CA2831361A1

CA2831361A1 - Power generation system, backup power supply, data center installation method, power generation system controller, power system, and power generation system operating method

Info

Publication number: CA2831361A1
Application number: CA2831361A
Authority: CA
Inventors: Sumito Tobe; Shinichi Inage; Masashi Toyota; Mitsuo Tsurugai; Tohru Akatsu; Mika Imai
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2012-10-31
Filing date: 2013-10-28
Publication date: 2014-04-30
Anticipated expiration: 2033-10-28
Also published as: JP2014113034A; AU2013251221A1; JP6266303B2; CA2831361C; AU2013251221B2; RU2568013C2; RU2013148374A

Abstract

Disclosed is a power generation system having a power generation facility based on renewable energy, a first storage battery to be charged with electrical power supplied from the power generation facility, a second storage battery for supplying electrical power to a power system, a connection switching device for switching the first storage battery and the second storage battery, and a controller for controlling the connection switching device. The controller controls switching the connection switching device at a switching timing that is determined in accordance with a predicted amount of electrical power generation by the power generation facility and with a predicted demand of the power system. Thus, it becomes possible to effectively use the output of renewable energy including its variation, and supply electrical power in accordance with the electrical power demand of users by discharging the storage battery.

Description

TITLE OF THE INVENTION:
POWER GENERATION SYSTEM, BACKUP POWER SUPPLY, DATA CENTER
INSTALLATION METHOD, POWER GENERATION SYSTEM CONTROLLER, POWER
SYSTEM, AND POWER GENERATION SYSTEM OPERATING METHOD
FIELD OF THE INVENTION:
The present invention relates to a power generation system, a backup power supply, a data center installation method, a power generation system controller, a power system, and a power generation system operating method.
BACKGROUND OF THE INVENTION:
A related art is disclosed, for instance, in Japanese Unexamined Patent Application Publication No. 2009-197587, which describes a wind power generation facility. Being capable of generating electrical power without allowing its wind power generation capability to be restricted by limitations imposed on a storage battery, this wind power generation facility not only increases the availability of its wind power generation capability, but also reduces the capacity required of the storage battery. The wind power generation facility includes a switching device which electrically connects a converter or an inverter with two storage batteries each other. Herein, the converter is connected with a wind turbine generator, and the inverter is connected with a utility grid.

2 SUMMARY OF THE INVENTION:
When a related-art output variation reduction technology for renewable energy provided by a storage battery is used, the variation in the output of the renewable energy cannot be predicted. Thus, the output variation cannot be perfectly eliminated. Consequently, a certain level of variation reduction has been regarded as a successful result in consideration of a power system's electrical power quality standard and of the output adjustment capability of an existing large-scale power station. However, when the renewable energy is used as a stable power supply for a microgrid or other isolated power system independent of a bulk power system, such a certain level of variation reduction is inadequate from the viewpoint of electrical power quality and frequency variation, in particular. Further, the output of wind power cannot be predicted with ease and adapted to follow the ever-changing electrical power consumption needs of users.
According to an aspect of the present invention, there is provided a power generation system having a power generation facility based on renewable energy, a converter for providing power conversion between alternating current (AC) and direct current (DC) , a first storage battery, and a second storage battery. The power generation system includes a controller that charges the output from the power generation facility into

3 either the first storage battery or the second storage battery, causes a storage battery not charged with the output from the power generation facility to be discharged into a power system, compares the total amount of the charge and the total amount of the discharge, and determines the timing at which a storage battery changeover is made between the storage battery to be charged and the storage battery to be discharged.
The present invention makes it possible to effectively use the output of renewable energy including its variation, and supply electrical power in accordance with the electrical power demand of users by discharging the storage battery.
BRIEF DESCRIPTION OF THE DRAWINGS:
FIG. 1 is a schematic diagram illustrating a configuration of a power generation system according to a first embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating a comparative example of a power generation system;
FIG. 3 is a schematic diagram illustrating a configuration of a power generation system according to a second embodiment and a third embodiment of the present invention;
FIG. 4 is a graph showing an operating method for use of the power generation system according to the second embodiment in an ideal state;
FIG. 5 is a graph showing an operating method for use

4 of the power generation systemaccording to the second embodiment in a state where wind velocity is low;
FIG. 6 is a graph showing an operating method for use of the power generation system according to the second embodiment in a state where wind velocity is high;
FIG. 7 is a graph showing an operating method for use of the power generation systemaccording to the second embodiment in a state where demand is high;
FIG. 8 is a graph showing an operating method for use of the power generation systemaccording to the second embodiment in a state where no wind blows;
FIG. 9 is a schematic diagram illustrating a configuration of the power generation system according to the third embodiment of the present invention;
FIG. 10 is a schematic diagram illustrating a configuration of a power generation system according to a fourth embodiment of the present invention;
FIG. 11 is a flowchart showing an operating method for use of a power generation system according to a fifth embodiment of the present invention;
FIG. 12 is a schematic diagram illustrating a configuration of a power generation system according to a sixth embodiment of the present invention;
FIG. 13 is a schematic diagram illustrating a configuration of a power generation systemaccording to a seventh embodiment of the present invention;
FIG. 14 is a functional block diagram illustrating a configuration of a power generation systemaccording to an eighth embodiment of the present invention; and

5 FIG. 15 is another functional block diagram illustrating another configuration of the power generation system according to the eighth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
First of all, a comparative example illustrating the basic configuration of a wind power generation system that uses a storage battery to absorb the output variation of renewable energy is shown in FIG. 2.
Referring to FIG. 2, reference numeral 1 denotes a wind turbine generator; reference numeral 2 denotes a converter;
reference numeral 3 denotes a storage battery; reference numeral 4 denotes a step-up transformer; and reference numeral 5 denotes a transmission system.
The output of the wind turbine generator 1 varies with changes in wind velocity . For the power system, it is necessary that electrical power demand and supply be balanced at all times.
If an unpredictable variation occurs, the balance between electrical power demand and supply is impaired to cause, for example, frequency variation. To maintain constant electrical power quality of the power system (tomaintain constant frequency

6 of the power system, in particular) , it is necessary that the variation be properly absorbed. Therefore, the output variation is absorbed by charging the storage battery 3 when the varied output is higher than an average output, and discharging the storage battery 3 when the varied output is lower than the average output, on the contrary. After the output variation is absorbed, the resulting voltage is converted to an appropriate voltage by the step-up transformer 4 and then delivered to the transmission system 5.
Embodiments of the present invention will now be described.
[ First Embodiment]
FIG. 1 shows a first embodiment of the present invention.
Referring to FIG. 1, reference numeral 1 denotes a wind turbine generator, which is an example of a generator based on renewable energy. Reference numeral 6 denotes a controller;
reference numeral 7 denotes a charging power conditioner;
reference numeral 8 denotes a charging storage battery (a storage battery to be charged) ; reference numeral 9 denotes a discharging storage battery (a storage battery to be discharged) ; reference numeral 10 denotes a discharging power conditioner; and reference numeral 11 denotes a power system connected to users.
The capacity of the power conditioner 7 is determined from the annual average expected output capacity of the wind

7 turbine generator 1. The capacity of the power conditioner is determined by the maximum demand of users. The whole output from the wind turbine generator 1 is temporarily charged into the storage battery 8 through the power conditioner 7.
5 Even if variation is caused by the wind turbine generator 1, it does not affect the power system. The storage battery 9 is discharged to supply electrical power to the power system 11 in accordance with demand.
The charging storage battery 8 and the discharging storage 10 battery 9 are switched by the controller 6 at an appropriate time. For example, when switching is made so that charging is performed for 12 hours of a day and that discharging is performed for the remaining 12 hours of the day, the appropriate time is a time at which the amount of electrical power stored by 12-hour charging is equal to the amount of electrical power supplied by 12-hour discharging.
The above-described power generation system according to the first embodiment includes a power generation facility, power conditioners or uninterruptible power supplies (UPS) , and two storage batteries. The power generation facility uses wind power, solar power, or other renewable energy to generate electrical power. The power conditioners or uninterruptible power supplies convert AC power to DC power or convert DC power to AC power. One of the storage batteries is charged with the whole output from the power generation facility, which uses

8 the renewable energy. The other storage battery supplies electrical power to users by discharging electrical power to a power system. The power generation system also includes a controller that switches between a charging storage battery and a discharging storage battery at a timing at which the total amount of electrical power charged into the charging storage battery by using the output from the power generation facility is equal to the total amount of electrical power discharged from the discharging battery to supply electrical power to the power system. An employed renewable energy operating method based on the storage batteries work so that the variation in the output of the renewable energy is entirely absorbed by the storage battery charged with the whole output from the power generation facility based on the renewable energy. Further, the storage battery discharged to supply electrical power to the power system makes is possible to supply electrical power to users in exact accordance with demand.
As described above, the power generation system according to the present embodiment has the wind turbine generator 1, which is a power generation facility using renewable energy;
the power conditioners or uninterruptible power supplies 7, 10, which are converters for performing power conversion between AC power and DC power; the first storage battery 8; and the second storage battery 9. The power generation system also includes the controller that charges the output from the power

