Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM FOR TESTING A TURBOMACHINE COMPRISING A PAIR OF TWIN
HYDRAULIC TURBINES
Field of the invention
The present invention relates to a hydraulic
turbomachine and, in particular, to a hydraulic turbomachine for
recovering and converting the kinetic energy of marine or river
currents, especially to provide electricity.
Discussion of prior art
Among clean natural energy sources, a currently unde-
rexploited energy source corresponds to water currents naturally
present around the world: open sea currents, tidal currents,
strait and estuary currents, stream or river currents.
Devices for recovering and converting the kinetic
energy of marine or river currents generally comprise a turbine
comprising an assembly of blades capable of rotating a shaft
when they are immersed in the current. Cross-flow turbines, for
which the direction of the current is generally perpendicular to
the rotation axis of the turbine, will be considered herein.
The operation of certain cross-flow turbines uses the
lift forces exerted by the current on the blades, which then
have, for example, an aerofoil section to drive the rotation
shaft. Such is especially the case for cross-flow turbines of
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Darrieus or Gorlov type, or turbines of the type described in
European patent application 1718863 filed by the Applicant.
A general feature of hydraulic turbines is the
presence of a total lift force perpendicular to the turbine
rotation axis and to the upstream current direction. Indeed, the
rotation of the blades around the rotation axis of the turbine
considered as a whole induces a rotary motion of the liquid
around the turbine, which superposes to the incident motion
perpendicular to the rotation axis. This results in a total lift
force ultimately exerted on the rotation turbine axis and which
is thus perpendicular to the flow direction and to the rotation
axis. The total lift force tends to vary around an average
value. The fluctuations observed around this average value are
periodically repeated on each 3600 rotation of the turbine. The
turbine holding device and possibly the system for anchoring the
turbine to the ground must then be designed to resist the total
lift force, in addition to the drag force. Further, the
turbomachine as a whole, that is, comprising the system of
conversion of the mechanical energy provided by the turbine
shaft, must withstand the fatigue caused by vibrations induced
by the variable total lift force.
To overcome these disadvantages, the Applicant has
provided in unpublished French patent application #07/58511 of
October 23, 2007 (B8450), a turbomachine for which, in opera-
tion, the general transverse lift applied to the turbomachine
holding devices is substantially null. This turbomachine
comprises first and second turbines symmetrical to each other
with respect to a plane and rotating in opposite directions when
they are immersed in a moving liquid; and a device for holding
the first and second turbines, comprising one or several posts
arranged symmetrically with respect to said plane. Each turbine
comprises a rotation shaft and blades connected to this shaft to
rotate the shaft when the blades are immersed in a moving
liquid. The first and second turbines will here be called twin
turbines. The above unpublished French patent application also
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provides a control device capable of maintaining the rotation
speeds of the first turbines equal (and opposite) and possibly a
mechanical (gear) control device capable of maintaining the
first and second blades symmetrical.
Summary of the invention
An object of an embodiment of the present invention is
to ensure that two twin towers rotate at the exact same speed
and keep a constant mutual angular relationship. In other words,
the speed and the angular position of the two towers are desired
to be synchronized.
An object of an embodiment of the present invention is
to perform this synchronization electrically, with no mechanical
coupling between the twin towers. This enables to avoid the use
of a non-adaptive bulky mechanical gear system, requiring a
regular maintenance.
An object of an embodiment of the present invention is
to perform this synchronization without using specific electric
machines imposing a direct electric coupling between them and
without introducing control structures integrating additional
loops for controlling each of the angular positions.
To achieve all or part of these and other objects, the
present invention provides a turbomachine comprising first and
second symmetrical cross-flow hydraulic turbines, connected to a
same holding device and rotating in opposite directions when
they are immersed in a moving liquid; a generator associated
with the shaft of each turbine; and means of electric regulation
of the power extracted from the second generator to ensure that
the shaft of the second turbine rotates at the same speed in a
same angular positioning relationship determined with respect to
the shaft of the first turbine.
According to an embodiment of the present invention,
the first generator is regulated to rotate at an optimal speed
according to the current of the liquid in which the turbine is
immersed.
