DC Bus Control System

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

[Technical field]

[0001] The present disclosure relates to a DC bus control system. [Background technology]

[0002] 2. Description of the Related Art In recent years, power supply systems utilizing renewable energy sources such as solar, wind, and wave power have been attracting attention as alternative power sources to fossil energy and atomic energy, and some of these have already been put to practical use.

[0003] In this type of power supply system, the generated power varies 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, it is desirable to connect a power source such as a solar cell or a wind power generator to the DC bus via a power converter with a wide input range and large capacity. However, in that case, the increase in the capacity of the power converter leads to an increase in the size, complexity, and cost of the entire system.

[0004] The present applicant has proposed a control system for efficiently controlling power fluctuations in a DC bus caused by fluctuations in the input power source and load (Patent Document 1). In the control system of Patent Document 1, a main stabilization device controls the DC bus voltage based on a storage index, and controls a storage device such as a fuel cell or a water electrolysis cell.

[0005] The storage index used here is the state of charge (SOC) of the storage device in the main stabilization device, and is calculated as a value obtained by integrating the charge and discharge current. The storage device used in the main stabilization device generally cannot extract all of the energy used for charging by discharging. Furthermore, it is not possible to accurately calculate the proportion of energy extracted by discharging. This causes a discrepancy between the storage amount (calculated value) used for control and the actual storage amount. As a result, each time the main stabilization device repeatedly charges and discharges the storage device, the discrepancy between the storage amount of the storage device and the calculated value increases, and in the case of excessive discharging, the storage amount is depleted, and in the case of excessive charging, the storage amount is saturated. As a result, it becomes impossible to control the DC bus, and the system cannot operate.

[0006] To avoid this problem, it is possible to measure the efficiency of charging and discharging and correct the charging rate, but accurate correction is difficult because charging and discharging efficiency generally depends on temperature, current, etc. Therefore, a discrepancy will eventually occur between the calculated amount of stored energy and the actual value, making it difficult to operate the system stably over the long term.

[0007] In addition, although an accurate value for the amount of stored energy can be obtained by stopping charging and discharging and measuring it, this hinders continuous operation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2019 / 103059 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a control system that can efficiently control power fluctuations in a DC bus caused by fluctuations in the input power source and load, and can operate stably and continuously for a long period of time by avoiding the suspension of control due to depletion of the storage capacity of the main stabilization device or saturation. [Means for solving the problem]

[0010] One aspect of the present invention is a DC bus control system for controlling power fluctuations of a DC bus connecting an input power source and a load, the system including a main stabilization device having a first charge / discharge element and a first power converter, and at least one semi-stabilization device having a second charge / discharge element, a charging element, or a discharging element and a second power converter, the first power converter being configured to obtain a bus voltage target value and to bidirectionally exchange DC power between the first charge / discharge element and the DC bus so that the voltage of the DC bus coincides with the bus voltage target value, the second power converter being configured to obtain a bus voltage target value and to bidirectionally exchange DC power between the first charge / discharge element and the DC bus so that the voltage of the DC bus coincides with the bus voltage target value, or a current target value is calculated according to a difference between a threshold value for charging or discharging of a discharging element and the voltage of the DC bus, and DC power is exchanged between the second charging / discharging element, charging element, or discharging element and the DC bus so that a current equal to the current target value flows through the second charging / discharging element, charging element, or discharging element, and the first power converter calculates the bus voltage target value based on a target value corresponding to a first storage amount index of the first charging / discharging element and a second storage amount index calculated by a method different from the first storage amount index of the first charging / discharging element. Effect of the Invention

[0011] According to the present invention, it is possible to efficiently control power fluctuations in the DC bus caused by fluctuations in the input power source and load, and to realize control such that the amount of power stored in the main stabilization device remains constant over the long term, thereby providing a control system that can operate stably and continuously for a long period of time. [Brief description of the drawings]

[0012] [Figure 1] 1 is an overall configuration diagram of a DC bus control system according to an embodiment; [Diagram 2] FIG. 13 is a configuration diagram showing another example of a semi-stabilizing device in the embodiment. [Diagram 3] 1 is a block diagram showing a configuration example of a power converter in a solar power generation system; [Figure 4] FIG. 2 is a block diagram showing an example of a configuration of a power converter in a main stabilizing device. [Diagram 5] 2 is a block diagram showing an example of the configuration of a power converter in a semi-stabilizing device; [Figure 6] 2 is a block diagram showing an example of the configuration of a power converter in a semi-stabilizing device; [Figure 7] 1 is a conceptual diagram showing a schematic relationship between the charging / discharging power of a power storage device, the input power of a water electrolysis cell, the output power of a fuel cell, and the bus voltage. [Figure 8A] FIG. 4 is an explanatory diagram of the operation of the main stabilizing device. [Figure 8B] FIG. 4 is an explanatory diagram of the operation of the main stabilizing device. [Figure 8C] FIG. 4 is an explanatory diagram of the operation of the main stabilizing device. [Figure 9A] FIG. 4 is an explanatory diagram of the operation of the semi-stabilizing device. [Figure 9B] FIG. 4 is an explanatory diagram of the operation of the semi-stabilizing device. [Figure 10A] FIG. 4 is an explanatory diagram of the operation of the semi-stabilizing device. [Figure 10B] FIG. 4 is an explanatory diagram of the operation of the semi-stabilizing device. [Figure 11] FIG. 4 is a diagram showing a simulation result of the system according to the first embodiment. [Figure 12] FIG. 13 is a diagram showing a simulation result of a system according to a conventional example. [Figure 13] FIG. 1 is a diagram for explaining a system problem according to a conventional example. [Figure 14] FIG. 1 is a diagram for explaining a system problem according to a conventional example. [Figure 15] FIG. 11 is a diagram showing a simulation result of the system according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] <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, as input power sources, a solar power generation system 10 and a wind power generation system 20, which are renewable energy power supply systems. These power generation systems 10 and 20 are connected in parallel, and their output sides are connected to a DC bus 70. The solar 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.

