Power conversion system

Abstract

To correctly determine an overvoltage caused by abnormality in a converter.SOLUTION: A power conversion system includes: a first DC circuit including a main battery; a second DC circuit including a sub-battery having a rated voltage lower than that of the main battery; a converter that outputs stepped-down power from the first DC circuit to the second DC circuit; a control device that commands a target output voltage to the converter; and a voltage sensor that measures a voltage of the second DC circuit. The control device executes: processing of setting a target output voltage to a second voltage value lower than a first voltage value when a voltage detected by a voltage sensor exceeds a predetermined upper limit value during a first predetermined time in a state where the target output voltage is set to the first voltage value; and processing of determining that an overvoltage occurs due to abnormality in the converter when the voltage detected by the voltage sensor exceeds the upper limit value during a second predetermined time after the processing of setting the second voltage value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a power conversion system. [Background technology]

[0002] Patent Document 1 describes a power conversion system. In this power conversion system, power is supplied to a DC circuit equipped with a sub-battery via a converter. The output voltage of the converter is monitored, and if the output voltage exceeds a predetermined upper limit, it is determined that an overvoltage has occurred and the operation of the converter is restricted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-188516 Summary of the Invention [Problem to be solved by the invention]

[0004] The converter output voltage fluctuates depending on the operating state of the series circuit to which it is supplied (e.g., the start or stop of a load connected to the series circuit). Therefore, even if the converter is operating normally, the converter output voltage may temporarily exceed the upper limit value for determining an overvoltage, depending on the operating state of the series circuit. Because such a temporary overvoltage is tolerated by the sub-battery, it must be distinguished from a converter abnormality and ignored. To achieve this, it is possible to determine that an overvoltage is due to a converter abnormality when the converter output voltage exceeds the upper limit value for a predetermined period of time. However, this approach would tolerate an overvoltage due to a converter abnormality until the predetermined period has elapsed, potentially damaging the sub-battery. On the other hand, if the predetermined period is set relatively short, a temporary overvoltage due to the operating state of the series circuit may be erroneously determined to be due to a converter abnormality. Because lead-acid batteries have a relatively small difference between their rated voltage and allowable voltage (the upper limit of the allowable charging voltage), the above-mentioned problem is more likely to occur when the sub-battery is a lead-acid battery.

[0005] In view of the above circumstances, this specification provides a technique for correctly determining an overvoltage caused by an abnormality in a converter. [Means for solving the problem]

[0006] The technology disclosed in this specification is embodied in a power conversion system. In a first aspect, the power conversion system includes a first DC circuit including a main battery, a second DC circuit including a sub-battery having a rated voltage lower than that of the main battery, a converter provided between the first DC circuit and the second DC circuit and outputting stepped-down power from the first DC circuit to the second DC circuit, a control device for issuing a target output voltage command to the converter, and a voltage sensor connected to the control device and measuring a voltage of the second DC circuit. The control device executes the following operations: when the target output voltage is set to a first voltage value and a voltage detected by the voltage sensor exceeds a predetermined upper limit value for a first predetermined time, the control device sets the target output voltage to a second voltage value lower than the first voltage value; and when the voltage detected by the voltage sensor exceeds the upper limit value for a second predetermined time after setting the second voltage value, the control device determines that an overvoltage has occurred due to an abnormality in the converter.

[0007] In the above-described power conversion system, when the target output voltage for the converter is set to a first voltage value, if the voltage detected by the voltage sensor exceeds the upper limit value for a first predetermined time, the target output voltage is set to a second voltage value lower than the first voltage value. That is, at this point, even if the voltage detected by the voltage sensor exceeds the upper limit value for the first predetermined time, it is not determined that an overvoltage has occurred due to an abnormality in the converter. Then, even after the target output voltage is set to the second voltage value, if the voltage detected by the voltage sensor exceeds the upper limit value for a second predetermined time, it is determined that an overvoltage has occurred due to an abnormality in the converter.