9 generation facility into either the first storage battery or the second storage battery, causes a storage battery not charged with the output from the power generation facility to be discharged into the power system, compares the total amount of the charge and the total amount of the discharge, and determines the timing at which a storage battery changeover is made between the storage battery to be charged and the storage battery to be discharged. Being configured as described above, the power generation system makes it possible to fully use of the output of the renewable energy, including its variation, and supply electrical power in accordance with the electrical power demand of users by discharging a storage battery. When the included controller switches between the charging storage battery and the discharging storage battery at a timing at which the total amount of electrical power charge is equal to the total amount of electrical power discharge, abetter operation can be performed.
[Second Embodiment]
FIG. 3 shows a second embodiment of the present invention.
Referring to FIG. 3, reference numeral 6 denotes a wind turbine generator, which is an example of a generator based on renewable energy; reference numeral 7 denotes a charging power conditioner; reference numeral 8 denotes a charging storage battery; reference numeral 9 denotes a discharging storage battery; reference numeral 10 denotes a discharging power conditioner; reference numeral 11 denotes a power system connected to users; and reference numeral 12 denotes a diesel generator.
5 The capacity of the power conditioner 7 is determined from the annual average expected output capacity of the wind turbine generator 6. The capacity of the power conditioner

10 is determined by the maximum demand of users. The whole output from the wind turbine generator 6 is temporarily charged 10 into the storage battery 8 through the power conditioner 7.
Even if variation is caused by the wind turbine generator 6, it does not affect the power system. The storage battery 9 is discharged to supply electrical power to the power system

11 in accordance with demand.
The charging storage battery 8 and the discharging storage -battery 9 are switched at an appropriate time. When switching is made so that, for example, charging is performed for 12 hours of a day and that discharging is performed for the remaining

12 hours of the day, the appropriate time is a time at which the amount of electrical power stored by 12-hour charging is equal to the amount of electrical power supplied by 12-hour discharging.
In the present embodiment, if the amount of electrical power to be supplied is estimated to be insufficient for demand when the charging amount and remaining electrical power amount of the charging storage battery 8 and discharging storage battery 9, the output from the wind turbine generator 6, and the electrical power demand of users are evaluated, the diesel generator is activated as a backup power supply. A sequence of operations for activating the diesel generator is performed through the controller 6. The present embodiment permits a microgrid which is isolated from a bulk power system to utilize the wind turbine generator as a stable power supply.
Referring to FIG. 4, an operating method according to the present embodiment for use in an ideal state will now be described. The horizontal axis represents the time of day.
Indicated from top to bottom are the relative daily electrical power demand of users, the relative output of the wind turbine generator, the SOC of the charging storage battery, the SOC
of the discharging storage battery, and the relative output of the diesel generator. The SOC is an acronym for "State Of Charge" and indicative of the state of charge of a storage battery.
The charge capacity of the storage batteries cannot be fully used. The use of the storage capacities is within the range of 30 to 100% mainly due to its limited life span.
In the present embodiment, it is assumed that the storage batteries are charged for 12 hours and discharged for 12 hours.
It is also assumed that switching is made at time T. Time T
shown in FIG. 4 is a time at which the integral value of demand determined from the demand of users prevailing on the previous day is reduced to half. At time T, the total amount indicated by the integral value of demand-1 is equal to the total amount indicated by the integral value of demand-2 . Storage battery-1 is fully charged with the output from the wind turbine generator beginning with a state where the SOC is 30%, and continuously charged until the SOC is 100%. As the output of wind power varies, the charging process varies in a staircase pattern.
Meanwhile, storage battery-2 is discharged, beginning with a state where the SOC is 100%, to supply electrical power to the power system. The discharge process continues until the SOC
is 30%. At time T, the SOC of storage battery-1 is 100%, whereas the SOC of storage battery-2 is 30%. Storage battery-1 and storage battery-2 switch their roles at time T. In other words , storage battery-1 cycle and storage battery-2 cycle between an SOC of 30% and an SOC of 100% are, respectively, repeated on a daily basis while they are a half-cycle apart. When the above-described operation is performed, the life of the storage batteries can be expected to be maximized.
FIG. 5 shows an operating method according to the present embodiment for use in a state where wind velocity is low. The horizontal axis represents the time of day. Indicated from top to bottom are the relative daily electrical power demand of users, the relative output of the wind turbine generator, the SOC of the charging storage battery, the SOC of the discharging storage battery, and the relative output of the

13 diesel generator.
When the wind velocity is low, a small amount of electrical power is charged into storage battery-1. Therefore, even if storage battery-1 is charged for 12 hours, its SOC does not reach 100%. Storage battery-2 which is to be discharged begins to be discharged in a state where its SOC is lower than 100%.
Therefore, it is difficult for the storage batteries to supply electrical power to the power system by themselves. In such a situation, the diesel generator can be activated as a backup power supply to maintain a proper balance between demand and supply for the power system.
FIG. 6 shows an operating method according to the present embodiment for use in a state where wind velocity is high. The horizontal axis represents the time of day. Indicated from top to bottom are the relative daily electrical power demand of users, the relative output of the wind turbine generator, the SOC of the charging storage battery, the SOC of the discharging storage battery, and the relative output of the diesel generator.
In a situation depicted in FIG. 6, as a wind power output is high, the SOC of storage battery-1 reaches 100% earlier than time T. In this instance, the wind turbine generator is subjected to pitch control to suppress the amount of electrical power generation.
FIG. 7 shows an operating method according to the present

14 embodiment for use in a state where electrical power demand is high. The horizontal axis represents the time of day.
Indicated from top to bottom are the relative daily electrical power demand of users, the relative output of the wind turbine generator, the SOC of the charging storage battery, the SOC
of the discharging storage battery, and the relative output of the diesel generator.
Storage battery-1 switches from charging to discharging at time T. If electrical power demand is high even when a discharge process starts beginning with an SOC of 100%, the SOC reaches 30% in a period of time shorter than 12 hours. In such an instance, the diesel generator is activated as a backup.
FIG. 8 shows an operating method according to the present embodiment for use in a state where no windblows . The horizontal axis represents the time of day. Indicated from top to bottom are the relative daily electrical power demand of users, the relative output of the wind turbine generator, the SOC of the charging storage battery, the SOC of the discharging storage battery, and the relative output of the diesel generator. If any electrical power remains in a storage battery in a situation depicted in FIG. 8, such remaining electrical power can be supplied to the power system. In this situation, however, electrical power generated by the diesel generator is basically supplied to the power system.
As described earlier, the power generation system according to the second embodiment includes a renewable energy operating method based on the batteries according to the first embodiment. Further, if the output of renewable energy is lower than demand in the microgrid isolated from a power system 5 including a diesel generator or other distributed power supply, the renewable energy operating method which uses a storage battery that permits the distributed power supply to operate as a backup can operate and utilize the diesel generator or other distributed power supply as a backup when the output of 10 renewable energy is zero or significantly low depending on weather, season, and time of day. This makes it possible to utilize renewable energy more effectively as a stable power supply for a microgrid isolated from a bulk power system.
According to the second embodiment, using a diesel engine

15 as a backup power supply makes it possible to effectively utilize renewable energy as a stable power supply for a microgrid isolated from a bulk power system.
[Third Embodiment]
A third embodiment of the present invention will now be described with reference to FIGS. 3 and 9. Portions identical with those of the foregoing embodiments will not be redundantly described.
FIG. 3 is a schematic diagram illustrating the power generation system according to the third embodiment. In the

16 power generation system according to the present embodiment, the wind turbine generator 1 is connected to the first storage battery 8 through the charging power conditioner 7. The second storage battery 9, on the other hand, is connected to the transmission system 5 through the discharging power conditioner 10. The power generation system according to the present embodiment includes a connection switching device (not shown in this figure) to switch the connections of the first storage battery 8 and the second storage battery 9. When switching is made by the connection switching device in a state shown in FIG. 3, the first storage battery 8 is connected to the discharging power conditioner 10, and the second storage battery 9 is connected to the charging power conditioner 7. The power generation system according to the present embodiment further includes a controller 6 that controls the wind turbine generator 1, the connection switching device, the power conditioner 7, the power conditioner 10, and the diesel generator 12. The diesel generator 12 is connected to the transmission system 5.
Electrical power generated by the wind turbine generator 1 is converted from AC power to DC power by the charging power conditioner 7 and charged into the storage battery 8. At the same time, the electrical power charged into the storage battery 9 is converted from DC power to AC power by the discharging power conditioner 10, output, and transmitted to the