[0015] The input power source may be any power source. If the input power source is a renewable energy power source system, it may be a power source that utilizes energy such as wave power or geothermal power other than those mentioned above, or may be a power source system such as hydroelectric (small hydroelectric) power generation, tidal power generation, tidal current power generation, or temperature difference power generation. It may also be a combination of these, including those mentioned above.

[0016] Furthermore, the number of power supply systems connected in parallel to one another is not particularly limited.

[0017] Connected to DC bus 70 are primary regulator 30 and secondary regulators 40, 50, and 60, as well as a load 90.

[0018] The main stabilization device 30 sets a variable bus voltage target value within a predetermined tolerance range centered on a reference bus voltage (reference voltage of the DC bus 70), and controls the charging and discharging of the storage device 31 by operating the power converter 32 so that the output voltage on the DC bus 70 side matches the bus voltage target value.

[0019] In addition, 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 controls the charging and discharging of the storage device 41 by operating the power converter 42 so that the input / output current matches the input / output current target value.

[0020] Here, the power storage devices 31 and 41 are, for example, batteries (secondary batteries), electric double layer capacitors, capacitors, flywheels, redox flow batteries, etc. Furthermore, the power converters 32 and 42 are, for example, insulated DC / DC converters or choppers, etc., and are capable of bidirectionally transmitting and receiving DC power as indicated by the arrows.

[0021] In the semi-stabilizer 50, the power converter 52 performs DC / DC conversion to supply DC power to the water electrolysis cell 51 (a type of charging operation) so that the input / output currents match the input / output current target values ​​calculated based on the difference between a charging threshold and the voltage of the DC bus, and electrolyzes water to generate hydrogen gas and oxygen gas. In addition, the semi-stabilizer 60 supplies DC power generated by an electrochemical reaction in the fuel cell 61 to the DC bus 70 via the power converter 62 (a type of discharging operation), and at that time, the power converter 62 performs DC / DC conversion so that the input / output currents match the input / output current target values ​​calculated based on the difference between a discharge threshold and the voltage of the DC bus.

[0022] The configurations of the semi-stabilizer 50 and the semi-stabilizer 60 described above are merely illustrative, and an alternative to the water electrolysis cell 51 may be a means for electrochemically producing CH-based bonds (CH, CH, etc.) or alcohol by reducing carbon dioxide, or a means for producing ammonia by reducing nitrogen, and an alternative to the fuel cell 61 may be a fuel cell that uses alcohol or the like, or a power generation means that burns chemical substances (hydrogen, CH-based bonds, alcohol, ammonia, etc.) to rotate a turbine or the like.

[0023] 2 shows another example of the configuration of the semi-stabilization device. As shown in the figure, the semi-stabilization devices 50 and 60 may be an integrated semi-stabilization device 50A in which the hydrogen storage device 53 is shared by both the semi-stabilization devices 50 and 60.

[0024] In Fig. 1, the power storage devices 31 and 41 are capable of absorbing (charging) and releasing (discharging) DC power. In addition, 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) is capable of generating power by converting gas into DC power. The power storage devices 31 and 41 constitute charge / discharge elements, the water electrolysis cell 51 (and the hydrogen storage device 53) constitutes a charge element, and the fuel cell 61 (and the hydrogen storage device 53) constitutes a discharge element.

[0025] As described above, each of the stabilizing devices 30, 40, 50, and 60 can be considered as a power buffer that transfers DC power to and from the DC bus 70 through the operation of the power converters 32, 42, 52, and 62. Furthermore, the primary stabilizing device 30 and the sub-stabilizing device 40 are power buffers having a charging and discharging function, the sub-stabilizing device 50 is a power buffer having a charging function, and the sub-stabilizing device 60 is a power buffer having a discharging function.

[0026] It should be noted that only one main stabilization device 30 having the function of setting the bus voltage target value is required, but only the required number of semi-stabilization devices may be provided depending on the number of parallel connections in the power supply system and the power required by the load 90.

