JP7577243B2 - DC Power Distribution System - Google Patents

Description

This application relates to a DC power distribution system.

In recent years, the use of storage batteries has expanded to respond to power outages and to shift the peak power supply to facilities. One example of a power supply system that uses storage batteries is a direct current (DC) power supply and distribution system that supplies and distributes DC power to consumers. When using storage batteries for peak shifting and power outages, if the battery is discharged too much due to peak shifting, it may no longer be able to function as a backup power source during a power outage.

In order to achieve appropriate power distribution according to the remaining capacity of the power storage device, a DC power distribution system has been proposed in which the power supply time to DC devices with low priority is set short and the power supply time to DC devices with high priority is set long (see, for example, Patent Document 1). In other words, during independent operation in response to a power outage, the power supply is cut off starting with DC devices with low priority, in order to extend the operation duration of DC devices with high priority as much as possible.

JP 2011-83088 A (paragraphs 0041 to 0047, Figures 3 to 4)

However, even when power is supplied from a storage battery during autonomous operation, power is supplied to the load via multiple power converters, and the power consumption of the power converters that make up the power supply system can sometimes result in the operating time being shorter than expected.

This application discloses technology for solving the problems described above, and aims to obtain a DC power distribution system that can reduce the power consumption of the system itself during autonomous operation and extend the time that power can be supplied to important loads.

The DC power distribution system disclosed in the present application includes a DC bus to which power is supplied as DC power from a grid power, a battery power converter arranged between the DC bus and a storage battery and performing power conversion for charging and discharging the storage battery, a plurality of load-side power converters arranged between each of a plurality of DC loads and the DC bus and converting the power supplied to the DC bus into DC power of a voltage according to the respective specifications and supplying the converted power, and a control unit that controls the battery power converter and the plurality of load-side power converters in a coordinated manner, and when the supply from the grid power is cut off, the control unit switches between a normal independent operation mode in which power is supplied to the plurality of DC loads as usual according to the state of charge of the storage battery, and a restricted operation in which the supply is limited to important loads having a high priority among the plurality of DC loads, and in the restricted operation, at least one of the power converters connected to the important loads among the load-side power converters and the power converters for the storage battery that perform power conversion by switching operation using switching elements is stopped in the switching operation to connect the input side and output side.

According to the DC power distribution system disclosed in the present application, the power consumption of the system itself can be reduced during independent operation, thereby obtaining a DC power distribution system that can extend the time during which power can be supplied from the storage battery to important loads.

1 is a block diagram showing a connection relationship between power sources and loads for explaining a configuration of a DC power distribution system according to a first embodiment. FIG. 1 is a circuit diagram showing a main circuit of a power converter constituting a DC power distribution system according to a first embodiment. 2 is a block diagram of a control unit constituting the DC power distribution system according to the first embodiment. FIG. 1 is a diagram for explaining setting of an operating region according to a charging rate of a storage battery in a DC power distribution system according to a first embodiment. FIG. 4 is a flowchart for explaining the operation of the DC power distribution system according to the first embodiment. 10 is a diagram for explaining setting of an operating range according to a modified example in accordance with a charging rate of a storage battery in the DC power distribution system according to the first embodiment. FIG. FIG. 11 is a block diagram showing a connection relationship between power sources and loads for explaining the configuration of a DC power distribution system according to a second embodiment. 11 is a flowchart for explaining an operation after transition to independent operation in the DC power distribution system according to the second embodiment. FIG. 11 is a block diagram for explaining an operation example 1 of a DC power distribution system according to a second embodiment. FIG. 11 is a block diagram for explaining an operation example 2 of the DC power distribution system according to the second embodiment. FIG. 11 is a block diagram for explaining an operation example 3 of the DC power distribution system according to the second embodiment. FIG. 11 is a block diagram for explaining an operation example 4 of the DC power distribution system according to the second embodiment. FIG. 11 is a block diagram for explaining an operation example 5 of the DC power distribution system according to the second embodiment. FIG. 13 is a block diagram for explaining an operation example 1 of a DC power distribution system according to a third embodiment. FIG. 13 is a block diagram for explaining an operation example 2 of the DC power distribution system according to the third embodiment. 2 is a block diagram showing an example of a hardware configuration of a control unit constituting the DC power distribution system according to each embodiment. FIG.

Embodiment 1.
Figures 1 to 5 are for explaining the configuration and operation of a DC power distribution system according to a first embodiment, with Figure 1 being a schematic block diagram showing the connection relationship between power sources and loads for explaining the configuration of the DC power distribution system, Figure 2 being a circuit diagram showing the main circuit of a power converter for a storage battery among multiple power converters that make up the DC power distribution system, and Figure 3 being a block diagram of a control unit that makes up the DC power distribution system. Figure 4 is a diagram for explaining the setting of an operating range for each operating mode according to the charging rate of the storage battery, and Figure 5 being a flowchart for explaining the operation of the DC power distribution system.

