Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
2000-03-10
2001-02-13
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
C363S069000, C363S071000
Reexamination Certificate
active
06188591
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems for supplying electric-motor loads with electrical energy, for example via the electrical on-board network of a ship or aircraft. According to one particular aspect, a plurality of electricity sources can be operated in parallel, for example diesel engines or gas turbines coupled to AC generators. Furthermore, control loops are proposed for network stabilization and for load sharing between loads that are coupled to one another.
BACKGROUND INVENTION
Conventional separate networks of this type, for example, include three-phase networks with synchronous generators. The real power is distributed via the rotation-speed frequency droop of the rotation-speed regulators for the diesel engines or turbine drives. The reactive load is distributed via the voltage droop of the generator voltage regulator. Droop devices as well as load sharing when two generators are operated in parallel, are described in the technical information document ASI NMA/TNG3 from Siemens AG, entitled “THYRIPART-Erregung in bürstenlosen Siemens-Synchrongeneratoren” [THYRIPART Excitation in Brushless Siemens Synchronous Generators] by Joachim Frauenhofer. The entire contents of this document are hereby included and are presupposed for the following statements.
In three-phase separate networks, it is conventional for an additional voltage value to be generated for load sharing of parallel-operating generators, from the output current of the generator, for the nominal/actual value comparison input of a voltage regulator. The additional voltage value allows the generator voltage to be reduced in proportion to the rising reactive current. However, this is dependent on the capability to influence the generator voltage externally from a separate functional component. Such DC generators or AC generators whose voltage can be controlled or regulated, have the disadvantages, however, that they are physically voluminous, heavy and costly to manufacture. Furthermore, there is a considerable requirement for intrinsically autonomous energy generation and power supply separate networks which are distinguished by being physically small and compact as well as being light in weight, particularly with regard to electricity generators.
U.S. Pat. No. 5,200,643 describes a power supply network that has a plurality of DC supply sources, which feed into amplifiers that have control inputs. Signals for the output actual voltage and the output actual current are combined with a reference signal. The aim in this case is to provide a signal for the control error, with the output voltage of each source being regulated.
U.S. Pat. No. 5,334,436 describes a fuel battery. However, when a plurality of sources are paralleled without any higher-level regulating device it is impossible to achieve sufficiently good and desirable load sharing or to ensure satisfactory network stability.
In order to overcome the disadvantages resulting from the above-mentioned patents, and to solve the equivalent problems, the present invention proposes an energy generation system, a power supply network, and a control loop.
SUMMARY OF THE INVENTION
The present invention provides for a DC voltage supply network to be used for supply networks in aircraft or vehicles, in particular ships, instead of a three-phase supply network, whose voltage can be regulated by means of a controllable rectifier or a DC voltage controller. On the one hand, this is associated with a considerable reduction in weight. On the other hand, no wattless component can be transported in this network, and thus does not result in any problems. All the loads can be coupled to this supply network, if necessary via converters.
This according to the present invention represents a departure from the approach of direct voltage regulation via the excitation of the generators using, instead of this, a rectifier, in particular a transistor rectifier, as a control element for a compensating voltage. This avoids supplying any wattless component into the network. Dynamic network load relief can be carried out without any wattless component by means of the arrangement according to the present invention. A controllable, voltage-regulated rectifier is used that can produce a constant output voltage from alternating current. The real-power distribution can be adjusted by varying, in particular parallel shifting, the droop characteristic or voltage droop for the corresponding rectifier appliance.
The present invention opens up the possibility of using one or more AC voltage generators, which are each excited by permanent magnets, with a low rotating mass and downstream of which a controllable, pulsed transistor rectifier is connected. Particularly when synchronous machines that have permanent-magnet excitation on the rotor are used, the physical size of the generator can be considerably reduced. The generators are driven, for example, by four-stroke diesel engines with a high boost pressure. Such engines can accept load only as quickly as the volume of boost air supplied by the exhaust-gas turbo charger rises.
According to a further embodiment of the present invention, which is based on energy sources whose speed or rotation speed is regulated, a regulator with a proportional-integral characteristic is proposed for this purpose. This allows, for example, the power capacity of the diesel engine as an energy source falls. This energy source stalls, and the network collapses.
With the method for load distribution, on which the system according to the present invention is based, a voltage droop occurs that results in a desired load distribution in that an additional voltage value for the nominal/actual value input of the voltage regulator is produced from the output current of the generator. The additional voltage value allows the voltage to fall in proportion to the rising rectifier output current. This voltage droop is assigned individually to each generating set, which comprises, for example, a diesel engine, generator and rectifier, irrespective of its power capacity. There is no need for any higher level device for load distribution.
Shifting the droop characteristic parallel results in a possibly desired, different load distribution. This is necessary in order to parallel the generators without resulting in a sudden load change on the drive machine, the diesel engine or any other energy source. Manual control of the paralleling of two or more generators is thus possible.
When a system or separate network according to the present invention is loaded predominantly with drives whose rotation speeds are regulated, then any sudden load change is passed on, without being reduced, via the generators to the diesel engines as kinetic energy sources. A diesel engine can accept such a sudden load change initially only by means of the kinetic energy of its rotating mass and the rotating mass of the generator and then, by means of its rotation-speed regulator, it can accept a load level corresponding to the amount of excess combustion air. If the sudden load change is greater than the instantaneous capability to accept the load, the diesel rotation speed falls, and thus the power capacity of the diesel engine as an energy source falls. This energy source stalls, and the network collapses.
In a known three-phase separate network with three-phase motors as a load, a sudden load change leads to a reduction in the rotation speed of the diesel engine, and thus to a frequency reduction. This results in a reduction in the general separate network load, depending on the load characteristic of the drive machine, and the network receives less power and is thus stabilized.
In contrast, the present invention is based on the achieving an appropriate stabilization behavior for energy generation and power supply systems, in which a DC voltage rail is arranged as the power supply network. The power supply network according to the present invention achieves the advantage that even when it is supplying DC voltage, the network can be stabilized with the same quality as the
Rüter Bernd
Rzadki Wolfgang
Kenyon & Kenyon
Siemens Aktiengesellschaft
Vu Bao Q.
Wong Peter S.
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