Power exchange system

Abstract

To stably transfer electric power between a DC power distribution system and a power transfer line while preventing overloading and overvoltage of the DC power distribution system and the power transfer line.SOLUTION: A power transfer system comprises: transfer power conversion devices 10a and 10b that are connected to DC buses 108a and 108b of DC power distribution systems 100a and 100b; and a power transfer line 20 connecting the transfer power conversion devices 10a and 10b to each other. Each of the transfer power conversion devices 10a and 10b has a DC bus target voltage, a transfer line upper limit voltage, a transfer line lower limit voltage when outputting power to the power transfer line 20. The transfer power conversion devices 10a and 10b control transferred power such that the DC bus target voltage is achieved, and performs control of the transferred power so as to maintain the transfer line upper limit voltage or the transfer line lower limit voltage if the voltage of the power transfer line 20 has reached the transfer line upper limit voltage or the transfer line lower limit voltage before the voltage of the DC buses 108a and 108b reaches the DC bus target voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a power sharing system.

Background Art

[0002] In recent years, with the spread of renewable energy such as solar cells that generate direct current power, and further, storage batteries that charge and discharge with direct current power, a direct current distribution system that efficiently utilizes them by connecting them in direct current has attracted attention. Furthermore, there is a power sharing system that connects direct current distribution systems to each other via a power converter to share power (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power sharing system described in the above Patent Document 1, if power sharing is performed beyond the available power of the power supply source's direct current distribution system or beyond the power sharing capacity of the power converter of the power supply source, there is a problem that the power supply source's system or the power converter of the power supply source will stop due to overload.

[0005] This application discloses a technology for solving the above problems, and regarding the power of each direct current distribution system, it aims to enable stable power sharing between each system and the sharing line without causing overload and overvoltage.

Means for Solving the Problems

[0006] The power sharing system disclosed in this application is for sharing power among a plurality of direct current distribution systems, At least one of the aforementioned multiple DC distribution systems receives power from a power source, and at least one of the other DC distribution systems has a DC load or charging equipment such as a battery. Multiple power converters connected to the DC buses of multiple DC power distribution systems, The system includes a power exchange line connecting multiple power exchange converters, Multiple power exchange converters have a DC bus target voltage, which is the target voltage value of the DC bus when outputting power to the power exchange line, a power exchange line upper limit voltage, which is the upper voltage limit of the power exchange line, and a power exchange line lower limit voltage, The aforementioned power exchange converter controls the power exchange so that the voltage of the DC bus becomes the target voltage of the DC bus, The power exchange converter controls the power exchange to maintain the upper limit voltage or lower limit voltage of the power exchange line if the voltage of the power exchange line reaches the upper limit voltage or lower limit voltage of the power exchange line before the voltage of the DC bus reaches the target voltage of the DC bus. [Effects of the Invention]

[0007] The power exchange system disclosed in this application enables stable power exchange between each DC distribution system and its exchange lines, while ensuring that each system and its exchange lines do not experience overload or overvoltage. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram showing the configuration of the power exchange system according to Embodiment 1. [Figure 2] This is a flowchart of power control by the power exchange converter in the power exchange system in Embodiment 1. [Figure 3] This is a block diagram showing an example of the hardware configuration of the power exchange converter in Embodiment 1. [Figure 4] This is a block diagram showing the configuration of the power exchange system according to Embodiment 1. [Figure 5] It is a block diagram showing the configuration of the power lending system according to Embodiment 1. [Figure 6] It is a block diagram showing the configuration of the power lending system according to Embodiment 1. [Figure 7] It is a block diagram showing the configuration of the power lending system according to Embodiment 1. [Figure 8] It is a block diagram showing the configuration of the power lending system according to Embodiment 1. [Figure 9] It is a block diagram showing the configuration of the power lending system according to Embodiment 1. [Figure 10] It is a block diagram showing the configuration of the power lending system according to Embodiment 2. [Figure 11] It is a block diagram showing the configuration of the power lending system according to Embodiment 2. [Figure 12] It is a block diagram showing the configuration of the power lending system according to Embodiment 2. [Figure 13] It is a block diagram showing the configuration of the power lending system according to Embodiment 2. [Figure 14] It is a block diagram showing the configuration of the power lending system according to Embodiment 2. [Figure 15] It is a block diagram showing the configuration of the power lending system according to Embodiment 2. [Figure 16] It is a block diagram showing the configuration of the power lending system according to Embodiment 3. [Figure 17] It is a block diagram showing the configuration of the power lending system according to Embodiment 3. [Figure 18] It is a block diagram showing the configuration of the power lending system according to Embodiment 3. [Figure 19] It is a block diagram showing the configuration of the power lending system according to Embodiment I3. [Figure 20] It is a block diagram showing the configuration of the power lending system according to Embodiment 3. [Figure 21] It is a block diagram showing the configuration of the power lending system according to Embodiment 3. [Figure 22]It is a block diagram showing the configuration of the power sharing system according to Embodiment 4. [Figure 23] It is a block diagram showing the configuration of the power sharing system according to Embodiment 4. [Figure 24] It is a block diagram showing the configuration of the power sharing system according to Embodiment 4. [Figure 25] It is a block diagram showing the configuration of the power sharing system according to Embodiment 4. [Figure 26] It is a block diagram showing the configuration of the power sharing system according to Embodiment 4. [Figure 27] It is a block diagram showing the configuration of the power sharing system according to Embodiment 4.

Mode for Carrying Out the Invention

[0009] Embodiment 1. This embodiment relates to a power sharing system that performs power sharing between DC power distribution systems. Hereinafter, this embodiment will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and their description will not be repeated.