As shown in Fig. 1, the DC power distribution system 1 according to the first embodiment is mainly connected to a DC bus 8 via a plurality of source-side power converters 4 and load-side power converters 5, and is provided with a control unit 3 that controls the distributed power. It also has an interface circuit 2 for receiving various commands, various setting values, etc., and transmitting and displaying measurement information via a user of the system or a higher-level control device represented by a server, energy management system, etc.

In this embodiment, the main power source 911 is assumed to be an AC system as the system power, but may be a DC power source. The storage battery 912 is assumed to be a lithium ion battery, but may be another type of storage battery such as a lead storage battery. The power received from the main power source 911 and the storage battery 912 (collectively referred to as power source 91) is combined on the DC bus 8, converted into DC power suitable for each DC load 92, and distributed.

The power receiving power converter 41 and the power converter for storage battery 42 constituting the power source side power converter 4 are respectively connected to a main power source 911 and a storage battery 912. The load power converter 51 and the load power converter 52 constituting the load side power converter 5 are respectively connected to one or more load devices 921 and load devices 922 (collectively DC loads 92).

Between the main power source 911 and the receiving power converter 41, and between the storage battery 912 and the storage battery power converter 42, there are provided switches 61 and 62 (collectively referred to as power source side switches 6), which can be switched between on and off. Similarly, between the load power converter 51 and the load device 921, and between the load power converter 52 and the load device 922, there are provided switches 71 and 72 (collectively referred to as load side switches 7), which can be switched between on and off.

The power supply side circuit breaker 6 and the load side circuit breaker 7 use equipment that can switch between on and off using external commands, and cut off during a power outage in response to a cut-off signal sent from the control unit 3. If the equipment is to be manually turned on when power is restored, it is sufficient that the equipment is at least capable of cutting off in response to an external command. The open/closed state of the circuit breaker may be output to the control unit 3.

The types of DC loads 92 to which power is distributed include, for example, general loads such as lighting loads and office automation equipment, power loads such as air conditioning loads, and IT equipment loads such as servers. In the DC power distribution system 1 of this embodiment, the DC loads 92 are classified as important loads or general loads as a priority for power distribution targets during a power outage. Therefore, the connection between the load-side power converter 5 and the DC loads 92 is allocated according to the importance and type of the DC loads 92.

Here, the configuration and characteristics of the power converter will be described. The receiving power converter 41 of the DC power distribution system 1 mainly uses a PWM converter (Pulse Width Modulation Converter), while the storage battery power converter 42 and the load side power converter 5 mainly use DC power converters such as chopper circuits. The storage battery power converter 42 uses a boost chopper circuit configured with two semiconductor switches S1 and S2 (here, IGBTs: Insulated Gate Bipolar Transistors) as shown in Figure 2. Note that for simplicity, only the main circuit is shown in Figure 2, and the control circuit, sensors, etc. are omitted.

In this circuit, the DC power of the storage battery is boosted (power converted) to higher voltage DC power by repeatedly switching the semiconductor switches S1 and S2 alternately on. It is generally known that losses occur during the switching operation of switching the semiconductor switches S1 and S2 on and off. Therefore, when there is no need to boost the voltage from the storage battery 912, the semiconductor switch S1 is always kept on and in a conductive state, thereby reducing losses due to the switching operation and enabling conductivity between the input and output (between the storage battery 912 and the DC bus 8).

This operation is called the conduction mode. Therefore, the DC power distribution system 1 of the present application is configured to use the conduction mode depending on the operating state, and to reduce losses due to power consumption by the system itself. Note that this conduction mode is not limited to the boost chopper circuit shown in Figure 2, but can also be performed by other conversion circuits such as a step-down chopper, a step-up/step-down chopper, or a PWM inverter.

In the conduction mode, the input and output can be made conductive while reducing losses due to switching operations, so power consumption can be reduced regardless of the type of power converter. However, there are some types of power converters that cannot operate in the same way as in the conduction mode, and such power converters are not subject to the conduction mode specifications.

Next, the configuration of the control unit 3 will be described with reference to Fig. 3, including general components for controlling switching between the grid-connected operation mode when grid-connected power is being supplied and the independent operation mode during a power outage, and a configuration for controlling the above-mentioned conduction mode operation. The configuration for mode switching control includes a state detection unit 31 that detects the state of each device in the system based on information from a sensor unit or the like of each device, and an operation mode determination unit 32 that determines the operation mode based on information or commands obtained from the state detection unit 31 and the interface circuit 2.

As a configuration for executing the above-mentioned conduction mode, the power converter includes an operation mode determination unit 32, a state detection unit 31, and an operation command generation unit 33 that generates operation commands to each power converter based on information and commands from the interface circuit 2. The power converter also includes a threshold database (represented as DB in the figure) 34 that holds information on thresholds and the like used for operation settings according to the charge state of the storage battery 912, and a priority database 35 that holds information on the priority of each DC load 92. The power converter also includes an equipment specification database 36 that holds information on the specifications of the equipment, such as the operating voltage range of each DC load 92 and the operating range of the power converter. The operation commands for each power converter include output voltage commands, signals related to starting and stopping the power converter, and charge/discharge power commands from the storage battery 912.