[0008] For example, suppose that a voltage fluctuation expected during normal operation causes the voltage detected by the voltage sensor to unintentionally increase, causing the detected voltage to exceed the upper limit for a first predetermined time. In this case, the target output voltage for the converter is set to a relatively low second voltage value. As a result, if the converter is normal, the voltage detected by the voltage sensor should also decrease as the target output voltage decreases. This prevents the overvoltage from being determined to be caused by a converter abnormality. In contrast, if the converter is abnormal, the voltage detected by the voltage sensor should continue to exceed the upper limit even if the target output voltage is reduced. Therefore, even after the target output voltage is reduced to the second voltage value, the voltage detected by the voltage sensor will exceed the upper limit for a second predetermined time, and it is determined that an overvoltage has occurred due to a converter abnormality. This configuration increases tolerance to voltage fluctuations expected during normal operation and allows the overvoltage caused by a converter abnormality to be correctly determined, distinguishing it from such voltage fluctuations.

[0009] In a second aspect, in the first aspect, after setting the second voltage value, the control device may further execute a process of resetting the target output voltage to the first voltage value if the detected voltage falls below the upper limit before the second predetermined time has elapsed. Note that, in another embodiment, the voltage value set as the target output voltage does not necessarily have to be the first voltage value, but may be another voltage value higher than the second voltage value.

[0010] In a third aspect, in the first or second aspect, the first predetermined time may be shorter than the second predetermined time. With this configuration, the time during which an overvoltage is applied to the sub-battery can be shortened.

[0011] In a fourth aspect, in any of the first to third aspects, the upper limit may be equal to or less than the upper limit of the charging voltage allowed by the sub-battery. In particular, according to the present technology, even if the upper limit of the voltage detected by the voltage sensor is set to the upper limit of the charging voltage allowed by the sub-battery, an overvoltage caused by an abnormality in the converter can be correctly detected by distinguishing it from voltage fluctuations and the like expected during normal operation.

[0012] In a fifth aspect, in any of the first to fourth aspects, the difference between the upper limit value and the second voltage value may be greater than the sum of a maximum control error expected in the converter output voltage with respect to the target output voltage, a maximum detection error expected by the voltage sensor, and a maximum voltage fluctuation expected during normal operation of the second DC circuit. With this configuration, even if the voltage detected by the voltage sensor unintentionally increases due to voltage fluctuations expected during normal operation, it is possible to avoid determining that an overvoltage has occurred due to an abnormality in the converter. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a schematic configuration of a power conversion system 10 according to an embodiment and a vehicle 100 on which the power conversion system 10 is mounted. [Figure 2] 4 is a flowchart showing an example of an overvoltage determination process executed by the control device 30. DETAILED DESCRIPTION OF THE INVENTION

[0014] A power conversion system 10 according to an embodiment and a vehicle 100 equipped with the system will be described with reference to the drawings. The vehicle 100 is an electric vehicle such as a hybrid electric vehicle (HEV) or a battery electric vehicle (BEV).

[0015] 1, vehicle 100 includes a three-phase AC circuit 102 and an inverter 104. Three-phase AC circuit 102 includes a motor 106. Motor 106 is a traction motor that drives the wheels of vehicle 100, and is, for example, a three-phase motor generator having a U-phase, a V-phase, and a W-phase.

[0016] 1, the power conversion system 10 includes a first DC circuit 12, a second DC circuit 14, and a converter 16. The first DC circuit 12 includes a main battery 18. The second DC circuit 14 includes a sub-battery 20 and one or more auxiliary devices 22. An inverter 104 is provided between the three-phase AC circuit 102 and the first DC circuit 12, and the converter 16 is provided between the first DC circuit 12 and the second DC circuit 14.

[0017] The main battery 18 is a battery that supplies power to the motor 106. The main battery 18 is a secondary battery in which a plurality of battery cells are connected in series. The inverter 104 converts DC power from the main battery 18 into three-phase AC power and supplies it to the motor 106, and also converts three-phase AC power from the motor 106 into DC power and supplies it to the main battery 18.

