U.S. patent application number 13/512697 was filed with the patent office on 2012-12-13 for controller for pendulum type wave-power generating apparatus.
This patent application is currently assigned to KOREA OCEAN RESEARCH AND DEVELOPMENT INSTITUTE. Invention is credited to Key-Yong Hong, Seung-Ho Shin, Tomiji Watabe.
Application Number | 20120313373 13/512697 |
Document ID | / |
Family ID | 46969629 |
Filed Date | 2012-12-13 |
United States Patent
Application |
20120313373 |
Kind Code |
A1 |
Shin; Seung-Ho ; et
al. |
December 13, 2012 |
CONTROLLER FOR PENDULUM TYPE WAVE-POWER GENERATING APPARATUS
Abstract
The present invention provides a controller for a pendulum type
wave-power generating apparatus. Electric power produced by
wave-power generation has been pointed out as being of low
efficiency and more expensive than wind-power generation. To
overcome the above problems, the present invention uses resonance
and impedance matching of the sea waves, thus making it possible to
markedly enhance the efficiency of wave-power generation. The
present invention does not use a wave-height meter which is
generally expensive and controls the generating apparatus in
response to variation of the conditions of the sea, thus
automatically maintaining the resonance and impedance matching
operation, thereby making high-efficiency operation possible. As a
result, the cost of the wave-power generation can be reduced, so
that the wave-power generation can be widely commercialized.
Inventors: |
Shin; Seung-Ho; (Daejeon,
KR) ; Hong; Key-Yong; (Daejeon, KR) ; Watabe;
Tomiji; (Hokkaido, JP) |
Assignee: |
KOREA OCEAN RESEARCH AND
DEVELOPMENT INSTITUTE
Gyeonggi-do
KR
|
Family ID: |
46969629 |
Appl. No.: |
13/512697 |
Filed: |
July 18, 2011 |
PCT Filed: |
July 18, 2011 |
PCT NO: |
PCT/KR11/05269 |
371 Date: |
August 30, 2012 |
Current U.S.
Class: |
290/42 |
Current CPC
Class: |
F15B 11/16 20130101;
Y02E 10/30 20130101; F05B 2220/706 20130101; F15B 2211/50 20130101;
F05B 2260/406 20130101; F03B 15/02 20130101; F05B 2270/202
20200801; F15B 13/06 20130101; F03B 15/00 20130101; F15B 1/04
20130101; F03B 13/182 20130101; F03B 13/22 20130101 |
Class at
Publication: |
290/42 |
International
Class: |
F03B 13/16 20060101
F03B013/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 2011 |
KR |
10-2011-0032891 |
Claims
1. A controller for a pendulum type wave-power generating apparatus
converting a pendulum motion of wave-power energy into a rotary
motion using a hydraulic transmission that has pressure
accumulators (31) and (41) on a hydraulic circuit thereof, thus
operating a generator (60), the controller comprising: pressure
control valves (33) and (43) controlling output volumes of
hydraulic motors (32) and (42) that operate the generator (60) such
that the output volumes are proportional to mean hydraulic
pressures in pipes (30) and (40) of the hydraulic circuit so that a
mean value of wave-power energy input into the hydraulic circuit is
equal to a mean value of a drive force of the generator (60),
whereby wave-power energy is able to be used regardless of a
variation in wave conditions on the sea.
2. The controller for the pendulum type wave-power generating
apparatus according to claim 1, wherein the pressure control valves
(33) and (43) use a force of the wave-power energy as input signals
and transmit pressures proportional to the input signals to the
generator (60) as output signals, wherein the mean hydraulic
pressures of the hydraulic circuit are used as the input
signals.
3. The controller for the pendulum type wave-power generating
apparatus according to claim 1, wherein the hydraulic transmission
comprises: a pump (20) connected to a pendulum (11) that is swung
in a pendulum motion by variation of a wave; the hydraulic motors
(32) and (42) respectively connected to the pipes (30) and (40)
coupled to opposite ends of the pump (20); and the generator (60)
operated by the hydraulic motors (32) and (42).
4. The controller for the pendulum type wave-power generating
apparatus according to claim 1, wherein the pressure accumulators
(31) and (41) respectively accumulate and store pressures (P1) and
(P2) in the pipes (30) and (40) of the hydraulic circuit.
5. The controller for the pendulum type wave-power generating
apparatus according to claim 1, wherein the pressure control valves
(33) and (43) are configured such that when the mean hydraulic
pressures of the pipes (30) and (40) connected to the hydraulic
motors (32) and (42) of the hydraulic transmission differ from each
other and a difference between the mean hydraulic pressures exceeds
a preset limiting value, a switching valve (50) communicates the
pipes (30) and (40) connected to the hydraulic motors (32) and (42)
with each other so that the mean hydraulic pressures in the pipes
(30) and (40) of the hydraulic motors (32) and (42) are equal to
each other.
