JP7314774B2 - Power conversion device and its control method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a power conversion device including a power converter connected to a power storage device to supply power to a load, and a control method thereof.

Conventionally, a power converter (hereinafter also referred to as a second power converter) to which power is supplied from a power converter (hereinafter also referred to as a first power converter) connected to a power generation facility and is connected to a power storage device to supply power to the load is known. For example, Patent Document 1 discloses a power supply system (power conversion device) that includes a power conditioner (second power converter) that can supply power converted from a storage battery (storage device) to a load during a power failure and when a solar panel (power generation facility) generates power, while supplying power output from the power conditioner (first power converter) during a power failure and when the solar panel does not generate power.

JP 2019-17141 A

In the above conventional power converter, the second power converter is supplied with power from the first power converter, but if the amount of power supplied to the second power converter is not adjusted, the power may be too much or too little. If too much power is supplied to the second power converter, the second power converter may receive power exceeding its acceptable capacity, and if too little power is supplied to the second power converter, the second power converter may not be able to supply sufficient power to the power storage device. As described above, the inventors of the present application have found that, in the above-described conventional power converter, there is a possibility that a problem may occur in the power converter that is connected to the power storage device and supplies power to the load.

The present invention has been made by the inventors of the present invention with a new focus on the above problem, and an object of the present invention is to provide a power conversion device and a control method thereof that can suppress the occurrence of problems in a power converter that is connected to a power storage device and supplies power to a load.

To achieve the above object, a power converter according to an aspect of the present invention is supplied with power from a first power converter that is connected to a power generation facility and supplies AC power to a load, and is connected to a power storage device and is provided with a second power converter that supplies AC power to the load. Give a control command to

According to this, in the power conversion device, the second power converter connected to the power storage device and supplying AC power to the load is supplied with power from the first power converter connected to the power generation equipment and supplying AC power to the load. That is, the AC power output from the first power converter is divided and supplied to the load and the second power converter. Here, if there is a shortage of active power and reactive power required by the load that is not supplied from the first power converter, the shortage must be supplied from the second power converter to the load. In this way, the second power converter is supplied with active power and reactive power from the first power converter and supplies active power and reactive power to the load, so the values of active power and reactive power in the second power converter change according to the situation.

Therefore, since the value of the apparent power in the second power converter changes, the value of the apparent power may become too large or too small. If the value of the apparent power becomes too large, the second power converter may receive apparent power exceeding the acceptable capacity, and if the value of the apparent power becomes too small, the second power converter may not be able to supply sufficient power to the power storage device.

Therefore, the control unit of the second power converter issues a control command to increase or decrease the output of the first power converter according to the magnitude relationship between the apparent power in the second power converter and a predetermined threshold. As a result, the values of active power and reactive power output from the first power converter are adjusted, so the values of active power and reactive power supplied from the first power converter to the second power converter can be adjusted. Therefore, since the value of the apparent power in the second power converter can be adjusted, it is possible to suppress the occurrence of problems in the second power converter (the power converter connected to the power storage device and supplying power to the load).

Further, the power generation equipment may be a power generation equipment that generates power using renewable energy.

According to this, the power generation equipment connected to the first power converter is a power generation equipment that generates power using renewable energy. Here, power generation by renewable energy such as photovoltaic power generation or wind power generation fluctuates greatly in output. Therefore, since the output of the first power converter tends to increase or decrease, the values of active power and reactive power supplied from the first power converter to the second power converter also tend to increase or decrease. As a result, since the value of the apparent power in the second power converter tends to become too large or too small, the occurrence of problems in the second power converter can be effectively suppressed by adjusting the value of the apparent power according to the present invention.

Further, the second power converter may be supplied with power from the plurality of first power converters, and the control unit may increase or decrease the output of the plurality of first power converters by issuing the control command.

According to this, since electric power is supplied to the second power converter from the plurality of first power converters, the values of the active power and the reactive power supplied to the second power converter tend to increase or decrease. Therefore, since the value of the apparent power in the second power converter tends to become too large or too small, the control unit of the second power converter increases or decreases the outputs of the plurality of first power converters according to the control command. As a result, it is possible to adjust the value of the apparent power in the second power converter, so that it is possible to suppress the occurrence of problems in the second power converter.

Further, the control unit may increase or decrease the output of the plurality of first power converters via control lines connected to the plurality of first power converters by issuing the control command to one first power converter among the plurality of first power converters.

According to this, the control unit of the second power converter issues a control command to one first power converter among the plurality of first power converters, whereby the control command is transmitted between the plurality of first power converters via the control line. As a result, the control unit of the second power converter can easily increase or decrease the outputs of the plurality of first power converters to adjust the value of the apparent power in the second power converter, thereby preventing problems from occurring in the second power converter.

Also, the control unit may issue the control command to increase or decrease the output of the first power converter at a constant rate.

According to this, the control unit of the second power converter increases or decreases the output of the first power converter at a constant rate, so the larger the output of the first power converter, the greater the increase or decrease of the output. That is, the control unit of the second power converter greatly increases or decreases the output of the first power converter because the output of the first power converter tends to increase or decrease more as the output of the first power converter increases. As a result, the control unit of the second power converter can adjust the value of the apparent power in the second power converter according to the magnitude of the output of the first power converter, thereby preventing problems from occurring in the second power converter.

Further, the control unit may issue a first control command to decrease the output of the first power converter when the apparent power in the second power converter exceeds the first threshold.

If the first power converter cannot supply sufficient reactive power to the load because the first power converter outputs AC power with a large power factor, etc., it is necessary to supply reactive power to the load from the second power converter. In this case, active power may be input to the second power converter from the first power converter, but reactive power is output from the second power converter to the load, so that the apparent power in the second power converter becomes a larger value than the input active power. In other words, even if the value of the active power input to the second power converter is equal to or less than the first threshold that indicates the acceptable capacity of the second power converter, the apparent power in the second power converter may exceed the first threshold. Therefore, the control unit of the second power converter issues the first control command to decrease the output of the first power converter when the apparent power in the second power converter exceeds the first threshold. As a result, the apparent power supplied from the first power converter to the second power converter can be reduced, so the apparent power in the second power converter can be reduced. Therefore, since it is possible to suppress the apparent power in the second power converter from exceeding the first threshold value, it is possible to suppress the occurrence of problems in the second power converter.

