Forced discharge control system for the smoothing capacitors in the inverter

Abstract

To improve the reliability of a forcible discharge control system for a smoothing capacitor provided in an inverter.SOLUTION: When a smoothing capacitor 42 is to be forcibly discharged, first discharge control is started in which an electric charge of the smoothing capacitor 42 is consumed by an on-vehicle component 12 via a DC-DC converter 50 while having a battery 20 disconnected from a high-voltage circuit 9. After that, when a voltage of the smoothing capacitor 42 decreases and reaches a predetermined threshold value V0, second discharge control is executed in which the smoothing capacitor is forcibly discharged by an active discharge circuit 61. If a continuous forcible discharge occurs, delay control for delaying an execution timing of the second discharge control is further executed.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The disclosed technology relates to a forced discharge control system for a smoothing capacitor included in an in-vehicle inverter.

Background Art

[0002] In vehicles such as electric vehicles and hybrid vehicles, the power of a high-voltage battery mounted thereon is controlled by an inverter and supplied to a motor. Thereby, the motor is driven to run. When the main switch of the vehicle is turned on, the high-voltage circuit to which the inverter and the battery are connected is in an energized state. And when the main switch of the vehicle is turned off, the battery is disconnected from the high-voltage circuit in order to cancel the energized state.

[0003] The inverter is provided with a smoothing capacitor for smoothing the current. When the inverter is in an energized state, a voltage is applied to the smoothing capacitor and it stores electric charges. Even when the battery is disconnected from the high-voltage circuit, electric charges remain in the smoothing capacitor, so the voltage of the inverter remains held.

[0004] Therefore, when the main switch of the vehicle is turned off, it is necessary to quickly discharge the electric charges of the smoothing capacitor, and the vehicle is provided with such forced discharge means. Not only when the main switch of the vehicle is turned off, but also in case of an abnormality such as a collision of the vehicle, it is required that the forced discharge means functions properly.

[0005] An example of control related to such forced discharge is disclosed in Patent Document 1. In the circuit of the inverter disclosed in Patent Document 1, a resistive forced discharge circuit (forced discharge unit) is provided.

[0006] In other words, two resistors (a first resistor with a high resistance value and a second resistor with a low resistance value) that discharge the charge from the smoothing capacitor are installed in the inverter's electrical circuit. Initially, the capacitor is discharged using only the first resistor, and once the voltage across the smoothing capacitor falls below a predetermined voltage value, the second resistor is also used to discharge it. This ensures that the charge from the smoothing capacitor is discharged quickly. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-205428 [Overview of the project] [Problems that the invention aims to solve]

[0008] As in the inverter described in Patent Document 1, discharging through a second resistor with low resistance can quickly reduce the voltage of the smoothing capacitor. However, a large current flows through the second resistor, causing it to heat up and its temperature to rise rapidly. Since the second resistor will be damaged if it rises above a predetermined temperature, the amount of current that can be discharged through the second resistor at one time is limited.

[0009] In this respect, the inverter in Patent Document 1 discharges at a voltage below a predetermined value in the second resistor, limiting the amount that can be discharged at once. However, in order to avoid damage to the second resistor, the voltage value must be set low. Since the first resistor is always connected, it is necessary to set a large resistance value so that almost no current flows through it under normal circumstances. Consequently, discharge through the first resistor takes time.

[0010] Furthermore, when the second resistor becomes hot, it takes time for its temperature to return to room temperature. Therefore, if discharge by the second resistor is repeated in a short period of time, the second resistor will be damaged as it discharges from a high temperature state. The circuit board will need to be replaced.

[0011] The disclosed technology eliminates these problems by utilizing devices other than inverters, thereby realizing a highly reliable forced discharge control system. [Means for solving the problem]

[0012] The disclosed technology relates to a forced discharge control system for smoothing capacitors.

[0013] The forced discharge system includes a drive battery mounted on the vehicle, a smoothing capacitor and an inverter including the forced discharge circuit therefor that controls the power supplied from the battery and outputs it to a drive motor, a step-down converter that steps down the voltage of the battery and supplies it to on-board low-voltage components, a high-voltage circuit that electrically connects the battery, the inverter, and the step-down converter, and a power switching means that can switch the battery between a state where it is connected to the high-voltage circuit and a state where it is disconnected from the high-voltage circuit.

[0014] The forced discharge circuit includes an active discharge circuit which includes a main resistor arranged in parallel with the smoothing capacitor and a current switching means that can switch the main resistor between a state where it is connected to the high-voltage circuit and a state where it is disconnected from the high-voltage circuit.

[0015] Furthermore, the forced discharge control system includes a control device that controls the step-down converter, the power supply switching means, and the energization switching means.

[0016] Then, when a predetermined forced discharge condition for forcibly discharging the smoothing capacitor is met, the control device starts a first discharge control, in which the battery is disconnected from the high-voltage circuit by the control of the power supply switching means, and the charge stored in the smoothing capacitor is consumed by the low-voltage component via the step-down converter.

[0017] Subsequently, when the voltage of the smoothing capacitor decreases and reaches a predetermined threshold, a second discharge control is performed by controlling the current switching means to forcibly discharge the charge of the smoothing capacitor using the active discharge circuit.

[0018] Furthermore, if a continuous forced discharge occurs before a predetermined time has elapsed, and the forced discharge conditions are met again, a delay control is executed to delay the execution timing of the second discharge control.

[0019] In other words, in this forced discharge system, a step-down converter is connected to the high-voltage circuit to which an inverter, which receives power from the drive battery and outputs high-voltage power to the motor, is connected. Furthermore, to quickly reduce the charge remaining in the smoothing capacitor of the inverter when the battery is disconnected from the high-voltage circuit, i.e., to force a discharge, the inverter is also equipped with a forced discharge circuit including a main resistor.

[0020] When a forced discharge situation arises, the control device utilizes not only the forced discharge circuit but also a buck converter. Specifically, it performs forced discharge by combining a first discharge control, which uses the buck converter to consume charge with low-voltage components, and a second discharge control, which uses the forced discharge circuit. Therefore, the charge of the smoothing capacitor can be rapidly reduced.

[0021] In this process, the first discharge control is initiated before the second discharge control. This reduces the amount of discharge in the active circuit, thereby suppressing the temperature rise of the main resistor. Consequently, damage to the main resistor can be suppressed.

[0022] However, the step-down converter stops working once a predetermined voltage is reached. Therefore, after that point, forced discharge by the active discharge circuit is the only option. A temperature rise in the main resistor is unavoidable. To quickly reduce the charge on the smoothing capacitor, it is preferable to make maximum use of forced discharge by the active discharge circuit.

[0023] In such a case, if repeated forced discharges are performed in a short period of time, the main resistor will be forced to discharge from a high-temperature state due to heat accumulation, resulting in damage. Therefore, in this forced discharge system, when continuous forced discharges occur, a delay control that delays the execution timing of the second discharge control is executed.

[0024] As a result, the time from the end of the previous forced discharge to the start of forced discharge by the active discharge circuit becomes longer. As a result, since repeated forced discharges in an extremely short time can be suppressed, excessive temperature rise of the main resistor can be avoided. Since the time for cooling the main resistor is extended, the temperature of the main resistor at the start of discharge can be lowered. Therefore, even when continuous forced discharges occur, damage to the main resistor can be suppressed, improving the reliability of the forced discharge system.

[0025] The forced discharge control system may also execute the delay control when the continuous forced discharges occur repeatedly a predetermined number of times or more.

[0026] It has been confirmed that as long as the temperature of the main resistor rises within a certain range, it will not be damaged. Therefore, if the number of times is less than a predetermined number, there is no problem even if continuous forced discharges occur repeatedly at short intervals. By not performing the delay control, the smoothing capacitor can be forced to discharge in a short time.

[0027] On the other hand, when the continuous forced discharges occur repeatedly a predetermined number of times or more, the delay control is executed. Thereby, excessive temperature rise of the main resistor can be reduced. Therefore, damage to the main resistor can be suppressed.

[0028] The forced discharge control system may also be such that when the control device detects an abnormality in the step-down converter, the second discharge control is executed before reaching the threshold value.

[0029] If the step-down converter is faulty, even if the first discharge control is performed, the charge of the smoothing capacitor cannot be dissipated by the low-voltage components. Therefore, the voltage of the smoothing capacitor cannot be quickly reduced to the threshold. On the other hand, if the second discharge control is performed before the threshold is reached, the active discharge circuit can quickly force the discharge of the charge from the smoothing capacitor.

[0030] Even if the step-down converter malfunctions, the smoothing capacitor can be forcibly discharged. Therefore, the reliability of the forced discharge system is improved.

[0031] If the inverter further includes a cooling mechanism that cools by circulating cooling water, the control device may execute the delay control when the temperature of the cooling water exceeds a predetermined upper limit or when it detects an abnormality in the cooling mechanism.

[0032] In such cases, the inverter becomes abnormally hot, so forced discharge begins while the main resistor is at a high temperature. Therefore, if forced discharge is performed as is, the main resistor will be damaged. On the other hand, if delay control is implemented in such cases, the temperature rise of the main resistor can be reduced. Therefore, damage to the main resistor can be suppressed.

[0033] Even if the cooling of the step-down converter is abnormal, the smoothing capacitor can be properly forced to discharge. Therefore, the reliability of the forced discharge system is improved.

[0034] The forced discharge control system may also further include a passive discharge circuit in which the forced discharge circuit is always connected in parallel with the smoothing capacitor and includes a sub-resistor with a resistance value greater than that of the main resistor.

[0035] This allows the smoothing capacitor to be discharged via a passive discharge circuit, albeit slowly, if forced discharge by an active discharge circuit becomes impossible due to some malfunction. Therefore, it functions as a fail-safe, further improving the reliability of the forced discharge system.

[0036] The forced discharge control system may also perform the first discharge control and the second discharge control in parallel by maintaining the first discharge control even after the voltage of the smoothing capacitor reaches the threshold.

[0037] This allows two forced discharges to occur in parallel, reducing the charge on the smoothing capacitor in a shorter time. It also reduces the discharge amount in the active discharge circuit, thus minimizing damage to the main resistor.

[0038] If the step-down converter is configured to operate at a predetermined operating limit voltage lower than the threshold voltage, the first discharge control may be terminated when the voltage of the smoothing capacitor reaches the operating limit voltage.

[0039] This way, the charge in the smoothing capacitor is discharged by the consumption of low-voltage components up to the limit where the step-down converter can be used, effectively reducing the amount of discharge in the active discharge circuit. Consequently, damage to the main resistor can be further suppressed.

[0040] The forced discharge control system is also particularly effective when the engine is located at the front of the vehicle and the drive motor is located in the tunnel section of the floor panel, connected to the rear of the engine.

[0041] Another method for forcibly discharging a smoothing capacitor is d-axis discharge using a motor. However, this method requires high-precision detection of the motor's rotation angle, and in the arrangement described above, there is a risk that the sensor may fail and forced discharge may become difficult if the vehicle collides with something.

[0042] In contrast, with forced discharge using an active discharge circuit, even if a vehicle with the aforementioned configuration is involved in a collision, forced discharge is possible as long as the inverter is not damaged. Therefore, it offers superior reliability. [Effects of the Invention]

[0043] According to the forced discharge control system applying the disclosed technology, a smoothing capacitor can be effectively forced discharged using a resistive forced discharge circuit without damaging the resistor. Therefore, the reliability of the forced discharge system can be improved. [Brief explanation of the drawing]

[0044] [Figure 1] This is a schematic diagram showing the structure of an automobile to which the disclosed technology is applied. [Figure 2] This is a schematic diagram showing the electrical circuits of major high-voltage electrical devices. [Figure 3] This is a block diagram of the PCM and its main peripheral devices related to forced discharge control. [Figure 4] This is an example of a time chart for combined forced discharge control under normal conditions. [Figure 5] This is an example of a flowchart for complex forced discharge control corresponding to Figure 4. [Figure 6] This is a flowchart following Figure 5. [Figure 7] This is a flowchart for controlling thermal degeneration. [Figure 8] This is an example of a time chart for combined forced discharge control during thermal degradation. [Figure 9] This is an example of a time chart for combined forced discharge control during thermal degradation. [Figure 10] This is an example of a flowchart for when a DC-DC converter malfunctions. [Figure 11] This is a flowchart following Figure 10. [Modes for carrying out the invention]

[0045] The following describes the technologies being disclosed. However, the following description is essentially illustrative.

[0046] <Vehicle> Figure 1 shows an example of a vehicle (automobile 1) to which the disclosed technology is applied. This automobile 1 is a hybrid vehicle capable of running using electricity. Automobile 1 may also be a so-called plug-in hybrid vehicle equipped with a power supply device that enables power supply from a predetermined external power source.

[0047] Automobile 1 is equipped with an engine 2 and a drive motor 3 as its power sources. These work together to drive the two rear wheels, thereby causing automobile 1 to move. In other words, automobile 1 can move using the output of either engine 2 or drive motor 3, or using the output of both drive motor 3 and engine 2.

[0048] In this automobile 1, the engine 2 is located at the front. That is, this automobile 1 is a so-called FR (front-engine, rear-wheel drive) vehicle. However, automobile 1 is not limited to FR vehicles; it may also be four-wheel drive.

[0049] Engine 2 is an internal combustion engine that uses gasoline as fuel for combustion. Engine 2 also generates rotational power by repeating the intake, compression, expansion, and exhaust cycles (a so-called four-stroke engine). Engine 2 can be of various types and forms, such as diesel engines, but the disclosed technology does not particularly limit the type or form of the engine.

[0050] In this automobile 1, the engine 2 is positioned approximately in the center of the engine compartment in the vehicle width direction, with its rotation axis (crankshaft) facing the front-to-rear direction of the vehicle body. The automobile 1 is equipped with various devices and mechanisms associated with the engine 2, such as an intake system, exhaust system, and fuel supply system, but their illustrations and explanations are omitted.

[0051] The drive motor 3 is a permanent magnet type synchronous motor driven by three-phase alternating current. The drive motor 3 is connected to the rear of the engine 2 via a clutch (not shown) with its rotation axis aligned. An automatic transmission 4 is connected to the rear of the drive motor 3 with its rotation axis aligned.

[0052] The automatic transmission 4 is a multi-speed automatic transmission (so-called AT). The automatic transmission 4 is connected to the differential gear 6 via a propeller shaft 5 that extends in the longitudinal direction of the vehicle body. Although not shown in the diagram, the floor panel covering the underside of the vehicle body has a tunnel section with an upward-curving U-shaped cross-section that extends from the engine compartment to the rear. In this automobile 1, the drive motor 3, automatic transmission 4, and propeller shaft 5 are located inside this tunnel section.

[0053] A pair of shafts 7,7 extend from the differential gear 6 to the left and right. Rear wheels are attached to each end of these shafts 7,7. As a result, the rotational power output from the engine 2 and drive motor 3 is shifted by the automatic transmission 4, then distributed to the left and right by the differential gear 6 and transmitted to each rear wheel.

[0054] In addition to the drive motor 3, the automobile 1 is equipped with high-voltage electrical devices such as a drive battery 20, a contactor 30 (power switching means), an inverter 40, and a DC-DC converter 50 (step-down converter). Each of these electrical devices is connected via a high-voltage circuit 9 consisting of cables and busbars that can handle high currents. The electrical circuits of these electrical devices will be described separately later.

[0055] This vehicle 1 is equipped with a high-voltage battery 20 with a rated voltage of 300V or more. Alternatively, it may be equipped with a battery with a rated voltage of around 50V (a so-called mild hybrid).

[0056] The battery 20 is connected to the high-voltage circuit 9 via the contactor 30. The contactor 30 switches the battery 20 between being connected to the high-voltage circuit 9 and being electrically and physically disconnected from the high-voltage circuit 9. When the contactor 30 switches to the connected state, power can be supplied from the battery 20 to the inverter 40 and the DC-DC converter 50.

[0057] The output side of the DC-DC converter 50 is connected to a low-voltage circuit 10, which consists of a low-voltage cable, CAN (Controller Area Network), etc. The DC-DC converter 50 steps down the 300V DC power supplied from the battery 20 to 12V DC power and outputs it to the low-voltage circuit 10.

[0058] The low-voltage circuit 10 is connected to on-board components 12 (low-voltage components), including a low-voltage battery 11 (a so-called lead-acid battery) with a rated voltage of approximately 12V. The on-board components 12 include, for example, various electrical equipment installed in the automobile 1, such as an air conditioner, an electric pump 14a (described later), and headlights, as well as control devices installed in the automobile 1. The DC power stepped down by the DC-DC converter 50 is supplied to these on-board components 12 via the low-voltage circuit 10.

[0059] Automobile 1 is equipped with a power control module (PCM) 13 as a control device. The PCM 13 comprehensively controls each component of the drive system installed in automobile 1, such as the engine 2, contactor 30, inverter 40, and DC-DC converter 50. For example, in the case of automobile 1, the control related to the forced discharge of the smoothing capacitor 42, which will be described later, is performed by the PCM 13.

[0060] The inverter 40 is a device that controls the operation of the drive motor 3 and is installed near the drive motor 3. The inverter 40 controls the DC power supplied from the battery 20 and outputs it to the drive motor 3. The drive motor 3, inverter 40, and DC-DC converter 50 each generate heat when in operation. Therefore, they are equipped with a water-cooled cooling system 14 (cooling mechanism).

[0061] The cooling system 14, as simplified in Figure 1, consists of an electric pump 14a, a cooling water path 14b, and a heat exchanger 14c that cools the cooling water by heat exchange with the outside air. When the electric pump 14a operates, the cooling water cooled by the heat exchanger 14c is circulated and supplied to the inverter 40, etc., via the cooling water path 14b, thereby cooling the inverter 40, etc.

[0062] <Electrical circuits of contactor 30, inverter 40, and DC-DC converter 50> Figure 2 shows a schematic diagram of the electrical circuits of the contactor 30, inverter 40, and DC-DC converter 50, which constitute the high-voltage electrical circuit.

[0063] (Contactor 30) The contactor 30 includes a main contactor 31 consisting of a positive contactor 31a and a negative contactor 31b, and a pre-charge contactor 32. The positive contactor 31a is connected to the positive terminal 20a of the battery 20. The negative contactor 31b is connected to the negative terminal 20b of the battery 20. The pre-charge contactor 32 is connected to the negative terminal 20b of the battery 20 in parallel with the negative contactor 31b, along with a predetermined pre-charge resistor 33.

[0064] The main contactor 31 switches between a state where the battery 20 is connected to the high-voltage circuit 9, and a state where it is electrically and physically disconnected from the high-voltage circuit 9. The main contactor 31 may also be configured with only one negative contactor 31b, omitting the positive contactor 31a. The pre-charge contactor 32 is installed to prevent welding of the main contactor 31 due to high current.

[0065] Specifically, after connecting the positive contactor 31a to the high-voltage circuit 9, and before connecting the negative contactor 31b to the high-voltage circuit 9, a pre-charge contactor 32 is connected to increase the voltage of the high-voltage circuit 9 with a small current. After this, connecting the negative contactor 31b suppresses the large current. The operation of such contactors 30 is controlled by the PCM 13.

[0066] In other words, when the PCM13 receives a request to turn on the main power of the vehicle 1, it controls the contactor 30 to connect the battery 20 to the high-voltage circuit 9. On the other hand, when the PCM13 receives a request to turn off the main power of the vehicle 1, it controls the contactor 30 to disconnect the battery 20 from the high-voltage circuit 9.

[0067] For example, when the ignition is turned on by key operation or the like, the PCM13 controls the contactor 30 in conjunction with it, connecting the battery 20 to the high-voltage circuit 9. Then, when the ignition is turned off, the PCM13 controls the contactor 30 to disconnect the battery 20 from the high-voltage circuit 9.

[0068] For example, if the automobile 1 has a function to remotely control the air conditioner, the PCM 13 controls the contactor 30 to connect the battery 20 to the high-voltage circuit 9 via that remote control. Then, when certain conditions are met, the PCM 13 controls the contactor 30 to disconnect the battery 20 from the high-voltage circuit 9.

[0069] For example, if vehicle 1 is a plug-in hybrid vehicle, the PCM 13 controls the contactor 30 to disconnect the battery 20 from the high-voltage circuit 9 when it starts supplying power from an external power source. Then, when power supply is finished, the PCM 13 controls the contactor 30 to connect the battery 20 back to the high-voltage circuit 9.

[0070] (Inverter 40) The inverter 40 includes a predetermined switching circuit 41 composed of multiple switching elements, a smoothing capacitor 42, a forced discharge circuit 60, and a voltmeter 43. The inverter 40 is provided with a positive terminal main wiring 44 connected to the positive terminal side of the high-voltage circuit 9 and a negative terminal main wiring 45 connected to the negative terminal side of the high-voltage circuit 9.

[0071] The switching circuit 41, smoothing capacitor 42, forced discharge circuit 60, and voltmeter 43 are each connected in parallel between the positive-side main wiring 44 and the negative-side main wiring 45. More specifically, the voltmeter 43, forced discharge circuit 60, smoothing capacitor 42, and switching circuit 41 are arranged in that order from the input side to the output side of the inverter 40. The switching circuit 41 is connected to the drive motor 3 via output wiring 46.

[0072] The operation of the inverter 40 is controlled by the PCM 13. That is, when the main power of the automobile 1 is on, the PCM 13 controls the switching circuit 41 according to the operating state of the automobile 1. In this way, the inverter 40 converts the DC power input from the high-voltage circuit 9 into three-phase AC power and outputs it to the drive motor 3.

[0073] The smoothing capacitor 42 smooths the DC power input to the inverter 40. That is, when the main power of the automobile 1 is turned on, the voltage of the battery 20 is applied to the smoothing capacitor 42. As a result, the smoothing capacitor 42 stores a charge corresponding to that voltage. The smoothing capacitor 42 discharges when the voltage drops and stores charge when the voltage rises. Therefore, the voltage between the positive terminal main wiring 44 and the negative terminal main wiring 45 is smoothed by the smoothing capacitor 42.

[0074] When the main power is cut off, the power supply from the battery 20 to the inverter 40 is interrupted. However, since charge remains in the smoothing capacitor 42, the high voltage between the positive terminal main wiring 44 and the negative terminal main wiring 45 is maintained by this residual charge. Therefore, the charge in the smoothing capacitor 42 needs to be discharged as quickly as possible. For this reason, the automobile 1 is equipped with a forced discharge circuit 60 in the inverter 40 as a means of forcibly discharging the smoothing capacitor 42.

[0075] One method for forcibly discharging a smoothing capacitor is to use a motor to dissipate its residual charge as heat (d-axis discharge). Specifically, a sensor such as a resolver detects the rotor's rotation angle, and the inverter is controlled so that the magnetic flux is directed in the d-axis direction where the motor does not rotate. In this state, current is supplied to the motor. This allows the residual charge to be dissipated by the heat generated by the stator coils without affecting the motor's operation.

[0076] However, in this vehicle 1, the drive motor 3 is connected to the rear of the engine 2, which is located at the front of the vehicle body. Furthermore, it is located inside a narrow tunnel section of the floor panel. Therefore, if vehicle 1 is involved in a frontal collision or the like, there is a risk that sensors such as resolvers attached to the drive motor 3 may malfunction.

[0077] This d-axis discharge method relies on detecting the rotor's rotation angle; therefore, in such cases, forced discharge of the smoothing capacitor is not possible. For this reason, a forced discharge circuit 60 is provided in this automobile 1.

[0078] The forced discharge circuit 60 includes an active discharge circuit 61 and a passive discharge circuit 62. The active discharge circuit 61 includes a main resistor 61a and a switch 61b (power supply switching means) arranged in parallel with the smoothing capacitor 42. The passive discharge circuit 62 includes a sub-resistor 62a that is always connected in parallel with the smoothing capacitor 42. The switch 61b switches the main resistor 61a either connected to the forced discharge circuit 60 or disconnected from the forced discharge circuit 60.

[0079] The main resistor 61a has low resistance (for example, between 50 ohms and 200 ohms) so that a relatively large current can flow through it. In contrast, the sub-resistor 62a has an extremely high resistance value (for example, between 100 kΩ and 200 kΩ) so that current cannot easily flow through it. The sub-resistor 62a has a resistance value at least 500 times greater than that of the main resistor 61a.

