Electric compressor

Abstract

To provide an electric compressor capable of improving quietness after stop command input.SOLUTION: An electric compressor includes a control section MC which controls drive of a motor M. The control section MC executes: synchronous speed reduction control, which is performed on conditions that a stop command to the motor M is inputted from the outside and a rotation number of a rotor M2 is equal to or less than a predetermined first rotation number N1 and more than a predetermined second rotation number N2, for reducing the rotation number by performing forced synchronous control using a current at a predetermined target current value; and stop control, which is performed on conditions that the rotation number reaches the second rotation number N2 by performing the synchronous speed reduction control, for stopping rotation of the rotor M2 by performing braking control for controlling drive of predetermined switching elements IGBT (Q2, Q4, Q6, etc.,) among a plurality of switching elements so as to apply a load to the motor M.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an electric compressor having an inverter and a motor, which is used to compress a refrigerant in an air conditioner for a vehicle or the like. [Background technology]

[0002] In an electric compressor having an inverter-type motor, DC power from a DC power source is converted to three-phase AC power by the inverter and supplied to the motor that drives the compressor. In this electric compressor, when the compressor stops, the pressure difference between the suction pressure region and the discharge pressure region of the refrigerant in the compression mechanism causes the compression mechanism to rotate in reverse, and it is known that this reverse rotation can cause abnormal noise.

[0003] An electric compressor disclosed in Patent Document 1 is known as an electric compressor designed to prevent reverse rotation. This electric compressor has a control unit that performs braking control when the compressor is stopped, as a measure to prevent reverse rotation and abnormal noise. Specifically, when an external command to stop operation is input, the control unit of this electric compressor cuts off current to multiple switching elements that make up the inverter (motor drive circuit), allows the motor rotor to rotate by inertia, and then performs braking control to prevent reverse rotation. Generally, electric compressors with inverter-type motors often employ sensorless control, that is, control that increases or decreases the rotation speed of the motor rotor while estimating the rotor position based on the current value flowing from the motor drive circuit to the motor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-287485 Summary of the Invention [Problem to be solved by the invention]

[0005] With the recent spread of electric vehicles, the level of quietness required for electric compressors mounted on vehicles has been increasing. In this regard, in the conventional electric compressor described in Patent Document 1, when the rotor rotates by inertia between the input of an operation stop command and the start of braking control, the sliding parts in the compression mechanism may collide with each other, generating abnormal noise and vibration. As a result, there is a risk of a decrease in quietness, and there is room for improvement. The inventors of the present application have confirmed through ingenuity that the higher the rotation speed of the motor (rotor) when the operation stop command is input, the higher the level of abnormal noise and vibration during inertial rotation. Therefore, in order to improve quietness when stopping operation of a conventional electric compressor, it is possible to consider, for example, performing braking control after decelerating the rotation speed of the motor using the above-mentioned sensorless control.

[0006] However, in an electric compressor that employs sensorless control, a minimum operable rotation speed is specified. In other words, it is difficult for sensorless control to control the rotor rotation speed (rotational speed) at a rotation speed lower than the minimum operable rotation speed. Therefore, the level of improvement in quietness depends on the minimum operable rotation speed of the sensorless control, and some ingenuity is required.

[0007] In view of the above circumstances, an object of the present invention is to provide an electric compressor that can improve noise reduction after a stop command is input from the outside compared to conventional electric compressors. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided an electric compressor including: a compression mechanism that compresses and discharges a refrigerant; a motor that drives the compression mechanism; a motor drive circuit connected between the motor and a DC power supply and having a plurality of switching elements; and a control unit that controls drive of the motor, including sensorless control that increases or decreases the rotation speed of the rotor while estimating the rotor position based on the value of current flowing from the motor drive circuit to the motor. The control unit of this electric compressor executes synchronous deceleration control and stop control. The synchronous deceleration control is performed when a stop command for the motor is input from an external device and the rotation speed of the rotor is equal to or lower than a predetermined first rotation speed and higher than a predetermined second rotation speed, and the rotation speed is reduced by forced synchronous control using a current of a predetermined target current value. The stop control is performed when the rotation speed reaches the second rotation speed through the synchronous deceleration control, and the rotation of the rotor is stopped by braking control that controls the drive of a predetermined switching element among the plurality of switching elements to apply a load to the motor. [Effects of the Invention]