Further, the control unit may repeat the first control command until the apparent power in the second power converter becomes equal to or less than the first threshold value.

According to this, the control unit of the second power converter repeats the first control command until the apparent power in the second power converter becomes equal to or less than the first threshold, thereby reducing the apparent power to equal to or less than the first threshold. Thereby, it is possible to suppress the occurrence of trouble in the second power converter.

Further, the control unit may issue a second control command to increase the output of the first power converter when the apparent power of the second power converter is equal to or less than a second threshold.

A decrease in the active power input from the first power converter to the second power converter or a decrease in reactive power output from the second power converter to the load may cause the apparent power in the second power converter to become a small value. In other words, the power storage device may not be sufficiently charged because the apparent power in the second power converter is less than or equal to the second threshold value indicating the value required to sufficiently charge the power storage device. Therefore, the control unit of the second power converter issues the second control command to increase the output of the first power converter when the apparent power in the second power converter is equal to or less than the second threshold. As a result, the apparent power in the second power converter can be increased to prevent the apparent power from becoming equal to or lower than the second threshold value, thereby preventing problems from occurring in the second power converter.

Further, the control unit may issue the first control command or the second control command such that the amount of decrease in the output of the first power converter in the first control command for decreasing the output of the first power converter when the apparent power in the second power converter exceeds the first threshold is greater than the amount of increase in the output of the first power converter in the second control command.

When the apparent power in the second power converter is large, the apparent power may exceed the acceptable capacity of the second power converter and affect the facility itself of the second power converter. On the other hand, when the apparent power in the second power converter is small, there is a problem such as the power storage device being unable to be sufficiently charged, but the possibility of affecting the equipment itself of the second power converter or the power storage device is low. Thus, it is more necessary to reduce the apparent power in the second power converter when the apparent power is large than to increase the apparent power when the apparent power is small. Therefore, the control unit of the second power converter issues the first control command or the second control command such that the amount of decrease in the output of the first power converter in the first control command is greater than the amount of increase in the output of the first power converter in the second control command. As a result, when the apparent power in the second power converter is large, the apparent power can be reduced relatively quickly, so that the second power converter can be protected. In this way, appropriate measures can be taken according to the magnitude of the problem that may occur in the second power converter.

Further, the control unit may determine whether or not to issue the second control command according to the chargeable capacity of the power storage device.

Even if the apparent power in the second power converter is equal to or less than the second threshold, if the chargeable capacity of the power storage device is small because the power storage device is sufficiently charged, there is no need to increase the power supplied to the power storage device. That is, in this case, since it is not necessary to increase the apparent power in the second power converter, it is not necessary to increase the output of the first power converter. Therefore, the control unit of the second power converter determines whether or not to issue the second control command according to the chargeable capacity of the power storage device. Thereby, the control unit of the second power converter can determine not to issue the second control command to increase the output of the first power converter even when the apparent power in the second power converter is equal to or less than the second threshold. In this way, the control unit of the second power converter can issue an appropriate control command in consideration of the state of charge of the power storage device.

Moreover, the present invention can be realized not only as a power conversion device including such a second power converter, but also as a power conversion device further including a first power converter and a power storage device. The present invention can also be implemented as a control method for a power conversion device that includes processing performed in the power conversion device. In addition, the present invention can be realized as a program for executing the processing included in the control method of the power conversion device, or as a recording medium such as a computer-readable CD-ROM in which the program is recorded. The program can be distributed via the recording medium and a transmission medium such as the Internet. The present invention can also be implemented as an integrated circuit that includes a processing unit included in the power converter.

According to the power conversion device of the present invention, it is possible to prevent problems from occurring in the power converter that is connected to the power storage device and supplies power to the load.

It is a figure which shows the structure of the power converter device which concerns on embodiment. It is a block diagram which shows the functional structure of the power converter device which concerns on embodiment. 4 is a flow chart showing a process (control method of the power converter) performed by the power converter according to the embodiment; It is a figure explaining the process which the power converter device which concerns on embodiment performs. It is a figure which shows an example of the process which the power converter device which concerns on embodiment performs. It is a figure which shows the other example of the process which the power converter device which concerns on embodiment performs. 4 is a graph showing the relationship between the voltage of the power storage device and the charging power target value according to the embodiment;

DESCRIPTION OF THE PREFERRED EMBODIMENTS A power conversion device and a control method thereof according to embodiments (including modifications thereof) of the present invention will be described below with reference to the drawings. It should be noted that the embodiments described below are all comprehensive or specific examples. Numerical values, components, arrangement positions and connection forms of components, control processing, order of control processing, and the like shown in the following embodiments are examples, and are not intended to limit the present invention.

(Embodiment)
[1 Description of Configuration of Power Converter 10]
First, the configuration of the power converter 10 will be described. FIG. 1 is a diagram showing the configuration of a power converter 10 according to this embodiment. Specifically, FIG. 1 shows the configuration of the power conversion device 10 and the connection relationship between the power conversion device 10 and the power generation equipment 20 , the load 30 and the power system 40 .

The power conversion device 10 is a device that converts power and supplies the converted power to a load. As shown in FIG. 1 , the power converter 10 includes a first power converter 100 , a second power converter 200 , and a power storage device 300 . In addition, the first power converter 100 is connected to the power generation facility 20, the first power converter 100 and the second power converter 200 are connected to the load 30 and the power system 40 via the switch 41. First, the power generation equipment 20, the load 30, and the power system 40 connected to the power converter 10 will be described.

The power generation equipment 20 is a power generation equipment that generates power using renewable energy. In the present embodiment, the power generation facility 20 is a photovoltaic power generation facility, for example, a small and medium-scale photovoltaic (PV) facility installed on the roof of a building owned by a customer, or a large-scale photovoltaic power plant (so-called mega solar). Thereby, the power generation equipment 20 outputs DC power to the power converter 10 (first power converter 100). The power generation equipment 20 is a wind power generation equipment or the like, and may output DC power to the power converter 10 (first power converter 100).

