WO2011118771A1

WO2011118771A1 - Charge/discharge system

Info

Publication number: WO2011118771A1
Application number: PCT/JP2011/057359
Authority: WO
Inventors: 健仁井家; 総一酒井
Original assignee: 三洋電機株式会社
Priority date: 2010-03-26
Filing date: 2011-03-25
Publication date: 2011-09-29

Abstract

Disclosed is a charge/discharge system provided with the following: a storage battery for storing power generated by a power generator, a discharge power conversion unit — for converting power — that discharges stored power, a power output unit for outputting power, supplied by the discharge power conversion unit, to the power system, and a control unit for controlling power that is output from the discharge power conversion unit to the power output unit in a manner such that the power changes according to voltage and the output characteristics have a power peak.

Description

Charge / discharge system

The present invention relates to a charge / discharge system, and more particularly, to a charge / discharge system including a storage battery capable of storing electric power generated by a power generation device.

In recent years, an increasing number of customers (for example, houses and factories) receiving AC power from substations are provided with power generation devices (solar cells, etc.) that use renewable energy such as wind power and solar power. is doing. Such a power generator is connected to a power system provided under the substation, and the power generated by the power generator is output to the power consuming device in the consumer. Further, surplus power that is not consumed by the power consuming device in the consumer is output to the power system. The flow of power from the consumer to the power system is called “reverse power flow”, and the power output from the customer to the power system is called “reverse power flow”.

Here, power suppliers such as electric power companies are obligated to stably supply power, and it is necessary to keep the frequency and voltage of the entire power system including the reverse power flow constant.

However, the output of the power generation device using renewable energy may change rapidly depending on the weather. Such an abrupt change in the output of the power generation apparatus has a significant adverse effect on the frequency stability of the interconnected power system. This adverse effect becomes more prominent as more consumers have power generation devices that use renewable energy. For this reason, when the number of customers who have power generation devices that use renewable energy increases in the future, it is necessary to maintain the stability of the power system by suppressing the rapid change in the output of the power generation devices. Will arise.

Therefore, conventionally, in order to suppress such a rapid change in the output of the power generation device, a power generation system including a storage battery capable of storing the power generated by the power generation device using renewable energy has been proposed. Such a power generation system is disclosed in, for example, Japanese Patent Application Laid-Open No. 2009-27797.

JP 2009-27797 A includes a solar cell, an inverter (power output unit) connected to the solar cell via a bus, and a power storage unit connected to the bus via a charge / discharge unit. A power generation system is disclosed. In the above Japanese Patent Application Laid-Open No. 2009-27797, when the power generated by the power generation device is smaller than the desired amount of power, the power generated by the power generation device and the power stored in the power storage unit are combined. The power is output to the power system via the power output unit. Thereby, since it is possible to suppress the fluctuation | variation of the output electric power to an electric power grid | system, it is possible to suppress the bad influence to the frequency etc. of an electric power grid | system.

JP 2009-27797 A

However, a general power output unit often has a maximum power tracking control function that tracks the maximum power value by changing the voltage, and the power output unit having such a maximum power tracking control function is not provided. When applied to a configuration in which the power characteristics from the charging / discharging unit are not adjusted as described in JP 2009-27797 A, there is a problem in that the power output unit may malfunction.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a charge / discharge system capable of suppressing malfunction of the power output unit.

In order to achieve the above object, a charging / discharging system according to one aspect of the present invention includes a storage battery that is connected to a power generation device and stores power generated by the power generation device, and power that discharges power stored in the storage battery. A discharge power conversion unit for conversion, a power output unit connected to the discharge power conversion unit and the power system, and outputting power supplied by the discharge power conversion unit to the power system, and output from the discharge power conversion unit to the power output unit And a control unit that controls the output power so that the power changes according to the voltage and has an output characteristic having a peak power.

According to the present invention, the control unit controls the power output from the discharge power conversion unit to the power output unit so that the power changes according to the voltage and has an output characteristic having a peak power. Since the power output from the power conversion unit has peak power, maximum power tracking control in which the power output unit tracks the maximum value of power by changing the voltage can be appropriately performed. As a result, the power output from the discharge power conversion unit does not have peak power, and the power output unit can be prevented from malfunctioning, unlike when the power is constant even when the voltage is changed. Therefore, the power generation device is connected to the power system via the power output unit, and a storage battery and a control unit are added later to a grid-connected power generation system that does not have a storage battery, thereby facilitating the charge / discharge system according to the present invention. Can be configured.

