DC Power Distribution System

Abstract

The present invention provides a DC power distribution system having low power loss even when the DC system voltage and the load supply voltage differ greatly.　The present invention comprises an AC-DC converter (20), a first sensor (51) for detecting the power generated by a power-generating device (5), a DC-DC converter for loads (30), a second sensor (52) for detecting the load supply power, and a switching-command-generating unit (10) for switching between two operating modes of the AC-DC converter. In operating mode 1, the voltage of a DC system (50) is set higher than the value obtained by multiplying the voltage effective value of the AC power by the square root of 2, and when the generated power is smaller than the load supply power, the switching-command-generating unit reduces the voltage of the DC system and switches the operating mode from operating mode 1 to operating mode 2.

Description

[Technical Field]

[0001] This application relates to a DC power distribution system. [Background technology]

[0002] In recent years, the installation of DC power sources such as storage batteries and power generation devices such as solar power generation devices has been increasing in homes, office buildings, factories, and train stations to cope with AC power grid outages and utilize natural energy. A DC power distribution system converts AC power from an AC power grid into DC power using an alternating current-direct current (AC-DC) converter and outputs it to the DC grid. It also supplies DC power from DC power sources and solar power generation devices to the DC grid. The DC power distribution system then supplies power from the DC grid to a load. Compared to an AC power distribution system, a DC power distribution system requires fewer power conversions when charging a DC power source and supplying power to a load, thereby reducing power loss associated with power conversion. Furthermore, a DC power distribution system eliminates the need for an AC-DC converter on the load side to convert AC to DC, improving cost efficiency.

[0003] In general, in a DC power distribution system, the DC system voltage, DC power supply voltage, and load supply voltage are all different. In this case, the DC system voltage is set higher than the DC power supply voltage and the load supply voltage. Therefore, the voltage of the DC power is stepped down as needed using a DC-DC converter (Direct Current-Direct Current converter) installed between the DC system and the DC power supply voltage, and between the DC system and the load. In this case, the larger the voltage step-down ratio in the DC-DC converter, the greater the power loss associated with the voltage step-down, which leads to a problem of reduced power utilization efficiency.

[0004] As a conventional DC power distribution system that can reduce the voltage step-down ratio, a DC power distribution system has been proposed in which the DC system voltage is periodically changed and power is stored in a power storage device provided in each load while a voltage corresponding to the load's own supply voltage is applied to the load (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-253118 Summary of the Invention [Problem to be solved by the invention]

[0006] DC power distribution systems may have a reverse power function that converts surplus power from solar power generation equipment and the like into AC power and outputs it to the AC power grid. For stable reverse power operation in a DC power distribution system, the DC system voltage must be set to a voltage sufficiently higher than the voltage of the AC power grid. In conventional DC power distribution systems, even if the DC system voltage, which is set to a high voltage for reverse power operation, is periodically changed, the voltage step-down ratio may not be sufficiently reduced. Therefore, conventional DC power distribution systems have a problem in that the effect of reducing the voltage to reduce power loss is reduced.

[0007] The present application has been made to solve the above-mentioned problems, and has as its object to provide a DC power distribution system that has small power loss even when the DC system voltage and the load supply voltage differ greatly. [Means for solving the problem]

[0008] The DC power distribution system of the present application includes an AC-DC converter having a forward power function of converting AC power input from a power grid into DC power and outputting it to the DC grid, and a reverse power function of converting DC power from the DC grid into AC power and outputting it to the power grid, a first sensor that detects the power generated by a power generation device connected to the DC grid, a load DC-DC converter that supplies power to a load connected to the DC grid, a second sensor that detects the power supplied from the DC grid to the load DC-DC converter and the load, and a switching command generation unit that generates a command to switch between two operation modes of the AC-DC converter. a DC-DC converter for DC power supply that inputs and outputs charge and discharge power of a DC power supply connected to a DC system; The two operation modes are operation mode 1 in which the reverse power function of the AC-DC converter is enabled, and operation mode 2 in which the reverse power function of the AC-DC converter is disabled, and in operation mode 1, the voltage of the DC system is set higher than the value obtained by multiplying the effective voltage value of the AC power by the square root of 2, and the switching command generation unit switches the operation mode of the AC-DC converter from operation mode 1 to operation mode 2 when the power generated by the power generation device detected by the first sensor is lower than the power supplied to the load DC-DC converter and the load detected by the second sensor. At the same time, when the operation mode of the AC-DC converter is operation mode 2, the DC-DC converter for the DC power supply outputs the discharge power of the DC power supply to the DC system. . [Effects of the Invention]

[0009] In the DC power distribution system of the present application, when the power generated by the power generation device detected by the first sensor is smaller than the power supplied to the load DC-DC converter and the load detected by the second sensor, the voltage of the DC system is reduced and the operation mode of the AC-DC converter is switched from operation mode 1 to operation mode 2. At the same time, when the operation mode of the AC-DC converter is operation mode 2, the DC-DC converter for the DC power supply outputs the discharge power of the DC power supply to the DC system. Therefore, power loss can be reduced even when the DC system voltage and the load supply voltage differ greatly. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram of a DC power distribution system according to a first embodiment. [Figure 2] 1 is a configuration diagram of an AC-DC converter according to a first embodiment. [Figure 3]1 is a configuration diagram of a DC-DC converter for a direct-current power supply according to a first embodiment. [Figure 4] 3 is a diagram illustrating the operation of an autonomous driving control unit in the first embodiment. FIG. [Figure 5] 1 is a configuration diagram of a DC-DC converter for load according to a first embodiment. [Figure 6] 4 is an explanatory diagram showing power consumption and power generated by a photovoltaic power generation device in an office building according to the first embodiment. FIG. [Figure 7] 4 is a flowchart showing a process of switching operation modes in the DC power distribution system according to the first embodiment. [Figure 8] FIG. 3 is an explanatory diagram of the operation mode switching process in the DC power distribution system according to the first embodiment. [Figure 9] FIG. 3 is an explanatory diagram of the operation mode switching process in the DC power distribution system according to the first embodiment. [Figure 10] 4 is a flowchart showing a process of switching operation modes in the DC power distribution system according to the first embodiment. [Figure 11] FIG. 10 is a configuration diagram of a DC power distribution system according to a second embodiment. [Figure 12] FIG. 10 is a configuration diagram of a DC power distribution system according to a third embodiment. [Figure 13] FIG. 2 is a diagram illustrating a hardware configuration for realizing a switching command generating unit according to the first to third embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a DC power distribution system according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the same reference numerals in the various drawings indicate the same or corresponding parts.