6. The controller for the pendulum type wave-power generating
apparatus according to claim 1, wherein each of the pressure
control valves (33) and (43) comprises: a first port (100)
connected to the corresponding pipe (30), (40) of the hydraulic
circuit so that the corresponding hydraulic pressure (P1), (P2) is
input into the first port (100); a cylinder (110) into which the
hydraulic pressure (P1), (P2) is applied from the first port (100);
a damper (111) installed in the cylinder (110), the damper (111)
being moved upwards or downwards by the hydraulic pressure (P1),
(P2) applied thereto from the first port (100); a third elastic
member (113) contracted by the hydraulic pressure (P1), (P2)
applied to the damper (111) from the first port (100); a chamber
(120) in which a spool (122) is moved upwards or downwards by the
damper (111), thus increasing or reducing a valve pressure (P3) in
the chamber (120); first and second elastic members (121) and (123)
respectively installed on and under the spool (122), the first and
second elastic members (121) and (123) being expanded or contracted
depending on movement of the spool (122); a second port (130)
through which the hydraulic pressure (P1), (P2) of the hydraulic
circuit is applied into the chamber (120); a third port (140) which
relieves the valve pressure (P3) from the chamber (120) to an
outside; and a fourth port (150) communicating with the second port
(130) or the third port (140) depending on the upward or downward
movement of the spool (122), the fourth port (150) transmitting the
valve pressure (P3) to the corresponding hydraulic motor (32), (42)
as a control signal (34), (44).
7. The controller for the pendulum type wave-power generating
apparatus according to claim 6, wherein each of the pressure
control valves (33), (43) transmits the valve pressure (P3) in the
chamber (120), which is increased or reduced by the hydraulic
pressure (P1), (P2) transmitted through the first port (100) or the
second port (130), to a servo (35), (45) of the hydraulic motor
(32), (42) through the fourth port (150) as a control signal,
wherein when the valve pressure (P3) is increased, the control
signal is transmitted such that the output volume is reduced, and
when the valve pressure (P3) is reduced, the control signal is
transmitted such that the output volume is increased.
8. The controller for the pendulum type wave-power generating
apparatus according to claim 7, wherein a case where the output
volume of each hydraulic motor 32, 42 is increased is a case
wherein as the wave-power energy increases, the pressure in the
pipe (30), (40) increases so that the damper (120) and the spool
(122) are moved upwards by the hydraulic pressure (P1), (P2) from
the first port, thus increasing the valve pressure (P3).
Description
TECHNICAL FIELD
[0001] The present invention relates, in general, to controllers
for pendulum type wave-power generating apparatuses. Wave-power
generation is a fascinating field that uses sea waves having high
energy density, but commercialization has been delayed by the
difficulty of reducing the cost of power generation. Wave power is
irregular wave energy, so it is difficult to handle it.
Commercialization is much more difficult, compared to other fields,
because of the severe environmental conditions of the sea. The
biggest problem is low power generation efficiency. Solving this
problem has been pointed out as the basic priority. The present
invention relates, more particularly, to a controller for pendulum
type wave-power generating apparatuses which controls the operation
conditions of a pendulum type wave-power generating apparatus in
response to the characteristics of sea waves so that high power
generation efficiency can always be maintained regardless of
variations in the state of the sea waves, thus reducing the cost of
power generation.
BACKGROUND ART
[0002] Sea waves are composite waves that are a combination of
different kinds of regular waves, but they are not completely
irregular and have spectrum structures in which most energy is
concentrated around regular waves of a specific height and
frequency. Using such characteristics, sea waves are converted into
regular waves of the same period as that of the center of the
spectrum. The response of wave-power generation with respect to the
regular waves of specified wave height and frequency is checked
using antenna theory. A method of commercialization has been
discovered that makes reference to the above behavior of the
response. There is a close correspondence between wave-power
generation and the antenna. The antenna theory can be used as an
effective tool when researching wave-power generation.
[0003] The problem is that sea waves are not regular. The waveform
of sea waves is distorted with respect to that of a sine wave. The
wave height and wave length are also not constant. However, in
terms of statistics, the wave nature can be obviously read from the
sea waves. Further, if the mean value is paid attention to, there
is regularity between the wave height and the wave period. For this
reason, sea waves are regarded as semi-regular waves and as a kind
of wave motion which continuously varies within a regular pattern.
Therefore, with regard to wave-power generation, if parameters of a
generation apparatus are adjusted (optimized) in response to
variation of characteristics attributable to the irregularity of
the sea waves, that is, in response to a variation in conditions,
satisfactory power generation can be automatically maintained. For
this, development of a controller for wave-power generating
apparatuses that can reduce the cost of power generation is
required.
DISCLOSURE
Technical Problem
[0004] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the prior art, and a first
object of the present invention is to control the output volume
value (the size of output volume) of a hydraulic motor in response
to a variation in irregular sea waves such that the generation load
is optimized, thus automatically maintaining satisfactory power
generation, thereby reducing the cost of power generation.
[0005] A second object of the present invention is to cope with
variation in the state of sea waves without using a separate wave
height meter, in an effort to realize a reduction in the cost of
power generation. The wave height meter is not only very expensive
but also requires high technology to process obtained data, thus
making common on-line use of it difficult. If data about irregular
waves could be obtained without using a wave height meter, the
practical effect of a wave-power generating apparatus would be
markedly enhanced.
[0006] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings. Furthermore, the objects, features and
advantages of the present invention can be realized by means
disclosed in the accompanying claims or combination thereof.
Technical Solution
[0007] In order to accomplish the above objects, the present
invention provides a controller for a pendulum type wave-power
generating apparatus converting a pendulum motion of wave-power
energy into a rotary motion using a hydraulic transmission that has
pressure accumulators (31) and (41) on a hydraulic circuit thereof,
thus operating a generator (60), the controller including: pressure
control valves (33) and (43) controlling output volumes of
hydraulic motors (32) and (42) that operate the generator (60) such
that the output volumes are proportional to mean hydraulic
pressures in pipes (30) and (40) of the hydraulic circuit so that a
mean value of wave-power energy input into the hydraulic circuit is
equal to a mean value of a drive force of the generator (60),
whereby wave-power energy is able to be used regardless of a
variation in wave conditions on the sea.
