Power conversion device, power conversion method, and DC power distribution system

Abstract

To provide a power conversion device which parallels off only a switch of a breaking part just above a short-circuit part without causing unnecessary power outage.SOLUTION: A power conversion device includes: a power converter which is provided between a power supply part and a plurality of breaking parts provided so that a breaking current value decreases as one progresses from an upstream to a terminal end of a power distribution system and converts power supplied from the power supply part to output DC power; and a control part which increases output current so that the breaking parts are paralleled off in order from the breaking part with the smallest breaking current value after output current of the power converter is lowered below the lowest breaking current value in the breaking current values required for opening the switches of the plurality of breaking parts when a short-circuit accident occurs in the power distribution system.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a power conversion device, a power conversion method, and a DC power distribution system.

Background Art

[0002] In recent years, DC power distribution systems that supply DC power to DC devices such as buildings, factories, and railway stations have attracted attention. When a short-circuit accident occurs in a DC power distribution system, conventionally, a fuse has been used to remove the short-circuit point.

[0003] However, in the method using a fuse, due to the characteristics of the fuse, when installed at two or more locations on the path from the power supply unit to the DC device, it is impossible to set the interrupting current, interrupting speed, etc. like a circuit breaker, so it is difficult to ensure protection coordination. Therefore, it is desirable to install a fuse at one location on the path from the power supply unit to the DC device to ensure protection coordination. However, when a fuse is installed at one location, the DC device side is disconnected from the power distribution system during a short-circuit accident, so the power outage range may become wide depending on the location where the fuse is installed.

[0004] On the other hand, in an AC power distribution system, when a short-circuit accident occurs, a method of removing the short-circuit point and protecting from overcurrent by interrupting and disconnecting a circuit breaker installed in the power distribution system is generally performed. This method using a circuit breaker may also be applied in a DC power distribution system, but the interruption of the circuit breaker is slow, and there is a possibility that a converter that creates a DC voltage may be destroyed by overcurrent.

[0005] Therefore, in Patent Document 1, a power converter that converts power from a power source to DC, having a constant power droop characteristic of controlling the current flowing through the power distribution line during a short circuit and flowing a current equal to or greater than the rated current through the power distribution line for a certain period of time, a switch installed between the power converter and the location where a short circuit occurs, and a relay having an operating characteristic of detecting a current equal to or greater than the rated current and gradually opening the switch within a certain period of time are provided in a DC power distribution system.

Prior Art Documents

[0006] [Patent Document 1] International Publication No. 2020 / 070905 [Overview of the project] [Problems that the invention aims to solve]

[0007] The above DC power distribution system, when a short-circuit fault occurs, controls the constant power droop characteristics at the power converter and limits the short-circuit current, thereby ensuring protective coordination with relays and switches and reliably opening the circuit. On the other hand, because the current to the power converter is increased in the circuit connected to the short-circuit, not only the switch directly above the short-circuit but also switches higher up in the path may open, potentially causing unnecessary power outages.

[0008] This disclosure is made to solve the problems described above, and aims to provide a power conversion device, a power conversion method, and a DC power distribution system that disconnect only the switch of the circuit breaker directly above the short-circuit location without causing unnecessary power outages. [Means for solving the problem]

[0009] The power conversion device according to this disclosure is installed between a power supply unit and a plurality of interruption units arranged such that the interruption current value decreases as the power distribution system progresses from upstream to the end, and includes a power converter that converts the power supplied from the power supply unit to output DC power, In the event of a short-circuit fault in the power distribution system, the power converter's output current is set lower to the lowest interruption current value among the interruption current values ​​required to open the switches of multiple circuit breakers, and then the output current is increased so that the circuit breakers are disconnected in order from the circuit breakers with the smallest interruption current values.

[0010] Furthermore, the power conversion method according to this disclosure comprises the steps of: a power converter converting power supplied from a power supply unit to output DC power; and a control unit, in the event of a short-circuit fault in the power distribution system, lowering the output current of the power converter to a value lower than the lowest interruption current value among a plurality of interruption units provided in the power distribution system, and then increasing the output current so that the interruption units are disconnected in order from the one with the smallest interruption current value.

[0011] Furthermore, the DC power distribution system according to this disclosure includes a power conversion device according to this disclosure that converts power supplied from a power supply unit into DC power, and a plurality of circuit breakers arranged such that the breaking current value decreases sequentially from the upstream to the end of the power distribution system. [Effects of the Invention]

[0012] According to the power converter of this disclosure, when a short-circuit fault occurs in a power distribution system, the power converter's output current is set lower to the lowest interruption current value among the interruption current values ​​required to open the switches of multiple circuit breakers. Then, a control unit is provided that increases the output current so that the circuit breakers are disconnected in order from the circuit breakers with the smallest interruption current values. This has the effect of disconnecting only the switch of the circuit breaker directly above the short-circuit location without causing unnecessary power outages.

[0013] Furthermore, according to the power conversion method of this disclosure, when a short-circuit fault occurs in a power distribution system, the output current of the power converter is set lower to the lowest interruption current value among the interruption current values ​​required to open the switches of multiple circuit breakers, and then the output current is increased so that the circuit breakers are disconnected in order from the circuit breakers with the smallest interruption current values. This has the effect of disconnecting only the switch of the circuit breaker directly above the short-circuit location without causing unnecessary power outages.

[0014] Also, according to the DC power distribution system of the present disclosure, when a short - circuit accident occurs in the power distribution system, after reducing the output current of the power converter below the lowest breaking current value among the breaking current values required to open the switches of a plurality of circuit breakers, the output current is increased in order from the circuit breaker with the smallest breaking current value to be disconnected in sequence, so that only the switch of the circuit breaker directly above the short - circuit location can be disconnected without causing an unnecessary power outage.