17 transmission system 5 in accordance with the demand of transmission system 5. When a certain switching condition is established, the controller 6 switches the connection switching device without disconnecting the transmission system 5 from a load. Subsequently, the electrical power generated by the wind turbine generator 1 is charged into the storage battery 9 and transmitted from the storage battery 8 to the transmission system 5 . Details of the switching condition for the connection switching device will be described later. Storage battery switching may be made , for example, at predetermined times each day. An alternative is to predetermine the number of times the storage battery switching is made and let the controller 6 determine time the storage battery switching in accordance with predicted demand or with predicted power generation.
Another alternative is to make the storage battery switching in a non-steady mannerin accordance with the amount of remaining storage battery power.
The rated capacity of the charging power conditioner 7 is determined from the annual average expected output capacity of the wind turbine generator 1.
The rated capacity of the discharging power conditioner 10 is determined by the maximum demand of users. The value of the maximum demand for electrical power may be equal, for instance, to the maximum value of electrical power used per hour by all users connected to the transmission system 5 for

18 a period of the last one year. Alternatively, the value of the maximum demand for electrical power may be determined by adding a predetermined margin of safety factor to the maximum demand. If the demand of the transmission system 5 changes without exceeding the capacity of the discharging power conditioner, the demand of the transmission system 5 can be supplied by the electrical power from the discharging storage battery, that is, the electrical power from a renewable energy power generator. Power conditioners generally achieve high efficiency when operated at a capacity close to its upper limit.
Therefore, when the capacities of the power conditioners are determined as described above, efficient power conversion can be performed.
The capacities of the storage batteries 8, 9 may be determined in accordance with the maximum demand of users of the transmission system 5 or with the annual average expected output capacity of the wind turbine generator 1. If the employed configuration causes the connection switching device to perform switching two times a day, most of the electrical power for the transmission system 5 coordinated can be supplied by the electrical power of the renewable energy power generator when the capacity is set to half the electrical power demand of a representative daybyusing its demand curve for the transmission system 5. Further, if the capacities of employed storage batteries are equal to half the amount of electrical power that

19 is expected to be generated each day by the wind turbine generator 1, the electrical power generated by renewable energy can be utilized without waste. On the contrary, if the employed configuration permits an increase in the amount of electrical power that is supplied to the transmission system 5 from the diesel generator 12 or from a bulk power system (not shown) , it is possible to reduce the capacity of a storage battery that significantly affects the cost. The capacities of the storage batteries depend on a period during which switching control is exercised. An excessively large capacity of a storage battery increases the cost. An unduly small capacity of a storage battery makes it impossible to fully use the electrical power generated by the renewable energy power generator.
The power generation system according to the present embodiment is configured so that the wind turbine generator 1 is connected to the power system through the storage batteries and the connection switching device. Therefore, it is inevitable that the whole output from the wind turbine generator 1 is temporarily charged into the storage battery 8 through the power conditioner 7. Hence, even if the electrical power from the wind turbine generator 1 varies, there is an advantage in that the transmission system 5 remains unaffected by such variation. Further, even if the amount of generated electrical power is too small to be transmitted to the transmission system 5 due to a low output of the renewable energy power generator, the generated electrical power can be supplied to the transmission system 5 by storing the whole amount of generated electrical power in a storage battery.
Furthermore, the storage battery 9 is discharged to supply 5 electrical power to the transmission system 5 through the discharging power conditioner 10 in accordance with demand.
Therefore, there is an advantage in that the electrical power supplied to the transmission system 5 can be higher than the instantaneous electrical power supply capacity of the wind 10 turbine generator 1. If a small-capacity storage battery is merely installed to suppress an output variation as shown in FIG. 2, such control cannot be exercised because excessive discharge impairs an output stabilization capability. However, when the power generation system according to the present 15 embodiment particularly uses a large-capacity storage battery chargeable with electrical power for half a day and an appropriatematching discharging power conditioner, electrical power can be supplied accordingly even if the demand suddenly peaks. This makes it possible to provide a power generation

20 system having high overload resistance.
From another point of view, the power generation system according to the present embodiment is cost-beneficial as it is advantageous in that it permits the use of a wind turbine generator 1 having a capacity smaller than the maximum instantaneous demand of the transmission system 5 as far as

21 the stability of the transmission system 5 is assured. The earlier-mentioned advantage can also be provided when a storage battery is separately installed to supply additional electrical power to the transmission system 5 at a peak time for instance.
In such an instance, however, a complex control process must be performed because the variation in the wind turbine generator needs to be taken into consideration in addition to the variation in the demand. Meanwhile, the power generation system according to the present embodiment is at an advantage in that it achieves the intended purpose simply by controlling the discharging power conditioner as a common uninterruptible power supply.
Even if the transmission system 5 is a large-scale system connected to a bulk power system through a thick transmission line, the power system can be stabilized. However, if the transmission system 5 is a small-scale system for a remote island, underpopulated area, or the like, the power generation system according to the present embodiment provides an increased advantage because the output variation in the wind turbine generator 1 is likely to exercise a significant influence upon the stability of the power system.
Owing to the stable electrical power supply effect of the power generation system according to the present embodiment, the wind turbine generator 1 can handle many, or preferably most, of electrical power supply operations for the transmission

22 system 5. This provides an advantage in that no more various backup power supply sources need to be prepared, connected, maintained, and frequently operated. For example, an independent power system can be configured by connecting only a power generation system having the renewable energy power generator according to the present embodiment and a diesel generator, as power supply sources, to the transmission system 5, or by allowing the aforementioned two power supplies to cover most of its electrical power demand. The power system having the above-described configuration makes it possible to reduce the use of a fuel for the diesel generator as far as control is exercised to reduce the frequency at which the diesel generator 12 is operated.
In the present embodiment, it is assumed that the wind turbine generator 1 is used as a power supply source for the storage batteries. However, the aforementioned advantage of the present embodiment can be similarly obtained if the amount of electrical power derived from employed renewable energy is not readily stabilized. Power supply sources that are based on such renewable energy and difficult to stabilize the power generation amount thereof include, for example, a solar thermal power generator, a solar photovoltaic power generator, various ocean energy power generators, and a hydraulic power generator .
The charging storage battery is a storage battery that is currently used for charging purposes and connected to the

23 charging power conditioner. The discharging storage battery is a storage battery that is currently used for discharging purposes and connected to the discharging power conditioner.
In other words, the charging storage battery 8 and the discharging storage battery 9 are not dedicated to a specific purpose. Hence, they may be referred to as the first storage battery and the second storage battery.
Next, DC voltage potential control exercised when switching is made between the charging storage battery 8 and discharging storage battery 9 according to the first and second embodiments will be described.
An exemplary configuration of the power generation system according to the present embodiment will now be described in detail with reference to FIG. 9. In the present embodiment, the storage battery 8 (formed of storage batteries 81-84 not shown) , the storage battery 9 ( formed of storage batteries 91-94 not shown) , the charging power conditioner 7 , and the discharging power conditioner 10 are connected through the connection switching device 20. The devices to be connected to the connection switching device 20 may be formed of a plurality of devices because of the product capacities of individual devices or in order to provide increased failure resistance on an individual device basis and improve the capability to continue with a system operation. Further, when the power conditioners connected in parallel with each other coordinate

24 to perform a balanced control process, there is an advantage in that the follow-up capability will improve when a momentary load variation occurs in the transmission system 5 . For example , the power generation system shown in FIG . 9 includes two charging power conditioners 72, four sets each of the storage battery 8 and storage battery 9, and four discharging power conditioners 101. Even if one of the four discharging power conditioners 101 becomes faulty, the power generation system according to the present embodiment can operate continuously as far as the demand of the transmission system 5 is within the capacity of the remaining operating power conditioners.
The charging power conditioner 7 is connected to the storage battery 91 through a switch 21a and connected to the storage battery 81 through a switch 22a. At the same time, the discharging power conditioner 10 is connected to the storage battery 91 through a switch 22b and connected to the storage battery 81 through a switch 21b. While the storage battery 81 is being chargedandthe storage battery 91 is being discharged, the switches 22a, 22b are closed and the switches 21a, 21b are open. If the connection switching device 20 performs switching in this state, the switches 21a, 21b, 22a, 22b switch so as to connect the storage battery 81 to the discharging power conditioner 10 and connect the storage battery 91 to the charging power conditioner 7. The parallel-connected storage batteries 82-84, 92-94 also change their connection states when switches 23-28 switch.
In the power generation system shown in FIG. 9, a chopper 71 is installed between the charging power conditioner 7 and the storage batteries, and a chopper 102 is installed between 5 the discharging power conditioner 10 and the storage batteries.
This makes it possible to not only absorb potential changes that occur when the storage batteries 8, 9 are charged or discharged, but also exercise management at all times to optimize the potentials of the storage batteries in terms of battery 10 life. Further, these choppers 71, 102 inhibit the power conditioners, the transmission system 5, and the power generator from being affected by a drastic potential difference between a discharged storage battery and a charged storage battery when the storage batteries are switched.
15 The sets of parallel-connected storage batteries 81-94 may be switched at the same timing from the set 81-84 to the set 91-94. An alternative is to sequentially verify the switching of one storage battery and then switch the next storage battery. If such sequential switching is performed in a 20 situation where the demand of the load connected to the transmission system 5 is such that no problem occurs when the discharging power conditioner related to the storage batteries targeted for switching is disconnected and stopped, the storage batteries 81 and 91 may be stopped during switching. In such