The load 30 is a power load consumed by the consumer, for example, the power consumption of home appliances such as air conditioners, or the power consumption for operating machines in a factory, but the load 30 may be any power load. The load 30 is, for example, a power load supplied with AC power (active power and reactive power) with a lagging power factor of about 0.7. A device that consumes the power load can also be called a load 30 .

The power system 40 is, for example, a commercial power system owned by a power generation company such as an electric power company, and power is supplied from power generation equipment owned by the power generation company through a substation or the like. The switch 41 is a switch for exchanging power between the power system 40 and the power converter 10 and for supplying power from the power system 40 to the load 30 . When the switch 41 is turned on (closed), power can be supplied from the power system 40 to the power converter 10 and the load 30 and power can be supplied from the power converter 10 to the power system 40 . When the switch 41 is turned off (open), power supply from the power system 40 to the power converter 10 and the load 30 is cut off, and power supply from the power converter 10 to the power system 40 is cut off.

That is, for example, the switch 41 is in the ON state during normal times, and the switch 41 is in the OFF state during power failure. The timing of turning on and off the switch 41 is not particularly limited, and the switch 41 may be turned off in a normal state and turned on in an emergency such as when the power generating equipment 20 cannot generate power.

Next, the first power converter 100, the second power converter 200, and the power storage device 300 included in the power converter 10 will be described.

The first power converter 100 is a device that is connected to the power generation facility 20 and supplies AC power to the load 30 . In the present embodiment, the first power converter 100 is a power converter that inputs DC power output from the power generation facility 20, converts it into AC power, and outputs the converted AC power. That is, the first power converter 100 is a power conditioner having the function of an inverter (DC/AC inverter) that converts DC power into AC power. The first power converter 100 also has a function of adjusting (increasing or decreasing) the value of AC power to be output. The first power converter 100 also supplies the output AC power to the load 30 , the second power converter 200 , and the power system 40 via the switch 41 .

In this embodiment, the power converter 10 includes a plurality of first power converters 100 . Therefore, each of the plurality of first power converters 100 is connected to the power generation equipment 20 and supplies AC power to the load 30 . Note that the power converter 10 may also include a plurality of power generation facilities 20 . That is, one power generation facility 20 may be arranged for a plurality of first power converters 100 , or one power generation facility 20 may be arranged for one first power converter 100 . Moreover, a plurality of power generation facilities 20 may be arranged for one first power converter 100 .

The second power converter 200 is a device that is supplied with power from the first power converter 100 and that is connected to the power storage device 300 to supply AC power to the load 30 . In the present embodiment, the power conversion device 10 includes a plurality of first power converters 100 , so power is supplied from the plurality of first power converters 100 to the second power converter 200 . That is, the second power converter 200 receives AC power output from the plurality of first power converters 100, converts it to DC power, and outputs the converted DC power to the power storage device 300 to charge the power storage device 300. The second power converter 200 inputs the DC power discharged by the power storage device 300 , converts it into AC power, outputs the converted AC power, and supplies the AC power to the load 30 . That is, the second power converter 200 is a power conditioner having the functions of a converter (AC/DC converter) that converts AC power into DC power and an inverter (DC/AC inverter) that converts DC power into AC power.

In addition, when the switch 41 is on, the second power converter 200 is configured to be able to be supplied with power from the power system 40 as well. That is, the second power converter 200 is supplied with power from the power system 40 when the power supplied from the first power converter 100 is insufficient when the switch 41 is on. On the other hand, when the switch 41 is off, the second power converter 200 is not supplied with power from the power system 40, but can be operated by being supplied with power from the first power converter 100. Thus, the second power converter 200 is configured to be capable of self-sustaining operation even when the switch 41 is off (during a power failure, etc.).

Second power converter 200 also has a function of controlling the output of first power converter 100 . Specifically, the second power converter 200 issues a control command to the first power converter 100 to increase or decrease the output of the first power converter 100 . A detailed description of how the second power converter 200 controls the output of the first power converter 100 will be given later.

Power storage device 300 is a device that can be charged with electricity from the outside and can discharge electricity to the outside. The power storage device 300 charges the power generated by the power generation equipment 20 and discharges the power to the load 30 via the second power converter 200 . Power storage device 300 is a stationary battery, but may be a battery for driving an automobile, a motorcycle, or the like, or for starting an engine. Examples of such vehicles include electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and gasoline vehicles.

Specifically, power storage device 300 has a plurality of power storage elements. The storage element is a secondary battery (single battery) capable of charging and discharging electricity, and is, for example, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. The electric storage element is not limited to the non-aqueous electrolyte secondary battery, and may be a secondary battery other than the non-aqueous electrolyte secondary battery, a capacitor, a primary battery, or a battery using a solid electrolyte.

[2 Description of Functional Configuration of Power Converter 10]
Next, the functional configuration of the power converter 10 will be described. FIG. 2 is a block diagram showing a functional configuration of power converter 10 according to the present embodiment. Specifically, FIG. 2 shows the functional configuration of the second power converter 200 included in the power converter 10. As shown in FIG.

As shown in FIG. 2 , the second power converter 200 includes a control section 210 and a storage section 220 . The control unit 210 is connected to the first power converter 100 at the end of the plurality of first power converters 100 . Also, the plurality of first power converters 100 are connected in a daisy chain by the control line 110 in order from the first power converter 100 at the end. Although not shown, the second power converter 200 may include an input unit such as a keyboard and a mouse, and a display unit such as a liquid crystal display.

The control unit 210 is a processing unit that controls the output of the first power converter 100 . Specifically, control unit 210 issues a control command to increase or decrease the output of first power converter 100 according to the magnitude relationship between the apparent power in second power converter 200 and a predetermined threshold. More specifically, control unit 210 issues a first control command to decrease the output of first power converter 100 when the apparent power in second power converter 200 exceeds the first threshold. In the present embodiment, control unit 210 repeatedly issues the first control command until the apparent power in second power converter 200 becomes equal to or less than the first threshold. Further, the control unit 210 issues a second control command to increase the output of the first power converter 100 when the apparent power in the second power converter 200 is equal to or less than the second threshold. At this time, control unit 210 determines whether or not to issue the second control command according to the amount of chargeable capacity of power storage device 300 .