[0010] FIG. 1 is a block diagram showing the configuration of the power sharing system according to Embodiment 1. The power sharing system includes DC power distribution systems 100a and 100b, power sharing converters 10a and 10b each composed of a DC / DC converter, and a power sharing line 20. The DC power distribution systems 100a and 100b are composed of solar cells (PV) 101a and 101b, solar cell DC / DC converters 104a and 104b that convert the power of the solar cells, storage batteries 102a and 102b, storage battery DC / DC converters 105a and 105b that convert the power of the storage batteries, power systems 103a and 103b, and AC / DC converters 106a and 106b that convert the power of the power systems. Here, the power system refers to a system that integrates power generation, transformation, transmission, and distribution in order to supply power to the power receiving equipment of consumers. Furthermore, the DC power distribution systems 100a and 100b consist of DC buses 108a and 108b that connect the outputs of each power converter, and DC loads 107a and 107b that are connected to the DC buses 108a and 108b.

[0011] The solar cell DC / DC converters 104a and 104b are connected between the solar cells 101a and 101b and the DC buses 108a and 108b. They control the maximum power generated by the solar cells 101a and 101b using a maximum power point tracking (MPPT) method, and essentially output the maximum power generated. Furthermore, if the DC bus voltage exceeds the set voltage, the output is suppressed to ensure that the output is at the set voltage.

[0012] The battery DC / DC converters 105a and 105b perform charging and discharging of the battery. By setting a target voltage, the DC bus voltage can be stabilized by discharging if the DC bus voltage is below the target voltage and charging if it is above the target voltage. An upper limit for charging and discharging power can also be set. In the operation of Embodiment 1, no charging operation is performed, and a discharge operation is performed to control the DC bus voltage to the target voltage, and when the upper limit power is reached, it operates at the upper limit power.

[0013] The AC / DC converters 106a and 106b convert AC power to DC power. They set a target voltage for the DC bus and control the output power to reach that voltage. Furthermore, if the AC / DC converter reaches its power limit, it will operate at that limit even if the voltage is below the target voltage. In this embodiment of the power exchange system, at least one of the multiple DC distribution systems receives power from a power source (solar cell (PV), power grid, etc.), and at least one of the other DC distribution systems has a DC load or charging equipment such as a storage battery.

[0014] The configuration of DC power distribution systems 100a and 100b is not limited to those described above; they may consist of only a part of the above, or they may have other demand facilities. For example, renewable energy sources such as fuel cells and wind power generation, DC / DC converters to convert their power, and even electric vehicles (EVs) and their DC / DC converters for charging and discharging may be connected. Furthermore, the AC / DC converters that convert power in the power grid may be bidirectionally controlled.

[0015] The power exchange converters 10a and 10b are connected to the DC buses 108a and 108b of the DC distribution systems 100a and 100b, respectively. Furthermore, the power exchange converters 10a and 10b are connected via a power exchange line 20, enabling bidirectional power exchange between the DC distribution systems. The power exchange converters 10a and 10b are each set to the following parameters: the upper limit of power output to the power exchange line 20 (exchange output upper limit power C), the upper limit of power input from the power exchange line 20 (exchange input upper limit power D), the DC bus target voltage, the exchange line upper limit voltage A, and the exchange line lower limit voltage B. The DC bus target voltage is set lower than the target voltage, which is the control voltage of the power converter to which the power to be exchanged is connected, and higher than the target voltage, which is the control voltage of the power converter to which the power to be not exchanged is connected.

[0016] The power exchange converters 10a and 10b control the power exchanged so that the DC bus voltage becomes the DC bus target voltage. The upper limit power exchange output C is the upper limit power when exchanging power to other systems, and the upper limit power exchange input D is the upper limit power when receiving and inputting power exchanged from other systems. If the exchanged power reaches the upper limit power exchange output C or the upper limit power exchange input D before reaching the target voltage, the power is exchanged at that level. Furthermore, if the voltage of the power exchange line 20 reaches the upper limit voltage A or the lower limit voltage B of the exchange line without reaching the target voltage or without reaching the upper limit power exchange output C or the upper limit power exchange input D, the power exchange is controlled to maintain that voltage.

[0017] At this time, if the voltage of DC buses 108a and 108b is higher than the target voltage, the power supply output is reduced to a minimum of 0, and the power supply input is not increased. Similarly, if the voltage of DC buses 108a and 108b is lower than the target voltage, the power supply input is reduced to a minimum of 0, and the power supply output is not increased. This control prevents unnecessary power supply from being provided or received when there is a surplus or deficit in power in multiple DC distribution systems.

[0018] Figure 2 is a flowchart of power control by the power exchange converter. This control is performed in the control unit inside the power exchange converters 10a and 10b. The control unit consists of a processor, such as a CPU (CENTRAL PROCESSING UNIT). Figure 3 is a block diagram showing an example of the hardware configuration of the power exchange converter 10. The hardware of the power exchange converter 10 consists of a processor 600 and a storage device 601. Although not shown, the storage device 601 comprises a volatile storage device such as random access memory and a non-volatile auxiliary storage device such as flash memory. Alternatively, a hard disk may be provided as an auxiliary storage device instead of flash memory. The processor 600 executes the program input from the storage device 601. In this case, the program is input to the processor 600 from the auxiliary storage device via the volatile storage device. The processor 600 may also output data such as calculation results to the volatile storage device of the storage device 601, or it may save the data to the auxiliary storage device via the volatile storage device. The processor 600 then reads the program stored in the storage device 601 and executes it.

[0019] In Figure 2, first, in step S200, the power transfer voltage measured inside the power transfer converters 10a and 10b is compared with the power transfer upper limit voltage A of the power transfer voltage held by the control unit. If the power transfer voltage exceeds the power transfer upper limit voltage A, the power transfer converters 10a and 10b control the voltage so that the power transfer voltage becomes the power transfer upper limit voltage A (step S201). Then, in the process of step S205, it is checked whether the power transfer output upper limit power C or power transfer input upper limit power D of the power transfer converters 10a and 10b has been exceeded, and if it has been exceeded, the power transfer output upper limit power C or power transfer input upper limit power D is corrected and the output voltage is changed (limiter processing). In step S200, if the supply line voltage does not exceed the supply line upper limit voltage A, in step S202, it is checked whether the supply line voltage is below the supply line lower limit voltage B. If it is below, the process proceeds to step S203, where the power is adjusted so that the supply line voltage is below the supply line lower limit voltage B. Then, in step S205, it is checked whether the supply power exceeds the supply output upper limit power C or the supply input upper limit power D. If it does, it is corrected to the supply output upper limit power C or the supply input upper limit power D, and then the output voltage is changed.