[0027] The monitoring and instruction device 80 collects status information (voltage, current, temperature, etc.) of each of the power generation systems 10 and 20, the main stabilization device 30, and the semi-stabilization devices 40, 50, and 60 to monitor their status and operation, and generates operation commands (start / stop commands, etc.) for each part and charge / discharge threshold commands, etc., based on the results of this monitoring. Various monitoring signals and commands can be transmitted and received between the monitoring and instruction device 80 and each of the above-mentioned parts via wired or wireless communication.

[0028] 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 its AC load. Also, an AC power system may be connected to the DC bus 70 via a DC / AC converter.

[0029] Next, there will be described the configuration of each part in Fig. 1. The configuration in Fig. 1 has a solar power generation system 10 and a wind power generation system 20 as input power sources.

[0030] The solar power generation system 10 and the wind power generation system 20 have a common function in that they both convert power generated using renewable energy into DC power by power converters 12 and 22 and supply the DC power to a DC bus 70. For this reason, the following description will be given taking the solar power generation system 10 as an example.

[0031] 3 is a block diagram showing an example of the configuration of the power converter 12 in the solar power generation system 10. The power converter 12 includes a DC / DC conversion unit 12A and a control circuit 12B.

[0032] The DC / DC conversion unit 12A converts the DC output voltage of the solar cell 11 into a DC voltage of a predetermined magnitude by the operation of a semiconductor switching element and outputs it to the DC bus 70, and is constituted by, for example, a step-up chopper.

[0033] In the control circuit 12B that controls the DC / DC conversion unit 12A, the output voltage and current of the solar cell 11 are detected by a voltage detector 12a and a current detector 12b, and these detected values ​​are input to an MPPT control unit 12c. The MPPT control unit 12c searches for the maximum output point of the solar cell 11 by a hill-climbing method or the like, and outputs the searched point to a voltage / current control unit 12d.

[0034] The voltage / current control unit 12d sends drive pulses generated by PWM (pulse width modulation) control or the like to the drive circuit 12e, and the drive circuit 12e turns on and off the semiconductor switching elements of the DC / DC conversion unit 12A based on the drive pulses.

[0035] In addition, the voltage of the DC bus 70 is detected by a voltage detector 12f, and this bus voltage detection value is input to a comparison unit 12g together with a bus voltage target value sent from a main stabilization device 30, which will be 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 a voltage / current control unit 12d.

[0036] Based on the control signal, the voltage / current control unit 12d calculates a drive pulse that matches the bus voltage detection value with the bus voltage target value, and for example, when the bus voltage detection value exceeds the bus voltage target value, performs a control operation to reduce the output voltage of the DC / DC conversion unit 12A (including stopping operation).

[0037] 4 is a block diagram showing an example of the configuration of the power converter 32 in the primary stabilizing device 30. The power converter 32 includes a DC / DC conversion section 32A and a control circuit 32B.

[0038] The DC / DC conversion unit 32A has a function of controlling charging and discharging of the power storage device 31 by bidirectionally transmitting and receiving DC power between the DC bus 70 and the power storage device 31, and is composed of an insulated DC / DC converter equipped with a semiconductor switching element, a chopper, etc. The power storage device 31 is provided with a sensor 31a that detects voltage, current, and temperature.

[0039] The control circuit 32B is configured as follows.

[0040] The voltage detector 32a detects the voltage of the DC bus 70, and the bus voltage target value calculation unit 32b calculates a bus voltage target value according to the first power storage amount index of the power storage device 31. The method of calculating the bus voltage target value will be described later.

[0041] As the stored power amount index, for example, a state of charge (SOC) obtained by integrating the charge / discharge current of the power storage device 31 detected by the sensor 31a can be used.

[0042] The offset integration unit 32c calculates a cumulative deviation of the bus voltage target value based on a 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 that is obtained by a method different from that of the first storage amount index, and for example, the terminal voltage (battery voltage) of the power storage device 31 detected by the sensor 31a can be used.

[0043] The target value of the second power storage index can be a value of the second power storage index corresponding to a predetermined power storage amount or power storage rate. The predetermined power storage amount or power storage rate can be appropriately determined according to the requirements of the system, and for example, a power storage amount of 50% of a full charge can be adopted, but is not limited to this. For example, the predetermined power storage amount or power storage rate can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80% of a full charge, or can be appropriately determined according to the purpose and use within the range of 47% to 54%, 45% to 55%, 40% to 60%, or 30% to 70% of a full charge.

[0044] The offset integrator 32c calculates the cumulative deviation as a value corresponding to the integral of the difference between the second power storage amount index and its target value, for example. More specifically, the cumulative deviation is calculated by multiplying the integral of the difference between the second power storage amount index and its target value by a predetermined gain.

[0045] Here, when the magnitude (absolute value) of the charge / discharge current of the power storage device 31 is larger than a predetermined value, the integration calculation is not performed, and the integration calculation is performed only when the magnitude of the charge / discharge current is smaller than the predetermined value. In other words, the cumulative deviation is obtained as a value obtained by integrating the difference between the second power storage amount index and the target value of the power storage amount index only when the magnitude of the charge / discharge current of the power storage device 31 is smaller than a predetermined value. The predetermined value here is determined, for example, as a value that is expected to allow the second power storage amount index (for example, terminal voltage) to accurately represent the amount of power stored in the power storage device 31 if the magnitude of the charge / discharge current of the power storage device 31 is smaller than that value.