Advantageous Effects
[0008] As described above, a pendulum type wave-power generation
apparatus is characterized in that it can be constructed at a
comparatively low cost and the efficiency thereof is superior. For
instance, in the case of a unit apparatus, estimated unit
generation cost has been reported as being .ltoreq.0.085$/kWh, so
it has already reached a practicable level.
[0009] A controller for pendulum type wave-power generating
apparatuses according to the present invention can further reduce
unit power cost compared to the level of the conventional
technique. Thus, the present invention can reliably eliminate the
obstacle (the problem of the high cost of power generation) to
commercializing the wave-power generation. Therefore, the present
invention makes it possible to devise a detailed plan for using
wave-power energy as well as measures to cope with stormy
conditions, thus promoting the commercialization of wave-power
generation.
[0010] Furthermore, the controller for pendulum type wave-power
generating apparatuses according to the present invention has a
simple and strong structure, thus ensuring the sufficient
durability against conditions of the sea.
[0011] Moreover, thanks to the above-mentioned effects, use of
wave-power energy for purposes of commercialization that has been
at a standstill becomes possible. This also has an effect on
environmental preservation.
DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a system circuit view showing the structure of a
pendulum type wave-power generating apparatus provided with a
controller for pendulum type wave-power generating apparatuses
according to an embodiment of the present invention to improve the
power generation efficiency.
[0013] FIG. 2 is of front sectional views of an embodiment of a
pressure control valve showing an initial stage of operation of a
pendulum in which internal valve pressure is increasing.
[0014] FIG. 3 is of front sectional views showing an embodiment of
the pressure control valve which transmits a control signal of an
increase of the output volume of a hydraulic pump as the valve
pressure (P3) is reduced, according to the present invention.
DESCRIPTION OF THE ELEMENTS IN THE DRAWINGS
[0015] 10: channel 11: pendulum [0016] 12: support point 20:
hydraulic pump [0017] 21: bed tank 30, 40: pipe [0018] 31, 41:
pressure accumulator 32, 42: hydraulic motor [0019] 33, 43:
pressure control valve 44, 54: control signal [0020] 50: switching
valve 60: generator [0021] 100: first port 101: iris diaphragm
[0022] 102: plunger 110: cylinder [0023] 111: damper 112: thin hole
[0024] 113: elastic member 114: lower chamber [0025] 115: upper
chamber 120: chamber [0026] 121: first elastic member 122: spool
[0027] 123: second elastic member 124: passage [0028] 130: second
port 140: third port [0029] 150: fourth port 160: drain pipe [0030]
170: tank recovery pipe P1, P2: pressure (hydraulic pressure)
[0031] P3: valve pressure
BEST MODE
[0032] The invention now will be described more fully hereinafter
with reference to the accompanying drawings, in which various
embodiments are shown. This invention may, however, be embodied in
many different forms, and should not be construed as limited to the
embodiments set forth herein. Furthermore, relative terms, such as
"front", "back", up", "down", "upper", "lower", "left", "right",
"lateral", etc., may be used herein to simplify the description of
the invention and describe one element's relationship to other
elements as illustrated in the Figures. It will be understood that
relative terms are intended to encompass different orientations of
the device in addition to the orientation depicted in the Figures.
It will be understood that, although terms, such as "first",
"second", "third" and "fourth", may be used herein to describe
various elements, these terms are not intended to attach relative
importance to the elements.
[0033] The present invention has the following characteristics in
order to achieve the above-mentioned objects.
[0034] Hereinafter, a preferred embodiment of the present invention
will be described in detail with reference to the attached
drawings. The terms and words used in the specification and claims
are not necessarily limited to typical or dictionary meanings, but
must be understood to indicate concepts selected by the inventor as
the best method of illustrating the present invention, and must be
interpreted as having meanings and concepts adapted to the scope
and sprit of the present invention for the sake of understanding
the technology of the present invention.
[0035] Therefore, the construction of the embodiment illustrated in
the specification and the drawings must be regarded as only
illustrative examples, which are not intended to limit the present
invention. Furthermore, it must be understood that various
modifications, additions and substitutions are possible at the
point of time of application of the present invention.
[0036] In an embodiment of the present invention, a pendulum type
wave-power generating apparatus converts pendulum motion of
wave-power energy into rotary motion using a hydraulic transmission
that has pressure accumulators 31 and 41 on a hydraulic circuit
thereof, thus operating a generator 60. A controller for the
wave-power generating apparatus includes pressure control valves 33
and 43 which control the output volumes of the hydraulic motors 32
and 42 that operate the generator 60 such that they are
proportional to mean hydraulic pressures in pipes 30 and 40 of the
hydraulic circuit so that the mean value of wave-power energy input
into the hydraulic circuit is equal to the mean value of the drive
force of the generator 60, thus making it possible to use
wave-power energy regardless of variations in the state of the
waves on the sea.
[0037] Furthermore, the pressure control valves 33 and 43 use the
force of the wave-power energy as input signals and transmit
pressures proportional to the input signals to the generator 60 as
output signals, wherein the mean hydraulic pressures of the
hydraulic circuit are used as the input signals.
[0038] The hydraulic transmission includes: a pump 20, which is
connected to a pendulum 11 that swings in a pendulum motion
resulting from variations of the wave; the hydraulic motors 32 and
42, which are respectively connected to the pipes 30 and coupled to
the opposite ends of the pump 20; and the generator 60, which is
operated by the hydraulic motors 32 and 42.
[0039] The pressure accumulators 31 and 41 respectively accumulate
and store pressures P1 and P2 in the pipes 30 and 40 of the
hydraulic circuit.