[0020] In step S202, if the supply line voltage is not below the supply line lower limit voltage B, the process proceeds to step S204, where the output power is adjusted to bring the DC bus voltage to the target voltage. Then, in step S205, it is checked whether the supply power exceeds the supply output upper limit power C or the supply input upper limit power D. If it does, the supply power is corrected to the supply output upper limit power C or the supply input upper limit power D, and then the output voltage is changed.

[0021] As described above, according to this embodiment, each of the multiple power exchange converters 10 has a DC bus target voltage, which is the target voltage value of the DC bus when outputting power to the power exchange line 20; an exchange line upper limit voltage A, which is the upper limit of the voltage of the power exchange line 20; and an exchange line lower limit voltage B, which is the lower limit of the voltage of the power exchange line 20. The power exchange converters 10 control the power to reach the DC bus target voltage, and if the voltage of the power exchange line 20 reaches the exchange line upper limit voltage A or the exchange line lower limit voltage B before the voltage of the DC bus 108 reaches the DC bus target voltage, the power exchange converters 10 control the power to maintain the exchange line upper limit voltage A or the exchange line lower limit voltage B.

[0022] Furthermore, the power exchange converter 10 has a power exchange output limit C, which is the upper limit of the power output to the power exchange line 20, and a power exchange input limit D, which is the upper limit of the power input from the power exchange line 20. If the power exchange output limit C or power exchange input limit D is reached before the DC bus target voltage, the power exchange line upper limit voltage A, and the power exchange line lower limit voltage B are reached, the power exchange converter 10 controls the power exchange to maintain the power exchange output limit C or power exchange input limit D.

[0023] Next, I will describe the specific operation. First, as Pattern 1, I will explain the case where (surplus power of one system) < (deficient power of the other system). For each target voltage and maximum power, the target voltage and maximum power for solar cell DC / DC converters 104a and 104b are set to 390V and 10kW, respectively. For battery DC / DC converters 105a and 105b, the target voltage is set to 370V, and the maximum power for battery DC / DC converters 105a and 105b is set to 2kW during discharge operation and 0kW during charging operation. For AC / DC converters 106a and 106b, the target voltage and maximum power are set to 350V and 10kW. Furthermore, the target voltage for the power exchange converters 10a and 10b is set to 380V, and the maximum power exchange output C and maximum power exchange input D are set to 3kW. In addition, the maximum exchange line voltage A for power exchange converters 10a and 10b is set to 290V, and the minimum exchange line voltage B is set to 280V.

[0024] With the above settings, in each DC distribution system, the target voltage of each converter becomes (target voltage of solar cell DC / DC converter) > (target voltage of power exchange converter) > (target voltage of battery DC / DC converter) > (target voltage of AC / DC converter). As a result, surplus power from the solar cells is exchanged with the other system, and if the power from the solar cells is insufficient to meet the load, power is exchanged from the other system.

[0025] The system operation is shown for the above configuration, where the power generated by solar cell 101a is 7kW, the power generated by solar cell 101b is 2kW, and the power of DC loads 107a and 107b is 5kW. In DC power distribution system 100a, if there is no power exchange converter, the PV generation is 7kW and the DC load is 5kW, so the solar cell DC / DC converter 104a will output 5kW of power and operate at a DC bus voltage of 390V. On the other hand, in DC power distribution system 100b, the PV generation is 2kW and the DC load is 5kW, so of the remaining 3kW, 2kW is discharged by the battery DC / DC converter 105b, and the remaining 1kW is supplied by the AC / DC converter 106b, and the DC bus voltage is controlled to 350V.

[0026] In this state, the operation of the power exchange converter 10 will be explained based on Figure 4. Power exchange converter 10a supplies power to the power exchange line 20 because the target voltage of the DC bus is 380V. On the other hand, power exchange converter 10b supplies power to the DC bus because the target voltage of the DC bus is 380V and the current voltage is 350V. Since the surplus power of the PV on the DC distribution system 100a side is 2kW, when the power exchange converter 10a supplies 2kW of power to the power exchange line 20, the voltage of the DC bus 108a drops, and the power exchange converter 10a outputs power to the power exchange line 20 side in order to maintain the target voltage of the power exchange converter 10a at 380V. When the voltage of the DC bus 108a is maintained at 380V in this way, the power exchange converter 10a is in a state where it is outputting 2kW of power to the power exchange line 20 side.

[0027] On the other hand, on the DC power distribution system 100b side, because the PV undervoltage is 3kW, even when the power exchange converter 10b is outputting 2kW due to the output of the power exchange converter 10a, the voltage of the DC bus 108b does not reach the target voltage of the power exchange converter 10b, which is 380V, so it attempts to further increase the power exchanged to the DC bus. However, this causes the voltage of the power exchange line 20 to decrease and reach 280V, which is the lower limit voltage B of the power exchange line of the power exchange converter 10b. In other words, if the input power from the power exchange converter 10a is 2kW, and the output power exchange converter 10b tries to draw more than 2kW of power, the power is insufficient, causing the voltage of the power exchange line 20 to decrease. As it decreases, there comes a time when it reaches 280V, which is the lower limit voltage B of the power exchange line.

[0028] Therefore, the power exchange converter 10b controls itself to maintain a power of 2kW in order to maintain the lower limit voltage B of the exchange line. The remaining 1kW for the DC load is then supplied from the battery DC / DC converter 105b, which has a higher target voltage, and the DC bus voltage is controlled to 370V. Through the above control, the surplus power of 2kW from the PV on the DC distribution system 100a side is transferred to the DC distribution system 100b side. In addition, the voltages of the respective DC buses 108a and 108b, and the voltage of the power transfer line 20 are appropriately controlled without voltage drops or increases due to overload, etc., thereby achieving power transfer.