It is a block diagram which shows the structure of the electric power generation system by 1st Embodiment of this invention. It is a figure which shows the electric power-voltage characteristic of a solar cell. It is a figure which shows the power-voltage characteristic of the electric power output from the DC-DC converter by 1st Embodiment of this invention. It is a flowchart for demonstrating the control flow of the electric power generation system by 1st Embodiment of this invention. It is a block diagram which shows operation | movement when the generated electric power of the electric power generation system by 1st Embodiment of this invention is larger than setting output electric power. It is a block diagram which shows operation | movement when the generated electric power of the electric power generation system by 1st Embodiment of this invention is smaller than setting output electric power. It is a block diagram which shows the structure of the electric power generation system by 2nd Embodiment of this invention. It is a flowchart for demonstrating the control flow of the electric power generation system by 2nd Embodiment of this invention. It is a figure for demonstrating the relationship between the magnitude | size of the load fluctuation | variation output to an electric power grid | system, and a fluctuation period. It is a figure for demonstrating transition of the generated electric power and target output electric power of the electric power generation system by 2nd Embodiment of this invention. It is a block diagram which shows operation | movement when the generated electric power of the electric power generation system by 2nd Embodiment of this invention is larger than target output electric power. It is a figure which shows the electric power-voltage characteristic of the electric power generating apparatus by 2nd Embodiment of this invention. It is a figure which shows the power-voltage characteristic of the electric power charged by the storage battery by 2nd Embodiment of this invention. It is a figure which shows the power-voltage characteristic of the electric power output to the electric power output part by 2nd Embodiment of this invention. It is a figure which shows the electric power-voltage characteristic of the electric power charged by the storage battery by a comparative example. It is a figure which shows the power-voltage characteristic of the electric power output to the electric power output part by a comparative example. It is a block diagram which shows operation | movement when the generated electric power of the electric power generation system by 2nd Embodiment of this invention is smaller than target output electric power. It is a figure which shows the power-voltage characteristic of the electric power discharged through the DC-DC converter from the storage battery by 2nd Embodiment of this invention. It is a figure which shows the power-voltage characteristic of the electric power output to the electric power output part by 2nd Embodiment of this invention. It is a figure which shows the power-voltage characteristic of the electric power discharged through the DC-DC converter from the storage battery by a comparative example. It is a figure which shows the power-voltage characteristic of the electric power output to the electric power output part by a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the structure of the power generation system (solar power generation system 1) according to the first embodiment of the present invention will be described with reference to FIGS.

The solar power generation system 1 according to the first embodiment is connected to a power generation device 2 including a solar battery that generates power using sunlight, a power storage device 3 capable of storing electric power generated by the power generation device 2, and a power system 50. The power output unit 4 includes an inverter that outputs the power stored in the power storage device 3 to the power system 50, and the charge / discharge control unit 5 that controls charging / discharging of the power storage device 3. Further, a load 60 is connected to the AC side bus connecting the power output unit 4 and the power system 50.

The power storage device 3 includes a storage battery 31 connected in series to the

DC side buses

6 a and 6 b and a charge / discharge unit 32 that charges and discharges the storage battery 31. As the storage battery 31, a secondary battery (for example, a Li-ion storage battery, a Ni-MH storage battery, etc.) that has low spontaneous discharge and high charge / discharge efficiency is used. The voltage of the storage battery 31 is about 48V.

Here, in the first embodiment, the charging / discharging unit 32 includes a DC-DC converter 33 provided between the power generation device 2 and the storage battery 31 and connected to the DC side bus 6a. The DC-DC converter 33 steps down the voltage supplied from the power generator 2 to the DC side bus 6a to a voltage suitable for charging the storage battery 31, thereby supplying power from the DC side bus 6a to the storage battery 31 side. It has a function to supply. The DC-DC converter 33 is an example of the “charging power conversion unit” in the present invention.

The DC-DC converter 33 performs so-called MPPT (Maximum Power Point Tracking) control. The MPPT control function is a function that automatically adjusts the operating voltage of the power generator 2 so that the power generated by the power generator 2 is maximized. Specifically, in the power-voltage characteristics (PV characteristics) of the solar cell shown in FIG. 2, for example, when the operating voltage is V1 and the generated power is operating at point A of P1, the operating voltage is changed from V1. If the generated power P2 at the voltage V2 is greater than P1 (P1 <P2) by changing to V2, the operating voltage of the power generator 2 is set to V2 (point B). Further, when the power generation apparatus 2 is operating at a point D where the operating voltage is V4 and the generated power is P1, the operating voltage is changed from V4 to V3, and the generated power P2 at the voltage V3 is larger than P1 (P1 < If P2), the operating voltage is set to V3 (C point). As described above, the MPPT control function monitors the increase / decrease in the generated power and controls the power generator 2 to operate at the maximum power point. In addition, a diode (not shown) is provided between the power generator 2 and the DC-DC converter 33 to prevent the current from flowing backward toward the normal power generator 2.