[0012] Embodiment 1 FIG. 1 is a configuration diagram of a DC power distribution system according to a first embodiment. The DC power distribution system 1 of this embodiment is provided between an AC input system 2, a load 3, a DC power source 4, and a power generation device 5. Here, the AC input system 2 is an AC system that supplies AC power to the DC power distribution system 1 from a commercial power system operated by an electric power company via AC power receiving equipment. The load 3 is an electrical device driven by DC power. The DC power source 4 is a storage battery that can be charged and discharged, for example. The power generation device 5 is a power generation device that outputs DC, such as a solar power generation device that generates power using renewable energy. The power generation device 5 is composed of a power generation unit using renewable energy and a power conversion unit. The power generation device 5 can supply DC power to the DC power distribution system 1.

[0013] The DC power distribution system 1 of this embodiment includes an AC-DC converter 20 that converts AC power input from an AC input system 2 into DC power and outputs it to a DC system 50, a load DC-DC converter 30 provided between the DC system 50 and a load 3, a DC power supply DC-DC converter 40 provided between the DC system 50 and a DC power source 4, and a switching command generator 10. The load DC-DC converter 30 converts DC power from the DC system 50 into a load supply voltage for the load 3 and supplies it to the load 3. The load 3 is an electrical device driven by DC power and is composed of one or more electrical devices. The power consumption of the load 3 varies depending on the operating state of the load 3, but remains almost unchanged if the operating state is constant. Therefore, during periods when the operating state of the load 3 does not fluctuate, the voltage supplied from the load DC-DC converter 30 can be adjusted to minimize power loss in the power supply circuit and input interface of the load 3, thereby minimizing the power consumption of the load 3 and improving economy. It is preferable that the load supply voltage be set within a limit range of input voltage determined for each load so as not to impede the operation of the load.

[0014] The DC-DC converter 40 for DC power supply converts the DC power of the DC system 50 into a charging voltage for the DC power supply 4 and supplies it to the DC power supply 4, and also converts the discharge power of the DC power supply 4 into a voltage for the DC system 50 and outputs it to the DC system 50. The switching command generator 10 controls the AC-DC converter 20 and the DC-DC converter 40 for DC power supply.

[0015] The AC electric circuit from the AC input system 2 to the AC-DC converter 20 is configured, for example, as a single-phase three-wire system or a three-phase three-wire system, but is shown as a single wire in Fig. 1. The DC system 50 is configured, for example, as a pair of DC electric circuits, one wire on the positive side and the other wire on the negative side, but is shown as a single wire in Fig. 1.

[0016] A first sensor 51 is provided between the power generation device 5 and the DC system 50 to detect the power generated by the power generation device 5. A second sensor 52 is provided between the load DC-DC converter 30 and the DC system 50 to detect the load power supplied to the load DC-DC converter 30 and the load 3. A third sensor 53 is provided between the DC power supply DC-DC converter 40 and the DC system 50 to detect the charge / discharge power supplied to the DC power supply DC-DC converter 40 and the DC power supply 4. A fourth sensor 54 is provided between the AC-DC converter 20 and the DC system 50 to detect the output power of the AC-DC converter 20. The first sensor 51, the second sensor 52, the third sensor 53, and the fourth sensor 54 detect power from current and voltage. The power detected by the first sensor 51, the second sensor 52, the third sensor 53, and the fourth sensor 54 are sent to the switching command generator 10.

[0017] A DC system voltage command generator 29 that generates a DC system voltage command is connected to the AC-DC converter 20. A load supply voltage command generator 39 that generates a load supply voltage command is connected to the load DC-DC converter 30. A charge / discharge power command generator 49 that generates a charge / discharge power command is connected to the DC power supply DC-DC converter 40. The DC system voltage command generator 29, the load supply voltage command generator 39, and the charge / discharge power command generator 49 may be built into the AC-DC converter 20, the load DC-DC converter 30, and the DC power supply DC-DC converter 40, respectively, or may be mounted on a single controller.

[0018] The DC power distribution system 1 is a system that is applied to, for example, ordinary homes, office buildings, factories, train stations, etc. The AC input system is a commercial power system operated by an electric power company. The DC power source and power generation device are, for example, a storage battery and a solar power generation device, respectively. Therefore, the devices that make up the DC power distribution system 1 may be located in separate locations. For example, the AC-DC converter 20 may be located in building A, and the DC-DC converter 40 for DC power supply and the DC power source 4 may be located in another building B.

[0019] The DC power distribution system 1 is capable of performing a power running operation (hereinafter referred to as a forward power operation) in which AC power input from the AC input system 2 is supplied to the load 3 and the DC power source 4 via the DC system 50, and a regenerative operation (hereinafter referred to as a reverse power operation) in which DC power input from the DC power source 4 and the power generation device 5 is supplied to the AC input system 2 via the DC system 50. In the DC power distribution system 1, the forward power operation and the reverse power operation are controlled by an AC-DC converter 20.

[0020] In order to perform reverse power operation in the DC power distribution system 1, the voltage of the DC system 50 is set sufficiently higher than the value obtained by multiplying the effective voltage of the AC input system 2 by the square root of 2. The voltage of the DC system 50 is also set higher than the load supply voltage of the load 3 and the charge / discharge voltage of the DC power source 4. For example, the effective voltage of the AC input system 2 is set to 400 V, the voltage of the DC system 50 is set to 740 V, the load supply voltage of the load 3 is set to 340 V, and the charge / discharge voltage of the DC power source 4 is set to 300 V. Power is supplied to the load 3 and the DC power source 4 at voltages stepped down from the voltage of the DC system 50 by the DC-DC converter for load 30 and the DC-DC converter for DC power source 40, respectively.

[0021] The switching command generator 10 controls the AC-DC converter 20 and the DC-DC converter 40 for DC power supply based on the power input from the first sensor 51, the second sensor 52, the third sensor 53, and the fourth sensor 54. Here, a state in which the AC-DC converter 20 is capable of performing reverse power operation is referred to as operation mode 1, and a state in which the AC-DC converter 20 is disabled for performing reverse power operation is referred to as operation mode 2. That is, operation mode 1 is a state in which the voltage of the DC system 50 is set sufficiently higher than the value obtained by multiplying the effective voltage value of the AC input system 2 by the square root of 2, and operation mode 2 is a state in which the voltage of the DC system 50 is set lower than the lower limit voltage in operation mode 1. The lower limit voltage in operation mode 1 is determined by adding margins such as a sensor error and a voltage utilization rate of the AC-DC converter 20 to the value obtained by multiplying the effective maximum voltage value of the AC input system 2 by the square root of 2. The switching command generation unit 10 generates a switching command for switching between operation mode 1 and operation mode 2, and sends the switching command to the AC-DC converter 20 and the DC-DC converter for DC power supply 40. The switching command generation unit 10 also sends commands to change parameters such as control thresholds and voltage command values ​​that accompany the switching of operation modes.