[0029] Next, we will explain Pattern 2, the case where (surplus power of one system) > (deficit power of the other system). The following describes the system operation when the power generated by the solar cell 101b on the DC power distribution system 100b side becomes 4kW, based on Pattern 1 above. If we assume there is no power exchange converter, in the DC power distribution system 100a, as in Pattern 1, the solar cell 101a has a surplus power of 2kW, and the voltage of the DC bus 108a is controlled to 390V. On the other hand, on the DC power distribution system 100b side, the DC load is 5kW compared to the 4kW generated by the solar cell 101b, so the remaining 1kW is discharged by the storage battery DC / DC 105b, and the DC bus voltage is controlled to 370V.

[0030] In this state, the operation of the power exchange converter will be explained based on Figure 5. The power exchange converter 10b increases the power supplied to the DC bus 108b, and when it reaches 1kW, it can output the power that was supplied by the discharge of the battery 102b, and can control the target DC bus voltage to 380V. As a result, the output power of the battery DC / DC converter 105b becomes 0kW. The power exchange converter 10a increases its power to supply the surplus power of the solar cell 101a, which is 2kW, to the power exchange line 20, as in the case of pattern 1, but since the power exchange converter 10b is controlled to 1kW, if it tries to output more than 1kW, the voltage of the power exchange line 20 will rise.

[0031] When the voltage of the power exchange line 20 rises to 290V, the power exchange converter 10a maintains its output voltage at 1kW to maintain 290V. This prevents overloading of the voltage of the power exchange line 20 while achieving the 1kW required by the DC distribution system 100b. Furthermore, the voltage of the DC bus 108a is controlled to 390V by the PV DC / DC converter 104a, which suppresses the output to 6kW and controls the voltage, even though the power generated by the solar cell 101a is 7kW, allowing it to operate stably at 390V.

[0032] Next, we will explain Pattern 3, the case where (surplus power from the power source) > (maximum input power of the power converter at the power destination). Figure 6 shows the system operation when the maximum input power D of the power converter 10b becomes 0.5kW, starting from the state in Pattern 2. If we consider that there is no power converter, the operation will be the same as in Pattern 2 when there is no power converter.

[0033] In this state, the operation of the power exchange converter 10 will be explained based on Figure 6. Power exchange converter 10b increases the power exchanged to the DC bus voltage. When the power exchanged reaches the upper limit power exchange input of 0.5kW, it maintains the output at 0.5kW. For the remaining 0.5kW to the DC load 107b, the battery DC / DC converter 105b outputs the power, and the voltage of the DC bus 108b becomes 370V. Meanwhile, power exchange converter 10a, as in the case of pattern 2, raises the exchange line voltage to the upper limit voltage of the exchange line, 290V, when the power exchanged reaches 0.5kW, and maintains the output power at 0.5kW in order to maintain that voltage. In this way, power exchange is achieved at the upper limit power D of the exchange input of the power exchange converter 10b, while preventing overload in the voltage of the power exchange line 20. Furthermore, the voltage of the DC bus 108a is controlled by the PV DC / DC converter 104a, which suppresses the output to 5.5kW and controls the voltage to 390V, even though the power generated by the solar cell 101a is 7kW, allowing it to operate stably at 390V.

[0034] Next, as Pattern 4, we will explain the case where (the maximum output power of the power converter at the power source) < (the power shortage at the power source). Figure 7 shows the system operation when the maximum power output C of the power exchange converter 10a becomes 0.5kW, starting from the state in Pattern 2. If we consider the absence of the power exchange converter, the operation will be the same as in Pattern 2 when the power exchange converter is absent. In that state, the operation of the power exchange converter 10 will be explained. The power exchange converter 10a increases the power supplied to the power exchange line 20 because there is a surplus power of 2kW from the solar cell 101a.

[0035] Since the maximum power output C of the power exchange converter 10a is 0.5kW, it maintains an output of 0.5kW. The power exchange converter 10b increases the power exchange to raise the voltage of the DC bus 108b to the target voltage of 380V. When the power exchange reaches 0.5kW, it exceeds the power exchange from power exchange converter 10a, so the voltage of the power exchange line 20 decreases and reaches 280V, which is the lower limit voltage B of the power exchange line of power exchange converter 10b. Therefore, the power exchange converter 10b maintains a power of 0.5kW to maintain the lower limit voltage B of the power exchange line. In this way, power exchange is achieved at the maximum power output C of the source while preventing overload in the voltage of the power exchange line 20. The remaining 0.5kW to the DC load 107b is output by the battery DC / DC converter 105b, and the voltage of the DC bus 108b becomes 370V. Furthermore, the voltage of the DC bus 108a is controlled by the PV DC / DC converter 104a, which suppresses the output to 5.5kW and controls the voltage to 390V, even though the power generated by the solar cell 101a is 7kW, allowing it to operate stably at 390V.

[0036] Next, as Pattern 5, we will explain the case where there is surplus power in both DC distribution systems. Now, let's explain the case where the power generated by solar cell 101b on the DC distribution system 100b side becomes 7kW, starting from the state in Pattern 2. Assuming there is no power exchange converter, DC distribution systems 100a and 100b are the same, with a DC load of 5kW against a PV generation of 7kW. Therefore, the solar cell DC / DC converters 104a and 104b will output 5kW of power while operating at a DC bus voltage of 390V.

[0037] The operation of the power exchange converter 10 in this state will be explained based on Figure 8. Power exchange converter 10a supplies power to the power exchange line 20 because the target voltage of the DC bus is 380V. Similarly, power exchange converter 10b also supplies power to the power exchange line 20 because the target voltage of the DC bus is 380V. As a result, the voltage of the power exchange line 20 rises with an output of approximately 0kW, and the voltage of the power exchange line 20 reaches 290V, which is the upper limit voltage A of the power exchange line for power exchange converters 10a and 10b, and each maintains operation at 0kW to maintain this voltage.

