DC-DC converter

Abstract

To achieve a DC-DC converter capable of detecting an abnormality of a current sensor while being reduced in size.SOLUTION: A DC-DC converter 1 includes: a conversion unit 4 performing power conversion between a high-voltage battery HB and an auxiliary battery LB; one current sensor 5 detecting a terminal current on a high-voltage battery HB side or a terminal current on an auxiliary battery LB side; a voltage sensor 7 detecting a voltage between terminals on the auxiliary battery LB side; and a control section 8 controlling power conversion at the conversion unit 4 such that the voltage between terminals approaches a final target voltage, based on the terminal current detected by the current sensor 5 and the voltage between terminals detected by the voltage sensor 7. At the startup of the DC-DC converter 1, the control section 8 controls the power conversion such that the voltage between terminals approaches a primary target voltage higher than the final target voltage within a predetermined period, and, after the predetermined period, controls the power conversion such that the voltage between terminals approaches the final target voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a DC-DC converter. [Background technology]

[0002] Vehicles such as electric vehicles and hybrid vehicles are equipped with a DC-DC converter that boosts or lowers the output voltage of a battery. For example, Patent Document 1 describes an in-vehicle control system that includes a battery, a boost converter, an inverter, a motor generator, and a control device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-157661 A Summary of the Invention [Problem to be solved by the invention]

[0004] The boost converter described in Patent Document 1 includes a first current sensor that detects a current flowing through the boost converter to control power conversion by the boost converter, and a second current sensor that detects the current or a current flowing to a battery, and an abnormality in the first current sensor or the second current sensor is diagnosed based on the amount of fluctuation in the detected value of the first current sensor and the amount of fluctuation in the detected value of the second current sensor. On the other hand, it is desirable to reduce the size of in-vehicle converters by eliminating unnecessary circuit elements as much as possible.

[0005] The present disclosure describes a DC-DC converter that is compact yet capable of detecting an abnormality in a current sensor. [Means for solving the problem]

[0006] A DCDC converter according to one aspect of the present disclosure is a DCDC converter for an electric vehicle that performs power conversion between a high-voltage battery and an auxiliary battery, and includes a conversion unit that performs power conversion between the high-voltage battery and the auxiliary battery, one current sensor that detects a terminal current on the high-voltage battery side or a terminal current on the auxiliary battery side, a voltage sensor that detects a terminal voltage on the auxiliary battery side, and a control unit that controls power conversion in the conversion unit so that the terminal voltage approaches a final target voltage based on the terminal current detected by the current sensor and the terminal voltage detected by the voltage sensor, and when the DCDC converter is started, the control unit controls the power conversion so that the terminal voltage approaches a primary target voltage that is higher than the final target voltage within a predetermined period, and controls the power conversion so that the terminal voltage approaches the final target voltage after the predetermined period.

[0007] In this DCDC converter, power conversion is controlled based on the terminal current on the high voltage battery side or the terminal current on the auxiliary battery side detected by one current sensor and the terminal voltage on the auxiliary battery side detected by a voltage sensor so that the terminal voltage approaches a final target voltage. Here, when the DCDC converter is started up, the terminal voltage is controlled to approach a primary target voltage higher than the final target voltage within a predetermined period, and the terminal voltage is controlled to approach the final target voltage after the predetermined period. This makes it possible to determine an abnormality in one current sensor by whether or not an inrush current is detected in the current sensor when the DCDC converter is started up. Since an extra circuit element for detecting an abnormality in one current sensor is not required, it is possible to detect an abnormality in the current sensor while reducing the size.

[0008] In the above aspect, the primary target voltage may be a maximum voltage that the converter can output to the auxiliary battery. In this case, the terminal voltage on the auxiliary battery side can be increased to a maximum when the DC-DC converter is started, and an abnormality in one current sensor can be reliably determined based on whether an inrush current is detected by the current sensor when the DC-DC converter is started.

