DC-DC converter

Abstract

To provide a DC-DC converter capable of more accurately determining a disconnection on an output terminal side.SOLUTION: A DC-DC converter 1 for electric vehicles performs power conversion between a high-voltage battery HB and an auxiliary battery LB, and includes: a conversion unit 4 performing power conversion between a high-voltage battery HB and an auxiliary battery LB; a voltage sensor 7 detecting a voltage between terminals of output terminals on the auxiliary battery LB side; and a control section 8 controlling power conversion at the conversion unit 4 based on the voltage between terminals detected by the voltage sensor 7. When a terminal current at the output terminal drops, the control section 8 controls the power conversion in a light load operation mode to suppress a rise in the voltage between terminals, and when the light load operation mode continues for a specific time, specifies the voltage between terminals detected by the current sensor 7 after the stop of a control of the power conversion, and determines the presence or absence of a disconnection between the conversion unit 4 and the auxiliary battery LB based on the voltage between terminals.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 a DC-DC converter that converts the power supplied from a main battery and outputs it to an electric load and a sub-battery as a power storage device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-100171 A Summary of the Invention [Problem to be solved by the invention]

[0004] The DC-DC converter described in the above Patent Document 1 includes a current sensor that detects the output current output from the output terminal of the DC-DC converter, and determines that a disconnection has occurred when the output current detected by the current sensor does not rise to an abnormality determination value. In this type of determination, depending on the state of the load or battery connected to the output terminal of the DC-DC converter, there are cases where a disconnection cannot be accurately determined.

[0005] The present disclosure describes a DC-DC converter that can more accurately determine an open circuit on the output terminal side. [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, a voltage sensor that detects the inter-terminal voltage of an output terminal on the auxiliary battery side, and a control unit that controls power conversion in the conversion unit based on the inter-terminal voltage detected by the voltage sensor.The control unit controls power conversion in a light-load operation mode that suppresses an increase in the inter-terminal voltage when the terminal current of the output terminal decreases, and when the light-load operation mode continues for a certain period of time, identifies the inter-terminal voltage detected by the voltage sensor after stopping control of the power conversion, and determines whether or not there is a break in the connection between the conversion unit and the auxiliary battery based on the inter-terminal voltage.

[0007] In this DC-DC converter, the control unit controls the conversion of the power output from the high-voltage battery based on the terminal voltage detected by the voltage sensor, and the converted power is output to the auxiliary battery. When the terminal current of the output terminal decreases, the control unit controls the power conversion in a light-load operation mode, and when the light-load operation mode continues for a certain period of time, the control unit judges whether or not there is a disconnection between the conversion unit and the auxiliary battery based on the terminal voltage specified after stopping the control of the power conversion. By operating in this manner, it is possible to distinguish between the phenomenon of a decrease in the terminal current in the light-load operation mode and the phenomenon of the interruption of the terminal current due to a disconnection based on the terminal voltage, and it is possible to more accurately judge the disconnection on the output terminal side.

[0008] In the above aspect, the control unit may control the power conversion by periodically switching a switching element included in the conversion unit, and may perform the switching intermittently in the light-load operation mode. In this case, when the terminal current of the output terminal decreases, the control unit can continue to control the power conversion while efficiently suppressing an increase in the terminal voltage in the light-load operation mode. As a result, when the terminal current increases again, the terminal voltage can be instantly stabilized.

[0009] In the above aspect, when the control unit determines that there is a disconnection after the control of the power conversion is stopped, the control unit may continue to stop the control of the power conversion. In this case, it is possible to prevent unnecessary power consumption in the DC-DC converter when the disconnection occurs on the output terminal side. Effect of the Invention

[0010] According to the present disclosure, it is possible to more accurately determine whether a wire is broken on the output terminal side. [Brief description of the drawings]

[0011] [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, output current, and switching state in the DC-DC converter of FIG. 1 in the light load operation mode. [Figure 4] FIG. 4 is a graph showing the time variations of the output voltage, output current, and switching state in the DC-DC converter of FIG. 1 in the light load operation mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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.

[0013] A schematic configuration of a DCDC converter according to an embodiment will be described with reference to FIG. 1. 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 an input terminal HBT on the step-down battery side to which a high-voltage battery HB is connected and a DC voltage output to an output 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] The inductor 15 and the capacitor 16 constitute 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. Both ends of the capacitor 16 form the output terminals of the conversion unit 4. 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.

[0019] 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 (output terminals) of the capacitor 16 connected to the auxiliary battery LB. Similarly, the converter 4 can also perform a pre-charge operation in which, before the start of the DCDC converter 1, 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 with the switch 2 turned off.

[0020] 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, that is, the DC voltage (terminal-to-terminal voltage) between the output terminals output from the DC-DC converter 1 to the auxiliary battery LB.

[0021] The current sensor 5 is a sensor that detects a terminal current at the output terminal 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.

[0022] 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 (switching) of the first transistor 12, the second transistor 13, and the third transistor 14, thereby controlling the power conversion.

[0023] The functions of the control unit 8 will be described in detail below.

[0024] The control unit 8 executes control such that the first transistor 12 periodically switches 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, and adjusts the on / off duty ratio of the first transistor 12 each time. At this time, the control unit 8 controls such 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.

[0025] 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.

[0026] On the other hand, when the terminal current drops to 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 be switched intermittently (e.g., to stop switching alternately periodically) to suppress an increase in the DC voltage between the output terminals (light load operation mode). In this case, the control unit 8 may control in the light load operation mode when the duty ratio of the first transistor 12 is set to the minimum value but 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.

[0027] 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.