[0040] The pressure control valves 33 and 43 are configured such
that if the mean hydraulic pressures of the pipes 30 and 40
connected to the hydraulic motors 32 and 42 of the hydraulic
transmission differ from each other and the difference between the
mean hydraulic pressures exceeds a preset limiting value, a
switching valve 50 communicates the pipes 30 and 40 connected to
the hydraulic motors 32 and 42 with each other so that the mean
hydraulic pressures in the pipes 30 and 40 of the hydraulic motors
32 and 42 become the same.
[0041] Each of the pressure control valves 33 and 43 includes: a
first port 100 which is connected to the corresponding pipe 30, 40
of the hydraulic circuit and into which the hydraulic pressure P1,
P2 is input; a cylinder 110 into which the hydraulic pressure P1,
P2 is applied from the first port 100; a damper 111 which is
installed in the cylinder 110 and is moved upwards or downwards by
the hydraulic pressure P1, P2 applied thereto from the first port
100; a third elastic member 113 which is contracted by the
hydraulic pressure P1, P2 applied to the damper 111 from the first
port 100; a chamber 120 in which a spool 122 is moved upwards or
downwards by the damper 111, thus increasing or reducing a valve
pressure P3 in the chamber 120; first and second elastic members
121 and 123 which are respectively installed on and under the spool
122 and are expanded or contracted depending on the movement of the
spool 122; a second port 130 through which the hydraulic pressure
P1, P2 of the hydraulic circuit is applied into the chamber 120; a
third port 140 which relieves the valve pressure P3 from the
chamber 120 to the outside; and a fourth port 150 which
communicates with the second port 130 or the third port 140
depending on the upward or downward movement of the spool 122 and
transmits the valve pressure P3 to the corresponding hydraulic
motor 32, 42 as a control signal 34, 44.
[0042] Each pressure control valve 33, 43 transmits the valve
pressure P3 in the chamber 120, which is increased or reduced by
the hydraulic pressure P1, P2 transmitted through the first port
100 or the second port 130, to a servo 35, 45 of the hydraulic
motor 32, 42 through the fourth port 150 as a control signal. If
the valve pressure P3 is increased, the control signal is
transmitted such that the output volume is reduced. If the valve
pressure P3 is reduced, the control signal is transmitted such that
the output volume is increased.
[0043] The case where the output volume of the hydraulic motor 32,
42 is increased refers to the case where as the wave-power energy
increases, the pressure in the pipe 30, 40 increases so that the
damper 120 and spool 122 are moved upwards by the hydraulic
pressure P1, P2 from the fist port, thus increasing the valve
pressure P3.
[0044] Hereinafter, the controller of the pendulum type wave-power
generating apparatus according to a preferred embodiment of the
present invention will be described in detail with reference to
FIGS. 1 through 3.
[0045] The controller of the pendulum type wave-power generating
apparatus according to the present invention converts the pendulum
motion into constant high-speed rotation using the hydraulic
transmission, thus operating the generator 60. The pressure
accumulators (spring pressure accumulators) 31 and 41 are provided
on the hydraulic circuit. The controller smoothens the output of
power generation using the characteristics of the pressure
accumulators and, simultaneously, calculates an incident wave from
the mean value of the circuit pressure (the mean hydraulic pressure
in the hydraulic circuit pipe) and controls the output volume of
the hydraulic motors 32 and 42 such that they correspond to the
incident power.
[0046] Eventually, regardless of wave conditions of the sea, the
impedance matching state can be maintained. The control signals
that are produced by determination, using the circuit pressures
(the pressures P1 and P2 in the pipes 30 and 40 of the hydraulic
circuit), of the pressure control valves 33 and 43 that are of the
controller of the pendulum type wave-power generating apparatus
after the pressure control valves 33 and 43 have given preset
operations to the hydraulic motors 32 and 42. All the signals that
are used are analog.
[0047] The pendulum type wave-power generating apparatus using the
controller of the present invention is focused on the wave nature
of the sea and accelerates the pendulum 11 using periodic
wave-power, thus generating the pendulum motion that resonates with
the wave. The hydraulic transmission converts the pendulum motion
into rotary motion, thus operating the generator 60. The apparatus
is characterized in that if two conditions of the resonance and
impedance matching are satisfied, the power generation efficiency
is maximized (in the same manner as that of an antenna). In other
words, the same method as optimizing the antenna can be used in the
wave-power generation. If the wave of the sea is constant like an
electric wave, the method of the antenna can be directly used in
the wave-power generation and the optimization of the system is
possible. However, because the waves of the sea cannot be constant,
the present invention uses the following means.
[0048] Statistical data about the sea waves that has been collected
by a separate process are organized, and characteristics of power,
wave heights and periods are arranged in a database. Here, the
characteristics are the mean of data obtained after have been
continuously measured for a predetermined time period (e.g., 20
minutes) rather than being obtained in a single measurement. Thus,
if such data is prepared, the mean wave height or the mean period
can be obtained, so that the mean power corresponding to them can
be determined. The present invention indirectly measures the mean
wave height without using a separate wave height meter, determines
the mean power using the wave height, and controls the hydraulic
motors 32 and 42 depending on the mean wave height so that the
output volumes of the hydraulic motors 32 and 42 are optimized.
Thereby, the efficiency of wave-power generation can be markedly
enhanced.
[0049] In the case of the waves of the sea, even each wave is
irregular, that is, the wave height and the period thereof vary.
