Power Conversion Systems

Abstract

To provide a power conversion system capable of improving a utilization efficiency of regenerative electric power.SOLUTION: A power conversion system comprises: a driving circuit of a dynamo-electric motor; a regenerative invalidation detection part that detects whether or not a regenerative invalidation occurs in a regenerative operation of the dynamo-electric motor; a first power inverter circuit that inverts a first DC power or a second DC power to an AC power and supplies it to a load; a second power inverter circuit to which an output side itself is connected to an output side of the first power inverter circuit in parallel; a storage battery that is connected to an input side of the second power inverter circuit; a voltage detection part that detects a voltage of the storage battery; a first control part that controls so as to output a constant AC voltage from the first power inverter circuit; a second control part that controls charging and discharging of the storage battery by controlling a predetermined charging and discharging power to the second power inverter circuit so as to be input and output; and an integrated control part that controls an operation of the second control part on the basis of the voltage of the storage battery whether or not the regenerative invalidation occurs.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to power conversion systems. [Background technology]

[0002] Conventionally, a power conversion system including a plurality of inverter circuits connected in parallel has been known. Patent Document 1 describes a power conversion system including a plurality of inverter circuits connected in parallel, in which each inverter circuit can switch its own operation mode between a voltage control mode and a current control mode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3648414 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the configuration described in Patent Document 1, each inverter circuit switches its own operating mode independently of the other inverter circuits. Therefore, when attempting to effectively utilize regenerative power by temporarily storing the regenerative power of an electric motor in a storage battery via a certain inverter circuit and discharging it as needed, each inverter circuit tries to independently optimize its own operating mode, which results in unnecessary power loss or power regeneration failure (when the opportunity to regenerate or discharge is lost due to protective operation, etc.), and reduces the efficiency of regenerative power utilization.

[0005] The present disclosure is made to solve the above-mentioned problems, and has an object to provide a power conversion system that can improve the utilization efficiency of regenerative power. [Means for solving the problem]

[0006] In order to solve the above problems, the power conversion system of the present disclosure includes a drive circuit that converts first DC power supplied from an external source into AC power to drive an electric motor and converts the regenerative power of the electric motor into second DC power; a regeneration loss detection unit that detects whether regeneration loss has occurred during regenerative operation of the electric motor; a first power conversion circuit that converts the first DC power or the second DC power into AC power and supplies it to a load; a second power conversion circuit whose output side is connected in parallel with the output side of the first power conversion circuit; a storage battery connected to the input side of the second power conversion circuit; a voltage detection unit that detects the voltage of the storage battery; a first control unit that controls the first power conversion circuit to output a constant AC voltage; a second control unit that controls the charging and discharging of the storage battery by controlling the second power conversion circuit to input and output a predetermined charging and discharging power; and an overall control unit that controls the operation of the second control unit based on whether regeneration loss has occurred and the voltage of the storage battery. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing a configuration of a power conversion system according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the internal configuration of a general control unit according to the first embodiment. [Figure 3] 6 is a flowchart illustrating details of a mode selection process according to the first embodiment. [Figure 4] FIG. 10 is a diagram showing the configuration of a power conversion system according to a second embodiment. [Figure 5] FIG. 10 is a diagram showing the internal configuration of a general control unit according to a second embodiment. [Figure 6] 10 is a flowchart illustrating details of a mode selection process according to the second embodiment. [Figure 7A] Vector diagram when no reactive current flows. [Figure 7B] Vector diagram when reactive current flows. [Figure 8] FIG. 10 is a diagram showing the configuration of a power conversion system according to a third embodiment. [Figure 9] FIG. 11 is a diagram showing the internal configuration of a general control unit according to a third embodiment. [Figure 10] 11 is a flowchart illustrating details of a mode selection process according to the third embodiment. [Figure 11] FIG. 10 is a diagram showing the configuration of a power conversion system according to a fourth embodiment. [Figure 12] FIG. 10 is a diagram showing the internal configuration of a general control unit according to a fourth embodiment. [Figure 13] FIG. 10 is a diagram showing the relationship between the output current of the first inverter circuit and the coefficient in a regenerative absorption mode. [Figure 14] FIG. 10 is a diagram showing the configuration of a power conversion system according to a fifth embodiment. [Figure 15] FIG. 13 is a diagram showing the internal configuration of a general control unit according to a fifth embodiment. [Figure 16] FIG. 10 is a diagram showing the relationship between the output current of the first inverter circuit and the coefficient in the assist discharge mode. [Figure 17] FIG. 13 is a diagram showing the configuration of a power conversion system according to a sixth embodiment. [Figure 18] FIG. 10 is a diagram schematically illustrating a state in which a predetermined high-frequency signal is superimposed on an AC voltage and input to a band-pass filter. [Figure 19] FIG. 13 is a diagram showing the configuration of a power conversion system according to a seventh embodiment. [Figure 20] FIG. 13 is a diagram showing the configuration of a power conversion system according to an eighth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the following description will be based on an example in which a power conversion system according to the present disclosure is mounted on a train. However, the scope of applicability of the power conversion system according to the present disclosure is not limited to trains. Furthermore, in the drawings, identical or corresponding elements are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0009] (Embodiment 1) FIG. 1 is a diagram illustrating a configuration of a power conversion system 100 according to a first embodiment of the present disclosure. The power conversion system 100 includes a variable voltage variable frequency control (VVVF control) drive circuit 10 that drives an electric motor 1 for running a train. During power running of the electric motor 1, the drive circuit 10 converts DC power (hereinafter referred to as "first DC power") supplied from an overhead line 2 into AC power and supplies the AC power to the electric motor 1. During regenerative running of the electric motor 1, the drive circuit 10 converts the regenerative power of the electric motor 1 into DC power (hereinafter referred to as "second DC power") and supplies the DC power to an input side 11a of a first inverter circuit 11. The drive circuit 10 also functions as a regeneration failure detection unit that detects whether regeneration failure occurs during regenerative running of the electric motor 1.

[0010] When the motor 1 is in power running, the first inverter circuit 11 converts the first DC power supplied from the overhead line 2 into AC power and outputs the AC power. When the motor 1 is in regenerative running, the first inverter circuit 11 converts the first DC power supplied from the overhead line 2 and the second DC power supplied from the drive circuit 10 into AC power and outputs the AC power. A part or all of the output power of the first inverter circuit 11 is supplied to the load 3 via a transformer 12. The type of the load 3 is not particularly limited, but may be, for example, a fluorescent lamp or an air conditioner in a train.

