WO2021200902A1

WO2021200902A1 - Direct-current bus control system

Info

Publication number: WO2021200902A1
Application number: PCT/JP2021/013467
Authority: WO
Inventors: 克彦津野; 藤井　克司; 佳代小池; 和田　智之
Original assignee: 国立研究開発法人理化学研究所
Priority date: 2020-03-31
Filing date: 2021-03-30
Publication date: 2021-10-07
Also published as: JPWO2021200902A1

Abstract

A direct-current bus control system that controls power fluctuation at a direct-current bus that connects an input power supply and a load, the direct-current bus control system including: a principal stabilization device that bidirectionally exchanges direct-current power between a first charging/discharging element and the direct-current bus such that the voltage of the direct-current bus coincides with a bus voltage target value; and an auxiliary stabilization device that exchanges direct-current power between a second charging/discharging element, a charging element, or a discharging element and the direct-current bus such that current flows at a current target value that is found in accordance with the difference between a threshold value for charging or discharging and the voltage of the direct-current bus. The principal stabilization device finds the bus voltage target value on the basis of: a target value that corresponds to a first stored power indicator for the first charging/discharging element; and a second stored power indicator that is found by a different method than the first stored power indicator for the first charging/discharging element and is not dependent on charging/discharging efficiency.

Description

DC bus control system

This disclosure relates to a DC bus control system.

In recent years, power supply systems that use renewable energy such as solar power, wind power, and wave power have been attracting attention as alternative power sources for fossil energy and nuclear energy, and some of these have already been put into practical use.

In this type of power supply system, the generated power fluctuates greatly depending on the weather, season, location, etc. Therefore, in order to maintain the voltage of the DC bus to which the power supply system is connected within a predetermined allowable range, the power supply of a solar cell, a wind power generator, etc. is supplied to the DC bus via a power converter having a wide input range and a large capacity. It is desirable to connect to. However, in that case, increasing the capacity of the power converter leads to an increase in size, complexity, and cost of the entire system.

The applicant has proposed a control system for efficiently controlling the power fluctuation of the DC bus caused by the fluctuation of the input power supply and the load (Patent Document 1). In the control system of Patent Document 1, the main stabilizer controls the DC bus voltage based on the storage amount index to control the power storage device such as a fuel cell or a water electrolysis cell.

The storage amount index used here is the charge rate (SOC) of the power storage device in the main stabilizer, and is obtained as a value obtained by integrating the charge / discharge current by calculation. The power storage device used in the main stabilizer generally cannot extract all of the energy used for charging by electric discharge. Moreover, it is not possible to accurately determine the ratio of energy taken out by electric discharge. For this reason, there is a discrepancy between the amount of electricity stored (calculated value) used for control and the actual amount of electricity stored. As a result, each time the main stabilizer repeatedly charges and discharges the power storage device, the discrepancy between the power storage amount of the power storage device and the calculated value increases. Saturates the amount of electricity stored. As a result, the DC bus cannot be controlled and the system cannot operate.

In order to avoid this problem, it is conceivable to measure the charge / discharge efficiency and correct the charge rate, but in general, the charge / discharge efficiency depends on the temperature, current, etc., so accurate correction is difficult. Therefore, in the future, there will be a discrepancy between the calculated value and the actual value of the amount of electricity stored, and it will be difficult to operate the system in a long-term and stable manner.

Also, the accurate value of the amount of electricity stored can be obtained by stopping charging and discharging, but continuous operation will be hindered.

International Publication No. 2019/103059

INDUSTRIAL APPLICABILITY The present invention can efficiently control the power fluctuation of the DC bus caused by the fluctuation of the input power supply and the load, and avoids the depletion of the stored amount of the main stabilizer and the stop of the control due to saturation. The purpose is to provide a control system capable of continuous operation in a long-term and stable manner.

One aspect of the present invention is a DC bus control system that controls power fluctuations of a DC bus that connects an input power source and a load, and mainly includes a first charge / discharge element and a first power converter. The first power converter comprises a stabilizer and a second charge / discharge element, a charge element, or at least one quasi-stabilizer having a discharge element and a second power converter, wherein the first power converter is a bus voltage. A target value is obtained, and DC power is bidirectionally transferred between the first charge / discharge element and the DC bus so that the voltage of the DC bus matches the bus voltage target value. The second power converter obtains a current target value according to the difference between the threshold value for charging or discharging the second charging / discharging element, the charging element, or the discharging element and the voltage of the DC bus, and obtains the current target value. DC power is transferred between the second charge / discharge element, charge element, or discharge element and the DC bus so that a current equal to the value flows through the second charge / discharge element, charge element, or discharge element. The first power converter has a target value corresponding to a first charge / discharge amount index of the first charge / discharge element and the first charge / discharge element of the first charge / discharge element. The bus voltage target value is obtained based on a second storage amount index obtained by a method different from the quantity index.

According to the present invention, it is possible to efficiently control the power fluctuation of the DC bus caused by the fluctuation of the input power supply and the load, and to control the storage amount of the main stabilizer to be constant for a long period of time. Therefore, it is possible to provide a control system capable of continuous operation over a long period of time and stably.

