Vehicle electric compressor

Abstract

To provide an electric compressor for a vehicle that can prevent a switching element of an inverter circuit from being damaged by capacitor discharge control that discharges a capacitor.SOLUTION: In an electric compressor 1 for a vehicle, a control unit 55 of an inverter device 5 supplies electric power to an electric motor that drives a compression mechanism performs capacitor discharge control to discharge charge accumulated in a first capacitor 51 and a second capacitor 21 by controlling switching elements Q1, Q4, and Q6 among a plurality of switching elements Q1 to Q6 of an inverter circuit 50. The control unit 55 is configured to the control the switching elements Q1, Q4, and Q6 such that a current flowing through the switching elements Q1, Q4, and Q6 is below an allowable current corresponding to a switching element temperature.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an electric compressor for vehicles mounted on vehicles.

Background Art

[0002] As an example of an electric compressor for vehicles, an in-vehicle electric compressor described in Patent Document 1 is known. The in-vehicle electric compressor described in Patent Document 1 detects non-energization (disconnection of the connector connecting the two) between a battery as a DC power source provided in a vehicle and an inverter circuit by a current sensor, and when non-energization is detected, controls a switching element of the inverter circuit to start discharging a capacitor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the in-vehicle electric compressor described in Patent Document 1 has the following problems.

[0005] Due to misdetection of the current sensor or the like, if non-energization is detected and capacitor discharge is started even though the battery and the inverter circuit are in an energized state, current will continue to flow through the switching element while a high voltage is maintained, which may cause excessive heat generation of the switching element and thermal destruction of the switching element.

[0006] In some cases, it is necessary to discharge not only the capacitor on the electric compressor side, but also the capacitor on the vehicle side. Generally, the capacitor on the vehicle side has a larger capacitance than the capacitor on the electric compressor side. Therefore, if such a requirement is met, the current flowing through the switching element (i.e., the heat generated by the switching element) may become larger than expected, potentially causing the switching element to thermally break down.

[0007] The present invention aims to provide an electric compressor for vehicles that can prevent damage (such as thermal breakdown) to the switching elements of an inverter circuit by controlling the discharge of a capacitor. [Means for solving the problem]

[0008] According to one aspect of the present invention, an electric compressor for a vehicle is provided, comprising an electric motor, a compression mechanism driven by the electric motor, and an inverter device that supplies power to the electric motor, all housed within a housing. This electric compressor for a vehicle includes a plurality of switching elements arranged between a positive bus and a negative bus connected to a DC power supply of a vehicle, an inverter circuit that converts DC power from the DC power supply of the vehicle into AC power and supplies it to the coil of the electric motor, a capacitor connected between the positive bus and the negative bus and positioned closer to the DC power supply of the vehicle than the inverter circuit, a temperature detection unit that detects the temperature of the plurality of switching elements or the temperature near the plurality of switching elements, and a control unit that performs capacitor discharge control to discharge the charge accumulated in the capacitor via at least some of the switching elements and the coil of the electric motor by controlling at least some of the switching elements, wherein during the capacitor discharge control, the current flowing through at least some of the switching elements is kept below an allowable current corresponding to the temperature detected by the temperature detection unit. Furthermore, the current flowing through at least some of the switching elements becomes equal to or greater than a lower limit current corresponding to the required discharge time and the temperature detected by the temperature sensing unit. The system includes a control unit configured to control at least some of the switching elements. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an electric compressor for vehicles that can prevent damage (such as thermal breakdown) to the switching elements of an inverter circuit by controlling the discharge of a capacitor. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic longitudinal cross-sectional view of an electric compressor for a vehicle according to an embodiment. [Figure 2] This is a circuit diagram of an electric compressor for a vehicle according to an embodiment. [Figure 3] This figure shows an example of a capacitor discharge circuit. [Figure 4] This flowchart shows an example of capacitor discharge control. [Figure 5] This flowchart shows an example of capacitor discharge control. [Figure 6] This figure shows an example of a target discharge current setting map. [Figure 7] This figure shows an example of the duty cycle of a switching element to be set. [Figure 8] This figure shows another example of the duty cycle of the switching element to be set. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the present invention will be described based on the attached drawings.

