WO2023012679A1

WO2023012679A1 - Apparatus for recovering electricity in a hydraulic system

Info

Publication number: WO2023012679A1
Application number: PCT/IB2022/057186
Authority: WO
Inventors: Nicola FRUET
Original assignee: Hp Energy Srl
Priority date: 2021-08-04
Filing date: 2022-08-03
Publication date: 2023-02-09
Also published as: IT202100021182A1

Abstract

The apparatus (100) for the production of electricity from gravitational potential energy of a mass of water comprises: at least one pump (3) arranged to operate as a turbine to exploit the geodetic jump (H) available to the water; a current generator (G) driven by the pump (3), an inverter (5) functionally connected to the current generator (G), a sensor (9) of the revolution number of electric generator and/or of the revolution number of the pump (3), and an ECU unit controlling the inverter (5) and the sensor (9) of the revolution number, provided with program means comprising a memory in which the characteristic curves of the pump (3) used as a turbine are loaded, wherein the control unit (ECU) is programmed to control the apparatus (100) and obtain: a) the maximum production of electricity in every condition, by adjusting the rotational speed of the pump (3) through the inverter (5), in feedback on the basis of the revolution number detected by the sensor (9); wherein the generator (G) is a generator with permanent magnets.

Description

APPARATUS FOR RECOVERING ELECTRICITY IN A HYDRAULIC SYSTEM

Technical Field

The present invention relates to a production apparatus for recovering electricity in a hydraulic system, in particular exploiting water geodetic (piezometric) heads available in aqueducts, sewers, irrigation systems, etc...

Background Art

Often the hydraulic systems for the community, such as aqueducts, sewers and large irrigation systems, comprise tanks for water arranged at different heights and connected to each other, pipes, pumps, control systems, etc.; in practice between the tanks is a geodetic head, often less than 150 meters, which in the past was not exploited to produce electricity: the water flows by gravity from the higher tanks to the lower ones.

Recently, however, in order to minimize the costs incurred by the managers of these systems for the purchase of electricity from the grid, technical solutions have been proposed that envisage recovering a part of the potential energy of the water, i.e., which envisage the exploitation of the geodetic or piezometric heads, even if modest, generally corresponding precisely to 150 meters, for the production of electricity in situ.

The intent is not to make the hydraulic system independent, offsetting electricity consumption with self-production - a result which can be obtained in some cases when the geodetic head allows it - but to allow the production of electricity able to offset only a part of consumption.

The German company KLEIN SCHANZLIN & BECKER AG, known as KSB Aktiengesellschaft, for some years now, has presented electricity production apparatuses that exploit the geodetic heads available in the above-mentioned hydraulic systems. As mentioned in a press release of 2008, http://www.ksb.com/ksb-en/Press/Press-Archive/Press- Archive-

2008/11158/turbine-systems-for-energv-generation.html, these apparatuses envisage operating the pumps normally present in hydraulic systems as turbines for pumping water from a tank at lower level to a tank at higher level. In point of fact, the basic idea is to connect an electric generator to the pumps, and when the water falls by gravity the pumps are made to rotate contrary to the direction of rotation required to pump water upwards, i.e., in such a way that the water enters the pump delivery and comes out of the suction. The expression commonly used by experts to identify pumps used as turbines is ‘Pump as Turbine' (PaT). The international patent application WO 86/03260 describes an example of a pump used as a turbine.

Each pump is characterized by corresponding operation curves, called characteristic curves: geodetic head H vs. flow rate Q, power P vs. flow rate Q, efficiency g vs. flow rate Q, torque C vs. flow rate Q. The characteristic curves are detected by the manufacturer within a pump rotation speed interval typically ranging between 1200 and 3100 revolutions per minute (rpm), for the normal operation of the pump. Pump manufacturers do not provide the characteristic curves for the pump used as a turbine, because it is after all an operation not contemplated in the design phase. In practice, it is the designers of systems with PaT who detect the characteristic curves of the pumps so as to choose the one from time to time most suitable to work as a turbine in a given system.

The lower cost of a pump with respect to a turbine, the size being the same, is one of the reasons that make it preferable to use a PaT in place of a traditional turbine. The cost of a PaT may be more than 50% lower than the cost of a turbine of the same size.

By contrast, the maximum efficiency of a PaT is certainly considerably lower than the maximum efficiency of a turbine of the same size, and is about 3% -8% less compared to the maximum efficiency of the machine used as a pump.