Further, the control unit 210 issues the first control command or the second control command such that the amount of decrease in the output of the first power converter 100 in the first control command for decreasing the output of the first power converter 100 when the apparent power in the second power converter 200 exceeds the first threshold is greater than the amount of increase in the output of the first power converter 100 in the second control command.

In the present embodiment, the power conversion device 10 includes a plurality of first power converters 100, so that the control unit 210 increases or decreases the outputs of the plurality of first power converters 100 by issuing the control command. Specifically, the control unit 210 issues a control command to one first power converter 100 out of the plurality of first power converters 100, thereby increasing or decreasing the output of the plurality of first power converters 100 via the control line 110 connected to the plurality of first power converters 100. At this time, the control unit 210 issues a control command to increase or decrease the output of the first power converter 100 at a constant rate.

The storage unit 220 is a memory that stores data and the like for the control unit 210 to control the output of the first power converter 100 . Specifically, the storage unit 220 stores control data 221 including data used for control by the control unit 210 . The control data 221 is, for example, a collection of data including a first threshold value and a second threshold value or values corresponding to them, data related to the power storage device 300 corresponding to FIG.

The control unit 210 reads these data from the control data 221 when performing control, and writes data to the control data 221 as necessary. These data may be written in the control data 221 in advance, or may be written (or updated) by the control unit 210 during control. In addition, when these data are changed, the data for control 221 may be updated each time, or these data may be accumulated.

[3 Description of Processing Flow of Power Converter 10]
Next, the processing performed by the power converter 10, that is, the control processing performed by the control unit 210 of the second power converter 200 will be described. Specifically, control processing performed by the control unit 210 of the second power converter 200 when the switch 41 shown in FIG. Note that the second power converter 200 can perform similar processing even when the switch 41 is in the ON state (normal time, etc.).

FIG. 3 is a flowchart showing a process (a control method of the power conversion device 10) performed by the power conversion device 10 according to this embodiment. Specifically, FIG. 3 is a flow chart showing a process of controlling the output of the first power converter 100 by the control unit 210 of the second power converter 200 . FIG. 4 is a diagram for explaining the processing performed by the power converter 10 according to the present embodiment. FIG. 5 is a diagram showing an example of processing performed by the power conversion device 10 according to the present embodiment, and FIG. 6 is a diagram showing another example of processing performed by the power conversion device 10 according to the present embodiment. Specifically, FIG. 5 shows an example in which the control unit 210 of the second power converter 200 issues the first control command, and FIG. 6 shows an example in which the control unit 210 of the second power converter 200 issues the second control command. FIG. 7 is a graph showing the relationship between the voltage of power storage device 300 and the charging power target value according to the present embodiment.

As described above, the control unit 210 of the second power converter 200 performs a control command (first control command, second control command) to increase or decrease the output of the first power converter 100 according to the magnitude relationship between the apparent power in the second power converter 200 and a predetermined threshold value (first threshold value, second threshold value). This will be briefly explained using the model in FIG.

As shown in FIG. 4, the first power converter 100 outputs active power P1 [kW] and reactive power Q1 [kvar]. Here, the first power converter 100 generally uses a power factor of AC power output close to 1, so below, the value of the reactive power Q1 output from the first power converter 100 is assumed to be 0 or a very small value. Accordingly, it can be assumed that the reactive power Q1 from the first power converter 100 is supplied to neither the load 30 nor the second power converter 200. FIG. In addition, when the reactive power Q1 from the first power converter 100 is not 0 or a very small value, all the reactive power Q1 is supplied to the second power converter 200. FIG. As for the active power P1 from the first power converter 100, the active power P2 [kW] is supplied to the load 30, and the remaining active power P3 (=P1-P2) [kW] is supplied to the second power converter 200.

In addition, since the load 30 lacks reactive power, the second power converter 200 supplies the load 30 with reactive power Q2 [kvar], which is the shortfall. When the reactive power Q1 from the first power converter 100 is supplied to the second power converter 200, the second power converter 200 outputs reactive power Q1+Q2.

In such a state, the control unit 210 performs the first control command R1 to decrease the output of the first power converter 100 according to the magnitude relationship between the apparent power S [kVA] (for example, the apparent power at point A) in the second power converter 200 and the first threshold value S1. Note that the point A is a measurement point located near the entrance of the power from the first power converter 100 of the second power converter 200 . Further, the control unit 210 performs the second control command R2 to increase the output of the first power converter 100 according to the magnitude relationship between the apparent power S [kVA] (for example, the apparent power at point A) in the second power converter 200 and the second threshold value S2.

Next, a specific description will be given with reference to FIGS. 3 and 5 to 7 as well. As shown in FIG. 3, first, the control unit 210 of the second power converter 200 determines whether or not the apparent power in the second power converter 200 exceeds the first threshold (S102).

For example, the control unit 210 measures the current value and the voltage value at the point A shown in FIG. 4 and calculates the apparent power S by multiplying the two. Instead of measuring the current and voltage values, the control unit 210 may calculate them from other information, acquire them from other devices, or acquire them from input by the user. Further, the control unit 210 reads and acquires the first threshold value from the control data 221 stored in the storage unit 220 . Then, control unit 210 compares apparent power S with first threshold S1 and determines whether apparent power S exceeds first threshold S1.

When the voltage value at the point A is controlled at a constant value, the control unit 210 acquires the current value at the point A by measurement or the like, and compares the current value with a predetermined threshold value corresponding to the first threshold value S1, thereby determining whether the apparent power S exceeds the first threshold value S1. Alternatively, control unit 210 may use another technique to determine whether apparent power S exceeds first threshold value S1, and the technique for making the determination is not particularly limited.

Then, when the control unit 210 determines that the apparent power in the second power converter 200 exceeds the first threshold (YES in S102), it issues a first control command to decrease the output of the first power converter 100 (S104).