In the first embodiment, the charging / discharging unit 32 includes a DC-DC converter 34 provided between the power output unit 4 and the storage battery 31 and connected to the DC side bus 6b. The DC-DC converter 34 is not connected to the power generator 2 (DC side bus 6a). That is, a path for supplying power from the power generation device 2 to the power storage device 3 (DC-DC converter 33) and a path for outputting power from the DC-DC converter 34 to the power output unit 4 are sandwiched between the power storage devices 3. It is separated. Therefore, DC side bus 6a and DC side bus 6b are also separated with power storage device 3 interposed therebetween.

Further, the DC-DC converter 34 boosts the voltage of the power supplied from the storage battery 31 to the DC side bus 6b to near the voltage of the DC side bus 6b, thereby supplying power from the storage battery 31 side to the DC side bus 6b. Has the function of discharging. The DC-DC converter 34 is an example of the “discharge power conversion unit” in the present invention.

The charge / discharge control unit 5 is connected to a DC-DC converter 33, a DC-DC converter 34, and a generated power detection unit 7 described later. Then, the charge / discharge control unit 5 performs charge / discharge control of the storage battery 31 by controlling the DC-DC converter 33 and the DC-DC converter 34. Specifically, the charge / discharge control unit 5 charges the storage battery 31 without outputting the power generated by the power generation device 2 to the power output unit 4, and sets output power to be described later from the storage battery 31 to the power output unit 4. It is comprised so that it may output to. The charge / discharge control unit 5 is an example of the “control unit” in the present invention.

Here, in the first embodiment, the charging / discharging control unit 5 is configured so that the output from the DC-DC converter 34 has a voltage-power characteristic (PV characteristic) as indicated by a solid line in FIG. The DC converter 34 is configured to be controlled. The power output unit 4 has an MPPT control function, like the DC-DC converter 33 described above. That is, in the power-voltage characteristic (PV characteristic) of the output of the DC-DC converter 34 shown in FIG. 3, the voltage (Vop) that maximizes the power output from the DC-DC converter 34 is searched. ing. As described above, the charge / discharge control unit 5 increases the voltage with respect to the output power of the DC-DC converter 34, reaches a maximum value at the voltage (Vop), and then decreases with the voltage. Since the DC-DC converter 34 is controlled so as to have the power, the power output unit 4 can easily perform the MPPT control. Note that the PV characteristics shown in FIG. 3 are adjusted so as to have a substantially symmetric shape with respect to a straight line passing through a voltage (Vop) at which the output power becomes maximum.

In the first embodiment, as a method for adjusting the PV characteristics as shown in FIG. 3, for example, by performing PWM (Pulse Width Modulation) control, the power output output from the DC-DC converter 34 is performed. The duty ratio of the pulse signal (the ratio between the pulse High and Low in one cycle) is changed according to the voltage. As a result, the power increases as the voltage increases, and the maximum power is obtained at the voltage (Vop). At a voltage higher than Vop, the PV characteristic is such that the power decreases as the voltage increases. can get. 3, the PV characteristic of the output power from the DC-DC converter 34 is configured such that the maximum power point can be changed by the control from the charge / discharge control unit 5.

Note that a diode (not shown) is provided between the power output unit 4 and the DC-DC converter 34 to prevent a current from flowing backward toward the DC-DC converter 34.

In addition, between the power generation device 2 and the DC-DC converter 33, a generated power detection unit 7 that detects the generated power of the power generation device 2 is provided. Based on the detection result of the generated power detection unit 7, the charge / discharge control unit 5 can acquire the generated power of the power generation device 2 at predetermined detection time intervals (for example, 30 seconds or less). For example, the charge / discharge control unit 5 acquires the generated power data of the power generation device 2 every 30 seconds. Note that the generated power detection time interval needs to be set to an appropriate value in consideration of the fluctuation cycle of the generated power of the power generator 2 and the like. Here, the detection time interval is set to be shorter than the lower limit cycle of the fluctuation cycle that can be handled by the load frequency control (LFC). Further, the charge / discharge control unit 5 acquires the output power of the power output unit 4 to recognize the difference between the power actually output from the power output unit 4 to the power system 50 and the generated power of the power generation device 2. Thus, the charge / discharge of the charge / discharge unit 32 can be feedback controlled.