Next, the operation settings of the DC power distribution system 1 according to the first embodiment will be explained with reference to the conceptual diagram of the setting of the operating range for each operating mode according to the fluctuation of the state of charge (hereinafter referred to as SoC (State of Charge)) of the storage battery in Fig. 4. The determination of the operating mode and the setting of the operating range are determined by the control unit 3 based on the SoC of the storage battery 912, the operating states of the main power source 911 and the receiving power converter 41.

The operating modes are broadly classified into two: a grid-connected operation mode in which power is supplied to the DC load 92 using power received from the main power source 911 and the storage battery 912, and an independent operation mode in which there is no connection to the main power source 911 and power is supplied to the DC load 92 only using power from the storage battery 912.

In the grid-connected operation mode, a normal operation range with no operational restrictions on charging and discharging from the storage battery 912 and a semi-restricted operation range in which discharging from the storage battery 912 is stopped are set depending on whether the SoC is equal to or greater than the threshold value Sth1. In the independent operation mode, an independent operation range in which power is supplied to multiple DC loads 92 as usual and a restricted operation range in which power is supplied only to one or more limited DC loads 92 that are predefined as important loads are set depending on whether the SoC is equal to or greater than the threshold value Sth1.

In addition, for each operation mode, a charge stop threshold Smax for preventing a reduction in the lifespan of the storage battery 912 due to overcharging and a discharge stop threshold Smin for preventing a reduction in the lifespan of the storage battery due to overdischarging are separately set in order to protect the storage battery 912. The region exceeding the charge stop threshold Smax is set as a charge stop region in which charging to the storage battery 912 is stopped, and the region below the discharge stop threshold Smin is set as a discharge stop region in which discharging from the storage battery 912 is stopped.

The threshold value Sth1 is set based on the required power amount roughly calculated in advance from the estimated power consumption and power supply time of the DC load 92 of high importance. For example, it is set to a value such that the amount of power obtained when the storage battery 912 is discharged from the threshold value Sth1 to the discharge stop threshold value Smin exceeds the required power amount, and is stored in the threshold value database 34 together with the charge stop threshold value Smax and the discharge stop threshold value Smin. In addition, the interface circuit 2 may instruct the threshold value Sth1 to be changed in real time.

Assuming the above configuration and settings, the operation of the DC power distribution system 1 will be described with reference to the flowchart in Fig. 5. It is assumed here that load device 921 is connected to an IT device load such as a server, and is set as an important load in terms of priority, and load device 922 is connected to a general load such as lighting, and is set as a general load in terms of load priority.

First, the operation mode determination unit 32 determines the operation mode based on the operation states of the main power source 911 and the power receiving power converter 41 detected by the state detection unit 31 (steps S100 to S110). As described above, when the main power source 911 and the power receiving power converter 41 are operating, it is determined that the operation mode is the interconnected operation mode in which power is supplied to the DC load 92 using power received from the main power source 911 and the storage battery 912. On the other hand, when the main power source 911 is out of power or the power receiving power converter 41 is broken, it is determined that the operation mode is the independent operation mode in which power is supplied to the DC load 92 only by the storage battery 912.

If it is determined that the system is in the grid-connected operation mode (step S120: No), the DC power distribution system 1 performs grid-connected operation to supply power received from the AC system, which is the main power source 911, to the DC load 92 (step S200). At that time, the system is operated so that the Soc is in a range of less than the charge stop threshold Smax and more than the discharge stop threshold Smin. Then, until it is determined that the system is in the independent operation mode due to a change in the situation, the system continues grid-connected operation control to switch between a normal operation range in which there is no limit on the charge and discharge operation from the storage battery 912, and a semi-limited operation range in which the discharge from the storage battery 912 is stopped, depending on the Soc.

Furthermore, during grid-connected operation, peak cut control is performed in response to commands from a higher-level control device or a user. Peak cut control refers to control in which power is discharged from the storage battery 912 to reduce the received power when the received power is greater than a predetermined peak cut command. Also, when the received power is less than the peak cut command, charging to the storage battery 912 may be performed. However, since the operation of this grid-connected operation mode is the same as general grid-connected operation, a detailed explanation will be omitted.

If too much power is consumed from the storage battery 912 due to peak cut control during grid-connected operation, there is a concern that the duration of power supply to the DC load 92 during independent operation may not be sufficiently secured. Therefore, as shown in Figure 4, when the Soc of the storage battery 912 falls below the threshold value Sth1, the discharge of the storage battery 912 for peak cut is limited. This operation ensures the duration of power supply to important loads during independent operation.

On the other hand, if a power outage occurs in the AC system or a failure occurs in the receiving power converter 41 and it is determined that the system is in the independent operation mode ("Yes" in step S120), the storage battery 912 becomes the main power source and performs independent operation to supply power to the DC load 92. When switching from grid-connected operation to independent operation, the operating range described in Figure 4 is determined based on the SoC of the storage battery.