Given this, the present invention uses a transmission circuit that
is configured such that the resonance and impedance matching of
each wave can be approximated. To achieve the above purpose, with
regard to individual waves, every time waves of different energies
are input, hydraulic energy corresponding to the energy of each
wave is accumulated in the pressure accumulators 31 and 41. The
hydraulic pressures accumulated in the pressure accumulators 31 and
41 are respectively supplied to the hydraulic motors 32 and 42. If
the energy of the sea waves increases, the discharge rate of the
pump 20 (the flow rate supplied to the hydraulic motors 32 and 42)
is increased, so that the mean pressure of the hydraulic circuit
that is provided with the hydraulic motors 32 and 42 (that is, the
pressures P1 and P2 in the pipes 30 and 40 of the hydraulic
circuit) is increased. If the output volumes of the hydraulic
motors 32 and 42 are extended so that the outputs of the hydraulic
motors 32 and 42 are increased, the consumption flow rate
increases, thus reducing the mean pressure of the hydraulic circuit
(of the pipes 30 and 40 of the hydraulic circuit). The mean
pressure of each of the pipes 30 and 40 of the hydraulic motors
also is a parameter that indicates the status of supply and demand
of energy used in the generation. In the present invention, this
parameter is used as a control signal.
[0050] In the present invention, assuming the operation of a
typical three-phase induction generator, a simple hydraulic
transmission providing constant speed operation is used. Therefore,
the output (Lm) of the hydraulic motor at a constant speed is
proportional to the torque of the motor. The torque (Tm) of the
motor is proportional to a multiple of the pressure (P) by the
output volume (Dm) of the motor, so that the output (Lm) of the
hydraulic motor at a constant speed is proportional to P.times.Dm.
The present invention realizes the desired control using this
relationship.
[0051] Conditions of the Wave-Power Generating Apparatus According
to the Present Invention
[0052] In order to realize the production of the present invention
on a commercial scale, enhancing the reliability of the product
must be focused on. For this, in terms of an increase in the
reliability for the price, it is preferable that among standardized
products of high quality, appropriate parts be selected and used as
parts of the apparatus. The hydraulic motors 32 and 42 used in the
present invention refer to standardized products that comply with
the above policy. Each hydraulic motor 32, 42 has a characteristic
that adds or subtracts the output volume (Dm) of the motor using a
pressure signal (analog). Hence, the control method of the present
invention is to control the output volume (Dm) of each hydraulic
motor 32, 42 using the pressure signal (analog) of the pressure
control valve 33, 43. The desired control can be easily implemented
by the hydraulic analog method, but also the control signal 34, 44
is transmitted through the thin pipe (connected to the fourth port
150 of the pressure control valve), so that there is no problem
even though it is exposed to the sea water. Based upon the premise
that the above-mentioned hydraulic motor has high reliability and a
simple structure, the present invention will be commercially
available as a standardized product.
[0053] As characteristics of the sea waves, variation of the wave
height and variation of the wave period are related to each other.
If the observational station is fixed, the larger the wave height,
the longer the wave period. In the wave-power generating apparatus,
the energy of the incident wave is designated by a mathematical
function in two kinds of variables of the wave height and the wave
period. Therefore, the method of measuring the two kinds of
variables and conducting the generation control using these values
must be precise. The controller of the present invention
intentionally uses only the value of the wave height in
consideration of the performance against the costs. The reasons for
this is as follows.
[0054] As stated above, the power (from 10 to 20 times the design
rating power) of the sea waves, for example, in a storm, may
destroy the apparatus. Thus, a positive incident power-cut is
needed to enhance the safety. If the power of the sea waves exceeds
the design rating power, it is required to reduce the input power
rather than to increase the power generation efficiency. As such,
requiring the control effect of the present invention is limited to
normal conditions in which the power of the sea waves is within the
design rating power. Hence, a normal `control error` attributable
to not using data about the period of the waves can be disregarded
in practical use.
[0055] If data about the period of the waves is not used, although
some of the characteristics may be sacrificed, there is an
advantage sufficient to overcome the sacrifice in that the
apparatus can be simplified.
[0056] The power (force of the wave-power energy)(per unit width)
of the sea waves: W(kW/m) is expressed by the following Equation
(1).
W.apprxeq.0.5H.sub.1/3.sup.2T.sub.1/3 Equation (1)
[0057] (where H.sub.1/3: significant wave height (m), T.sub.1/3
significant wave period(s))
[0058] The controller of the pendulum type wave-power generating
apparatus according to the present invention conforms the case
where T.sub.1/3: significant wave period=a constant in Equation
(1). Therefore, W is regarded as being proportional to
H.sub.1/3.sup.2. The sea waves having such characteristics act as
the input, thus operating the pendulum 11. Then, the pendulum 11
swings and absorbs wave-power energy. The absorbed power: E(kW) is
expressed as the following Equation (2).
E=2.times.10.sup.-3 T.sub.p.theta..sub.0/T.sub.1/3 Equation (2)
[0059] (where T.sub.p: the mean value (Nm) of load torque applied
to the pendulum shaft, .theta..sub.0: a swing angle (radian) of the
pendulum)
[0060] If the load applied to the pendulum is controlled so that
Equation (1)=Equation (2), in other words, if
W=E [0061] Equation (3) is satisfied, the efficiency of wave-power
generation can be maximized (impedance match). Because the pendulum
11 operates the pump 20 of the hydraulic transmission, the mean
value T.sub.p of load torque applied to the pendulum shaft is
proportional to the mean value of the output pressure of the pump
20. In this case, a proportional constant is appropriately selected
such that the swing angle .theta..sub.0 of the pendulum is
proportional to the wave height H.sub.1/3 and Equation 3 is
satisfied (the value of the proportional constant is determined by
characteristics of the pressure accumulators 31 and 41). The swing
angle, the load torque and the hydraulic pressure of the pump 20
are proportional to the wave height, and the input of the pump 20
is proportional to the square of the wave height. As shown in
Equation (1), in response to a variation in the wave height of the
incident wave, the incident power varies in proportion to the
square of the wave height, but because the swing angle of the
pendulum 11 and absorption power are proportional to the square of
the swing angle, the swing angle is proportional to the wave
height. Further, if the proportional constant is appropriately
determined, the incident power becomes equal to the absorption
power. In other words, impedance matching is satisfied.