25 an instance, it is preferred that the storage batteries be

26 switched in a time zone in which demand is low.
Exercising control to switch the connection switching device means the execution of a sequence of switching steps and operations for switching the charging storage battery 8 and the discharging storage battery 9. When the connection switching device operates to perform a sequence of switching steps, for example, by first switching the storage battery 81 and the storage battery 91 and then switching the storage battery 82 and the storage battery 92, the switching operations performed until all the storage batteries 81-94 are switched may be included in the switching of the connection switching device.
When, on the contrary, partial switching is performed in a situation where the storage battery 8 and the storage battery 9 are both formed of a plurality of storage batteries, such partial switching may also be included in the switching of the connection switching device.
In the power generation system shown in FIG. 9, a bypass 103 may be formed between the discharging power conditioner 10 and the diesel generator 12. This ensures that switching can be performed without causing a temporary blackout when switching is performed to supply electrical power to the transmission system 5 by activating the diesel generator 12 in a situation where the electrical power supplied from the discharging storage battery 9 is insufficient or when switching is performed to supply electrical power to the transmission

27 system 5 from a storage battery alone after stopping the diesel generator 12 that is operating.
Conditions under which control is exercised to switch the connection switching device or the determination of switching time will now be described. As the demand of the transmission system 5 changes on a 24-hour cycle, it is preferred that the power generation system according to the present embodiment exercise storage battery switching control to allow two storage batteries to be charged once each day and discharged once each day. In the power generation system according to the present embodiment, the amount of charge is largely dependent on the variation in the amount of electrical power generated by the power generator, and the amount of electrical power transmitted from the discharging power conditioner to the transmission system 5 is largely dependent on the variation in the demand of the transmission system 5. Therefore, the switching time is determined in accordance with a predicted demand curve of the transmission system 5 and with a predicted power generation curve of the power generator. More specifically, the switching time is determined between the last switching and the next switching in accordance with the comparison between the amount of electrical power charged into the charging storage battery 8 and the amount of electrical power discharged from the discharging storage battery 9. When the switching time is set so that the amount of electrical power

28 charged into a storage battery each day is close to the amount of electrical power discharged from the storage battery each day in a situation where the storage battery is charged for 12 hours each day and discharged for the remaining 12 hours each day, a large amount of electrical power derived from the renewable energy can be transmitted to the power system. The switching time can be applied without a change irrespective of the actual amount of charge.
[Fourth Embodiment]
A fourth embodiment of the present invention will now be described with reference to FIG. 10. Portions identical with those of the foregoing embodiments will not be redundantly described.
To supply electrical power continuously to the load connected to the transmission system 5 when the connections of the storage battery 8 and storage battery 9 are switched, it is necessary that either the storage battery 8 or the storage battery 9 remain connected to the discharging power conditioner 10. In the power generation system according to the third embodiment, which is shown in FIG. 9, the switch 22b is closed at first in order to connect a charged storage battery 9 to the discharging power conditioner 10 . Subsequently, the switch 21b is opened to disconnect the storage battery 81 from the discharging power conditioner 10. During this storage battery

29 switching process, the switch 22b and the switch 21b are both closed so that the storage battery 8 and the storage battery 9 are connected in parallel to the discharging power conditioner 10. At the time of storage battery switching, the charging storage battery, which has been charged until immediately before, has a high voltage, and on the contrary, the discharging storage battery, which has been discharged until immediately before, has a low voltage. As such being the case, when the storage batteries are connected in parallel to each other in order to switch their roles, an electrical current may flow from the charging storage battery to the discharging storage battery due to the potential difference between the storage batteries.
This problem may result in the loss of electrical power and accelerate the aging of the storage batteries. However, this problem is alleviated by using the power generation according to the fourth embodiment, which is described below.
In order to avoid the flow of the electrical current between the storage batteries, the power generation system according to the present embodiment which is shown in FIG. 10 includes two DC input circuits for the discharging power conditioner 10. Each of these DC input circuits is provided with a chopper.
Referring to FIG. 10, a chopper 105 is installed for the storage battery 9, and a chopper 106 is installed for the storage battery 8. This makes it possible to adjust the voltage of the charging storage battery and the voltage of the discharging storage battery and simultaneously connect these storage batteries to the discharging power conditioner without generating a potential difference between the DC input circuits.
Consequently, the connections of the storage batteries 8, 9 5 to the discharging power conditioner can be switched without stopping the storage batteries 8, 9.
In the power generation system according to the present embodiment, the storage battery switching process is performed in the following sequence. First of all, the storage batteries 10 8, 9 are parallel-connected through the choppers. Subsequently, the electrical power supply source for transmitting electrical power to the transmission system 5 is then switched from a storage battery having served as a discharging storage battery to a storage battery having served as a charging storage battery.
15 The storage battery switching process is completedwhen a storage battery serving as a charging storage battery is disconnected from the discharging power conditioner and connected to the charging power conditioner.
20 [Fifth Embodiment]
A fifth embodiment of the present invention will now be described with reference to FIG. 11. Portions identical with those of the foregoing embodiments will not be redundantly described.
25 FIG. 11 is a flowchart illustrating a process of determining the storage battery switching timing according to the fifth embodiment.
In the present embodiment, the amount of charge and the amount of discharge of both the charging storage battery 8 and the discharging storage battery 9 are input to the controller 6. Further, the output of the wind turbine generator 1 is predicted from previous power generation data about the wind turbine generator 1, which was measured and stored by the controller 6. At the same time, the electrical power demand of users is predicted from previous electrical power supply data, which was measured and stored by the controller 6. The controller 6 compares these two predicted values with the charge and discharge amounts of the two storage batteries, calculates the switching time of the connection switching device 20 in accordance with the comparison, and issues a command so as to switch the connection switching device 20 accordingly. If the evaluation of the two predicted values indicates that the amount of electrical power supply is insufficient to meet demand, the diesel generator is activated as needed as a backup power supply.
A command for controlling the diesel generator in accordance with a calculated activation time and output of the diesel generator may be issued. On the contrary, if the evaluation of the two predicted values indicates that the amount of electrical power supply is greater than demand, a command for controlling the wind turbine generator 1 may be issued so as to properly suppress the amount of electrical power generation in accordance with a calculated difference between the electrical power supply and demand. A sequence of the above operations is performed through the controller 6. The present invention makes it possible to utilize a wind turbine generator as a stable power supply for a microgrid isolated from a bulk power system.
The charge amount and discharge amount to be input to the controller 6 may be calculated in the controller as indicated below. A measured value indicative of the amount of electrical power remaining in the storage batteries 8, 9 is input to the controller 6 on a periodic basis or on a trigger. The difference between the measured value indicative of the amount of electrical power remaining in the storage batteries at the time of last switching and the measured value indicative of the amount of electrical power currently remaining in the storage batteries is then determined. Next, the amount of electrical power charged into the charging storage battery 8 since the last switching and the amount of electrical power discharged from the discharging storage battery are calculated.
The output of the wind turbine generator 1 and the demand to be met by the wind turbine generator 1 need not be predicted each time the controller 6 determines the time at which storage battery switching is performed. In such a situation, for example, the demand and the output of the wind turbine generator may be predicted at the beginning of each day to use the predicted values to calculate a predicted time each day . Further, a value indicative of the output of the wind turbine generator and a value indicative of the demand may be input in advance to the controller 6 and used as the predicted output of the wind turbine generator land the predicted demand. Alternatively, relevant values calculated by an external computing device capable of predictingwith increased accuracymay be input fromthe outside.
If it is estimated that the daily and monthly variations in the demand, which affect the balance between charging and discharging and the operating time of the diesel generator, will be within an allowable range, the switching time predetermined in accordance with the predicted output and predicted demand may be set when the power generation system is initially installed, and continuously used for control purposes without being changed until it is changed for maintenance purposes.
It is assumed that storage battery switching time T is a time at which a predicted charge amount of the charging storage battery is equal to a predicted discharge amount of the discharging storage battery during a period between the last switching and the next switching. When the charge/discharge amount of each storage battery is grasped to vary the timing at which the storage batteries are switched, the electrical power generated by the wind turbine generator can be utilized more effectively by suppressing the variation in the output of the wind turbine generator and reducing the operating time of the diesel generator. Further, as the storage battery switching timing is varied, the storage batteries can cope with changes in the charge/discharge characteristics due to aging.
As the charging storage battery and the discharging storage battery do not differ in the charge/discharge amount, the degree of storage battery aging can be uniformed to suppress the aging of the storage batteries on the whole Here, the predicted charge amount of the charging storage battery is calculated from the integral value of a predicted output curve of the wind turbine generator, and the predicted discharge amount of the discharging storage battery is calculated from the integral value of a demand curve.
FIG. 11 is a flowchart illustrating an operating method according to the present embodiment, which is described below.
Here, it is assumed that the initial SOC of the charging storage battery is 30% and that the initial SOC of the discharging storage battery is 100%. It should be noted, however, that the operation can be performed in the same sequence in an initial state where the charge amount required for the SOC of the charging battery to reach 100% is substantially equal to or close to the discharge amount required for the SOC of the discharging battery to reach

