engine and generator to warm-up, enhancing maintenance of the system. The operating characteristics of the engine and generator are sensed and stored for access by an operator and warnings are provided if these conditions exceed acceptable limits.
One object of one aspect of this invention is to enable operation of such a generating set without there having to be an energy storage device connected in parallel with the DC link to provide a short term energy reserve when the load applied to the DC link voltage varies suddenly.
According to one aspect of this invention there is provided an AC power generating system including inverter means which are operable to convert an intermediate DC voltage into an AC power output, means for generating and maintaining the intermediate DC voltage at one level and voltage sensor means operable to monitor the intermediate DC voltage, wherein control means are provided for the inverter means, said control means being responsive to the voltage sensor means and being operable to control operation of the inverter means so the voltage and/or the frequency of the AC power output is/are reduced in response to a fall in the intermediate DC voltage to a certain level caused by the application of a step load to the AC power output, whereby to provide a transient off-loading effect which will give the generating means time to respond and thereby allow the intermediate DC voltage to be restored to said one level.
The means for generating and maintaining the intermediate DC voltage of a preferred embodiment of this aspect of the invention include generator means operable to generate a variable voltage AC power supply and rectifier means having an output and operable to rectify the variable voltage AC power supply to establish the intermediate DC voltage.
Conveniently the generator means are driven by a variable speed prime mover, the control means of the generator means comprising speed control means operable to control the speed of the prime mover. Preferably the generator means-are a prime mover driven permanent magnet generator.
If the neutral of the AC output of the generating set disclosed by WO98/28832 were to be connected to the neutral terminal of the generator, the variable voltage three-phase output of the generator would have to be rectified by a half wave rectifier. As a result large and costly inductors would need to be used for the intermediate DC link. Furthermore, there would be a risk that a DC component could be established in the windings of the generator. This could result in torque pulsations due to the DC component of the generator current.
U.S. Pat. No. 4,507,724 discloses a polyphase inverter system which converts DC power developed by a DC source into polyphase AC power to drive a load. The DC source may be a generator and rectifier arrangement which includes control and protection circuitry for operating the generator. In any event, the DC source includes two terminals at first and second voltages and a neutral or common terminal which is at a voltage midway between the first and second voltages. The neutral of the polyphase AC power developed by the inverter is connected to the neutral or common terminal of the DC source.
U.S. Pat. No. 3,775,663 discloses a solid state inverter having an electronic neutral which is an additional single phase inverter operated as a current source or sink to maintain the potential at the neutral terminal at a controlled voltage independent of ne
Al-Khayat Nazar
Al-Tayie Jawad
Brown Neil
Dalby Denis Hedley
Dziuba Robert Pawel
Cuevas Pedro J.
Gron Gary M.
Newage International Limited
Ponomarenko Nicholas
Schelkopf J. Bruce
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