[0046] The deviation between the bus voltage target value and the bus voltage detection value is calculated by a subtractor 32d, and the cumulative deviation is added to the voltage deviation by an 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 a charge / discharge control unit 32f.

[0047] The voltage, current, temperature, and charge / discharge threshold of the power storage device 31 are input to the charge / discharge control unit 32f, and while taking into account this input information, the charge / discharge control unit 32f performs PWM control or the like to generate drive pulses so that the bus voltage detection value coincides with the bus voltage target value. The drive circuit 32g turns on and off the semiconductor switching elements of the DC / DC conversion unit 32A in accordance with the drive pulses. The DC / DC conversion unit 32A controls the charge / discharge of the power storage device 31 as described above so as to coincide the bus voltage detection value with the bus voltage target value.

[0048] In general, the amount of stored electricity in the storage device 31 can be estimated approximately from its terminal voltage. The terminal voltage also varies depending on the magnitude of the charge / discharge current, but when the charge / discharge current is sufficiently small (below the above-mentioned predetermined value), the terminal voltage can be considered to represent the amount of stored electricity in the storage device 31. When a steady state in which the change in power generation or power consumption is small is achieved as a result of control by the main stabilization device, the charge / discharge current of the main stabilization device becomes zero. 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 stored electricity in the storage device 31. In this embodiment, the difference between the terminal voltage and its target value is integrated, and the obtained integral value is added to the target value to control the bus voltage as a new target value. This control based on the integral value of the error can be considered as integral control of PID control when the control based on the amount of stored electricity is considered as proportional control. As a result, the offset of the steady-state electricity storage index can be removed. In other words, the amount of stored electricity in the electricity storage device 31 can be maintained at the target value of the second electricity storage amount index, and the actual amount of stored electricity in the electricity storage device 31 does not run out or overflow, allowing stable continuous operation for a long period of time.

[0049] Furthermore, the control circuit 32B (charge / discharge control section 32f) may stop charging / discharging the power storage device 31 for an extremely short period of time that does not affect the control of the system, and forcibly provide a period during which the charge / discharge current is zero. The length of this period is set to a length that allows the terminal voltage of the storage battery to stabilize and represent the actual amount of stored power. The control circuit 32B can be expected to achieve the same effect as above by providing a period during which the charge / discharge current is zero, either periodically or irregularly, measuring the terminal voltage of the power storage device 31 during this period as a second indicator of the amount of stored power, integrating the difference with a target amount of stored power, and using the result for control.

[0050] The charge / discharge threshold value of the power storage device 31 may be set by the control circuit 32B itself, or may be received as a command from the monitoring / instruction device 80 of FIG.

[0051] Fig. 5 is a block diagram showing an example of the configuration of the power converter 42 in the semi-stabilizing device 40 of Fig. 1. The power converter 42 includes a DC / DC conversion unit 42A and a control circuit 42B. The power converter 42 has a function similar to that of the power converter 32 of Fig. 4A in that it transmits and receives DC power bidirectionally between the DC bus 70 and the power storage device 41. The power storage device 41 is provided with a sensor 41a that detects voltage, current, and temperature, similar to the power storage device 31. The control circuit 42B includes a voltage detector 42a, a comparator 42b, a subtractor 42c, a charge / discharge control unit 42d, and a drive circuit 42e.

[0052] The power converter 42 shown in Fig. 5 differs from the power converter 32 in Fig. 4A in the following respects. In the control circuit 42B, the charge / discharge control unit 42d calculates input / output current target values ​​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 for 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 the charge / discharge of the power storage device 41, and the input / output current target value may be determined according to the difference between the threshold value and the voltage of the DC bus 70.

[0053] Furthermore, the comparison unit 42b provided in the control circuit 42B compares the charge / discharge threshold of the power storage device 41 with the bus voltage detection value, and outputs a charge command or a discharge command according to the magnitude relationship between the charge threshold or the discharge threshold and the bus voltage detection value, thereby controlling the operation of the charge / discharge control unit 42d. Note that the charge / discharge threshold may be set by the control circuit 42B itself, or may be received as a command from the monitoring / instruction device 80.

[0054] 6 is a block diagram showing an example of the configuration of the power converter 52 in the semi-stabilizing device 50. The power converter 52 includes a DC / DC conversion unit 52A and a control circuit 52B.

[0055] The DC / DC conversion unit 52A has a function of converting the DC power of the DC bus 70 to a predetermined magnitude and supplying it to the water electrolysis cell 51, and is configured with an insulated DC / DC converter equipped with a semiconductor switching element, a chopper, 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, performs a kind of charging operation.

[0056] A control circuit 52B that controls the DC / DC conversion unit 52A is configured generally similarly to the control circuit 42B in FIG.