As described above, in the first embodiment, the storage battery 31 is charged once instead of outputting the generated power of the power generation device 2 to the power system 50 as it is. The charge / discharge control unit 5 is configured to preset output power from the storage battery 31 and perform power smoothing control. Specifically, when the generated power of the power generation device 2 is larger than the preset output power (set output power), the storage battery 31 is charged with the power corresponding to the excess, and the generated power of the power generation device 2 Is smaller than the preset output power, control is performed so that the power corresponding to the shortage is supplemented from the storage battery 31. Thereby, since the generated power of the power generator 2 is input / output to the storage battery 31 in small increments, the capacity of the storage battery 31 is reduced unlike the case of using the storage battery 31 for the purpose of peak cutting of power as in the past. Is possible.

Next, a control flow of the solar power generation system 1 according to the first embodiment will be described with reference to FIGS.

First, in step S 1 shown in FIG. 4, the generated power P 1 of the power generation device 2 at a certain time is detected by the generated power detection unit 7 and taken into the charge / discharge control unit 5.

In step S2, as shown in FIG. 5, the generated power P1 of the power generator 2 is charged to the storage battery 31 via the DC bus 6a and the DC-DC converter 33. At this time, the DC-DC converter 33 steps down the voltage supplied from the power generator 2 to the DC side bus 6a to a voltage suitable for charging the storage battery 31. That is, the generated power P 1 generated in the power generation device 2 is not supplied to the power output unit 4 but is charged in the storage battery 31.

Also, in step S3, the preset set output power P2 is output from the storage battery 31 to the power output unit 4 via the DC-DC converter 34. At this time, the DC-DC converter 34 boosts the voltage of the power supplied from the storage battery 31 to the DC side bus 6b to near the voltage of the DC side bus 6b.

As shown in FIG. 5, when the generated power P1 of the power generator 2 is larger than the set output power P2 (P1> P2), the generated power P1 is charged in the storage battery 31, and the set output power P2 is the power. As a result, the storage battery 31 is charged with power corresponding to the difference (P1−P2) between the generated power P1 and the set output power P2.

As shown in FIG. 6, when the generated power P1 of the power generator 2 is smaller than the set output power P2 (P1 <P2), the generated power P1 is larger than the set output power P2 (P1> P2). Similarly to the case, the generated power P 1 is charged in the storage battery 31, and the set output power P 2 is output to the power output unit 4. As a result, power corresponding to the difference (P2−P1) between the set output power P2 and the generated power P1 is discharged from the storage battery 31.

In addition, when the generated power P1 and the set output power P2 are equal (P1 = P2), the generated power P1 is similarly charged in the storage battery 31, and the set output power P2 is output to the power output unit 4. In this case, since the generated power P1 and the set output power P2 are equal, there is no change in the power charged in the storage battery 31. Further, the generated power P1 of the power generation device 2 varies from moment to moment due to the weather or the like, and the operations of Step S1 to Step S3 are repeated until the operation of the photovoltaic power generation system 1 is completed.

The solar power generation system 1 of the first embodiment can obtain the following effects by the above configuration.

In the first embodiment, as described above, the charge / discharge control unit 5 changes the power output from the DC-DC converter 34 to the power output unit 4 so that the power changes according to the voltage and has the peak power. Since the power output from the DC-DC converter 34 has a peak power, the power output unit 4 changes the voltage to follow the maximum power value ( MPPT) control can be performed appropriately. Thus, unlike the case where the power output from the DC-DC converter 34 does not have peak power and the power is constant even when the voltage is changed, the power output unit 4 can be prevented from malfunctioning. it can. Therefore, the power storage device 3 and the charge / discharge control unit 5 are added later to a grid-connected power generation system in which the power generation device 2 is connected to the power system 50 via the power output unit 4 and does not have the power storage device 3. The power generation system according to the present invention can be easily configured.

In the first embodiment, as described above, the power output unit 4 is configured such that maximum power follow-up control is performed so that the power output from the DC-DC converter 34 is maximized, and charging / discharging is performed. The control unit 5 causes the power output from the DC-DC converter 34 to the power output unit 4 so that the power output unit 4 can easily perform the maximum power tracking control. By configuring so that the output characteristic is controlled, the charge / discharge control unit 5 can easily perform the maximum power follow-up control by the power output unit 4 so that the output characteristic of the power output from the DC-DC converter 34 is improved. Therefore, the maximum power tracking control can be appropriately performed using the conventional power output unit 4 having the maximum power tracking control function.