Basically, in grid-connected operation, the SoC operates in a range between the discharge stop threshold Smin and the charge stop threshold Smax, so immediately after the transition to independent operation, for example, it is determined whether the SoC of the storage battery 912 is equal to or greater than the threshold Sth1 (step S300). If it is equal to or greater than the threshold Sth1 ("Yes" in step S300), it is determined that the storage battery 912 is in an independent operation operating range in which full load can be supplied from the storage battery 912 to the load devices 921 and 922 (step S600), and the independent operation continues until it falls below the threshold Sth1.

On the other hand, if the SoC of the storage battery 912 falls below the threshold value Sth1 ("No" in step S300), it is determined that the storage battery 912 is in a restricted operating range in which power is supplied only to important loads with high importance, and operation control is performed to supply power only to the important loads (steps S410 onward). Therefore, the operation command generation unit 33 selects the load device 921 as the target for power supply based on the priority information held in the priority database 35 for determining whether the load is a general load or an important load.

Furthermore, based on the equipment specification information constituting the power supply system from the storage battery 912 to the important load (load device 921), at least one power converter in the power supply system is selected as a target for conduction mode operation (step S410), and an operation command is generated based on the selection result.

For example, the storage battery power converter 42 is selected as the target for the conduction mode as the operating configuration that minimizes power consumption based on the output voltage range of the storage battery 912, the operating range (voltage) of the load device 921, and the operating characteristics of the storage battery power converter 42 and the load power converter 51. At this time, the input voltage of the load power converter 51 changes when DC power is directly supplied from the storage battery 912, but a command (operation command) is also generated regarding the operation to compensate for the change and maintain the output voltage to the load device 921. Furthermore, an operation command is generated to stop the operation of devices other than the above power supply system, such as the load power converter 52.

If the operating range of the load device 921 is within the output voltage range of the storage battery 912 and there is no problem with the efficiency of the load device 921, the load power converter 51 may also be subject to the conduction mode in addition to the storage battery power converter 42. Alternatively, if selecting the load power converter 51 has a greater effect of reducing power consumption than the storage battery power converter 42, only the load power converter 51 may be selected for the conduction mode. Furthermore, in addition to selecting the conduction mode, a combination for reducing power consumption, such as changing the output voltage, may be determined.

When an operation command is received by a device in the system from the operation command generating unit 33, power is supplied from the storage battery 912 to the load device 921 with high importance at least one of them is restricted to operate in a conductive mode (step S420). In this state, when the SoC of the storage battery 912 falls below the discharge stop threshold Smin ("Yes" in step S430), the independent operation is stopped (step S430) and the operation is terminated.

In other words, in the limited operating range, the switching operation of at least one of the battery power converter 42 and the load power converter 51 is stopped and operated in a conductive mode depending on the voltage of the battery 912 and the distribution voltage to the DC load 92 of high importance. This operation makes it possible to reduce losses caused by switching, reduce losses caused when power is supplied from the battery 912 to the load device 921, and increase the power supply time compared to when the supply target is simply limited.

It is also possible to set in advance whether the switching operation of the battery power converter 42 or the load power converter 51 is to be stopped, and this information may be stored in the equipment specification database 36 or the like. In this case, too, the decision is made in consideration of the load on the device and the effect of reducing losses, based on the loss characteristics and rated voltages of the battery power converter 42 and the load power converter 51, respectively, and the relationship between the battery voltage and the rated voltage of the load device 921, etc.

Variant examples.
6 is a diagram corresponding to FIG. 4 for explaining the setting of the operating range when different thresholds are set for the charging rate of the storage battery during grid-connected operation and during independent operation as a variation example. In the above example, the same threshold Sth1 is used as the threshold for transitioning to the semi-limited operating range during grid-connected operation and the threshold for transitioning to the limited operating range during independent operation, but this is not limited to this. As shown in FIG. 6, a second threshold Sth2 having a value different from the threshold Sth1 during independent operation may be used as the threshold during grid-connected operation.

By setting different thresholds, it becomes possible to set optimal operation settings for grid-connection operation without being bound by threshold value Sth1, which is set based on the duration of the important load.

Embodiment 2.
In the above-mentioned embodiment 1, an example in which the power supply is configured only by a storage battery and a main power supply is shown, but the present invention is not limited to this. In the present embodiment 2, an example in which the power supply is configured by adding a solar panel will be described. Figures 7 to 13 are for explaining the configuration and operation of the DC power distribution system according to the embodiment 2. Figure 7 is a schematic block diagram showing the connection relationship between the power supply and the load for explaining the configuration of the DC power distribution system, and Figure 8 is a flowchart for explaining the operation after switching to independent operation.