Brief Description of the Drawings

[0015] [Figure 1] It is a configuration diagram of the DC power distribution system according to Embodiment 1. [Figure 2] It is a configuration diagram of the power conversion device according to Embodiment 1. [Figure 3] It is a diagram showing the operation of the power conversion device according to Embodiment 1 in time series. [Figure 4] It is a diagram showing the time - series change of the output current in the short - circuit accident mode of the power conversion device according to Embodiment 1. [Figure 5] It is a configuration diagram of the power conversion device according to Embodiment 2. [Figure 6] It is a configuration diagram of the DC power distribution system according to Embodiment 2. [Figure 7] It is a configuration diagram of the power conversion device according to Embodiment 3. [Figure 8] It is a diagram showing the time - series change of the output current in the short - circuit accident mode of the power conversion device according to Embodiment 3. [Figure 9] It is an over - current operation characteristic curve of the circuit breaker showing the relationship between the output current output by the power conversion device according to Embodiment 4 and time.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments will be described in detail based on the drawings. The embodiments described below are examples. Also, each embodiment can be executed in appropriate combination.

[0017] Embodiment 1. FIG. 1 is a configuration diagram of a DC power distribution system according to Embodiment 1. FIG. 2 is a configuration diagram of a power conversion device according to Embodiment 1. FIG. 3 is a diagram showing the operation of the power conversion device according to Embodiment 1 in time series. FIG. 4 is a diagram showing the time series change of the output current in the short-circuit accident mode of the power conversion device according to Embodiment 1.

[0018] As shown in FIG. 1, the DC power distribution system 100 according to this embodiment is composed of a power supply unit 1, a power conversion device 2, a cutoff unit 3, a load 4, and a power distribution line 6. Note that the DC power distribution system 100 shown in FIG. 1 includes four cutoff units 31, 32, 33, 34 and three loads 41, 42, 43, but this is an example, and the arrangement method, the number of arrangements, etc. are not limited to this.

[0019] The power supply unit 1 supplies power to the power conversion device 2. The power supplied from the power supply unit 1 to the power conversion device 2 is AC power or DC power. In the case of an AC power supply for the power supply unit 1, a commercial power supply may be used, and in the case of a DC power supply, a solar cell, a storage battery, etc. may be used. Also, in the case of a DC power supply, a DC power supply obtained by converting an AC power supply by an AC / DC converter may be used.

[0020] The power conversion device 2 converts the power supplied from the power supply unit 1 into DC power. Details will be described later using FIG. 2.

[0021] The cutoff unit 3 is provided between the power conversion device 2 and the load 4 in the power distribution line 6. When the cutoff unit 3 detects a current equal to or greater than the cutoff current value required for opening the switch of the cutoff unit 3, it outputs a trip command to the switch to open it, thereby cutting off the overcurrent. Here, the cutoff current value refers to the current value of the cutoff current required to open the switch of the cutoff unit 3. Note that for the cutoff unit 3, for example, an MCCB (Molded Case Circuit Breaker) or a semiconductor cutoff device may be used.

[0022] As shown in Figure 1, the four interruption units 31, 32, 33, and 34 are installed for each branched system, supplying power to the end load 4. The interruption units 3 are installed in the distribution line 6 such that the interruption current value of each interruption unit 3 decreases as you move from upstream to the end. That is, in Figure 1, the interruption current value of interruption unit 32 is greater than the interruption current values ​​of interruption units 33 and 34. Here, "upstream" refers to the power supply unit 1 side of the distribution line 6, and "end" refers to the load 4 side, which is farther from the power supply unit 1, in the distribution line 6.

[0023] Furthermore, the short-circuit points 51 and 52 in Figure 1 indicate the locations where short-circuit faults occurred. Specifically, short-circuit point 51 is on the secondary side of the circuit breaker 33, and short-circuit point 52 is on the secondary side of the circuit breaker 32. Although Figure 1 shows two locations, short-circuit points 51 and 52, this does not mean that two short-circuit locations occurred. The two locations are shown for convenience when explaining the difference in operation of the power converter 2 in the case of short-circuit point 51 and short-circuit point 52, which will be described later.

[0024] Load 4 is a DC device that operates by receiving DC power from power converter 2. Load 4 can be any electrical device capable of operating by receiving DC power, such as lighting fixtures, air conditioners, televisions, and other home appliances. Alternatively, it may be a DC / DC converter, DC / AC inverter, etc., that converts the DC voltage from power converter 2 to a different voltage.

[0025] Next, the configuration of the power converter 2 will be explained using Figure 2. Figure 2 is a diagram of the configuration of the power converter 2. As an example, Figure 2 shows the configuration of the power converter 2 when the power supplied from the power supply unit 1 is AC power.

[0026] As shown in Figure 2, for example, the power converter 2 includes a power converter 20, an inductor 23, a capacitor 24, a current sensor 25, a control unit 26, and a voltage sensor 27. The power converter 20 also includes a rectifier 21 and a switching circuit 22.

[0027] The rectifier unit 21 of the power converter 20 converts the power input from the power supply unit 1 into DC power. The switching circuit 22 of the power converter 20 limits the DC power output from the rectifier unit 21. The method of limiting the DC power will be described later in the explanation of the control unit 26. The switching circuit 22 includes a gate driver.