[0038] Next, as Pattern 6, we will describe the case where there is no surplus power in the DC distribution systems on both sides. Figure 9 is a block diagram showing the case where both solar cells 101a and 101b in DC power distribution systems 100a and 100b generate 2kW of power. Assuming there is no power exchange converter, in DC power distribution system 100a, the solar cell DC / DC converter 104a performs MPPT control and outputs 2kW. Since the DC load 107a is 5kW, the battery DC / DC converter 102a outputs 2kW to cover the remaining 3kW, and the AC / DC converter 106a outputs the remaining 1kW, and the voltage of the DC bus 108a is controlled to 350V. Similar control is performed in DC power distribution system 100b.

[0039] The operation of the power exchange converter 10 in this state will be explained based on Figure 9. Since the target voltage of the DC bus of the power exchange converter 10a is 380V, it attempts to supply power to the DC bus 108a. Similarly, the power exchange converter 10b also attempts to supply power to the DC bus 108b. Therefore, no power is supplied to the power exchange line 20, and the voltage of the power exchange line 20 becomes 0V, but this is not a problem as there is no power to be exchanged.

[0040] If it is necessary to maintain the power of the power exchange line even when this power exchange is not taking place, it is possible to maintain 280V by supplying power to the power exchange line 20 even when the DC bus voltage is below the target voltage. In this case, instead of setting the exchange input 0 as the lower limit, the power can be maintained at 280V by controlling the power exchange output to the power exchange line 20 in a way that maintains the exchange line voltage. Furthermore, in order to maintain the lower limit voltage B of the power exchange line 20 at 280V, the control that outputs power to the power exchange line side is given a droop characteristic in which the lower limit voltage B of the power exchange line is increased according to the control power. As a result, the power output from each converter is equal, so each power exchange converter outputs almost 0kW of power just enough to maintain 280V, preventing unnecessary power exchange.

[0041] As described above, the power exchange converter 10 sets the upper limit power exchange output C, the upper limit power exchange input D, the target voltage of the DC bus, the upper limit voltage of the power exchange line A, and the lower limit voltage of the power exchange line B. The power exchange converters 10a and 10b control the power exchange so that the voltage of the DC bus becomes the target voltage of the DC bus. If the power exchange reaches the upper limit power exchange output C or the upper limit power exchange input D before reaching the target voltage, the power is exchanged using that power. Furthermore, if the voltage of the power exchange line 20 reaches the upper limit voltage of the power exchange line A or the lower limit voltage of the power exchange line B without reaching the target voltage or the available power or allowable power, the power exchange is controlled to maintain that voltage. By performing such control, it is possible to automatically exchange surplus power to the deficit side within the range of the power exchange of the upper limit power exchange output C or the upper limit power exchange input D, without the voltage of the DC bus and the voltage of the power exchange line 20 becoming overvoltage or undervoltage.

[0042] Embodiment 2. Next, Embodiment 2 will be described. Figures 10 and 11 are block diagrams showing the configuration of the power exchange system according to Embodiment 2. Figures 10 and 11 are originally connected between G and G by the power exchange line 20 and are connected in a continuous line. The same applies to Figures 12 to 27, which will be explained later. As shown in Figures 10 and 11, in Embodiment 2, four DC power distribution systems 100a, 100b, 100c, and 100d are connected to a power exchange line 20 via power exchange converters 10a, 10b, 10c, and 10d, and the internal configuration of the DC power distribution system is the same as in Embodiment 1. The target voltage of the DC bus in the power exchange converters 10a, 10b, 10c, and 10d is 380V, the upper limit voltage A of the power exchange line in power exchange converters 10a, 10b, 10c, and 10d is 290V, and the lower limit voltage B of the power exchange line in power exchange converters 10a, 10b, 10c, and 10d is 280V. Furthermore, the set values ​​for the upper limit power exchange output C and upper limit power exchange input D in power exchange converters 10a, 10b, 10c, and 10d are all 3kW.

[0043] The target voltage and maximum power of each converter are the same as in Embodiment 1. The target voltage and maximum power of the solar cell DC / DC converters 104a, 104b, 104c, and 104d are 390V and 10kW, respectively. The target voltage of the battery DC / DC converters 105a, 105b, 105c, and 105d is 370V. The maximum power of the battery DC / DC converters 105a, 105b, 105c, and 105d is 2kW during discharge operation and 0kW during charge operation. The target voltage and maximum power of the AC / DC converters 106a, 106b, 106c, and 106d are 350V and 10kW.

[0044] Next, as Pattern 7, we will explain the case where the total power generated by the solar cells in the entire system is greater than the total DC load power of the entire system. In this configuration, the operation of the system when solar cell 101a generates 2.5 kW, solar cells 101b, 101c, and 101d generate 7 kW, and DC loads 107a, 107b, 107c, and 107d generate 5 kW will be explained based on Figures 12 and 13. First, let's consider the case where there is no power exchange converter. In DC distribution systems 100b, 100c, and 100d, the PV power generation is 7kW and the DC load power is 5kW, so there is a surplus power of 2kW in each case. Also, in DC distribution system 100a, the DC load power is 5kW and the PV power generation is 2.5kW, so there is a power deficit of 2.5kW with PV alone.

[0045] In this state, when the power exchange converter 10 operates, it will operate as shown in Figures 12 and 13. Power exchange converter 10a will convert to receive the 2.5kW of power that is lacking, and power exchange converters 10b, 10c, and 10d, which have a power surplus, will output power preferentially from the power exchange converter that recognizes the lowest detected voltage, because the upper limit voltage A of the exchange line is all 290V, due to differences in voltage detection within each power exchange converter. For example, if power exchange converter 10b recognizes the same 290V as 291V, power exchange converter 10c as 290V, and power exchange converter 10d as 289V, power exchange converter 10d will output the surplus 2kW, and power exchange converter 10c will output the remaining 0.5kW.

[0046] This is because the power exchange converter 10 suppresses the power exchange when it recognizes that the voltage is above the upper limit A of the exchange line, and the higher the detected voltage, the more it is suppressed and not output. In this way, the output order of the power exchange converter 10 is determined, and power exchange is carried out while the exchange line voltage and the DC bus voltage of each DC distribution system are stably controlled. In addition, the power exchange converter 10a outputs 2.5kW of power to the DC bus 108a so that the DC bus voltage becomes 380V.