For example, as shown in FIG. 5, it is assumed that the first power converter 100 outputs active power P1=150 [kW] (reactive power is 0) to a load 30 with an apparent power of 100 [kVA] and a lagging power factor of 0.7. In this case, the first power converter 100 supplies the load 30 with active power P2=70 [kW], and the second power converter 200 is supplied with the remaining active power P3=80 [kW]. In addition, since the load 30 requires reactive power Q2=approximately 71 [kvar], the second power converter 200 supplies the load 30 with the shortfall of reactive power Q2=approximately 71 [kvar].

As a result, active power P3=80 [kW] is input to second power converter 200, and reactive power Q2=about 71 [kvar] is output, so apparent power S in second power converter 200 is about 107 [kVA]. Here, the second power converter 200 has an installed capacity of 100 [kVA] and is set so as not to exceed 95 [kVA]. That is, it is assumed that the first threshold value S1 is set to 95 [kVA]. Therefore, the control unit 210 determines that the apparent power S (=approximately 107 [kVA]) in the second power converter 200 exceeds the first threshold value S1 (=95 [kVA]), and issues the first control command R1 to decrease the output of the first power converter 100.

For example, the control unit 210 issues a first control command R1 to decrease the output of the first power converter 100 at a constant rate of 3%. That is, the control unit 210 issues the first control command R1 to one first power converter 100 out of the plurality of first power converters 100 to reduce the output at a constant rate of 3%. As a result, the first control command R1 to decrease the output at a constant rate of 3% is sequentially transmitted to each first power converter 100 via the control line 110 . In this way, the plurality of first power converters 100 receives the first control command R1 and reduces the output at a constant rate of 3%.

After that, the control unit 210 repeatedly issues the first control command until the apparent power in the second power converter 200 becomes equal to or less than the first threshold (S102 to S104). Thus, in the second power converter 200, the active power P3=80 is less than or equal to the first threshold value S1=95, so the control unit 210 tries to accept the active power P3. However, the control unit 210 determines that the apparent power S=about 107 exceeds the first threshold value S1 due to the presence of the reactive power Q2=about 71, and issues the first control command R1 to decrease the output of the first power converter 100. FIG. Then, control unit 210 repeatedly issues first control command R1 until it determines that apparent power S is equal to or less than first threshold value S1 (NO in S102).

Then, when control unit 210 determines that the apparent power in second power converter 200 is equal to or less than the first threshold (NO in S102), it determines whether the apparent power in second power converter 200 is equal to or less than the second threshold (S106). Here, the determination of whether the apparent power in the second power converter 200 is equal to or less than the second threshold, which is performed by the control unit 210, can be performed in the same manner as the determination of whether the apparent power in the second power converter 200 exceeds the first threshold. Note that the second threshold is a value equal to or less than the first threshold.

When control unit 210 determines that the apparent power in second power converter 200 exceeds the second threshold (NO in S106), the process ends.

When determining that the apparent power in the second power converter 200 is equal to or less than the second threshold value (YES in S106), the control unit 210 determines whether or not to issue the second control command (S108). Specifically, control unit 210 determines whether or not to issue the second control command according to the amount of chargeable capacity of power storage device 300 . Then, when the control unit 210 determines to issue the second control command (YES in S108), it issues the second control command to increase the output of the first power converter 100 (S110). If the control unit 210 determines not to issue the second control command (NO in S108), the process ends.

For example, as shown in FIG. 6, it is assumed that the first power converter 100 outputs active power P1=120 [kW] (reactive power is 0) to a load 30 with an apparent power of 100 [kVA] and a lagging power factor of 0.7. In this case, the first power converter 100 supplies the load 30 with active power P2=70 [kW], and the second power converter 200 is supplied with the remaining active power P3=50 [kW]. In addition, since the load 30 requires reactive power Q2=approximately 71 [kvar], the second power converter 200 supplies the load 30 with the shortfall of reactive power Q2=approximately 71 [kvar].

As a result, active power P3 = 50 [kW] is input to second power converter 200, and reactive power Q2 = about 71 [kvar] is output, so apparent power S in second power converter 200 is about 87 [kVA]. Here, the second threshold S2 is set to 95 [kVA], like the first threshold S1. Note that the second threshold S2 may be a value smaller than the first threshold S1. Accordingly, control unit 210 determines that apparent power S (=approximately 87 [kVA]) in second power converter 200 is equal to or lower than second threshold value S2 (=95 [kVA]).

In the above, an example of the values of the first threshold S1 and the second threshold S2 is shown, but the values of the first threshold S1 and the second threshold S2 are not particularly limited, and may be any numerical value, and are appropriately determined according to the equipment configuration. Also, the first threshold S1 and the second threshold S2 may not be fixed values, and the control unit 210 may change the value of the first threshold S1 or the second threshold S2 depending on the situation or based on a predetermined formula or predetermined rule.

Next, when control unit 210 determines that apparent power S is equal to or less than second threshold value S2, control unit 210 refers to the relationship between the voltage of power storage device 300 and the charging power target value as shown in FIG. For example, as shown in FIG. 7, when the voltage of power storage device 300 is V0, the charging power target value of power storage device 300 is 50 kW. When the voltage of power storage device 300 is V1, which is lower than V0, the charging power target value of power storage device 300 is greater than 50 kW. When the voltage of power storage device 300 is V2, which is higher than V0, the charging power target value of power storage device 300 is lower than 50 kW.

Therefore, control unit 210 acquires the voltage from power storage device 300 by measurement or the like, and compares the magnitude of the voltage with V0. When control unit 210 determines that the voltage of power storage device 300 is lower than V0, control unit 210 determines that the chargeable capacity of power storage device 300 is greater than 50 kW because the charge power target value of power storage device 300 is greater than 50 kW. As a result, control unit 210 can determine that power storage device 300 can be charged with power greater than active power P3 = 50 [kW], and therefore determines to issue the second control command, and issues second control command R2 to increase the output of first power converter 100.

For example, the control unit 210 issues the second control command R2 to increase the output of the first power converter 100 at a constant rate of 1%. That is, the control unit 210 issues the second control command R2 to one first power converter 100 out of the plurality of first power converters 100 to increase the output at a constant rate of 1%. Thereby, the second control command R2 to increase the output at a constant rate of 1% is sequentially transmitted to each first power converter 100 via the control line 110 . Thus, the plurality of first power converters 100 receives the second control command R2 and increases the output at a constant rate of 1%.