[0011] A first DC capacitor 13 that smoothes the input voltage is connected in parallel to the input side 11a of the first inverter circuit 11. A backflow prevention diode 30 is connected in series between the input side 11a of the first inverter circuit 11 and the overhead line 2. The backflow prevention diode 30 prevents power from flowing from the first inverter circuit 11 toward the overhead line 2. This allows the first inverter circuit 11 to continue operating for a short period of time using the power stored in the first DC capacitor 13, even if the power supply from the overhead line 2 is cut off. Meanwhile, a first AC capacitor 14 is connected in parallel between the transformer 12 on the output side 11b of the first inverter circuit 11 and the load 3.

[0012] The first inverter circuit 11 is controlled by a first control unit 15. The first control unit 15 can be configured, for example, by an integrated circuit such as an ASIC or FPGA, or a CPU controlled by software. The first control unit 15 controls the switching operation of the first inverter circuit 11 so that a constant AC voltage is applied to the load 3. The first control unit 15 controls the switching operation of the first inverter circuit 11 so that a constant AC voltage is output at the load end (the detection point of the first AC voltage sensor 18) based on the input voltage of the first inverter circuit 11 detected by the first DC voltage sensor 16 and the output voltage of the first inverter circuit 11 detected by the first AC voltage sensor 18. In other words, the voltage of the first inverter circuit 11 is controlled by the first control unit 15.

[0013] The power conversion system 100 also includes a second inverter circuit 19, the output side 19b of which is connected in parallel to the output side 11b of the first inverter circuit 11. A second AC capacitor 20 is connected in parallel and an AC reactor 21 is connected in series between the output side 19b of the second inverter circuit 19 and the load 3. A second DC capacitor 22 and a storage battery 23 are connected in parallel to the input side 19a of the second inverter circuit 19.

[0014] The second inverter circuit 19 is controlled by a second control unit 24. The second control unit 24 can be configured, for example, by an integrated circuit such as an ASIC or FPGA, or a software-controlled CPU. The second control unit 24 controls the output current of the second inverter circuit 19 by controlling the switching operation of the second inverter circuit 19 based on the input voltage of the second inverter circuit 19 detected by a second DC voltage sensor 25, the output current of the second inverter circuit 19 detected by a second AC current sensor 26, and the output voltage of the second inverter circuit 19 detected by a second AC voltage sensor 27. That is, the second inverter circuit 19 is current-controlled by the second control unit 24. At this time, the phase of the output voltage of the second control unit 24 is PLL-controlled so as to be synchronized with the phase of the voltage at the load end (the detection point of the second AC voltage sensor 27). This allows the second inverter circuit 19 to output an AC current having an arbitrary phase difference with respect to the voltage at the load end.

[0015] As described above, the voltage applied to the load 3 is maintained at a constant value by the first inverter circuit 11, and the output side 19b of the second inverter circuit 19 is also connected to the load 3. Therefore, controlling the output current of the second inverter circuit 19 is equivalent to controlling the input / output power of the second inverter circuit 19. In other words, it can be said that the second control unit 24 controls the input / output power of the second inverter circuit 19.

[0016] The power conversion system 100 further includes a general control unit 28 that controls the operation of the second control unit 24. The general control unit 28 transmits a command value for charge / discharge power to the second control unit 24 based on a regeneration inactivation signal transmitted from the drive circuit 10 and the voltage of the storage battery 23 detected by a monitoring unit 29. The regeneration inactivation signal transmitted from the drive circuit 10 takes a value of 1 or 0, and is 1 when regeneration inactivation occurs during regenerative operation of the electric motor 1, and is 0 otherwise. The voltage of the storage battery 23 detected by the monitoring unit 29 is, more precisely, the open circuit voltage (OCV) of the storage battery 23. As is well known, a positive correlation is established between the open circuit voltage of the storage battery 23 and the charge amount.

[0017] The power conversion system 100 according to the first embodiment has three operating modes: a "regenerative absorption mode," an "assisted discharge mode," and a "standby mode," and selection of these three operating modes is performed by the integrated control unit 28. In the regenerative absorption mode, the storage battery 23 is charged with regenerative power from the electric motor 1 via the second inverter circuit 19. In the assisted discharge mode, the power stored in the storage battery 23 is supplied to the load 3 via the second inverter circuit 19, thereby assisting the power supply from the first inverter circuit 11 to the load 3. In the standby mode, neither charging nor discharging of the storage battery 23 is performed.

[0018] FIG. 2 is a diagram showing the internal configuration of the overall control unit 28. The overall control unit 28 can be configured, for example, by an integrated circuit such as an ASIC or FPGA, or a CPU controlled by software. The overall control unit 28 may also be provided inside the first control unit 15 or the second control unit 24. The overall control unit 28 includes a mode selection unit 28a and a power selection unit 28b. The mode selection unit 28a selects an operation mode based on a regeneration disable signal transmitted from the drive circuit 10 and the voltage of the storage battery 23 detected by the monitoring unit 29. The power selection unit 28b selects a command value for charge / discharge power based on the operation mode selected by the mode selection unit 28a and transmits the command value to the second control unit 24.

[0019] In the regenerative absorption mode in which charging power is supplied to the storage battery 23 via the second inverter circuit 19, the command value for charging and discharging power is a negative value. This means that charging power flows from the output side 19b of the second inverter circuit 19 to the input side 19a. In the first embodiment, the command value for charging and discharging power in the regenerative absorption mode is expressed as -Pc [kW]. On the other hand, in the assist discharge mode in which discharging of the storage battery 23 is performed via the second inverter circuit 19, the command value for charging and discharging power is a positive value. This means that discharging power flows from the input side 19a of the second inverter circuit 19 to the output side 19b. In the first embodiment, the command value for charging and discharging power in the assist discharge mode is expressed as +Pd [kW]. Furthermore, in the standby mode in which neither charging nor discharging of the storage battery 23 is performed, the command value for charging and discharging power is 0 kW.

[0020] 3 is a flowchart illustrating the details of the mode selection process in the mode selection unit 28a of the integrated control unit 28. As shown in the flowchart of FIG. 3, when regeneration invalidation has occurred (S101=YES) and the voltage of the storage battery 23 is less than the first voltage threshold Vthr1 (S102=YES), the mode selection unit 28a selects the regeneration absorption mode (S104). Here, the first voltage threshold Vthr1 is set slightly lower than the maximum voltage specified for the storage battery 23. When the voltage of the storage battery 23 is less than this value, it means that the charge amount of the storage battery 23 has not reached the upper limit and there is still room for charge (see the diagram in the upper right of FIG. 3).

[0021] In the regenerative absorption mode, the storage battery 23 is charged with regenerative power from the electric motor 1 via the second inverter circuit 19. Specifically, the regenerative power from the electric motor 1 is converted into second DC power by the drive circuit 10, and this second DC power is converted into AC power by the first inverter circuit 11. This AC power is converted into DC power by the second inverter circuit 19, and the storage battery 23 is charged with this DC power. At this time, the second control unit 24 controls the switching operation of the second inverter circuit 19 so that charging power equal to the command value of charging / discharging power transmitted from the integrated control unit 28 flows from the second inverter circuit 19 to the storage battery 23. The regenerative absorption mode continues while regenerative failure occurs (S101=YES) and the voltage of the storage battery 23 is less than the first voltage threshold Vthr1 (S102=YES).

[0022] Furthermore, if regeneration invalidation has not occurred (S101=NO) and the voltage of the storage battery 23 is equal to or higher than the second voltage threshold Vthr2 (S103=YES), the mode selection unit 28a selects the assist discharge mode (S106). Here, the second voltage threshold Vthr2 is set slightly higher than the minimum voltage specified for the storage battery 23. If the voltage of the storage battery 23 is equal to or higher than this value, it means that the charge amount of the storage battery 23 has not reached the lower limit and there is room for discharge (see the illustration in the upper right of FIG. 3).

[0023] In the assist discharge mode, power stored in the storage battery 23 is supplied to the load 3 via the second inverter circuit 19. In detail, DC power discharged from the storage battery 23 is converted to AC power by the second inverter circuit 19, and this AC power is supplied to the load 3, thereby assisting the power supply to the load 3 by the first inverter circuit 11. At this time, the second control unit 24 controls the switching operation of the second inverter circuit 19 so that discharge power equal to the charge / discharge power command value transmitted from the overall control unit 28 flows from the storage battery 23 to the second inverter circuit 19. The assist discharge mode continues as long as regeneration failure has not occurred (S101=NO) and the voltage of the storage battery 23 is equal to or higher than the second voltage threshold Vthr2 (S103=YES).

[0024] Furthermore, if regeneration lapse has occurred (S101=YES) and the voltage of the storage battery 23 is equal to or higher than the first voltage threshold Vthr1 (S102=NO), that is, if regeneration lapse is occurring but the storage battery 23 does not have any available charge capacity, the mode selection unit 28a selects a standby mode in which neither charging nor discharging of the storage battery 23 is performed (S105).

[0025] Furthermore, if regeneration lapse has not occurred (S101=NO) and the voltage of the storage battery 23 is less than the second voltage threshold Vthr2 (S103=NO), that is, if regeneration lapse is not occurring but the storage battery 23 does not have any discharge capacity, the mode selection unit 28a selects a standby mode in which neither charging nor discharging of the storage battery 23 is performed (S105).

[0026] As described above, the power conversion system 100 according to the first embodiment includes the first inverter circuit 11 and the second inverter circuit 19 connected in parallel, and the storage battery 23 is connected to the input side 19a of the second inverter circuit 19. The first control unit 15 controls the first inverter circuit 11 to output a constant AC voltage. The second control unit 24 controls the charging and discharging of the storage battery 23 by controlling the second inverter circuit 19 to input and output predetermined charging and discharging power. The overall control unit 28 controls the operation of the second control unit 24 based on whether regeneration failure has occurred during regenerative operation of the electric motor 1 and the voltage of the storage battery 23.

[0027] Due to the above-mentioned features, in the power conversion system 100 according to the first embodiment, the operations of the first inverter circuit 11 and the second inverter circuit 19 are optimized as a whole, and the efficiency of use of the regenerative power of the electric motor 1 is improved.

[0028] (Embodiment 2) In the above-described first embodiment, if the voltage of the storage battery 23 is equal to or lower than the second voltage threshold Vthr2 when the second inverter circuit 19 starts operating, the assist discharge mode cannot be selected until the storage battery 23 is charged in the regenerative absorption mode.

[0029] To address the above problem, in the second embodiment, the "boost charging mode" is selected if the voltage of the storage battery 23 is equal to or lower than the second voltage threshold Vthr2 when the second inverter circuit 19 starts operating. In the boost charging mode, the storage battery 23 is charged by the first DC power supplied from the overhead line 2 via the second inverter circuit 19.

[0030] 4 is a diagram showing the configuration of a power conversion system 200 according to the present embodiment 2. An integrated control unit 228 of the power conversion system 200 transmits to a second control unit 24 a command value for a reactive current flowing through an output side 19b of a second inverter circuit 19, in addition to a command value for charge / discharge power similar to that of the first embodiment.

[0031] 5 is a diagram showing the internal configuration of the general control unit 228. The general control unit 228 includes a mode selection unit 228a, a power selection unit 228b, and a reactive current selection unit 228c. The mode selection unit 228a selects an operation mode based on the regeneration disable signal transmitted from the drive circuit 10 and the voltage of the storage battery 23 detected by the monitoring unit 29.

[0032] Based on the operation mode selected by the mode selection unit 228a, the power selection unit 228b selects a command value for charge / discharge power and transmits it to the second control unit 24. In the second embodiment, the command value for charge / discharge power in the boost charge mode is expressed as −Pu [kW].

[0033] The reactive current selection unit 228c selects a reactive current command value based on the operation mode selected by the mode selection unit 228a and transmits it to the second control unit 24. In the second embodiment, the reactive current command value in operation modes other than the boost charging mode is 0 A. The reactive current command value in the boost charging mode is Id, which is defined by the following equation:

[0034]

number

[0035] In the above equation, VCq is the voltage applied to the load 3, i.e., the load voltage, Vmax is the maximum voltage that can be output by the second inverter circuit 19, ω is the angular frequency of the output voltage of the second inverter circuit 19, L is the inductance value of the AC reactor 21, and Iq is the effective current flowing through the output side 19b of the second inverter circuit 19, i.e., the current corresponding to the charging current of the storage battery 23.

[0036] Fig. 6 is a flowchart illustrating in detail the mode selection process in the mode selection unit 228a of the integrated control unit 228. As shown in the flowchart in Fig. 6, when the voltage of the storage battery 23 is equal to or lower than a third voltage threshold Vthr3 that is lower than the second voltage threshold Vthr2 (S207=NO), the mode selection unit 228a selects the boost charging mode (S208) until the voltage of the storage battery 23 exceeds a fourth voltage threshold Vthr4 that is higher than the second voltage threshold Vthr2 (S209=YES).

[0037] In the boost charging mode, the storage battery 23 is charged by the first DC power supplied from the overhead line 2 via the second inverter circuit 19. In detail, the first DC power supplied from the overhead line 2 is converted into AC power by the first inverter circuit 11, and this AC power is converted into DC power by the second inverter circuit 19, and the storage battery 23 is charged by this DC power.

[0038] At this time, the second control unit 24 controls the switching operation of the second inverter circuit 19 so that charging power equal to the command value of charging / discharging power transmitted from the general control unit 228 flows from the second inverter circuit 19 to the storage battery 23, and so that the reactive current flowing through the output side 19b of the second inverter circuit 19 is equal to the command value Id of the reactive current transmitted from the general control unit 228. Note that controlling the reactive current flowing through the output side 19b of the second inverter circuit 19 specifically means controlling the phase difference between the output voltage and output current of the second inverter circuit 19.

[0039] 7A is a vector diagram showing the case where the reactive current flowing through the output side 19b of the second inverter circuit 19 is 0 A, i.e., where no reactive current flows. When no reactive current flows, the output voltage Vo2 of the second inverter circuit 19 is determined by the vector sum of the load voltage VCq and the impedance drop ωLIq due to the active current Iq. Therefore, if an attempt is made to increase the active current Iq flowing through the output side 19b of the second inverter circuit 19, which corresponds to the charging current of the storage battery 23, the output voltage Vo2 of the second inverter circuit 19 also increases accordingly.

[0040] However, the maximum voltage Vmax that can be output by the second inverter circuit 19 is limited by the voltage of the storage battery 23. Nevertheless, the boost charging mode is selected when the voltage of the storage battery 23 drops. This makes it difficult to increase the charging current of the storage battery 23 that corresponds to the active current Iq flowing through the output side 19b of the second inverter circuit 19.

[0041] 7B is a vector diagram showing the case where a reactive current Id flows to the output side 19b of the second inverter circuit 19. When the reactive current Id flows, the output voltage Vo2 of the second inverter circuit 19 is determined by the vector sum of the vector obtained by subtracting the impedance drop ωLId due to the reactive current Id from the load voltage VCq, and the impedance drop ωLIq due to the active current Iq. In other words, the presence of the reactive current Id makes it possible to increase the charging current of the storage battery 23 corresponding to the active current Iq while suppressing the output voltage Vo2 of the second inverter circuit 19. This makes it possible to ensure the charging current required for boost charging even when the voltage of the storage battery 23 is low.

[0042] As described above, the power conversion system 200 according to the second embodiment has a boost charging mode in which the storage battery 23 is charged with the first DC power supplied from the overhead line 2 via the second inverter circuit 19. When the voltage of the storage battery 23 is equal to or lower than the third voltage threshold Vthr3 which is lower than the second voltage threshold Vthr2, the integrated control unit 228 selects the boost charging mode until the voltage of the storage battery 23 exceeds the fourth voltage threshold Vthr4 which is higher than the second voltage threshold Vthr2.

[0043] Due to the above-described features, in the power conversion system 200 according to the second embodiment, it is possible to reduce the time required from when the operation of the second inverter circuit 19 starts until the assist discharge mode can be selected.

[0044] Furthermore, in the boost charging mode, the integrated control unit 228 controls the second control unit 24 so that the reactive current Id flows to the output side 19b of the second inverter circuit 19. This makes it possible to increase the charging current of the storage battery 23 while suppressing the output voltage Vo2 of the second inverter circuit 19, thereby ensuring the charging current required for boost charging.

[0045] (Embodiment 3) In the first embodiment described above, when regeneration is not in an invalid state but the storage battery 23 does not have an allowance for assisted discharge, a standby mode is selected in which neither charging nor discharging of the storage battery 23 is performed. However, if a long period continues in which neither charging nor discharging of the storage battery 23 is performed, the temperature of the cells of the storage battery 23 drops, and the charge rate during charging deteriorates.

[0046] To address the above problem, in the third embodiment, even if regeneration is not in an expired state and there is no capacity for assisted discharge in the storage battery 23, the "warm-up mode" is selected if the cell temperature of the storage battery 23 is equal to or lower than the first temperature threshold value Tthr1. In the warm-up mode, charging and discharging of the storage battery 23 are repeated at regular intervals via the second inverter circuit 19, thereby preventing a drop in the cell temperature of the storage battery 23.

[0047] 8 is a diagram showing the configuration of a power conversion system 300 according to the present embodiment 3. A central control unit 328 of the power conversion system 300 transmits a command value for charge / discharge power to the second control unit 24 based on the temperature of the cells of the storage battery 23 detected by a monitoring unit 329 in addition to the regeneration invalidation signal and the voltage of the storage battery 23 as in the first embodiment.

[0048] 9 is a diagram showing the internal configuration of the general control unit 328. The general control unit 328 includes a mode selection unit 328a and a power selection unit 328b. The mode selection unit 328a selects an operation mode based on the regeneration disable signal transmitted from the drive circuit 10 and the voltage and cell temperature of the storage battery 23 detected by a monitoring unit 329.

[0049] The power selection unit 328b selects a command value for charge / discharge power based on the operation mode selected by the mode selection unit 328a and transmits it to the second control unit 24. In the third embodiment, the command value for charge / discharge power in the warm-up mode is, for example, switched every five seconds between charge power of -Pm [kW] and discharge power of +Pm [kW]. That is, the charge power and discharge power in the warm-up mode are equal in magnitude except that the direction of power flow is opposite. Also, |Pm|<<|Pc| and |Pm|<<|Pd|.

[0050] Fig. 10 is a flowchart illustrating in detail the mode selection process in the mode selection unit 328a of the overall control unit 328. As shown in the flowchart in Fig. 10, the mode selection unit 328a selects the warm-up mode (S311) when regeneration invalidation has not occurred (S101=NO), the voltage of the storage battery 23 is less than the second voltage threshold Vthr2 (S103=NO), and the temperature of the cells of the storage battery 23 is equal to or less than the first temperature threshold Tthr1 (S310=NO).

[0051] In the warm-up mode, charging and discharging of the storage battery 23 are repeated at regular intervals via the second inverter circuit 19, thereby preventing a drop in the cell temperature of the storage battery 23. At this time, by repeating charging and discharging so that the balance between charging power and discharging power is equal, it is possible to prevent a drop in the cell temperature without changing the overall charge amount of the storage battery 23. This makes it possible to prevent a deterioration in the charge rate of the storage battery 23. The warm-up mode continues as long as regeneration failure has not occurred (S101=NO), the voltage of the storage battery 23 is less than the second voltage threshold Vthr2 (S103=NO), and the cell temperature of the storage battery 23 is equal to or less than the first temperature threshold Tthr1 (S310=NO).

[0052] As described above, the power conversion system 300 according to the third embodiment has a warm-up mode that prevents a drop in the temperature of the cells of the storage battery 23 by repeatedly charging and discharging the storage battery 23 at regular intervals via the second inverter circuit 19. The integrated control unit 328 selects the warm-up mode when regeneration lapse has not occurred, the voltage of the storage battery 23 is less than the second voltage threshold Vthr2, and the temperature of the cells of the storage battery 23 is equal to or less than the first temperature threshold Tthr1.

[0053] Due to the above-described features, the power conversion system 300 according to the second embodiment can prevent a drop in the cell temperature and a deterioration in the charge rate without changing the charge amount of the storage battery 23 overall.

[0054] (Fourth embodiment) In the above-described first embodiment, if the charging power supplied to the storage battery 23 via the second inverter circuit 19 becomes too large in the regenerative absorption mode, the output current of the first inverter circuit 11 may exceed the maximum value specified, and the first inverter circuit 11 may become overloaded.

[0055] To address the above problem, the power conversion system 400 according to the fourth embodiment is provided with a mechanism for limiting the charging power of the storage battery 23 in order to prevent overload of the first inverter circuit 11 in the regeneration absorption mode.

[0056] 11 is a diagram showing the configuration of a power conversion system 400 according to the fourth embodiment. A central control unit 428 of the power conversion system 400 transmits a command value for charge / discharge power to the second control unit 24 based on the output current of the first inverter circuit 11 transmitted from the first control unit 15, in addition to the regeneration invalidation signal and the voltage of the storage battery 23, which are the same as those in the first embodiment.

[0057] As described in the first embodiment, the first inverter circuit 11 is controlled to apply a constant voltage to the load 3. Therefore, the output current of the first inverter circuit 11 is determined by the power consumed by the load 3 and the charging / discharging power of the storage battery 23.

[0058] 12 is a diagram showing the internal configuration of the overall control unit 428. The overall control unit 428 includes a mode selection unit 428a, a power selection unit 428b, and a power limiting unit 428d. The mode selection unit 428a selects an operation mode based on the regeneration disable signal transmitted from the drive circuit 10 and the voltage of the storage battery 23 detected by the monitoring unit 29. The power selection unit 428b selects a command value for charge / discharge power based on the operation mode selected by the mode selection unit 428a.

[0059] The power limiting unit 428d imposes a limit on the command value of charge / discharge power by multiplying the command value of charge / discharge power selected by the power selecting unit 428b by a coefficient that depends on the output current of the first inverter circuit 11. The power limiting unit 428d transmits the command value of charge / discharge power to which the limit has been imposed to the second control unit 24.

[0060] 13 is a diagram showing the relationship between the output current of the first inverter circuit 11 and the coefficient in the regenerative absorption mode. When the output current of the first inverter circuit 11 is less than the first current threshold Ithr1, the power limiting unit 428d multiplies the charge / discharge power command value selected by the power selecting unit 428b by a coefficient of 1.0. In other words, when the output current of the first inverter circuit 11 is less than the first current threshold Ithr1, the charge / discharge power command value selected by the power selecting unit 428b is sent directly to the second control unit 24. In the fourth embodiment, the first current threshold Ithr1 is set to, for example, a value that is 90 percent of the maximum current that the first inverter circuit 11 can output.

[0061] In contrast, when the output current of the first inverter circuit 11 is equal to or greater than the first current threshold Ithr1, the power limiting unit 428d multiplies the command value for charge / discharge power selected by the power selecting unit 428b by a coefficient of 0. That is, when the output current of the first inverter circuit 11 is equal to or greater than the first current threshold Ithr1, 0 kW is sent to the second control unit 24 as the command value for charge / discharge power. As a result, the charge power supplied to the storage battery 23 via the second inverter circuit 19 becomes 0. This prevents the first inverter circuit 11 from being overloaded in the regenerative absorption mode due to the charge power supplied to the storage battery 23 via the second inverter circuit 19 becoming too large.

[0062] As described above, in the regenerative absorption mode, the general control unit 428 of the power conversion system 400 according to the fourth embodiment limits the charging power supplied to the storage battery 23 via the second inverter circuit 19 based on the output current of the first inverter circuit 11 transmitted from the first control unit 15. Specifically, when the output current of the first inverter circuit 11 is equal to or greater than the first current threshold Ithr1, the general control unit 428 controls the second control unit 24 so that the charging power supplied to the storage battery 23 via the second inverter circuit 19 becomes zero.

[0063] Due to the above-mentioned features, in the power conversion system 400 according to the fourth embodiment, in the regenerative absorption mode, the charging power supplied to the storage battery 23 via the second inverter circuit 19 is prevented from becoming too large, and the first inverter circuit 11 is prevented from becoming overloaded.

[0064] (Embodiment 5) In the above-mentioned embodiment 1, in the assisted discharge mode, if the discharge power supplied from the storage battery 23 via the second inverter circuit 19 becomes excessively large and exceeds the power consumed by the load 3, part of the output power of the second inverter circuit 19 may flow into the output side 11b of the first inverter circuit 11, and power may flow from the output side 11b of the first inverter circuit 11 to the input side 11a.

[0065] When the above-described power flow occurs, the first DC capacitor 13 is charged and its voltage rises due to the presence of the reverse current prevention diode 30. When the voltage of the first DC capacitor 13 reaches a specified value or higher, an overvoltage protection circuit (not shown) operates to protect the first inverter circuit 11 from overvoltage, forcibly shutting off the first inverter circuit 11 and causing it to stop operating. To address this problem, the power conversion system 500 according to the fifth embodiment is provided with a mechanism for limiting the discharge power of the storage battery 23 in order to prevent overvoltage of the first inverter circuit 11 in the assisted discharge mode.

[0066] 14 is a diagram showing the configuration of a power conversion system 500 according to the fifth embodiment. A central control unit 528 of the power conversion system 500 transmits a command value for charge / discharge power to the second control unit 24 based on the output current of the first inverter circuit 11 transmitted from the first control unit 15, in addition to the regeneration invalidation signal and the voltage of the storage battery 23, which are the same as those in the first embodiment.

[0067] 15 is a diagram showing the internal configuration of the overall control unit 528. The overall control unit 528 includes a mode selection unit 528a, a power selection unit 528b, and a power limiting unit 528d. The mode selection unit 528a selects an operation mode based on a regeneration disable signal transmitted from the drive circuit 10 and the voltage of the storage battery 23 detected by the monitoring unit 29. The power selection unit 528b selects a command value for charge / discharge power based on the operation mode selected by the mode selection unit 528a.

[0068] The power limiting unit 528d imposes a limit on the command value of charge / discharge power by multiplying the command value of charge / discharge power selected by the power selecting unit 528b by a coefficient that depends on the output current of the first inverter circuit 11. The power limiting unit 528d transmits the command value of charge / discharge power to which the limit has been imposed to the second control unit 24.

[0069] 16 is a diagram showing the relationship between the coefficient and the output current of the first inverter circuit 11 in the assisted discharge mode. When the output current of the first inverter circuit 11 is equal to or greater than the second current threshold Ithr2 and less than the third current threshold Ithr3, the power limiting unit 528d multiplies the command value for charge / discharge power selected by the power selecting unit 528b by a coefficient proportional to the output current of the first inverter circuit 11.

[0070] In the fifth embodiment, the second current threshold Ithr2 is set, for example, to the value of the output current of the first inverter circuit 11 when the first inverter circuit 11 outputs power equal to the command value of the charge / discharge power of the second inverter circuit 19, i.e., +Pd [kW]. Also, the third current threshold Ithr3 is set, for example, to a value twice the second current threshold Ithr2.

[0071] Furthermore, when the output current of the first inverter circuit 11 is equal to or greater than the third current threshold Ithr3, the power limiting unit 528d multiplies the charge / discharge power command value selected by the power selecting unit 528b by a coefficient of 1.0. That is, when the output current of the first inverter circuit 11 is equal to or greater than the third current threshold Ithr3, the charge / discharge power command value selected by the power selecting unit 528b is sent to the second control unit 24 as is.

[0072] On the other hand, when the output current of the first inverter circuit 11 is less than the second current threshold Ithr2, the power limiting unit 528d multiplies the command value for charge / discharge power selected by the power selecting unit 528b by a coefficient 0. That is, when the output current of the first inverter circuit 11 is less than the second current threshold Ithr2, 0 kW is transmitted to the second control unit 24 as the command value for charge / discharge power. This prevents the output power of the second inverter circuit 19 from becoming excessively large in the assisted discharge mode, and a portion of this power flows into the output side 11b of the first inverter circuit 11, preventing power from flowing from the output side 11b to the input side 11a of the first inverter circuit 11.

[0073] As described above, in the assisted discharge mode, the overall control unit 528 of the power conversion system 500 according to the fifth embodiment limits the discharge power supplied from the storage battery 23 via the second inverter circuit 19 based on the output current of the first inverter circuit 11 transmitted from the first control unit 15. Specifically, when the output current of the first inverter circuit 11 is less than the second current threshold Ithr2, the overall control unit 528 controls the second control unit 24 so that the discharge power supplied from the storage battery 23 via the second inverter circuit 19 becomes zero.

[0074] Due to the above-mentioned features, in the power conversion system 500 according to the fifth embodiment, in the assisted discharge mode, the output power of the second inverter circuit 19 becomes excessively large, and a part of this power flows into the output side 11b of the first inverter circuit 11, preventing power from flowing from the output side 11b to the input side 11a of the first inverter circuit 11. Therefore, an overvoltage of the first inverter circuit 11 in the assisted discharge mode is prevented.

[0075] (Embodiment 6) In the above-described first embodiment, if the load 3 is cut off or the power required by the load 3 becomes extremely small in the assisted discharge mode, the discharge power supplied from the storage battery 23 via the second inverter circuit 19 has no destination. As a result, the output power of the second inverter circuit 19 flows into the output side 11b of the first inverter circuit 11, and power flows from the output side 11b to the input side 11a of the first inverter circuit 11.

[0076] As described in the fifth embodiment above, when such a power flow occurs, the first DC capacitor 13 is charged and its voltage rises due to the presence of the reverse current prevention diode 30. When the voltage of the first DC capacitor 13, i.e., the voltage on the input side 11a of the first inverter circuit 11, reaches a specified value or higher, an overvoltage protection circuit (not shown) operates to protect the first inverter circuit 11 from overvoltage, and the first inverter circuit 11 is forcibly shut down and stops operating.

[0077] In order to address the above problem, in this embodiment 6, when it is detected that the voltage on the input side 11a of the first inverter circuit 11 has reached a predetermined value or higher, a request to stop the power output of the second inverter circuit 19 is sent from the first control unit to the second control unit.

[0078] Fig. 17 is a diagram showing the configuration of a power conversion system 600 according to the sixth embodiment. When it is detected that the voltage of the first DC capacitor 13 detected by the first DC voltage sensor 16, i.e., the voltage on the input side 11a of the first inverter circuit 11, has reached a specified value or more, a first control unit 615 of the power conversion system 600 controls the switching operation of the first inverter circuit 11, thereby superimposing a predetermined high-frequency signal on the AC voltage output from the first inverter circuit 11, as schematically shown in Fig. 18.

[0079] The second control unit 624 includes a band-pass filter 624a, and inputs the output voltage of the first inverter circuit 11 detected by the second AC voltage sensor 27 to the band-pass filter 624a. The frequency characteristics of the band-pass filter 624a are designed to pass the frequency of the high-frequency signal but to block the frequency of the AC voltage output by the first inverter circuit 11.

[0080] When the second control unit 624 detects the above-mentioned high-frequency signal component from the output of the bandpass filter 624a, it determines that a request to stop the power output of the second inverter circuit 19 has been sent to it from the first control unit 615, and stops the power output from the second inverter circuit 19. This prevents the output power of the second inverter circuit 19 from flowing into the output side 11b of the first inverter circuit 11, and prevents power from flowing from the output side 11b of the first inverter circuit 11 to the input side 11a.

[0081] As described above, in the power conversion system 600 according to the sixth embodiment, when the first control unit 615 detects that the voltage on the input side 11a of the first inverter circuit 11 has reached or exceeded a specified value, the first control unit 615 transmits a request to stop the power output of the second inverter circuit 19 to the second control unit 624. In detail, the transmission of the request to stop the power output from the first control unit 615 to the second control unit 624 is performed by superimposing a predetermined high-frequency signal on the AC voltage output from the first inverter circuit 11.

[0082] Due to the above-mentioned features, in the power conversion system 600 according to the sixth embodiment, when the load 3 is cut off or the power required by the load 3 becomes extremely small in the assisted discharge mode, the output power of the second inverter circuit 19 flows into the output side 11b of the first inverter circuit 11, and power is prevented from flowing from the output side 11b to the input side 11a of the first inverter circuit 11. Therefore, an overvoltage of the first inverter circuit 11 is prevented.

[0083] The means for transmitting the request to stop power output from the first control unit 615 to the second control unit 624 is not limited to the method of superimposing a predetermined high-frequency signal on the AC voltage output from the first inverter circuit 11. For example, if a time delay required for transmission is tolerable, the request may be transmitted from the first control unit 615 to the second control unit 624 via the integrated control unit 28. Furthermore, if a time delay is not tolerable but there is ample wiring space, a dedicated signal line may be provided between the first control unit 615 and the second control unit 624. In contrast, the method of superimposing a predetermined high-frequency signal on the AC voltage according to the sixth embodiment can be applied even if a time delay is not tolerable and there is limited wiring space.

[0084] Furthermore, although the premise is different from that of the sixth embodiment, if the load 3 is not interrupted and the minimum power consumption of the load 3 is known in advance, the general control unit 28 may control the second control unit 24 so that the discharge power supplied from the storage battery 23 via the second inverter circuit 19 is less than the minimum power consumption of the load 3. This ensures that all of the output power of the second inverter circuit 19 is consumed by the load 3 and that the output power of the first inverter circuit 11 is always equal to or greater than zero. This prevents the output power of the second inverter circuit 19 from flowing into the output side 11b of the first inverter circuit 11 and prevents power from flowing from the output side 11b to the input side 11a of the first inverter circuit 11. This prevents overvoltage in the first inverter circuit 11.

[0085] (Embodiment 7) In the seventh embodiment, an overvoltage in the first inverter circuit 11 is prevented by a method different from that in the sixth embodiment.

[0086] FIG. 19 is a diagram showing the configuration of a power conversion system 700 according to the seventh embodiment. The power conversion system 700 includes a first insulated gate bipolar transistor (IGBT) 732 that functions as a switch, and a blocking diode 733 connected in parallel therewith. In detail, the collector terminal of the first IGBT 732 is connected to the input side 11a of the first inverter circuit 11, and the emitter terminal of the first IGBT 732 is connected to the overhead line 2. The first IGBT 732 is normally off, and prevents power from flowing from the input side 11a of the first inverter circuit 11 toward the overhead line 2. The blocking diode 733 functions in the same way as the blocking diode 30 according to the sixth embodiment.

[0087] In the assisted discharge mode, when the first control unit 715 detects that the voltage of the first DC capacitor 13 detected by the first DC voltage sensor 16, i.e., the voltage on the input side 11a of the first inverter circuit 11, has risen to or above a specified value, e.g., the voltage on the overhead line 2, due to the load 3 being cut off or the power consumption of the load 3 becoming extremely small, the first control unit 715 applies a voltage signal to the gate terminal of the first IGBT 732 to turn on the first IGBT 732. When the first IGBT 732 is turned on, power begins to flow from the input side 11a of the first inverter circuit 11 to the overhead line 2, and the voltage of the first DC capacitor 13, i.e., the voltage on the input side 11a of the first inverter circuit 11, drops. This activates an overvoltage protection circuit (not shown), preventing the first inverter circuit 11 from being forcibly cut off.

[0088] As described above, the power conversion system 700 according to the seventh embodiment includes the first IGBT 732 as a switch connected in series between the input side 11a of the first inverter circuit 11 and the overhead line 2. When the first control unit 715 detects that the voltage on the input side 11a of the first inverter circuit 11 has reached a specified value or higher, it turns on the first IGBT 732 to allow power to flow from the input side 11a of the first inverter circuit 11 toward the overhead line 2.

[0089] Due to the above-mentioned features, in the power conversion system 700 according to the seventh embodiment, when the load 3 is cut off or the power consumption of the load 3 becomes extremely small in the assisted discharge mode, the first inverter circuit 11 is prevented from becoming overvoltage.

[0090] (Embodiment 8) In the eighth embodiment, an overvoltage in the first inverter circuit 11 is prevented by a method that is different from those in the sixth and seventh embodiments.

[0091] 20 is a diagram showing the configuration of a power conversion system 800 according to the eighth embodiment. The power conversion system 800 includes a second IGBT 834 connected in parallel with the first DC capacitor 13 to the input side 11a of the first inverter circuit 11, and a discharge resistor 835. In detail, the collector terminal of the second IGBT 834 is connected to the power supply line of the input side 11a of the first inverter circuit 11, and the emitter terminal of the second IGBT 834 is connected to one end of the discharge resistor 835. The other end of the discharge resistor 835 is connected to the GND line of the input side 11a of the first inverter circuit 11. The second IGBT 834 is normally off.

[0092] In the assist discharge mode, when the first control unit 715 detects that the voltage of the first DC capacitor 13 detected by the first DC voltage sensor 16, i.e., the voltage on the input side 11a of the first inverter circuit 11, has exceeded a specified value, for example, the voltage of the overhead line 2, due to the load 3 being shut off or the power consumption of the load 3 becoming extremely small, the first control unit 715 applies a voltage signal to the gate terminal of the second IGBT 834 to turn on the second IGBT 834. When the second IGBT 834 is turned on, the first DC capacitor 13 discharges through the discharge resistor 835, and the voltage on the input side 11a of the first inverter circuit 11 drops. This activates an overvoltage protection circuit (not shown), preventing the first inverter circuit 11 from being forcibly shut off.

[0093] As described above, the power conversion system 800 according to the eighth embodiment includes the second IGBT 834 connected in parallel to the first DC capacitor 13 on the input side 11a of the first inverter circuit 11, and the discharge resistor 835. When the first control unit 815 detects that the voltage of the first DC capacitor 13, i.e., the voltage on the input side 11a of the first inverter circuit 11, has reached or exceeded a specified value, the first control unit 815 turns on the second IGBT 834 to discharge the first DC capacitor 13.

[0094] Due to the above-mentioned features, in the power conversion system 800 according to the eighth embodiment, when the load 3 is cut off or the power consumption of the load 3 becomes extremely small in the assisted discharge mode, the first inverter circuit 11 is prevented from becoming overvoltage.

[0095] The first control unit 815 may turn on the second IGBT 834 and stop the power output from the second inverter circuit 19, for example, in the same manner as in the sixth embodiment. As a result, the voltage of the first DC capacitor 13 becomes equal to or higher than a specified value, and the first DC capacitor 13 is discharged. After a short time has passed, the power output from the second inverter circuit 19 is also stopped. This eliminates the need to excessively increase the capacitance of the first DC capacitor 13, thereby avoiding an increase in the circuit size.

[0096] Although several embodiments of the present disclosure have been described, these embodiments are presented as examples and are not intended to limit the scope of the disclosure. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the disclosure. Furthermore, these embodiments can be freely combined. These embodiments and their modifications are included within the scope and spirit of the disclosure, as well as the disclosure described in the claims and their equivalents. [Explanation of symbols]

[0097] 1 electric motor 2. Overhead lines 3. Load 10 Drive circuit (regeneration failure detection section) 11 First inverter circuit (first power conversion circuit) 11a Input side 11b Output side 12. Transformers 13 DC capacitor 14 First AC capacitor 15 First control section 16 First DC voltage sensor 17 First AC current sensor 19 Second inverter circuit (second power conversion circuit) 20 Second AC capacitor 21 AC reactor 22 Second DC Capacitor 23 Storage battery 24 Second control section 25 Second DC voltage sensor 26 Second AC current sensor 27 Second AC voltage sensor 28 General Control Unit 28a Mode selection section 28b Power selection section 29 Monitoring Department 30 Reverse current prevention diode 100 Power Conversion System 200 Power Conversion System 228 General Control Unit 228a Mode selection section 228b Power selection unit 228c Reactive current selection section 300 Power Conversion System 328 General Control Unit 328a Mode selection section 328b Power selection unit 400 Power Conversion System 428 General Control Unit 428a Mode selection section 428b Power selection unit 428d Power Limiter 500 Power Conversion System 528 General Control Unit 528a Mode selection section 528b Power selection unit 528d Power Limiter 600 Power Conversion System 615 First control section 624 Second control section 624a Bandpass Filter 700 Power Conversion System 715 First control section 732 First IGBT (first switch) 733 Reverse current prevention diode 800 Power Conversion System 815 First control section 834 Second IGBT (Second Switch) 835 Discharge resistor

Claims

1. a drive circuit that converts a first DC power supplied from an external source into AC power to drive an electric motor and converts regenerative power of the electric motor into a second DC power; a regeneration failure detection unit that detects whether or not a regeneration failure has occurred during a regenerative operation of the electric motor; a first power conversion circuit that converts the first DC power or the second DC power into AC power and supplies the AC power to a load; a second power conversion circuit having an output side connected in parallel to an output side of the first power conversion circuit; a storage battery connected to an input side of the second power conversion circuit; a voltage detection unit that detects the voltage of the storage battery; a first control unit that controls the first power conversion circuit to output a constant AC voltage; a second control unit that controls charging and discharging of the storage battery by controlling the second power conversion circuit so that a predetermined charging and discharging power is input and output; an integrated control unit that controls the operation of the second control unit based on whether the regeneration invalidation has occurred and the voltage of the storage battery; A power conversion system comprising:

2. The power conversion system includes: a regenerative absorption mode in which the regenerative power of the motor is charged to the storage battery via the second power conversion circuit; an assist discharge mode in which the power stored in the storage battery is supplied to the load via the second power conversion circuit; a standby mode in which neither charging nor discharging of the storage battery is performed; and 2. The power conversion system according to claim 1, wherein the integrated control unit selects one of the regeneration absorption mode, the assist discharge mode, and the standby mode based on whether the regeneration lapse has occurred and the voltage of the storage battery.

3. The general control unit When the regeneration failure occurs and the voltage of the storage battery is less than a first voltage threshold, the regeneration absorption mode is selected; When the regeneration failure has not occurred and the voltage of the storage battery is equal to or higher than a second voltage threshold that is lower than the first voltage threshold, the assist discharge mode is selected; 3. The power conversion system according to claim 2, wherein the standby mode is selected when the regeneration lapse has occurred and the voltage of the storage battery is equal to or greater than the first voltage threshold, or when the regeneration lapse has not occurred and the voltage of the storage battery is less than the second voltage threshold.

4. the power conversion system further has a boost charging mode in which the storage battery is charged with the first DC power via the second power conversion circuit; 4. The power conversion system according to claim 3, wherein, when the voltage of the storage battery is equal to or lower than a third voltage threshold that is lower than the second voltage threshold, the integrated control unit selects the boost charging mode until the voltage of the storage battery exceeds a fourth voltage threshold that is higher than the second voltage threshold, and controls the second control unit so that, in the boost charging mode, a reactive current flows to the output side of the second power conversion circuit.

5. The reactive current is expressed by the following equation, where Id is the reactive current, VCq is the voltage applied to the load, Vmax is the maximum voltage that can be output by the second power conversion circuit, ω is the angular frequency of the output voltage of the second power conversion circuit, L is the inductance value of the AC reactor on the output side of the second power conversion circuit, and Iq is the active current flowing through the output side of the second power conversion circuit: [Equation 1] 5. The power conversion system of claim 4, defined according to:

6. the power conversion system further has a warm-up mode in which charging and discharging of the storage battery are repeated at regular intervals via the second power conversion circuit, thereby preventing a decrease in the temperature of the cells of the storage battery; The power conversion system according to any one of claims 3 to 5, wherein the integrated control unit selects the warm-up mode when the regeneration lapse has not occurred, the voltage of the storage battery is less than the second voltage threshold, and the temperature of the cells of the storage battery is less than or equal to a first temperature threshold.

7. The power conversion system according to any one of claims 3 to 6, wherein the integrated control unit controls the second control unit so that, in the regenerative absorption mode, the charging power supplied to the storage battery via the second power conversion circuit is limited based on the output current of the first power conversion circuit transmitted from the first control unit.

8. 8. The power conversion system according to claim 7, wherein the integrated control unit controls the second control unit so that charging power supplied to the storage battery via the second power conversion circuit becomes zero when the output current of the first power conversion circuit is equal to or greater than a first current threshold.

9. The integrated control unit controls the second control unit so that the discharge power supplied from the storage battery via the second power conversion circuit is limited based on the output current of the first power conversion circuit transmitted from the first control unit in the assisted discharge mode. The power conversion system according to any one of claims 3 to 8.

10. 10. The power conversion system according to claim 9, wherein the integrated control unit controls the second control unit so that discharge power supplied from the storage battery via the second power conversion circuit becomes zero when the output current of the first power conversion circuit is less than a second current threshold.

11. The power conversion circuit includes: a backflow prevention diode connected in series between the input side of the first power conversion circuit and the overhead line; a first DC voltage sensor that detects a voltage on the input side of the first power conversion circuit; Furthermore, The power conversion system according to any one of claims 1 to 10, wherein the first control unit, when detecting that the voltage on the input side of the first power conversion circuit has reached a specified value or higher, sends a request to the second control unit to stop the power output of the second power conversion circuit.

12. 12. The power conversion system according to claim 11, wherein the transmission of the request to stop the power output from the first control unit to the second control unit is performed by superimposing a predetermined high-frequency signal on the AC voltage output from the first power conversion circuit.

13. The power conversion system according to claim 11 , wherein the request to stop the power output is transmitted from the first control unit to the second control unit via the general control unit.

14. 12. The power conversion system according to claim 11, wherein the request to stop the power output from the first control unit to the second control unit is transmitted via a signal line provided between the first control unit and the second control unit.

15. The power conversion circuit includes: Further, a reverse current prevention diode is connected in series between the input side of the first power conversion circuit and the overhead line, The integrated control unit controls the second control unit so that the discharge power supplied from the storage battery via the second power conversion circuit is less than the minimum power consumption of the load. The power conversion system according to any one of claims 1 to 10.

16. The power conversion circuit includes: a backflow prevention diode connected in series between the input side of the first power conversion circuit and the overhead line; a first switch connected in series between an input side of the first power conversion circuit and an overhead line; a first DC voltage sensor that detects a voltage on the input side of the first power conversion circuit; Furthermore, When the first control unit detects that the voltage on the input side of the first power conversion circuit has reached a specified value or higher, it turns on the first switch to allow power to flow from the input side of the first power conversion circuit to the overhead line. The power conversion system according to any one of claims 1 to 10.

17. The power conversion circuit includes: a backflow prevention diode connected between the input side of the first power conversion circuit and an overhead line; a second switch having one end connected to a power supply line on the input side of the first power conversion circuit; a discharge resistor connected between the other end of the second switch and a GND line on the input side of the first power conversion circuit; a first DC voltage sensor that detects a voltage on the input side of the first power conversion circuit; Furthermore, The first control unit turns on the second switch when it detects that the voltage on the input side of the first power conversion circuit has reached a specified value or higher. The power conversion system according to any one of claims 1 to 10.

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