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According to an embodiment of the present invention,
said angular position relationship is determined according to
the flow conditions of the liquid in which the turbine is
immersed.
According to an embodiment of the present invention,
the first and second generators comprise a speed control loop
acting on a rectifying block associated with the output of each
of the generators, the speed control loop of the first generator
being controlled by an optimal speed calculated according to the
current, and the speed loop of the second generator being
controlled by the speed of the first generator corrected by an
error signal (z B) reflecting the angular position difference
between the two generators.
According to an embodiment of the present invention,
the speed correction loop of the second generator comprises a
device for measuring the differences between the angular
positions of each of the turbines and a reference position, and
a comparison between these two angular positions, with a shift
corresponding to the imposed angular position difference, this
difference being provided via a loop filter to correct the speed
signal applied to the first regulation loop.
According to an embodiment of the present invention,
the turbomachine comprises a large number of additional pairs of
hydraulic turbines, each hydraulic turbine of the additional
pairs being controlled in the same way as the second turbine.
Brief Description of the Drawings
The foregoing objects, features, and advantages of the
present invention, as well as others, will be discussed in
detail in the following non-limiting description of specific
embodiments in connection with the accompanying drawings, among
which:
Fig. 1A shows an example of a hydraulic turbine and
Figs. 1B and 1C very schematically show very simplified front
and top views of an example of twin hydraulic towers;
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Fig. 2 is an electric diagram of connection of twin
towers to a system;
Fig. 3 is a control diagram of twin towers according
to an embodiment of the present invention; and
5 Fig. 4 shows another example of an electric diagram of
connection of twin towers to a system.
Detailed description
For clarity, the same elements have been designated
with the same reference numerals in the different drawings.
Fig. 1A shows an embodiment of a turbine column
comprising an assembly of four turbines 1 having a common axis.
As an example, a turbine unit 1 comprises a rotation shaft 2 and
a hub 3 attached to rotation axis 2 and from which arms 4
project. Each arm 4 supports a foil (or blade) 5 at its end
opposite to hub 3. Each foil 5, for example, "V"-shaped, may
comprise end winglets 6 at its tips.
Call tower the assembly formed of a turbine column and
of the device for holding the turbine column. Examples of towers
are described in European patent application 06709514.1 filed by
the Applicant.
As schematically illustrated in front view and in top
view by Figs. 1B and 1C, twin towers having their rotation axes
2A, 2B substantially parallel to each other and connected to a
same frame, schematized by a post 8, are considered herein. Each
tower comprises, on a same shaft, a stack of turbines lA, 1B and
a generator 10A, 10B providing electric power on conductors 12A,
12B. These twin towers are provided to rotate in reverse direc-
tions. Since they are submitted to a same liquid flow F, they
naturally rotate substantially at the same speed. This cancels
the two equal and opposite total lift forces, perpendicular to
the flow direction, which apply on each of the twin towers when
they are immersed in a moving liquid.
The present invention applies to any type of cross-
flow turbine. As an example, the present invention applies to
cross-flow turbines of Darrieus type, of Gorlov type (for
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example, the turbines described in publications "Helical
Turbines for the Gulf Stream: Conceptual Approach to Design of a
Large-Scale Floating Power Farm" by Gorlov (Marine Technology,
vol. 35, n 3, July 1998, pages 175-182), etc.), or to turbines
of the type described in European patent application 1718863
filed by the Applicant.
As illustrated in Fig. 1C, the two towers are desired
to rotate at the exact same speed to keep a constant regulated
angular relationship (a). In other words, the speed and the
relative position of the two towers are desired to be
synchronized.
According to an embodiment of the present invention,
each tower of a pair of twin towers is connected to the system
by an electric power converter.
In the embodiment illustrated in Fig. 2, generator 10A
of a first tower is connected via a controlled rectifying bridge
14A to a D.C. bus 15A and the power on the D.C. bus is
transferred by a power inverter 20A to an A.C. bus 21 of a
system or of a load 22.