[0028] The inductor 23 and capacitor 24 smooth the current and voltage output from the switching circuit 22 and output DC power to the outside from the power converter 2. The current sensor 251 measures the output current of the switching circuit 22. The current sensor 251 outputs the measured current value to the current control unit 264. The current sensor 252 measures the output current that has been smoothed by the inductor 23 and capacitor 24. The current sensor 252 outputs the measured current value to the short-circuit detection unit 261. The voltage sensor 27 measures the voltage that has been smoothed by the inductor 23 and capacitor 24. The voltage sensor 27 outputs the measured voltage value to the short-circuit detection unit 261.

[0029] Furthermore, as shown in Figure 2, for example, the control unit 26 includes a short-circuit detection unit 261, a voltage control unit 262, a current limit unit 263, a current control unit 264, and a PWM unit 265. When a short-circuit fault occurs in the power distribution system, the control unit 26 lowers the output current of the power converter 20 to the lowest interruption current value among the multiple interruption units 3 provided in the power distribution system, and then increases the output current so that the interruption units 3 with the smallest interruption current values ​​are disconnected in order.

[0030] The short-circuit detection unit 261 determines whether or not a short-circuit fault has occurred in the power distribution system. Specifically, the short-circuit detection unit 261 determines that a short-circuit fault is occurring if the voltage measurement value input from the voltage sensor 27 does not exceed a predetermined voltage threshold, and switches the current limit unit 263 to short-circuit fault mode. In addition, the short-circuit detection unit 261 determines that a short-circuit fault is occurring if the current measurement value input from the current sensor 252 exceeds a predetermined current threshold, and switches the current limit unit 263 to short-circuit fault mode. In other words, the short-circuit detection unit 261 has predetermined voltage thresholds and current thresholds, compares the voltage measurement value input from the voltage sensor 27 with the voltage threshold, and compares the current measurement value input from the current sensor 252 with the current threshold, and determines that a short-circuit fault is occurring if the voltage measurement value does not exceed the voltage threshold or the current measurement value exceeds the current threshold, and switches the current limit unit 263 to short-circuit fault mode.

[0031] The voltage control unit 262 calculates a current command value from a predetermined voltage command value and a voltage measurement value input from the voltage sensor 27, and outputs it to the current limit unit 263. Here, the current command value is calculated by performing PI control on the difference between the predetermined voltage command value and the voltage measurement value input from the voltage sensor 27.

[0032] When the short-circuit detection unit 261 determines that a short-circuit fault is present and outputs a command from the short-circuit detection unit 261 to transition to the short-circuit fault mode, the current limit unit 263 lowers the current limit value to the minimum interruption current value and then gradually increases it. The current command value output from the voltage control unit 262 changes in accordance with the change in the current limit value. That is, when the current limit value is controlled, the current command value is also lowered to the minimum interruption current value and then gradually increases accordingly. In this way, the current command value controlled by the current limit unit 263 is output to the current control unit 264. The current command value is output to the current control unit 264 intermittently.

[0033] The current control unit 264 calculates the standard deviation from the current command value output from the current limit unit 263 and limited to the current limit value range, and the current measurement value output from the current sensor 251, and outputs it to the PWM unit 265. The PWM unit 265 converts the standard deviation output from the current control unit 264 into a switching signal. The switching signal converted in the PWM unit 265 is output to the switching circuit 22.

[0034] Next, the processing operation of the control unit 26 will be described.

[0035] The short-circuit detection unit 261 determines that a short-circuit fault has occurred if the current measurement input from the current sensor 252 exceeds a predetermined current threshold, or if the voltage measurement input from the voltage sensor 27 does not exceed a predetermined voltage threshold, and outputs a command to the current limit unit 263 to transition to short-circuit fault mode.

[0036] During a short-circuit fault, a large current (hereinafter referred to as the short-circuit current) flows from the capacitor 24 to the short-circuit location. In addition, the output voltage output of the power converter 2 also decreases due to the short-circuit fault. Therefore, the short-circuit detection unit 261 can determine whether or not a short-circuit fault has occurred by pre-determining the current threshold and voltage threshold, and can output a command to the current limit unit 263 to transition to the short-circuit fault mode.

[0037] The voltage control unit 262 calculates a current command value from a predetermined voltage command value and a voltage measurement value input from the voltage sensor 27. The calculated current command value is output to the current limit unit 263.

[0038] The current limit unit 263 receives a command from the short-circuit detection unit 261 and transitions to the short-circuit fault mode. The current limit unit 263 then sets the current limit value below the minimum interruption current value and gradually increases it. The current command value output from the voltage control unit 262 changes accordingly. The current command value determined in this way is output from the current limit unit 263 to the current control unit 264.

[0039] The current control unit 264 calculates the standard deviation from the current command value output from the current limit unit 263 and the current measurement value output from the current sensor 251, and outputs it to the PWM unit 265.

[0040] The PWM unit 265 converts the standard deviation output from the current control unit 264 into a switching signal. The switching signal converted in the PWM unit 265 is output to the switching circuit 22, which limits the DC power output from the rectifier unit 21.

[0041] In this way, by limiting the DC power output from the power converter 2, the circuit breakers 3 are disconnected in order from the smallest breaking current value. In the power distribution system, the circuit breakers 3 are installed so that the breaking current value decreases as you move from upstream to the end, so it is possible to disconnect the short-circuit point 5 while preventing a large-scale power outage caused by the disconnection of the upper circuit breakers 3.

[0042] Furthermore, when the circuit breaker 3 directly above the short-circuit point 5 is disconnected and the short-circuit point 5 is removed from the power distribution path, the line impedance on the output side of the power converter 2 changes significantly, causing a change in the output current or output voltage of the power converter 2. Specifically, because the line impedance becomes larger compared to when a short-circuit fault occurs, the output current temporarily increases or the output voltage increases.