[0022] 2 is a configuration diagram of an AC-DC converter according to this embodiment. The AC-DC converter 20 according to this embodiment includes an AC-DC converter 21 that performs power conversion, a fifth sensor 55 that detects the current and voltage of the AC input system 2, a sixth sensor 56 that detects the current and voltage of the DC system 50, an output voltage controller 22 that controls the output voltage of the AC-DC converter 21, a current command generator 23 that generates a current command value Iac_ref for the AC-DC converter 21, and a command value filter 24 that processes a DC system voltage command Vref. If insulation between the AC input system 2 and the AC-DC converter 21 is required, an insulation tolerance must be provided between the AC input system 2 and the AC-DC converter 21. The sixth sensor 56 may be substituted by the fourth sensor 54 shown in FIG. 1.

[0023] The DC system voltage command Vref is input from the DC system voltage command generating unit 29. If the DC system voltage command Vref fluctuates widely, using the DC system voltage command Vref as is may result in an overshoot in the voltage of the DC system 50 output from the AC-DC converting unit 21. The command value filter unit 24 is provided to suppress abrupt fluctuations in the input DC system voltage command Vref. The command value filter unit 24 is, for example, a low-pass filter, and can suppress abrupt fluctuations in the DC system voltage command Vref. The time constant of the low-pass filter is set in advance in accordance with the control characteristics of the AC-DC converting unit 21. If the control response of the AC-DC converting unit 21 is small and there is little possibility of an overshoot occurring in the output voltage, the command value filter unit 24 may be omitted. The command value filter unit 24 may also include a limiter that sets upper and lower limits for the DC system voltage command Vref.

[0024] The DC system voltage command Vref may be set by a user of the DC power distribution system 1 via a user interface, by a higher-level control device (external controller) that performs energy management control, or in conjunction with switching between operation mode 1 and operation mode 2 performed by a switching command generation unit described later.

[0025] The current command generating unit 23 generates a current command value Iac_ref based on the DC system voltage command Vref passed through the command value filter unit 24 and the voltage of the DC system 50 detected by the sixth sensor 56. The current command generating unit 23 may generate a current command value Iac_ref that has been subjected to limiter processing that sets upper and lower limits. The current command generating unit 23 may generate a power command value instead of a current command value.

[0026] The output voltage control unit 22 controls the voltage that the AC-DC conversion unit 21 outputs to the AC input system 2 based on the current command value Iac_ref generated by the current command generation unit 23, the current and voltage of the AC input system 2 detected by the fifth sensor 55, and the current and voltage of the DC system 50 detected by the sixth sensor 56.

[0027] 3 is a configuration diagram of a DC-DC converter for a DC power supply according to this embodiment. DC-DC converter 40 of this embodiment includes DC-DC conversion unit 41 that performs power conversion, seventh sensor 57 that detects the current and voltage of DC system 50, eighth sensor 58 that detects the current and voltage on the DC power supply 4 side, output voltage control unit 42 that controls the output voltage of DC-DC conversion unit 41, current command generation unit 43 that generates a current command value Ibat_ref for DC-DC conversion unit 41, command value filter unit 44 that processes charge / discharge power command Pbat_ref, and autonomous operation control unit 45. Seventh sensor 57 may be substituted with third sensor 53 shown in FIG. 1.

[0028] The charge / discharge power command Pbat_ref is input from the charge / discharge power command generation unit 49. The command value filter unit 44 is, for example, a low-pass filter, and can suppress sudden fluctuations in the charge / discharge power command Pbat_ref. The time constant of the low-pass filter is set in advance in accordance with the control characteristics of the DC-DC conversion unit 41. If the control response of the DC-DC conversion unit 41 is small and there is little possibility of an overshoot occurring in the output voltage, the command value filter unit 44 may be omitted. Furthermore, the command value filter unit 44 may include a limiter that sets upper and lower limits for the charge / discharge power command Pbat_ref.

[0029] The charge / discharge power command Pbat_ref is determined according to the charge / discharge capability and remaining capacity of the DC power supply 4. For example, if the DC power supply 4 is configured with a secondary battery, the charge / discharge power command Pbat_ref is determined according to the state of charge (SOC) and state of health (SOH) of the secondary battery.

[0030] The autonomous driving control unit 45 switches to autonomous driving and generates an autonomous driving charge / discharge power command Pbat_ind for performing autonomous driving based on the current and voltage of the DC system detected by the seventh sensor 57. The autonomous driving control unit 45 sends the generated autonomous driving charge / discharge power command Pbat_ind to the current command generation unit 43. Note that autonomous driving here refers to a state in which the DC-DC conversion unit 41 generates an autonomous driving charge / discharge power command Pbat_ind to maintain the voltage of the DC system within a target voltage range and outputs power based on that command. Furthermore, heteronomous operation refers to a state in which the DC-DC conversion unit 41 outputs power based on a charge / discharge power command Pbat_ref received from an external controller or the like. Note that the operation of the autonomous driving control unit 45 will be described later.

[0031] The current command generating unit 43 generates a current command value Ibat_ref based on the charge / discharge power command Pbat_ref that has passed through the command value filter unit 44, the autonomous driving charge / discharge power command Pbat_ind generated by the autonomous driving control unit 45, and the current and voltage on the DC power supply 4 side detected by the eighth sensor 58. The current command generating unit 43 may also generate a current command value Ibat_ref that has been subjected to limiter processing that sets upper and lower limits.

[0032] The output voltage control unit 42 controls the voltage output by the DC-DC conversion unit 41 based on the current command value Ibat_ref generated by the current command generation unit 43, the current and voltage of the DC system 50 detected by the seventh sensor 57, and the current and voltage on the DC power supply 4 side detected by the sixth sensor 56.

[0033] FIG. 4 is a diagram illustrating the operation of the autonomous driving control unit in this embodiment. In FIG. 4, the vertical axis represents the voltage of the DC system 50, and the horizontal axis represents the output power of the DC-DC conversion unit 41. On the horizontal axis, the power output by the DC-DC conversion unit 41 to the DC system 50 is taken as positive. Therefore, on the negative side of the horizontal axis, the DC-DC conversion unit 41 outputs (charges) power to the DC power source 4. In FIG. 4, VH represents the upper limit stop voltage, VL represents the lower limit stop voltage, and Vc and Vd represent the upper and lower limits of the threshold voltage when the DC-DC conversion unit 41 starts autonomous driving. Furthermore, +Pdc represents the maximum output power when the DC-DC conversion unit 41 outputs to the DC system 50, and −Pdc represents the maximum output power when the DC-DC conversion unit 41 outputs to the DC power source 4.