The PaTs can be inserted both along the large supply pipes that bring water from the springs to the urban centers, to cope with topographic gradients, and in hydraulic systems such as those described above, replacing the flow rate and pressure regulating/reduction valves. In the first case the head- flow rate pair is rather constant in time, because the flow which circulates in the external aqueducts is generally constant. In the second case, on the contrary, the variability of hydraulic conditions is ample; furthermore, because of the link between flow rate and pressure drop in the channels, the curve that describes the head available for energy recovery according to flow is decreasing monotone.

In practice, therefore, the adjustment of an electricity production apparatus based on the use of PaT - in particular when the PaT replaces the flow and pressure regulating/reduction valves in the hydraulic system - may not be at all easy.

This type of apparatus is described in Patent Document No. BS2015A000023.

It follows that the performance obtainable from known apparatuses are often not optimal.

Therefore, these apparatuses are involved in further refinements aimed at improving the performance thereof in terms of energy production.

It is instead desirable to have an apparatus for recovering electricity that allow obtaining the highest possible performance in all operating conditions, with a simple adjustment.

Description of the Invention

The main aim of the present invention is therefore to provide an apparatus for recovering electricity in hydraulic systems characterized by modest water geodetic heads, exploiting a PaT, which allows to always obtain the maximum possible production of electricity, even if operating conditions vary, e.g. if water flow varies.

Another object of the present invention is to provide a method to produce electricity with a PaT exploiting the water geodetic heads available in hydraulic systems such as aqueducts, sewers, irrigation systems, etc., allowing to obtain the best performance desired by the manager of the system and is simple to adjust in any operating condition.

Therefore, in a first aspect the present invention relates to an apparatus according to claim 1, for the production of electricity from gravitational potential energy of a mass of water, e.g. water in a hydraulic system such as an aqueduct.

In particular, the apparatus comprises at least a pump, e.g., centrifugal, radial, axial, single-stage, multi-stage, mixed flow, etc., adapted to operate as a turbine to exploit the geodetic head at the disposal of water. In practice the falling water is introduced into the pump at the relative delivery.

A current generator, AC or DC, synchronous or asynchronous, is driven by the pump preferably directly, or alternatively by means of a gearbox.

The generator is in turn equipped with an inverter, which can have variable frequency if the generator is alternating current, or fixed frequency if the generator is direct current. The inverter can work in two configurations, passing instantly from one to another and vice versa, according to the operating conditions in which it operates at a given instant.

In a first configuration, called drive, the inverter can intervene in the adjustment of the rotation speed of the current generator and, therefore, of the pump connected to it, acting as a motor and accelerating the pump-electric generator system. In this configuration the inverter draws current from the grid to which the generator is connected.

In a second configuration, called regenerative, the inverter can intervene in the adjustment of the rotation speed of the current generator and, therefore, of the pump connected to it, acting as a magnetic brake; the inverter prevents the pump-current generator system from exceeding a threshold value of the rotation speed and, as explained below, this value is in turn established according to the needs of the apparatus’ manager.

During operation, as soon as the torque supplied by the water to the pump exceeds the threshold value set to maintain the rotation speed set for the drive configuration, e.g., 3000 revolutions per minute, the inverter automatically switches to the regenerative configuration to recover electric power.

The apparatus also comprises a sensor for the number of revolutions of the electric generator and/or the number of revolutions of the pump.

Optionally, and as a precaution, the apparatus also has a pressure sensor set to detect the pressure difference (differential) of the water at input and output of the PaT pump.

Preferably, but not necessarily, the apparatus also comprises at least one flow rate sensor designed to detect the water flow rate values supplied to the pump delivery. This sensor is not necessary if the hydraulic system with which the apparatus is associated operates with constant water flow rate, set up by the manager and thus known beforehand. Conversely, the flow rate sensor is required if the water flow rate varies over time.

As explained later, the sensors are logically connected to a control unit, which collects and processes the signals supplied by the sensors themselves.

Preferably, but not necessarily, the apparatus also comprises at least one regulating valve for regulating the water flow rate upstream of the pump. The valve, also connected to the control unit or manually operable by an operator, allows making a fine adjustment of the water flow rate, to partially or completely shut off the flow of water.

As mentioned above, the apparatus comprises a control unit of the inverter and of the sensor for the number of revolutions and, if any, of the flow rate sensor, of the pressure sensor and of the regulating valve. The control unit is preferably of the electronic type and has program means comprising a memory in which are loaded the characteristic curves of the pump used as a turbine.