Controlled rectifier 14A is very schematically shown,
and will actually be a single-phase or polyphase rectifying
bridge according to the nature of the generator. D.C. interface
15A comprises two conductors, one of which is grounded. Between
these two conductors, a braking device 23 comprising a resistor
RA is installed, this resistor being switchable to ensure the
braking function. Also, between the conductors of the D.C. bus,
a power storage system 24A which may be connected to the other
terminal of the bus directly or via a power regulation device
25A may be arranged. These various elements of a
rectifying/ inverting system will not be described herein since
they are known per se. Similarly, control signals MLIA2 of power
inverter 20A will not be described herein, since they are
conventional devices intended to transform a D.C. voltage into
an A.C. signal having a frequency adapted to A.C. bus 21
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connected to the system or to the load. The control mode will
depend on the connection to the system.
Generator 10B is connected to A.C. bus 21 by a similar
chain having its elements designated with suffix B instead of A.
A major aspect of the present invention lies in
signals MLIA1 and MLIA2 for controlling controlled converters
14A, 14B.
Fig. 3 shows a diagram of a mode of provision of
control signals MLIA1, MLIB1 of controlled rectifiers 14A, 14B
of generators 10A, 10B of Fig. 2.
According to the present invention, one of the genera-
tors, for example, generator 10A, is selected as a master system
and the other generator is selected as a slave system. Generator
10A is associated with a speed control loop which receives a
speed reference from a rotation calculation block 30. Block 30
takes into account the speed of the hydraulic current to
determine an optimum rotation speed of the turbine. It for
example is a device for searching the optimum operating point,
currently designated as MPPT (Maximum Power Point Tracking).
Thus, block 30 provides a reference speed QA* to an add input of
a subtractor 31A having its subtract input receiving a signal
provided by a block 32A for detecting rotation speed DA of
generator 10A. Subtractor 31A provides an error signal to a
speed control block 33A, which provides a reference signal for
current-controlled rectifier block 14A. Output signal igGA* of
speed control block 33A is provided to an add input of a
subtractor 34A having its subtract input receiving a signal for
measuring the current igGA effectively provided. The resulting
error signal is transformed into a pulse-width modulation signal
in a current control block 35A. If the generator is a polyphase
generator, block 35A calculates the signals to be applied to the
various phases of a polyphase rectifying bridge. The foregoing
description is relatively short since it relates to a
conventional circuit for controlling a generator with a deter-
mined rotation speed, signal MLIA1 controlling the switching of
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the controlled rectifying block and thus the resistant torque to
be applied to the generator so that it maintains its rotation
speed constant.
The present invention more specifically aims at the
control of the second generator, which is controlled in slave
mode, on the one hand, to rotate at the same speed as the first
generator and, on the other hand, to have a determined angular
position shift with respect to this first generator.
Conventionally, such a control is performed by provid-
ing, on the one hand, a speed control loop and, on the other
hand, an angular position control loop. According to the present
invention, only speed control loops are used, which simplifies
the assembly and the settings. Thus, a first speed control loop
similar to the previously-described loop, comprising elements of
same nature 33B, 34B, and 35B for providing a signal MLIB1 to
controlled rectifier block 14B, is associated with generator
10B.
A speed correction loop comprising elements 40B, 41B,
42B providing a speed correction signal A B to a first add input
of an adder 43B which further receives speed signal QA of the
first turbine is associated with this first speed control loop.
Adder 43B provides a signal QB* which is compared with speed
signal QB of the second generator provided by a speed detection
and calculation circuit 36B. The speed correction loop is
intended to ensure a determined angular relationship between the
two generators. This loop comprises a block 41B for comparing
the angular positions of the two turbines, capable of quickly
responding to high-frequency signals. Block 41B compares angle
OA of the first turbine with respect to a selected reference
frame with angle OB of the second turbine with respect to the
same reference frame, signal OA being previously added an angle
a. Angle a is the interval which is desired to be imposed
between the angular positions of the two turbines. Thus, block
41B provides a signal which, after passing through a loop filter
42B, forms a speed correction signal AQB.