[0034] The autonomous operation charge / discharge power command Pbat_ind generated by the autonomous operation control unit 45 is set as follows. The autonomous operation charge / discharge power command Pbat_ind is set to be equal to the charge / discharge power command Pbat_ref at Vc and Vd, which are the upper and lower limits of the threshold voltage. In a voltage region lower than the threshold voltage Vd, the autonomous operation charge / discharge power command Pbat_ind is set to increase the output power to the DC system as the DC system voltage decreases, so as to prevent a drop in the DC system voltage. At this time, the maximum value of the autonomous operation charge / discharge power command Pbat_ind is set by the maximum output power of the DC-DC conversion unit 41+Pdc. In a voltage region higher than the threshold voltage Vc, the autonomous operation charge / discharge power command Pbat_ind is set to decrease the output power to the DC system as the DC system voltage increases, so as to prevent a rise in the DC system voltage. If the DC system voltage rises even when the output power to the DC system is reduced, the autonomous operation charge / discharge power command Pbat_ind is set so that the output power of the DC-DC conversion unit 41 becomes negative, i.e., so that power is charged to the DC power source 4.

[0035] When the voltage of the DC system 50 detected by the seventh sensor 57 is equal to or higher than Vd and equal to or lower than Vc, the current command generating unit 43 generates a current command value Ibat_ref based on the charge / discharge power command Pbat_ref sent from the command value filter unit 44. Note that the voltage of the DC system that is equal to or higher than Vd and equal to or lower than Vc is referred to as a steady-state voltage. Therefore, when the voltage of the DC system is a steady-state voltage, the DC-DC converting unit 41 outputs power based on the charge / discharge power command Pbat_ref.

[0036] When the voltage of the DC system 50 detected by the seventh sensor 57 is less than Vd or exceeds Vc, the autonomous driving control unit 45 sends the autonomous driving charge / discharge power command Pbat_ind to the current command generation unit 43. The current command generation unit 43 generates a current command value Ibat_ref based on the autonomous driving charge / discharge power command Pbat_ind sent from the autonomous driving control unit 45. Therefore, when the voltage of the DC system is not a steady voltage, the DC-DC conversion unit 41 outputs power based on the autonomous driving charge / discharge power command Pbat_ind. As shown in FIG. 4, the region in which the DC-DC conversion unit 41 outputs power based on the autonomous driving charge / discharge power command Pbat_ind is shown as the autonomous driving region.

[0037] That is, when the voltage of the DC system 50 is equal to or higher than Vd or equal to or lower than Vc, the DC-DC converter 41 performs heteronomous operation based on the charge / discharge power command Pbat_ref. When the voltage of the DC system 50 is lower than Vd or higher than Vc, the DC-DC converter 41 performs autonomous operation based on the autonomous operation charge / discharge power command Pbat_ind.

[0038] If the DC-DC conversion unit 41 continues to operate autonomously and output maximum output power, but the voltage of the DC system 50 exceeds the upper limit stop voltage VH or falls below the lower limit stop voltage VL, the autonomous operation control unit 45 stops the operation of the DC distribution system 1.

[0039] 5 is a configuration diagram of a DC-DC load converter according to this embodiment. The DC-DC load converter 30 of this embodiment includes a DC-DC conversion unit 31 that performs power conversion, a ninth sensor 59 that detects the voltage and current of the DC system 50, a tenth sensor 60 that detects the current and voltage on the load 3 side, an output voltage control unit 32 that controls the output voltage of the DC-DC conversion unit 31, and a command value filter unit 33 that processes the load supply voltage command Vload_ref. The ninth sensor 59 may be substituted by the second sensor 52 shown in FIG. 1.

[0040] The load supply voltage command Vload_ref is input from a load supply voltage command generator 39. The command value filter 33 is, for example, a low-pass filter, and is capable of suppressing sudden fluctuations in the load supply voltage command Vload_ref. The time constant of the low-pass filter is set in advance in accordance with the control characteristics of the DC-DC converter 31. If the control response of the DC-DC converter 31 is small and there is little possibility of an overshoot occurring in the output voltage, the command value filter 33 may be omitted. Furthermore, the command value filter 33 may include a limiter that sets upper and lower limits for the load supply voltage command Vload_ref.

[0041] The load supply voltage command Vload_ref is determined depending on the rated voltage of the load 3, the amount of voltage drop in the wiring to the load 3, and the like.

[0042] The output voltage control unit 32 controls the voltage output by the DC-DC conversion unit 31 based on the load supply voltage command Vload_ref that has passed through the command value filter unit 33, the current and voltage of the DC system detected by the ninth sensor 59, and the current and voltage on the load 3 side detected by the tenth sensor 60.

[0043] From the viewpoint of energy conservation, the DC power distribution system 1 is designed to reduce the amount of power purchased from the AC grid. Furthermore, normal operation of the DC power distribution system 1 is also performed to reduce the amount of power purchased from the AC grid. Therefore, even in forward power operation, the DC power distribution system 1 supplies most of the power required by the load 3 from the power generation device 5 and the DC power source 4, reducing the amount of power supplied from the AC input grid 2 and increasing the frequency of reverse power operation. On the other hand, if the power generation device 5 is a solar power generation device, the amount of power generated will be nearly zero on cloudy days and at night. In situations where the power generation device 5 cannot generate power, the DC power distribution system 1 must mainly supply power from the AC input grid 2 to the load 3 and supply charging power to the DC power source 4.

[0044] FIG. 6 is an explanatory diagram showing an example of the power consumption and power generated by a photovoltaic power generation system over time in a typical office building. In FIG. 6, the upper graph shows the power consumption in the office building, and the lower graph shows the power generated by the photovoltaic power generation system. The power consumption in the office building corresponds to the power consumption of the load 3 in the DC power distribution system 1 of this embodiment. As shown in FIG. 6, the power consumption in the office building is characterized by being high during the day and low at night. This characteristic coincides with the characteristic of the power generated by the photovoltaic power generation system. Therefore, in the DC power distribution system 1 of this embodiment, reverse power operation is not required at night, and the load power is low, so it is not necessary to maintain a high DC grid voltage. Generally, the power loss in the AC-DC converter and DC-DC converter is reduced as the step-up / step-down ratio decreases. Therefore, setting the DC grid voltage at night lower than the daytime DC grid voltage can be expected to reduce losses in the DC power distribution system 1 as a whole. Note that the load DC-DC converter and the load can be considered together as a constant power load. Therefore, when the load power is low, the DC grid voltage can be lowered to prevent the current from exceeding the rated current of the wiring even if the current increases.

[0045] Next, a description will be given of a procedure for switching the operation mode in the DC power distribution system 1 of this embodiment. In the following description, it is assumed that the DC power source 4 is configured by a secondary battery. FIG. 7 is a flowchart showing the operation mode switching process in the DC power distribution system 1 of this embodiment. The operation mode switching process shown in FIG. 7 is a process for switching from operation mode 1 to operation mode 2. After the process starts, in step S01, the switching command generation unit 10 determines whether the DC power distribution system 1 is in a steady state. If in step S01 the DC power distribution system 1 is in an unsteady state, such as during start-up or fall (NO), the switching command generation unit 10 ends the switching process. If in step S01 the DC power distribution system 1 is in a steady state (YES), the switching command generation unit 10 proceeds to step S02. Here, the steady state refers to a state in which the DC power distribution system 1 is operating normally, not in a transient operation state, and performing forward power operation or reverse power operation.