As has been said, the characteristic curves are detected from time to time by the designer and loaded in the memory of the control unit which uses them to operate all the apparatus components in the most appropriate way.

According to the present invention the control unit is programmed to control the apparatus and to obtain: a) maximum production of electricity in all operating conditions, by adjusting the rotation speed of the pump through the inverter, in feedback based on the number of revolutions detected by the specific sensor.

Thanks to the presence of the inverter and the sensor for the number of revolutions, the apparatus is able to optimize the function a) in any operating condition. By contrast, conventional apparatuses do not allow so much versatility and are much more difficult to adjust and less versatile.

More in detail, the maximum production of electricity referred to at point a) is obtained in one of the following ways: al) the water flow rate is substantially constant and known beforehand and we proceed by sampling the number of revolutions of the pump or of the electric generator, by means of the corresponding sensor, comparing such sampled values with the characteristic curves loaded into the memory and operating the inverter to adjust the rotation speed of the electric generator and, therefore, the rotation speed of the pump connected to it, and keep it stable at the number of revolutions corresponding to the maximum production of electricity, or, a2) the flow rate and/or pressure of water vary, the apparatus comprises the flow rate sensor and/or the pressure sensor, and we proceed by sampling, by means of such sensors, the flow rate values and/or the pressure values of the water supplied by the pump, comparing such sampled values with the characteristic curves loaded in the memory and operating the inverter to adjust the rotation speed of the electric generator and, therefore, the rotation speed of the pump connected to it, and keep it stable at the number of revolutions corresponding to the maximum production of electricity for the flow rate and/or pressure values detected.

During the steps al) and a2) it is the inverter which regulates the number of revolutions of the pump PaT. If the water flow rate regulating valve is present, it is also possible to obtain a fine adjustment of the number of revolutions, and/or of the flow rate, by operating the water flow rate regulating valve upstream of the pump.

The sampling of the number of revolutions of the pump or of the electric generator also corresponds in practice to the sampling of the torque, considering that to a certain number of revolutions corresponds a univocal torque value of the electric generator or of the pump PaT, according to the characteristic curves. The frequency of sampling is chosen using the Nyquist theorem based on the frequency whereby the water flow rate changes in the hydraulic system. This is not a particularly relevant figure considering that in the above-described hydraulic systems the water flow rate is kept approximately constant by the manager. As already mentioned, optionally the apparatus also has the flow rate sensor and the control unit is also programmed to obtain, in addition to the adjustment referred to in step a): b) a certain flow rate of water flowing through the pump.

Such adjustment is implemented in feedback according to the number of revolutions of the pump or of the electric generator, if the water flow rate is constant and known beforehand, or, if the water flow rate is variable or in any case not known beforehand, according to the flow rate value measured by the flow rate sensor, and is obtained by means of one of: bl) adjusting the inverter by means of the control unit, to bring the current generator and, therefore, the pump connected to it to the desired number of revolutions, so that, through the pump which rotates at the desired number of revolutions, only the desired water flow rate can pass; b2) if the water flow rate regulating valve is present upstream of the pump: adjusting by means of the control unit of such valve; b3) if the water flow rate regulating valve is present: adjusting both the regulating valve and the inverter by means of the control unit, i.e., by making a mixed adjustment of bl) and b2).

If the apparatus also has the pressure sensor, the control unit can also be programmed to obtain the following adjustment in the hydraulic system, in addition to the adjustment referred to in step a) and in addition or as an alternative to the adjustment in step b): c) a certain water pressure at the pump outlet.

The adjustment referred to at point c) is carried out in feedback according to the pressure value measured by the pressure sensor, and is obtained by means of one of: cl) adjusting the inverter by means of the control unit, to bring the current generator and, therefore, the pump connected to it to the desired number of revolutions, so that, through the pump which rotates at the desired number of revolutions, only the desired water flow rate can pass, corresponding to the desired pressure according to the characteristic curves loaded in the memory of the control unit; c2) if the water flow rate regulating valve is present: by regulating such valve by means of the control unit, so that the set water flow rate corresponds to the desired pressure according to the characteristic curves of the pump; c3) by adjusting both the regulating valve and the inverter by means of the control unit, i.e., by making a mixed adjustment of cl) and c2).