[0012] Figure 1 is a schematic longitudinal cross-sectional view of an electric compressor for vehicles (hereinafter simply referred to as "electric compressor") 1 according to one embodiment of the present invention. The electric compressor 1 according to this embodiment is an inverter-integrated electric compressor having an inverter device integrated into it. The electric compressor 1 can be mounted on a vehicle and constitute a part of the refrigerant circuit of a vehicle air conditioning system, and can be configured to compress and discharge refrigerant.

[0013] Referring to Figure 1, the electric compressor 1 includes an electric motor 2, a compression mechanism 3 driven by the electric motor to compress the refrigerant, a main housing 4 housing the electric motor 2 and the compression mechanism 3, an inverter device 5 supplying power to the electric motor 2, and an inverter housing 6 housing the inverter device 5. The main housing 4 and the inverter housing 6 constitute the housing of the electric compressor 1. In other words, the electric compressor 1 has the electric motor 2, the compression mechanism 3, and the inverter device 5 inside the housing.

[0014] The electric motor 2 is, for example, a three-phase synchronous motor (brushless DC motor). The compression mechanism 3 is, for example, a scroll compression mechanism. The electric motor 2 and the compression mechanism 3 are arranged in series within the main housing 4 in the axial direction of the output shaft 2a of the electric motor 2, and the output shaft 2a of the electric motor 2 is connected to the compression mechanism 3 (orbital scroll in the case of a scroll compression mechanism).

[0015] The inverter device 5 includes a circuit board 7 on which various electronic components are mounted. The circuit board 7 is attached to the inverter housing 6 by a plurality of fixing members.

[0016] The inverter housing 6 is integrally provided with the main housing 4. The inverter housing 6 is located on one end of the main housing 4 in the axial direction, specifically on the side opposite to the compression mechanism 3, with the electric motor 2 in between. In this embodiment, the inverter housing 6 includes a housing body 61 formed integrally with the main housing 4 and a cover member 62 that is removable from the housing body 61.

[0017] The housing main body 61 has a bottom wall 611 and a peripheral wall 612 that rises from the periphery of the bottom wall 611 and defines an opening facing the bottom wall 611. The cover member 62 is attached to the housing main body 61 so as to close the opening of the housing main body 61. A part of the bottom wall 611 of the housing main body 61 (which is also the bottom wall of the inverter housing 6) constitutes a partition wall 8 that partitions the inside of the main housing 4 and the inside of the inverter housing 6. Further, the electric motor 2 and the inverter device 5 are electrically connected via a power supply line 9 that penetrates through the partition wall 8 in an airtight and liquid-tight state.

[0018] A refrigerant inlet 4a for allowing refrigerant from the outside to flow into the main housing 4 is formed in a portion of the main housing 4 on the side of the partition wall 8. The refrigerant that flows into the main housing 4 from the refrigerant inlet 4a flows through the inside of the main housing 4 (the gap of the electric motor 2) and reaches the compression mechanism 3. The compression mechanism 3 is driven by the electric motor 2 to compress and discharge the refrigerant.

[0019] The refrigerant that flows into the main housing 4 from the refrigerant inlet 4a is, for example, the refrigerant that has passed through an expansion valve and an evaporator in the refrigerant circuit of the vehicle air conditioner, and is a low-temperature and low-pressure refrigerant. Therefore, the partition wall 8 and the electric motor 2 can be cooled by the refrigerant that flows into the main housing 4 from the refrigerant inlet 4a. The refrigerant that has flowed through the main housing 4 is compressed by the compression mechanism 3 to become a high-temperature and high-pressure refrigerant and is discharged from the compression mechanism 3. Then, the (high-temperature and high-pressure) refrigerant discharged from the compression mechanism 3 flows out from a refrigerant outlet 4b formed in the main housing 4.

[0020] FIG. 2 is a circuit configuration diagram of the electric compressor 1.

[0021] Referring to FIG. 2, the electric compressor 1 is connected to an in-vehicle battery (hereinafter simply referred to as "battery") VB as a DC power source of the vehicle via a connector 20. Then, DC power is supplied from the battery VB to the electric compressor 1 via the connector 20, and more specifically, to an inverter circuit 50 of the inverter device 5 described later.

[0022] The inverter device 5 of the electric compressor 1 includes an inverter circuit 50, a first capacitor 51, a temperature sensing unit 52, a voltage sensing unit 53, a current sensing unit 54, and a control unit 55. At least some of these are mounted on a circuit board 7. Here, Figure 1 shows one circuit board 7, but it is not limited to this, and the inverter device 5 may include multiple circuit boards, and the inverter circuit 50, the first capacitor 51, etc. that constitute the inverter device 5 may be distributed across the multiple circuit boards.

[0023] The inverter circuit 50 is connected to the battery VB via the connector 20 and the system main relay SMR. More specifically, the inverter circuit 50 has a positive busbar 56P and a negative busbar 56N. The positive busbar 56P of the inverter circuit 50 is connected to the positive terminal of the battery VB via the connector 20 and the system main relay SMR, and the negative busbar 56N of the inverter circuit 50 is connected to the negative terminal of the battery VB via the connector 20.

[0024] In this embodiment, the system main relay SMR is configured to be closed by the vehicle's control unit (vehicle ECU) 100 when the vehicle's start button is turned ON, and opened when the vehicle's start button is turned OFF. When the system main relay SMR is closed, the battery VB and the electric compressor 1 (inverter device 5) are electrically connected, and when the system main relay SMR is opened, the battery VB and the electric compressor 1 (inverter device 5) are electrically disconnected.

[0025] The inverter circuit 50 includes a plurality (six in this case) of switching elements Q1 to Q6 positioned between the positive busbar 56P and the negative busbar 56N connected to the battery VB, and the same number (six in this case) of diodes D1 to D6 as the switching elements Q1 to Q6. While not particularly limited, the switching elements Q1 to Q6 may be IGBTs (Insulated Gate Bipolar Transistors). The inverter circuit 50 is configured to convert DC power from the battery VB into three-phase AC power and supply it to the electric motor 2 by controlling (PMW control) the switching elements Q1 to Q6.

[0026] In this embodiment, the multiple switching elements Q1 to Q6 are arranged within the inverter housing 6 so as to be in thermal contact with the partition wall 8 (see Figure 1). Here, thermal contact with the partition wall 8 means that heat exchange is possible with the partition wall 8, and includes direct contact with the partition wall 8, proximity to the partition wall 8, and indirect contact with the partition wall 8 via a heat exchange member with high thermal conductivity. Therefore, the multiple switching elements Q1 to Q6 can be cooled through the partition wall 8 by a (low-temperature) refrigerant flowing into the main housing 4.

[0027] Further explanation of the inverter circuit 50 is provided. The inverter circuit 50 has a U-phase arm, a V-phase arm, and a W-phase arm provided in parallel between the positive busbar 56P and the negative busbar 56N. Two switching elements Q1 and Q2 are connected in series to the U-phase arm, and diodes D1 and D2 are connected in antiparallel to each of the switching elements Q1 and Q2, respectively. Two switching elements Q3 and Q4 are connected in series to the V-phase arm, and diodes D3 and D4 are connected in antiparallel to each of the switching elements Q3 and Q4, respectively. Two switching elements Q5 and Q6 are connected in series to the W-phase arm, and diodes D5 and D6 are connected in antiparallel to each of the switching elements Q5 and Q6, respectively.

[0028] Furthermore, the midpoints of the U-phase arm, V-phase arm, and W-phase arm are connected to the other ends of the U-phase coil, V-phase coil, and W-phase coil of the electric motor 2, which are star-connected at one end of each arm. Specifically, the midpoint of the U-phase arm located between switching elements Q1 and Q2 is connected to the U-phase coil, the midpoint of the V-phase arm located between switching elements Q3 and Q4 is connected to the V-phase coil, and the midpoint of the V-phase arm located between switching elements Q5 and Q6 is connected to the W-phase coil.

[0029] Then, by controlling the ratio of the ON periods of the switching elements Q1, Q3, and Q5 on the positive busbar 56P side of each phase arm and the ratio of the ON periods of the switching elements Q2, Q4, and Q6 on the negative busbar 56N side, that is, by controlling the switching elements Q1 to Q6 by duty cycle (PWM control), the inverter circuit 50 can convert the DC power from the battery VB into three-phase AC power and supply it to the electric motor 2, thereby driving the electric motor 2.

[0030] The first capacitor 51 is connected between the positive bus 56P and the negative bus 56N of the inverter circuit 50. The first capacitor 51 is located on the battery VB side of the inverter circuit 50, that is, between the inverter circuit 50 and the connector 20. The first capacitor 51 is a smoothing capacitor that smooths the DC power supplied from the battery VB to the inverter circuit 50.

[0031] The temperature detection unit 52 detects the temperature of the switching elements Q1 to Q6 or the temperature near the switching elements Q1 to Q6 (hereinafter, these are collectively referred to simply as "switching element temperature").

[0032] The voltage detection unit 53 is positioned between the inverter circuit 50 and the first capacitor 51, and detects the potential difference between the positive busbar 56P and the negative busbar 56N between the inverter circuit 50 and the first capacitor 51.

[0033] The current detection unit 54 detects the current flowing through the electric motor 2. In this embodiment, the current detection unit 54 is located on the negative bus 56N between the inverter circuit 50 and the first capacitor 51. However, it is not limited to this configuration, and the current detection unit 54 may also be located on the positive bus 56P between the inverter circuit 50 and the first capacitor 51.

[0034] The control unit 55 is configured to control the switching elements Q1 to Q6 (PWM control) in order to drive the electric motor 2 and, consequently, the compression mechanism 3, based on operation commands from the vehicle air conditioning system control device (air conditioning ECU) 101.

[0035] Furthermore, the control unit 55 is configured to perform control (hereinafter referred to as "capacitor discharge control") to discharge the capacitor when it receives a capacitor discharge command from the vehicle ECU 100. In this embodiment, the vehicle ECU 100 is configured to output the capacitor discharge command to the control unit 55, provided that at least the vehicle's start button is turned OFF (i.e., the system main relay SMR is opened).

[0036] In this embodiment, in addition to the first capacitor 51, a second capacitor 21 is provided on the battery VB side of the connector 20 and connected in parallel to the battery VB. The second capacitor 21 is connected between the positive terminal wiring 22P, which connects the positive terminal of the battery VB to the positive bus 56P of the inverter circuit 50 via the connector 20, and the negative terminal wiring 22N, which connects the negative terminal of the battery VB to the negative bus 56N of the inverter circuit 50 via the connector 20. The second capacitor 21, like the first capacitor 51, has the function of smoothing the DC power supplied from the battery VB to the inverter circuit 50.

[0037] Therefore, in this embodiment, the control unit 55 is configured to discharge the first capacitor 51 and the second capacitor 21 by the capacitor discharge control. That is, the control unit 55 is configured to discharge the charge accumulated in the first capacitor 51, as well as the charge accumulated in the second capacitor 21, by performing the capacitor discharge control. Here, the first capacitor 51 is the capacitor on the electric compressor side, and the second capacitor 21 is the capacitor on the vehicle side.

[0038] Specifically, when the control unit 55 receives the capacitor discharge command, it controls (turns on) at least some of the switching elements among the plurality of switching elements Q1 to Q6, in this case switching elements Q1, Q4, and Q6, to energize the first capacitor 51 and the second capacitor 21 and the coils of the electric motor 2 (U-phase coil, V-phase coil, and W-phase coil). As a result, a capacitor discharge circuit including the switching elements Q1, Q4, and Q6 and the coils of the electric motor 2 is generated, and as shown by the arrows in Figure 3, the charge stored in the first capacitor 51 and the charge stored in the second capacitor 21 are discharged through the switching elements Q1, Q4, and Q6 and the coils of the electric motor 2 (U-phase coil, V-phase coil, and W-phase coil).

[0039] The capacitor discharge control performed by the control unit 55 will be described further.