30%. The SOC is an acronym for "State Of Charge" and indicative of the state of charge of a storage battery. The charge capacity of the storage batteries cannot be fully used. The use of the storage capacities is within the range of 30 to 100% mainly due to its limited life span. Depending on the characteristics of employed storage batteries, however, a different numerical 5 value range may be used for control purposes.
Judgments described in the flowchart of FIG. 11 may be formulated periodically at predetermined time intervals by the controller 6 for accuracy enhancement or may be formulated on a trigger, that is, for example, may be formulated only at the 10 beginning of each day to reduce the load imposed on the controller 6 or may be formulated when the SOC of the discharging storage battery is 50%.
First of all, the controller 6 predicts a time To at which the SOC of the charging storage battery 8 is 100% from a measured 15 value indicative of the amount of electrical power charged into the charging storage battery 8 and from a predicted output of the wind turbine generator 1 in step 1000. At the same time, the controller 6 predicts a time Td at which the SOC of the discharging storage battery 9 is 30% from a measured value 20 indicative of the amount of electrical power remaining in the discharging storage battery 9 and from a predicted demand. The operating method according to the present embodiment will now be described under ideal conditions where the predicted time Tc is substantially the same as the predicted time Td. If the 25 last judgment formulated by the controller 6 before switching indicates that the time Tc at which the SOC of the charging storage battery 8 is 100% is substantially equal to or close to the time Td at which the SOC of the discharging storage battery is 30% (step 1001) , the increase/decrease in the SOC of each storage battery is 70% at time Tc = time Td. Thus, the controller 6 issues a command for causing the connection switching device 20 to perform switching so that the charging storage battery and the discharging storage battery switch their roles (step 1002) . Under the above conditions, switching may be performed at time Tc.
The operating method according to the present embodiment for use in a state where the output of the wind turbine generator is lower than demand will now be described. In this instance, time Tc predicted by the controller 6 at which the SOC of the charging storage battery reaches 100% is later, that is, greater, than time Td predicted by the controller 6 at which the SOC
of the discharging storage battery reaches 30%. In other words, it is predicted that time Tc > time Td (step 1101) . In this instance, if the storage batteries are switched at time Td at which the SOC of the discharging storage battery is 30%, the SOC of the charging storage battery does not reach 100%. As a result, the storage batteries differ in the amount of increase/decrease in the SOC.
As such being the case, if the judgment formulated by the controller 6 predicts that Tc > Td, the controller 6 performs a new judgment process concerning the charge/discharge amount as described below. The controller 6 determines a predicted charge amount of the charging storage battery 8 and a predicted discharge amount of the discharging storage battery 9 for a period between the last switching time and time T, and checks for a time at which the charge amount and discharge amount are substantially equal to or close to each other within a period between the switching time or the current check time and predicted time Td. If it is predicted that the storagebatteries agree with each other in the amount of increase/decrease in the SOC at time T which is earlier than time Td (step 1111), the controller 6 exercises control to switch the storage batteries at time T (step 1112). If it is predicted that the charge amount and the discharge amount are substantially equal to or close to each other at two or more times, the latest time T before time Td is determined as the switching time in order to reduce the number of switchings. If the storage batteries agree with each other in the amount of increase/decrease in the SOC at time T which is earlier than time Td, the storage batteries can be switched at time T to continuously transmit electrical power from the next time on within a range equivalent to the amount of electrical power generated by the wind turbine generator 1 and charged during a period between the last switching and time T. This ensures that electrical power can be continuously transmitted without affecting the balance between the amounts of electrical power remaining in the charging storage battery and in the discharging storage battery even if the amount of electrical power generated by the wind turbine generator during the relevant switching period is insufficient to meet demand. This makes it possible to refrain from activating the diesel generator unnecessarily during the relevant switching period.
At the beginning of a period subsequent to the relevant switching period, the charging storage battery and the discharging storage battery start a charge/discharge process while there is a small margin for charging/discharging. In other words, the imbalance between a power generation amount and demand is left uncorrected. It should be noted that the demand and the amount of electrical power generated by the renewable energy power generator greatly vary. Therefore, if control is exercised to leave the imbalance uncorrected, an inverse imbalance arises to delay the possibility of achieving a balance.
A concrete example is cited below for explanation purposes.
If it is predicted that the SOC of the charging storage battery is 90% at time Td and that the SOC of the discharging storage battery is 30% at time Td, and if it is predicted that the SOC
of the charging storage battery is 80% at time T (< Td) and that the SOC of the discharging storage battery is 50% at time T (< Td), the charging storage battery and the discharging storage battery switch their roles at time T at which they agree with each other in the amount of increase/decrease in the SOC.
Next, a case (step 1121) where it is predicted that the SOC of the charging storage battery is still below 100% at predicted time Td at which the SOC of the discharging storage battery is 30%, and that the storage batteries do not agree with each other in the amount of increase/decrease in the SOC
before time Td will be described. The storage batteries are switched at an optimum time (step 1122) so that the output of the wind turbine generator is utilized more effectively in accordance with the predicted output of the wind turbine generator, with the predicted demand, and with the SOC of each storage battery. However, even if it is predicted that Tc <
Td, control is exercised to reduce the amount of electrical power transmission or stop a power transmission operation as far as control is exercised to transmit electrical power from the transmission system 5 to the bulk power system or reduce the electrical power output of the wind turbine generator 1.
A concrete example is cited below for explanation purposes.
If it is not predicted that the SOC of the charging storage battery is 60% at time Td and that the SOC of the discharging storage battery is 30% at time Td, and if it is not predicted that the storage batteries substantially agree with each other in the amount of increase/decrease in the SOC at any earlier time, it is conceivable that the electrical power supplied from . , the diesel generator 12 may be received to reset the charge and discharge states of the storage batteries to an SOC of 100%
and an SOC of 30%, respectively. In such an instance, time Tc at which the SOC of the charging storage battery 8 is 100%
5 is set as the switching time, and the diesel generator 12 is activated to supply electrical power to the transmission system 5 to prevent the SOC of the discharging storage battery 9 from decreasing below 30%. While the diesel generator is supplying electrical power, the controller 6 predicts time Td in accordance 10 with the amount of electrical power discharged from the discharging storage battery 9, with the demand of the transmission system 5, and with the amount of electrical power generated from the diesel generator 12 when formulating the judgments indicated in the flowchart of FIG. 11. Further, if 15 it is judged that predicted time Tc < Td even after the output of the diesel generator 12 is added, control is exercised to increase the amount of electrical power generated by the diesel generator 12. After the storage batteries are switched at time Tc, control is exercised to stop the diesel generator.
20 The operating method according to the present embodiment for use in a state where the output of the wind turbine generator is higher than demand will now be described. In this state, it is predicted that time Tc < time Td (step 1201) , and that the SOC of the discharging storage battery does not reach 30%
25 at predicted time To at which the SOC of the charging storage battery is 100%, and further that the storage batteries differ in the amount of increase/decrease in the SOC. In this instance, if there is time T at which the storage batteries substantially agree with each other in the amount of increase/decrease in the SOC before time Tc (step 1211) , the storage batteries are switched at time T (step 1212) . This makes it possible to suppress any unnecessary output of the wind turbine generator.
Details and operations of a control configuration are the same as when the output of the wind turbine generator is lower than demand.
A concrete example is cited below for explanation purposes.
If it is predicted that the SOC of the charging storage battery is 100% at time Tc and that the SOC of the discharging storage battery is 40% at time Tc, and if it is predicted that the SOC
of the charging storage battery is 80% at time T (< Tc) and that the SOC of the discharging storage battery is 50% at time T (< Tc) , the charging storage battery and the discharging storage battery switch their roles at time T at which they agree with each other in the amount of increase/decrease in the SOC, which is 50%.
Next, a case (step 1221) where it is predicted that the SOC of the discharging storage battery is still below 30% at predicted time Tc at which the SOC of the charging storage battery is 100%, and that the storage batteries do not agree with each other in the amount of increase/decrease in the SOC before time Tc will be described. The storage batteries are switched at an optimum time (step 1222) so that the output of the wind turbine generator is utilized more effectively in accordance with the predicted output of the wind turbine generator, with the predicted demand, and with the SOC of each storage battery.
However, even if it is predicted that Tc < Td, control is exercised to reduce or stop the electrical power output from the diesel generator 12 as far as electrical power is supplied to the transmission system 5 from the diesel generator 12 or from the bulk power system.
A concrete example is cited below for explanation purposes.
If it is predicted that the SOC of the charging storage battery is 100% at time Tc and that the SOC of the discharging storage battery is 70% at time Tc, and if it is predicted that the storage batteries do not substantially agree with each other or are not close to each other in the amount of increase/decrease in the SOC at any earlier time, it is conceivable that control is exercised in one of two different manners depending on the conditions. If the transmission system 5 is in an underpopulated area with the power system placed in a vulnerable area, excess electrical power has no place to go. Therefore, the controller 6 issues a command to the wind turbine generator 1 so as to reduce the amount of electrical power generated by the wind turbine generator 1. The transmission system 5 is connected to the bulk power system so as to permit the selling =