[0018] The sub-battery 20 is a battery that supplies power to the auxiliary device 22. The sub-battery 20 is a secondary battery in which a plurality of battery cells are connected in series. The sub-battery 20 is electrically connected to the auxiliary device 22 and can supply power to the auxiliary device 22. The auxiliary device 22 operates using power supplied from the sub-battery 20. The rated voltage of the sub-battery 20 is lower than the rated voltage of the main battery 18. In this embodiment, the sub-battery 20 is a lead-acid battery with a rated voltage of 12 V. The rated voltage of the main battery 18 is, for example, 200 V to 600 V. The auxiliary device 22 is, for example, a room lamp or a car navigation device.

[0019] As shown in FIG. 1 , the converter 16 includes a voltage conversion circuit 24, a feedback circuit 26, and a controller 28. The voltage conversion circuit 24 electrically connects the first DC circuit 12 and the second DC circuit 14. The first DC circuit 12 is a high-voltage DC circuit including a main battery 18, and the second DC circuit 14 is a low-voltage DC circuit including a sub-battery 20. The voltage conversion circuit 24 is a step-down DC-DC converter that steps down the DC power supplied from the first DC circuit 12 and outputs it to the second DC circuit 14. Note that the voltage conversion circuit 24 may be a bidirectional DC-DC converter. That is, in addition to the step-down operation described above, the voltage conversion circuit 24 may also be capable of performing a step-up operation in which the voltage conversion circuit 24 steps up the DC power supplied from the second DC circuit 14 and outputs it to the first DC circuit 12.

[0020] The feedback circuit 26 is a voltage divider circuit that divides the voltage output from the voltage conversion circuit 24 to the second DC circuit 14 and outputs the divided voltage. The feedback circuit 26 includes a first resistor element 26a and a second resistor element 26b. One end of the first resistor element 26a is connected to the power supply terminal of the second DC circuit 14. One end of the second resistor element 26b is connected to the other end of the first resistor element 26a. The other end of the second resistor element 26b is connected to ground. That is, the first resistor element 26a and the second resistor element 26b are connected in series between the power supply terminal of the second DC circuit 14 and ground. The connection point between the first resistor element 26a and the second resistor element 26b is connected to an input terminal (not shown) of the controller 28. As a result, the output voltage from the feedback circuit 26 is input to the controller 28.

[0021] The controller 28 is a computer device having a processor, memory, etc. The target output voltage for the voltage conversion circuit 24 is input to the controller 28 from the control device 30. As described above, the output voltage from the feedback circuit 26 is also input to the controller 28. Based on these inputs, the controller 28 controls the operation of the voltage conversion circuit 24. As a result, the operation of the voltage conversion circuit 24 is feedback-controlled so that the output voltage from the voltage conversion circuit 24 to the second DC circuit 14 becomes equal to the target output voltage.

[0022] As shown in FIG. 1, the power conversion system 10 further includes a control device 30. The control device 30 is a computer device having a processor, memory, etc. The control device 30 determines a target output voltage for the voltage conversion circuit 24 and issues a command to the converter 16. In this embodiment, the target output voltage for the voltage conversion circuit 24 is input from the control device 30 to a controller 28 of the converter 16. Typically, the target output voltage for the voltage conversion circuit 24 is set to a first voltage value V1. The first voltage value V1 is a value higher than the rated voltage of the sub-battery 20. In this embodiment, since the rated voltage of the sub-battery 20 is 12 volts, the first voltage value V1 may be a value of, for example, 13 to 15 volts.

[0023] 1, the power conversion system 10 further includes a voltage sensor 32. The voltage sensor 32 measures the voltage of the second DC circuit 14. The control device 30 is communicatively connected to the voltage sensor 32 and can monitor the voltage detected by the voltage sensor 32.

[0024] Next, the overvoltage determination process executed by the control device 30 will be described with reference to Fig. 2. By executing this overvoltage determination process, the control device 30 can determine an overvoltage caused by an abnormality in the converter 16. Examples of abnormalities in the converter 16 include a failure in the voltage conversion circuit 24, a failure (e.g., a ground fault) in the feedback circuit 26, and a failure in the controller 28.

[0025] 2, the control device 30 determines whether the voltage conversion circuit 24 is operating in a state where the target output voltage for the voltage conversion circuit 24 is set to a first voltage value V1 (S10). Here, the target output voltage for the voltage conversion circuit 24 means the target output voltage output from the voltage conversion circuit 24 to the second DC circuit 14 side. Furthermore, the voltage conversion circuit 24 being operating means that the voltage conversion circuit 24 is performing a step-down operation.

[0026] If the answer is YES in step S10, the control device 30 determines whether the voltage detected by the voltage sensor 32 exceeds a predetermined upper limit value VH for a first predetermined time (S12). Here, the upper limit value VH is the upper limit value of the charging voltage allowed by the sub-battery 20. In this embodiment, the upper limit value VH is the upper limit value (approximately 16 V) of the charging voltage allowed by a lead-acid battery with a rated voltage of 12 V. The upper limit value VH is also higher than the first voltage value V1. As an example, the first predetermined time may be less than 1 second, for example, 100 to 500 milliseconds. The first predetermined time is a relatively short time. Therefore, even if a voltage exceeding the upper limit value VH is applied to the sub-battery 20 for the first predetermined time, the sub-battery 20 will not be damaged.

[0027] If the voltage detected by the voltage sensor 32 exceeds the upper limit value VH for a first predetermined time (YES in step S12), the control device 30 sets the target output voltage for the voltage conversion circuit 24 to a second voltage value V2 (S14). That is, when step S12 returns YES, it is not immediately determined that an overvoltage has occurred due to an abnormality in the converter 16. The second voltage value V2 is lower than the first voltage value V1. Furthermore, the difference between the upper limit value VH and the second voltage value V2 is greater than the sum of the maximum control error expected in the output voltage of the voltage conversion circuit 24 relative to the target output voltage, the maximum detection error expected by the voltage sensor 32, and the maximum voltage fluctuation expected in normal operation of the second DC circuit 14. That is, the second voltage value V2 is significantly lower than the upper limit value VH.

[0028] After the process of step S14, the control device 30 determines whether the voltage detected by the voltage sensor 32 exceeds the upper limit value VH for a second predetermined time (S16, S18). Here, the second predetermined time is longer than the first predetermined time. As an example, the second predetermined time may be 1 second or more, for example, 1.5 to 3 seconds. Although the second predetermined time is longer than the first predetermined time, it is a relatively short time. Therefore, even if a voltage exceeding the upper limit value VH is applied to the sub-battery 20 for the second predetermined time, the sub-battery 20 will not be damaged.

[0029] For example, suppose that the voltage detected by voltage sensor 32 unintentionally increases due to voltage fluctuations expected during normal operation, and the detected voltage exceeds upper limit value VH for a first predetermined time (YES in step S12). In this case, the target output voltage for voltage conversion circuit 24 is set to a relatively low second voltage value V2 (S14). As a result, if converter 16 is normal, the detected voltage by voltage sensor 32 should also decrease as the target output voltage decreases (NO in step S16). In contrast, if an abnormality occurs in converter 16, the detected voltage by voltage sensor 32 should continue to exceed upper limit value VH even if the target output voltage is decreased. Therefore, even after the target output voltage is decreased to second voltage value V2, the detected voltage by voltage sensor 32 will exceed upper limit value VH for a second predetermined time (YES in step S16).

[0030] Based on this, if the voltage detected by voltage sensor 32 exceeds upper limit value VH for a second predetermined time (YES in step S16), control device 30 determines that an overvoltage has occurred due to an abnormality in converter 16 (S20). On the other hand, if the detected voltage falls below upper limit value VH before the second predetermined time has elapsed (NO in step S16), control device 30 resets the target output voltage for voltage conversion circuit 24 to first voltage value V1 (S22) when the second predetermined time has elapsed (YES in step S18). In other words, the target output voltage is reset to a normal value. After executing the process of step S20 or step S22, control device 30 ends the overvoltage determination process shown in FIG. 2.

[0031] In this way, in the above-described power conversion system 10, after the process (S14) of setting the target output voltage for the voltage conversion circuit 24 to the second voltage value V2, the control device 30 compares the voltage detected by the voltage sensor 32 with the upper limit value VH to determine whether or not the overvoltage is caused by an abnormality in the converter 16. This increases the tolerance to voltage fluctuations and the like that are expected during normal operation, and makes it possible to correctly detect an overvoltage caused by an abnormality in the converter 16 by distinguishing it from such voltage fluctuations and the like.

[0032] In the above-described embodiment, the first predetermined time is shorter than the second predetermined time. This configuration can shorten the time during which an overvoltage is applied to the sub-battery 20. However, the first predetermined time does not necessarily have to be shorter than the second predetermined time. That is, in other embodiments, the first predetermined time may be equal to the second predetermined time. In still other embodiments, the first predetermined time may be longer than the second predetermined time.

[0033] In the above-described embodiment, the upper limit value VH is the upper limit value of the charging voltage allowed by the sub-battery 20. With this configuration, an overvoltage caused by an abnormality in the converter 16 can be correctly detected, distinguishing it from voltage fluctuations and the like expected during normal operation. However, the upper limit value VH does not necessarily have to be the upper limit value of the charging voltage allowed by the sub-battery 20. That is, in other embodiments, the upper limit value VH may be smaller than the upper limit value of the charging voltage allowed by the sub-battery 20.

[0034] In the above-described embodiment, the difference between the upper limit value VH and the second voltage value V2 is greater than the sum of the maximum control error expected in the output voltage of the voltage conversion circuit 24 relative to the target output voltage, the maximum detection error expected by the voltage sensor 32, and the maximum voltage fluctuation expected during normal operation of the second DC circuit 14. With this configuration, it is possible to avoid determining that an overvoltage has occurred due to an abnormality in the converter 16 when the voltage detected by the voltage sensor 32 unintentionally increases due to voltage fluctuations expected during normal operation, etc. However, the difference between the upper limit value VH and the second voltage value V2 does not necessarily have to be greater than the above sum.

[0035] In the above-described embodiment, the control device 30 does not necessarily have to set the first voltage value V1 as the target output voltage in step S22. That is, in other embodiments, the control device 30 may set another voltage value higher than the second voltage value V2 as the target output voltage in step S22.

[0036] Although several specific examples have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility either alone or in combination. [Explanation of symbols]

[0037] 10: Power conversion system, 12: First DC circuit, 14: Second DC circuit, 16: Converter, 18: Main battery, 20: Sub-battery, 22: Auxiliary equipment, 24: Voltage conversion circuit, 26: Feedback circuit, 26a, 26b: Resistance elements, 28: Controller, 30: Control device, 32: Voltage sensor, 100: Vehicle, 102: Three-phase AC circuit, 104: Inverter, 106: Motor

Claims

1. a first DC circuit including a main battery; a second DC circuit including a sub-battery having a rated voltage lower than the rated voltage of the main battery; a converter provided between the first DC circuit and the second DC circuit, the converter outputting stepped-down power from the first DC circuit to the second DC circuit; a control device that commands a target output voltage to the converter; a voltage sensor connected to the control device and measuring a voltage of the second DC circuit; Equipped with The control device a process of setting the target output voltage to a second voltage value lower than the first voltage value when a voltage detected by the voltage sensor exceeds a predetermined upper limit value for a first predetermined time period while the target output voltage is set to a first voltage value; a process of determining that an overvoltage has occurred due to an abnormality in the converter when the voltage detected by the voltage sensor exceeds the upper limit value for a second predetermined time period after the process of setting the second voltage value; A power conversion system that performs the above.

2. 2. The power conversion system according to claim 1, wherein, after the process of setting the second voltage value, the control device further executes a process of resetting the target output voltage to the first voltage value if the detected voltage falls below the upper limit value before the second predetermined time has elapsed.

3. The power conversion system according to claim 1 , wherein the first predetermined time is shorter than the second predetermined time.

4. The power conversion system according to claim 1 , wherein the upper limit is equal to or less than an upper limit of a charging voltage allowed by the sub-battery.

5. 2. The power conversion system according to claim 1, wherein a difference between the upper limit value and the second voltage value is greater than a sum of a maximum control error expected in the output voltage of the converter with respect to the target output voltage, a maximum detection error expected in the voltage sensor, and a maximum voltage fluctuation expected during normal operation of the second DC circuit.

Images