[0046] In step S02, the switching command generation unit 10 determines whether the operation mode of the DC power distribution system 1 is operation mode 1. The determination in step S02 can be made by reading out the operation state of the DC power distribution system 1 stored in a memory unit or the like. In step S02, if the operation mode of the DC power distribution system 1 is not operation mode 1 (NO), the switching command generation unit 10 ends the switching process. In step S02, if the operation mode of the DC power distribution system 1 is operation mode 1 (YES), the switching command generation unit 10 proceeds to step S03.

[0047] In step S03, the switching command generation unit 10 determines whether the sum of the load power Pload supplied to the load DC-DC converter 30 and the load 3 detected by the second sensor 52 and the charge-discharge power Pbat supplied to the DC power supply DC-DC converter 40 and the DC power supply 4 detected by the third sensor 53 is greater than the power generation power Pg of the power generation device 5 detected by the first sensor 51. In step S03, when the sum of Pload and Pbat is less than or equal to Pg (NO), the switching command generation unit 10 ends the switching process. In step S03, when the sum of Pload and Pbat is greater than Pg (YES), the switching command generation unit 10 proceeds to step S04. Here, Pg is positive in the direction flowing from the power generation device 5 into the DC system 50, Pload is positive in the direction flowing out from the DC system 50 to the load DC-DC converter 30 side, and Pbat is positive in the direction flowing out from the DC system 50 to the DC power supply DC-DC converter 40 side (charging direction). When the relationship Pg < Pload + Pbat holds, since no reverse power flow operation occurs in the AC input system 2 and there is no problem even if the operation mode 1 is switched, the switching command generation unit 10 proceeds to step S04.

[0048] Note that since the determination in step S03 is a process of determining whether a reverse power flow operation occurs, it may be determined whether a reverse power flow operation has occurred from the output power Pacdc of the AC-DC converter 20 detected by the first sensor 51 provided between the AC-DC converter 20 and the DC system 50.

[0049] For each power used in step S03, a value filtered to remove the influence of noise such as noise is used. When not using the filtered value, it is preferable to use a value excluding the influence of noise, such as using the average value over a certain period.

[0050] In step S04, the switching command generator 10 determines whether the state of charge SOC of the secondary battery, which is the DC power supply 4, is greater than a first threshold value SOCth1 of remaining capacity. Here, the first threshold value SOCth1 of remaining capacity is set to, for example, 80% of the capacity when fully charged. In step S04, if the SOC is equal to or less than SOCth1 (NO), the switching command generator 10 ends the switching process. In step S04, if the SOC is greater than SOCth1 (YES), the switching command generator 10 proceeds to step S05.

[0051] The processing from step S05 onward is processing for switching the operation mode from operation mode 1 to operation mode 2. In step S05, the DC system voltage command generation unit 29 calculates an optimal value of the DC system voltage command Vref. Several methods can be considered for calculating the optimal value of the DC system voltage command Vref. For example, there is a method in which the loss characteristics of the power conversion of each of the AC-DC converter 20, the load DC-DC converter 30, and the DC power supply DC-DC converter 40 are stored in advance and used for calculation. Specifically, the DC power distribution system 1 has a storage unit, and functions representing the loss characteristics using the power information (input power information or output power information) of each of the AC-DC converter 20, the load DC-DC converter 30, and the DC power supply DC-DC converter 40 as variables are stored in this storage unit. A plurality of these functions are prepared for each DC system voltage. By using these functions, it is possible to calculate the loss of each converter if the power and DC system voltage are known. Therefore, by calculating the losses of each converter while changing the DC system voltage, the DC system voltage at which the total loss is smallest can be set as the optimal value for Vref. At this time, information on the wiring impedance of the DC system can also be stored, and the current value flowing in the DC system can be calculated by dividing the detected power value by the DC system voltage value. By calculating the current value flowing in the DC system, the loss in the DC system due to the wiring impedance can be calculated, making it possible to find a more optimal Vref.

[0052] Alternatively, for simplicity, the higher of the load supply voltage to the load 3 and the voltage of the DC power supply 4 may be set as Vref. This makes it possible to reduce the step-down ratio from the DC system voltage to the load 3 and the DC power supply 4. Furthermore, it is also possible to actually vary Vref and set the optimum value of Vref using a hill-climbing method or the like so that Pacdc+Pg-(Pload+Pbat) is minimized.

[0053] Next, in step S06, the switching command generator 10 determines whether the DC system voltage command Vref calculated in step S05 is smaller than the lower limit voltage Vlim_low of the AC-DC converter 20. If Vref is smaller than Vlim_low (YES) in step S06, the switching command generator 10 stops the operation of the AC-DC converter 20 in step S07. By the switching command generator 10 stopping the operation of the AC-DC converter 20, it is possible to start independent operation of the DC power supply DC-DC converter 40 in step S08, and to realize a DC system voltage corresponding to Vref calculated in step S05. Here, the independent operation of the DC power supply DC-DC converter 40 means a state in which the DC power supply DC-DC converter 40 controls the charge / discharge power of the DC power supply 4 in order to control the DC system voltage. The difference from autonomous operation will be explained. In autonomous operation, when the AC-DC converter 20 controls the DC system voltage and the DC system voltage falls outside a certain range (the voltage range from Vc to Vd), the DC-DC converter 40 for DC power supply increases or decreases the power command Pbat_ref given to itself to operate so that the voltage does not deviate from the voltage range from VH to VL. On the other hand, in standalone operation, the AC-DC converter 20 does not control the DC system voltage. The DC-DC converter 40 for DC power supply controls the DC system voltage and charges or discharges the power required to maintain the DC system voltage at the command voltage.

[0054] The standalone operation of the DC-DC converter 40 for DC power supply performed here requires a change in operation from the autonomous operation that transitions when the DC system voltage falls below the threshold voltage Vd in operation mode 1. In autonomous operation that transitions when the DC system voltage falls below the threshold voltage Vd in operation mode 1, the DC-DC converter 40 for DC power supply controls the DC system voltage to be Vd, but in standalone operation in operation mode 2, the DC-DC converter 40 for DC power supply needs to control the DC system voltage to Vref. In operation mode 1, if the DC system voltage is a steady voltage, the DC-DC converter 40 for DC power supply is in a heteronomous operation state in which it charges and discharges in accordance with a charge / discharge power command value, and the DC system voltage is controlled by the AC-DC converter 20.