of electrical power or receive electrical power supplied from a remote area, control is exercised so that electrical power generated by the wind turbine generator 1 except for the electrical power consumed by the transmission system 5 is transmittedto the bulkpower system. Therefore, if it is judged that predicted time Tc > Td, time Tc is set as storage battery switching time T. Control is then exercised to transmit electrical power to the bulk power system after the storage batteries are switched at time Tc. This makes it possible to utilize the electrical power generated by the power generation facility while reducing the waste. While electrical power is being transmitted to the bulk power system, the controller 6 predicts time Td in accordance with the amount of electrical power discharged from the discharging storage battery 9, with the demand of the transmission system 5, and with the amount of electrical power transmitted to the bulk power system when formulating the judgments indicated in the flowchart of FIG.
11. If it is still judged that predicted time Tc > Td even when control is exercised to transmit electrical power, control is exercised to increase the amount of electrical power transmission or further decrease the amount of electrical power generated by the wind turbine generator 1.
A state where the charge amount and the discharge amount are substantially equal or close to each other or the difference between them is not greater than a predeterminedvalue represents a state where they are perfectly equal to each other or within a certain range. The range is allowable by the system even if the charge amount of the charging storage battery 8 is not in balance with the discharge amount of the discharging storage battery 9. The range can be defined so that a predetermined value must not be exceeded. The most desirable state is a state where the charge amount and the discharge amount are perfectly equal to each other. However, even when control is exercised in such a manner that the charge amount and the discharge amount are close to each other, it contributes toward achieving a balance between charging and discharging. Further, it works to suppress the aging of the storage batteries and shorten the period of diesel generator activation. More specifically, it is preferred that the difference between the charge amount and the discharge amount be an SOC of not more than 20%. It is more preferable that the difference be an SOC of not more than 5%.
The present embodiment has been described with reference to the comparison between the amount of electrical power charged into the charging storage battery 8 and the amount of electrical power discharged from the discharging storage battery 9. It should be noted, however, that the comparison is made on an absolute value basis.
The control flowchart described in conjunction with the present embodiment is such that a status reset can be performed to maintain the periodicity of control by constantly switching the storage batteries each day at a predetermined time without regard to the prevailing charge/discharge state.
5 [Sixth Embodiment]
A sixth embodiment of the present invention will now be described with reference to FIG. 12. Portions identical with those of the foregoing embodiments will not be redundantly described.
10 Means for solving the earlier-mentioned problem relates to a data center having a storage battery as an emergency backup power supply for power failure. The storage battery included in the data center to serve as a backup power supply is divided into two or more storage batteries. These storage batteries 15 are configured as the storage batteries according to the first to fifth embodiments, or more specifically, as the storage battery that is to be fully charged with the output from the power generation facility, which uses renewable energy in accordance with the first to fifth embodiments, and as the 20 storage battery that is to be discharged to supply electrical power to the power system for users of electrical power. This makes it possible not only to effectively utilize the storage battery in the data center, which is merely used as a backup power supply under normal conditions, but also to steadily 25 utilize the renewable energy while suppressing the cost of storage batteries.
FIG. 12 is a schematic diagram illustrating the sixth embodiment. Referring to FIG. 12, the renewable energy power generator 1 (wind turbine generator) is connected to the charging storage battery 8 through the charging power conditioner 7.
The discharging storage battery 9 is connected to a power system 13, which is coupled to the data center, through the discharging power conditioner 10. The controller 6 controls the renewable energy power generator 1, the power conditioners, the storage batteries, and the power system 13. The power system 13 is connected to a data center 14 and to an external system 16 that supplies electrical power to the data center. The charging storage battery 8 and the discharging storage battery 9 are handled as a set and adapted to function as a storage battery 15 that serves as a backup power supply for the data center.
The power system 13 is a system for the whole facility including the data center. If the facility is the data center itself, the power system 13 is a system in the data center 14. Further, the power system 13 may be a system for an area where electrical power is mainly consumed by the data center facility. The renewable energy power generator 1, the power conditioners, and the storage batteries can be collectively handled as a backup power supply fromwhich electrical power is obtained under normal conditions and under emergency conditions.
In the present embodiment, the storage battery 15 provided as a backup power supply is divided into two storage batteries, namely, the charging storage battery 8 and the discharging storage battery 9. The capacity of the power conditioner 7 is determined from the annual average expected output capacity of the wind turbine generator 1. The capacity of the power conditioner 10 is determined by the maximum demand of users.
The whole output from the wind turbine generator 1 is temporarily charged into the storage battery 8 through the power conditioner 7. Even if variation is caused by the wind turbine generator 1, it does not affect the power system. The storage battery 9 is discharged to supply electrical power to the power system 13 coordinated with the data center in accordance with the demand thereof. The controller 6 switches the charging storage battery 8 and the discharging storage battery 9 at an appropriate time.
The power generation system according to the present embodiment operates so that the renewable energy power generator, which is unstable due to its significant output variation, can be steadily utilized as an emergency/non-emergency power supply for the data center.
Further, when the employed configuration is such that most of the electrical power consumed by the data center is supplied from the power generation system according to the present embodiment, the features of the power generation system, which causes the storage batteries to be fully charged with electrical power generated by the wind turbine generator 1 and switches the storage batteries at an appropriate time, can be utilized to produce a significant effect particularly under load conditions under which the electrical power consumption of users is readily predictable . To permit the power generation system according to the present embodiment to make the utmost use of electrical power generated by the renewable energy power generator 1 which is often subject to variation without allowing the intervention of the other power supplies, it is necessary to achieve a balance between a storage battery engaged in charging and a storage battery engaged in discharging. When readily predictable load conditions are considered in combination with the above-mentioned balance, it is possible to improve the efficiency of the supply of electrical power derived from renewable energy. Furthermore, as servers and air-conditioners at the data center basically consume electrical power for 24 hours a day, the diurnal load variation of the data center is smaller than that of the other small-scale systems. Therefore, the output conditions of the discharging storage battery can be uniformed to suppress the aging thereof.
Moreover, the data center intrinsically needs a backup storage battery system. Therefore, when the backup storage battery system is established by using renewable energy, the power generation system according to the present embodiment permits the backup storage battery system to be readily implemented as a highly available system.
The term "readily predictable load" does not necessarily indicate that a short-term transient load variation of the power system is readily predictable. As far as the total amount of electrical power use during an interval between storage battery switchings is readily predictable, the power generation system according to the present embodiment is at an advantage in that it can exercise accurate control to achieve a balance between a storage battery engaged in charging and a storage battery engaged in discharging and efficiently use the electrical power generated from renewable energy. For example, the amount of electrical power consumption may minutely vary at frequent intervals depending on the volume of processing performed by the servers at the data center. However, it is unlikely that the amount of electrical power use at the data center abruptly will increase on one day and decrease on the following day.
In the power generation system according to the present embodiment, it is preferred that two storage batteries be switched and used for charging for 12 hours each day and for discharging for the remaining 12 hours. The reason is that the amount of electrical power use in any power system, including that of the data center, often varies on a cycle of 24 hours.
Particularly, the processing load on the data center, which provides data services, varies with the time of activity of local residents. Such processing load varies, for example, on a cycle of 24 hours. When a demand variation cycle is divided into two to set the switching time in such a manner that the charge amount is equal to the discharge amount, the intended purpose is achieved by exercising control in the same manner 5 for the next cycle. Hence, control can be exercised with ease.
The resulting ease of prediction will increase the accuracy of storage battery control and enhance the efficiency of the power generation system.
Further, the time for storage battery switching should 10 preferably be set so that the amount of electrical power stored by a 12-hour charging operation is equal to the amount of electrical power supplied by a 12-hour discharging operation.
If the cycle is changed due, for instance, to the introduction of daylight-saving time, it is preferred that the switching 15 time setting be corrected as appropriate.
However, the cycle of load variation may not always be 24 hours. If, for example, the data center provides data services to two or more areas differing in local time, multiple peaks of processing load appear. Under such conditions, it 20 might be better to change the storage battery switching cycle as appropriate to a cycle other than two times each day. In other words, it is preferred that control be exercised in accordance with conditions imposed by a user of the present embodiment to switch two sets of storage batteries so as to 25 divide a load variation cycle into a charging operation and a discharging operation. Moreover, if the number of sets of storage batteries is to be increased, it is preferred that the resulting number of sets be a multiple of 2.
Under normal conditions, the storage battery 15 provided as a backup power supply is used for the stabilization of renewable energy as mentioned earlier. Meanwhile, if a power failure occurs in the main power system 16, the storage battery functions as a normal backup power supply to supply electrical power to the data center. For the supply of electrical power, 10 the power conditioner 10 for the discharging storage battery may be used. If the SOC of the discharging storage battery is 30% while the storage battery 15 is functioning as a backup power supply, priority is given to the supply of electrical power to the data center and the storage batteries are switched 15 immediately. If the power generation system is configured so that the amount of electrical power used by the data center is larger than the amount of electrical power generated from renewable energy, the SOC reached by a storage battery engaged in charging before switching gradually decreases so that the electrical power cannot be supplied sooner or later. However, while the supply of electrical power from the power system is restricted, electrical power larger in amount than the electrical power initially charged into a backup storage battery can be steadily supplied in a continuous manner to the data center for a long period of time due to the renewable energy.