Figure 9 is a block diagram corresponding to Figure 7 showing an example of operation during grid-connected operation as operation example 1, Figure 10 is a block diagram corresponding to Figure 7 showing an example of operation during independent operation when the solar panel is generating power as operation example 2, and Figure 11 is a block diagram corresponding to Figure 7 showing an example of operation during independent operation when power generation by the solar panel is stopped as operation example 3. Also, Figures 12 and 13 are block diagrams corresponding to Figure 7 showing examples of operation during independent operation when power generation by the solar panel is stopped under different conditions as operation examples 4 and 5, respectively. Note that Figures 2 to 4 described in embodiment 1 are used for the basic configuration of the control unit and the basic operations in independent operation.

The DC power distribution system 1 according to the second embodiment is an example of an extension of the DC power distribution system 1 described in the first embodiment, in which a solar panel 913, which is a power generation facility, is added as a power source 91 and the types of DC loads 92 are increased as shown in FIG. 7. The solar panel 913 is connected to the DC bus 8 via a switch 63 and a PV power converter 43. As the DC load 92, a load device 923 and a load device 924 are newly added, and the load device 923 is connected to the DC bus 8 via a load power converter 53 and a switch 73, and the load device 924 is connected to the DC bus 8 via a switch 74 without going through a power converter.

Here, the power converters other than the receiving power converter 41 have the function of either stepping up or stepping down the DC power according to the voltage of the device. As shown in Figure 9, the power obtained from multiple power sources 91 with different input forms and voltages is supplied to multiple DC loads 92 as DC voltages with different voltages.

For example, the power source side power converter 4 is AC 400V, the battery power converter 42 is DC 400V, and the PV power converter 43 is DC 350V, so that the input power form and voltage are different, but they are set to output the same 750V DC power to the DC bus 8. Similarly, the load side power converter 5 is input with the same 750V DC, but is set to output DC power of different voltages, with the load power converter 51 being DC 600V, the load power converter 52 being DC 380V, and the load power converter 53 being DC 282V. In the second embodiment, the priority order of the DC load 92 is set to load devices 921 and 924 as general loads, and load devices 922 and 923 as important loads.

Next, the operation of the DC power distribution system 1 according to the second embodiment will be described. The solar panel 913 and the PV power converter 43 basically operate by performing maximum power point tracking control (hereinafter referred to as MPPT (Maximum Power Point Tracking) control) to maximize the power generated by the solar panel 913, and continue generating power regardless of the operating mode. However, when power generation is not expected due to time periods such as nighttime or weather conditions such as rain, a command to stop is issued by a schedule function or a higher-level control device.

In the limited operating range, there is no change in the fact that power supply to DC loads 92 classified as general loads in the predetermined priority order of DC loads 92 is stopped, but whether or not to use the conduction mode is determined based on whether or not power can be generated from the solar panel 913. Basically, the power generated from the solar panel 913 via the PV power converter 43 is sufficiently greater than the power suppressed by switching to the conduction mode, so continuing to operate the PV power converter 43 is prioritized over using the conduction mode.

In this second embodiment, the operation is basically the same as that described in the first embodiment, except for the operation according to the state of the solar panel 913 and the PV power converter 43. However, since there is a difference in the operation in the limited operating range, the operation from step S300 onwards will be described with reference to the flowchart in Figure 8. In other words, the operation will be described when a power outage occurs in the AC system, the discharge of the storage battery 912 progresses after the transition to independent operation, the SoC falls below the threshold value Sth1, and the transition to the limited range is made.

If it is determined that the operating range is limited ("No" in step S300), for example, the state detection unit 31 collects information indicating the power generation status of the solar panel 913, such as the operating state of the PV power converter 43 and time information related to sunlight, and information indicating the load state (distribution voltage). Then, it is determined whether or not the solar panel 913 can obtain power that exceeds the power suppressed by the conversion to the conduction mode described above, that is, whether or not effective power generation is possible from the solar panel 913 (step S310). At that time, even if the current amount of power generation is high, if it is determined that the power generation duration is short, such as near sunset, it may be determined that power generation is not possible.

During the daytime or other times when the solar panel 913 continues to generate power, the operation mode determination unit 32 determines that the solar panel 913 is generating sufficient power, i.e., is capable of generating power ("Yes" in step S320). The operation command generation unit 33 selects the load devices 922 and 923 as targets for power supply based on the priority information for determining whether the loads are general loads or important loads, which is stored in the priority database 35 (step S510).

Depending on the selection result, the operation command generating unit 33 generates an operation command to stop the load power converter 51, which is a device other than the power supply system leading to the important load, and to stop the power supply to the general load by opening the switch 71 and the switch 74. Then, as shown in FIG. 10, the load power converter 51, which is a device other than the power supply system leading from the storage battery 912 and the solar panel 913 to the load device 922 and the load device 923, is stopped, and the switch 71 and the switch 74 are opened to stop the power supply to the general load (step S520).

Then, until the SoC of the storage battery 912 falls below the discharge stop threshold Smin ("No" in step S430), proceed to step S310 and constantly check the power generation status of the solar panel 913.