[0057] 6, the voltage of the DC bus 70 is detected by the voltage detector 52a, and the deviation between the charging threshold and the detected bus voltage value is calculated by the subtractor 52c, and this voltage deviation is input to the charging control unit 52d. The detected bus voltage value is input to the comparing unit 52b together with the charging threshold, and the comparing unit 52b outputs a charging command to the charging control unit 52d when the detected bus voltage value exceeds the charging threshold. Here, the charging threshold corresponds to the starting voltage of electrolysis by the water electrolysis cell 51. In other words, the charging threshold is a threshold related to charging of the water electrolysis cell 51.

[0058] The charge control unit 52d calculates an input / output current target value based on the voltage deviation input from the subtractor 52c, generates a drive pulse as a charge command so that the input / output current of the DC / DC conversion unit 52A coincides with the input / output current target value, and outputs the drive pulse to the drive circuit 52e. The drive circuit 52e turns on and off the semiconductor switching element of the DC / DC conversion unit 52A in accordance with the drive pulse, thereby supplying DC power to the water electrolysis cell 51 and electrolyzing water.

[0059] The DC / DC conversion unit 52A controls the DC power supplied to the water electrolysis cell 51 through the above operation, and operates to make the input / output currents coincide with the input / output current target values.

[0060] 1, the power generation operation by the fuel cell 61 is considered to be a discharge operation, and the water electrolysis cell 51, charge threshold, and charge control unit 52d of the semi-stabilization device 50 shown in Fig. 6 may be replaced with the fuel cell 61, a discharge threshold, and a discharge control unit, respectively. In this case, the discharge threshold corresponds to the start voltage of power generation by the fuel cell 61.

[0061] In the semi-stabilizing device 60, when the bus voltage detection value falls below the discharge threshold, a drive pulse equivalent to a 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 supplied to the DC bus 70 via the DC / DC conversion unit.

[0062] The DC / DC conversion unit operates to control the power generated by the fuel cell 61 through the above operation, while making the input / output currents coincide with the input / output current target values.

[0063] 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, but for convenience, the sensors are omitted from the illustration.

[0064] Moreover, the charge threshold and the discharge threshold may be set by each control circuit itself, or may be received as a command from the monitoring and indicating device 80 .

[0065] The configurations and operations of power converters 12, 32, 42, and 52, and in particular control circuits 12B, 32B, 42B, and 52B, shown in Figures 3 to 6 are merely illustrative and do not limit the technical scope of the present invention in any way, and it goes without saying that configurations different from these may be adopted.

[0066] Next, Fig. 7 is a conceptual diagram that shows the charging and discharging power of the power storage device 41 of the semi-stabilizer 40, the input power of the water electrolysis cell 51 of the semi-stabilizer 50, and the output power of the fuel cell 61 of the semi-stabilizer 60, respectively, according to the voltage of the DC bus 70. The horizontal width of the triangular symbol in Fig. 7 indicates the magnitude of each power, and the wider the width, the larger the power value.

[0067] 7 illustrates an example in which 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 in Fig. 1. The charging and discharging operations of each unit are controlled according to the voltage of the DC bus 70 to which the generated power is supplied, and the charging and discharging thresholds of the power storage device 41, the water electrolysis cell 51, and the fuel cell 61, etc.

[0068] For example, as shown in (a) for the power storage device 41, the higher the bus voltage is above the charge threshold of the power storage device 41, the greater the charging power supplied to the power storage device 41, and the lower the bus voltage is below the discharge threshold of the power storage device 41, the greater the discharging power released from the power storage device 41. Similarly, the higher the bus voltage is above the charge threshold of the water electrolysis cell 51, the greater the charging power supplied to the water electrolysis cell 51, and the lower the bus voltage is below the discharge threshold of the fuel cell 61, the greater the discharging power generated by the fuel cell 61.

[0069] The (b) for the power storage device 41 is a case where the charge threshold and the discharge threshold are set lower than those in (a) in accordance with the reference bus voltage, and the (c) is a case where the charge threshold and the discharge threshold are set higher than those in (a). A similar threshold setting change operation can also be performed for the charge threshold of the water electrolysis cell 51 and the discharge threshold of the fuel cell 61.

[0070] In this way, by controlling the charge and discharge operations by changing the charge threshold and discharge threshold of the power storage device 41, the water electrolysis cell 51, and the fuel cell 61, it is possible to individually adjust the DC power exchanged between the DC bus 70 and the semi-stabilizing devices 40, 50, and 60. In other words, it is possible to finely control the operation of each of them as a power buffer.

[0071] As described above, the charge threshold and the discharge threshold can be changed based on a command from the monitoring and indicating device 80, or the power converters 42, 52, and 62 can change them themselves.

[0072] 8A and 8B are diagrams illustrating the operation of primary stabilizer 30.

[0073] As shown by the dashed line (thick line) in Fig. 8A, the main stabilization device 30 exchanges DC power between the DC bus 70 and the power storage device 31, and controls the charging and discharging of the power storage device 31. The control circuit 32B in the power converter 32 sets a bus voltage target value based on a first charge amount index (e.g., charging rate) of the power storage device 31, for example, in accordance with the characteristics shown in Fig. 8B.

