Power supply system for automobile

Abstract

To provide a power supply system for an automobile which can improve durability of a relay for connecting a capacitor precharged by an auxiliary power supply with a main power supply.SOLUTION: A power supply system for an automobile comprises: a power supply; a capacitor connected to an output side of a positive electrode relay and an output side of a negative electrode relay; an auxiliary power supply which precharges the capacitor; a power supply voltage sensor which detects a power supply voltage as a voltage of the power supply; and a capacitor voltage sensor which detects a capacitor voltage as a voltage of the capacitor. The power supply system includes: setting a voltage value obtained by adding a detection error of the capacitor voltage sensor based on temperature characteristics of the capacitor voltage sensor to the power supply voltage detected by the power supply voltage sensor as a precharge target voltage (step S3); and switching the positive electrode relay and the negative electrode relay to a conduction state (step S6) when a difference between the precharge target voltage and the capacitor voltage detected by the capacitor voltage sensor becomes a predetermined difference or less (Yes in step S5).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an automotive power supply system that electrically connects and disconnects a power supply and an electrical device by means of a relay.

Background Art

[0002] Patent Document 1 describes a control device for an electric circuit including a positive electrode side contactor that conducts the positive electrode side of a power supply and an electrical device, a negative electrode side contactor that conducts the negative electrode side of the power supply and the electrical device, a resistance part for current control, and a precharge contactor connected in series to the resistance part, and a precharge circuit connected in parallel to the negative electrode side contactor, and a smoothing capacitor that suppresses fluctuations in the voltage of a part on the electrical device side from the positive electrode side contactor and the negative electrode side contactor. This control device is configured to precharge the capacitor by conducting the precharge contactor, and to switch the negative electrode side contactor to a conductive state when the difference (voltage difference) between the power supply voltage and the capacitor voltage becomes equal to or less than a threshold value. Further, since there are detection errors in such power supply voltage and capacitor voltage, the control device described in Patent Document 1 switches the negative electrode side contactor to a conductive state after a predetermined time has elapsed after the voltage difference at which the negative electrode side contactor can be in a conductive state becomes equal to or less than a threshold voltage obtained by adding the maximum value of the detection error of the power supply voltage and the maximum value of the detection error of the capacitor voltage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the electric circuit described in Patent Document 1, since the resistance part is connected in series to the pre-charge contactor, the current flowing when the pre-charge contactor is switched to the conducting state can be reduced, and it is possible to suppress a decrease in the durability of the pre-charge contactor. However, when such a pre-charge circuit is provided, the electric circuit becomes larger in size, and it is necessary to switch between the pre-charge contactor and the negative-side contactor, which may complicate the control.

[0005] Also, in order to pre-charge the capacitor without providing a pre-charge circuit, the capacitor can be pre-charged from a relatively low-voltage auxiliary power supply. However, when such a configuration is adopted, the allowable voltage difference that allows connecting the high-voltage power supply and the capacitor becomes smaller than when a pre-charge circuit is provided. Therefore, even if the contactor is connected based on the maximum value of the detection error of the capacitor voltage as described in Patent Document 1, a large current may flow when the contactor is brought into the conducting state, and the durability of the contactor may decrease. Further, when the contactor is connected based on the elapsed time after the voltage difference becomes equal to or less than a predetermined difference in consideration of such a detection error, it takes time until the power supply and the electrical device are operated in the conducting state, and the control responsiveness of the electrical device and the like may decrease.

[0006] The present invention has been made paying attention to the above technical problems, and an object thereof is to provide an automotive power supply system capable of improving the durability of a relay that connects a capacitor pre-charged by an auxiliary power supply and a main power supply.