The present embodiment has been described on the assumption that the power generation system according to the present embodiment is applied to a data center. However, the same advantage as described above is obtained as far as the load is readily predictable. For example, even in an isolated area or other area with a vulnerable power system, a system for steadily supplying electrical power to a distribution center, a factory, a vegetable plant, or the like can be established with the necessity for continuous transport of power generation fuel and the like eliminated or suppressed as far as a renewable energy power generator, the power generation system according to the present embodiment, and an auxiliary diesel generator are installed.
It should be noted that when the backup power supply according to the present embodiment is to be installed at a data center, the rated capacities of the renewable energy power generator 1, the power conditioners, and the storage batteries must be properly determined. For example, let us assume that the intended purpose is to operate the data center continuously for at least 24 hours as an emergency power supply while the supply of electrical power from the bulk power system is interrupted. The procedure to be generally performed under normal conditions is to predict the amount of 24-hour electrical power use by the data center from previously measured data, determine the storage battery capacity that is more than adequate for the predicted value with a safety margin taken into consideration, and prepare storage batteries having the determined capacity. If the backup power supply according to the present embodiment is used in the above situation, the total rated capacity of the two storage batteries can be rendered smaller than that of storage batteries generally used as a backup power supply by reducing particularly the amount of margin.
[ Seventh Embodiment A seventh embodiment of the present invention will now be described with reference to FIG. 13. Portions identical with those of the foregoing embodiments will not be redundantly described.
In the seventh embodiment, a solar photovoltaic power generator 50 is used as the renewable energy power generator 1 according to the foregoing embodiments. In the present embodiment, too, two sets of storage batteries 8, 9 are employed and switched two times each day. The sixth embodiment has been described with reference to the load variation cycle of a demand curve. In the present embodiment, however, the storage battery switching time is determined in accordance with the periodicity of a predicted curve indicative of a power generation amount.
Unlike the variation in the power generation amount of wind turbine generators that is not readily predicted, the power generation amount of solar photovoltaic power generators peaks while the sun is up during daytime and varies on a cycle of approximately 24 hours. One cycle of a predicted curve indicative of a power generation amount is divided into two to switch the storage batteries in such a manner that the charge amount is equal to the discharge amount.
Even if the periodicity of the predicted power generation amount curve is different from the periodicity of a demand curve, the computational load on control scheme determination can be reduced to increase the accuracy and efficiency of storage battery control as far as the switching time is determined in accordance with information about a combined cycle derived from two different cycles.
Further, as regards sunlight, the weather of the next day is more or less predictable. Therefore, if the power generation amount is insufficient to meet demand due to a cloudy weather during the latter half of today in a situation where the power generator according to the present embodiment is operated by switching the two storage batteries so as to charge or discharge them once each day for instance, it is possible to predict to a certain extent whether the insufficiency can be compensated for by the next charging. This makes it possible to use a weather forecast to determine whether or not to activate the diesel generator during the latter half of today, and decide not to activate the diesel generator during an interval between storage battery switchings during the latter half of today.

Consequently, the amount of fuel consumed by the diesel generator can be reduced.
The present embodiment adopts a solar photovoltaic power generator to determine the storage battery switching time in 5 accordance with the cycle of the predicted curve indicative of a power generation amount. However, the present embodiment is also applicable to a case where the periodicity can be recognized to determine a time zone in which, for example, wind power is readily obtained no matter whether a wind turbine 10 generator or the like is adopted.
It is conceivable that the amount of electrical power generated by the solar photovoltaic power generator 50 may continuously decrease due to the failure of a panel or a module.
Even if a module is partly faulty, electrical power can be 15 continuously transmitted as the influence upon the amount of power generation is limited. It is therefore conceivable that the power generation system according to the present embodiment may be continuously operated without correcting a fault due to cost considerations especially if the power generation system 20 is installed on a remote island or in an isolated area. In such an instance, the power generation system needs to detect such a fault, determine the possible decrease in the amount of electrical power generation, and reflect the determined decrease in a control process for achieving a balance between 25 the charge amount and the discharge amount.

In the present embodiment in which the solar photovoltaic power generator 50 is used as the renewable energy power generator 1, the power generation system includes a fault diagnostic device 51 for the renewable energy power generator.
If the fault diagnostic device 51 detects a fault in one or more modules for instance, the information about the detected fault is transmitted to the controller 6. The controller 6 then determines the number of faulty modules and predicts the resulting decrease in the amount of electrical power generation.
If the fault diagnostic device 51 is capable of determining the number of defective modules or predicting the resulting decrease in the amount of electrical power generation, the fault diagnostic device 51 may accomplish such a task. The result of calculations performed to predict the decrease in the amount of electrical power generation that will be caused by faulty modules is used to correct data about the predicted amount of electrical power generation that is handled by the controller 6. The corrected data is then reflected in the determination of the switching time for switching the connection switching device 20. This ensures that the balance between charging and discharging is maintained even when the renewable energy power generator 1 deviates from a normal, ideal operating state. This makes it possible to increase the availability of renewable energy and suppress the aging of storage batteries.
Even if a wind turbine generator is used as the renewable energy power generator 1 and some of a number of wind turbines fail to generate electrical power, the decrease in the amount of electrical power generation can be similarly predicted from a fault state to exercise control with the predicted decrease reflected in the earlier-mentioned switching control as far as the other wind turbines are able to continuously generate electrical power.
[Eighth Embodiment]
An eighth embodiment of the present invention will now be described with reference to FIGS. 14 and 15. Portions identical with those of the foregoing embodiments will not be redundantly described.
FIG. 14 is a functional block diagram illustrating the controller used in the eighth embodiment.
As is the case with the foregoing embodiments, the controller 6 shown in FIG . 14 is connected to the power generation system, which includes a power generation facility, a first converter, a first storage battery, a second storage battery, a second converter, and a connection switching device. The power generation facility uses renewable energy. The first converter operates so that the electrical power to be supplied from the power generation facility is converted from AC power to DC power. The first storage battery is charged with the electrical power converted by the first converter. The second converter operates so that the electrical power to be supplied from the second storage battery is converted from DC power to AC power and supplied to the power system. The connection switching device switches the first storage battery and the second storage battery.
Referring to FIG. 14, the controller 6 includes a switching time computation section, a memory section, a switching time judgment section, and a power generator command section. The switching time computation section computes the switching time in accordance with the comparison between the amount of electrical power charged into the charging storage battery 8 during an interval between a connection switching device switching control process and the next connection switching device switching control process and the amount of electrical power discharged from the discharging storage battery during the same interval. The memory section stores the switching time. The switching time judgment section transmits a switching command to the connection switching device in accordance with the switching time computed by the switching time computation section.
FIG. 15 is another functional block diagram illustrating the controller 6. Referring to FIG. 15, the controller 6 includes a memory section, a predicted curve computation section, an electrical power amount estimation section, a switching time determination section, a switching time judgment section, and a power generator command section.
The memory section stores time-series data, which includes, for example, a measured value indicative of the electrical power supplied from the discharging storage battery to the power system, a measured value indicative of the electrical power supplied from the power generation facility to the charging storage battery, a measured value indicative of the amount of electrical power stored in the charging storage battery and in the discharging storage battery, and weather information.
The predicted curve computation section calculates a predicted power generation amount curve and a predicted demand curve in accordance with the measured value indicative of the electrical power supplied from the discharging storage battery to the transmission system 5 and with the measured value indicative of the electrical power supplied from the renewable energy power generation facility to the charging storage battery.
In accordance with the predicted power generation amount curve and predicted demand curve calculated by the predicted curve computation section and with the measured value indicative of the amount of electrical power stored in the charging storage battery and in the discharging storage battery, the electrical power amount estimation section predicts the amount of electrical power to be charged into the charging storage battery during an interval between the last control process for switching the connection switching device and a predetermined time and the amount of electrical power to be discharged from the discharging storage battery during the same interval.
5 The switching time determination section estimates the time at which the predicted amount of electrical power to be charged is close to the predicted amount of electrical power to be discharged, and determines the time at which control is exercised to switch the connection switching device.
10 The switching time judgment section transmits a switching command to the connection switching device in accordance with the switching time computed by the switching time computation section.
In accordance with the determined switching time and with 15 the measured values, the power generator command section issues a command to the diesel generator, to the renewable energy power generator, and to the bulk power system in order to specify the amount of electrical power supply.
The functional block diagrams illustrating the controller 20 6 according to the present embodiment may be applied to the configuration of hardware separate from the controller 6. For example, the predicted curve computation section and the switching time computation section may be implemented externally to the controller 6.