[0062] If the discharge rate of the pump 20 and the mean values of
the consumption rates of the hydraulic motors 32 and 42 are
balanced, the mean values of the pressures P1 and P2 in the
hydraulic circuit pipes 30 and 40 become constant. An excess or
deficiency amount is regulated by absorption or discharge of the
pressure accumulators 31 and 41 and expressed as a variation in
pressure. In this case, Equation 3 must also be satisfied to
realize the high efficiency operation. Here, if the consumption
rates are increased or reduced by adjusting the output volumes of
the hydraulic motors 32 and 42 in response to the variation of the
mean values of the pressures P1 and P2 of the pipes 30 and 40 so
that the state of Equation (3) is satisfied, the high efficiency
operation can be automatically maintained. That is, if the wave
height is varied by variations in the conditions of the sea, the
mean values of the pressures P1 and P2 of the pipes lose the
balance and will vary. At this time, the pressure control valves 33
and 43 of the present invention increases or reduces the output
volume (the size of output volume) of the hydraulic motors 32 and
42 in response to the pressures P1 and P2 of the pipes of the
hydraulic circuit, thus reviving the impedance matching conditions,
thereby stabilizing the mean value of each pipe pressure P1, P2 at
another predetermined value.
[0063] FIG. 1 is a system circuit view showing the structure of the
pendulum type wave-power generating apparatus provided with the
controller according to the embodiment of the present invention to
improve the power generation efficiency. This will be explained in
detail below.
[0064] The apparatus converts wave-power energy into the swing
energy of the pendulum 11 and converts it into continuous rotary
motion using the hydraulic transmission, thus operating the
generator 60, wherein because of the two factors of: {circle around
(1)} the wave-power energy being efficiently used for the operation
of the generator 60; and {circle around (2)} preventing period
variation from occurring in the generation output are satisfied,
the apparatus can be of practical use. The structure and operation
of the power generation system having the controller of the
pendulum type wave-power generating apparatus according to the
present invention will be described with reference to FIG. 1.
[0065] Referring to FIG. 1, waves enter the apparatus from the
right side of a channel 10 and apply wave-power to a flat board of
the pendulum 11 which pivots around a support point 12 at the left
side of the channel 10, thus swinging the pendulum 11. This
pendulum motion is transmitted to the pump (hydraulic pump 20). The
pump 20 sucks oil from a bed tank 21 and alternately sends pressing
oil to the pipe (30, referred to as `the first pipe` for the sake
of explanation, Pressure P1) or the pipe (40, referred to as `the
second pipe` for the sake of explanation, Pressure P2) depending on
the direction in which the pendulum 11 moves. The pressure
accumulator 31 is provided on the first pipe 30. The hydraulic
motor 32 is connected to the first pipe 30. The pressure
accumulator 41 is provided on the second pipe 40. The hydraulic
motor 42 is connected to the second pipe 40. The hydraulic motors
32 and 42 operate as a pair on the generator 60. Because there is a
phase difference of 180.degree. between the hydraulic motors 32 and
42, periodic torque variations of the hydraulic motors 32 and 42
are offset by overlap between the two motors. Thereby, the output
of power generation can become smooth. One stroke of the oil
discharge of the pump 20, for example, includes discharging oil for
a 1/2 T second to the hydraulic motor 32, and resting for a
subsequent 1/2 T second (the discharge rate per one stroke
corresponds to the amount required to continuously rotate the
hydraulic motor 32 for the one period of a T second). Because the
flow rate of the hydraulic motor 32 is constant and the
instantaneous discharge rate of the hydraulic pump 20 varies, a
difference in the flow rate therebetween is accumulated in the
pressure accumulator 31. Of course, the case of the hydraulic motor
42 is the same as that of the hydraulic motor 32.
[0066] The pressure accumulator 31 connected to the first pipe 30
and the pressure accumulator 41 connected to the second pipe 40 are
of the spring type, wherein each increases the pressure in
proportion to the volume of oil accumulated therein, and
accumulated energy is proportional to the square of the volume of
oil accumulated therein. Thus, the pressure of the first pipe 30
varies depending on the size of the volume of oil accumulated in
the pressure accumulator 31. The pressure of the second pipe 40
varies depending on the size of the volume of oil accumulated in
the pressure accumulator 41.
[0067] If the incident wave height is increased by variation in the
conditions of the sea, the swing angle of the pendulum 11 and the
discharge rate of the hydraulic pump 20 are increased. Because the
required flow rates of the hydraulic motors 32 and are constant,
extra oil accumulates in the pressure accumulators 31 and 41, so
that the mean value of the pressure p1 in the first pipe 30 and the
mean value of the pressure P2 in the second pipe 40 are increased.