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According to an aspect of the present invention, it is
not provided to have several detectors, that is, a position
detector and a speed detector, for each of the turbines. Only an
angular position detector providing angular positions OA and OB
with respect to a selected reference is provided for each
turbine. Such detectors may be used, on the one hand, to provide
an indication to angular position detector 41B, and on the other
hand, for speed calculations in blocks 33A and 33B. Speed
controllers 33A, 33B generate active current reference values
which are an image of the electromagnetic torques applied to
current controllers 35A and 35B which generate the PWM (pulse-
width modulation) control signals. The structure according to
the present invention is particularly appropriate for the need
for a quick and accurate synchronization, without using any
mechanical coupling of the hydraulic towers, whatever the water
flow conditions, that is, in laminar state as well as in a
turbulent state characterized by fast unexpected flow rate
variations. In such a context, this structure has an increased
resistance with respect to other synchronization structures and
methods.
This is an example only of implementation of the
present invention. In particular, the regulation signals
according to the present invention may be applied to a system
other than that shown in Fig. 2. For example, as shown in Fig.
4, generators 10A and 10B may be coupled by rectifiers 14A and
14B to a common D. C. bus 15, connected via an electronic power
circuit 24 to a storage circuit 25, and the power on this common
D.C. bus is transferred by a power inverter 20 to a system 22.
An example of application to the case of two twin
hydrogeneration towers have been described hereabove. However,
the relative shift angle coordination control may be applied for
any number of cross-flow hydrogenerator towers with a master
tower imposing its speed and position reference to the other
slave towers.
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The discussed architectures are based on synchronous
machines, but they may also be based on induction machines, with
the specificities thereof being taken into account.
Controlled rectifiers 14A, 14B may be polyphase bridge
5 structures controlled by pulse-width modulation (PWM)
implementing controllable electronic components, or devices
implementing structures with polyphase diode bridges and voltage
step-up D.C.-D.C. converters controlled by pulse-width
modulation.
10 The control systems aim at imposing relative shift
angles between towers (with or without MPPT), at imposing
operating points (through the imposition of speeds), and at
managing power transfers. For this purpose, they are provided
with means for processing the measurement data for decision
making and monitoring, such means being conventional for those
skilled in the art of servo-control.
Operating conditions
According to cases, system 22 may be either a powerful
system, or a low-power system (a microsystem or an isolated
system), or a load.
In the situation where the machines are provided with
individual A.C./A.C. chains, four setting modes can be defined:
a) case of a powerful system present when each power
inverter on the system side sets its D.C. bus voltage and each
rectifier imposes the operating point to the machine (torque,
speed, angle shift) HP, Q) operation) ;
b) case of a low-power system with a droop setting
((P, Q) operation) ;
c) case of an isolated system/microsystem when a gene-
rator operates as a master by setting the voltage of the common
D.C. bus and the others are droop-controlled ((V, f) operation;
d) case where a storage element is present and the
supervision system imposes the different references.
In the case where the provided electric power is
injected to a non-isolated system, the electric generation
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system operates in (P, Q) operating mode. The power inverter on
the system side regulates the D. C. bus by ensuring the transfer
of active and reactive powers P and Q. The A.C. /D. C. interfaces
of the towers operate in speed regulation by setting the
operating point of the hydrogeneration towers and having as an
upper stage the coordinated tower control loop, which generates
the shift references between the hydrogeneration towers, as
shown in Fig. 3.
In this operating mode, there always is a way to set
reactive power Q independently from active power P, to within
the apparent installed power of the system power inverter.
In (V, f) operating mode, the hydraulic generator
system, as shown in Fig. 1, is connected to a low-power/isolated
system or to a load. In this case of operation, without storage,
a hydrogeneration tower controls the voltage of the common D.C.
bus via its rectifying system and the other hydrogeneration
towers provide in synchronized fashion the rest of necessary
power to this bus (they will be controlled in terms of speed via
their rectifying system).
In the case of an operation in (V, f) mode with a
storage system, a supervision system imposes the references to
each tower and to the storage interface.
In this case, hydrogeneration tower A is in charge of
the regulation of the D.C. bus. Assuming that hydrogeneration
tower A takes care of the control of the D.C. bus, then the
other hydrogeneration tower will have its speed controlled at
the operating points corresponding to the imposed/modified shift
angles between towers so that the rest of the power necessary to
the D.C. bus is provided.