[0009] In the above aspect, the control unit may control the power conversion so that the inter-terminal voltage approaches the final target voltage when the terminal current is less than a predetermined rated current. In this case, power can be stably supplied to the load connected to the auxiliary battery.

[0010] In the above aspect, the control unit may control the power conversion so that the inter-terminal voltage decreases as the terminal current increases when the terminal current exceeds a predetermined rated current. In this case, it is possible to prevent excessive power from being supplied to a load connected to the auxiliary battery. Effect of the Invention

[0011] According to the present disclosure, it is possible to detect an abnormality in a current sensor while reducing the size. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a circuit diagram showing a schematic configuration of a DC-DC converter according to an embodiment. [Diagram 2] FIG. 2 is a graph showing the relationship between the output current and the output voltage in the DC-DC converter of FIG. [Diagram 3] FIG. 3 is a graph showing the time variations of the output voltage and the output current in the DC-DC converter of FIG. 1 in the initial operation mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, a DC-DC converter according to an embodiment will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicated descriptions will be omitted.

[0014] With reference to FIG. 1, a schematic configuration of a DCDC converter according to an embodiment will be described. FIG. 1 is a circuit diagram showing a schematic configuration of a DCDC converter according to an embodiment. The DCDC converter 1 shown in FIG. 1 is mounted on an electric vehicle such as a hybrid vehicle (HV) or an electric vehicle (EV), and is a device that performs power conversion between a DC voltage input to a terminal HBT on the high-voltage battery side to which a high-voltage battery HB is connected and a DC voltage output to a terminal LBT on the low-voltage battery side to which an auxiliary battery LB is connected. The DCDC converter 1 includes a conversion unit 4, a current sensor 5, two voltage sensors 6 and 7, and a control unit 8. The conversion unit 4 is connected to both ends of the high-voltage battery HB and both ends of the auxiliary battery LB, and converts power between the DC power of the high-voltage battery HB and the DC power of the auxiliary battery. A specific connection relationship will be described below.

[0015] The vehicle capacitor 3 is connected across the high voltage battery HB via the switch 2. The switch 2 turns on / off the connection between the high voltage battery HB and the vehicle capacitor 3 and the conversion unit 4.

[0016] The conversion unit 4 includes a transformer 11 having a primary winding 11A and a secondary winding 11B, a first transistor 12, a second transistor 13, a third transistor 14, an inductor 15, and a capacitor 16.

[0017] The first transistor 12 is a switching element such as a field effect transistor (FET) that is turned on / off by a control signal provided from the control unit 8. The drain of the first transistor 12 is connected to one end of the primary winding 11A, and the source is connected to the negative electrode of the high-voltage battery HB. The other end of the primary winding 11A of the transformer 11 is connected to the positive electrode of the high-voltage battery HB via the switch 2. The first transistor 12 periodically turns on and off the DC voltage input from the high-voltage battery HB, generating an AC voltage across the primary winding 11A.

[0018] The second transistor 13 and the third transistor 14 constitute a synchronous rectifier circuit, and are switching elements such as FETs that are turned on / off by a control signal provided from the control unit 8. The second transistor 13 has a drain connected to one end of the secondary winding 11B of the transformer 11, and a source connected to the negative electrode of the auxiliary battery LB. The third transistor 14 has a drain connected to the other end of the secondary winding 11B, and a source connected to the negative electrode of the auxiliary battery LB and the source of the second transistor 13. The synchronous rectifier circuit constituted by the second transistor 13 and the third transistor 14 has a function of rectifying the secondary current output from the secondary winding 11B.

[0019] The inductor 15 and the capacitor 16 configure a smoothing circuit. The inductor 15 is connected between the drain of the third transistor 14 and the positive electrode of the auxiliary battery LB. One end of the capacitor 16 is connected to the drain of the third transistor 14 via the inductor 15, and the other end is connected to the source of the third transistor 14. The capacitor 16 is also connected between the positive electrode and the negative electrode of the auxiliary battery LB. This smoothing circuit smoothes the secondary current output from the synchronous rectification circuit formed by the second transistor 13 and the third transistor 14, and outputs a DC voltage according to the on / off duty ratio of the first transistor 12 to the auxiliary battery LB.

[0020] When the switch 2 is turned on, the converter 4 steps down the DC voltage input from the high-voltage battery HB and outputs the DC voltage to the auxiliary battery LB. That is, the first transistor 12 periodically performs chopper control, so that a primary current flows through the primary winding 11A and a secondary current flows through the secondary winding 11B. The secondary current is rectified by a synchronous rectifier circuit including a second transistor 13 and a third transistor 14, and smoothed by a smoothing circuit including an inductor 15 and a capacitor 16. As a result, a DC voltage is output from both ends of the capacitor 16. Similarly, the converter 4 can also perform a pre-charge operation in which the converter 4 boosts the DC voltage of the auxiliary battery LB and outputs the boosted DC voltage to both ends of the vehicle capacitor 3 while the switch 2 is turned off before the start of the DCDC converter 1.

[0021] The voltage sensor 6 and the voltage sensor 7 are sensors that detect the input DC voltage and the output DC voltage in the conversion unit 4 and notify the control unit 8 of the detection result. The voltage sensor 6 is connected to the high-voltage side terminal of the vehicle capacitor 3 and detects the terminal-to-terminal voltage of the vehicle capacitor 3. The voltage sensor 7 is connected to the positive electrode of the auxiliary battery LB and detects the terminal-to-terminal voltage on the auxiliary battery LB side, i.e., the DC voltage output from the DC-DC converter 1 to the auxiliary battery LB.

[0022] The current sensor 5 is a sensor that detects a terminal current on the auxiliary battery LB side and notifies the control unit 8 of the detection result. The current sensor 5 is connected between the positive electrode of the auxiliary battery LB and the inductor 15.

[0023] The control unit 8 is a device that controls the power conversion in the conversion unit 4. The control unit 8 is an electronic control unit composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. For example, a program stored in the ROM is loaded onto the RAM and executed by the CPU, thereby realizing the function of the control unit 8. That is, the control unit 8 applies control signals to the gate of the first transistor 12, the gate of the second transistor 13, and the gate of the third transistor 14, respectively, thereby controlling the on / off of the first transistor 12, the second transistor 13, and the third transistor 14, thereby controlling the power conversion.

[0024] The functions of the control unit 8 will be described in detail below.

[0025] The control unit 8 adjusts the duty ratio of the first transistor 12 based on the terminal current detected by the current sensor 5 and the DC voltage detected by the voltage sensor 6 or the voltage sensor 7. At this time, the control unit 8 controls so that the on-period of the first transistor 12 is synchronized with the on-period of the second transistor 13, and the on-period of the first transistor is synchronized with the off-period of the third transistor 14. Specifically, when outputting a DC voltage to the auxiliary battery LB, the control unit 8 controls the power conversion in the following three modes (constant voltage operation mode, current limit operation mode, light load operation mode) according to the current value of the terminal current detected by the current sensor 5 and the DC voltage detected by the voltage sensor 7.

[0026] That is, when the terminal current is less than a predetermined rated current, the control unit 8 feedback-controls the duty ratio of the first transistor 12 so that the DC voltage detected by the voltage sensor 7 approaches the target voltage (constant voltage operation mode). The value of the rated current and the value of the target voltage are set by a host ECU (Electronic Control Unit) capable of communicating with the control unit 8 and stored in the control unit 8. Also, when the terminal current is equal to or greater than the predetermined rated current, the control unit 8 feedback-controls the duty ratio of the first transistor 12 so that the DC voltage detected by the voltage sensor 7 decreases as the terminal current increases (current limiting operation mode). This prevents excessive power from being supplied to the auxiliary battery LB.

[0027] On the other hand, when the terminal current is less than a minimum current value (e.g., 0.1 A) close to 0 A that is smaller than a predetermined rated current, the control unit 8 controls the first transistor 12 to switch intermittently (e.g., to stop switching alternately periodically) (light load operation mode). In this case, the control unit 8 may control the first transistor 12 in the light load operation mode when the duty ratio of the first transistor 12 is set to the minimum value and the DC voltage detected by the voltage sensor 7 exceeds the target voltage. As a result, even if the power consumption of the load on the auxiliary battery LB side is low and there is no problem even if the DCDC converter 1 is stopped, the operation of the DCDC converter 1 is continued, so that power can be smoothly supplied without restarting the DCDC converter 1 when the power consumption increases.

[0028] 2 is a graph showing the relationship between the output current and the output voltage in the DC-DC converter 1. By controlling the three modes by the control unit 8, when the output current, which is the terminal current on the auxiliary battery LB side, is equal to or greater than the minimum current and less than the rated current, the output voltage is set to be constant at the target voltage. On the other hand, when the output current is equal to or greater than the rated current, the output voltage is set to decrease linearly from the target voltage as the output current increases. When the output current is less than the minimum current, an excessive increase in the output voltage is suppressed by intermittent switching operation.

[0029] Moreover, when the control unit 8 starts the DCDC converter 1 (when the control unit 8 starts the control operation of the power conversion), the control unit 8 controls the power conversion in the initial operation mode. In detail, the control unit 8 feedback-controls the duty ratio of the first transistor 12 in the same manner as the above three modes so that the DC voltage detected by the voltage sensor 7 gradually increases within a predetermined period after the start-up and approaches the primary target voltage. Then, the control unit 8 feedback-controls the duty ratio of the first transistor 12 in the same manner as the above three modes so that the DC voltage detected by the voltage sensor 7 approaches the final target voltage after the above predetermined period has elapsed. The value of the primary target voltage and the value of the final target are set by a higher-level ECU and stored in the control unit 8, and the value of the primary target voltage is higher than the value of the final target voltage. It is preferable that the value of the primary target voltage is set to the value of the maximum voltage that the conversion unit 4 can output to the auxiliary battery LB. The value of the final target voltage may be the same value as the value of the target voltage referred to in the above constant voltage operation mode and the above current limiting operation mode.

[0030] FIG. 3 is a graph showing the time change of the output voltage and the output current in the initial operation mode in the DCDC converter 1. During operation in the initial operation mode, the output voltage is set to rise linearly from the initial voltage of the auxiliary battery LB to the primary target voltage in a predetermined period after the DCDC converter 1 is started. After the predetermined period has elapsed, the output voltage is set to approach the final target voltage. In this way, in the predetermined period after the start time, the output voltage temporarily rises to the primary target voltage higher than the final target voltage, so that an inrush current occurs in the output current (terminal current on the auxiliary battery LB side) of the DCDC converter 1. By utilizing this property, the control unit 8 can determine the presence or absence of a failure of the current sensor 5 by determining the presence or absence of an inrush current in the terminal current detected by the current sensor 5 in the initial operation mode. In other words, the control unit 8 can distinguish between a decrease in the output current in the light load operation mode and a decrease in the output current detected when the current sensor 5 is broken. Furthermore, the control unit 8 can notify the ECU of the determination result.

[0031] In the DCDC converter 1 described above, power conversion is controlled based on the terminal current on the auxiliary battery LB side detected by one current sensor 5 during normal operation and the terminal voltage on the auxiliary battery LB side detected by the voltage sensor 7 so that the terminal voltage approaches the final target voltage. Then, when the DCDC converter 1 is started up, the terminal voltage is controlled to approach a primary target voltage higher than the final target voltage within a predetermined period, and the terminal voltage is controlled to approach the final target voltage after the predetermined period. This makes it possible to determine an abnormality in one current sensor 5 by whether or not an inrush current is detected in the current sensor 5 when the DCDC converter 1 is started up. Since an extra circuit element or another current sensor for detecting an abnormality in one current sensor 5 is not required, it is possible to detect an abnormality in the current sensor 5 while reducing the size.

[0032] In this embodiment, the primary target voltage may be the maximum voltage that the conversion unit 4 can output to the auxiliary battery LB. In this case, the terminal voltage on the auxiliary battery LB side can be increased to the maximum when the DCDC converter 1 is started, and an abnormality in one current sensor 5 can be reliably determined based on whether or not an inrush current is detected by the current sensor 5 when the DCDC converter 1 is started.

[0033] In this embodiment, when the terminal current on the auxiliary battery LB side is less than a predetermined rated current, the control unit 8 controls the power conversion so that the terminal voltage on the auxiliary battery LB side approaches the final target voltage. In this case, power can be stably supplied to the load connected to the auxiliary battery LB.

[0034] In this embodiment, the control unit 8 controls the power conversion so that the terminal voltage on the auxiliary battery LB side decreases as the terminal current on the auxiliary battery LB side increases when the terminal current on the auxiliary battery LB side is equal to or greater than a predetermined rated current. In this case, it is possible to prevent excessive power from being supplied to the load connected to the auxiliary battery LB.

[0035] Although one embodiment of the present disclosure has been described in detail above, the DC-DC converter according to the present disclosure is not limited to the above embodiment.

[0036] The current sensor 5 in this embodiment is connected to detect the terminal current on the auxiliary battery LB side, but may be connected to detect the terminal current on the high-voltage battery HB side. For example, the current sensor 5 may be connected to the terminal of the switch 2, the terminal of the vehicle capacitor 3, or the terminal of the primary winding 11A. In this case, the control unit 8 controls the power conversion of the conversion unit 4 based on the value of the terminal current on the high-voltage battery HB side detected by the current sensor 5. The current sensor 5 may be a sensor such as a current transformer. In this case, the control unit 8 can determine whether or not the current sensor 5 has a failure by determining whether or not an inrush current occurs in the terminal current detected by the current sensor 5 in the initial operation mode.

[0037] In the present embodiment, the DC-DC converter 1 is of a transformer-insulated type, but may be of a non-insulated type. Also, a so-called forward converter is shown, but may be of another type. [Explanation of symbols]

[0038] 1...DCDC converter, 2...switch, 3...vehicle capacitor, 4...conversion unit, 5...current sensor, 6, 7...voltage sensor, 8...control unit, 11...transformer, 11A...primary winding, 11B...secondary winding, 12, 13, 14...transistor, 15...inductor, 16...capacitor, HB...high voltage battery, LB...auxiliary battery, HBT...terminal on the high voltage battery side, LBT...terminal on the auxiliary battery side.

Claims

1. A DC-DC converter for an electric vehicle that performs power conversion between a high-voltage battery and an auxiliary battery, a conversion unit that performs power conversion between the high voltage battery and the auxiliary battery; A current sensor for detecting a terminal current on a high voltage battery side or a terminal current on an auxiliary battery side; a voltage sensor for detecting a terminal voltage on the auxiliary battery side; a control unit that controls power conversion in the conversion unit based on the terminal current detected by the current sensor and the inter-terminal voltage detected by the voltage sensor so that the inter-terminal voltage approaches a final target voltage, The control unit controls the power conversion at the time of startup of the DC-DC converter so that the inter-terminal voltage approaches a primary target voltage higher than the final target voltage within a predetermined period of time, and controls the power conversion after the predetermined period of time so that the inter-terminal voltage approaches the final target voltage.

2. The DC-DC converter according to claim 1 , wherein the primary target voltage is a maximum voltage that the conversion unit can output to the auxiliary battery.

3. The DC-DC converter according to claim 1 , wherein the control unit controls the power conversion so that the inter-terminal voltage approaches the final target voltage when the terminal current is less than a predetermined rated current.

4. The DC-DC converter according to any one of claims 1 to 3, wherein the control unit controls the power conversion so that, when the terminal current exceeds a predetermined rated current, the inter-terminal voltage decreases as the terminal current increases.

Images