The pressure control valve 33 receives the pressure P1 as a control
signal and controls the output volume Dm of the hydraulic motor 32
using its output signal, thus increasing the required flow rate of
the hydraulic motor 32. As a result, the discharge rate of the
hydraulic pump 20 is balanced with the required flow rate of the
hydraulic motor 32, so that the mean value of the pressure P1 of
the first pipe 30 is stabilized at a new value.
[0068] In the same manner, the pressure control valve 43 receives
the pressure P2 in the second pipe 40 as a control signal and
controls the output volume Dm of the hydraulic motor 42, thus
increasing the required flow rate of the hydraulic motor 42. As a
result, the discharge rate of the hydraulic pump 20 is balanced
with the required flow rate of the hydraulic motor 42, so that the
mean value of the pressure P2 of the second pipe 40 is stabilized
into another new value.
[0069] Energy Ew(kNm) of an incident wave applied to the pendulum
11 of a width B for a period of a T second is expressed by the
following Equation (4).
E.sub.W.apprxeq.0.5.times.H.sup.2.times.T.sup.2.times.B(kNm)
Equation (4)
[0070] (where H: a significant wave height(m), T: a significant
wave period(s), B: width (m) of the pendulum)
[0071] If it is assumed that oil (volume V) discharged from the
pump 20 has accumulated in the pressure accumulators 31, 41 once,
energy E.sub.0 of the discharge oil is expressed as the following
Equation (5).
E.sub.0=(Ap).sup.2/(2k)=kV.sup.2/2A.sup.2(Nm) Equation (5)
[0072] (where A: an area (m.sup.2) of a piston of the pressure
accumulator, P: hydraulic pressure (Pa), k: spring constant
(N/m))
[0073] The hydraulic pressure P is proportional to a displacement x
of the piston in the pressure accumulator 31, 41 (therefore, it is
proportional to the volume V of oil accumulated in the pressure
accumulators 31, 41).
[0074] In the above-mentioned system structure, when the spring
constant of the spring of the pressure accumulator is adjusted such
that the mean value of the pressure P1 or the mean value of the
pressure P2 when in the normal conditions is proportional to the
incident wave height, and when Equation (3) is satisfied, the
conditions becomes as follows.
[0075] (1) The size of the swing angle of the pendulum is
proportional to the incident wave height.
[0076] (2) The power of the incident wave is proportional to the
square of the incident wave height.
[0077] (3) The power absorbed by the pendulum is proportional to
the square of the pressure of the pressure accumulator.
[0078] (4) The efficiency of the wave-power generation becomes
maximized.
[0079] In other words, as is well known, when the mean value of the
pressure P1 or the mean value of the pressure P2 is proportional to
the wave height, the swing angle of the pendulum is also
proportional to the wave height. E.sub.W of Equation (4) is
proportional to the square of the wave height H, E.sub.0 of
Equation (5) is proportional to the square of the volume V, and the
volume V is proportional to the weight height H. Therefore, if an
appropriate parameter is selected, in the state in which the
parameter is fixed, the conditions of the impedance match, such as
Equation (6) that is derived from Equations (4) and (5), are
satisfied within a wide range of wave heights H.
E.sub.W=E.sub.0 Equation (6)
[0080] In this state, to promote the stable power generation, the
output volume Dm of each hydraulic motor 32, 42 is increased or
reduced depending on the variation in the discharge rate of the
pump 20. The purpose of the pressure control valves 33 and 43 is to
achieve the above purpose. The pressure control valve 33 increases
or reduces the output volume of the hydraulic motor 32 using the
servo 35, and the other pressure control valve 43 increases or
reduces the output volume of the hydraulic motor 42 using the servo
45.
[0081] The pressure P1 in the first pipe is determined by the
volume of oil accumulated in the pressure accumulator 31, and the
pressure P2 in the second pipe is determined in the same manner as
that of the pressure P1. However, after the apparatus has been
operated for a long period of time, the pressures in the first and
second pipes may vary. The reason for this is because although
there is slight oil leakage, errors accumulate over a long period
of time. If this compounding is neglected, power distribution
between the two hydraulic motors 32 and 42 becomes unbalanced. To
prevent this problem, the switching valve 50 compares the control
signal 34 of the pressure control valve 33 and the control signal
44 of the pressure control valve 43, and if the difference between
the two exceeds a predetermined limit, the switching valve 50
connects the first pipe to the second pipe, thus equalizing the
pressures in the two pipes. After the pressures in the two pipes
have been equalized, the connection between the two pipes is
interrupted. Thereby, the balanced load distribution to the two
hydraulic motors 32 and 42 can be automatically maintained.
[0082] FIGS. 2 and 3 are front sectional views showing the pressure
control valve according to the present invention. In detail,
although FIG. 2 illustrates one of the pressure control valves that
is provided on the first pipe 30, the principle and structure
thereof are the same as those of the pressure control valve
provided on the second pipe 40. The pressure control valve includes
a part which extracts the mean value of the pressure (hydraulic
pressure, P1)(which is periodically varying) in the first pipe
using a displacement of plunger 102, and a spool type pressure
control valve which converts the displacement into hydraulic
pressure.
[0083] Of the pressure control valves, FIG. 2 will be explained
with reference to the pressure control valve 33 provided on the
first pipe 30. As shown in FIG. 2, the plunger 102 is placed
upright in the lower end of the pressure control valve 33, and the
hydraulic pressure P1 of the first pipe 30 that has passed through
an iris diaphragm 101 pushes the plunger 102 upwards with a force
proportional to the pressure P1. This force is transmitted to the
third elastic member 113 via the damper 111 and makes an upward
displacement proportional to the pressure (hydraulic pressure, p1).