It is an overall block diagram of the DC bus control system which concerns on embodiment. It is a block diagram which shows another example of the metastability apparatus in embodiment. It is a block diagram which shows one configuration example of the power converter in a photovoltaic power generation system. It is a block diagram which shows one configuration example of the power converter in a main stabilizer. It is a block diagram which shows one configuration example of the power converter in a metastabilizer. It is a block diagram which shows one configuration example of the power converter in a metastabilizer. It is a conceptual diagram which schematically shows the relationship between the charge / discharge electric power of a power storage device, the input electric power of a water electrolysis cell, the output electric power of a fuel cell, etc., and a bus voltage. It is operation explanatory drawing of the main stabilizer. It is operation explanatory drawing of the main stabilizer. It is operation explanatory drawing of the main stabilizer. It is operation explanatory drawing of the metastability device. It is operation explanatory drawing of the metastability device. It is operation explanatory drawing of the metastability device. It is operation explanatory drawing of the metastability device. It is a figure which shows the simulation result of the system which concerns on 1st Embodiment. It is a figure which shows the simulation result of the system which concerns on the prior art example. It is a figure explaining the system problem which concerns on the prior art example. It is a figure explaining the system problem which concerns on the prior art example. It is a figure which shows the simulation result of the system which concerns on 2nd Embodiment.

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

<First Embodiment>
FIG. 1 is an overall configuration diagram of a DC bus control system according to this embodiment. The DC bus control system shown in FIG. 1 includes a photovoltaic power generation system 10 and a wind power generation system 20 which are renewable energy power supply systems as input power sources. These

power generation systems

10 and 20 are connected in parallel, and the output side thereof is connected to the DC bus 70. The photovoltaic power generation system 10 includes a solar cell 11 and a power converter 12, and the wind power generation system 20 includes a wind power generator 21 and a power converter 22.

The input power supply may be arbitrary. When the input power source is a renewable energy power source system, energy such as wave power or geothermal power may be used in addition to the above-mentioned ones, or hydraulic (small hydraulic) power generation, tidal power generation, tidal power generation, temperature. It may be a power supply system such as differential power generation. Further, these combinations may be used, including those described above.

Furthermore, the number of power supply systems connected in parallel with each other is not particularly limited.

The main stabilizer 30 and the

metastabilizers

40, 50, and 60 are connected to the DC bus 70, and the load 90 is connected to the DC bus 70.

The main stabilizer 30 sets a variable bus voltage target value within a predetermined allowable range centered on the reference bus voltage (reference voltage of the DC bus 70), and the output voltage on the DC bus 70 side is the bus voltage target value. The power converter 32 is operated so as to match the above, and the power storage device 31 is charged / discharged.

Further, the semi-stabilizing device 40 calculates an input / output current target value based on the difference between the charge / discharge threshold value and the voltage of the DC bus, and powers the input / output current so as to match the input / output current target value. The converter 42 is operated to control the charge / discharge of the power storage device 41.

Here, the

power storage devices

31 and 41 are, for example, a battery (secondary battery), an electric double layer capacitor, a capacitor, a flywheel, a redox flow battery, or the like. Further, the

power converters

32 and 42 are, for example, an isolated DC / DC converter or a chopper, and can transfer and receive DC power in both directions as shown by arrows.

In the quasi-stabilizer 50, the power converter 52 performs DC / DC conversion so that the input / output current matches the input / output current target value calculated based on the difference between the charge threshold value and the voltage of the DC bus. DC power is supplied to the water electrolysis cell 51 (a kind of charging operation), and water is electrolyzed to generate hydrogen gas and oxygen gas. Further, the quasi-stabilizer 60 supplies the DC power generated by the electrochemical reaction of the fuel cell 61 to the DC bus 70 via the power converter 62 (a kind of discharge operation), but at that time, the discharge threshold value. The power converter 62 performs DC / DC conversion so that the input / output current matches the input / output current target value calculated based on the difference between the voltage and the voltage of the DC bus.

The configurations of the quasi-stabilizing device 50 and the quasi-stabilizing device 60 described above are merely exemplary, and as an alternative to the water electrolysis cell 51, a CH system is obtained by electrochemically reducing carbon dioxide. A means for producing bonds (CH4, C2H4, etc.) or alcohol, or a means for producing ammonia by reducing nitrogen may be used, and as an alternative to the fuel cell 61, a fuel cell using alcohol or the like or a chemical substance may be used. It may be a power generation means for rotating a turbine or the like by burning (hydrogen, CH system, alcohol, ammonia, etc.).

FIG. 2 is another configuration example of the metastability device. As shown in the figure, the metastability device 50A having an integral structure may be used in which the above-mentioned

metastabilization devices

50 and 60 share the hydrogen storage device 53.

In FIG. 1, the

power storage devices

31 and 41 are capable of absorbing (charging) and discharging (discharging) DC power. Further, the water electrolysis cell 51 (and the hydrogen storage device 53 in FIG. 2) converts DC power into gas and stores it, and the fuel cell 61 (and the hydrogen storage device 53) converts gas into DC power for power generation. Operation is possible. The

power storage devices

31 and 41 constitute a charging / discharging element, the water electrolysis cell 51 (and the hydrogen storage device 53) constitutes a charging element, and the fuel cell 61 (and the hydrogen storage device 53) constitutes a discharging element.

As described above, each of the

stabilizers

30, 40, 50, and 60 is regarded as a power buffer that transfers DC power to and from the DC bus 70 by the operation of the

power converters

32, 42, 52, and 62, respectively. be able to. The main stabilizing device 30 and the semi-stabilizing device 40 are power buffers having a charging / discharging function, the semi-stabilizing device 50 is a power buffer having a charging function, and the semi-stabilizing device 60 is a power buffer having a discharging function.

The number of main stabilizers 30 having a bus voltage target value setting function may be one, but only the required number of metastabilizers may be provided according to the number of parallel power supply systems and the required power of the load 90. ..

The monitoring / indicating device 80 collects state information (voltage, current, temperature, etc.) of each of the

power generation systems

10 and 20, the main stabilizing device 30, and the

semi-stabilizing devices

40, 50, and 60, and monitors and operates the state. In addition to monitoring, operation commands (start / stop commands, etc.) for each part, charge / discharge threshold commands, etc. are generated based on these monitoring results. Various monitoring signals and commands can be transmitted / received between the monitoring / instruction device 80 and each of the above-described units by wire or wirelessly.

The load 90 may be a DC load such as a DC motor, or a DC / AC converter that converts DC power into AC power and an AC load thereof. Further, an AC power system may be connected to the DC bus 70 via a DC / AC converter.

Next, the configuration of each part in FIG. 1 will be described. In the configuration of FIG. 1, a solar power generation system 10 and a wind power generation system 20 are provided as input power sources.

The photovoltaic power generation system 10 and the wind power generation system 20 have a common function in that the generated power using renewable energy is converted into DC power by the

power converters

12 and 22 and supplied to the DC bus 70. Therefore, in the following, the solar power generation system 10 will be described as an example.

FIG. 3 is a block diagram showing a configuration example of the power converter 12 in the photovoltaic power generation system 10. The power converter 12 includes a DC / DC converter 12A and a control circuit 12B.

The DC / DC converter 12A converts the DC output voltage of the solar cell 11 into a DC voltage of a predetermined size by the operation of the semiconductor switching element and outputs it to the DC bus 70. For example, the DC / DC converter 12A is composed of a boost chopper. There is.

In the control circuit 12B that controls the DC / DC converter 12A, the output voltage and current of the solar cell 11 are detected by the voltage detector 12a and the current detector 12b, and these detected values are input to the MPPT control unit 12c. .. The MPPT control unit 12c searches for the maximum output point of the solar cell 11 by a mountain climbing method or the like and outputs it to the voltage / current control unit 12d.

The voltage / current control unit 12d sends a drive pulse generated by PWM (pulse width modulation) control or the like to the drive circuit 12e, and the drive circuit 12e is a semiconductor switching element of the DC / DC converter 12A based on the drive pulse. On and off.

Further, the voltage of the DC bus 70 is detected by the voltage detector 12f, and this bus voltage detection value is input to the comparison unit 12g together with the bus voltage target value sent from the main stabilizer 30 described later. The comparison unit 12g generates a control signal according to the deviation between the bus voltage detection value and the bus voltage target value, and outputs the control signal to the voltage / current control unit 12d.

The voltage / current control unit 12d calculates a drive pulse that matches the bus voltage detection value with the bus voltage target value based on the control signal. For example, the bus voltage detection value sets the bus voltage target value. If it exceeds, the control operation is performed so as to reduce the output voltage of the DC / DC converter 12A (including stopping the operation).

FIG. 4 is a block diagram showing a configuration example of the power converter 32 in the main stabilizer 30. The power converter 32 includes a DC / DC converter 32A and a control circuit 32B.

The DC / DC converter 32A has a function of bidirectionally transmitting and receiving DC power between the DC bus 70 and the power storage device 31 to control charging and discharging of the power storage device 31, and is an insulated type equipped with a semiconductor switching element. It is composed of a DC / DC converter, a chopper, and the like. A sensor 31a for detecting voltage / current and temperature is installed in the power storage device 31.

The configuration of the control circuit 32B is as follows.

The voltage of the DC bus 70 is detected by the voltage detector 32a, and the bus voltage target value calculation unit 32b calculates the bus voltage target value according to the first storage amount index of the power storage device 31. The calculation method of the bus voltage target value will be described later.

As the storage amount index, for example, a charge rate (SOC: State of Charge) obtained by integrating the charge / discharge current of the power storage device 31 detected by the sensor 31a can be used.

The offset integration unit 32c calculates the cumulative deviation of the bus voltage target value based on the difference (offset) between the second storage amount index of the power storage device 31 and the target value of the second storage amount index. The second storage amount index is an index of the storage amount of the power storage device 31 obtained by a method different from the first storage amount index. For example, the terminal voltage (battery voltage) of the power storage device 31 detected by the sensor 31a. Can be used.

Further, the target value of the second storage amount index can be the value of the second storage amount index corresponding to the predetermined storage amount or the storage rate. The predetermined storage amount or storage rate may be appropriately determined according to the requirements of the system. For example, it is conceivable to adopt a storage amount of 50% of the full charge, but the storage amount is not limited to this. For example, the predetermined storage amount or storage rate is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, fully charged. It may be 80%, or may be appropriately determined according to the purpose and application within the range of 47% to 54%, 45% to 55%, 40% to 60%, and 30% to 70% of the full charge. ..

The offset integration unit 32c obtains the above-mentioned cumulative deviation as a value corresponding to the integrated value of the difference between the second storage amount index and the target value, for example. More specifically, the cumulative deviation is obtained as a value obtained by multiplying a value obtained by integrating the difference between the second storage amount index and the target value by a predetermined gain.

Here, if the magnitude (absolute value) of the charge / discharge current of the power storage device 31 is larger than the predetermined value, the integral calculation is not performed, and if the magnitude of the charge / discharge current is smaller than the predetermined value, the integral calculation is performed. good. That is, the cumulative deviation may be obtained as a value obtained by integrating the difference between the second storage amount index and the target value of the storage amount index only when the magnitude of the charge / discharge current of the power storage device 31 is smaller than a predetermined value. As for the predetermined value here, for example, if the magnitude of the charge / discharge current of the power storage device 31 is smaller than that value, the second power storage amount index (for example, terminal voltage) accurately represents the power storage amount of the power storage device 31. It is determined as a value that can be expected.

The deviation between the bus voltage target value and the bus voltage detection value is calculated by the subtractor 32d, and the cumulative deviation is added to the voltage deviation by the adder 32e. The output of the subtractor 32d is a new bus voltage target value corrected by the cumulative deviation, and the new bus voltage target value is input to the charge / discharge control unit 32f.

The voltage / current, temperature, and charge / discharge threshold of the power storage device 31 are input to the charge / discharge control unit 32f, and the charge / discharge control unit 32f sets the bus voltage detection value to the bus while considering these input information. PWM control or the like is performed so as to match the voltage target value, and a drive pulse is generated. The drive circuit 32g turns on and off the semiconductor switching element of the DC / DC converter 32A according to the drive pulse. The DC / DC converter 32A controls the charging / discharging of the power storage device 31 as described above to match the bus voltage detection value with the bus voltage target value.

Generally, the amount of electricity stored in the electricity storage device 31 can be roughly estimated from the terminal voltage thereof. The terminal voltage varies depending on the magnitude of the charge / discharge current, but when the charge / discharge current is sufficiently small (when it is equal to or less than the above-mentioned predetermined value), the terminal voltage can be regarded as representing the amount of electricity stored in the power storage device 31. As a result of control by the main stabilizer, the charge / discharge current of the main stabilizer becomes 0 when a steady state with a small change in power generation or power consumption is achieved. Therefore, the terminal voltage when the steady state is achieved and the charge / discharge current is small can be used as an index representing the actual (accurate) amount of electricity stored in the power storage device 31. In the present embodiment, the difference between the terminal voltage and its target value is integrated, and the bus voltage is controlled by adding the obtained integrated value to the target value as a new target value. The control based on the integrated value of this error can be regarded as the integrated control of the PID control when the control based on the amount of stored electricity is regarded as the proportional control. As a result, the offset of the electricity storage index can be constantly removed. That is, the stored amount of the power storage device 31 can be maintained at the target value of the second storage amount index, and the continuous operation for a long period of time is stable without the actual stored amount of the power storage device 31 being exhausted or overflowing. You will be able to do it.

Further, the control circuit 32B (charge / discharge control unit 32f) stops the charge / discharge of the power storage device 31 for a very short time without affecting the control of the system, and forcibly provides a period during which the charge / discharge current becomes zero. May be good. The length of this period shall be such that the terminal voltage of the storage battery stabilizes so as to represent the actual amount of electricity stored. The control circuit 32B provides a period in which the charge / discharge current is set to 0 periodically or irregularly, measures the terminal voltage of the power storage device 31 during this period as a second storage amount index, and determines the difference from the target storage amount. By integrating and using it for control, the same effect as above can be expected.

The charge / discharge threshold value of the power storage device 31 may be set by the control circuit 32B by itself, or may be received as a command from the monitoring / indicating device 80 of FIG.

FIG. 5 is a block diagram showing a configuration example of the power converter 42 in the metastability device 40 of FIG. The power converter 42 includes a DC / DC converter 42A and a control circuit 42B. The power converter 42 has the same function as the power converter 32 of FIG. 4A in that DC power is bidirectionally transferred between the DC bus 70 and the power storage device 41. Similar to the power storage device 31, the power storage device 41 is provided with a sensor 41a for detecting voltage, current, and temperature. The control circuit 42B includes a voltage detector 42a, a comparison unit 42b, a subtractor 42c, a charge / discharge control unit 42d, and a drive circuit 42e.

The power converter 42 shown in FIG. 5 differs from the power converter 32 shown in FIG. 4A in the following points. In the control circuit 42B, the charge / discharge control unit 42d calculates the input / output current target value based on the deviation between the charge / discharge threshold value and the bus voltage detection value. The charge / discharge control unit 42d further performs charge / discharge control on the power storage device 41 so that the input / output current of the DC / DC conversion unit 42A matches the input / output current target value. Here, the charge / discharge threshold value may be a threshold value (charge threshold value and discharge threshold value) related to charge / discharge of the power storage device 41, and the input / output current target value may be set according to the difference between the threshold value and the voltage of the DC bus 70. ..

Further, the comparison unit 42b provided in the control circuit 42B compares the charge / discharge threshold value of the power storage device 41 with the bus voltage detection value, and charges or discharges a charge command or a charge command or a charge command according to the magnitude relationship between the discharge threshold value and the bus voltage detection value. A discharge command is output to control the operation of the charge / discharge control unit 42d. The charge / discharge threshold value may be set by the control circuit 42B by itself, or may be received as a command from the monitoring / indicating device 80.

FIG. 6 is a block diagram showing a configuration example of the power converter 52 in the metastability device 50. The power converter 52 includes a DC / DC converter 52A and a control circuit 52B.

The DC / DC converter 52A has a function of converting the DC power of the DC bus 70 into a predetermined size and supplying it to the water electrolysis cell 51, and is an isolated DC / DC converter or chopper equipped with a semiconductor switching element. It is composed of etc. The water electrolysis cell 51 electrolyzes water using the DC power supplied from the DC / DC conversion unit 52A, and stores the generated hydrogen gas in an external storage device (not shown), in other words, a kind. Performs charging operation.

The control circuit 52B that controls the DC / DC converter 52A is generally configured in the same manner as the control circuit 42B in FIG.

That is, in the control circuit 52B of FIG. 6, the voltage of the DC bus 70 is detected by the voltage detector 52a, the deviation between the charging threshold and the bus voltage detected value is calculated by the subtractor 52c, and this voltage deviation is the charging control. It is input to the unit 52d. Further, the bus voltage detection value is input to the comparison unit 52b together with the charge threshold value, and the comparison unit 52b outputs a charge command to the charge control unit 52d when the bus voltage detection value exceeds the charge threshold value. Here, the charge threshold value corresponds to the starting voltage of electrolysis by the water electrolysis cell 51. That is, the charging threshold is a threshold for charging the water electrolysis cell 51.

The charge control unit 52d calculates the input / output current target value based on the voltage deviation input from the subtractor 52c, and charges the input / output current of the DC / DC conversion unit 52A so as to match the input / output current target value. A drive pulse as a command is generated and output to the drive circuit 52e. In the drive circuit 52e, DC power is supplied to the water electrolysis cell 51 to electrolyze water by turning on and off the semiconductor switching element of the DC / DC conversion unit 52A according to the drive pulse.

The DC / DC conversion unit 52A operates so as to match the input / output current with the input / output current target value while controlling the DC power supplied to the water electrolysis cell 51 by the above operation.

Regarding the semi-stabilizing device 60 of FIG. 1, the power generation operation by the fuel cell 61 is considered as a discharging operation, and the water electrolysis cell 51, the charging threshold, and the charging control unit 52d of the semi-stabilizing device 50 shown in FIG. 6 are fueled, respectively. The battery 61, the discharge threshold, and the discharge control unit may be replaced with each other. The discharge threshold value in this case corresponds to the starting voltage of power generation by the fuel cell 61.

In the quasi-stabilizer 60, when the bus voltage detection value falls below the discharge threshold, a drive pulse corresponding to the discharge command is output to the discharge control unit to operate the DC / DC conversion unit, and the power generated by the fuel cell 61 is generated. , Is supplied to the DC bus 70 via the DC / DC conversion unit.

The DC / DC converter operates so as to match the input / output current with the input / output current target value while controlling the generated power of the fuel cell 61 by the above operation.

The water electrolysis cell 51 and the fuel cell 61 are also provided with sensors for detecting voltage, current, temperature, etc., and these detected values are input to the charge control unit 52d and the discharge control unit. The illustration is omitted.

Further, the charge threshold value and the discharge threshold value may be set by each control circuit by themselves, or may be received as a command from the monitoring / instruction device 80.

The configurations and operations of the

power converters

12, 32, 42, and 52 shown in FIGS. 3 to 6, and particularly the control circuits 12B, 32B, 42B, and 52B, are merely exemplary and the techniques of the present invention. Needless to say, the target range is not limited, and a configuration different from these may be adopted.

Next, FIG. 7 shows the charge / discharge power of the power storage device 41 of the quasi-stabilizer 40 according to the voltage of the DC bus 70, the input power of the water electrolysis cell 51 of the quasi-stabilizer 50, and the fuel of the quasi-stabilizer 60. It is a conceptual diagram which shows each of the output power of a battery 61 schematically. The horizontal width of the triangle symbol in FIG. 7 indicates the magnitude of each electric power, and the wider the width, the larger the electric power value.

FIG. 7 illustrates a case where the input power source is a renewable energy power source system, and the renewable energy power source system is, for example, the solar power generation system 10 and / or the wind power generation system 20 of FIG. The charge / discharge operation of each part is controlled according to the voltage of the DC bus 70 to which the generated power is supplied, the charge / discharge threshold of the power storage device 41, the water electrolysis cell 51, the fuel cell 61, and the like.

For example, as shown in (a) regarding the power storage device 41, the higher the bus voltage is higher than the charge threshold of the power storage device 41, the larger the charging power supplied to the power storage device 41, and the bus voltage is the discharge threshold of the power storage device 41. The lower the value, the larger the discharge power discharged from the power storage device 41. Similarly, the higher the bus voltage is higher than the charging threshold of the water electrolysis cell 51, the larger the charging power supplied to the water electrolysis cell 51, and the lower the bus voltage is lower than the discharge threshold of the fuel cell 61, the more the fuel cell 61 The discharge power generated from is large.

Regarding the power storage device 41, (b) is a case where the charge threshold value and the discharge threshold value are set lower than (a) according to the reference bus voltage, and (c) is a case where the charge threshold value and the discharge threshold value are set higher than (a). .. The same threshold setting change operation is also possible for the charge threshold of the water electrolysis cell 51 and the discharge threshold of the fuel cell 61.

In this way, the DC bus 70 and the

semi-stabilizing devices

40, 50, and 60 are controlled by changing the charge threshold and the discharge threshold of the power storage device 41, the water electrolysis cell 51, and the fuel cell 61 to control the charge / discharge operation. The DC power delivered to and from is individually adjusted. In other words, it is possible to finely control the operation of each power buffer.

As described above, the charge threshold value and the discharge threshold value can be changed based on the command from the monitoring / indicating device 80, or the

power converters

42, 52, and 62 can perform themselves.

8A and 8B are operation explanatory views of the main stabilizer 30.

As shown by a broken line (thick line) in FIG. 8A, the main stabilizer 30 transfers DC power between the DC bus 70 and the power storage device 31 to control the charge / discharge of the power storage device 31. The control circuit 32B in the power converter 32 sets a bus voltage target value based on the first storage amount index (for example, charge rate) of the power storage device 31 according to the characteristics shown in FIG. 8B, for example.

This bus voltage target value is set so as to be higher as the first storage amount index is larger and lower as the first storage amount index is smaller within the allowable range of the voltage of the DC bus 70, and this bus voltage target value is set. The control circuit 32B controls the DC / DC converter 32A so that the bus voltage detection values match.

9A and 9B are operation explanatory views of the

metastabilizing devices

40 and 50.

As shown by a broken line (thick line) in FIG. 9A, the power converter 42 of the quasi-stabilizer 40 charges the power storage device 41 using the DC power of the DC bus 70, and the power converter 52 of the quasi-stabilizer 50 The DC power of the DC bus 70 is supplied to the water electrolysis cell 51 to electrolyze the water.

The charging characteristics in this case are as shown in FIG. 9B, and the

power converters

42 and 52 are controlled so that the charging current increases as the voltage of the DC bus 70 becomes higher than the charging threshold of the power storage device 41 or the water electrolysis cell 51, respectively. do.

10A and 10B are operation explanatory views of the

metastabilizing devices

40 and 60.

As shown by a broken line (thick line) in FIG. 10A, the power converter 42 of the quasi-stabilizer 40 discharges the power storage device 41 to supply DC power to the DC bus 70, and the power converter 62 of the quasi-stabilizer 60. Operates the fuel cell 61 to generate electricity and supplies DC power to the DC bus 70.

The discharge characteristics in this case are as shown in FIG. 10B, and the

power converters

42 and 62 are controlled so that the discharge current increases as the voltage of the DC bus 70 becomes lower than the discharge threshold of the power storage device 41 or the fuel cell 61, respectively. ..

According to the DC bus control system according to the present embodiment, changes in the power input / output balance of the entire system are first dealt with by current input / output to the main stabilizing device 30 (storage device 31) having a fast response speed. By doing so, the response to other devices is relaxed. At this time, when the current flows into the main stabilizing device 30, the first storage amount index is increased by charging the power storage device 31, and the bus voltage is raised. On the contrary, in the case of the outflow of the current from the main stabilizer 30, the discharge of the power storage device 31 reduces the first storage amount index and lowers the bus voltage. These operations are performed by the power converter 32 (DC / DC converter 32A and control circuit 32B) of the main stabilizer 30.

On the other hand, the metastabilizing device charges or discharges by increasing or decreasing the amount of current flowing into the charging element or the discharging element according to the fluctuation of the bus voltage. This operation is performed by the power converter of the metastabilizer.

These series of operations are performed so that the current input / output to the main stabilizer 30 becomes zero, and as a result, the total current input / output to the entire system is controlled to be zero. Therefore, at a certain DC bus voltage, a steady state is reached when the inflow / outflow of the current of the metastability device reaches a constant value.

According to this embodiment, since the operation of each device is performed in an analog manner using the voltage of the DC bus line as a signal, the system control can be performed by the distributed processing by the operation of each device, and the centralized overall control is performed. Is not needed. As a result, the problem of error, which is a problem when centralized management is performed, can be solved. The reaction speed of the main stabilizer must follow the power fluctuations of the system, but since the main stabilizer absorbs the fast fluctuations, the operation of the semi-stabilizer can be relatively slow, and there is no problem. Since the direction of the current can also be controlled, it can be used in devices such as water electrolysis cells and fuel cells that can absorb or release electric power in only one direction and are not suitable for high-speed output fluctuations. Further, by setting the operating voltage threshold value of these devices and changing the inflow / outflow ratio of the current with respect to the DC bus voltage, it becomes possible to use a plurality of devices as metastabilizing devices. Further, since the operation signal of each device is the DC bus voltage, the number of metastabilizing devices can be increased or decreased relatively easily.

Further, according to the present embodiment, since the main stabilizing device 30 determines the target value of the DC bus voltage based on the second storage amount index of the power storage device 31, the storage amount of the power storage device 31 is determined. It can be kept constant, and long-term continuous operation can be performed stably.

The simulation performed to verify this effect will be described below.

FIG. 11 is a diagram showing a simulation result in the control system of the present embodiment. In this simulation, the charge rate (SOC) obtained by integrating the charge / discharge current of the power storage device 31 is used as the first storage amount index, and the terminal voltage (battery voltage) of the power storage device 31 is used as the second storage amount index. Was used. Further, 50V was set as the target value of the second storage amount index.

FIG. 11A shows the time-series changes of the generated power 1101, the power supply (input) power 1102, and the load (output) power 1103 of the solar cell. FIG. 11B shows the power consumption 1104 in the water electrolysis cell and the power generation 1105 in the fuel cell. When the system has a net input power, it is electrolyzed (charged) in the water electrolysis cell, and when it has a net output power, the DC current is supplied (discharged) by the electrochemical reaction of hydrogen in the fuel cell. Will be done.

FIG. 11C shows the time-series changes of the terminal voltage (battery voltage) 1106 and the charge / discharge current 1107 of the power storage device 31. It can be seen that the power storage device 31 terminal voltage 1106 is controlled so as to approach the target value of 50 V, and becomes 50 V at the timing when the power storage device 31 is not charged / discharged, that is, at the timing when the charge / discharge current is zero.

FIG. 12 shows a similar simulation result in the case where the power converter 32 of the main stabilizer 30 does not have the offset integrator 32c (that is, the configuration of Patent Document 1) as a comparative example. FIG. 12 (a) shows the time-series changes of the generated power 1201, the power supply (input) power 1202, and the load (output) power 1203 of the solar cell, which are the same changes as in FIG. 11 (a). FIG. 12B shows the power consumption 1204 in the water electrolysis cell and the power generated 1205 in the fuel cell, and shows almost the same changes as in FIG. 11B. FIG. 12C shows the time-series changes in the terminal voltage (battery voltage) 1206 and the charge / discharge current 1207 of the power storage device 31. In this comparative example, the generated power and the power consumption fluctuate, and the voltage 1206 (index of the actual stored amount) of the power storage device 31 decreases each time charging / discharging occurs.

As described above, in the DC bus control system according to the present embodiment, the power converter 32 in the main stabilizer 30 has an offset integrating unit 32c, and the power storage amount index (battery voltage) is constantly from the target value. Since the offset is removed, the battery voltage of the power storage device 31, that is, the power storage amount can be kept constant. Further, when the charge / discharge current of the power storage device 31 is large, the integration calculation of the battery voltage for offset calculation is not performed, so that the control based on the inaccurate storage amount can be prevented and stable operation can be performed. As described above, in the DC bus control system according to the present embodiment, since the power storage device 31 of the main stabilizer 30 can maintain a constant storage amount for a long period of time, stable and long-term continuous operation is possible. It becomes.

<Second embodiment>
In the DC bus control system according to the first embodiment, when the generated power is within the power absorption capacity of the water electrolysis cell and the power consumption of the load is within the power generation capacity of the fuel cell, the main stabilizer 30 is used. The charge / discharge current of the power storage device 31 is controlled to 0 and operates stably. When the generated power exceeds the power absorption capacity of the water electrolysis cell or the power consumption of the load exceeds the power generation capacity of the fuel cell, this system does not stop abnormally and the power storage device 31 absorbs or supplies the power. , Continuous operation is possible.

However, even when the generated power or the load power returns to the capacity of the water electrolysis cell or the fuel cell, the discharge or charge from the power storage device 31 of the main stabilizer 30 continues until the excessive storage amount is eliminated. Therefore, the control capability of this system temporarily decreases until the excessive amount of electricity is eliminated. This point will be described below.

The following description using FIGS. 13 to 15 is a diagram showing an operation in a configuration in which the offset integrating unit 32c is not provided in the main stabilizer 30 power converter 32 (that is, the configuration of Patent Document 1). ..

FIG. 13 is a diagram illustrating the operation of the system when the generated power and the load power are within the capacities of the water electrolysis cell and the fuel cell. FIG. 13A shows the time change of the generated power 1301 and the load power 1302. FIG. 13B shows the time variation of the power consumption 1303 of the water electrolysis cell and the power generated 1304 in the fuel cell. FIG. 13C shows the time change of the control target value 1305 of the bus voltage. FIG. 13D shows the time change of the voltage 1306 and the current 1307 of the power storage device 31.

As shown in FIG. 13, when the generated power and the load power are in an appropriate range, the charge / discharge current of the power storage device 31 is kept at 0, and the water electrolysis cell and the fuel cell operate according to the generated power and the load power. ..

FIG. 14 is a diagram illustrating the operation of the system when the generated power exceeds the power absorption capacity of the water electrolysis cell. FIG. 14A shows the time change of the generated power 1401 and the load power 1402. FIG. 14B shows the time variation of the power consumption 1403 of the water electrolysis cell and the power generated 1404 in the fuel cell. FIG. 14C shows the time change of the voltage 1405 and the current 1406 of the power storage device 31. FIG. 14D shows the time change of the control target value 1407 of the bus voltage.

Since the generated power exceeds the power absorption capacity of the water electrolysis cell, the power storage device 31 absorbs the surplus power, and the power storage amount of the power storage device 31 increases. Even if the generated power returns to the capacity of the system, discharge continues from the power storage device 31 of the main stabilizer 30 until the excessive storage amount of the power storage device 31 is eliminated (the period in the figure). T1). During this period, electric power is supplied only from the power storage device 31, and no electric power is supplied from the fuel cell. There is no power supply from the fuel cell because the bus voltage remains high. During this period, when the load power is supplied from this system, the power exceeding the power supply capacity of the power storage device 31 of the main stabilizer 30 cannot be supplied, and the system deviates from the control of the main control device. Become.

Here, the case where the generated power is excessive has been described, but the same problem occurs when the load power is excessive.

In this embodiment, this problem is dealt with as follows.

The bus voltage target value calculation unit 32b determines the bus voltage target value based on the first storage amount index of the power storage device 31. Here, the first storage amount index is a value obtained by integrating the charge / discharge current of the power storage device 31. In the present embodiment, an upper limit and a lower limit are set for the first storage amount index. The upper limit is a value corresponding to the maximum operation of charging the water electrolysis cell or the battery (a value indicating the maximum operation) or a value slightly higher than that. Further, the lower limit is a value corresponding to the maximum operation of the fuel cell or battery discharge (a value indicating the maximum operation) or a value slightly lower than that.

As a result, the relationship between the first storage amount index and the target value determined by the bus voltage target value calculation unit 32b is shown in FIG. 8C. Since the first storage amount index takes only a value between the lower limit value and the upper limit value, the bus voltage target value also takes a value corresponding to this range.

FIG. 15 is a diagram illustrating the operation of the system when power exceeding the power absorption capacity of the water electrolysis cell is supplied when the upper limit and the lower limit are set as described above for the first storage amount index. Here, the offset integration unit 32c does not perform the offset integration and the addition processing thereof.