Here, as described above, the amount of decrease in the output of the first power converter 100 in the first control command is, for example, 3%, and the amount of increase in the output of the first power converter 100 in the second control command is, for example, 1%. In this way, the command values in the first control command and the second control command are set such that the amount of decrease in the output of the first power converter 100 in the first control command is greater than the amount of increase in the output of the first power converter 100 in the second control command. Thereby, the control unit 210 issues the first control command or the second control command such that the amount of decrease in the output of the first power converter 100 in the first control command is greater than the amount of increase in the output of the first power converter 100 in the second control command.

Note that the command values in the first control command and the second control command are not limited to 3% and 1%, and may be any numerical values such as 5% and 3%, and are appropriately determined according to the equipment configuration and the like. Also, the command value does not have to be a fixed value, and control unit 210 may change the command value according to the situation or based on a predetermined formula or predetermined rule. For example, even if the control unit 210 determines to issue the second control command, if it determines that the power supplied to the power storage device 300 will exceed the charging power target value of the power storage device 300 if the current command value is used to issue the second control command, the control unit 210 may decrease the command value in the second control command. Alternatively, control unit 210 may gradually decrease or gradually increase the command value each time the first control command or the second control command is issued.

After that, the control unit 210 repeatedly compares the apparent power in the second power converter 200 with the first threshold value and the second threshold value, and issues a first control command or a second control command (S102 to S110).

When control unit 210 determines that the voltage acquired from power storage device 300 is V0 or more, it determines that the chargeable capacity of power storage device 300 is 50 kW or less because the target charging power value of power storage device 300 is 50 kW or less. Accordingly, control unit 210 determines that power storage device 300 cannot be charged with power greater than active power P3=50 [kW], and determines not to issue the second control command.

As described above, the process of controlling the output of the first power converter 100 by the control unit 210 of the second power converter 200 ends. Note that the time interval at which the control unit 210 executes the above control process is not particularly limited, such as 0.1 second, 1 second, 10 seconds, 1 minute, 10 minutes, etc., and an appropriate numerical value is determined by the user. Also, the control unit 210 may execute the control process at a timing arbitrarily determined by the user instead of executing the control process at regular time intervals.

[5 Explanation of effects]
As described above, according to the power converter 10 according to the present embodiment, the second power converter 200 connected to the power storage device 300 and supplying AC power to the load 30 is supplied with power from the first power converter 100 connected to the power generation facility 20 and supplying AC power to the load 30. That is, the AC power output from the first power converter 100 is divided and supplied to the load 30 and the second power converter 200 . Here, if there is a shortage of the active power and reactive power required by the load 30 that is not supplied from the first power converter 100 , the shortage must be supplied from the second power converter 200 to the load 30 . In this way, the second power converter 200 is supplied with active power and reactive power from the first power converter 100 and supplies active power and reactive power to the load 30, so the values of the active power and reactive power in the second power converter 200 change according to the situation.

Therefore, since the value of the apparent power in the second power converter 200 changes, the value of the apparent power may become too large or too small. If the value of the apparent power becomes too large, the second power converter 200 may receive the apparent power exceeding the acceptable capacity, and if the value of the apparent power becomes too small, the second power converter 200 may not be able to supply sufficient power to the power storage device 300.

Therefore, the control unit 210 of the second power converter 200 issues a control command to increase or decrease the output of the first power converter 100 according to the magnitude relationship between the apparent power in the second power converter 200 and a predetermined threshold. As a result, the values of active power and reactive power output from the first power converter 100 are adjusted, so the values of active power and reactive power supplied from the first power converter 100 to the second power converter 200 can be adjusted. Therefore, since the value of the apparent power in the second power converter 200 can be adjusted, the occurrence of trouble in the second power converter 200 (the power converter connected to the power storage device 300 and supplying power to the load 30) can be suppressed.

Moreover, the power generation equipment 20 connected to the first power converter 100 is the power generation equipment 20 that generates power using renewable energy. Here, power generation by renewable energy such as photovoltaic power generation or wind power generation fluctuates greatly in output. Therefore, since the output of the first power converter 100 tends to increase or decrease, the values of active power and reactive power supplied from the first power converter 100 to the second power converter 200 also tend to increase or decrease. As a result, since the value of the apparent power in the second power converter 200 tends to become too large or too small, by adjusting the value of the apparent power according to the present invention, it is possible to effectively suppress the occurrence of problems in the second power converter 200.

In addition, since power is supplied to the second power converter 200 from a plurality of first power converters 100, the values of active power and reactive power supplied to the second power converter 200 tend to increase or decrease. Therefore, since the value of the apparent power in the second power converter 200 tends to become too large or too small, the control unit 210 of the second power converter 200 increases or decreases the output of the plurality of first power converters 100 according to the control command. As a result, the value of the apparent power in the second power converter 200 can be adjusted, so that the occurrence of problems in the second power converter 200 can be suppressed.

Further, the control unit 210 of the second power converter 200 issues a control command to one first power converter 100 out of the plurality of first power converters 100, whereby the control command is transmitted between the plurality of first power converters 100 via the control line 110. As a result, the control unit 210 of the second power converter 200 can easily increase or decrease the outputs of the plurality of first power converters 100 to adjust the value of the apparent power in the second power converter 200. Therefore, the occurrence of problems in the second power converter 200 can be suppressed.

In addition, since the control unit 210 of the second power converter 200 increases or decreases the output of the first power converter 100 at a constant rate, the larger the output of the first power converter 100, the greater the increase or decrease of the output. That is, the control unit 210 of the second power converter 200 greatly increases or decreases the output of the first power converter 100 because the output of the first power converter 100 tends to increase or decrease as the output of the first power converter 100 increases. As a result, the control unit 210 of the second power converter 200 can adjust the value of the apparent power in the second power converter 200 according to the magnitude of the output of the first power converter 100, so that the second power converter 200 can be prevented from malfunctioning.

Further, even when the outputs of the plurality of first power converters 100 are different, the control unit 210 of the second power converter 200 gives a control instruction of a constant ratio to the plurality of first power converters 100, so that the plurality of first power converters 100 can be provided with a control instruction that increases or decreases more as the output increases. In this way, the control section 210 of the second power converter 200 can give control instructions to the plurality of first power converters 100 according to the magnitude of the output.

Further, when the first power converter 100 outputs AC power with a large power factor, etc., and the first power converter 100 cannot supply sufficient reactive power to the load 30, the second power converter 200 needs to supply reactive power to the load 30. In this case, active power is input to the second power converter 200 from the first power converter 100, but reactive power is output from the second power converter 200 to the load 30, so that the apparent power in the second power converter 200 becomes a value larger than the input active power. That is, even if the value of the active power input to the second power converter 200 is equal to or less than the first threshold value indicating the acceptable capacity of the second power converter 200, the apparent power in the second power converter 200 may exceed the first threshold value. Therefore, the control unit 210 of the second power converter 200 issues the first control command to decrease the output of the first power converter 100 when the apparent power in the second power converter 200 exceeds the first threshold. As a result, the apparent power supplied from the first power converter 100 to the second power converter 200 can be reduced, so the apparent power in the second power converter 200 can be reduced. Therefore, since it is possible to suppress the apparent power in the second power converter 200 from exceeding the first threshold value, it is possible to suppress the occurrence of troubles in the second power converter 200 .

Further, the control unit 210 of the second power converter 200 repeats the first control command until the apparent power in the second power converter 200 becomes equal to or less than the first threshold, thereby reducing the apparent power to equal to or less than the first threshold. Thereby, it is possible to suppress the occurrence of troubles in the second power converter 200 .

In addition, the apparent power in the second power converter 200 may become a small value due to a decrease in the active power input from the first power converter 100 to the second power converter 200 or a decrease in reactive power output from the second power converter 200 to the load 30. In other words, when the apparent power in the second power converter 200 is equal to or lower than the second threshold value indicating the value required to sufficiently charge the power storage device 300, the power storage device 300 may not be sufficiently charged. Therefore, the control unit 210 of the second power converter 200 issues a second control command to increase the output of the first power converter 100 when the apparent power in the second power converter 200 is equal to or less than the second threshold. As a result, it is possible to increase the apparent power in the second power converter 200 and prevent the apparent power from becoming equal to or less than the second threshold value, thereby preventing problems from occurring in the second power converter 200.

Moreover, when the apparent power in the second power converter 200 is large, the apparent power may exceed the acceptable capacity of the second power converter 200 and may affect the equipment of the second power converter 200 itself. On the other hand, when the apparent power in the second power converter 200 is small, there is a problem that the power storage device 300 cannot be sufficiently charged, but the equipment itself of the second power converter 200 or the power storage device 300 is unlikely to be affected. Thus, it is more necessary to decrease the apparent power in the second power converter 200 when the apparent power is large than to increase the apparent power when the apparent power is small. Therefore, the control unit 210 of the second power converter 200 issues the first control command or the second control command such that the amount of decrease in the output of the first power converter 100 in the first control command is greater than the amount of increase in the output of the first power converter 100 in the second control command. As a result, when the apparent power in the second power converter 200 is large, the apparent power can be reduced relatively quickly, so that the second power converter 200 can be protected. In this way, appropriate measures can be taken according to the magnitude of the problem that may occur in the second power converter 200 .

Further, even if the apparent power in the second power converter 200 is equal to or less than the second threshold, if the chargeable capacity of the power storage device 300 is small because the power storage device 300 is sufficiently charged, it is not necessary to increase the power supplied to the power storage device 300. That is, in this case, since it is not necessary to increase the apparent power in the second power converter 200 , it is not necessary to increase the output of the first power converter 100 . Therefore, control unit 210 of second power converter 200 determines whether or not to issue the second control command according to the magnitude of the chargeable capacity of power storage device 300 . Thereby, the control unit 210 of the second power converter 200 can determine not to issue the second control command to increase the output of the first power converter 100 even when the apparent power in the second power converter 200 is equal to or lower than the second threshold. Thus, the control unit 210 of the second power converter 200 can issue an appropriate control command considering the state of charge of the power storage device 300 .

[6 Description of modified example]
Although the power converter 10 according to the present embodiment has been described above, the present invention is not limited to the above embodiment. In other words, the embodiments disclosed this time are illustrative in all respects and are not restrictive, and the scope of the present invention is indicated by the claims, and includes all changes within the meaning and scope equivalent to the claims.

For example, in the above embodiment, the power conversion device 10 includes a plurality of first power converters 100 , second power converters 200 and power storage devices 300 . However, the power converter 10 may include only one first power converter 100, or may include a plurality of other components, and the number of components included in the power converter 10 is not particularly limited. Moreover, the power conversion device 10 may be configured not to include components other than the second power converter 200 . For example, the power electronics device 10 may not include the power storage device 300 and may be connected to an external power storage device to charge and discharge the external power storage device. Moreover, the power conversion device 10 may not include the first power converter 100 and may be connected to an external first power converter to control the external first power converter.

Further, in the above embodiment, the power generation facility 20 is a power generation facility that generates power using renewable energy such as a solar power generation facility or a wind power generation facility, and outputs DC power to the first power converter 100. However, the power generation facility 20 may be a power generation facility that generates power without using renewable energy and outputs DC power to the first power converter 100 . Alternatively, the power generation equipment 20 may be a power generation equipment that generates power using renewable energy, or a power generation equipment that outputs AC power such as geothermal power generation equipment or biomass power generation equipment. Alternatively, the power generation facility 20 may be a power generation facility that generates power without using renewable energy and outputs AC power to the first power converter 100 . When the power generation equipment 20 outputs DC power, the first power converter 100 is a device having a DC/AC inverter function, but when the power generation equipment 20 outputs AC power, the first power converter 100 may be a device having an AC/AC converter function.

Moreover, in the above-described embodiment, the power conversion device 10 is configured to be connectable to the power system 40 . However, the power converter 10 may be configured to be unconnectable to the power system 40 . In other words, the power conversion device 10 may be configured to always perform self-sustained operation.

Moreover, in the above-described embodiment, the second power converter 200 has the control unit 210 and the storage unit 220 . However, the second power converter 200 does not include the storage unit 220, and may store information in an external recording medium and acquire the information from the recording medium.

Further, in the above embodiment, the control unit 210 of the second power converter 200 issues a control command to one first power converter 100 to increase or decrease the output of the plurality of first power converters 100 via the control line 110. However, the control unit 210 may increase or decrease the outputs of the plurality of first power converters 100 by issuing control commands to all of the plurality of first power converters 100 . Also, the control unit 210 may increase or decrease the output of some first power converters 100 among the plurality of first power converters 100 instead of all of the plurality of first power converters 100 .

Moreover, in the above-described embodiment, the control unit 210 of the second power converter 200 issues a control command to increase or decrease the outputs of the plurality of first power converters 100 at a constant rate. However, the control unit 210 may issue a control command to increase or decrease the outputs of the plurality of first power converters 100 by a constant amount instead of a constant ratio. Alternatively, the control unit 210 may issue a control command to increase or decrease the output of the first power converter 100 by a different ratio or a different amount for each first power converter 100 .

Further, in the above-described embodiment, the control unit 210 of the second power converter 200 repeats the first control command and the second control command. However, the control unit 210 may issue the first control instruction and the second control instruction only once, or may issue only one of the first control instruction and the second control instruction.

Further, in the above embodiment, the control unit 210 of the second power converter 200 issues the first control command or the second control command such that the amount of decrease in the first control command is greater than the amount of increase in the second control command. However, the control unit 210 may issue the first control command or the second control command such that the amount of decrease in the first control command is less than or equal to the amount of increase in the second control command.

Further, in the above embodiment, the control unit 210 of the second power converter 200 determines whether or not to issue the second control command when it is determined that the apparent power in the second power converter 200 is equal to or less than the second threshold. However, when the control unit 210 determines that the apparent power in the second power converter 200 is equal to or less than the second threshold value, the control unit 210 may issue the second control command.

The present invention can also be implemented as a control method for the power conversion device 10 including processing performed in the power conversion device 10 . That is, the control method of the power conversion device 10 is a control method performed by the power conversion device 10 provided with a second power converter 200 connected to the power generation equipment 20 to supply AC power to the load 30 and connected to the power storage device 300 to supply AC power to the load 30. Provides a control command to increase or decrease the output.

Further, the present invention can also be implemented as a program for executing processes included in the control method of the power converter 10 . That is, the control unit 210 of the second power converter 200 may be realized by reading and executing a software program recorded in a recording medium such as a hard disk or a semiconductor memory by a program execution unit such as a CPU or processor. Furthermore, the present invention can be implemented as a computer-readable non-temporary recording medium in which the program is recorded, such as a flexible disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray (registered trademark) Disc), semiconductor memory. The program can be distributed via the recording medium and a transmission medium such as the Internet.

The present invention can also be implemented as an integrated circuit that includes the processing unit included in the power conversion device 10 . That is, each functional block of the second power converter 200 shown in FIG. 2 may be implemented as an LSI (Large Scale Integration) integrated circuit. These may be made into one chip individually, or may be made into one chip so as to include part or all of them. Although LSI is used here, it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration. Also, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after the LSI is manufactured, or a reconfigurable processor that can reconfigure the connections and settings of the circuit cells inside the LSI may be used. Furthermore, if an integration technology that replaces the LSI appears due to advances in semiconductor technology or another derived technology, the technology may naturally be used to integrate the functional blocks. Adaptation of biotechnology, etc. is possible.

In this way, the second power converter 200 may be configured with dedicated hardware for each component, or may be realized by executing a software program suitable for each component.

Moreover, the form constructed by combining arbitrary components in the above embodiment and its modification is also included in the scope of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be applied to a power converter or the like that includes a power converter that is connected to a power storage device to supply power to a load.

10 power conversion device 20 power generation facility 30 load 40 power system 41 switch 100 first power converter 110 control line 200 second power converter 210 control unit 220 storage unit 221 control data 300 power storage device

Claims (12)

Power is supplied from a first power converter connected to a power generation facility to supply AC power to a load, and a second power converter connected to a power storage device to supply AC power to the load,
The second power converter has a control unit that controls the output of the first power converter,
The control unit issues a control command to increase or decrease the output of the first power converter according to the magnitude relationship between the apparent power of the second power converter and a predetermined threshold. The power converter according to claim 1, wherein the power generation facility is a power generation facility that generates power using renewable energy. Power is supplied to the second power converter from a plurality of the first power converters,
The power converter according to claim 1 or 2, wherein the control unit increases or decreases outputs of the plurality of first power converters by issuing the control command. The power conversion device according to claim 3, wherein the control unit increases or decreases the output of the plurality of first power converters via control lines connected to the plurality of first power converters by issuing the control command to one of the plurality of first power converters. The power converter according to any one of claims 1 to 4, wherein the control unit issues the control command to increase or decrease the output of the first power converter at a constant rate. The power conversion device according to any one of claims 1 to 5, wherein the control unit performs a first control command to reduce the output of the first power converter when the apparent power in the second power converter exceeds the first threshold. The power converter according to claim 6, wherein the control unit repeats the first control command until the apparent power in the second power converter becomes equal to or less than the first threshold. The power conversion device according to any one of claims 1 to 7, wherein the control unit performs a second control command to increase the output of the first power converter when the apparent power in the second power converter is equal to or less than the second threshold. The power conversion device according to claim 8, wherein the control unit performs the first control command or the second control command such that the amount of decrease in the output of the first power converter in the first control command for decreasing the output of the first power converter when the apparent power in the second power converter exceeds the first threshold is greater than the amount of increase in the output of the first power converter in the second control command. The power conversion device according to claim 8 or 9, wherein the control unit determines whether or not to issue the second control command according to a chargeable capacity of the power storage device. moreover,
The power converter according to any one of claims 1 to 10, comprising the first power converter and the power storage device. Power is supplied from a first power converter connected to a power generation facility to supply AC power to a load, and a second power converter connected to a power storage device to supply AC power to the load A control method performed by a power conversion device,
A power converter control method in which the second power converter issues a control command to increase or decrease the output of the first power converter according to the magnitude relationship between the apparent power of the second power converter and a predetermined threshold.

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