This is the pressure accumulator provided with a small damper. This
displacement is transmitted to the second elastic member 123 which
biases the spool 122 upwards, thus increasing or reducing the force
of the second elastic member 123. The spool 122 may communicate the
fourth port 150 of the pressure control valve 33 with the second
port 130 or communicate the fourth port 150 with the third port
140. This operation is governed by the combination of three kinds
of axial forces including the first and second elastic members 121
and 123 that are applied to the spool 122 and the valve pressure P3
in the chamber 120.
[0084] At the initial stage of the operation of the pendulum 11, as
shown in FIG. 2, because the first elastic member 121, which
generates a constant and strong axial force, biases the spool 122
downwards, the second port 130 communicates with the fourth port
150, so that the pressure P1 is high when applied to the second
port 130 through the first pipe 30 and applied towards P3 of the
chamber 120. Thereby, the valve pressure P3 in the chamber 120 is
increased, thus pushing the spool 122 upwards in the chamber 120.
Thus, the second port 130 that has been connected to the first pipe
30 is closed, so that the increase in the valve pressure P3 in the
chamber 120 stops. At this time, the magnitude of the valve
pressure P3 is proportional to the intensity of the resultant force
applied to the spool 122 downwards.
[0085] On the other hand, the valve pressure P3 may decrease. As
shown in FIG. 3, in an embodiment, when the pressure in the first
pipe 30 increases and the pressure p1 is applied into the first
port 100, thus moving the plunger 102 upwards, the damper 111 is
moved upwards. Then, the third elastic member 113 is compressed and
a damper guide 116 is moved upwards, so that the second elastic
member 123 is compressed and the force of the second elastic member
123 offsets the force of the first elastic member 121 that biases
the spool 122 downwards, thus reducing the valve pressure P3 in the
chamber. At this time, the valve pressure P3 is used as the control
signal 34 of the output volume of the hydraulic motor 32 and is
transmitted through the fourth port 150. In this case, as the
wave-power energy increases, the discharge rate of the hydraulic
pump 20 is also increased. Thus, the reduced valve pressure P3 in
the pressure control valve 33 is transmitted as the control signal
through the fourth port 150 connected to the servo 35 of the
hydraulic motor 32. Thereby, the output volume of the hydraulic
motor 32 is increased. Of course, in the case where the valve
pressure increases, the reduced valve pressure P3 in the pressure
control valve 33 is transmitted as the control signal 34, so that
the output volume of the hydraulic motor 32 is increased (of
course, as shown in FIG. 1, the first pipe 30 that transmits the
pressure P1 to the pressure control valve 33 and the second pipe 40
that transmits the pressure P2 to the other pressure control valve
43 are connected to the switching valve 50, so that when signals
are transmitted from the pressure control valves 33 and 43, the
pressures (hydraulic pressures P1 and P2) in the first and second
pipes 30 and 40 are applied to the switching valve 50, and a member
in the switching valve 50 is thus moved in one direction, thus
connecting the first and second pipes 30 and 40 to each other,
thereby balancing the pressures P1 and P2 in the first and second
pipes 30 and 40 that have become unbalanced).
[0086] In other words, this embodiment illustrates the case where
when the valve pressure P3 is high, the output volume Dm is small,
and as the valve pressure P3 is reduced, the output volume Dm is
increased (of course, as stated above, the principle of the
above-mentioned operation is also applied in the same manner to the
pressure control valve 43 provided on the second pipe 40).
[0087] Although the hydraulic pressure (pressure P3) of the first
pipe 30 periodically varies at wave period T, the present invention
is configured such that the variable constituent is prevented from
being transmitted to the valve pressure P3. To achieve the above
purpose, the present invention is provided with the damper 111. The
damper guide 116 is provided on the upper end of the damper 111.
The damper 111 uses the inner surface of the cylinder 110 as a
guide surface and is guided by the damper guide 116, so that the
damper 111 can be smoothly moved upwards or downwards by the
movement of the plunger 102.
[0088] The interior of the cylinder 110 is partitioned into a lower
chamber 114 and an upper chamber 115 by the damper 111. A strong
damping operation is conducted by oil flowing along a thin hole 112
which is formed between the two chambers. Thereby, the periodic
variable constituent of the sea wave is eliminated, and the valve
pressure P3 corresponding to the mean values of the conditions of
the sea waves per unit time (for example, the mean values when
waves are input five to ten times) can be simply obtained. [0089]
the embodiment of the present invention and specifications of this
case
[0090] In the case of the incident wave height H=2 m, the incident
wave period T=6 s, the coast of the water depth h=3 m and the
pendulum width B=4 m, the power Pw of a wave applied to the
pendulum 11.apprxeq.96 kW. This value is a short-time means value
and takes into account the characteristics of the sea waves. It is
greater than a long-time mean value obtained from Equation (4). The
amplitude .theta..sub.0 of the pendulum 11.apprxeq.40.degree. to
60.degree.. The power of the generator 60 is 40 kW (three-phase
induction AC generator, six pole, 1200 rpm(maximum)), as it is
expected that the efficiency .eta. of the generator 60=power
generating output/incident wave input.apprxeq.42%. A6VM55 (Dm=54.8
cm.sup.3/rev, maximum) of Rexroth company of Germany is used as
each hydraulic motor 32, 42. The capacity of each pressure
accumulator 31, 41 is 10 liters, and the maximum pressure thereof
is 20 Mpa. In each pressure control valve 33, 43, the diameter of
the spool 122 ranges from 10 mm to 20 mm. This is not large as a
control element.
[0091] Although the preferred embodiment of the present invention
has been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *