Power conversion system and control method for power conversion system

Abstract

To provide a power conversion system that has a simple configuration and is capable of detecting the open / closed state of a contactor even in a no-load state, and appropriately controlling the voltage of a DC bus.SOLUTION: A power conversion system includes a DC bus, a capacitor, a power converter, and a control device, and the power converter includes a control unit that controls a DC bus voltage to bring it close to a target value on the basis of a control gain that is greater than the control gain when the power converter operates alone by an amount equal to the capacitance of the capacitor, and a hunting detection unit that detects whether hunting has occurred on the basis of a deviation between a measured value of the DC bus voltage and the target value, and the control device includes a limiting processing unit that, when the power converter detects the occurrence of hunting, limits the power input / output between the DC bus and a power source or a load depending on the number of power converters excluding the power converter in which the hunting has occurred.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion system and a control method for a power conversion system. [Background technology]

[0002] In a system in which multiple units, each including a power converter and a storage battery, are connected in parallel to a DC bus, a contactor (input switch) that can switch between connecting and disconnecting each unit is provided between the DC bus and the unit. For example, Patent Document 1 describes a technology that, when a power converter is disconnected by opening a contactor, adjusts the proportional gain according to a change in the number of power converters in operation to prevent hunting from occurring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-176255 Summary of the Invention [Problem to be solved by the invention]

[0004] Detecting the open / closed state of a contactor requires additional components, such as auxiliary contacts and wiring, which increases costs and size. Therefore, it is desirable to be able to determine the open / closed state of a contactor without adding such components. While a load connected to the DC bus is operating, it is possible to detect whether a contactor has opened by, for example, monitoring the power output from each power converter. However, in a no-load state (when the load is stopped), each power converter maintains a constant DC voltage, and only the storage battery needs to supply power equivalent to the loss (standby power of the power converter). This eliminates differences in DC voltage between the power converters, making it difficult to detect whether a contactor has opened by monitoring voltage, current, or power. Furthermore, if a load is applied to the storage battery in the charging direction without detecting that the contactor is open, the storage battery cannot absorb the load power, causing the DC bus to overvoltage and potentially resulting in a system shutdown.

[0005] An object of the present disclosure is to provide a power conversion system and a control method for a power conversion system that have a simple configuration and can detect the open / closed state of a contactor even in a no-load state and appropriately control the voltage of a DC bus. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, a power conversion system includes a DC bus, a capacitor connected to the DC bus, a plurality of power converters connected in parallel to the DC bus via open / close contactors, and a control device that adjusts the power input / output between the DC bus and a power source or a load, wherein the power converters include a control unit that controls a DC bus voltage input from or output to the DC bus to approach a target value based on a control gain that is greater than the control gain when the power converter operates alone by an amount equal to the capacitance of the capacitor, and a hunting detection unit that detects whether hunting has occurred based on a deviation between a measured value of the DC bus voltage and the target value, and the control device includes a limiting processing unit that, when the power converters detect the occurrence of hunting, limits the power input / output between the DC bus and the power source or the load in accordance with the number of power converters excluding the power converter that has experienced hunting.

[0007] According to one aspect of the present disclosure, a control method for a power conversion system includes a DC bus, a capacitor connected to the DC bus, a plurality of power converters connected in parallel to the DC bus via open / close contactors, and a control device that adjusts power input / output between the DC bus and a power source or a load, the control method including the steps of: controlling the power converter to control a DC bus voltage input from or output to the DC bus to approach a target value based on a control gain that is greater than a control gain when the power converter operates alone by an amount equal to the capacitance of the capacitor; detecting, by the power converter, whether hunting has occurred based on a deviation between a measured value of the DC bus voltage and the target value; and, when the power converter detects the occurrence of hunting, limiting the power input / output between the DC bus and the power source or the load in accordance with the number of power converters excluding the power converter that has experienced hunting. [Effects of the Invention]

[0008] According to the above aspect, the open / closed state of the contactor can be detected to appropriately control the voltage of the DC bus. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the overall configuration of a power conversion system according to a first embodiment. [Figure 2] 1 is a block diagram showing a functional configuration of a power converter according to a first embodiment. [Figure 3] 2 is a block diagram showing the functional configuration of a control device according to the first embodiment. FIG. [Figure 4] 4 is a flowchart showing an example of processing of the power converter according to the first embodiment. [Figure 5] FIG. 2 is a diagram for explaining functions of the power conversion system according to the first embodiment. [Figure 6] 5 is a flowchart showing an example of processing by the control device according to the first embodiment. [Figure 7] FIG. 1 is a schematic block diagram showing the configuration of a computer according to a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment Hereinafter, the embodiment will be described in detail with reference to FIGS.

[0011] (Overall configuration of power conversion system) Fig. 1 is a diagram showing the overall configuration of a power conversion system according to Embodiment 1. As shown in Fig. 1, the power conversion system 1 includes a DC bus 2, a PCS 3, a capacitor 4, a storage battery unit 10, and a control device 20.

[0012] A capacitor 4 and a plurality of storage battery units 10 (10a, 10b, . . . , 10n) are connected in parallel to the DC bus 2.

[0013] The PCS 3 exchanges DC power with the storage battery units via the DC bus 2. The PCS 3 functions as a load that converts DC power discharged from the storage battery units 10 into AC power and outputs it to other electrical machines or the power grid. The PCS 3 also functions as a power source that converts AC power supplied from the power grid into DC power and outputs (charges) it to the storage battery units 10.

[0014] Capacitor 4 is a smoothing capacitor for stabilizing the voltage of the DC bus.

[0015] Each battery unit 10 is connected in parallel to the DC bus 2. Each battery unit 10 includes a contactor 11, a power converter 12, and a battery 13.

[0016] The contactor 11 is provided between the DC bus 2 and the power converter 12. The contactor 11 switches between a connected state and a disconnected state between the power converter 12 and the DC bus 2 by opening and closing.

[0017] The power converter 12 controls the power output to the DC bus 2 or the storage battery 13 so that the voltage of the DC bus becomes a target voltage. Furthermore, the power converter 12 according to this embodiment estimates the open / closed state of the contactor 11 by detecting whether hunting has occurred. The functional configuration of the power converter 12 will be described in detail later.

[0018] The storage battery 13 may be a single storage battery or may be a plurality of storage batteries connected in series.

[0019] The control device 20 adjusts the power input / output between the DC bus 2 and the PCS 3 (power source or load). A specific functional configuration of the control device 20 will be described later.

[0020] (Functional configuration of power converter) Fig. 2 is a block diagram showing the functional configuration of the power converter according to the first embodiment. As shown in Fig. 2, the power converter 12 includes a measurement value acquisition unit 121, a control unit 122, a hunting detection unit 123, and a stop processing unit 124.

[0021] The measurement value acquisition unit 121 acquires a measurement value of the DC bus voltage input from the DC bus 2 to the power converter 12 or output from the power converter 12 to the DC bus 2.

[0022] The control unit 122 performs feedback control to bring the DC bus voltage input from or output to the DC bus 2 closer to a target value based on a control gain that is set to a value greater than the control gain when the power converter 12 operates alone by the capacitance of the capacitor 4.

[0023] The hunting detection unit 123 detects whether hunting has occurred based on the deviation between the measured value and the target value of the DC bus voltage.

[0024] When the occurrence of hunting is detected, the stop processing unit 124 stops the operation of the power converter 12 (its own device).

[0025] (Functional configuration of the control device) 3 is a block diagram showing the functional configuration of the control device according to the first embodiment. As shown in FIG. 3, the control device 20 includes an acquisition unit 201 and a restriction processing unit 202.

[0026] The acquisition unit 201 acquires the hunting detection result from each power converter 12.

[0027] When power converter 12 detects the occurrence of hunting, limiting processing unit 202 limits the power input / output to / from PSC 3 (power source or load) according to the number of power converters excluding the power converter in which hunting has occurred.

[0028] (Example of power converter processing) Fig. 4 is a sequence diagram showing an example of processing of the power conversion system according to the first embodiment. Fig. 5 is a diagram for explaining the function of the power conversion system according to the first embodiment. Here, the flow of processing of the power converter 12 will be explained with reference to Figs. 4 and 5. For example, as shown in Fig. 5, assume that there is no load (the load is stopped). At this time, each power converter 12 is only supplying power from the storage battery 13 to compensate for the loss (standby power of the power converter).

[0029] First, the measurement value acquisition unit 121 acquires a measurement value of the DC bus voltage input from the DC bus 2 to the power converter 12 or output from the power converter 12 to the DC bus 2 (step S101).

[0030] The control unit 122 performs feedback control to adjust the DC bus voltage input from or output to the DC bus 2 to approach the target value based on the deviation between the measured value and the target value of the DC bus voltage and the control gain. Note that the control gain according to this embodiment is a high gain that is greater than the control gain when the power converter 12 operates alone by the capacitance of the capacitor 4. Assume that the capacitance of the capacitor of the power converter 12 is 100 uF and the capacitance of the capacitor 4 connected to the DC bus 2 is 5 mF. In this case, for example, the control gain of the power converter 12 alone is set to 0.05 (= 500 [rad / s] * 100 [uF]), and the control gain taking the capacitor 4 into consideration is set to 2.5 (= 500 [rad / s] * 5 [mF]). Note that these numerical values ​​and formulas are merely examples and may be changed as desired.

[0031] When a high gain that takes capacitor 4 into consideration is used in this way, feedback control stabilizes the DC bus voltage when contactor 11 is closed, but overcompensation occurs when the contactor opens, making hunting more likely to occur. In other words, as shown in the example of Figure 5, if the contactor 11 of a certain storage battery unit 10a opens due to some abnormality, the control unit 122 performs feedback control using high gain, causing the DC bus voltage to hunt. As a result, if hunting occurs, it can be assumed that the contactor 11 has opened.

[0032] Next, the hunting detection unit 123 determines whether the occurrence of hunting has been detected based on the deviation between the measured value and the target value of the DC bus voltage (step S103). Specifically, the hunting detection unit 123 detects the occurrence of hunting when the number of times that the deviation between the measured value and the target value of the DC bus voltage exceeds a threshold value is equal to or greater than the determination number within a predetermined time period (step S103; YES). The threshold value includes an upper threshold value (+a [V] of the target value) and a lower threshold value (-b [V] of the target value).

[0033] If the occurrence of hunting is detected (step S103; YES), the stop processing unit 124 presumes that the contactor 11 is opened, and stops the operation of the power converter 12 (step S104). In the example of FIG. 5, the operation of the power converter 12 of the storage battery unit 10a in which hunting is detected is stopped. Furthermore, the hunting detection unit 123 notifies the control device 20 that the occurrence of hunting has been detected (step S105). Note that while FIG. 4 shows an example in which the hunting detection unit 123 notifies the control device 20 that the occurrence of hunting has been detected, this is not limiting. In other embodiments, instead of notifying the control device 20 that hunting has been detected, the stop processing unit 124 may notify the control device 20 that the operation of the power converter 12 has been stopped.

[0034] Furthermore, if the number of times the threshold is exceeded is less than the number of determination times even after a predetermined time has elapsed, the hunting detection unit 123 determines that hunting has not occurred and resets the counted number of times (step S103; NO). This makes it possible to prevent erroneous detection of hunting (abnormal opening of the contactor 11) due to temporary fluctuations in the DC bus voltage.

[0035] The power converter 12 constantly and repeatedly executes the series of processes shown in FIG. 4 to adjust the DC bus voltage and monitor hunting.

[0036] (Example of control device processing) 6 is a flowchart showing an example of processing by the control device according to the first embodiment. Here, the flow of processing by the control device 20 will be described with reference to FIGS.

[0037] The limiting processing unit 202 determines whether the number of operating power converters 12 has changed (step S201). For example, as shown in FIG. 5, the power conversion system 1 has three power converters 12. When the acquiring unit 201 acquires a notification of hunting detection (or a notification of the operation of the power converter 12 being stopped) from the power converter 12 of the storage battery unit 10a, the limiting processing unit 202 determines that the number of operating power converters has changed (changed to 3-1=2) (step S201; YES). In this case, the limiting processing unit 202 instructs the PCS 3 to limit the power input / output to / from the DC bus 2 to the power corresponding to the number of power converters 12 currently in operation (2) (step S202). 5, if there are two power converters 12 in operation and the power that can be input or output from each power converter 12 is 100 kW, the limiting processing unit 202 instructs the PCS 3 to limit the power input or output from the PCS 3 to 200 kW or less (100 kW x 2 converters).Then, the next time the PCS 3 starts operation (for example, when applying a load in the direction of charging the battery unit 10), it applies a load of 200 kW or less in accordance with the instruction of the control device 20.In this way, the load applied to the DC bus 2 is limited to a load corresponding to the number of operating power converters 12, thereby preventing the DC bus 2 from becoming overvoltage.

[0038] If there is no change in the number of operating vehicles (step S201; NO), the restriction processing unit 202 ends the process without doing anything.

[0039] The control device 20 constantly and repeatedly executes the series of processes shown in FIG.

[0040] (Action and effect) As described above, the power conversion system 1 according to this embodiment includes a DC bus 2, a capacitor 4 connected to the DC bus 2, multiple power converters 12 connected in parallel to the DC bus 2 via switchable contactors 11, and a control device 20 that adjusts the power input / output between the DC bus 2 and the PCS 3 (power source or load). Each power converter 12 includes a control unit 122 that controls the DC bus voltage input from or output to the DC bus 2 to approach a target value based on a control gain that is greater than the control gain when the power converter 12 operates alone by the capacitance of the capacitor 4, and a hunting detection unit 123 that detects whether hunting has occurred based on the deviation between the measured value of the DC bus voltage and the target value. The control device 20 includes a limiting unit 202 that, when a power converter 12 detects the occurrence of hunting, limits the power input / output from / to the PSC 3 (power source or load) depending on the number of power converters 12 excluding the power converter 12 that has experienced hunting.

[0041] As described above, conventional technologies require additional auxiliary contacts and wiring to detect the open / closed state of the contactor. Furthermore, it is difficult to detect the open / closed state of the contactor based on measured values ​​such as voltage when there is no load. In contrast, the power conversion system 1 according to the present embodiment increases the control gain by the capacitance of the capacitor 4, as described above, thereby making hunting more likely to occur when the contactor 11 is opened. This makes it possible to estimate whether the contactor has been opened based on the presence or absence of hunting, even when there is no load, without adding additional components such as auxiliary contacts. Furthermore, when a contactor is opened and the number of power converters 12 connected to the DC bus 2 is reduced, the power from the PCS 3 is limited, thereby preventing the DC bus 2 from becoming overvoltage. This allows the system to continue operating stably even when the contactor 11 is opened due to some abnormality.

[0042] Moreover, the power converter 12 further includes a stop processing unit 124 that stops the operation of the power converter 12 when the occurrence of hunting is detected.

[0043] By doing this, when the power converter 12 is disconnected from the DC bus 2 due to an abnormal opening of the contactor 11, the power conversion system 1 can stop operation of the power converter 12, thereby preventing unnecessary consumption of power from the storage battery 13.

[0044] Furthermore, the hunting detection unit 123 detects that hunting has occurred when the number of times that the deviation between the measured value and the target value of the DC bus voltage exceeds the threshold value becomes equal to or greater than the determination number within a predetermined time period.

[0045] In this way, the power conversion system 1 can prevent erroneous detection of hunting (abnormal opening of the contactor 11) caused by temporary fluctuations in the DC bus voltage.

[0046] <Other embodiments> Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes are possible. In other embodiments, the order of the above-described processes may be changed as appropriate.

[0047] <Computer configuration> 7 is a schematic block diagram showing the configuration of a computer according to the first embodiment. The computer 900 includes a processor 901, a main storage device 902, an auxiliary storage device 903, and an interface 904. The power converter 12 and the control device 20 described above are implemented in the computer 900. The operations of the above-described processing units are stored in the auxiliary storage device 903 in the form of a program. The processor 901 reads the program from the auxiliary storage device 903, loads it into the main storage device 902, and executes the above-described processing in accordance with the program. The processor 901 also allocates a storage area in the main storage device 902 to be used in the above-described processing in accordance with the program.

[0048] The program may be for realizing some of the functions to be performed by the computer 900. For example, the program may be combined with other programs already stored in the auxiliary storage device 903 or other programs implemented in other devices to perform the functions. In other embodiments, the computer may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions realized by the processor may be realized by the integrated circuit.

[0049] Examples of the auxiliary storage device 903 include a hard disk drive (HDD), a solid state drive (SSD), a magnetic disk, a magneto-optical disk, a compact disc read-only memory (CD-ROM), a digital versatile disc read-only memory (DVD-ROM), and a semiconductor memory. The auxiliary storage device 903 may be an internal medium directly connected to the bus of the computer 900, or an external medium (external storage device 910) connected to the computer 900 via the interface 904 or a communication line. Furthermore, when this program is distributed to the computer 900 via a communication line, the computer 900 that receives the program may load the program into the main storage device 902 and execute the above-described processing. In at least one embodiment, the auxiliary storage device 903 is a non-transitory tangible storage medium.

[0050] <Additional Notes> The above-described embodiment can be understood, for example, as follows.

[0051] (1) According to a first aspect, the power conversion system 1 includes a DC bus 2, a capacitor 4 connected to the DC bus 2, a plurality of power converters 12 connected in parallel to the DC bus 2 via openable / closeable contactors 11, and a control device 20 that adjusts the power input / output between the DC bus 2 and a PCS 3 (power source or load). The power converter 12 includes a control unit 122 that controls the DC bus voltage input from or output to the DC bus 2 to approach a target value based on a control gain that is greater than the control gain when the power converter 12 operates alone by the capacitance of the capacitor 4, and a hunting detection unit 123 that detects whether hunting has occurred based on the measured value of the DC bus voltage and the deviation from the target value. The control device 20 includes a limiting processing unit 202 that, when the power converter 12 detects the occurrence of hunting, limits the power input / output between the DC bus 2 and the PCS 3 (power source or load) in accordance with the number of power converters 12 excluding the power converter 12 in which hunting has occurred.

[0052] In the power conversion system 1, the control gain is increased by the capacitance of the capacitor 4, thereby making hunting more likely to occur when the contactor 11 is opened. This makes it possible to estimate whether the contactor has been opened based on the presence or absence of hunting, even when there is no load, without adding an auxiliary contact or other component to the contactor 11. Furthermore, when the contactor is opened and the number of power converters 12 connected to the DC bus 2 is reduced, the power from the PCS 3 is limited, thereby preventing the DC bus 2 from becoming overvoltage. This makes it possible to continue stable operation of the system even when the contactor 11 is opened due to some abnormality.

[0053] (2) According to the second aspect, in the power conversion system 1 according to the first aspect, the power converter 12 further includes a stop processor 124 that stops the operation of the power converter when occurrence of hunting is detected.

[0054] By doing this, when the power converter 12 is disconnected from the DC bus 2 due to an abnormal opening of the contactor 11, the power conversion system 1 can stop operation of the power converter 12, thereby preventing unnecessary consumption of power from the storage battery 13.

[0055] (3) According to the third aspect, in the power conversion system 1 according to the first or second aspect, the hunting detection unit 123 detects that hunting has occurred when the number of times that the deviation between the measured value and the target value of the DC bus voltage exceeds a threshold value is equal to or greater than the determination number within a predetermined time period.

[0056] In this way, the power conversion system 1 can prevent erroneous detection of hunting (abnormal opening of the contactor 11) caused by temporary fluctuations in the DC bus voltage.

[0057] (4) According to a fourth aspect, a control method for a power conversion system 1 includes the power conversion system 1 including a DC bus 2, a capacitor 4 connected to the DC bus 2, a plurality of power converters 12 connected in parallel to the DC bus 2 via openable / closeable contactors 11, and a control device 20 that adjusts the power input / output between the DC bus 2 and a PCS 3 (power source or load), the control method including the steps of: the power converter 12 controlling the DC bus voltage input from or output to the DC bus 2 to approach a target value based on a control gain that is greater than the control gain when the power converter 12 operates alone by the capacitance of the capacitor 4; the power converter 12 detecting whether hunting has occurred based on the deviation between the measured value of the DC bus voltage and the target value; and, when the power converter 12 detects the occurrence of hunting, the control device 20 limiting the power input / output between the DC bus 2 and the PCS 3 (power source or load) in accordance with the number of power converters 12 excluding the power converter 12 in which hunting has occurred.

[0058] This makes it possible to estimate whether the contactor 11 has been opened based on the presence or absence of hunting, even when there is no load, without adding an auxiliary contact or other component to the contactor 11. Furthermore, when the contactor is opened and the number of power converters 12 connected to the DC bus 2 is reduced, the power from the PCS 3 is limited, thereby preventing the DC bus 2 from becoming overvoltage. This makes it possible to continue stable operation of the system even when the contactor 11 is opened due to some abnormality. [Explanation of symbols]

[0059] 1 Power Conversion System 2 DC bus 3 PCS 4 capacitors 10 Battery unit 11 Contactor 12 Power Converter 121 Measurement value acquisition unit 122 Control Unit 123 Hunting detection unit 124 Stop processing unit 13 Storage battery 20 Control device 201 Acquisition Department 202 Restriction processing unit

Claims

1. DC bus and a capacitor connected to the DC bus; a plurality of power converters connected in parallel to the DC bus via openable and closable contactors; a control device that adjusts the power input / output between the DC bus and a power source or a load; A power conversion system comprising: The power converter includes: a control unit that controls a DC bus voltage input from or output to the DC bus to approach a target value based on a control gain that is set to a value larger by an amount corresponding to the capacitance of the capacitor than a control gain when the power converter operates alone; a hunting detection unit that detects whether hunting has occurred based on a deviation between the measured value of the DC bus voltage and the target value; and the control device has a limiting processing unit that, when the occurrence of hunting is detected in the power converter, limits power input / output between the DC bus and a power source or a load in accordance with the number of power converters excluding the power converter in which hunting has occurred. Power conversion systems.

2. The power converter further includes a stop processing unit that stops operation of the power converter when occurrence of hunting is detected. The power conversion system of claim 1 .

3. the hunting detection unit detects the occurrence of hunting when the number of times that the deviation between the measured value and the target value of the DC bus voltage exceeds a threshold value becomes equal to or greater than a determination number within a predetermined time period; The power conversion system according to claim 1 or 2.

4. DC bus and a capacitor connected to the DC bus; a plurality of power converters connected in parallel to the DC bus via openable and closable contactors; a control device that adjusts the power input / output between the DC bus and a power source or a load; A control method for a power conversion system comprising: a step of controlling the DC bus voltage input from or output to the DC bus to approach a target value based on a control gain that is set to a value larger by an amount corresponding to the capacitance of the capacitor than a control gain when the power converter operates alone; The power converter detects whether hunting has occurred based on a deviation between the measured value of the DC bus voltage and the target value; when the control device detects occurrence of hunting in the power converter, limiting power input / output between the DC bus and a power source or a load in accordance with the number of power converters excluding the power converter in which hunting has occurred; A control method for a power conversion system having the following:

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