[0074] This bus voltage target value is set within the allowable range of the voltage of the DC bus 70 so that it is higher the larger the first energy storage index is and lower the smaller the first energy storage index is, and the control circuit 32B controls the DC / DC conversion unit 32A so that the bus voltage detection value matches this bus voltage target value.

[0075] 9A and 9B are diagrams illustrating the operation of semi-stabilizers 40 and 50. FIG.

[0076] As shown by the dashed line (thick line) in FIG. 9A, the power converter 42 of the semi-stabilizer 40 charges the power storage device 41 using the DC power from the DC bus 70, and the power converter 52 of the semi-stabilizer 50 supplies the DC power from the DC bus 70 to the water electrolysis cell 51 to electrolyze water.

[0077] 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 increases above the charging threshold of the power storage device 41 or the water electrolysis cell 51.

[0078] 10A and 10B are diagrams illustrating the operation of semi-stabilizers 40 and 60. FIG.

[0079] As shown by the dashed line (thick line) in Figure 10A, the power converter 42 of the semi-stabilizer 40 discharges the storage device 41 to supply DC power to the DC bus 70, and the power converter 62 of the semi-stabilizer 60 operates the fuel cell 61 to generate power and supply DC power to the DC bus 70.

[0080] 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.

[0081] According to the DC bus control system of this embodiment, a change in the balance of power input and output of the entire system is first dealt with by inputting and outputting current to and from the primary stabilization device 30 (electrical storage device 31), which has a fast response speed, thereby mitigating the response to other devices. In this case, when a current flows into the primary stabilization device 30, the first storage amount index increases as the electrical storage device 31 charges, and the bus voltage increases. Conversely, when a current flows out of the primary stabilization device 30, the first storage amount index decreases as the electrical storage device 31 discharges, and the bus voltage drops. These operations are performed by the power converter 32 (DC / DC conversion unit 32A and control circuit 32B) of the primary stabilization device 30.

[0082] On the other hand, the semi-stabilizer increases or decreases the amount of current flowing into the charging element or discharging element in response to fluctuations in the bus voltage, and this operation is performed by a power converter of the semi-stabilizer.

[0083] This series of operations is performed so that the current input and output to the primary stabilizer 30 becomes zero, and as a result, the total current input and output to the entire system is controlled to become zero. Therefore, at a certain DC bus voltage, a steady state is reached when the current inflow and outflow of the semi-stabilizers become constant values.

[0084] According to this embodiment, the operation of each device is performed in an analog manner using the voltage of the DC bus line as a signal, so that system control can be performed by distributed processing based on the operation of each device, and centralized overall control is not necessary. As a result, the problem of errors that arise when centralized management is performed can also be eliminated. The reaction speed of the main stabilizer needs to follow the power fluctuations of the system, but since the main stabilizer absorbs fast fluctuations, the operation of the semi-stabilizer can be relatively slow without any problem, and since the direction of the current can be controlled, it can be used with devices that can only absorb or release power in one direction, such as water electrolysis cells and fuel cells, and are not suitable for high-speed output fluctuations. Furthermore, by changing the setting of the operating voltage threshold of these devices and the ratio of current inflow and outflow to the DC bus voltage, it becomes possible to use multiple devices as semi-stabilizers. In addition, since the operating signal of each device is the DC bus voltage, it is relatively easy to increase or decrease the number of semi-stabilizers.

[0085] Furthermore, according to this embodiment, the main stabilization device 30 determines the target value of the DC bus voltage based on the second storage capacity index of the storage device 31, so that the storage capacity of the storage device 31 can be kept constant, and long-term continuous operation can be stably performed.

[0086] A simulation performed to verify this effect will now be described.

[0087] 11 is a diagram showing a simulation result of the control system of this embodiment. In this simulation, the state of charge (SOC) obtained by integrating the charge / discharge current of the power storage device 31 was used as the first power storage amount index, and the terminal voltage (battery voltage) of the power storage device 31 was used as the second power storage amount index. In addition, 50V was set as the target value of the second power storage amount index.

[0088] Fig. 11(a) shows the time series changes in the power generated by the solar cell 1101, the power source (input) power 1102, and the load (output) power 1103. Fig. 11(b) shows the power consumed by the water electrolysis cell 1104 and the power generated by the fuel cell 1105. When there is a net input power to the system, electrolysis (charging) is performed in the water electrolysis cell, and when there is a net output power, a direct current is supplied (discharged) by the electrochemical reaction of hydrogen in the fuel cell.

[0089] 11(c) shows time series changes in terminal voltage (battery voltage) 1106 and charge / discharge current 1107 of the power storage device 31. It can be seen that the terminal voltage 1106 of the power storage device 31 is controlled to approach its target value of 50 V, and is 50 V when the power storage device 31 is not being charged or discharged, that is, when the charge / discharge current is zero.