Advantageously, therefore, the apparatus always allows obtaining the best adjustment according to the manager’s needs.

Another adjustment option provided by the apparatus of the present invention relates to the water level in the tank or basin that supplies the pump used as a turbine. Preferably the apparatus comprises a level sensor, designed to measure the water level in the tank and the control unit is programmed to implement any one of the adjustments bl), b2) or b3) in feedback according to the value detected by the level sensor, to keep the water level in the tank constant over time. This function is particularly useful when the hydraulic system manager needs to preserve the supply of water in a basin.

In a second aspect, the present invention relates to a method according to any of claims 8-14 for producing electricity in a hydraulic system, in a simple and effective way under any operating conditions.

Brief Description of the Drawings

Further characteristics and advantages of the invention will become better apparent from the examination of the following detailed description of a preferred, but not exclusive embodiment, illustrated only by way of nonlimiting example, with the support of the attached drawings, in which:

Figure 1 is a schematic view of a hydraulic system wherein an apparatus is installed according to the present invention;

Figure 2 is a conceptual and schematic view of an apparatus according to the present invention;

Figures 3 to 13 are flow charts explaining the operation of the apparatus according to the present invention;

Figure 14 is a flow rate/power graph of an apparatus according to the present invention;

Figure 15 is a flow rate/geodetic head graph of an apparatus according to the present invention.

Embodiments of the Invention

With reference to figure 1, a hydraulic system of small size, e.g., an aqueduct, comprises a water storage basin 1. A water pipeline 2 conveys the water from the basin 1 to a pump 3 used as a turbine, i.e., supplied with water at the delivery thereof. To the pump 3 an electric generator G is coupled, in turn connected to an external power grid or to an internal network of the system, called island. The water swirled in the pump 3 is discharged into a second basin 4.

Advantageously, the electric generator G is with permanent magnets.

The electric generator G is coupled to the pump 3 directly or through a gearbox. The geodetic head at the disposal of water is indicated by the letter H.

With reference to figure 2, an apparatus 100 according to the present invention comprises a pump 3 used as a turbine, i.e., a PaT, arranged along the water pipeline 2 and connected to a generator G.

According to the invention, the generator G is a permanent magnet generator. Advantageously, the generator G is of the asynchronous type.

Alternatively, the generator G is of the synchronous type.

Preferably, the generator G is of the direct current type.

In accordance with a first embodiment, the inverter 5 is fixed frequency, in this case the generator G is direct current.

Alternatively, the inverter 5 is variable frequency, in this case, however, the generator G is of the alternating current type.

In this regard, the inverter 5 is configured to adjust the rotation speed of the generator G and of the pump 3, which is connected to the rotation shaft thereof. Optionally, as shown in the illustration, a valve 6 for regulating the water flow rate intercepts the pipeline 2 upstream of the pump 3. A pressure sensor 7 and a flow rate sensor 8, also optional, intercept the pipeline 2 upstream of the pump 3 to detect the pressure and the water flow rate respectively at inlet of the pump 3. For safety and maintenance reasons a bypass circuit can be mounted (not shown) with a valve system upstream of the pump 3, e.g., a manual or servoassisted valve system, which allows the diversion of the water flow when the apparatus has to be stopped to perform maintenance, or in case of failure of the pump 3.

The operation of the valve 6 and of any bypass valve can be done manually, by means of the direct intervention of a human operator, but preferably occurs automatically as explained below.

A sensor 9 instantly detects the number of revolutions of the electric generator G and, therefore, the number of revolutions of the pump 3 that rotates with it.

A control unit ECU, preferably of the electronic program type, is logically connected to the sensors 7 and 8 (if any), to the sensor 9, to the valve 6 (if any) and to the inverter 5, to check the operation thereof, and is connected to an external power grid through the connection 10 or to the island, e.g., an internal network of the hydraulic system which supplies the internal user points through the connection 11.

The control unit ECU knows the characteristic curves of the pump 3, which have been loaded in a memory.

The operation will now be described of the apparatus in relation to the state of the pump 3.

The apparatus 100 is in standby and the pump 3 is ready to start and waiting for the start signal from the control unit. The start signal can be provided by an operator or may be subject to the occurrence of a condition of the hydraulic system or other components of the apparatus 100.