[0080] The voltmeter 43 measures the voltage input to the inverter 40, in other words, the voltage between the positive terminal main wiring 44 and the negative terminal main wiring 45 (corresponding to the voltage of the battery 20 or the high-voltage circuit 9), and outputs the measured data to the PCM 13.

[0081] The DCDC converter 50 has a second voltmeter 51, a load resistor 52, an output capacitor 53, a step-down circuit 54, and a transformer 55. The DCDC converter 50 is also provided with a second positive-side main wiring 56 connected to the positive side of the high-voltage circuit 9 similar to the inverter 40, and a second negative-side main wiring 57 connected to the negative side of the high-voltage circuit 9.

[0082] Each of the second voltmeter 51, the load resistor 52, the output capacitor 53, the step-down circuit 54, and the transformer 55 is connected in parallel between the second positive-side main wiring 56 and the second negative-side main wiring 57. Specifically, the second voltmeter 51, the load resistor 52, the output capacitor 53, the step-down circuit 54, and the transformer 55 are arranged in this order from the input side to the output side of the DCDC converter 50. The step-down circuit 54 is connected to the low-voltage circuit 10 via the transformer 55.

[0083] The operation of the DCDC converter 50 is controlled by the PCM 13. That is, in a state where the main power supply of the automobile 1 is on, the PCM 13 controls the step-down circuit 54 according to the driving state of the automobile 1. By doing so, the DCDC converter 50 steps down the DC power input from the high-voltage circuit 9 and outputs it to the low-voltage circuit 10.

[0084] The second voltmeter 51 measures the voltage between the second positive-side main wiring 56 and the second negative-side main wiring 57 (corresponding to the voltage of the battery 20 to the high-voltage circuit 9), and outputs the measurement data to the PCM 13.

[0085] <Forced Discharge Control by PCM13> Fig. 3 shows a block diagram of the PCM 13 and its main peripheral devices related to the forced discharge control. The PCM 13 inputs and outputs signals to and from the voltmeters 43, 51, the cooling system 14, the inverter 40, the contactor 30, the DCDC converter 50, etc. in relation to the forced discharge control. Note that the forced discharge system in the disclosed technology is composed of these electrical devices.

[0086] The PCM13 is equipped with a forced discharge control unit 13a as a functional component. Based on signals input from the voltmeter 43, cooling system 14, etc., the forced discharge control unit 13a outputs control signals to the inverter 40, contactor 30, DC-DC converter 50, etc. As a result, the PCM13 performs control to effectively and quickly force-discharge the residual charge of the smoothing capacitor 42.

[0087] In other words, the PCM13 performs a combined forced discharge control (combined forced discharge control) that utilizes the DC-DC converter 50 (first discharge control) and the inverter 40's active discharge circuit 61 (second discharge control). As a result, this forced discharge system is configured to effectively and quickly discharge the residual charge of the smoothing capacitor 42.

[0088] Specifically, when predetermined forced discharge conditions for forcibly discharging the smoothing capacitor 42 are met, the battery 20 is disconnected from the high-voltage circuit 9 by the control of the contactor 30, and control (first discharge control) is initiated to consume the charge stored in the smoothing capacitor 42 through the DC-DC converter 50 using the on-board components 12.

[0089] Subsequently, when the voltage across the smoothing capacitor 42 decreases and reaches a predetermined threshold, the switch 61b controls the active discharge circuit 61 to forcibly discharge the charge from the smoothing capacitor 42 (second discharge control).

[0090] The main resistor 61a of the active discharge circuit 61 has a small resistance value. Therefore, if the main resistor 61a is used to discharge the capacitor, the residual charge of the smoothing capacitor 42 will decrease rapidly, and its voltage can be lowered in a short time. However, in this case, a large current flows through the main resistor 61a, causing it to heat up and its temperature to rise rapidly. Since the main resistor 61a will be damaged if it rises above a predetermined temperature, the amount that can be discharged through the main resistor 61a at one time is actually limited.

[0091] Therefore, in order to quickly discharge the residual charge of the smoothing capacitor 42, it is necessary to reduce the amount of discharge at the main resistor 61a. Note that since the sub-resistor 62a has a large resistance value, although the passive discharge circuit 62 can discharge, the amount of discharge per unit time is small (discharge requires a long time).

[0092] In contrast, in this automobile 1, a DC-DC converter 50 is connected to the high-voltage circuit 9. If the residual charge of the smoothing capacitor 42 is supplied to the DC-DC converter 50 through the high-voltage circuit 9, that residual charge can be consumed by the on-board components 12 via the DC-DC converter 50.

[0093] Therefore, by using both forced discharge using the DC-DC converter 50 and forced discharge using the active discharge circuit 61, the residual charge of the smoothing capacitor 42 can be effectively reduced, and the voltage of the smoothing capacitor 42 can be lowered in a short time.

[0094] (Time chart of combined forced discharge control under normal conditions) Figure 4 shows an example of a time chart for combined forced discharge control under normal conditions. The voltage change across the smoothing capacitor 42 is highlighted for easier understanding.

[0095] When the main power supply of automobile 1 is on, the main contactor 31 is on. The battery 20 is connected to the high-voltage circuit 9, and power is supplied from the battery 20 to the inverter 40 and the DC-DC converter 50. The DC-DC converter 50 is operating. Therefore, the smoothing capacitor 42 has a charge stored in it that corresponds to the voltage Vc of the battery 20. At this time, the switch 61b of the active discharge circuit 61 is off.

[0096] Then, when the main power supply of the automobile 1 is turned off, the PCM 13 turns off the negative contactor 31b in conjunction with it (at timing t1). As a result, the battery 20 is disconnected from the high-voltage circuit 9. Power supply from the battery 20 to the high-voltage circuit 9 is cut off. At this time, the positive contactor 31a remains in the ON state and turns off after a predetermined time has elapsed. This time difference is used to diagnose a fault in the contactor 30.

[0097] The PCM13 determines that the forced discharge conditions have been met and starts the first discharge control. In other words, the DC-DC converter 50 can operate until it reaches the operating limit voltage V1 (for example, 190V). The PCM13 controls the DC-DC converter 50 so that it operates even when the main power is turned off.

[0098] As a result, the charge in the smoothing capacitor 42 is consumed by the onboard component 12, and the voltage across the smoothing capacitor 42 decreases.

[0099] Subsequently, when the voltage across the smoothing capacitor 42 drops and reaches a predetermined threshold (V0, for example, 275V) (at timing t2), the PCM 13 performs a second discharge control. That is, it turns on switch 61b and starts forced discharge in the active discharge circuit 61.

[0100] The threshold voltage V0 is greater than the operating limit voltage V1. The threshold voltage V0 is the voltage at which damage to the main resistor 61a can be avoided even when continuously discharged through the main resistor 61a until a predetermined target voltage (V2, the voltage at which forced discharge is no longer necessary, for example, 15V) is reached. The threshold voltage V0 is pre-set in the PCM13 based on experiments and other factors.

[0101] As a result, forced discharge using the DC-DC converter 50 and forced discharge using the active discharge circuit 61 are performed in parallel. Discharge of the smoothing capacitor 42 is accelerated, and the voltage of the smoothing capacitor 42 decreases further.

[0102] When the voltage across the smoothing capacitor 42 reaches the operating limit voltage V1 (at timing t3), the DC-DC converter 50 stops operating. Therefore, the first discharge control ends. Since the forced discharge using the DC-DC converter 50 is utilized to its limit, the burden of forced discharge by the active discharge circuit 61 can be reduced.

[0103] Then, when the voltage across the smoothing capacitor 42 reaches the target voltage V2, the PCM13 turns off the switch 61b and terminates the second discharge control (at timing t4). After that, the passive circuit slowly discharges the charge from the smoothing capacitor 42 over time.

[0104] In this way, by using both forced discharge with the DC-DC converter 50 and forced discharge with the active discharge circuit 61, the residual charge of the smoothing capacitor 42 can be effectively reduced. Therefore, the voltage of the smoothing capacitor 42 can be reduced in a short time without damaging the active discharge circuit 61.

[0105] (Flowchart of combined forced discharge control under normal conditions) Figures 5 and 6 show an example of a flowchart for the combined forced discharge control corresponding to Figure 4.

[0106] The PCM13 reads measurement data input from the voltmeter 43, etc. (step S1). When the main power is turned off (step S2), the PCM13 determines whether or not thermal degradation occurs (step S3). If it is determined that thermal degradation occurs (No in step S3), the PCM13 sets the time until the negative electrode contactor 31b is turned off to a delayed time (step S4). On the other hand, if it is determined that there is no thermal degradation, the PCM13 sets the time until the negative electrode contactor 31b is turned off to the normal time (step S5).

[0107] Then, the PCM13 reads the set time (step S6) and turns off the negative electrode contactor 31b after that time has elapsed (step S7, timing t1 in Figure 4). After that, the PCM13 maintains the operation of the DCDC converter 50 and starts the first discharge control (step S8).

[0108] The PCM13 determines whether the voltage across the smoothing capacitor 42 has dropped and reached the threshold V0 (step S9). If it determines that the threshold V0 has been reached, the PCM13 turns on the switch 61b and starts forced discharge in the active discharge circuit 61, i.e., the second discharge control (step S10).

[0109] Then, the PCM13 determines whether the voltage across the smoothing capacitor 42 has dropped further and reached the operating limit voltage V1 (step S11). If it determines that the operating limit voltage V1 has been reached, the PCM13 stops the operation of the DC-DC converter 50 and terminates the first discharge control (step S12).

[0110] Next, the PCM13 determines whether the voltage across the smoothing capacitor 42 has dropped further and reached the target voltage V2 (step S13). If it determines that the target voltage V2 has been reached, the PCM13 turns off the switch 61b and terminates the second discharge control (step S14). After that, the passive discharge circuit 62 discharges the smoothing capacitor 42 until all charge is gone (step S15).

[0111] <Thermal Degeneration> As described above, the DC-DC converter 50 ceases to operate when the voltage falls below its operating limit. Therefore, subsequent forced discharge is carried out solely by the active discharge circuit 61.

[0112] Therefore, even when using the DC-DC converter 50, the main resistor 61a generates heat and its temperature rises. According to the inventors' experimental results, damage to the main resistor 61a can be suppressed even when the threshold V0 is set to a desired value, provided that only one forced discharge occurs.

[0113] However, when the main resistor 61a becomes hot, it takes time for its temperature to return to room temperature. Therefore, if forced discharge is repeated in a short period of time, heat will accumulate in the main resistor 61a. If forced discharge is started from a high temperature state, the main resistor 61a will be damaged even with a normal discharge amount.

[0114] Therefore, in this forced discharge system, when such short-duration forced discharges occur continuously, it is configured to undergo thermal degeneration in order to suppress damage to the main resistor 61a.

[0115] Specifically, if the forced discharge condition is met again before a predetermined time has elapsed, and a series of forced discharges in a short period of time (continuous forced discharge) occurs, the PCM13 executes a second discharge control, that is, a control that delays the timing of the forced discharge by the active discharge circuit 61 (delay control).

[0116] By delaying the timing of the forced discharge by the active discharge circuit 61, the temperature of the main resistor 61a can be reduced during the delay period. The length of the delay period is adjusted according to the cause of thermal degradation.

[0117] (Specific examples of thermal degeneracy) Figure 7 shows a flowchart of the control related to thermal degeneration. Figures 8 and 9 show time charts of the combined forced discharge control during thermal degeneration, corresponding to Figure 4, categorized by cause.

[0118] The forced discharge system is required to function properly even in abnormal situations. For example, a failure in the DC-DC converter 50 may cause the voltage of the inverter 40 to drop very little. In such cases, the smoothing capacitor 42 must be properly forced to discharge.

[0119] Furthermore, a malfunction in the cooling system 14 may cause the temperature of the inverter 40 to rise excessively. In such cases, the smoothing capacitor 42 must be properly forced to discharge. The forced discharge system is configured to properly undergo thermal degradation even in these situations.

[0120] By reading measurement data, the PCM13 constantly monitors the input voltages of the inverter 40 and the DC-DC converter 50 based on measurement data input from voltmeters 43 and 51. The PCM13 also constantly monitors the temperature of the cooling water flowing through the inverter 40 and the operation of the cooling system 14 based on measurement data input from the cooling system 14.

[0121] Then, when the forced discharge conditions are met and it becomes necessary to perform forced discharge control of the smoothing capacitor 42, the PCM 13 determines whether or not to enter thermal degeneration (step S3 in Figure 5).

[0122] In other words, the PCM13 determines the elapsed time ts1 since the last forced discharge. Specifically, it determines whether the elapsed time ts1 since the end of the last forced discharge by the active discharge circuit 61 exceeds a predetermined time (continuous forced discharge determination time tc, for example, 20 seconds) (step S20).

[0123] As a result, if the elapsed time ts1 is within the continuous forced discharge determination time tc, the PCM13 determines that it is a continuous forced discharge (step S21). On the other hand, if the elapsed time ts1 is not within the continuous forced discharge determination time tc, the PCM13 determines that it is not a continuous forced discharge (No in step S20) and performs normal combined forced discharge control (from step S5 onwards in Figure 5).

[0124] (Multiple consecutive discharges) If PCM13 determines that a continuous forced discharge has occurred, it determines whether the continuous forced discharge has occurred repeatedly more than a predetermined number of times (step S22).

[0125] Based on experiments and other factors, the PCM13 has an upper limit n (e.g., 3 times) set for the number of times damage to the main resistor 61a can be suppressed. When the PCM13 determines that continuous forced discharge has occurred n times or more (No in step S22), it sets a predetermined delay time (first delay time, e.g., 3 seconds) (step S23) and enters thermal degeneration (step S24).

[0126] When continuous forced discharge occurs repeatedly, heat accumulates in the main resistor 61a in proportion to the number of times it occurs. As a result, the temperature of the main resistor 61a at the start of forced discharge rises with each subsequent discharge. In other words, the temperature of the main resistor 61a is higher than normal before the forced discharge is performed. Therefore, as shown by the dashed line L2 in Figure 8, if the first and second discharge controls are performed in the same manner as under normal conditions, the main resistor 61a may be damaged.

[0127] Therefore, in such cases, as shown by the dashed line L1 in Figure 8, the system waits for a set first delay time from the normal shut-off timing of the negative electrode contactor 31b without executing the first discharge control and the second forced discharge control, thereby delaying the execution timing of the first discharge control and the second forced discharge control.

[0128] The delay increases the time elapsed between the end of the previous forced discharge and the execution of the second discharge control, allowing the temperature of the main resistor 61a to be lower than under normal conditions. Therefore, even if the temperature of the main resistor 61a is higher than normal at the start of the forced discharge, damage to the main resistor 61a can be suppressed.

[0129] (Abnormality in cooling system 14) If the PCM13 determines that continuous forced discharge is occurring, it also determines the temperature of the cooling water in the inverter 40 (step S25). Specifically, it determines whether the temperature of the cooling water in the inverter 40 is below a predetermined upper limit of water temperature Th.

[0130] As a result, if the temperature of the cooling water in the inverter 40 is determined to be above a predetermined upper limit of water temperature Th (No in step S25), the PCM 13 sets a predetermined delay time (second delay time, for example, 60 seconds) (step S26) and enters thermal degradation (step S24).

[0131] In other words, because the inverter 40 is not being cooled sufficiently, the temperature of the main resistor 61a is higher than normal. Therefore, as shown by the dashed line L2 in Figure 8, if the first and second discharge control are performed as in normal conditions, the main resistor 61a may be damaged.

[0132] Therefore, in such cases, as shown in Figure 8, the system waits for a set second delay time from the normal shut-off timing of the negative electrode contactor 31b without executing the first discharge control and the second forced discharge control, thereby delaying the execution timing of the first discharge control and the second forced discharge control.

[0133] The delay increases the time elapsed between the end of the previous forced discharge and the execution of the second discharge control, allowing the temperature of the main resistor 61a to be lower than under normal conditions. Therefore, even if the temperature of the main resistor 61a is higher than normal at the start of the forced discharge, damage to the main resistor 61a can be suppressed.

[0134] The PCM13 also determines whether or not there is an abnormality in the cooling system 14 (step S27). For example, if the cooling water path 14b is damaged and leaking water, the temperature of the inverter 40 will rise. The PCM13 detects an abnormality in the cooling system 14 from the energization status of the electric pump 14a, etc. In this case as well, the PCM13 sets a predetermined delay time (second delay time, for example 60 seconds) (step S26) and enters thermal degradation (step S24).

[0135] (Abnormality of DC-DC converter 50) In some cases, the DC-DC converter 50 may not operate due to a collision with vehicle 1 or some other trouble. In that case, even if the first discharge control is performed, the voltage of the inverter 40 (smoothing capacitor 42) will hardly drop and will not reach the threshold V0.

[0136] In such cases, the PCM13 detects an abnormality in the DC-DC converter 50 during the previous forced discharge. Specifically, at a predetermined timing after the negative contactor 31b is turned off (timing t2 in Figure 4), it determines whether the voltage of the smoothing capacitor 42 has fallen below the threshold V0 based on the measurement data from the voltmeter 43 (step S28).

[0137] As a result, if the PCM 13 determines that the input voltage of the inverter 40 is not below the threshold V0, it determines that the input voltage of the inverter 40 will not decrease even in this forced discharge, sets a predetermined delay time (third delay time, for example 20 seconds) (step S29), and enters thermal degradation (step S24).

[0138] In this case, as shown in Figure 9, the DC-DC converter 50 does not operate. Even if the first discharge control is performed, the voltage of the smoothing capacitor 42 hardly drops. Therefore, as shown in Figure 9, the second discharge control is performed after waiting until the third delay time has elapsed from the normal shut-off timing of the negative electrode contactor 31b.

[0139] Figures 10 and 11 illustrate flowcharts for when the DC-DC converter 50 malfunctions. In this case, the PCM 13 skips steps S8 and S9 in the flowchart of Figure 5, and steps S11 and S12 in the flowchart of Figure 6. The other processes are the same as in the previous flowcharts, so the same reference numerals are used for the same processes and their detailed explanations are omitted.

[0140] After the third delay time has elapsed due to thermal degradation, the PCM13 turns off the negative contactor 31b (step S7). Then, at a predetermined timing (timing t5 in Figure 9), the PCM13 turns on the switch 61b and starts forced discharge in the active discharge circuit 61, i.e., the second discharge control (step S10). As a result, the charge of the smoothing capacitor 42 decreases, and the voltage of the smoothing capacitor 42 decreases.

[0141] Subsequently, the PCM13 determines whether the voltage across the smoothing capacitor 42 has decreased and reached the target voltage V2 (step S13). If it determines that the target voltage V2 has been reached (timing t6 in Figure 9), the PCM13 turns off the switch 61b and terminates the second discharge control (step S14). After that, the smoothing capacitor 42 is discharged using a passive circuit until all charge is gone (step S15).

[0142] Furthermore, the first delay time is the shortest, and the second delay time is the longest. The third delay time is shorter than the second delay time, but longer than the first delay time. These differences are based on the cause of thermal degeneration.

[0143] (Release of thermal degeneracy) After entering thermal degeneracy, PCM13 releases thermal degeneracy when predetermined conditions are met.

[0144] In other words, as shown in Figure 7, the PCM13 determines the elapsed time ts2 since the previous forced discharge. Specifically, it determines whether the elapsed time ts2 since the end of the most recent forced discharge has exceeded a predetermined time (degradation release determination time tf, for example, 5 minutes) (step S30).

[0145] As a result, if the elapsed time ts2 exceeds the degeneracy release determination time tf, the PCM13 releases the thermal degeneracy (step S31).

[0146] Thus, this forced discharge system allows for the smoothing capacitor 42 to be discharged quickly and effectively. Furthermore, it prevents damage to the main resistor 61a, or in other words, failure of the electronic circuit board of the inverter 40. Therefore, the reliability of the forced discharge control system can be improved.

[0147] Furthermore, the disclosed technology is not limited to the embodiments described above, but also encompasses various other configurations. For example, although the embodiments described above show an example of application to a hybrid vehicle, the disclosed technology can also be applied to electric vehicles driven solely by a motor. The control device is not limited to a PCM. A separate, dedicated device may be used. [Explanation of Symbols]

[0148] 1. Automobile (vehicle) 2 engines 3. Drive motor 4 Automatic transmission 9 High-voltage circuits 10 Low-voltage circuits 12. Automotive components (low-voltage components) 13. PCM (Control Device) 13a Forced discharge control unit 14. Cooling System (Cooling Mechanism) 20 batteries 30 Contactors 31 Main Contactor (Power Switching Mechanism) 31a Positive contactor 31b Negative contactor 40 Inverters 42 Smoothing Capacitors 50 DC-DC converter (buck converter) 60 Forced discharge circuit 61 Active discharge circuit 61a Main resistor 61b Switch (means for switching the power supply) 62 Passive Discharge Circuits 62a Sub-resistor

Claims

1. The vehicle's drive battery and An inverter that includes a smoothing capacitor and its forced discharge circuit, controls the power supplied from the battery and outputs it to the drive motor, A step-down converter that reduces the voltage of the battery and supplies it to low-voltage components in the vehicle, A high-voltage circuit electrically connects the battery, the inverter, and the step-down converter, A power switching means that can switch between a state in which the battery is connected to the high-voltage circuit and a state in which it is disconnected from the high-voltage circuit, Equipped with, The forced discharge circuit includes an active discharge circuit which includes a main resistor arranged in parallel with the smoothing capacitor and a current switching means that can switch the main resistor between a state in which it is connected to the high-voltage circuit and a state in which it is disconnected from the high-voltage circuit. A forced discharge control system for a smoothing capacitor further comprising the step-down converter, the power supply switching means, and a control device for controlling the power supply switching means, When the control device meets predetermined forced discharge conditions for forcibly discharging the smoothing capacitor, it initiates a first discharge control in which the charge stored in the smoothing capacitor is consumed by the low-voltage component via the step-down converter, while the battery is disconnected from the high-voltage circuit by the control of the power supply switching means, and then, when the voltage of the smoothing capacitor drops to a predetermined threshold, it executes a second discharge control in which the charge of the smoothing capacitor is forcibly discharged by the active discharge circuit by the control of the power supply switching means. A forced discharge control system for a smoothing capacitor, which further performs delay control to delay the execution timing of the second discharge control if a continuous forced discharge occurs before a predetermined time has elapsed, in which the forced discharge condition is met again.

2. In the forced discharge control system for a smoothing capacitor according to claim 1, A forced discharge control system for a smoothing capacitor, which executes the delay control when the continuous forced discharge occurs repeatedly more than a predetermined number of times.

3. In the forced discharge control system for a smoothing capacitor according to claim 1 or 2, A forced discharge control system for a smoothing capacitor, wherein when the control device detects an abnormality in the step-down converter, it executes the second discharge control before the threshold is reached.

4. In the forced discharge control system for a smoothing capacitor according to claim 3, The inverter further includes a cooling mechanism that cools by circulating cooling water, A forced discharge control system for a smoothing capacitor, wherein the control device executes the delay control when the temperature of the cooling water exceeds a predetermined upper limit or when it detects an abnormality in the cooling mechanism.

5. In the forced discharge control system for a smoothing capacitor according to claim 1 or 2, A forced discharge control system for a smoothing capacitor, wherein the forced discharge circuit further comprises a passive discharge circuit that is always connected in parallel with the smoothing capacitor and includes a sub-resistor with a resistance value greater than that of the main resistor.

6. In the forced discharge control system for a smoothing capacitor according to claim 1 or 2, A forced discharge control system for a smoothing capacitor, which maintains the first discharge control even after the voltage of the smoothing capacitor reaches the threshold, thereby executing the first discharge control and the second discharge control in parallel.

7. In the forced discharge control system for a smoothing capacitor according to claim 6, The step-down converter is configured to operate at a predetermined operating limit voltage that is lower than the threshold voltage. A forced discharge control system for a smoothing capacitor, which terminates the first discharge control when the voltage of the smoothing capacitor reaches the operating limit voltage.

8. In the forced discharge control system for a smoothing capacitor according to claim 1 or 2, The engine is installed at the front of the aforementioned vehicle. A forced discharge control system for a smoothing capacitor, wherein the drive motor is located in the tunnel section of the floor panel with the drive motor connected to the rear of the engine.

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