[0043] Therefore, the short-circuit detection unit 261 determines that a short-circuit fault is not occurring if the current measurement value measured by the current sensor 252 changes to a predetermined current change threshold or if the voltage measurement value measured by the voltage sensor 27 exceeds a voltage change threshold during a short-circuit fault mode, and outputs a command to the current limit unit 263 to switch from the short-circuit fault mode to the normal mode.

[0044] The current limit unit 263 switches to normal mode when it receives a command from the short-circuit detection unit 261. In normal mode, the current command value input from the voltage control unit 262 is output directly to the current control unit 264.

[0045] Furthermore, the short-circuit detection unit 261 may store in advance current change thresholds and voltage change thresholds used when determining that a short-circuit fault condition does not exist.

[0046] Next, using the short-circuit points 51 and 52 shown in Figure 1 as examples, the operation of the power converter 2 in the event of a short-circuit fault will be explained using Figures 3 and 4.

[0047] Figure 3 shows the operation of the power converter 2 in a time series. Figure 4 shows the time series change of the output current output by the power converter 2 in a short-circuit fault mode. Note that in Figure 3 (a), the vertical axis represents the current value Io and the horizontal axis represents time t, and in (b), the vertical axis represents the voltage value Vo and the horizontal axis represents time t. Figure 4 is a relationship diagram in which the vertical axis represents the current value and the horizontal axis represents time.

[0048] Furthermore, in Figure 4, I33 represents the tripping current value of the tripping unit 33, and I32 represents the tripping current value of the tripping unit 32. That is, the current limiting unit 263 increases the current limit value to the tripping current value I33 of the tripping unit 33 at time t33, and to the tripping current value I32 of the tripping unit 32 at time t32, and this indicates that the power converter 2 is outputting the result. Note that Figure 4 shows an example in which the current limit value is increased linearly, but this is just one example and is not limited to this. For example, the current limiting unit 263 may set the rate of increase of the current limit value so that it can be opened, taking into account the operating characteristics of each of the tripping units 3.

[0049] First, we will explain the operation of the power converter 2 when a short-circuit fault occurs at the short-circuit point 51.

[0050] At time ta shown in Figure 3, when a short-circuit fault occurs, a short-circuit current flows from the capacitor 24 of the power converter 2 towards the short-circuit location. Consequently, the output voltage output of the power converter 2 decreases to approximately 0V.

[0051] At time tb, the short-circuit detection unit 261 determines that a short-circuit fault has occurred if the current measurement input from the current sensor 252 exceeds a predetermined current threshold I1, or if the voltage measurement input from the voltage sensor 27 does not exceed a predetermined voltage threshold V1, and outputs a command to the current limit unit 263 to transition to short-circuit fault mode.

[0052] Between times tb and tc, the current limit unit 263 transitions from normal mode to short-circuit fault mode, lowering the current limit value below the minimum interrupting current value and then gradually increasing it. In Figure 3, as an example, the current limit value is lowered to 0A and then gradually increased.

[0053] Then, at time tc, the current limit value in the current limit section 263 reaches the tripping current value I33 of the tripping section 33 directly above the short-circuit point 51. Once the tripping time has elapsed, the switch of the tripping section 33 opens, and the short-circuit point 51 is disconnected. At that time, a current with a tripping current value I33 is also output from the power converter 20 to the upper tripping section 32. However, since the tripping current value I32 of the tripping section 32 is greater than the tripping current value I33, the switch of the tripping section 32 does not open.

[0054] Between times tc and td, the impedance increases due to the disconnection of the short-circuit point 51, causing the output current to temporarily decrease. The output voltage also increases. At time td, the short-circuit determination unit 261 determines that there is no short-circuit fault if the current measurement value measured by the current sensor 252 changes by a predetermined current change threshold ΔI1 or more, or if the voltage measurement value measured by the voltage sensor 27 exceeds the voltage change threshold ΔV1, and outputs a command to the current limit unit 263 to switch from short-circuit fault mode to normal mode. Upon receiving the command from the short-circuit determination unit 261, the current limit unit 263 switches from short-circuit fault mode to normal mode.

[0055] In this way, by operating the power converter 2, only the circuit breaker 33 directly above the short-circuit point 51 is disconnected, and power supply to the load 4 can be resumed without stopping the power converter 2.

[0056] Next, we will explain the operation of the power converter 2 when a short-circuit fault occurs at the short-circuit point 52.

[0057] At time ta shown in Figure 3, when a short-circuit fault occurs, a short-circuit current flows from the capacitor 24 of the power converter 2 towards the short-circuit location. Consequently, the output voltage output of the power converter 2 decreases to approximately 0V.

[0058] At time tb, the short-circuit detection unit 261 determines that a short-circuit fault has occurred if the current measurement input from the current sensor 252 exceeds a predetermined current threshold I1, or if the voltage measurement input from the voltage sensor 27 does not exceed a predetermined voltage threshold V1, and outputs a command to the current limit unit 263 to transition to short-circuit fault mode.

[0059] Between times tb and tc, the current limit unit 263 transitions from normal mode to short-circuit fault mode, lowering the current limit value below the minimum interrupting current value and then gradually increasing it. In Figure 3, as an example, the current command value is reduced to 0A and then gradually increased.

[0060] As shown in Figure 4, the current limit unit 263 gradually increases the current limit value, increasing the current command value to the interruption current value I33 at time t33. At this time, the output current value output by the power converter 2 is the interruption current value I33, which is a sufficient current value to open the switches of the interruption units 33 and 34. However, since no current flows below the short-circuit point 52, the switches of the interruption units 33 and 34 below the interruption unit 32 are not opened.