Having received the start signal, the control unit ECU releases any mechanical braking systems of the pump 3 or of the generator G, and commands the inverter 5 to push the alternator G and, therefore, the pump 3 in rotation up to the set speed, dependent on the power/pressure/flow rate curve of the pump 3 used as turbine PaT loaded in the memory. In this phase the inverter 5 operates as an electric motor that draws current from the external grid or from the island. Once the desired rotational speed, e.g., 1500 rpm, is reached, the pump 3 is operated as turbine PaT, swirling the water falling along the pipeline 2, and kept stable in these conditions.

Having checked that the pump 3 is operating stably, i.e., its operating parameters remain essentially stable over time, the electricity produced by the generator G can be introduced into the power grid or into the internal island of the hydraulic system. The control unit ECU is programmed to control the apparatus and to pursue a strategy between a), b) and possibly c) described above.

During the shutdown process, the assembly formed by the pump 3 and by the generator G is gradually slowed down and then finally stopped in order not to damage any component. The impeller of the pump 3 is blocked and, if the bypass circuit is present, the water is diverted to bypass the pump 3. The slowdown is effected by the inverter 5 which can also operate as a magnetic brake, as described above.

In the event of the control unit ECU detecting an abnormal condition in the controlled components, it immediately interrupts the power input to the external grid or the island, and stops the pump-generator assembly as explained above or alternatively by means of instant braking (as in the case of lack of power supply to the apparatus). The control unit ECU has preferably a buffer battery in order to operate even when there is no external power supply. The control unit ECU generates an alarm signal. If necessary to ensure the water supply, e.g., in an aqueduct, the control unit ECU sets the bypass of the pump 3 to continue the flow of water. Even when the impeller of pump 3 is blocked, the pump 3 allows the flow of most of the water: the flow rate through the stopped pump 3 depends on the pump model and can generally be greater or lesser compared to the flow rate with rotating pump.

At the same time during the procedures described above, the control unit ECU continues to process the signals coming from the sensors 7 (if any) and 8-9 to make sure the pump 3 is working properly as required by the system manager and that there are no faults.

The operation will now be described of the apparatus 100 in relation to the maximum performance desired by the manager.

When the manager of the apparatus 100 wishes to obtain the maximum production of electricity from the generator G, this is achieved in two ways by the control unit ECU.

Figure 3 is a flow chart relating to a first mode al). From a standby situation, the control unit ECU commands the inverter 5 to drive the electric generator G in rotation until the number of revolutions are reached corresponding to the maximum production of electricity (set rpm); this datum is supplied by the manufacturer of the generator G and in any case univocally corresponds to a power value in the characteristic curves of the pump 3 used as turbine PaT stored in the control unit ECU. The inverter 5 draws current to function as the motor of the generator G.

The water is made to swirl in the pump 3. If the water flow rate regulating valve 6 is fitted, this can be used to obtain a fine adjustment of the number of revolutions of the pump 3. Once the number of revolutions has been reached for the maximum production of electricity, the generator G produces electricity and the control unit ECU provides for its input into the grid or distribution to the island inside the hydraulic system, at the same time placing the inverter in the regenerative mode.

The control unit ECU constantly checks (with a certain sampling frequency) by means of the sensor 9 for the number of revolutions if the maximum power of the pump 3 has been achieved. If this is the case, it continues to inject electricity into the grid, as just described, otherwise it makes a new adjustment of the number of revolutions of the pump 3 by means of the inverter 5 in the drive mode.

In practice the control unit ECU makes a fine adjustment of the rotation speed of the pump 3, by means of the inverter 5, in feedback on the basis of the signal generated by the sensor 9.

Figure 4 is a flow chart relating to a further adjusting mode that, in addition to what has been said in al), provides that the control unit ECU also acts on the regulating valve 6 of the water flow rate to obtain a fine adjustment of the number of revolutions, and/or of the flow rate.

When the manager of the apparatus 100 wishes to obtain a given flow rate of water in the pipeline 2, e.g., because the downstream basin 4 cannot receive a flow rate higher than a nominal flow rate, or because the gradual emptying or filling of one of the basins 1 or 4 is to be obtained, this is achieved in three ways by the control unit ECU. Adjustment b) can be obtained in addition to adjustment a), i.e., the manager can set the flow rate and the apparatus 100 adjusts itself to obtain the maximum production of electricity at such flow rate. Figure 5 is a flow chart relating to a first mode bl). From a standby situation, the control unit ECU commands the inverter 5 to drive the electric generator G in rotation until the number of revolutions (set rpm) are reached corresponding to the desired water flow rate through the pump 3; the control unit ECU takes this datum from the stored characteristic curves of the pump 3 used as a turbine PaT. The inverter 5 draws current to function as the motor of the generator G.