[0040] In this embodiment, when the control unit 55 receives the capacitor discharge command, it starts monitoring the switching element temperature detected by the temperature detection unit 52, monitoring the voltage detected by the voltage detection unit 53, and monitoring the current detected by the current detection unit 54. Here, the potential difference detected by the voltage detection unit 53 is the potential difference between the positive bus 56P and the negative bus 56N, and corresponds to the terminal voltage (capacitor voltage) of the first capacitor 51 and the second capacitor 21. The current detected by the current detection unit 54 corresponds to the discharge current of the first capacitor 51 and / or the second capacitor 21 when the capacitor discharge circuit is generated. Therefore, below, the potential difference detected by the voltage detection unit 53 may be referred to as the "capacitor voltage equivalent value," and the current detected by the current detection unit 54 may be referred to as the "capacitor discharge current." The control unit 55 determines whether or not the capacitor discharge control is necessary based on the capacitor voltage equivalent value detected by the voltage detection unit 53. When capacitor discharge control is required, the control unit 55 sets a target discharge current based on the switching element temperature detected by the temperature detection unit 52, sets the duty cycle of the switching elements Q1, Q4, and Q6 based on the set target discharge current and the capacitor discharge current detected by the current detection unit 54, and controls the switching elements Q1, Q4, and Q6 with the set duty cycle.

[0041] Figures 4 and 5 are flowcharts illustrating an example of the capacitor discharge control performed by the control unit 55. This flowchart is initiated when the control unit 55 receives the capacitor discharge command.

[0042] In step S1, the control unit 55 reads the potential difference detected by the voltage detection unit 53, i.e., the capacitor voltage equivalent value.

[0043] In step S2, the control unit 55 determines whether the read capacitor voltage equivalent value is equal to or greater than the discharge required voltage, which is the reference value that necessitates the capacitor discharge control. If the read capacitor voltage equivalent value is equal to or greater than the discharge required voltage, the control unit 55 proceeds to the process in step S3. If the read capacitor voltage equivalent value is less than the discharge required voltage, the control unit 55 terminates this flow.

[0044] In step S3, the control unit 55 reads the switching element temperature detected by the temperature detection unit 52.

[0045] In step S4, the control unit 55 sets the target discharge current based on the read switching element temperature. The control unit 55 sets the target discharge current as follows:

[0046] In this embodiment, the control unit 55 has a target discharge current setting map as shown in Figure 6. In this target discharge current setting map, the X axis is the temperature of the switching element, and the Y axis is the discharge current value (= current flowing through the switching element = phase current value of the electric motor 2). The solid line in Figure 6 indicates the allowable current of the switching element, which is the maximum current that will not cause thermal damage to the switching element, and the dashed line in Figure 6 indicates the lower limit current required to complete the discharge of the first capacitor 51 and the second capacitor 21 within a preset required discharge time (it is not necessary to complete it completely, but it is sufficient to complete it approximately). Here, the allowable current and the lower limit current are set considering the temperature characteristics (especially resistance fluctuations) of the capacitor discharge circuit, which is generated to discharge the charge stored in the first capacitor 51 and the charge stored in the second capacitor 21, that is, the capacitor discharge circuit including the switching elements Q1, Q4 and Q6 and the coil of the electric motor 2.

[0047] The control unit 55 then sets the target discharge current to a current that is less than or equal to the allowable current and greater than or equal to the lower limit current, based on the read temperature of the switching element, i.e., the current within the hatched area in Figure 6. In other words, the control unit 55 basically sets a target discharge current with a higher current value the lower the temperature of the switching element. Although not particularly limited, in this embodiment, in order to suppress the heat generation of the switching elements Q1, Q4 and Q6 as much as possible, the control unit 55 sets the target discharge current to a current with a current value relatively close to the lower limit current, based on the temperature of the switching element.

[0048] In step S5, the control unit 55 controls the switching elements Q1, Q4, and Q6 with a duty cycle of 50%. This generates the capacitor discharge circuit and initiates the capacitor discharge control, that is, the discharge of the charge stored in the first capacitor 51 and the discharge of the charge stored in the second capacitor 21.

[0049] In step S6, the control unit 55 reads the current detected by the current detection unit 54, i.e., the capacitor discharge current.

[0050] In step S7, the control unit 55 calculates the difference between the set target discharge current and the read capacitor discharge current.

[0051] In step S8, the control unit 55 sets the duty cycles of the switching elements Q1, Q4, and Q6 based on the calculated difference.