[0047] Next, as Pattern 8, we will explain the case where the total power generated by the solar cells in the entire system is less than the total DC load power of the system. This configuration demonstrates the system's operation when the power generated by solar cells 101a, 101b, and 101c is 3kW, the power generated by solar cell 101d is 7.5kW, and the power supplied by DC loads 107a, 107b, 107c, and 107d is 5kW. First, let's consider the case where there is no power exchange converter. In DC distribution system 100d, the PV power generation is 7.5kW and the DC load power is 5kW, so there is a surplus power of 2.5kW. Also, in DC distribution systems 100a, 100b, and 100c, the DC load power is 5kW and the PV power generation is 3kW, so there is a power deficit of 2kW in each case if only PV is used.

[0048] Figures 14 and 15 show the operation of the power exchange converter 10 in that state. Power exchange converter 10d converts the surplus power of 2.5kW to be exchanged, while power exchange converters 10a, 10b, and 10c, which are experiencing power shortages, all have a lower limit voltage B of 280V. Due to differences in voltage detection within each power exchange converter, power is preferentially received from the power exchange converter that recognizes the highest detected voltage. For example, if power exchange converter 10a recognizes the same 280V as 279V, power exchange converter 10b as 280V, and power exchange converter 10c as 281V, power exchange converter 10c receives the 2kW shortage, and power exchange converter 10b receives the remaining PV surplus of 0.5kW. This is because, when the power exchange converter 10 recognizes that the voltage is below the lower limit B of the exchange line, it suppresses the power that will be exchanged. Power is suppressed and not exchanged starting with power with the lowest detected voltage. In this way, the order in which the power exchange converter 10 receives power is determined, and the exchange line voltage and the DC bus voltage of each DC distribution system are stably controlled, and power exchange is carried out.

[0049] Thus, even when there are three or more DC distribution systems, it is possible to stably exchange power without the voltage of the power exchange line 20 and the voltage of the DC bus of each DC distribution system becoming abnormal.

[0050] Embodiment 3. Next, Embodiment 3 will be described. Figures 16 and 17 are block diagrams showing the configuration of the power exchange system according to Embodiment 3. As shown in Figures 16 and 17, in Embodiment 3, similar to Embodiment 2, four DC distribution systems 100a, 100b, 100c, and 100d are connected to the power exchange line 20 via power exchange converters 10a, 10b, 10c, and 10d. The configuration within the DC distribution system is also the same as in Embodiment 2.

[0051] In the power exchange converters 10a, 10b, 10c, and 10d, the target voltage of the DC bus is 380V, but the upper limit voltage A and lower limit voltage B of the exchange line differ from those in Embodiment 2. Specifically, the upper limit voltage A of the exchange line for power exchange converter 10a is 290V, for power exchange converter 10b it is 295V, for power exchange converter 10c it is 300V, and for power exchange converter 10d it is 305V. Furthermore, the lower limit voltage B of the exchange line for power exchange converter 10a is 265V, for power exchange converter 10b it is 270V, for power exchange converter 10c it is 275V, and for power exchange converter 10d it is 280V. The set values ​​for the maximum power output C and the maximum power input D are both 3kW.

[0052] The target voltage and maximum power of each converter are the same as in Embodiments 1 and 2. The target voltage and maximum power of the solar cell DC / DC converters 104a, 104b, 104c, and 104d are 390V and 10kW, respectively. The target voltage of the battery DC / DC converters 105a, 105b, 105c, and 105d is 370V. The maximum power of the battery DC / DC converters 105a, 105b, 105c, and 105d is 2kW during discharge operation and 0kW during charge operation. The target voltage and maximum power of the AC / DC converters 106a, 106b, 106c, and 106d are 350V and 10kW.

[0053] Next, as Pattern 9, we will explain the case where (total surplus power of the DC distribution system) > (total deficit power of the DC distribution system). In this setting, we will show the system operation when the power generated by solar cell 101a is 2.5kW, the power generated by solar cells 101b, 101c, and 101d is 7kW, and the power of DC loads 107a, 107b, 107c, and 107d is 5kW. First, let's consider the case where there is no power exchange converter. In DC distribution systems 100b, 100c, and 100d, the PV power generation is 7kW and the power of the DC load is 5kW, so there is a surplus of 2kW in each case. Also, in DC distribution system 100a, the power of the DC load is 5kW and the PV power generation is 2.5kW, so there is a power deficit of 2.5kW with PV alone.

[0054] In that state, when the power exchange converter 10 operates, it operates as shown in Figures 18 and 19. Power exchange converter 10a converts to receive the 2.5kW of power that is lacking, and of the power exchange converters 10b, 10c, and 10d, which have a power surplus, power exchange converter 10d, which has the highest upper limit voltage A of 305V, outputs the surplus 2kW. Furthermore, power exchange converter 10c, which has the next highest upper limit voltage A of 300V, outputs the remaining 0.5kW, and the voltage of the power exchange line 20 becomes 300V as it outputs.

[0055] This is because, in the power exchange converter, when the voltage of the power exchange line 20 reaches the upper limit voltage A of the exchange line, the power to be exchanged is suppressed. Therefore, higher voltages are output without suppression, and the last output adjusts its power to maintain the exchange voltage. In other words, power is output preferentially from the highest upper limit voltage A of the exchange line. The power exchange converter 10a outputs 2.5kW of power to the DC bus 108a so that the DC bus 108a reaches the target voltage of 380V, so the voltage of the DC bus becomes 380V.

[0056] Next, we will explain Pattern 10, which is a different case from Pattern 9, where (total value of surplus power in the DC distribution system) > (total value of deficit power in the DC distribution system). This configuration demonstrates the system's operation when solar panels 101a and 101b generate 2.5kW, solar panels 101c and 101d generate 7kW, and DC loads 107a, 107b, 107c, and 107d generate 5kW.