[0055] When the operation of the AC-DC converter 20 is stopped and the standalone operation of the DC-DC converter 40 for DC power supply is started by the processing of steps S07 and S08, it is necessary to mechanically disconnect the electrical connection between the AC-DC converter 20 and the DC system 50 so that power is not supplied from the AC-DC converter 20 to the DC system 50. If the electrical connection between the AC-DC converter 20 and the DC system 50 is not disconnected, for example, when the voltage of the DC system 50 is lower than the effective voltage of the AC input system 2 multiplied by the square root of 2, power is supplied from the AC input system 2 to the DC system 50 via a parasitic diode of a switching semiconductor element of the AC-DC converter 20, a diode connected in parallel to the switching semiconductor element, or the like, and the voltage of the DC system 50 rises.

[0056] Fig. 8 is an explanatory diagram of the operation mode switching process in the DC power distribution system of this embodiment. Fig. 8 shows the DC system voltage command Vref in the switching process from step S06 to step S08 in Fig. 7. In Fig. 8, the horizontal axis represents time and the vertical axis represents voltage. As shown in Fig. 8, if Vref calculated in step S05 is also smaller than Vlim_low, the DC-DC converter 40 for DC power supply starts independent operation.

[0057] In step S06, if Vref is equal to or higher than Vlim_low (NO), the switching command generator 10 continues operation of the AC-DC converter 20. Therefore, the DC-DC converter 40 for DC power supply does not start independent operation. At this time, if the relationship between the threshold voltage Vd for independent operation of the DC-DC converter 40 for DC power supply, Vref, and the lower limit operating voltage Vlim_low of the AC-DC converter 20 is Vd≧Vref≧Vlim_low, there is a possibility that the DC-DC converter 40 for DC power supply will switch to independent operation. Therefore, in step S09, the switching command generator 10 changes Vd to a value smaller than Vref.

[0058] Fig. 9 is an explanatory diagram of the operation mode switching process in the DC power distribution system of this embodiment. Fig. 9 shows the DC system voltage command Vref and the threshold voltage Vd for independent operation of the DC power supply DC-DC converter 40 in the switching process from step S06 to step S09 in Fig. 7. In Fig. 9, the horizontal axis represents time and the vertical axis represents voltage. As shown in Fig. 9, by changing Vd to a value smaller than Vref, it is possible to prevent the DC power supply DC-DC converter 40 from switching to independent operation.

[0059] Next, a description will be given of a procedure for switching from operation mode 2 to operation mode 1 in the DC power distribution system 1 of this embodiment. In the following description, it is assumed that the DC power source 4 is configured by a secondary battery.

[0060] Fig. 10 is a flowchart showing the operation mode switching process in the DC power distribution system 1 of this embodiment. The operation mode switching process shown in Fig. 10 is a process for switching from operation mode 2 to operation mode 1. After the process starts, in step S11, the switching command generator 10 determines whether the sum of the load power Pload supplied to the load DC-DC converter 30 and the load 3, detected by the second sensor 52, and the charge / discharge power Pbat supplied to the DC power supply DC-DC converter 40 and the DC power supply 4, detected by the third sensor 53, is greater than the power generation power Pg of the power generator 5, detected by the first sensor 51. In step S11, if the sum of Pload and Pbat is equal to or less than Pg (NO), the switching command generator 10 proceeds to step S18. In step S18, the switching command generator 10 shifts the operation mode to operation mode 1 and ends the switching process. When switching to operation mode 1, if the DC-DC converter 40 for DC power supply is operating in an independent manner, the DC system voltage command generation unit 29 first increases Vref toward a voltage value that exceeds the lower limit operating voltage Vlim_low of the AC-DC converter 20. The purpose of this is to increase the DC system voltage to Vlim_low or higher before starting up the AC-DC converter 20. Thereafter, the AC-DC converter 20 is started up, and the independent operation of the DC-DC converter 40 for DC power supply is stopped. If the DC-DC converter 40 for DC power supply is not operating in an independent manner, the switching to operation mode 1 is completed by returning the DC system voltage command Vref to the AC-DC converter 20 to a steady voltage.

[0061] In step S11, the power generation power Pg and the load power Pload may be calculated using time-series predicted power generation power and time-series predicted load power, respectively. Using the predicted power allows the operation mode to be switched before an increase in Pg or a decrease in Pload actually occurs. For example, using the time-series predicted power in step S11 allows the operation mode to be switched in advance from a nighttime period when the power generation by solar power generation is low and the load power consumption is low to a morning period when the power generation by solar power generation and the load power consumption are both increasing. This prevents a sudden rise in the DC grid voltage due to the power generation by solar power generation during the switch to operation mode 1, which would suppress the solar power generation, or an overvoltage in the DC grid voltage, which would cause the DC distribution system to shut down. If, in step S11, the sum of Pload and Pbat is greater than Pg (YES), the switching command generator 10 proceeds to step S12.

[0062] In step S12, the switching command generation unit 10 determines whether the DC power supply DC-DC converter 40 is in an independent operation state. The determination in step S12 can be made by reading out the operation state of the DC power supply DC-DC converter 40 stored in a memory unit or the like. If the DC power supply DC-DC converter 40 is not in an independent operation state (NO) in step S12, the switching command generation unit 10 ends the switching process. If the DC power supply DC-DC converter 40 is in an independent operation state (YES) in step S12, the switching command generation unit 10 proceeds to step S13.

[0063] In step S13, the DC system voltage command generating unit 29 adjusts Vref based on the remaining capacity of the DC power supply 4. Specifically, as the remaining capacity of the DC power supply 4 decreases and the SOC drops, the DC system voltage command generating unit 29 increases Vref toward a voltage value that exceeds the lower limit operating voltage Vlim_low of the AC-DC converter 20. The purpose of this adjustment is to make the DC system voltage equal to or higher than Vlim_low when it is necessary to start the AC-DC converter 20 when the remaining capacity of the DC power supply 4 becomes low.

[0064] In step S14, the switching command generator 10 determines whether the state of charge SOC of the secondary battery, which is the DC power source 4, is equal to or less than a second threshold value SOCth2 of the remaining capacity. Here, the second threshold value SOCth2 of the remaining capacity is set to, for example, 20% of the capacity when fully charged. In step S14, if the SOC exceeds SOCth2 (NO), the switching command generator 10 ends the switching process. In step S14, if the SOC is equal to or less than SOCth2 (YES), the switching command generator 10 proceeds to step S15. If the state of charge SOC is equal to or less than the second threshold value SOCth2 of the remaining capacity, it can be determined that charging from the DC system 50 to the DC power source 4 is necessary.

[0065] In step S15, the switching command generator 10 starts up the AC-DC converter 20. Thereafter, the independent operation of the DC-DC converter 40 for DC power supply is stopped. Furthermore, the switching command generator 10 controls Pbat_ref so as to charge the DC power supply 4. By this operation, the DC power distribution system 1 charges the DC power supply 4 using power input from the AC input system 2 and simultaneously supplies power to the load 3.