[0052] In step S9, the control unit 55 controls the switching elements Q1, Q4, and Q6 with a set duty cycle. As a result, the charge stored in the first capacitor 51 and the charge stored in the second capacitor 21 are discharged while the current flowing through the switching elements Q1, Q4, and Q6 is limited to less than or equal to the allowable current.

[0053] In step S10, the control unit 55 determines whether the required discharge time has elapsed since the capacitor discharge command was input or since the start of discharge. If the required discharge time has not elapsed, the control unit 55 proceeds to the process in step S11. On the other hand, if the required discharge time has elapsed, the control unit 55 proceeds to the process in step S13 (Figure 5).

[0054] In step S11, the control unit 55 reads the potential difference detected by the voltage detection unit 53, i.e., the capacitor voltage equivalent value.

[0055] In step S12, the control unit 55 determines whether the read capacitor voltage equivalent value is equal to or greater than the discharge required voltage. If the read capacitor voltage equivalent value is equal to or greater than the discharge required voltage, the control unit 55 returns to the process in step S6. If the read capacitor voltage equivalent value is less than the discharge required voltage, the control unit 55 terminates this flow.

[0056] In step S13, the control unit 55 stops the capacitor discharge control.

[0057] In step S14, the control unit 55 determines whether a predetermined cooling period for the switching element has elapsed since the capacitor discharge control was stopped. If the cooling period for the switching element has elapsed, the control unit 55 returns to the process of step S1.

[0058] Figure 7 shows an example of the duty cycle of switching elements Q1, Q4, and Q6 set by the control unit 55. Figure 7(a) shows the case when the switching element temperature is low, and Figure 7(b) shows the case when the switching element temperature is high.

[0059] When the capacitor discharge command is input to the control unit 55, normally the system main relay SMR is open, and the first capacitor 51 and the second capacitor 21 are electrically disconnected from the battery VB. Therefore, the value corresponding to the capacitor voltage detected by the voltage detection unit 53 decreases as the first capacitor 51 and the second capacitor 21 discharge. In other words, until the required discharge time elapses, the value corresponding to the capacitor voltage gradually decreases with the passage of time from the start of the capacitor discharge control. Also, when the value corresponding to the capacitor voltage decreases, the capacitor discharge current detected by the current detection unit 54 also decreases. Therefore, when the target discharge current is constant, in order to maintain the target discharge current, as shown in FIGS. 7(a) and (b), the duty ratio set in step S8 increases as time passes (T1 < T2 < T3). When the temperature of the switching element is high, a lower current value of the target discharge current is set compared to when the temperature of the switching element is low (see FIG. 6). Therefore, the control duty ratio (FIG. 7(b)) when the temperature of the switching element is high has a smaller increase in the duty ratio than the duty ratio (FIG. 7(a)) when the temperature of the switching element is low.

[0060] FIG. 8 is a diagram showing another example of the duty ratios of the switching elements Q1, Q4, and Q6 set by the control unit 55. FIG. 8(a) shows the case where the temperature of the switching element is low, and FIG. 8(b) shows the case where the temperature of the switching element is high.

[0061] If, for some reason, the capacitor discharge command is input to the control unit 55 when the system main relay SMR is closed, in other words, if the capacitor discharge command is mistakenly input to the control unit 55, the first capacitor 51 and the second capacitor 21 remain electrically connected to the battery VB. In this case, even after the start of the capacitor discharge control, the potential difference (equivalent to the capacitor voltage) detected by the voltage detection unit 53 remains constant (does not decrease). Therefore, when the target discharge current is constant, a nearly constant duty cycle corresponding to the target discharge current is set in step S8 (T1≒T2≒T3) until the required discharge time has elapsed, as shown in Figures 8(a) and (b). When the switching element temperature is high, a lower target discharge current is set compared to when the switching element temperature is low. Therefore, the control duty cycle when the switching element temperature is high (Figure 8(b)) is set to be smaller than the control duty cycle when the switching element temperature is low (Figure 8(a)).