On the other hand, if it is determined that the power generated from the solar panel 913 is insufficient, i.e., power generation is not possible ("No" in step S320), the system transitions to the restricted operating range operation (step S410) described in embodiment 1. Then, as shown in FIG. 11, the power supply to the general loads (load devices 921, 924) is stopped, and the operation of the storage battery power converter 42 is transitioned to a conduction mode based on a preset setting table to reduce losses. When transitioning the operation of the storage battery power converter 42 to the conduction mode, control is performed to transition the operation so that the voltage of the DC bus 8 does not change suddenly.

Example of operation under different conditions.
Here, an example of operation (operation control of the power converter) under different conditions will be described when power generation by the solar panel 913 stops. As shown in Fig. 12, under conditions (e.g., DC 350 V) where the storage battery voltage falls within the operating voltage range of the important loads (load devices 922 and 923), the storage battery power converter 42, the load power converter 52, and the load power converter 53 are all set to the conduction mode.

On the other hand, as shown in FIG. 13, under conditions where the battery voltage is lower (e.g., 320 V DC) than the operating voltage range of the important loads (load devices 922 and 923), the switching operation of the battery power converter 42 is turned on to perform power conversion. At that time, the power conversion operation of the battery power converter 42 is controlled so that the voltage of the DC bus 8 becomes an output voltage (e.g., 350 V DC) that falls within the operating voltage range of the important loads. Then, the load power converters 52 and 53 are placed in a conductive mode, and the DC voltage of the DC bus 8 (350 V in this example) is supplied directly to the important loads.

As in the second embodiment, when the number of DC loads 92 increases and power generation facilities such as solar panels 913 are added, it is possible to reduce losses by minimizing the number of operating power converters and stopping the supply to general loads while fully utilizing the power generated by the solar panels 913. This makes it possible to extend the time during which power can be supplied from the storage battery 912 to important loads, compared to when the supply to the general loads is simply stopped.

In particular, in operation example 4 described in Fig. 12 as an operation example under different conditions, the conversion loss is suppressed by setting both stages of the power converter from the storage battery 912 to the important load in the conduction mode. Also, even under the conditions described in Fig. 11, if the important load can be operated with the voltage of the storage battery 912 (400V in this example), the storage battery power converter 42 may also be set to the conduction mode.

On the other hand, in operation example 5 described in Figure 13, by setting one of the two stages of power converters from the storage battery 912 to the important load to a conduction mode, it is possible to expect an effect equivalent to that of operation example 3 described in Figure 11 (reduction of conversion loss).

In this embodiment, the configuration shown in Figure 7 is shown, but it goes without saying that the same effect can be obtained by adding further load equipment, or by adding power generation equipment such as a fuel cell, or an electric vehicle used as a storage battery, etc.

Furthermore, for example, if there is an overlapping region in the operating voltage ranges of multiple important loads, the battery power converter 42 may be set to the common voltage region and the load side power converter 5 for the important load may be set to a conductive mode, thereby reducing the number of switching targets. However, the target power converters should be devices that can at least either respond to changes in input voltage or vary the output voltage in response to an operation command.

In either case, it is necessary to select a combination that can suppress power consumption without placing an excessive burden on the DC load 92 and the devices in the system (especially the power converter). In this case, the combination may be selected based on a preset setting table, or the operation command generation unit 33 or the like may select or determine the combination based on information stored in the device specification database 36 or the like.

Embodiment 3.
In this third embodiment, the configuration and operation of power distribution in the case of supplying full load in the independent operation mode will be described on the premise of the configuration and operation of the first or second embodiment described above. Figures 14 and 15 are for explaining the configuration and operation of the DC power distribution system according to the third embodiment, in which Figure 14 is a block diagram corresponding to Figure 7 of the second embodiment, showing a state in which power is distributed to the full load in the independent operation operation range as an operation example 1, and Figure 15 is a block diagram corresponding to Figure 7 of the second embodiment, showing a state in which supply to the load is stopped to avoid a voltage drop of the DC bus in the independent operation operation range as an operation example 2. Note that Figures 2 to 4 and Figures 7 to 10 used in the first and second embodiments are used.

The configuration of the DC power distribution system 1 according to the third embodiment is the same as that shown in FIG. 7 described in the second embodiment, but there is a difference in the operation of the control unit 3, and therefore an operation example will be described. The storage battery 912 and the storage battery power converter 42 are basically selected to have a capacity capable of supplying sufficient power to important loads during independent operation, but due to cost issues, they may not have a capacity capable of supplying sufficient power to all DC loads 92.

In the third embodiment, in order to deal with a case where the power supply capacity becomes insufficient in the full load supply mode, the priority of the DC loads 92 is determined in more detail. In addition to classifying the DC loads 92 as important loads or general loads as in the second embodiment, a second priority is set to further assign a rank to the DC loads 92 classified as general loads according to their importance.