[0066] In step S16, the switching command generator 10 determines whether the state of charge SOC of the secondary battery, which is the DC power supply 4, is greater than a first threshold value SOCth1 of remaining capacity. If the SOC is equal to or less than SOCth1 (NO) in step S16, the switching command generator 10 returns to the processing of step S16. If the SOC is greater than SOCth1 (YES) in step S16, the switching command generator 10 proceeds to step S17.

[0067] In step S17, the switching command generator 10 starts independent operation of the DC power supply DC-DC converter 40 and stops the AC-DC converter 20. In this way, in the processes from step S12 to step S17, the AC-DC converter 20 switches between a stopped state and an operating state depending on the state of charge of the DC power supply 4, and the AC-DC converter 20 operates intermittently.

[0068] In a DC power distribution system configured as described above, when the power generated by the power generation device is smaller than the power supplied to the load by the load DC-DC converter, the voltage of the DC system is reduced and the operation mode of the AC-DC converter is switched from operation mode 1 to operation mode 2, so that the step-down ratio when stepping down the DC system voltage to the load supply voltage for supplying to the load and to the charging voltage for charging the DC power supply is small. As a result, in the DC power distribution system of this embodiment, even if the steady-state voltage of the DC system voltage and the load supply voltage are significantly different, the voltage of the DC system is reduced when the power generated by the power generation device is small, so power loss can be reduced.

[0069] In the DC power distribution system of this embodiment, the power generation device is a DC power generation device such as a solar power generation device, but it may also be an AC power generation device such as a wind power generation device. If the power generation device is an AC power generation device, an AC-DC converter may be installed between the power generation device and the DC system.

[0070] Embodiment 2 FIG. 11 is a configuration diagram of a DC power distribution system according to a second embodiment. A DC power distribution system 1 according to this embodiment is provided between a DC input system 7 and a load 3, a DC power source 4, and a power generation device 5. Here, the DC input system 7 is a DC system operated by an electric power company. As shown in FIG. 11, the configuration of the DC power distribution system 1 according to this embodiment is the same as the configuration of the DC power distribution system according to the first embodiment shown in FIG. 1, except that the AC input system 2 is replaced with the DC input system 7 and the AC-DC converter 20 is replaced with a DC-DC converter 70. Other configurations of the DC power distribution system 1 according to this embodiment are the same as those of the DC power distribution system according to the first embodiment.

[0071] The DC power distribution system 1 of this embodiment includes a DC-DC converter 70 that converts DC power input from a DC input system 7 into DC power of a different voltage and outputs it to a DC system 50, a load DC-DC converter 30 provided between the DC system 50 and a load 3, a DC power supply DC-DC converter 40 provided between the DC system 50 and a DC power source 4, and a switching command generation unit 10. The load DC-DC converter 30 converts the DC power of the DC system 50 into a load supply voltage for the load 3 and supplies it to the load 3. The load 3 is an electric device driven by a DC voltage and is made up of one or more electric devices.

[0072] The DC power distribution system 1 of this embodiment is capable of performing a forward power operation in which DC power input from the DC input system 7 is supplied to the load 3 and the DC power source 4 via the DC system 50, and a reverse power operation in which DC power input from the DC power source 4 and the power generation device 5 is supplied to the DC input system 7 via the DC system 50. In the DC power distribution system 1, the forward power operation and the reverse power operation are controlled by a DC-DC converter 70.

[0073] In the DC power distribution system 1 of this embodiment, the DC-DC converter 70 may be configured as an insulated bidirectional converter. In this case, reverse power operation is possible regardless of the relationship between the voltage of the DC system 50 and the voltage of the DC input system 7. However, since there is a limit to the step-up / step-down ratio of the DC-DC converter 70, there is also a limit to the voltage difference between the DC input system 7 and the DC system 50. This limit voltage is the lower limit voltage Vlim_low of operation mode 1. Furthermore, the voltage of the DC system 50 is set higher than the load supply voltage of the load 3 and the charge / discharge voltage of the DC power source 4. For example, the voltage of the DC input system 7 is set to 1500 V, the voltage of the DC system 50 is set to 740 V, the load supply voltage of the load 3 is set to 340 V, and the charge / discharge voltage of the DC power source 4 is set to 300 V. Power is supplied to the load 3 and the DC power source 4 at voltages stepped down from the voltage of the DC system 50 by the load DC-DC converter 30 and the DC power source DC-DC converter 40, respectively.

[0074] The process of switching operation modes in the DC power distribution system 1 of this embodiment is similar to the flowcharts shown in FIGS. 7 and 10 of the first embodiment. However, in FIGS. 7 and 10, the AC-DC converter 20 needs to be replaced with the DC-DC converter 70. For example, in the DC power distribution system 1 of this embodiment, when switching from operation mode 1 to operation mode 2, step S06 in FIG. 7 is a process of stopping the DC-DC converter 70. Furthermore, when switching from operation mode 2 to operation mode 1, step S15 in FIG. 10 is a process of starting the DC-DC converter 70 and stopping the stand-alone operation of the DC power supply DC-DC converter 40. Similarly, step S17 in FIG. 10 is a process of starting the stand-alone operation of the DC power supply DC-DC converter 40 and stopping the DC-DC converter 70.

[0075] In a DC power distribution system configured as described above, when the power generated by the power generation device is smaller than the power supplied to the load by the load DC-DC converter, the voltage of the DC system is reduced and the operation mode of the DC-DC converter is switched from operation mode 1 to operation mode 2, so that the step-down ratio when stepping down the DC system voltage to the load supply voltage for supplying to the load and to the charging voltage for charging the DC power supply is small. As a result, in the DC power distribution system of this embodiment, even if the steady-state voltage of the DC system voltage and the load supply voltage differ greatly, the voltage of the DC system is reduced when the power generated by the power generation device is small, so power loss can be reduced.

[0076] Embodiment 3 Fig. 12 is a configuration diagram of a DC power distribution system according to a third embodiment. A DC power distribution system 1 according to this embodiment is provided between an AC input system 2, a load 3, and a power generation device 5. As shown in Fig. 12, the configuration of the DC power distribution system 1 according to this embodiment is the same as the configuration of the DC power distribution system according to the first embodiment shown in Fig. 1 except that the DC-DC converter for DC power supply 40, the charge / discharge power command generating unit 49, and the third sensor 53 are removed. Other configurations of the DC power distribution system 1 according to this embodiment are the same as the configuration of the DC power distribution system according to the first embodiment.

[0077] The operation mode switching process in the DC power distribution system 1 of this embodiment is similar to the flowcharts shown in Figs. 7 and 10 of the first embodiment. However, it is necessary to exclude the operation of the DC power supply DC-DC converter in Figs. 7 and 10. Specifically, the operation of the DC power supply DC-DC converter in step S08 of Fig. 7 is excluded. Also, the operation of the DC power supply DC-DC converter in steps S15 and S17 of Fig. 10 is excluded. Furthermore, Pbat is excluded in step S03 of Fig. 7 and step S11 of Fig. 10.