[0061] Subsequently, when the current limit unit 263 increases the current limit value to the interruption current value I32 of the interruption unit 32 directly above the short-circuit point 52, the output current output from the power converter 2 opens the switch of the interruption unit 32, and the short-circuit point 52 is disconnected.

[0062] Between times tc and td, the impedance increases due to the disconnection of the short-circuit point 52, causing the output current to temporarily decrease. The output voltage also increases. At time td, the short-circuit detection unit 261 determines that there is no short-circuit fault if the current measurement value measured by the current sensor 252 changes by a current change of more than or equal to a predetermined current change threshold ΔI1, or if the voltage measurement value measured by the voltage sensor 27 exceeds the voltage threshold, and outputs a command to the current limit unit 263 to switch from short-circuit fault mode to normal mode. Upon receiving the command from the short-circuit detection unit 261, the current limit unit 263 switches from short-circuit fault mode to normal mode.

[0063] In this way, by operating the power converter 2, only the circuit breaker 32 directly above the short-circuit point 52 is disconnected, and power supply to the load 4 can be resumed without stopping the power converter 2.

[0064] As described above, the power converter 2 according to this embodiment is equipped with a control unit 26 that, in a power distribution system where circuit breakers 3 with small breaking current values ​​required to open the switches of the circuit breakers 3 are provided from upstream to the terminal, determines that a short-circuit fault has occurred in the short-circuit determination unit 261, and then lowers the output current of the power converter 20 to the lowest breaking current value among the multiple circuit breakers 3 provided in the power distribution system, and then increases the output current so that the circuit breakers 3 with small breaking current values ​​are disconnected in order. This configuration has the effect of disconnecting only the switches of the circuit breakers 3 directly above the short-circuit location without causing unnecessary power outages.

[0065] Furthermore, the power converter 2 includes a current limit unit 263 in the control unit 26 that, when the short-circuit determination unit 261 determines that a short-circuit fault is occurring, lowers the current limit value to the minimum interruption current value and then gradually increases it. With this configuration, the short-circuit location can be disconnected by opening only the switch of the interruption unit 3 directly above the short-circuit location, so that the entire power distribution system does not lose power and power can be supplied to the load 4 continuously. Specifically, even if a short-circuit fault occurs at the short-circuit point 52 shown in Figure 1, power can be supplied to the load 41 continuously. Also, even if a short-circuit fault occurs at the short-circuit point 51, power can be supplied to both the load 41 and the load 43 continuously.

[0066] Embodiment 2. This embodiment will be explained with reference to Figures 5 and 6. Figure 5 is a diagram showing the configuration of a power conversion device according to this embodiment. Figure 6 is a diagram showing the configuration of a DC power distribution system according to this embodiment.

[0067] In Embodiment 1, a power converter 2 is shown that, when a short-circuit detection unit 261 determines that a short-circuit fault has occurred, sets the output current of the power converter 20 to a value lower than the lowest interruption current value among the multiple interruption units 3 provided in the power distribution system, and then increases the output current so that the interruption units 3 are disconnected in order from the lowest interruption current value. In Embodiment 2, a power converter 2a is shown that is newly equipped with a short-circuit location detection unit 266 in the control unit 26a. The other configurations are the same as in Embodiment 1, and the same numbers are used for the same configurations as in Embodiment 1, and their descriptions are omitted.

[0068] The power converter 2a according to this embodiment includes a control unit 26 that, in a power distribution system where circuit breakers 3 with small breaking current values ​​required to open the switches of the circuit breakers 3 are provided from upstream to the terminal, determines that a short-circuit fault has occurred in the short-circuit determination unit 261. The control unit 26 then lowers the output current of the power converter 20 to a value lower than the lowest breaking current value among the multiple circuit breakers 3 provided in the power distribution system, and then increases the output current so that the circuit breakers 3 are disconnected in order from the circuit breakers with the smallest breaking current values. This configuration has the effect of disconnecting only the switches of the circuit breakers 3 directly above the short-circuit location without causing unnecessary power outages.

[0069] Furthermore, as shown in Figure 5, the power converter 2a includes a short-circuit location determination unit 266 in the control unit 26a. The short-circuit location determination unit 266 determines the short-circuit location by comparing a short-circuit location determination threshold with the current measurement value measured by the current sensor 252. Here, the short-circuit location determination threshold is a current threshold for determining the short-circuit location, and is predetermined using the cutoff current value. Note that the short-circuit location determination threshold includes the cutoff current value or a certain range of values ​​before and after the cutoff current value.

[0070] The short-circuit detection unit 266 determines the short-circuit location by comparing a predetermined short-circuit detection threshold with the measured current value. The short-circuit detection threshold may be stored in advance by the short-circuit detection unit 266, or it may be stored in a storage unit (not shown) provided in the power converter 2a. Alternatively, it may be stored in an external interface and input to the short-circuit detection unit 266 as needed.

[0071] Let's explain using Figure 6. Assume that a short-circuit fault has occurred at the short-circuit point 52 shown in Figure 6. The short-circuit location determination unit 266 has predetermined and stored short-circuit location determination thresholds using the interruption current values ​​I31 to I34 (hereinafter, the short-circuit location determination thresholds will be referred to as Icb31, Icb32, Icb33, and Icb34). Note that each interruption unit 3 is provided such that the interruption current values ​​I31 to I34 decrease as you move from the upstream to the terminal in the power distribution system.

[0072] The current measurement value obtained from the current sensor 252 is input to the short-circuit location determination unit 266. The short-circuit location determination unit 266 compares the current measurement value input from the current sensor 252 with a plurality of pre-stored short-circuit location determination thresholds Icb31 to Icb34. As a result, if the short-circuit location determination threshold is greater than the short-circuit location determination threshold Icb32 and less than the short-circuit location determination threshold Icb33, it is determined that the short-circuit location, i.e., the short-circuit point 52 shown in Figure 6, is on the secondary side of the interruption unit 32.