FIG. 15 (a) shows the time change of the generated power 1501 and the load power 1502, which is the same as that of FIG. 14 (a). FIG. 15B shows the time variation of the power consumption 1503 of the water electrolysis cell and the power generation 1504 of the fuel cell. FIG. 15C shows the time change of the voltage 1505 and the current 1506 of the power storage device 31. FIG. 15E shows the time change of the control target value 1507 of the bus voltage. It should be noted that the vertical scale in FIG. 15 (d) is significantly different from the vertical scale in FIG. 14 (e).

As this result shows, the bus voltage drops in a short time after the state in which the generated power exceeds the power absorption capacity of the water electrolysis cell is resolved, charging in the water electrolysis cell is completed, and power is supplied from the fuel cell. Is possible. That is, by setting an upper limit on the first storage amount index, even if the generated power is excessive, the system can be returned to the normal state in a relatively short time after the situation is resolved.

When the load power is excessive, the same effect as described above can be obtained by setting the lower limit in the first storage amount index.

As shown in FIG. 15C, after the control of the system is restored, there is a difference between the first storage amount index (value obtained by calculation and used for control) and the actual storage amount of the power storage device 31. It turns out that it happens. If such errors in the amount of electricity stored are accumulated, there is a high possibility that the long-term operation of the system will be hindered.

In the DC bus control system according to the present embodiment, the main stabilizer 30 also considers the integrated value (cumulative deviation) of the difference between the second storage amount index (battery voltage) and its target value by the offset integrating unit 32c. The bus voltage target value is determined. Therefore, the difference between the calculated storage amount index (first storage amount index) and the actual storage amount as described above can be automatically eliminated in the long term.

That is, according to the present embodiment, when excessive power generation or power consumption occurs, normal control can be restored in a short time after the elimination, and stable continuous operation for a long period of time becomes possible.

10: Solar power generation system 11: Solar cell 12: Power converter 12A: DC / DC converter 12B: Control circuits 12a, 12f: Voltage detector 12b: Current detector 12c: MPPT control unit 12d: Voltage / current control unit 12e: Drive circuit 12g: Comparison unit 20: Wind power generation system 21: Wind power generator 22: Power converter 30: Main stabilizer 31: Power storage device 31a: Sensor 32: Power converter 32A: DC / DC conversion unit 32B: Control circuit 32a: Voltage detector 32b: Bus voltage target value calculation unit 32c: Offset integration unit 32d: Subtractor 32e: Adder 32f: Charge / discharge control unit 32g: Drive circuit 40: Semi-stabilizing device 41: Power storage device 41a: Sensor 42: Power converter 42A: DC / DC converter 42B: Control circuit 42a: Voltage detector 42b: Comparison unit 42c: Subtractor 42d: Charge / discharge control unit 42e: Drive circuit 50, 50A: Semi-stabilizer 51: Water electrolytic cell 52: Power converter 52A: DC / DC converter 52B: Control circuit 52a: Voltage detector 52b: Comparison unit 52c: Subtractor 52d: Charge control unit 52e: Drive circuit 53: Hydrogen storage device 60: Semi-stable Chemical device 61: Fuel cell 62: Power converter 70: DC bus 80: Monitoring / indicating device 90: Load

Claims

It is a DC bus control system that controls the power fluctuation of the DC bus that connects the input power supply and the load.
A main stabilizer having a first charge / discharge element and a first power converter,
Includes a second charge / discharge element, a charge element, or at least one metastabilizer having a discharge element and a second power converter.
The first power converter obtains a bus voltage target value, and DC power is supplied between the first charge / discharge element and the DC bus so that the voltage of the DC bus matches the bus voltage target value. Is configured to give and receive in both directions
The second power converter obtains a current target value according to the difference between the threshold value for charging or discharging the second charging / discharging element, the charging element, or the discharging element and the voltage of the DC bus, and obtains the current target value. DC power is applied between the second charge / discharge element, charge element, or discharge element and the DC bus so that a current equal to the target value flows through the second charge / discharge element, charge element, or discharge element. It is configured to give and receive,
The first power converter has a method different from the target value corresponding to the first storage amount index of the first charge / discharge element and the first storage amount index of the first charge / discharge element. The bus voltage target value is obtained based on the obtained second storage amount index.
A DC bus control system characterized by this.
The second storage amount index is the terminal voltage of the first charge / discharge element.
The bus voltage target value is a cumulative deviation obtained by integrating the difference between the second storage amount index and the target value into the target value corresponding to the first storage amount index of the first charge / discharge element. Obtained by adding the corresponding value,
The DC bus control system according to claim 1.
The cumulative deviation integrates the difference between the second storage amount index and the target value of the second storage amount index only when the magnitude of the charge / discharge current of the first charge / discharge element is smaller than a predetermined value. Is the value
The DC bus control system according to claim 2.
The first power converter is provided with a period during which the first charge / discharge element is not charged / discharged.
The cumulative deviation is a value obtained by integrating the difference between the second storage amount index and the target value of the second storage amount index for the period.
The DC bus control system according to claim 2 or 3.
The first storage amount index is a value obtained by integrating the charge / discharge currents of the first charge / discharge elements.
The DC bus control system according to any one of claims 1 to 4.
A predetermined upper limit and lower limit are set for the first storage amount index.
The DC bus control system according to claim 5.
The upper limit is a value corresponding to the maximum operation of charging of the second charging / discharging element or the charging element.
The lower limit is a value corresponding to the maximum operation of the second charge / discharge element or the discharge of the discharge element.
The DC bus control system according to claim 6.
The DC bus control system according to any one of claims 1 to 7, further including a renewable energy power supply system as the input power source.
The DC bus control system according to claim 8, further comprising the load.