[0078] In the DC power distribution system of this embodiment, Vref in operation mode 2 must be higher than the lower limit operating voltage Vlim_low of the AC-DC converter 20. If the DC system voltage is lower than Vlim_low, the AC-DC converter 20 will stop operating. Therefore, Vref in operation mode 2 of the DC power distribution system of this embodiment is higher than Vref in operation mode 2 of the DC power distribution system of Embodiment 1. Therefore, in the DC power distribution system of this embodiment, the amount of voltage drop in the DC system when the power generated by the power generation device is low is smaller than in the DC power distribution system of Embodiment 1. However, even if the steady-state voltage of the DC system voltage is significantly different from the load supply voltage, the voltage of the DC system is dropped when the power generated by the power generation device is low, so power loss can be reduced.

[0079] The switching command generation unit 10 includes a processor 100 and a storage device 101, as shown in FIG. 13, which illustrates an example of hardware. The storage device includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory, although not shown. Alternatively, a hard disk auxiliary storage device may be used instead of the flash memory. The processor 100 executes a program input from the storage device 101. In this case, the program is input to the processor 100 from the auxiliary storage device via the volatile storage device. The processor 100 may output data such as calculation results to the volatile storage device of the storage device 101, or may store the data in the auxiliary storage device via the volatile storage device.

[0080] Although the present application describes various exemplary embodiments, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are conceivable within the scope of the technology disclosed in this application, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with a component of another embodiment. [Explanation of symbols]

[0081] REFERENCE SIGNS LIST 1 DC power distribution system, 2 AC input system, 3 Load, 4 DC power source, 5 Power generation device, 7 DC input system, 10 Switching command generation unit, 20 AC-DC converter, 21 AC-DC conversion unit, 22 Output voltage control unit, 23 Current command generation unit, 24 Command value filter unit, 29 DC system voltage command generation unit, 30 Load DC-DC converter, 31 DC-DC conversion unit, 32 Output voltage control unit, 33 Command value filter unit, 39 Load supply voltage command generation unit, 40 DC power supply DC-DC converter, 41 DC-DC conversion unit, 42 Output voltage control unit, 43 Current command generation unit, 44 Command value filter unit, 45 Autonomous operation control unit, 49 Charging / discharging power command generation unit, 50 DC system, 51 First sensor, 52 Second sensor, 53 Third sensor, 54 Fourth sensor, 55 Fifth sensor, 56 Sixth sensor, 57 Seventh sensor, 58 Eighth sensor, 59 ninth sensor, 60 tenth sensor, 70 DC-DC converter, 100 processor, 101 storage device.

Claims

1. an AC-DC converter having a forward power function of converting AC power input from an electric power system into DC power and outputting the DC power to the DC system, and a reverse power function of converting DC power from the DC system into AC power and outputting the AC power to the electric power system; a first sensor for detecting power generated by a power generation device connected to the DC system; a load DC-DC converter for supplying power to a load connected to the DC system; a second sensor for detecting power supplied from the DC system to the load DC-DC converter and the load; a switching command generation unit that generates a command to switch between two operation modes of the AC-DC converter; a DC power supply DC-DC converter that inputs and outputs charging and discharging power of a DC power supply connected to the DC system, the two operation modes are an operation mode 1 in which the reverse power function of the AC-DC converter is enabled, and an operation mode 2 in which the reverse power function of the AC-DC converter is disabled, and in the operation mode 1, the voltage of the DC system is set higher than a value obtained by multiplying the effective voltage value of the AC power by the square root of 2; the switching command generation unit reduces the voltage of the DC system and switches the operation mode of the AC-DC converter from operation mode 1 to operation mode 2 when the power generated by the power generation device detected by the first sensor is smaller than the power supplied to the load DC-DC converter and the load detected by the second sensor, and when the operation mode of the AC-DC converter is operation mode 2, the DC power supply DC-DC converter outputs discharge power of the DC power supply to the DC system.

2. 2. The DC power distribution system according to claim 1, wherein a first threshold value related to the remaining capacity of the DC power supply and a second threshold value smaller than the first threshold value are set in advance, and when the operation mode of the AC-DC converter is in operation mode 2, the AC-DC converter is stopped if the remaining capacity of the DC power supply is larger than the first threshold value, and the AC-DC converter is started if the remaining capacity of the DC power supply is equal to or smaller than the second threshold value.

3. 3. The DC power distribution system according to claim 1, wherein the DC-DC converter for DC power supply increases the voltage output to the DC system as the remaining capacity of the DC power supply decreases.

4. a storage unit that stores power conversion loss characteristics of the AC-DC converter, the load DC-DC converter, and the DC power supply DC-DC converter relative to the voltage of the DC system; and a DC system voltage command generation unit that generates a DC system voltage command that is a voltage that the AC-DC converter outputs to the DC system, 3. The DC power distribution system according to claim 1, wherein the DC system voltage command generation unit generates a DC system voltage command that minimizes the sum of power conversion losses of the AC-DC converter, the load DC-DC converter, and the DC power supply DC-DC converter, based on the loss characteristics stored in the storage unit.

5. a storage unit configured to store a time-series predicted power generation power of the power generation device and a time-series predicted load power of the load; 2. The DC power distribution system according to claim 1, wherein the switching command generation unit reduces the voltage of the DC system during a time period in which the predicted power generation power is smaller than the predicted load power, and switches the operation mode of the AC-DC converter from operation mode 1 to operation mode 2.

6. a DC-DC converter having a forward power function of converting DC power input from an electric power system into DC power of a different voltage and outputting the converted DC power to the DC system, and a reverse power function of converting DC power from the DC system into DC power of a different voltage and outputting the converted DC power to the electric power system; a first sensor for detecting power generated by a power generation device connected to the DC system; a load DC-DC converter for supplying power to a load connected to the DC system; a second sensor for detecting power supplied from the DC system to the load DC-DC converter and the load; a switching command generation unit that generates a command to switch between two operation modes of the DC-DC converter; a DC power supply DC-DC converter that inputs and outputs charging and discharging power of a DC power supply connected to the DC system, the two operation modes are an operation mode 1 in which the reverse power function of the DC-DC converter is enabled, and an operation mode 2 in which the reverse power function of the DC-DC converter is disabled, the switching command generation unit reduces the voltage of the DC system and switches the operation mode of the DC-DC converter from operation mode 1 to operation mode 2 when the power generated by the power generation device detected by the first sensor is smaller than the power supplied to the load DC-DC converter and the load detected by the second sensor, and when the operation mode of the DC-DC converter is operation mode 2, the DC power supply DC-DC converter outputs discharge power of the DC power supply to the DC system.

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