[0062] As described above, in this embodiment, when the control unit 55 receives the capacitor discharge command, it controls the switching elements Q1, Q4, and Q6 to discharge the first capacitor 51 and the second capacitor 21 via the switching elements Q1, Q4, and Q6 and the coil of the electric motor 2, thereby performing the capacitor discharge control. At that time, the control unit 55 controls the switching elements Q1, Q4, and Q6 so that the current flowing through them is less than or equal to the allowable current of the switching elements Q1, Q4, and Q6 according to the temperature of the switching elements. In other words, the current flowing through the switching elements Q1, Q4, and Q6 is limited to less than or equal to the allowable current.

[0063] Therefore, the capacitor discharge control prevents damage (thermal breakdown, etc.) to the switching elements Q1, Q4, and Q6. Furthermore, even if the capacitor discharge command is mistakenly input to the control unit 55 while the battery VB and the first capacitor 51 and the second capacitor 21 are electrically connected, damage (thermal breakdown, etc.) to the switching elements Q1, Q4, and Q6 is prevented.

[0064] The control unit 55 is configured to control the switching elements Q1, Q4, and Q6 during capacitor discharge control so that the current flowing through them is equal to or greater than a lower limit current corresponding to the required discharge time and the switching element temperature. The lower limit current is the current required to complete the discharge of the first capacitor 51 and the second capacitor 21 within the required discharge time. Therefore, the discharge of the first capacitor 51 and the second capacitor 21 can be completed within the required discharge time while preventing damage (thermal breakdown, etc.) to the switching elements Q1, Q4, and Q6.

[0065] Specifically, in this embodiment, the control unit 55 is configured to set a target discharge current that is less than or equal to the allowable current and greater than or equal to the lower limit current based on the switching element temperature, set the duty cycle of the switching elements Q1, Q4, and Q6 based on the set target discharge current and the capacitor discharge current detected by the current detection unit 54, and control the switching elements Q1, Q4, and Q6 with the set duty cycle. This enables stable capacitor discharge control that prevents damage (such as thermal breakdown) to the switching elements Q1, Q4, and Q6 and completes the discharge of the first capacitor 51 and the second capacitor 21 within the required discharge time.

[0066] In the above-described embodiment, the control unit 55 performs the capacitor discharge control by controlling the switching elements Q1, Q4, and Q6. However, it is not limited to this. By energizing the first capacitor 51 and the second capacitor 21 and the coils of the electric motor 2 (U-phase coil, V-phase coil, and W-phase coil), the control unit 55 can perform the capacitor discharge control by controlling any of the switching elements Q1 to Q6.

[0067] In the above-described embodiment, the control unit 55 sets a target discharge current that is less than or equal to the allowable current and greater than or equal to the lower limit current based on the switching element temperature. However, it is not limited to this. When the required discharge time is not set or when the required discharge time is sufficiently long, the control unit 55 may simply set a target discharge current that is less than or equal to the allowable current based on the switching element temperature.

[0068] In the above-described embodiment, the control unit 55 sets the target discharge current to a current value relatively close to the lower limit current based on the switching element temperature. However, it is not limited to this. For example, if shortening the discharge time is prioritized, the control unit 55 may set the target discharge current to a current value relatively close to the allowable current based on the switching element temperature. Also, if it is necessary to balance the suppression of heat generation of the switching elements Q1, Q4, and Q6 with shortening the discharge time, the control unit 55 may set the target discharge current to a current value intermediate between the allowable current and the lower limit current based on the switching element temperature.

[0069] In the above embodiment, the control unit 55 initiates the capacitor discharge control by controlling the switching elements Q1, Q4, and Q6 with a duty cycle of 50% (step 5 in Figure 4). In other words, the initial value of the duty cycle of the switching elements Q1, Q4, and Q6 when performing the capacitor discharge control is set to 50%. However, it is not limited to this. The control unit 55 can initiate the capacitor discharge control by controlling the switching elements Q1, Q4, and Q6 with an arbitrary duty cycle (initial value). For example, the control unit 55 may initiate the capacitor discharge control by controlling the switching elements Q1, Q4, and Q6 with a duty cycle (initial value) corresponding to the target discharge current set in step S4 in Figure 4.