[0028] In addition, when the control unit 8 is executing the control of power conversion in the light-load operation mode, the control unit 8 also executes a process of determining whether or not there is a disconnection between the conversion unit 4 and the auxiliary battery LB (disconnection determination process) as described below. That is, when the control of power conversion in the light-load operation mode continues for a certain period of time, the control unit 8 specifies the DC voltage detected by the voltage sensor 7 after stopping the control of power conversion, i.e., the intermittent switching of the first to third transistors 12 to 14. Then, when the specified DC voltage drops to a minimum voltage close to 0V or less, the control unit 8 determines that there is a disconnection between the output terminal of the conversion unit 4 and the auxiliary battery LB. On the other hand, when the specified DC voltage exceeds the minimum voltage, the control unit 8 determines that there is no disconnection between the output terminal of the conversion unit 4 and the auxiliary battery LB. Thereafter, when the control unit 8 determines that there is no disconnection, it resumes the control of power conversion in the light-load operation mode, and when it determines that there is a disconnection, it continues to stop the control of power conversion in the light-load operation mode.

[0029] 3 and 4 are graphs showing the time variations of the output voltage, output current, and switching state in the light load operation mode of the DC-DC converter 1. Fig. 3 is a graph showing the time variations of each value when no disconnection occurs on the output terminal side, and Fig. 4 is a graph showing the time variations of each value when a disconnection occurs on the output terminal side.

[0030] As shown in FIG. 3, when the control of power conversion in the light-load operation mode is being executed, the first to third transistors 12 to 14 are intermittently turned on / off, so that the output current of the conversion unit 4 drops to near zero while the output voltage is maintained near the target voltage. When the light-load operation mode continues for a certain period of time, the control of power conversion is stopped, and the intermittent switching of the first to third transistors 12 to 14 is stopped. As a result, the output voltage drops from a voltage near the target voltage. If no break occurs on the output terminal side, the output voltage drops to the voltage across the auxiliary battery LB. By utilizing this property, the control unit 8 can determine that there is no break on the output terminal side by detecting that the output voltage exceeds a minimum voltage close to 0V. Thereafter, the control unit 8 resumes the control of power conversion in the light-load operation mode. On the other hand, as shown in FIG. 4, if a break occurs on the output terminal side, the output voltage drops to a voltage close to 0V after the control of power conversion is stopped. By utilizing this property, the control unit 8 can determine that there is a break on the output terminal side by detecting that the output voltage is less than a minimum voltage close to 0V. In this case, the control unit 8 continues to suspend the control of power conversion in the light load operation mode.

[0031] By performing this type of disconnection determination process, the control unit 8 can distinguish between a decrease in output current in the light load operation mode and a decrease in output current due to a disconnection on the output terminal side. Furthermore, the control unit 8 can notify the ECU of the result of the disconnection determination process.

[0032] In the DC-DC converter 1 described above, the control unit 8 controls the conversion of the power output from the high-voltage battery HB based on the terminal voltage detected by the voltage sensor 7 during normal operation, and the converted power is output to the auxiliary battery LB. Then, when the terminal current of the output terminal drops, the control unit 8 controls the power conversion in a light-load operation mode, and when the light-load operation mode continues for a certain period of time, the control unit 8 judges whether or not there is a disconnection between the conversion unit 4 and the auxiliary battery LB based on the terminal voltage specified after stopping the control of the power conversion. By operating in this manner, it is possible to distinguish between the phenomenon of a drop in the terminal current in the light-load operation mode and the phenomenon of the interruption of the terminal current due to a disconnection based on the terminal voltage, and it is possible to more accurately judge the disconnection on the output terminal side. In addition, the DC-DC converter 1 itself can judge the disconnection, and autonomous disconnection detection is possible.

[0033] In this embodiment, the control unit 8 controls the power conversion by periodically switching the first to third transistors 12 to 14 (switching elements) included in the conversion unit 4, and may perform the switching intermittently in the light-load operation mode. In this case, when the terminal current of the output terminal decreases, the control unit 8 can continue to control the power conversion while efficiently suppressing an increase in the inter-terminal voltage in the light-load operation mode. As a result, when the terminal current increases again, the inter-terminal voltage can be instantly stabilized.

[0034] In this embodiment, if the control unit 8 determines that a disconnection occurs after the control of the power conversion is stopped, the control unit 8 may continue to stop the control of the power conversion. In this case, it is possible to prevent unnecessary power consumption in the DC-DC converter 1 when a disconnection occurs on the output terminal side.

[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 circuit configuration of the conversion unit 4 is not limited to the configuration of a forward converter, and may be the configuration of a flyback converter. In addition, the conversion unit 4 is not limited to an insulating converter, and may be a non-insulating converter. [Explanation of symbols]

[0037] 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, LBT...output terminal.

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 voltage sensor for detecting a terminal-to-terminal voltage of an output terminal on the auxiliary battery side; a control unit that controls power conversion in the conversion unit based on the inter-terminal voltage detected by the voltage sensor, The control unit controls the power conversion in a light-load operation mode that suppresses an increase in the inter-terminal voltage when a terminal current of the output terminal decreases, and when the light-load operation mode continues for a certain period of time, identifies the inter-terminal voltage detected by the voltage sensor after stopping control of the power conversion, and determines whether or not there is a disconnection between the conversion unit and the auxiliary battery based on the inter-terminal voltage.

2. 2. The DC-DC converter according to claim 1, wherein the control unit controls the power conversion by periodic switching of a switching element included in the conversion unit, and performs the switching intermittently in the light load operation mode.

3. The DC-DC converter according to claim 1 , wherein the control unit, when determining that the disconnection occurs after the control of the power conversion is stopped, continues to stop the control of the power conversion.

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