Here, it is desirable to judge the insufficiency of power supply capacity using the output power information from each power converter. This is because in the autonomous operation range, the voltage of the DC bus 8 is maintained using the battery power converter 42 and the PV power converter 43, but if the power consumption of the DC load 92 exceeds the supply capacity, the voltage of the DC bus 8 cannot be maintained and drops. Therefore, by detecting this voltage drop, it is possible to judge the insufficiency of power supply capacity.

However, it is not realistic to install a sensor capable of measuring power in all power converters. Therefore, in the third embodiment, the measurement value of the voltage (DC bus voltage) of the DC bus 8, which is always obtained in one of the power converters, is used to determine the insufficiency of the power supply capacity. Then, the presence or absence of the insufficiency of the power supply capacity is determined based on whether or not the DC bus voltage is below the voltage threshold Vth. If it is determined that the power supply capacity is insufficient, the power supply to the DC loads 92 is sequentially stopped according to the second priority until the power supply shortage is resolved.

For example, the maximum power supply capacity of the storage battery 912 is assumed to be 50 kW. Furthermore, the priority of the DC load 92 is set such that load device 922 and load device 923 are set as important loads, load device 921 and load device 924 are set as general loads, and load device 921 has a higher second priority than load device 924.

In the independent operation mode and independent operation range, the total power (power demand) consumed by the four DC loads 92 is assumed to be 80 kW (30 kW + 10 kW + 10 kW + 30 kW), as shown in Figure 14. In contrast, the solar panel 913 is capable of supplying 40 kW of power during power generation. Then, if the storage battery 912 is caused to supply 40 kW, the total (power supply) will be 80 kW (40 kW + 40 kW), which means there is sufficient power supply capacity.

If time passes from a state in which the solar panel 913 is generating power and it becomes nighttime, for example, and power generation from the solar panel 913 stops, the power supply will be insufficient even if the storage battery 912 supplies a maximum of 50 kW of power, and the DC bus voltage will drop. For example, the operation mode determination unit 32 compares the DC bus voltage detected by the state detection unit 31 with a voltage threshold value Vth, and if the voltage is below the voltage threshold value Vth, it is determined that there is a power supply shortage.

Then, in the operation command generating unit 33, an operation command is generated to open the switch 74 in order to stop the power supply to the load device 924, which is the lowest in the second priority order, and the operation proceeds to that shown in FIG. 15. In the second operation example shown in FIG. 15, the shortage in the power supply is resolved by disconnecting the load device 924, but if the shortage is not resolved, the power supply to the higher-level load device 921 is stopped. If the power generation of the solar panel 913 is resumed thereafter and the power supply increases, the load devices 921 and 924 may be reconnected from the higher-level DC load 92 by input from the user or a command from the higher-level control device.

In this example, the storage battery 912 and the storage battery power converter 42 are selected so that they can adequately supply power to the important loads, but it is also possible that the power supply capacity of the storage battery 912 is insufficient for the important loads. In such a case, the important loads are assigned an order of importance (third priority), and, as with general loads, when there is an insufficient power supply capacity, the DC loads 92 with the lowest importance are disconnected in order.

In this way, even if the power supply capacity from the power source 91 is insufficient during autonomous operation and it is difficult to supply power to all of the DC loads 92, the power supply can be continued by disconnecting the DC loads 92 starting with those with the second or third lowest priority.

The control unit 3 constituting the DC power distribution system 1 of the present application may be configured as a single piece of hardware 30 including a processor 301 and a storage device 302 as shown in FIG. 16. Although not shown, the storage device 302 includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Also, instead of the flash memory, a hard disk auxiliary storage device may be included. The processor 301 executes a program input from the storage device 302. In this case, the program is input to the processor 301 from the auxiliary storage device via the volatile storage device. Also, the processor 301 may output data such as the calculation results to the volatile storage device of the storage device 302, or may store the data in the auxiliary storage device via the volatile storage device.

Furthermore, although various exemplary embodiments and examples are described in this application, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Thus, countless variations not illustrated are envisioned within the scope of the technology disclosed in this specification. For example, this includes cases in which at least one component is modified, added, or omitted, and further cases in which at least one component is extracted and combined with components of other embodiments.

For example, the load side power converters 5 convert to different DC voltages, but this is not limiting, and there may be multiple load side power converters 5 that convert to the same voltage, and the priorities may be the same or different. In addition, if the main power source 911, which is the system power, is a DC power source, the receiving power converter 41 may be omitted if its voltage substantially matches the voltage required for the DC bus 8.