[0057] First, let's consider the case where there is no power exchange converter. In DC distribution systems 100c and 100d, the PV power generation is 7kW and the power of the DC load is 5kW, so there is a surplus of 2kW in each case. Also, in DC distribution systems 100a and 100b, the power of the DC load is 5kW and the PV power generation is 2.5kW, so there is a power deficit of 2.5kW with PV alone.

[0058] In this state, when the power exchange converter 10 is operated, it operates as shown in Figures 20 and 21. Power exchange converters 10c and 10d convert the surplus 2kW to be exchanged, and power exchange converter 10a, which has a power shortage, has the lowest lower limit voltage B of 265V, so power exchange converter 10a receives the shortage of 2.5kW, and power exchange converter 10b, which has the next highest lower limit voltage B of 270V, receives the remaining surplus 1.5kW and controls the voltage of the exchange line to 270V.

[0059] This is because, in the power exchange converter, when the exchange line voltage reaches the lower limit voltage B, the power received is suppressed. Therefore, power with a low setting of the lower limit voltage B is not suppressed and power is received, and the last power recipient adjusts its power to maintain the voltage. In other words, power is received preferentially from those with a low lower limit voltage B. Power exchange converter 10a outputs 2.5kW of power to DC bus 108a so that the DC bus reaches the target voltage of 380V, so the voltage of DC bus 108a becomes 380V. DC bus 108b becomes 370V because the battery DC / DC converter 105b outputs the remaining 1kW, and DC buses 108c and 108d become 380V because power exchange converters 10c and 10d distribute the surplus power to control the DC bus to the target voltage of 380V.

[0060] As described above, the upper limit voltage A of the power exchange line is increased in the order of the power exchange converters that wish to exchange power. Conversely, the lower limit voltage B of the power exchange line is decreased in the order of the power exchange converters that wish to receive power. In this way, the order in which power is exchanged and received can be controlled as desired while stably controlling the voltage of the power exchange line and the voltage of the DC bus.

[0061] Embodiment 4. Next, Embodiment 4 will be described. Figures 22 and 23 are block diagrams showing the configuration of the power exchange system according to Embodiment 4. As shown in Figures 22 and 23, Embodiment 4 has the same configuration as Embodiment 2, but differs in that the upper limit voltage A and lower limit voltage B of the power exchange converters 10a, 10b, 10c, and 10d have a droop characteristic. The upper limit voltage A of the power exchange converters 10a, 10b, 10c, and 10d is 300V, and the lower limit voltage B of the power exchange converters 10a, 10b, 10c, and 10d is 270V. However, they have a droop characteristic that changes the upper limit voltage A and lower limit voltage B of the power exchange converters with a slope of 4V for every 1kW of output power, and the upper limit voltage A of the power exchange converters has the characteristic of decreasing as the output power being exchanged increases. Furthermore, the lower limit voltage B of the power exchange line has the characteristic of increasing as the amount of power being exchanged increases. Due to this characteristic, for power exchange converters controlled by the upper limit voltage A or the lower limit voltage B of the power exchange line, the output of the power exchange converter is controlled by the voltage of the power exchange line 20, making it possible to distribute the exchanged power evenly.

[0062] The target voltage and maximum power of each converter are the same as in Embodiment 1. Specifically, the target voltage and maximum power of the solar cell DC / DC converters 104a, 104b, 104c, and 104d are 390V and 10kW, the target voltage of the battery DC / DC converters 105a, 105b, 105c, and 105d is 370V, the maximum power of the battery DC / DC converters 105a, 105b, 105c, and 105d is 2kW during discharge operation and 0kW during charge operation, and the target voltage and maximum power of the AC / DC converters 106a, 106b, 106c, and 106d are 350V and 10kW.

[0063] As Pattern 11, we will describe the case where (total surplus power of the DC distribution system) > (total deficit power of the DC distribution system). In this setting, we will describe the system operation when the power generated by solar cell 101a is 3.5kW, the power generated by solar cells 101b, 101c, and 101d is 7kW, and the power of DC loads 107a, 107b, 107c, and 107d is 5kW. First, let's consider the case where there is no power exchange converter. In DC distribution systems 100b, 100c, and 100d, the PV power generation is 7kW and the DC load power is 5kW, so there is a surplus of 2kW in each case. Also, in DC distribution system 100a, the DC load power is 5kW and the PV power generation is 3.5kW, so there is a power deficit of 1.5kW if only PV is used.

[0064] In this state, when the power exchange converter 10 operates, it operates as shown in Figures 24 and 25. Power exchange converter 10a converts to receive the 1.5kW of power that is lacking, and power exchange converters 10b, 10c, and 10d, which have a power surplus, have a droop characteristic where the upper limit voltage A of the exchange line is 300V when the exchange line voltage limit is 0kW, so their output powers are equalized and each outputs 0.5kW. For example, if we consider them operating one by one, the first unit will output 1.5kW, and as a result, for example, the upper limit voltage A of the exchange line will drop by 6V due to the droop characteristic and will be controlled at 294V.

[0065] Next, when the second unit operates, its output is 0kW, so the upper limit voltage of the power exchange line is controlled to 300V. Since this is greater than 294V, the output is increased, and when the output of the first and second units reaches 0.75kW, the upper limit voltage A of the power exchange line decreases by 3V each, setting the upper limit voltage A of the power exchange line to 297V. The units then operate at 297V, and the exchanged power is divided equally. Therefore, when the third unit operates, it outputs 0.5kW equally to each unit, and the power exchange line 20 is controlled to 298V, which is the upper limit voltage A of each unit. The power exchange converter 10a outputs 1.5kW of power to the DC bus 108a so that the DC bus 108a reaches the target voltage of 380V, so the DC bus voltage becomes 380V.

[0066] Next, we will explain another pattern, Pattern 12, where (total surplus power of the DC distribution system) > (total deficit power of the DC distribution system). In this setting, we will show the system operation when the power generated by solar cells 101a and 101b is 2.5kW, the power generated by solar cells 101c and 101d is 7kW, and the power of DC loads 107a, 107b, 107c, and 107d is 5kW. First, let's consider the case where there is no power exchange converter. In DC distribution systems 100c and 100d, the PV power generation is 7kW and the DC load power is 5kW, so there is a surplus power of 2kW in each case. Also, in DC distribution systems 100a and 100b, the DC load power is 5kW and the PV power generation is 2.5kW, so there is a power deficit of 2.5kW with PV alone.