In the first embodiment, as described above, the charge / discharge control unit 5 performs PWM control on the power output from the DC-DC converter 34 and is output from the DC-DC converter 34 to the power output unit 4. By configuring the power so that the power changes according to the voltage and has an output characteristic having a peak power, the duty ratio of the pulse signal for power control (High and Low of the pulse in one cycle) The power (current) output from the DC-DC converter 34 can be changed, so that the power output from the DC-DC converter 34 to the power output unit 4 can be easily changed. The output can be controlled so that the power changes according to the voltage and the output characteristic has the peak power.

Moreover, in 1st Embodiment, while connecting the electrical storage apparatus 3 to the electric power generating apparatus 2 via the direct current side bus 6a as mentioned above, via the direct current side bus 6b provided separately from the direct current side bus 6a. It is connected to the power output unit 4 and configured to output power from the DC-DC converter 34 to the power output unit 4 via the DC bus 6b, so that power can be supplied from the power generator 2 to the power storage device 3. Since the supply path (DC side bus 6a) and the path (DC side bus 6b) for outputting power from the DC-DC converter 34 to the power output unit 4 are separated with the power storage device 3 interposed therebetween, the power storage device 3 and the operation of discharging power from the DC-DC converter 34 to the power output unit 4 can be prevented from interfering with each other.

In the first embodiment, as described above, the charge / discharge control unit 5 is substantially symmetric with respect to the straight line through which the power output from the DC-DC converter 34 to the power output unit 4 passes the voltage corresponding to the peak power. Unlike the case where the power output from the DC-DC converter 34 is controlled to have an asymmetric output characteristic, the power output from the DC-DC converter 34 is controlled by controlling the output power to have a proper output characteristic. Since the same operation is performed before and after the voltage corresponding to the peak power, the operation for controlling the power output from the DC-DC converter 34 can be easily performed.

(Second Embodiment)
Next, the configuration of the solar power generation system 1a according to the second embodiment will be described with reference to FIG. In the second embodiment, the DC side bus 6a charged with the power generated by the power generation device 2 and the DC side bus 6b discharged with the power output unit 4 are separated with the power storage device 3 interposed therebetween. Unlike the above-described first embodiment, an example in which the power generation device 2 and the power output unit 4 are directly electrically connected by the DC side bus 6c will be described. Other parts are the same as those in the first embodiment.

In the solar power generation system 1a according to the second embodiment, as shown in FIG. 7, the power generation device 2 and the power output unit 4 are directly electrically connected via the DC side bus 6c. The storage battery 31 is connected in parallel to the DC side bus 6c. Between the power generation device 2 and the storage battery 31, the voltage supplied from the power generation device 2 to the DC side bus 6 c is stepped down to a voltage suitable for charging the storage battery 31, whereby the storage battery is connected from the DC side bus 6 c side. A DC-DC converter 33a having a function of supplying power to the 31 side is provided. Moreover, between the electric power output part 4 and the storage battery 31, the voltage of the electric power supplied from the storage battery 31 to the direct current side bus 6c is boosted to the vicinity of the voltage of the direct current side bus 6c, so that the direct current side from the storage battery 31 side is increased. A DC-DC converter 34a having a function of discharging electric power is provided on the bus 6c side. The DC-

DC converters

33a and 34a are examples of the “charge power conversion unit” and the “discharge power conversion unit” of the present invention, respectively.

Here, in the second embodiment, the DC-DC converter 33a adjusts the power input to the DC-DC converter 33a so as to change according to the voltage and to have a peak power characteristic (see FIG. 13). To do. In addition, the input characteristic (PV characteristic) of the electric power input to the DC-DC converter 33a is a PV characteristic approximate to the output characteristic (see FIG. 12) of the electric power generated by the power generator 2. That is, the power gradually increases with the voltage, and the power suddenly decreases with the voltage after the voltage at which the output power becomes maximum. Similarly to the DC-DC converter 33a, the DC-DC converter 34a also changes the power output from the DC-DC converter 34a to the power output unit 4 according to the voltage and has a PV characteristic having peak power. It is adjusted so that it may become (refer FIG. 18). As a result, the power output unit 4 can easily perform MPPT control.

Next, a control flow of the solar power generation system 1a according to the second embodiment will be described with reference to FIGS.