The adjustment of the number of revolutions is performed continuously by the control unit ECU by means of the inverter 5 in feedback on the basis of the value of the water flow rate detected by the sensor 8. When the water flow rate corresponds to the desired value, the control unit ECU commands the input of electrical current into the grid and the inverter 5 switches to the regenerative mode.

Figure 6 is a flow chart relating to a second mode b2) which differs from mode bl ) because the fine adjustment of the water flow rate flowing through the pump 3 is performed not only by acting on the inverter 5, but also by acting on the valve 6, if any, for the adjustment of the water flow rate in the pipeline 2. The adjustment is always in feedback by the control unit ECU.

Figure 7 is a flow chart relating to a third mode b3) which corresponds to a mixed adjustment between the modes bl) and b2), i.e. the control unit ECU adjusts both the number of revolutions of the pump 3 and the degree of opening of the flow rate regulating valve 6.

When the manager of the apparatus 100 wishes to obtain a given water pressure in the pipeline 2, this is optionally achieved in three ways by the control unit ECU connected by a pressure sensor 7, absolute or differential, able to detect the difference in pressure upstream and downstream of the pump 3. Adjustment c) is obtainable in addition to adjustment a), and alternatively or in addition to adjustment b), i.e., the manager can set the pressure and the apparatus 100 is adjusted to obtain the maximum production of electricity at such pressure.

Figure 8 is a flow chart relating to a first mode cl ). From a standby situation, the control unit ECU commands the inverter 5 to drive the electric generator G in rotation until the number of revolutions (set rpm) are reached corresponding to the desired pressure through the pump 3; the control unit ECU takes this datum from the stored characteristic curves of the pump 3 used as a turbine PaT. The inverter 5 draws current to function as the motor of the generator G.

The adjustment of the number of revolutions is performed continuously by the control unit ECU by means of the inverter 5 in feedback on the basis of the pressure value detected by sensor 7. When the water pressure corresponds to the desired value, the control unit ECU commands the input of electricity into the grid and the inverter 5 switches to the regenerative mode.

Figure 9 is a flow chart relating to a second mode c2) which differs from mode cl) because the adjustment of the pressure of the water flowing through the pump 3 is not performed by acting on the inverter 5, and therefore on the number of revolutions, but by acting on the valve 6, if any, for the adjustment of water flow rate in the pipeline 2. The adjustment is always in feedback by the control unit ECU.

Figure 10 is a flow chart relating to a third mode c3) which corresponds to a mixed adjustment between the modes cl) and c2), i.e. the control unit ECU adjusts both the number of revolutions of the pump 3 and the degree of opening of the flow rate regulating valve 6.

When the manager of the apparatus 100 wishes to maintain a determinate water level in the basin 1, this is achieved in three ways by the control unit ECU.

Figures 11-13 are flow charts explaining how to get this result. In practice, the charts of Figures 11-13 correspond to the charts of Figures 5-7, respectively; the only difference consists in the fact that the feedback is based on the value of the water level in basin 1 detected by a suitable sensor connected to the control unit ECU:

A hydraulic system is assumed with maximum flow rate of 14 1/s along the pipeline 2 and geodetic head H of 100 m.

Figure 14 is a graph of some characteristic curves of the pump 3, with the water flow rate on the abscissa and power on the ordinate. From the curves in Figure 14 it can be seen that the maximum power obtainable from the generator G at 2900 rpm is about 5.9 kW.

The curves are all loaded into the memory of the control unit ECU, which uses them continually to calculate the best operating parameters according to the performance to be optimized selected by the manager.

It is assumed that, for reasons of water availability - e.g., due to the lack of water caused by a period of drought, or merely less demand by users - the available flow rate is reduced to 6.5 1/s. In this case to obtain maximum power the control unit ECU will have to reduce the rotation speed to 2200 rpm.

Figure 15 is a graph of some characteristic curves of pump 3, with the water flow rate on the abscissa and the geodetic head on the ordinate. From the curves of figure 15 it can be seen that the head H used by the pump 3 at 6.5 1/s at 2200 rpm is approximately 26 m. In this new configuration the pump 3 delivers about 640 W, which corresponds to maximum power output in the range of 1200 to 2900 rpm. At this point the flow rate curves intersect, and it is preferable to adjust the apparatus 100 so that the pump 3 maintains the minimum rotation speed, production being equal.