Means for Solving the Problems

[0007] In order to achieve the above object, the present invention provides a vehicle power supply system including a power source, an electrical device supplied with power from the power source or supplying power to the power source, a positive electrode wire connecting the positive electrode of the power source and the electrical device, a negative electrode wire connecting the negative electrode of the power source and the electrical device, a positive electrode relay capable of selectively interrupting the positive electrode wire, a negative electrode relay capable of selectively interrupting the negative electrode wire, a controller for controlling the positive electrode relay and the negative electrode relay, a capacitor connected to a portion of the positive electrode wire on the electrical device side relative to the positive electrode relay and a portion of the negative electrode wire on the electrical device side relative to the negative electrode relay, an auxiliary power source for precharging the capacitor, a power source voltage sensor for detecting a power source voltage which is the voltage of the power source, and a capacitor voltage sensor for detecting a capacitor voltage which is the voltage of the capacitor. The controller switches the positive electrode relay and the negative electrode relay to a conductive state when a difference between a voltage value obtained by adding a detection error of the capacitor voltage sensor based on the temperature characteristics of the capacitor voltage sensor to the power source voltage detected by the power source voltage sensor and the capacitor voltage detected by the capacitor voltage sensor is equal to or less than a predetermined difference.

Effect of the Invention

[0008] According to the present invention, when a difference between a voltage value obtained by adding a detection error of the capacitor voltage sensor based on the temperature characteristics of the capacitor voltage sensor to the detected power source voltage and the detected capacitor voltage is equal to or less than a predetermined difference, the positive electrode relay and the negative electrode relay are switched to a conductive state. That is, a precharge target voltage for charging the capacitor is set to a voltage value considering the detection error of the capacitor voltage sensor. Therefore, even when the temperature of the capacitor voltage sensor fluctuates and a detection error occurs, an increase in the difference between the actual capacitor voltage and the power source voltage at the time of switching the positive electrode relay and the negative electrode relay to a conductive state can be suppressed. As a result, when the positive electrode relay and the negative electrode relay are switched to a conductive state, a large current flowing through the positive electrode relay and the negative electrode relay can be suppressed, so that the durability of the positive electrode relay and the negative electrode relay can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

[0010] The present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples when the present invention is embodied, and do not limit the present invention.

[0011] FIG. 1 schematically shows an electrical circuit diagram for explaining an example of an automotive power supply system according to an embodiment of the present invention. The power supply system shown in FIG. 1 is configured to supply power to a motor generator (not shown) as a driving power source of a vehicle and to charge the power generated by the motor generator. It includes a power storage device 1 as a power source for exchanging power with the motor generator. This motor generator corresponds to the "electrical device" in the embodiment of the present invention.

[0012] This power storage device 1 can be configured in the same manner as a power storage device provided as a driving power source for conventional electric vehicles and hybrid vehicles. That is, it can be configured by a secondary battery such as a lithium-ion battery, a capacitor, or an all-solid-state battery. Note that the power storage device 1 may be configured by a battery pack in which a plurality of secondary batteries are connected in series.

[0013] A power control unit (hereinafter referred to as PCU) 2 is connected to the power storage device 1. That is, a driving positive electrode wire 3 connected to the positive electrode of the power storage device 1 and a driving negative electrode wire 4 connected to the negative electrode of the power storage device 1 are connected to the PCU 2. This PCU 2 includes a converter 5 for changing the voltage input to the motor generator, a relatively large-capacity capacitor 6, and an inverter (not shown) that converts the DC power charged in the power storage device 1 into AC power and outputs it to the motor generator, or converts the AC power generated by the motor generator into DC power and outputs it to the power storage device 1.

[0014] The converter 5 shown in FIG. 1 is composed of a reactor 7 for suppressing current fluctuations and two switches 8, 9. One end of the reactor 7 is connected to the driving positive electrode wire 3. The other end of the reactor 7 is connected to the midpoint between the two switches 8, 9 connected in series. These switches 8, 9 are composed of insulated gate bipolar transistors (hereinafter referred to as IGBTs) 10, 11 and diodes 12, 13 that determine the direction of current flow of these IGBTs 10, 11. Each IGBT 10, 11 is PWM-controlled. By increasing the on-duty of the upper IGBT 10 in FIG. 1, the voltage on the output side of the converter 5 is decreased, and by increasing the on-duty of the lower IGBT 11 in FIG. 1, the voltage on the output side of the converter 5 is increased.