[0073] As described above, the power converter 2a according to this embodiment includes a short-circuit location determination unit 266 that determines the short-circuit location by comparing a predetermined short-circuit location determination threshold with the current measurement value measured by the current sensor 252. This makes it easier to identify the short-circuit location than the power converter 2 according to Embodiment 1, and allows for prompt repair of the short-circuit location.

[0074] Furthermore, in the power converter 2 according to Embodiment 1, the short-circuit detection unit 261 determines that there is no short-circuit fault and outputs a command to the current limit unit 263 to switch from short-circuit fault mode to normal mode. Only after obtaining information about the short-circuit location from the interruption unit 3 directly above the short-circuit location via communication, signals, etc., can the short-circuit location be identified. On the other hand, in the power converter 2a according to this embodiment, the short-circuit location can be determined by comparing the current measurement value measured by the current sensor 252 with a predetermined short-circuit location determination threshold at the timing before the short-circuit detection unit 261 outputs a command to the current limit unit 263 to switch from short-circuit fault mode to normal mode. Therefore, the short-circuit location can be identified quickly without incurring costs for setting up equipment for communication with the interruption unit 3.

[0075] In this embodiment, an example was described in which the short-circuit location determination unit 266 is provided separately from the short-circuit location determination unit 261. However, the short-circuit location determination unit 261 may also be configured to include the short-circuit location determination unit 266. In this case, the short-circuit location determination unit 261 can further improve the accuracy of the determination result by identifying the short-circuit location based on the comparison result between the current measurement value measured by the current sensor 252 and a predetermined short-circuit location determination threshold, and the determination result that it is not in a short-circuit fault state.

[0076] Embodiment 3. This embodiment will be explained with reference to Figures 7 and 8. Figure 7 is a configuration diagram of the power converter according to this embodiment. Figure 8 is a diagram showing the time-series change of the output current in the short-circuit fault mode of the power converter according to this embodiment.

[0077] In Embodiment 1, a power converter 2 is shown that, when a short-circuit detection unit 261 determines that a short-circuit fault has occurred, sets the output current of the power converter 20 to a value lower than the lowest interruption current value among the multiple interruption units 3 provided in the power distribution system, and then increases the output current so that the interruption units 3 are disconnected in order from the smallest interruption current value. In Embodiment 3, the method of increasing the current limit value differs from Embodiment 1, and a power converter 2b is shown that is equipped with a current limit unit 263a that increases the current limit value in stages, starting from the smallest interruption current value among the interruption current values ​​of each interruption unit 3. The other configurations are the same as in Embodiment 1, and the same numbers are used for the same configurations as in Embodiment 1, and their descriptions are omitted.

[0078] The power converter 2b according to this embodiment includes a control unit 26 that, in a power distribution system where circuit breakers 3 with small breaking current values ​​required to open the switches of the circuit breakers 3 are provided from upstream to the terminal, determines that a short-circuit fault has occurred in the short-circuit determination unit 261. The control unit 26 then lowers the output current of the power converter 20 to a value lower than the lowest breaking current value among the multiple circuit breakers 3 provided in the power distribution system, and then increases the output current so that the circuit breakers 3 are disconnected in order from the circuit breakers with the smallest breaking current values. This configuration has the effect of disconnecting only the switches of the circuit breakers directly above the short-circuit location without causing unnecessary power outages.

[0079] Figure 8 shows the time-series change of the output current output by the power converter 2b in a short-circuit fault mode. In Figure 8, the vertical axis represents the current value and the horizontal axis represents time. Although the DC distribution system shown in Figure 1 is equipped with four interruption units 3, for the sake of explanation only the interruption current values ​​I32 and I33 of interruption units 32 and 33, and their corresponding times T32 and T33 are shown, and other values ​​are omitted.

[0080] When the short - circuit determination unit 261 determines that a short - circuit accident has occurred, the current limit unit 263a reduces the current limit value below the lowest cut - off current value and then increases it step by step. Specifically, as shown in FIG. 8, the current limit unit 263a increases the current limit value step by step in ascending order of the cut - off current values of the cutoff units 3. In a power distribution system provided with cutoff units 3 with decreasing cut - off current values from the upstream to the end, after reducing the current limit value below the lowest cut - off current value, the current limit value is increased step by step from the lowest cut - off current value, such as the cut - off current value I33, the cut - off current value I32, etc.

[0081] Note that the current limit unit 263a does not necessarily have to set the current limit value to the same numerical value as the cut - off current value. For example, in the DC power distribution system 100 shown in FIG. 1, if the cut - off current values of each of the cutoff units 3 are I33 < I34 < I31 < I32 and the current limit value is set as IA, the current limit unit 263a reduces the current limit value below the lowest cut - off current value, that is, lower than I33, and then increases the current limit value IA step by step so that I33 ≤ IA < I34, I34 ≤ IA < I31, I31 ≤ IA < I32, I32 ≤ IA. By doing so, for example, when the current limit value is set as I34 ≤ IA < I31 and the short - circuit determination unit 261 determines that it is not in a short - circuit accident state, since the switch of the cutoff unit 34 is open, it can be determined that the secondary side of the cutoff unit 34 is the short - circuit location.