[0009] In the electric compressor according to one aspect of the present invention, the control unit executes synchronous deceleration control, which reduces the rotational speed of the rotor by forced synchronous control using a current of a predetermined target current value, when a stop command is input from an external device and the rotor rotational speed is equal to or lower than a predetermined first rotational speed and higher than a predetermined second rotational speed. Therefore, for example, by simply presetting the first rotational speed to a value equal to the minimum operable rotational speed, even if the rotor rotational speed at the time of input of the stop command is lower than the minimum operable rotational speed determined by the sensorless control, the rotor rotational speed is reduced (decelerated) by the synchronous deceleration control without coasting. As a result, quietness during shutdown is improved compared to conventional compressors. Furthermore, the control unit stops the rotation of the rotor by the stop control after the rotational speed reaches the second rotational speed by the synchronous deceleration control. This quickly prevents or suppresses reverse rotation of the rotor (compression mechanism) and the generation of abnormal noise due to this reverse rotation.

[0010] As described above, according to one aspect of the present invention, it is possible to provide an electric compressor that can improve noise reduction after a stop command is input from outside compared to conventional electric compressors. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic external appearance of an electric compressor according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram including a motor drive circuit and a control unit of the electric compressor. [Figure 3] FIG. 2 is a block diagram showing a configuration example of the control unit when performing motor drive control and sensorless deceleration control. [Figure 4] FIG. 3 is a block diagram showing a configuration example of the control unit when executing synchronous deceleration control. [Figure 5] FIG. 4 is a diagram showing an example of a timing chart of a control operation of the control unit. [Figure 6] FIG. 10 is a diagram showing another example of the timing chart. [Figure 7] 5 is a conceptual diagram showing an example of a change in a target rotational speed value (speed command value) due to the synchronous deceleration control. FIG. [Figure 8] 6 is a conceptual diagram showing another example of a change in the target rotational speed value (speed command value) due to the synchronous deceleration control. FIG. [Figure 9] FIG. 3 is a flowchart illustrating a schematic flow of a control operation by the control unit. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0023] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is a diagram showing the outline of the appearance of an electric compressor 100 according to an embodiment of the present invention, and Fig. 2 is a block diagram of the electric compressor 100 including an inverter INV having a motor drive circuit PM and a control unit MC, which will be described later.

[0013] The electric compressor 100 in this embodiment is incorporated in a refrigerant circuit of an automotive air conditioner mounted on a vehicle, for example, and draws in, compresses, and discharges the refrigerant for the automotive air conditioner. The electric compressor 100 is a so-called inverter-integrated electric compressor, and includes a housing C, a compression mechanism P that compresses and discharges the refrigerant by rotation, a motor M that drives the compression mechanism P, and an inverter INV that has a drive circuit PM and a control unit MC for supplying power to the motor M.

[0014] The housing C accommodates the compression mechanism P, the motor M, and the inverter INV. In this embodiment, the housing C includes a main housing C1, an inverter housing C2, and cover members C3 and C4. These (C1 to C4) are fastened together with bolts or the like. The main housing C1 accommodates the compression mechanism P and the motor M, and the inverter housing C2 accommodates the inverter INV. The interior of the housing C is partitioned into a first space that accommodates the compression mechanism P and the motor M, and a second space that accommodates the inverter INV.

[0015] In this embodiment, the housing C is fixed to the vehicle. That is, the electric compressor 100 includes a housing C that accommodates the compression mechanism P, the motor M, and the inverter INV (the drive circuit PM and the control unit MC) therein and is fixed to the vehicle.