[0070] Alternatively, the process in step S5 of Figure 4 may be omitted, and the control unit 55 may start the capacitor discharge control by controlling the switching elements Q1, Q4, and Q6 in step S9 of Figure 4. In this case, it is preferable to suppress overshoot, hunting, etc., by setting an upper limit for the duty cycle, for example.

[0071] Furthermore, the control unit 55 may monitor the capacitor voltage equivalent value, set the duty cycle based on the target discharge current and the capacitor voltage equivalent value, and control the set switching elements Q1, Q4, and Q6. In this case, for example, in Figure 4, the process in step S5 is omitted, the capacitor voltage equivalent value is read in step S6 in the same way as in step S1, the process in step S7 is omitted, and the duty cycle is set in step S8 based on the target discharge current set in step S4 and the capacitor voltage equivalent value read in step S6.

[0072] In the above-described embodiment, the control unit 55 discharges the first capacitor 51 and the second capacitor 21 by the capacitor discharge control. However, it is not limited to this. The control unit 55 can discharge the second capacitor 21 in the same manner as above even when the first capacitor 51 is absent, and can discharge the first capacitor 51 in the same manner as above even when the second capacitor 21 is absent.

[0073] Although embodiments and modifications thereof of the present invention have been described above, the present invention is not limited to the embodiments and modifications described above, and further modifications are possible based on the technical concept of the present invention. [Explanation of Symbols]

[0074] 1…Electric compressor, 2…Electric motor, 3…Compression mechanism, 4…Main housing, 5…Inverter device, 6…Inverter housing, 20…Connector, 21…Second capacitor, 50…Inverter circuit, 51…First capacitor, 52…Temperature detection unit, 53…Voltage detection unit, 54…Current detection unit, 55…Control unit, 56P…Positive busbar, 56N…Negative busbar, Q1~Q6…Switching elements, VB…Vehicle battery

Claims

1. An electric compressor for vehicles, comprising an electric motor, a compression mechanism driven by the electric motor, and an inverter device that supplies power to the electric motor, within a housing, The inverter device is, An inverter circuit including a plurality of switching elements positioned between a positive busbar and a negative busbar connected to the vehicle's DC power supply, which converts DC power from the vehicle's DC power supply into AC power and supplies it to the coil of the electric motor, A capacitor connected between the positive busbar and the negative busbar, and positioned on the DC power supply side of the vehicle than the inverter circuit, A temperature detection unit that detects the temperature of the plurality of switching elements or the temperature near the plurality of switching elements, A control unit that performs capacitor discharge control to discharge the charge accumulated in the capacitor via at least some of the switching elements and the coils of the electric motor by controlling at least some of the switching elements, wherein the control unit is configured to control at least some of the switching elements such that the current flowing through at least some of the switching elements becomes less than or equal to an allowable current corresponding to the temperature detected by the temperature detection unit, and the current flowing through at least some of the switching elements becomes greater than or equal to a lower limit current corresponding to the required discharge time and the temperature detected by the temperature detection unit, Vehicle-mounted electric compressors, including those mentioned above.

2. The inverter device includes a voltage detection unit that detects the potential difference between the positive bus and the negative bus between the capacitor and the inverter circuit. The control unit performs the capacitor discharge control when the potential difference detected by the voltage detection unit is equal to or greater than the discharge required voltage. The electric compressor for a vehicle according to claim 1.

3. The inverter device includes a current detection unit that detects the discharge current of the capacitor by the capacitor discharge control, The control unit sets a target discharge current less than or equal to the allowable current based on the temperature detected by the temperature detection unit, sets the duty cycle of at least some of the switching elements based on the target discharge current and the discharge current of the capacitor detected by the current detection unit, and controls at least some of the switching elements with the set duty cycle. The electric compressor for a vehicle according to claim 1.

4. The electric compressor for a vehicle according to any one of claims 1 to 3, wherein the control unit performs capacitor discharge control based on a capacitor discharge command from the vehicle.

5. It is configured to be connected to the DC power supply of the vehicle via a connector, In addition to discharging the charge stored in the capacitor through the capacitor discharge control, the control unit also discharges the charge stored in the vehicle-side capacitor, which is located on the DC power supply side of the vehicle than the connector and connected in parallel to the DC power supply of the vehicle. The electric compressor for a vehicle according to claim 4.

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