It has in practice been ascertained that the described invention achieves the intended objects.

In particular, the fact is emphasized that the expedient of providing a permanent magnet generator makes it possible to optimize the production of electricity compared with the use of other types of generators.

Claims

1) Apparatus (100) for the production of electricity from gravitational potential energy of a mass of water, comprising: at least one pump (3) arranged to operate as a turbine to exploit the geodetic jump (H) available to the water; a current generator (G) driven by the pump (3), an inverter (5) functionally connected to the current generator (G), a sensor (9) of the revolution number of electric generator and/or of the revolution number of the pump (3), and an ECU unit controlling the inverter (5) and the sensor (9) of the revolution number, provided with program means comprising a memory in which the characteristic curves of the pump (3) used as a turbine are loaded, wherein the control unit (ECU) is programmed to control the apparatus (100) and obtain: a) the maximum production of electricity in every condition, by adjusting the rotational speed of the pump (3) through the inverter (5), in feedback on the basis of the of the revolution number detected by the sensor (9); characterized by the fact that said generator (G) is a generator with permanent magnets.

2) Apparatus (100) according to claim 1, characterized by the fact that said generator (G) is of an asynchronous type.

3) Apparatus (100) according to claim 1, characterized by the fact that said generator (G) is of a synchronous type.

4) Apparatus (100) according to one or more of the preceding claims, characterized by the fact that said generator (G) is direct current.

5) Apparatus (100) according to one or more of the preceding claims, characterized by the fact that said inverter (5) is fixed frequency, said generator (G) being direct current.

6) Apparatus (100) according to one or more of the preceding claims, characterized by the fact that said inverter (5) is variable frequency, said generator (G) being alternating current. 7) Apparatus (100) according to one or more of the preceding claims, characterized by the fact that said inverter (5) is configured to adjust the rotational speed of said generator (G) and of said pump (3).

8) Apparatus (100) according to one or more of the preceding claims, characterized by the fact that the maximum production of electricity referred to in point (a) is obtained: al) under conditions of constant water flow rate known in advance, by sampling the revolution number detected by the special sensor (9), comparing these sampled values with the characteristic curves in the memory and operating the inverter (5) to adjust the rotational speed of the electric generator (G) and, therefore, the rotational speed of the pump (3), and keep it stable at the revolution number corresponding to the maximum production of electricity for the known value of flow rate, or a2) under conditions of water flow rate and/or pressure varying over time, or in any case not known in advance, where the apparatus (100) comprises at least flow rate sensor (8) and/or a pressure sensor (7), the sampling occurs by means of said sensors (7, 8) of the flow rate values and/or the pressure values of the water fed by the pump (3), by comparing these sampled values with the characteristic curves in the memory and operating the inverter (5) to adjust the rotational speed of the electric generator (G) and, therefore, the rotational speed of the pump (3) connected thereto, and to keep it stable at the revolution number corresponding to the maximum production of electricity for the detected values of flow rate and/or pressure.

9) Apparatus (100) according to one or more of the preceding claims, comprising at least one valve (6) for adjusting the flow rate of the water fed to said pump (3), operated by said control unit (ECU) to achieve fine adjustment of the revolution number of said pump (3) and/or of the water flow rate.

10) Apparatus (100) according to one or more of the preceding claims, characterized by the fact that said control unit (ECU) is programmed to obtain: (b) a determined water flow rate flowing through the pump (3), 18 and this adjustment is obtained by using the characteristic curves in the memory, in feedback: based on the revolution number detected by the special sensor (9), under constant and previously known water flow rate conditions, or based on the flow rate value measured by a flow rate sensor (8), under conditions of water flow rate varying over time or in any case not known in advance, by means of one of either: bl) by adjusting the inverter (5) by the control unit (ECU), to bring the current generator (G) and thus the pump (3) connected thereto to the desired revolution number, so that only the desired water flow rate can flow through the pump (3) rotating at the desired revolution number; or b2) the apparatus comprises a control valve (6) for adjusting the water flow rate upstream of the pump (3) and the control unit (ECU) adjusts this valve with or without the intervention of the inverter (5) on the pump (3); or b3) adjusting by the control unit (ECU) both the control valve (6) and the inverter (5), i.e. by implementing a mixed adjustment between bl) and b2).