Claims

WHAT IS CLAIMED IS:

1. A power generation system comprising:
a power generation facility that uses a renewable energy;
a first storage battery that is to be charged with electrical power supplied from the power generation facility;
a second storage battery that supplies electrical power to a power system;
a connection switching device that switches the first storage battery and the second storage battery; and a controller that controls the connection switching device, wherein the controller controls switching the connection switching device at a switching timing that is determined in accordance with a predicted amount of an electrical power generation by the power generation facility and with a predicted demand of the power system.

2. The power generation system according to claim 1, wherein the controller determines a switching timing at which the connection switching device is to be switched in accordance with a comparison between a predicted amount of charge into the storage battery to be charged and a predicted amount of discharge from the storage battery to be discharged.

3 . The power generation system according to claim 1 or 2, wherein the controller controls switching the connection switching device two times each day.

4 . The power generation system according to any one of claims 1 to 3, wherein the controller controls switching the connection switching device at a timing of a second switching control process that is determined in accordance with a predicted amount of electrical power to be charged into either of the storage batteries during an interval between a first switching control process and the second switching control process, and with a predicted amount of electrical power to be discharged from either of the storage batteries during an interval between the second switching control process and a third switching control process .

. The power generation system according to any one of claims 1 to 3, wherein the controller determines the timing of a second switching control process in accordance with a predicted amount of electrical power to be charged into the storage battery to be charged during an interval between a first switching control process and the second switching control process, and with a predicted amount of electrical power to be discharged from the storage battery to be discharged during the interval between the first switching control process and the second switching control process, and controls switching the connection switching device.

6. The power generation system according to any one of claims 1 to 5, wherein the controller controls a diesel generator connected to the power system.

7. The power generation system according to any one of claims 1 to 6, wherein the controller controls switching the connection switching device at a predicted timing at which a difference between an amount of electrical power charged into the storage battery to be charged and an amount of electrical power discharged from the storage battery to be discharged is not greater than a predetermined value.

8. The power generation system according to any one of claims 1 to 7, further comprising:
a first converter that converts electrical power supplied from the power generation facility from AC power to DC power and supplies the converted electrical power to the first storage battery;

a second converter that converts electrical power supplied from the second storage battery from DC power to AC
power and supplies the converted electrical power to the power system; and a chopper that is installed between the first converter and the first storage battery, or between the second converter and the second storage battery.

9. The power generation system according to claim 8, wherein the second converter includes two or more input circuits to be connected to the storage battery to be discharged, and wherein the input circuits include choppers respectively.

10. A backup power supply comprising:
a power generation facility that uses renewable energy;
a first storage battery;
a second storage battery;
a connection switching device that switches the first storage battery and the second storage battery; and a controller, wherein electrical power supplied from the power generation facility is charged into one of the storage batteries , wherein the remaining storage battery not charged with the electrical power supplied from the power generation facility supplies electrical power to a load, and wherein the controller controls switching the connection switching device at a switching timing that is determined in accordance with a predicted amount of electrical power to be supplied to the load.

11. A method for installing a data center, the method comprising the step of:
installing the backup power supply according to claim at the data center.

12. A power generation system controller comprising:
a switching time computation section that inputs a measured value indicative of an amount of electrical power in a storage battery to be charged with electrical power supplied from a power generation facility based on a renewable energy and a measured value indicative of an amount of electrical power in a storage battery to be discharged to a power system, compares an amount of electrical power charged into a storage battery to be charged during an interval between an instant at which controls switching the two storage batteries so as to interchange connections to the power system and to the power generation facility and an instant at which controls performing the next switching with an amount of electrical power discharged from the storage battery to be discharged during the same interval, and computes a switching timing in accordance with the comparison;
a memory section that stores the switching timing; and a switching time judgment section that transmits a command for switching the two storage batteries in accordance with the switching timing.

13. A controller for the power generation system according to claims 1 to 9, the controller comprising:
a memory section;
a predicted curve computation section that calculates a predicted power generation amount curve and a predicted demand curve in accordance with a measured value indicative of electrical power supplied from the storage battery to be discharged to the power system and with a measured value indicative of electrical power supplied from the power generation facility to the storage battery to be charged;
an electrical power amount estimation section that predicts an amount of electrical power to be charged into the storage battery to be charged during an interval between the last control process for switching the connection switching device and a predetermined time, and an amount of electrical power to be discharged from the storage battery to be discharged during the same interval, in accordance with the predicted power generation amount curve and predicted demand curve calculated by the predicted curve computation section, and with the measured values indicative of electrical power in the storage battery to be charged and electrical power in the storage battery to be discharged; and a switching time determination section that estimates a time at which the amount of electrical power to be charged is close to the amount of electrical power to be discharged, and determines a time at which controls switching the connection switching device.

14. The power generation system according to any one of claims 1 to 9, comprising:
a first converter that converts electrical power supplied from the power generation facility from AC power to DC power;
a first storage battery that is charged with the electrical power converted by the first converter;
a second storage battery;
a second converter that converts electrical power supplied from the second storage battery from DC power to AC
power and supplies the converted electrical power to a power system;
a connection switching device that switches the first storage battery and the second storage battery; and a controller that controls the power generation system, wherein the controller is input measured values indicative of electrical power in the first storage battery and in the second storage battery, a predicted demand curve of the power system, and a predicted power generation amount curve of the power generation facility, allows either the first storage battery or the second storage battery to be charged with electrical power charged into the storage battery to be charged and with the output from the power generation facility after the last control process for switching the connection switching device, allows the storage battery not charged with the output from the power generation facility to be discharged into the power system, compares a total amount of the charge with a total amount of the discharge, and determines a switching timing for switching the storage battery to be charged and the storage battery to be discharged in accordance with the comparison.

15. The power generation system according to claim 8 or 14, wherein a rated capacity of the second converter is smaller than a rated capacity of the power generation facility.

16. The power generation system according to any one of claims 1 to 9, wherein a capacity of the first storage battery or of the second storage battery is not smaller than half a daily electrical power demand calculated in accordance with the demand curve of the power system.

17 . A power system whose demand is entirely supplied by the power generation system according to any one of claims 1 to 9 and by a diesel generator.

18 . A method for operating a power generation system that includes a power generation facility based on a renewable energy and at least two storage batteries, the method comprising the steps of :
dividing a period of one day into two periods of time;
allowing one of the batteries to be charged with the whole electrical power generated by the power generation facility based on renewable energy during one of the two periods of time;
and supplying the electrical power of the charged battery to a power system during the other of the two periods of time .