[0090] FIG. 12 shows a similar simulation result as a comparative example in which the power converter 32 of the main stabilization device 30 does not have the offset integration unit 32c (i.e., the configuration of Patent Document 1). FIG. 12(a) shows the time-series changes in the generated power 1201 of the solar cell, the power source (input) power 1202, and the load (output) power 1203, which are the same as those in FIG. 11(a). FIG. 12(b) shows the power consumption 1204 in the water electrolysis cell and the power generation 1205 in the fuel cell, which show almost the same changes as those in FIG. 11(b). FIG. 12(c) shows the time-series changes in the terminal voltage (battery voltage) 1206 and the charge / discharge current 1207 of the storage device 31. In this comparative example, the generated power and power consumption fluctuate, and the voltage 1206 (an index of the actual amount of stored power) of the storage device 31 drops every time charging or discharging occurs.

[0091] As described above, in the DC bus control system according to this embodiment, the power converter 32 in the main stabilization device 30 has the offset integration section 32c and removes the steady offset from the target value of the power storage amount index (battery voltage), so that the battery voltage of the power storage device 31, i.e., the power storage amount, can be kept constant. Also, by not performing integral calculation of the battery voltage for offset calculation when the charge / discharge current of the power storage device 31 is large, control based on an inaccurate power storage amount can be avoided, and stable operation can be performed. As described above, in the DC bus control system according to this embodiment, the power storage device 31 of the main stabilization device 30 can maintain a constant power storage amount for a long period of time, so that stable continuous operation for a long period of time is possible.

[0092] <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 charge / discharge current of the power storage device 31 of the main stabilization device 30 is controlled to 0, thereby ensuring stable operation. 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, the system can continue to operate by having the power storage device 31 absorb or supply power without abnormally shutting down.

[0093] However, even if the generated power or load power returns to within the capacity of the water electrolysis cell or fuel cell, discharging or charging from the power storage device 31 of the primary stabilization device 30 continues until the excess amount of stored power is eliminated. Therefore, the control capability of the present system temporarily decreases until the excess amount of stored power is eliminated. This point will be explained below.

[0094] The following explanation using Figs. 13 to 15 shows the operation of a configuration in which power converter 32 of main stabilization device 30 is not provided with offset integrator 32c (that is, the configuration of Patent Document 1).

[0095] Fig. 13 is a diagram illustrating the operation of the system when the generated power and load power are within the capabilities of the water electrolysis cell and fuel cell. Fig. 13(a) shows the time variations in generated power 1301 and load power 1302. Fig. 13(b) shows the time variations in power consumption 1303 of the water electrolysis cell and power generated 1304 by the fuel cell. Fig. 13(c) shows the time variations in control target value 1305 of the bus voltage. Fig. 13(d) shows the time variations in voltage 1306 and current 1307 of the power storage device 31.

[0096] As shown in FIG. 13, when the generated power and the load power are within an appropriate range, the charging / discharging 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.

[0097] 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. 14(a) shows the time changes in generated power 1401 and load power 1402. Fig. 14(b) shows the time changes in power consumption 1403 of the water electrolysis cell and power generated in the fuel cell 1404. Fig. 14(c) shows the time changes in voltage 1405 and current 1406 of the power storage device 31. Fig. 14(d) shows the time change in control target value 1407 of the bus voltage.

[0098] Because the generated power exceeds the power absorption capacity of the water electrolysis cell, the power storage device 31 absorbs the surplus power, and the amount of power stored in the power storage device 31 increases. Even if the generated power returns to within the capacity of the system, the power storage device 31 in the primary stabilization device 30 continues to discharge until the excessive amount of power stored in the power storage device 31 is eliminated (period T1 in the figure). During this period, power is supplied only from the power storage device 31, and power is not supplied from the fuel cell. There is no power supply from the fuel cell because the bus voltage is maintained high. During this period, if the system were to supply load power, it would be unable to supply power that exceeds the power supply capacity of the power storage device 31 in the primary stabilization device 30, and the system would deviate from the control of the main controller.

[0099] Although the case where the generated power is excessive has been described here, the same problem occurs when the load power is excessive.

[0100] In this embodiment, this problem is addressed as follows.

[0101] 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 this embodiment, an upper limit and a lower limit are set for the first storage amount index. The upper limit is set to a value corresponding to the maximum operation of charging the water electrolysis cell or the battery (a value indicating maximum operation) or a value slightly higher than that. Also, the lower limit is set to a value corresponding to the maximum operation of discharging the fuel cell or the battery (a value indicating maximum operation) or a value slightly lower than that.

[0102] 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 as shown in Fig. 8C. Since the first storage amount index can only take values ​​between the lower limit value and the upper limit value, the bus voltage target value also takes values ​​corresponding to this range.

[0103] 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 and lower limits are set for the first power storage amount index as described above. Note that in this example, the offset integration unit 32c does not integrate the offset and add it.

[0104] Figure 15(a) shows the time variations in generated power 1501 and load power 1502, which are the same as Figure 14(a). Figure 15(b) shows the time variations in power consumption 1503 of the water electrolysis cell and power generation 1504 in the fuel cell. Figure 15(c) shows the time variations in voltage 1505 and current 1506 of the power storage device 31. Figure 15(e) shows the time variations in control target value 1507 of the bus voltage. Note that the vertical scale in Figure 15(d) is significantly different from that of Figure 14(e).