[0015] A positive electrode side system main relay (hereinafter referred to as SMRB) 14 that can selectively cut off the connection between the positive electrode of the power storage device 1 and the PCU 2 is provided on the driving positive electrode wire 3. Similarly, a negative electrode side system main relay (hereinafter referred to as SMRG) 15 that can selectively cut off the connection between the negative electrode of the power storage device 1 and the PCU 2 is provided on the driving negative electrode wire 4. This SMRB 14 corresponds to the "positive electrode relay" in the embodiment of the present invention, and the SMRG 15 corresponds to the "negative electrode relay" in the embodiment of the present invention.

[0016] These SMRB14 and SMRG15 are configured in the same way as conventional relays. For example, by energizing a solenoid (not shown), a movable member made of a magnetic material is moved by its electromagnetic force to close the contacts (to be in a conductive state). That is, by bringing SMRB14 and SMRG15 into a conductive state, the power storage device 1 and the PCU 2 are brought into a conductive state. Therefore, by controlling the PCU 2, it is configured such that desired power can be supplied to the motor generator.

[0017] In addition, smoothing capacitors 16 for suppressing fluctuations in the voltage input from the power storage device 1 to the PCU 2 are provided in the driving positive electrode wire 3 and the driving negative electrode wire 4. This capacitor 16 corresponds to the "capacitor" in the embodiment of the present invention and is connected to a portion between SMRB14 and the PCU 2 in the driving positive electrode wire 3 and a portion between SMRG15 and the PCU 2 in the driving negative electrode wire 4. Note that the capacitor 16 has a lower capacitance than the capacitor 6.

[0018] In the example shown in FIG. 1, an auxiliary power source 17 for charging the capacitor 16 is provided. This auxiliary power source 17 is a power source for supplying power to auxiliary devices (not shown) provided in the vehicle and has an output voltage lower than that of the power storage device 1.

[0019] The auxiliary power source 17, the driving positive electrode wire 3, and the driving negative electrode wire 4 are connected via a bidirectional DCDC converter 18. This bidirectional DCDC converter 18 can be configured in the same way as a conventional bidirectional DCDC converter. Therefore, by controlling the bidirectional DCDC converter 18, it is configured such that the output voltage of the auxiliary power source 17 can be boosted and applied to the capacitor 16.

[0020] In the example shown in FIG. 1, a VB sensor 19 for detecting the voltage of the power storage device 1 (power supply voltage), a VD sensor 20 for detecting the voltage of the capacitor 16 (capacitor voltage), a PCU temperature sensor 21 for detecting the temperature of the PCU 2, and a water temperature sensor 22 for detecting the temperature of the cooling water for cooling the PCU 2 and the power storage device 1 are provided. Note that the VB sensor 19 corresponds to the "power supply voltage sensor" in the embodiment of the present invention, and the VD sensor 20 corresponds to the "capacitor voltage sensor" in the embodiment of the present invention.

[0021] Based on the signals from the above-described VB sensor 19, VD sensor 20, PCU temperature sensor 21, and water temperature sensor 22, a controller (ECU) 23 for controlling the SMRB 14 and the SMRG 15 is provided.

[0022] This controller 23 can be configured in the same manner as the controller provided in a conventional vehicle, and is mainly configured by a microcomputer. Based on the signals input from the respective sensors 19, 20, 21, 22 and the arithmetic expressions and maps stored in advance, etc., it is configured to determine an output signal for switching the conduction state and the non-conduction state of the SMRB 14 and the SMRG 15.

[0023] FIG. 2 shows a flowchart for explaining an example of the control executed by the controller 23. The control example shown in FIG. 2 is executed when there is a request to switch the SMRB 14 and the SMRG 15 from the non-conduction state to the conduction state. In other words, it is executed when there is a request to operate the motor generator. In this control example, first, the power supply voltage value (VB) is acquired (step S1). That is, the signal of the VB sensor 19 is acquired.

[0024] Due to its characteristics, the VD sensor 20 has a detection error according to temperature. Therefore, following step S1, the detection error of the VD sensor 20 is estimated (step S2). Specifically, the temperature of the VD sensor 20 is estimated based on the signal input from the PCU temperature sensor 21 or the signal input from the water temperature sensor 22, and the detection error of the VD sensor 20 is estimated based on the estimated temperature and a predetermined temperature characteristic. Note that the detection error caused by the temperature of the VD sensor 20 can be obtained by, in advance through experiments, changing the temperature of the VD sensor 20 while applying a constant voltage to the VD sensor 20 and subtracting the applied voltage from the detection value of the VD sensor 20 at that time. In this way, the detection error is obtained for each temperature of the VD sensor 20, and the temperature characteristic data can be stored in the controller 23.

[0025] Next, a target voltage for precharging the capacitor 16 is set (step S3). Specifically, a voltage obtained by adding the detection error of the VD sensor 20 estimated in step S2 to the power supply voltage value detected by the VB sensor 19 is set as the target voltage. That is, when the detection error of the VD sensor 20 estimated in step S2 is a negative value, that is, when the detection value of the VD sensor 20 is smaller than the actual voltage value, a voltage value smaller than the detection error and smaller than the detection value of the VB sensor 19 is set as the target voltage value. When the detection error of the VD sensor 20 estimated in step S2 is a positive value, that is, when the detection value of the VD sensor 20 is larger than the actual voltage value, a voltage value larger than the detection error and larger than the detection value of the VB sensor 19 is set as the target voltage value.

[0026] Subsequently, based on the target voltage set in step S3, pre-charging is executed (step S4). That is, the bidirectional DCDC converter 18 is switched to the conducting state. Then, it is determined whether the voltage value (VD sensor value) detected by the VD sensor 20 has reached the pre-charge target voltage (step S5). Note that the magnitude of the current flowing when SMRB14 and SMRG15 are in the conducting state only needs to be equal to or less than a predetermined current value due to the characteristics of SMRB14 and SMRG15. Therefore, the VD sensor value and the pre-charge target voltage only need to be within the tolerance determined based on that current value.

[0027] If it is negatively determined in step S5 because the VD sensor value has not reached the pre-charge target voltage, the process returns to step S4. That is, pre-charging is continued. On the contrary, if it is positively determined in step S5 because the VD sensor value has reached the pre-charge target voltage, SMRB14 and SMRG15 are switched to the conducting state (ON) (step S6), and then a Ready ON signal is output (step S7), and this routine is terminated once.

[0028] FIG. 3 shows the actual voltage change of the capacitor 16 when the above control example is executed. The actual voltage change of the capacitor 16 when the detected value of the VB sensor 19 is used as the pre-charge target voltage is shown by a dashed line.

[0029] In the example shown in FIG. 3, the actual voltage of the capacitor 16 at time t0 is zero, and the control example shown in FIG. 2 is being executed due to a requirement to operate the motor generator at time t1, etc. Therefore, the precharge target voltage is set based on the power supply voltage VB and the detection error of the VD sensor 20, and precharge is executed toward that precharge target voltage. Therefore, in the example shown in FIG. 3, the actual voltage of the capacitor 16 starts to increase from time t1, and as the difference between the precharge target voltage and the detected value of the VD sensor 20 gradually decreases, the rate of change of the actual voltage value of the capacitor 16 decreases. This is because the bidirectional DCDC converter 18 is feedback-controlled based on the deviation between the precharge target voltage and the detected value of the VD sensor 20. In the example shown in FIG. 3, since the detection error of the VD sensor 20 estimated in step S2 is a negative value, the precharge target voltage is set to a voltage value that is smaller than the detected value of the VB sensor 19 by the detection error amount.

[0030] Then, at time t2, since the difference between the VD sensor value and the precharge target voltage becomes equal to or less than a predetermined difference and is positively determined in step S5, the SMRB 14 and the SMRG 15 are switched to the conductive state. As a result, since the power storage device 1 and the capacitor 16 are in a conductive state, the actual voltage value of the capacitor 16 is the same as the power supply voltage VB. Note that the difference between the VD sensor value and the precharge target voltage at time t2 is an error that inevitably occurs in control.

[0031] On the one hand, as shown by the dashed line in FIG. 3, when the detected value of the VB sensor 19 is used as the precharge target voltage, the detected value of the VD sensor 20 changes so as to trace the solid line shown in FIG. 3. On the other hand, as shown by the dashed line in FIG. 3, the actual voltage value increases at a value lower than the detected value by the detection error. Then, when the detected value of the VD sensor 20 coincides with the precharge target voltage at time t2, the SMRB14 and SMRG15 are switched to the conducting state. Therefore, since there is a large deviation between the actual voltage value of the capacitor 16 and the precharge target voltage at the time when the SMRB14 and SMRG15 are switched to the conducting state, a large current flows through the SMRB14 and SMRG15.

[0032] As described above, a voltage value obtained by adding the detection error based on the temperature characteristics of the VD sensor 20 to the power supply voltage detected by the VB sensor 19 is set as the precharge target voltage. When the difference between the precharge target voltage and the voltage value of the capacitor 16 detected by the VD sensor 20 becomes equal to or less than a predetermined difference, the SMRB14 and SMRG15 are switched to the conducting state. That is, the precharge target voltage for charging the capacitor 16 is set to a voltage value considering the detection error of the VD sensor 20. Therefore, even when the temperature of the VD sensor 20 fluctuates and a detection error occurs, it is possible to suppress an increase in the difference between the actual voltage of the capacitor 16 and the power supply voltage at the time when the SMRB14 and SMRG15 are switched to the conducting state. As a result, since it is possible to suppress a large current from flowing through the SMRB14 and SMRG15, the durability of the SMRB14 and SMRG15 can be improved. Consequently, it is possible to improve output performance such as outputting a large current from the power storage device 1 over a long period of time, and to reduce the frequency of component replacement in consideration of the life of the SMRB14 and SMRG15.

Description of Reference Numerals

[0033] 1 Power storage device 2 PCU 3 Positive drive electrode wire 4 Negative drive electrode wire 14 Positive electrode side system main relay (SMRB) 15 Negative electrode side system main relay (SMRG) 16 Capacitor 17 Auxiliary machine power supply 18 Bidirectional DCDC converter 19 VB sensor 20 VD sensor 21 PCU temperature sensor 22 Water temperature sensor 23 Controller

Claims

【Claim 1】 A vehicle power supply system comprising a power supply, an electrical device supplied with power from the power supply or supplying power to the power supply, a positive electrode wire connecting the positive electrode of the power supply and the electrical device, a negative electrode wire connecting the negative electrode of the power supply and the electrical device, a positive electrode relay capable of selectively interrupting the positive electrode wire, a negative electrode relay capable of selectively interrupting the negative electrode wire, a controller for controlling the positive electrode relay and the negative electrode relay, a capacitor connected to a portion of the positive electrode wire on the electrical device side of the positive electrode relay and a portion of the negative electrode wire on the electrical device side of the negative electrode relay, an auxiliary power supply for pre-charging the capacitor, a power supply voltage sensor for detecting a power supply voltage which is the voltage of the power supply, and a capacitor voltage sensor for detecting a capacitor voltage which is the voltage of the capacitor, wherein: the controller: switches the positive electrode relay and the negative electrode relay to a conductive state when a difference between a voltage value obtained by adding a detection error of the capacitor voltage sensor based on the temperature characteristics of the capacitor voltage sensor to the power supply voltage detected by the power supply voltage sensor and the capacitor voltage detected by the capacitor voltage sensor is equal to or less than a predetermined difference. A vehicle power supply system characterized by the above.

Images