[0082] As described above, the power converter 2b according to this embodiment differs from the power converter 2 according to Embodiment 1, which has a current limiting unit 263 that linearly increases the current limit value, in that it has a current limiting unit 263a that increases the current limit value in stages. As a result, the current limiting unit 263a increases the current limit value in stages from a small interruption current value so that the switches of the interruption unit 3 are opened one by one, thus shortening the time it takes to open the switches of the interruption unit 3 at the short-circuit location. Furthermore, since the current limiting unit 263a increases the current limit value in stages from a small interruption current value so that the switches of the interruption unit 3 are opened one by one in sequence, it becomes possible to determine the short-circuit location at the time the short-circuit determination unit 261 determines that there is no short-circuit fault condition.Therefore, as in the power converter 2a according to Embodiment 2, it is not necessary to determine the short-circuit location by comparing the interruption current value of each interruption unit 3 with the current measurement value measured by the current sensor 252, making it possible to determine the short-circuit location more easily.

[0083] Embodiment 4. This embodiment will be explained using Figure 9. Figure 9 is an overcurrent operation characteristic curve of the interruption unit showing the relationship between the output current and time of the power converter according to this embodiment.

[0084] Embodiment 3 shows a power converter 2b equipped with a current limiting unit 263a that, when a short-circuit detection unit 261 determines that a short-circuit fault has occurred, gradually increases the current limit value of each interrupting unit 3, starting from the smallest interrupting current value. Embodiment 4 shows a power converter 2c equipped with a current limiting unit 263a that, when gradually increasing the current limit value, determines the duration for which the current limit value at each stage is maintained (hereinafter referred to as "duration") based on the overcurrent operation characteristic curve of each interrupting unit 3. The other configurations are the same as in Embodiment 1, and the same numbers are used for the same configurations as in Embodiment 1, and their descriptions are omitted.

[0085] The power converter 2c according to this embodiment includes a control unit 26 that, in a power distribution system where circuit breakers 3 with small breaking current values ​​required to open the switches of the circuit breakers 3 are provided from upstream to the terminal, determines that a short-circuit fault has occurred in the short-circuit determination unit 261. The control unit 26 then lowers the output current of the power converter 20 to a value lower than the lowest breaking current value among the multiple circuit breakers 3 provided in the power distribution system, and then increases the output current so that the circuit breakers 3 are disconnected in order from the circuit breakers with the smallest breaking current values. This configuration has the effect of disconnecting only the switches of the circuit breakers directly above the short-circuit location without causing unnecessary power outages.

[0086] Furthermore, in this embodiment, when the current limit unit 263a increases the current limit value in steps, it determines the duration of each step based on the overcurrent operation characteristic curve, and the power converter 2c outputs the determined duration current. Details will be described later with reference to Figure 9.

[0087] Figure 9 shows the overcurrent operation characteristic curves for each of the 3 interruption units, with the horizontal axis representing current value and the vertical axis representing time. For explanatory purposes, only the overcurrent operation characteristic curves for interruption units 32 and 33 are shown, while the overcurrent operation characteristic curves for interruption units 31 and 34 are omitted. Overcurrent operation characteristic curve A shows the overcurrent operation characteristic curve for interruption unit 33, and overcurrent operation characteristic curve B shows the overcurrent operation characteristic curve for interruption unit 32.

[0088] For example, referring to overcurrent operation characteristic curve A, it can be seen that when the current value is iA or greater, it takes tA [sec] to open the switch of the interruption unit 33, regardless of the magnitude of the current value. Similarly, referring to overcurrent operation characteristic curve B, it can be seen that when the current value is iB or greater, it takes tB [sec] to open the switch of the interruption unit 32, regardless of the magnitude of the current value. Furthermore, when the interruption current value is set to be less than iA, it takes longer than tA to open the switch of the interruption unit 33.

[0089] Therefore, when the current limiting unit 263a increases the current limiting value in steps, it determines the duration of each step based on the overcurrent operation characteristic curve of each interrupting unit 3. This allows the switch of the interrupting unit 3 to be opened in a shorter time, thereby disconnecting the short-circuit point 5.

[0090] As described above, the power converter 2c according to this embodiment includes a current limiting unit 263a that, when increasing the current limiting value in steps, determines the duration of each step based on the overcurrent operation characteristic curve and increases the current limiting value in steps so that the switches of the interruption unit 3 are opened in order from the value with the smallest interruption current. This allows the switches of the interruption unit 3 to be opened in a shorter time and the short-circuit point 5 to be disconnected.

[0091] The various aspects of this disclosure are summarized below as an appendix.