First, in step S 11 shown in FIG. 8, the generated power P 1 of the power generation device 2 at a certain time is detected by the generated power detection unit 7 and taken into the charge / discharge control unit 5. In step S12, the charge / discharge control unit 5 calculates the target output power P2 by the moving average method using the average value of the 40 generated power data included in the past 20 minutes. The moving average method is a calculation method in which the target output power at a certain point in time is an average value of the generated power of the power generation device 2 in the past period from that point. Past generated power data is sequentially stored in the memory 5a. Hereinafter, a period for acquiring generated power data used for calculation of target output power is referred to as a sampling period. The sampling period is a range between the lower limit period T2 and the upper limit period T1 of the load fluctuation period corresponding to the load frequency control (LFC), particularly in the range from the second half (near the long period) to the period exceeding T1, which does not extend for a long time. It is preferable to do. A specific value of the sampling period is, for example, a period of about 10 minutes or more and about 30 minutes or less in a power system having a “load fluctuation magnitude—fluctuation period” characteristic as shown in FIG. The sampling period is about 20 minutes. In this case, since the charge / discharge control unit 5 acquires the generated power data of the power generator 2 approximately every 30 seconds, the average value of the 40 generated power data included in the past 20 minutes is calculated as the target output power. is doing.

As described above, in the second embodiment, the target output power is calculated from the generated power of the past power generator 2, and the discharge of the storage battery 31 is controlled so that the discharge amount of the storage battery 31 becomes the target output power. Charge / discharge control, which is control for outputting electric power to the electric power system 50, is performed. That is, as shown in FIG. 10, when the generated power of the power generation device 2 is larger than the target output power, the charge / discharge control unit 5 charges the storage battery 31 with the power corresponding to the excess amount and reduces the shortage amount. By supplementing the corresponding power from the storage battery 31, it is configured to suppress adverse effects on the power system 50 due to fluctuations in the generated power of the power generation device 2 due to the presence or absence of clouds or the like.

Next, in step S13, it is determined whether or not the generated power P1 of the power generator 2 is larger than the target output power P2. In step S13, when it is determined that the generated power P1 of the power generator 2 is larger than the target output power P2, the process proceeds to step S14, and the power corresponding to the target output power P2 as shown in FIG. Is output from the power generator 2 to the power output unit 4 via the DC bus 6c. Further, the process proceeds to step S15, and the storage battery 31 is charged with the power (P1-P2) corresponding to the difference between the generated power P1 of the power generator 2 and the target output power P2 via the DC-DC converter 33a.

Note that the power generated by the power generation device 2 has a PV characteristic in which the power changes according to the voltage and has peak power, as shown in FIG. And the electric power input from the electric power generating apparatus 2 is PWM-controlled, and as shown in FIG. 13, the characteristic approximated to the output characteristic of the electric power generated by the electric power generating apparatus 2 (the electric power changes according to the voltage). And a characteristic having a peak power). As a result, the PV characteristic (the characteristic obtained by subtracting the PV characteristic shown in FIG. 13 from the PV characteristic shown in FIG. 12) of the power output from the power generator 2 to the power output unit 4 is shown in FIG. As described above, the PV characteristic approximated to the output characteristic of the power generated by the power generation device 2 (the PV characteristic having the peak power and the power changes according to the voltage) is obtained.

Note that, as indicated by the solid line, the dotted line, and the one-dot chain line in FIG. The shape of the PV characteristic also changes depending on the weather as shown by the solid line, the dotted line, and the one-dot chain line in FIG.

As shown in FIG. 15, the DC-DC converter according to the comparative example is configured such that the power input to the DC-DC converter is substantially constant regardless of the voltage. Thus, when the power according to the comparative example shown in FIG. 15 is subtracted from the power generated by the power generator 2 (see FIG. 12), the PV characteristics as shown in FIG. 16 are obtained. That is, there is a region where the power is negative in the region where the voltage is low and the region where the voltage is high. In a region where the voltage is high, there is a region where the power is negative and the voltage is almost constant regardless of the voltage. In a region where the electric power is substantially constant regardless of the voltage, it becomes difficult for the power output unit 4 to find a point where the electric power is maximum, and malfunction may occur.

If it is determined in step S13 that the generated power P1 of the power generator 2 is equal to or less than the target output power P2, the process proceeds to step S16, where the generated power P1 of the power generator 2 and the target output power P2 are equal. It is determined whether or not. If it is determined in step S16 that the generated power P1 of the power generator 2 and the target output power P2 are not equal (that is, the generated power P1 of the power generator 2 is smaller than the target output power P2), step S16 is performed. Proceeding to S17, as shown in FIG. 17, all the generated power P1 of the power generator 2 is output to the power output unit 4 via the DC side bus 6c.