[0067] In this state, when the power exchange converters are activated, the operation will be as shown in Figures 26 and 27. Power exchange converters 10c and 10d convert the surplus 2kW to be exchanged, and power exchange converters 10a and 10b, which have a power deficit, have a droop characteristic in which the lower limit voltage B of the exchange line becomes 270V when the power exchange line is 0kW, so the power is balanced and 2kW is exchanged from each.

[0068] The voltage of DC buses 108a and 108b becomes 370V because the battery DC / DC converter 105b outputs the difference, and the voltage of DC buses 108c and 108d becomes 380V because the surplus PV is shared by the power converters 10c and 10d to control it to the target voltage of the DC bus, which is 380V.

[0069] In this way, by introducing a droop characteristic to the upper limit voltage of the power transfer line, which decreases as the power transfer output increases, and further increasing the lower limit voltage of the power transfer line, which increases as the power transfer input increases, the supplied power or the received power can be equalized.

[0070] Although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the technology disclosed herein. These include, for example, modifications, additions, or omissions of at least one component, as well as the extraction of at least one component and its combination with components of other embodiments.

[0071] The various aspects of this disclosure are described below, with supplementary notes.

[0072] (Note 1) A power exchange system that allows power to be exchanged between multiple DC power distribution systems, At least one of the aforementioned multiple DC distribution systems receives power from a power source, and at least one of the other DC distribution systems has a DC load or charging equipment such as a battery. Multiple power converters connected to the DC buses of multiple DC power distribution systems, The system includes a power exchange line connecting multiple power exchange converters, Multiple power exchange converters have a DC bus target voltage, which is the target voltage value of the DC bus when outputting power to the power exchange line, a power exchange line upper limit voltage, which is the upper voltage limit of the power exchange line, and a power exchange line lower limit voltage, The aforementioned power exchange converter controls the power exchange so that the voltage of the DC bus becomes the target voltage of the DC bus, The power exchange converter is a power exchange system that controls the power exchange to maintain the upper limit voltage or lower limit voltage of the power exchange line if the voltage of the power exchange line reaches the upper limit voltage or lower limit voltage of the power exchange line before the voltage of the DC bus reaches the target voltage of the DC bus. (Note 2) The aforementioned power exchange converter has a power exchange output limit power, which is the upper limit of the power output to the power exchange line, and a power exchange input limit power, which is the upper limit of the power input from the power exchange line. The power sharing system according to Appendix 1, wherein if the power sharing output limit power or the power sharing input limit power is reached before the DC bus target voltage, the power sharing line upper limit voltage, and the power sharing line lower limit voltage are reached, the power sharing power converter controls the power sharing to maintain the power sharing output limit power or the power sharing input limit power. (Note 3) The power exchange system according to Appendix 1 or Appendix 2, wherein the upper limit voltage of the power exchange line is set to increase in order of the power exchange converters that are to be exchanged. (Note 4) The power exchange system according to any one of the appendices 1 to 3, wherein the lower limit voltage of the power exchange line is set lower in order of the power exchange converters that wish to receive power. (Note 5) The power exchange system according to any one of the appendices 1 to 4, wherein the upper limit voltage of the exchange line has a droop characteristic in which the upper limit voltage of the exchange line decreases as the output power being exchanged increases. (Note 6) The power exchange system according to any one of the appendices 1 to 5, wherein the lower limit voltage of the exchange line has a droop characteristic that increases as the amount of power being exchanged increases. [Explanation of Symbols]

[0073] 10a~10d Power exchange converter, 20 Power exchange line, 100a~100d DC distribution system, 107a~107d DC load, 108a~108d DC bus.

Claims

1. A power exchange system that allows power to be exchanged between multiple DC power distribution systems, At least one of the aforementioned multiple DC distribution systems receives power from a power source, and at least one of the other DC distribution systems has a DC load or charging equipment such as a battery. Multiple power converters connected to the DC bus of multiple DC power distribution systems, The system includes a power exchange line connecting multiple power exchange converters, Multiple power exchange converters have a DC bus target voltage, which is the target voltage value of the DC bus when outputting power to the power exchange line, a power exchange line upper limit voltage, which is the upper voltage limit of the power exchange line, and a power exchange line lower limit voltage, The aforementioned power exchange converter controls the power exchange so that the voltage of the DC bus becomes the target voltage of the DC bus, The power exchange converter is a power exchange system that controls the power exchange to maintain the upper limit voltage or lower limit voltage of the power exchange line if the voltage of the power exchange line reaches the upper limit voltage or lower limit voltage of the power exchange line before the voltage of the DC bus reaches the target voltage of the DC bus.

2. The aforementioned power exchange converter has a power exchange output limit power, which is the upper limit of the power output to the power exchange line, and a power exchange input limit power, which is the upper limit of the power input from the power exchange line. The power sharing system according to claim 1, wherein if the power sharing output limit power or the power sharing input limit power is reached before the DC bus target voltage, the power sharing line upper limit voltage, and the power sharing line lower limit voltage are reached, the power sharing power converter controls the power sharing to maintain the power sharing output limit power or the power sharing input limit power.

3. The power exchange system according to claim 1 or claim 2, wherein the upper limit voltage of the power exchange line is set to increase in order of the power exchange converters that are to be exchanged.

4. The power exchange system according to claim 1 or claim 2, wherein the lower limit voltage of the power exchange line is set lower in order of the power exchange converters that wish to receive power exchange.

5. The power exchange system according to claim 1 or claim 2, wherein the upper limit voltage of the power exchange line has a droop characteristic that decreases as the output power being exchanged increases.

6. The power exchange system according to claim 1 or claim 2, wherein the lower limit voltage of the power exchange line has a droop characteristic that increases as the amount of power being exchanged increases.

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