[0105] 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 electrolysis cell is resolved, charging in the electrolysis cell ends, and power supply from the fuel cell becomes possible. In other words, by setting an upper limit on the first power storage amount index, even if excessive power is generated, the system can be returned to a normal state in a relatively short time after the state is resolved.

[0106] When the load power is excessive, a lower limit is set for the first power storage amount index, and thus the same effect as above can be obtained.

[0107] 15(c), after the control of the system is restored, a difference occurs between the first stored power amount index (a value obtained by calculation and used for control) and the actual stored power amount of the power storage device 31. If such errors in the stored power amount accumulate, there is a high possibility that long-term operation of the system will be hindered.

[0108] In the DC bus control system according to this embodiment, the main stabilization device 30 determines the bus voltage target value by using the offset integration unit 32c, taking into consideration the integral value (accumulated deviation) of the difference between the second power storage index (battery voltage) and the target value. Therefore, the difference between the calculated power storage index (first power storage index) and the actual power storage amount as described above can be automatically eliminated in the long term.

[0109] That is, according to this embodiment, when excessive power generation or consumption occurs, normal control can be restored in a short time after the occurrence of the excessive power generation or consumption, and stable continuous operation for a long period of time is possible. [Explanation of symbols]

[0110] 10: Solar power generation system 11: Solar cell 12: Power converter 12A: DC / DC conversion section 12B: Control circuit 12a, 12f: Voltage detector 12b: Current detector 12c: MPPT control unit 12d: Voltage / current control section 12e: Drive circuit 12g: Comparison section 20: Wind power generation system 21: Wind turbine 22: Power converter 30: Main stabilizer 31: Power storage device 31a: Sensor 32: Power converter 32A: DC / DC conversion section 32B: Control circuit 32a: Voltage detector 32b: Bus voltage target value calculation unit 32c: Offset integral section 32d: Subtractor 32e: Adder 32f: Charge / discharge control unit 32g: Drive circuit 40: Metastabilizer 41: Power storage device 41a: Sensor 42: Power converter 42A: DC / DC conversion section 42B: Control circuit 42a: Voltage detector 42b: Comparison section 42c: Subtractor 42d: Charge / discharge control unit 42e: Drive circuit 50,50A: Metastabilizer 51: Water electrolysis cell 52: Power converter 52A: DC / DC conversion section 52B: Control circuit 52a: Voltage detector 52b: Comparison section 52c: Subtractor 52d: Charging control unit 52e: Drive circuit 53: Hydrogen storage device 60: Metastabilizer 61: Fuel cell 62: Power converter 70: DC bus 80: Monitoring and indication device 90: Load

Claims

1. A DC bus control system for controlling power fluctuations of a DC bus connecting an input power source and a load, comprising: a primary stabilization device having a first charging / discharging element and a first power converter; At least one semi-stabilizing device having a second charge / discharge element, a charging element, or a discharging element and a second power converter; Including, the first power converter is configured to obtain a bus voltage target value, and to bidirectionally exchange DC power between the first charging / discharging element and the DC bus such that a voltage of the DC bus coincides with the bus voltage target value; the second power converter is configured to calculate a current target value according to a difference between a threshold value related to charging or discharging of the second charging / discharging element, the charging element, or the discharging element and the voltage of the DC bus, and to exchange DC power between the second charging / discharging element, the charging element, or the discharging element and the DC bus such that a current equal to the current target value flows through the second charging / discharging element, the charging element, or the discharging element; the first power converter determines the bus voltage target value based on a target value corresponding to a first power storage amount index of the first charging / discharging element and a second power storage amount index determined by a method different from the first power storage amount index of the first charging / discharging element; 1. A DC bus control system comprising:

2. the second charge amount indicator is a terminal voltage of the first charge / discharge element, the bus voltage target value is calculated by adding a value corresponding to an accumulated deviation obtained by integrating a difference between the second power storage amount index and a target value of the second power storage amount index to a target value corresponding to a first power storage amount index of the first charging / discharging element; 2. The DC bus control system of claim 1.

3. The cumulative deviation is a value obtained by integrating a difference between the second storage amount index and a target value of the second storage amount index only when the magnitude of the charging / discharging current of the first charging / discharging element is smaller than a predetermined value.

3. The DC bus control system of claim 2.

4. the first power converter provides a period during which charging / discharging of the first charging / discharging element is not performed; The cumulative deviation is a value obtained by integrating a difference between the second power storage amount index and a target value of the second power storage amount index over the period.

4. A DC bus control system according to claim 2 or 3.

5. The first storage amount index is a value obtained by integrating the charge / discharge current of the first charge / discharge element.

5. A DC bus control system according to any one of claims 1 to 4.

6. A predetermined upper limit and a lower limit are set for the first storage amount indicator.

6. The DC bus control system of claim 5.

7. The upper limit is a value corresponding to a maximum operation of charging the second charging / discharging element or the charging element, The lower limit is a value corresponding to the maximum discharge operation of the second charge / discharge element or the discharge element; 7. The DC bus control system of claim 6.

8. 8. The DC bus control system of claim 1, further comprising a renewable energy power supply system as the input power source.

9. 9. The DC bus control system of claim 8, further comprising said load.

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