Further, the process proceeds to step S18, and the power (P2-P1) corresponding to the difference between the target output power P2 and the generated power P1 of the power generator 2 is discharged to the power output unit 4 via the DC-DC converter 34a. As shown in FIG. 18, the electric power discharged from the storage battery 31 is a PV characteristic approximating the electric power generated by the power generation device 2 (PV having a peak electric power as the electric power changes depending on the voltage). The DC-DC converter 34a. As a result, the PV characteristics when the power output from the power generator 2 to the power output section 4 and the power discharged from the storage battery 31 to the power output section 4 are combined (the PV characteristics shown in FIG. 12). As shown in FIG. 19, the characteristic obtained by adding up the PV characteristics shown in FIG. 18 has a peak power as the power changes according to the voltage.

Note that the electric power generated by the power generation apparatus 2 changes from moment to moment depending on the weather and the like, and the shape of the PV characteristic of the electric power output from the storage battery 31 to the electric power output unit 4 is also shown by the solid line, dotted line, As shown by the one-dot chain line, it varies depending on the weather. As a result, as shown in FIG. 19, the combined power of the power generated by the power generation device 2 and the power discharged from the storage battery 31 is also changed according to the weather and output.

As shown in FIG. 20, the DC-DC converter according to the comparative example is configured such that the power discharged from the DC-DC converter to the power output unit is substantially constant regardless of the voltage. Thus, when the power generated by the power generation device 2 (see FIG. 12) and the power according to the comparative example shown in FIG. 20 are combined, the PV characteristics as shown in FIG. 21 are obtained. In other words, in the region where the voltage is high, there is a region where the power is almost constant regardless of the voltage. In a region where the electric power is substantially constant regardless of the voltage, it becomes difficult for the power output unit 4 to find a point where the electric power is maximum, and malfunction may occur.

If it is determined in step S16 that the generated power P1 of the power generator 2 is equal to the target output power P2, the process proceeds to step S19, where the power P1 (= P2) generated in the power generator 2 is the power. It is output to the output unit 4.

In 2nd Embodiment, while connecting the electric power generating apparatus 2 and the electric power output part 4 via the direct current | flow side bus | bath 6c as mentioned above, the electrical storage apparatus 3 is connected to the direct current | flow side bus | bath 6c, and charge / discharge control is carried out. By configuring the unit 5 to control the power output from the DC-DC converter 34a to the power output unit 4 so as to have an output characteristic approximate to the output characteristic of the power generated by the power generation device 2, Since the output characteristics of the power generated by the power generated by the power generator 2 and the power discharged from the DC-DC converter 34a approximate the output characteristics of the power generated by the power generator 2, the maximum power A conventional power output unit 4 having a tracking control function can be used.

The solar power generation system 1a of the second embodiment can obtain the following effects by the above configuration.

In the second embodiment, even when the charge / discharge control unit 5 performs PWM control of the DC-DC converter 33a, even when the power charged in the power storage device 3 is subtracted from the power generated by the power generation device 2, the power output unit Since the output characteristic of the power output to 4 approximates the output characteristic of the power generated by the power generator 2, the conventional power output unit 4 having the maximum power tracking control function can be used.

In the second embodiment, since the current input to the DC-DC converter 33a can be changed by changing the duty ratio of the power, the power input to the DC-DC converter 33a ( Current) can be controlled such that the power changes according to the voltage and the input characteristic has a peak power.

The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

For example, in the first and second embodiments described above, an example in which a solar cell is used as a power generator has been described. However, the present invention is not limited to this, and other renewable energy power generators such as a wind power generator may be used. .

In the first and second embodiments, an example in which a Li-ion battery or a Ni-MH battery is used as a storage battery has been described. However, the present invention is not limited to this, and other secondary batteries may be used.

In the first and second embodiments, the example in which the voltage of the storage battery is 48V has been described. However, the present invention is not limited to this, and a voltage other than 48V may be used.

Moreover, although the said 1st and 2nd embodiment demonstrated the case where the power consumption in the load used in a consumer was not assumed, this invention is not limited to this, In setting of setting output power (calculation of target output power) The power consumed by at least a part of the load used in the consumer may be detected, and the set output power may be set (calculation of the target output power) in consideration of the load power consumption or the load power fluctuation amount. .

Further, the present invention is not limited to the specific values such as the sampling period and the bus voltage described in the above embodiment, and can be appropriately changed.