[0016] The compression mechanism P is, for example, a scroll-type compression mechanism having a fixed scroll and an orbiting scroll that mesh with each other, and is connected to a drive shaft X. The orbiting scroll is connected to the drive shaft X so as to be capable of orbital movement around the axis of the fixed scroll, and a compression chamber is formed between the orbiting scroll and the fixed scroll. The orbital movement of the orbiting scroll changes the volume of the compression chamber. Low-pressure refrigerant is drawn into the main housing C1 from the low-pressure section of the refrigerant circuit through a suction port (not shown) and is compressed in the compression chamber while being guided to the center of the compression mechanism P. The refrigerant guided to the center of the compression mechanism P is discharged to the high-pressure section of the refrigerant circuit through a discharge port (not shown).

[0017] The motor M is, for example, a synchronous motor formed by a three-phase brushless motor. The motor M has a stator M1 including a stator coil and a rotor M2 including a permanent magnet. The stator coil has a star-connected U-phase coil, a V-phase coil, and a W-phase coil. The stator M1 is fixed to the inner circumferential surface of the main housing C1. The rotor M2 is formed in a cylindrical shape and is fixed to the drive shaft X with the drive shaft X inserted through its hollow portion. In other words, the rotor M2 is integrated with the drive shaft X and rotates integrally with the drive shaft X.

[0018] The inverter INV converts DC power from an external DC power source B, such as a battery (not shown), into three-phase AC power and supplies it to the motor M. The inverter INV has a circuit configuration including a motor drive circuit (power module) PM and a control unit MC that controls the drive of the motor M.

[0019] The motor drive circuit PM is connected between the motor M and a DC power supply B and has a plurality of identical insulated gate bipolar transistors (hereinafter referred to as "IGBTs") Q1 to Q6 as switching elements. The drive (on / off) of each IGBT Q1 to Q6 is controlled by a control unit MC, so that the IGBTs Q1 to Q6 convert DC voltage into AC voltage and supply it to the motor M. The IGBTs Q1 to Q6 are divided into a U-phase arm, a V-phase arm, and a W-phase arm that are connected in parallel with each other between a high-voltage line H (in other words, a high-voltage side line) and a ground line L (in other words, a ground side line) of the DC power supply B.

[0020] The U-phase arm has two IGBTs (Q1, Q2) connected in series between the high-voltage line H and the ground line L. Diodes D1, D2 are connected in anti-parallel to the two IGBTs (Q1, Q2), respectively. Similarly, the V-phase arm has two IGBTs (Q3, Q4), and diodes D3, D4 are connected in anti-parallel to the two IGBTs (Q3, Q4), respectively. The W-phase arm has two IGBTs (Q5, Q6), and diodes D5, D6 are connected in anti-parallel to the two IGBTs (Q5, Q6), respectively.

[0021] The IGBTs (Q1, Q3, Q5) are high-side elements (i.e., power supply side elements), and the IGBTs (Q2, Q4, Q6) are low-side elements (i.e., ground side elements). The IGBTs (Q1, Q2), IGBTs (Q3, Q4), and IGBTs (Q5, Q6) are each a pair of high-side and low-side elements in the same phase. The midpoints of the U-phase arm, V-phase arm, and W-phase arm are connected to one end of the coil of the corresponding phase of the motor M. Shunt resistors Ru, Rv, and Rw are provided on the ground line L side of the low-side elements, IGBTs (Q2, Q4, Q6), to detect the current flowing through each phase.

[0022] The control unit MC controls the driving of the motor M. For example, external commands are input to the control unit MC from an air conditioning control device on the vehicle side that controls the entire vehicle air conditioning system. The air conditioning control device outputs (transmits) commands to the control unit MC, such as an operation command for the motor M (electric compressor 100) and a stop command for the motor M. The control unit MC has a computer such as a microcomputer and stores programs that execute various controls in response to commands from the outside (air conditioning control device).

[0023] Here, the electric compressor 100 does not use a rotation angle sensor that detects the position of the rotor M2 of the motor M, but instead employs sensorless control that increases or decreases the number of rotations (also called rotational speed) of the rotor M2 while estimating the position of the rotor M2 based on the current value of the current flowing from the motor drive circuit PM to the motor M. This sensorless control is executed by a control unit MC.