[0092] (Note 1) A power converter is provided between the power supply unit and a plurality of interruption units arranged so that the interruption current value decreases as the power distribution system progresses from upstream to the end, and which converts the power supplied from the power supply unit to output DC power. When a short-circuit fault occurs in the power distribution system, the control unit lowers the output current of the power converter to the lowest of the interrupting current values ​​required to open the switches of the multiple interrupting units, and then increases the output current so that the interrupting units are disconnected in order from the ones with the smallest interrupting current values. A power conversion device equipped with the following features. (Note 2) The control unit, A short-circuit detection unit determines a short-circuit fault condition when the voltage measurement input from the voltage sensor does not exceed a predetermined voltage threshold or when the current measurement input from the current sensor exceeds a predetermined current threshold. A voltage control unit that calculates a current command value from a predetermined voltage command value and a voltage measurement value input from the voltage sensor, When the short-circuit detection unit determines that a short-circuit fault condition exists, the current limit unit lowers the current limit value to a value lower than the minimum interruption current value and then increases it; A current control unit that calculates the standard deviation from the current command value limited to within the range of the current limit value and the current measurement value, A PWM unit converts the standard deviation output from the current control unit into a switching signal and outputs it to the power converter, A power conversion device as described in Appendix 1, comprising the following features. (Note 3) The power converter according to Appendix 2, wherein the short-circuit determination unit determines that the device has transitioned from a short-circuit fault state to a normal state when the current measurement value measured by the current sensor changes by a predetermined current change threshold or when the voltage measurement value measured by the voltage sensor becomes equal to or greater than a voltage change threshold. (Note 4) A power conversion device according to any one of the appendices 1 to 3, comprising a short-circuit location determination unit for determining a short-circuit location, wherein the short-circuit location determination unit determines a short-circuit location by comparing the current measurement value input from the current sensor with a predetermined short-circuit location determination threshold value obtained from the interruption current values ​​of a plurality of interruption units. (Note 5) The power conversion device according to claim 4, which identifies the short-circuit location based on the comparison result of the current measurement value and the interruption current value and the determination result of determining that the state has transitioned from a short-circuit fault state to a normal state. (Note 6) The power conversion device according to any one of the appendices 1 to 5, wherein the current limiting unit sets the current limiting value to be smaller than the minimum interruption current value, then sets the current limiting value to be equal to or exceed the smallest interruption current value, and increases it in stages according to the interruption current value. (Note 7) The power conversion device according to Appendix 6, wherein when the current limiting unit increases the current limiting value in stages, the duration for which the current limiting value at each stage is maintained is determined based on the overcurrent operation characteristic curve of the interrupting unit. (Note 8) The power converter converts the power supplied from the power supply unit and outputs DC power, The control unit, in the event of a short-circuit fault in the power distribution system, lowers the output current of the power converter to the lowest interruption current value among the interruption current values ​​required to open the switches of the multiple interruption units, and then increases the output current so that the interruption units are disconnected in order from the one with the smallest interruption current value. A power conversion method comprising the following features. (Note 9) A power conversion device described in any one of the appendices 1 to 7 that converts power supplied from a power supply unit into DC power, Multiple interruption units are provided such that the interruption current value decreases sequentially from the upstream to the terminal of the power distribution system, A DC power distribution system equipped with the following features. [Explanation of Symbols]

[0093] 100 DC power distribution system, 1 power supply unit, 2, 2a, 2b, 2c power converter, 20 power converter, 21 rectifier unit, 22 switching circuit, 23 inductor, 24 capacitor, 25, 251, 252 current sensor, 26, 26a control unit, 261 short circuit detection unit, 262 voltage control unit, 263, 263a current limit unit, 264 current control unit, 265 PWM unit, 266 short circuit location detection unit, 27 voltage sensor, 3, 31, 32, 33, 34 circuit breaker, 4, 41, 42, 43 load, 5, 51, 52 short circuit point, 6 distribution line

Claims

1. A power converter is provided between the power supply unit and a plurality of interruption units arranged so that the interruption current value decreases as the power distribution system progresses from upstream to the end, and which converts the power supplied from the power supply unit to output DC power. When a short-circuit fault occurs in the power distribution system, the control unit lowers the output current of the power converter to the lowest of the interrupting current values ​​required to open the switches of the multiple interrupting units, and then increases the output current so that the interrupting units are disconnected in order from the ones with the smallest interrupting current values. A power conversion device equipped with the following features.

2. The control unit, A short-circuit detection unit determines a short-circuit fault condition when the voltage measurement input from the voltage sensor does not exceed a predetermined voltage threshold or when the current measurement input from the current sensor exceeds a predetermined current threshold. A voltage control unit that calculates a current command value from a predetermined voltage command value and a voltage measurement value input from the voltage sensor, When the short-circuit detection unit determines that a short-circuit fault condition exists, the current limit unit lowers the current limit value to a value lower than the minimum interruption current value and then increases it; A current control unit that calculates the standard deviation from the current command value limited to within the range of the current limit value and the current measurement value, A PWM unit converts the standard deviation output from the current control unit into a switching signal and outputs it to the power converter, The power conversion device according to claim 1, comprising:

3. The power conversion device according to claim 2, wherein the short-circuit determination unit determines that the device has transitioned from a short-circuit fault state to a normal state when the current measurement value measured by the current sensor changes by a current change of a predetermined current change threshold or when the voltage measurement value measured by the voltage sensor becomes equal to or greater than a voltage change threshold.

4. The power conversion device according to claim 2, further comprising a short-circuit location determination unit for determining a short-circuit location, wherein the short-circuit location determination unit determines a short-circuit location by comparing the current measurement value input from the current sensor with a predetermined short-circuit location determination threshold value obtained from the interruption current values ​​of a plurality of interruption units.

5. The power conversion device according to claim 4, which identifies the short-circuit location based on the comparison result of the current measurement value and the interruption current value and the determination result that the state has transitioned from a short-circuit fault state to a normal state.

6. The power conversion device according to claim 2, wherein the current limiting unit first sets the current limiting value to be smaller than the minimum interruption current value, then sets the current limiting value to be equal to or exceed the smallest interruption current value, and increases it in stages according to the interruption current value.

7. The power conversion device according to claim 6, wherein, when the current limiting unit increases the current limiting value in stages, the duration for which the current limiting value is maintained at each stage is determined based on the overcurrent operation characteristic curve of the interrupting unit.

8. The power converter converts the power supplied from the power supply unit and outputs DC power, When a short-circuit fault occurs in the power distribution system, the control unit first lowers the output current of the power converter to the lowest interruption current value among the multiple interruption current values ​​of the interruption units provided in the power distribution system, and then increases the output current so that the interruption units are disconnected in order from the one with the smallest interruption current value. A power conversion method comprising the following features.

9. A power conversion device according to claim 1, which converts power supplied from a power supply unit into DC power, Multiple interruption units are provided such that the interruption current value decreases sequentially from the upstream to the terminal of the power distribution system, A DC power distribution system equipped with the following features.

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