In the first and second embodiments, the example in which the output characteristic of the power input to the DC-DC converter is adjusted by changing the duty ratio of the power input to the DC-DC converter has been described. The present invention is not limited to this, and the output characteristics of the power input to the DC-DC converter may be adjusted by a method other than the method of changing the duty ratio of the power. For example, the input characteristics of the power input to the DC-DC converter may be adjusted by providing a resistor in the DC-DC converter and adjusting the magnitude of the current input to the DC-DC converter.

In the first embodiment, the PV characteristics of the power input to the DC-DC converter 34 are substantially symmetrical with respect to a straight line passing through the voltage (Vop) at which the output power is maximized (see FIG. 3). However, the present invention is not limited to this example, and the PV characteristics of the power input to the DC-DC converter 34 are represented by the P− of the power generated by the power generator. The PV characteristic may be approximated to the V characteristic (see FIG. 12).

Claims

A storage battery connected to a power generator and storing the power generated by the power generator;
A discharge power conversion unit that converts power stored in the storage battery into power to be discharged;
A power output unit connected to the discharge power conversion unit and the power system, and outputs power supplied by the discharge power conversion unit to the power system;
A charge / discharge system comprising: a control unit that controls the power output from the discharge power conversion unit to the power output unit so that the power changes according to the voltage and has an output characteristic having a peak power.
The charge / discharge system according to claim 1, wherein the power output unit performs maximum power tracking control based on the control of the discharge power conversion unit by the control unit.
The control unit performs PWM control on the power output from the discharge power conversion unit, thereby changing the power output from the discharge power conversion unit to the power output unit according to the voltage and the peak power The charge / discharge system according to claim 1, wherein the charge / discharge system is controlled to have an output characteristic.
A charge power conversion unit for converting the power generated by the power generation device into power for charging the storage battery;
The charge / discharge system according to claim 1, wherein the control unit controls the charge power conversion unit to perform maximum power tracking control on an output from the power generation device.
A power detector for detecting the power generated by the power generator;
The charge / discharge system according to claim 4, wherein the charge power conversion unit performs maximum power tracking control based on an output of the power detection unit.
The said control part controls the electric power output to the said electric power output part from the said discharge electric power conversion part so that it may become a substantially symmetrical output characteristic with respect to the straight line which passes the voltage corresponding to peak electric power. The described charge / discharge system.
The charge / discharge system according to claim 6, wherein the control unit changes a peak power of power output from the discharge power conversion unit to the power output unit.
The power generation device and the power output unit are connected via a bus, and the storage battery is connected to the bus.
The said control part controls the electric power output to the said electric power output part from the said discharge electric power conversion part so that it may become the output characteristic approximated to the output characteristic of the electric power generated by the said electric power generating apparatus. Charging and discharging system.
The control unit outputs the power output from the discharge power conversion unit to the power output unit. The power gradually increases with the voltage, and the power suddenly decreases with the voltage after the voltage at which the output power becomes maximum. The charge / discharge system according to claim 8, wherein the charge / discharge system is controlled to have characteristics.
The control unit is configured such that the output power of the power output from the discharge power conversion unit to the power output unit is a peak power compared with a degree of increase in power with respect to a voltage in a voltage region smaller than a voltage corresponding to the peak power. The charge / discharge system according to claim 9, wherein control is performed such that a degree of power decrease with respect to a voltage in a voltage region larger than a voltage corresponding to is increased.
The power supplied from the discharge power conversion unit is added to the power generated by the power generation device when the generated power of the power generation device is a predetermined value or less, and is supplied to the power output unit. Item 9. The charge / discharge system according to Item 8.
A charge power conversion unit for converting the power generated by the power generation device into power for charging the storage battery;
The charge / discharge system according to claim 8, wherein the control unit controls the power input to the charging power conversion unit so that the power changes according to the voltage and has a characteristic having a peak power.
The control unit performs PWM control on the power input to the charging power conversion unit, whereby the power input to the charging power conversion unit has a characteristic in which the power changes according to the voltage and has a peak power. The charge / discharge system according to claim 12, wherein the charge / discharge system is controlled as follows.
The charge / discharge system according to claim 12, wherein the control unit controls the electric power input to the charging power conversion unit so as to have a characteristic approximate to an output characteristic of electric power generated by the power generation device.
When the generated power of the power generation device is equal to or greater than a predetermined value, the power charged in the storage battery is subtracted from the power generated by the power generation device to approximate the output characteristics of the power generated by the power generation device. The charging / discharging system of Claim 14 with which the electric power which has an output characteristic is output to the said electric power output part.