As described above, the DC power distribution system 1 of the present application includes a DC bus 8 to which power is supplied as DC power from the grid power (main power source 911) (directly or via a power receiving converter 41), a battery power converter 42 that is disposed between the DC bus 8 and the storage battery 912 and performs power conversion for charging and discharging the storage battery 912, a plurality of load-side power converters 5 that are disposed between each of a plurality of DC loads 92 and the DC bus 8 and convert the power supplied to the DC bus 8 into DC power of a voltage according to the respective specifications and supply the converted power, and a control unit 3 that controls the battery power converter 42 and the plurality of load-side power converters 5 in cooperation with each other, and the control unit 3 When the supply from the grid power (main power source 911, power receiving power converter 41) is cut off, the system switches between a normal independent operation mode in which power is normally supplied to a plurality of DC loads 92 according to the charging state of the storage battery 912 and a limited operation mode in which the supply is limited to important loads having a high priority among the plurality of DC loads 92, and in the limited operation mode, at least one of the power converters that perform power conversion by switching operation of switching elements S1 and S2 among the load side power converters 5 connected to the important loads and the storage battery power converter 42 is configured to stop switching operation and to make the input side and output side conductive. As a result, the power consumption of the system itself can be suppressed during independent operation by reducing the power consumption by the switching operation, and the time during which power can be supplied from the storage battery 912 to the important loads can be extended.

When the charge state of the storage battery 912 falls below the threshold value Sth1, the control unit 3 switches from normal independent operation to limited operation, so that the capacity of the storage battery 912 can be maximized to continue the operation time of the important load for the required time. In addition, since the threshold value Sth1 can be set lower than when conduction is not performed, the normal independent operation time can also be extended.

The control unit 3 can minimize the power consumption of the system itself during independent operation by selecting the target for which switching operation is stopped to maximize the reduction in power consumption based on the specifications of the important load, the power converter connected to the important load, and the power converter for the storage battery 42. In this case, the target may be stored in advance as a table, or the target may be selected so that the total consumption is minimized by calculating the adjustment allowance for the operating range, the consumption amount, etc. from the specifications.

If an additional power source (e.g., solar panel 913) is provided to supply power to the DC bus 8, and the control unit 3 is configured to release conduction by stopping the switching operation during the limiting operation while power is being supplied from the additional power source, the power from the additional power source can be effectively utilized to extend the operating time of important loads.

In this case, in normal independent operation, if the amount of power supply from the storage battery 912 and the additional power source is insufficient for the amount of power demand of the multiple DC loads 92, the control unit 3 will disconnect the loads with the lowest priority among the multiple DC loads 92 until the amount of power demand falls below the amount of power supply, thereby allowing independent operation to continue even if the grid power is cut off.

Furthermore, at that time, if the control unit 3 determines whether the amount of power supply is insufficient compared to the amount of power demand based on the voltage of the DC bus 8, the above control can be achieved without installing excessive sensors.

1: DC power distribution system, 2: Interface circuit, 3: Control unit, 31: Status detection unit, 32: Operation mode determination unit, 33: Operation command generation unit, 34: Threshold database, 35: Priority order database, 36: Equipment specification database, 4: Power source side power converter, 42: Power converter for storage battery, 5: Load side power converter, 6: Power source side switch, 7: Load side switch, 8: DC bus, 91: Power source, 911: Main power source (grid power), 912: Storage battery, 913: Solar panel (additional power source), 92: DC load, Smax: Charging stop threshold, Smin: Discharging stop threshold, Sth1: Threshold, Vth: Voltage threshold.

Claims (6)

A DC bus that receives power as DC power from the grid;
a battery power converter arranged between the DC bus and the battery and performing power conversion for charging and discharging the battery;
a plurality of load-side power converters provided between a plurality of DC loads and the DC bus, the load-side power converters converting power supplied to the DC bus into DC power having a voltage corresponding to each of the loads' specifications and supplying the converted power; and a control unit controlling the storage battery power converter and the plurality of load-side power converters in cooperation with each other,
The control unit is
when the supply from the grid power is cut off, switching is made between a normal independent operation mode in which power is normally supplied to the plurality of DC loads according to a charging state of the storage battery and a limited operation mode in which power is supplied only to important loads having a high priority among the plurality of DC loads;
a power converter connected to the important load among the load-side power converters and a power converter for the storage battery that performs power conversion by switching operation using a switching element among the load-side power converters, and at least one of the power converters is stopped from switching operation and conductive between the input side and the output side of the DC power distribution system, in the limiting operation. The DC distribution system of claim 1, characterized in that the control unit switches from the normal independent operation to the limited operation when the charge state of the storage battery falls below a threshold value. The DC power distribution system according to claim 1 or 2, characterized in that the control unit selects the target for stopping the switching operation that maximizes the reduction in power consumption based on the specifications of the important load, the power converter connected to the important load, and the power converter for the storage battery. an additional power source for powering the DC bus;
The DC power distribution system according to any one of claims 1 to 3, characterized in that, in the limiting operation, the control unit cancels the conduction caused by stopping the switching operation while power is being supplied from the additional power source. The DC power distribution system of claim 4, characterized in that, when the amount of power supply from the storage battery and the additional power source is insufficient for the amount of power demand of the multiple DC loads during normal independent operation, the control unit disconnects the multiple DC loads starting with the loads with the lowest priority until the amount of power demand becomes equal to or less than the amount of power supply. The DC power distribution system according to claim 5, characterized in that the control unit determines whether the power supply is insufficient relative to the power demand based on the voltage of the DC bus.

Images