[0024] In this embodiment, the control unit MC is configured to be able to perform motor drive control, which drives the motor M by sensorless control in response to an external command; sensorless deceleration control, which reduces (decelerates) the rotation speed of the rotor M2 by sensorless control; synchronous deceleration control, which reduces (decelerates) the rotation speed of the rotor M2 by forced synchronous control using a current of a predetermined target current value (in other words, a command current value); and stop control (also called brake control) for stopping the rotation of the rotor M2 (compression mechanism P).

[0025] In other words, when an operation command for the motor M is input to the control unit MC from the outside (air conditioning control device) (the control unit MC receives the operation command), the control unit MC executes motor drive control based on the external operation command. When a stop command for the motor M is input to the control unit MC from the outside (the control unit MC receives the stop command), the control unit MC autonomously executes sensorless deceleration control, forced synchronous control, and stop control as appropriate. Sensorless control is used as the control method for both motor drive control and sensorless deceleration control, and forced synchronous control (also called forced commutation control or open-loop control) is used as the control method for synchronous deceleration control. In motor drive control, the control unit MC increases or decreases the rotation speed of the rotor M2 in response to an external command, and in sensorless deceleration control and synchronous deceleration control, the control unit MC autonomously and forcibly reduces (decels) the rotation speed of the rotor M2.

[0026] At least one of the electric compressor 100 and the vehicle's air conditioning control device has a pressure sensor that detects the pressure (Ps) in the suction pressure region and the pressure (Pd) in the discharge pressure region of the refrigerant. Signals indicating the detected values ​​of the pressure (Pd) and the pressure (Ps) by the pressure sensor mounted on the electric compressor 100 or the pressure sensor mounted on the vehicle side are input to the control unit MC.

[0027] FIG. 3 is a block diagram showing an example of the configuration of the control unit MC when sensorless control (motor drive control and sensorless deceleration control) is performed.

[0028] In the control unit MC, the current detection unit 1 detects the U-phase current, the V-phase current, and the W-phase current by measuring the voltages across the shunt resistors Ru, Rv, and Rw. A first conversion calculation unit 2 calculates rotor coordinate system values ​​based on the detected phase current values ​​and inputs the calculated values ​​to a current calculation unit 3. A rotor position detection unit 4 calculates the phases and electrical angles of the current and induced voltage based on the detected applied voltage and the phase currents detected by the current detection unit 1, thereby estimating the rotor position. A rotational speed calculation unit 5 calculates the rotational speed (rotational number) of the rotor M2, for example, using dθm / dt, based on the rotor position (θm) detected by the rotor position detection unit 4. The current current value of the motor M calculated by the current calculation unit 3 and the current rotational speed value (current rotational speed value) of the rotor M2 calculated by the rotational speed calculation unit 5 are input to a storage unit 6 using a nonvolatile memory such as an EEPROM, where they are stored (or updated).

[0029] In motor drive control, the rotational speed value calculated by rotational speed calculation unit 5 is calculated by adder 8 using a target rotational speed value (also called a speed command value) input from outside to target rotational speed input unit 7, and the calculated target rotational speed value is input to voltage calculation unit 9. The target rotational speed value input to target rotational speed input unit 7 is a command value input from outside (for example, an air conditioning control device).

[0030] In sensorless deceleration control, control unit MC reads out, for example, a predetermined first rotation speed N1 that has been set in advance and stored in memory unit 6 as the target rotation speed value, and inputs it to target rotation speed input unit 7. Then, the rotation speed value calculated by rotation speed calculation unit 5 is calculated by adder 8 together with the target rotation speed value (first rotation speed N1) from target rotation speed input unit 7, and the calculated target rotation speed value is input to voltage calculation unit 9.

[0031] In motor drive control and sensorless deceleration control, a voltage calculation unit 9 calculates a voltage value that is the basis of a PWM signal, based on the current value calculated by the current calculation unit 3 and the target rotational speed value calculated by the adder 8, and inputs the calculated value to a second conversion calculation unit 10. The calculated value by the second conversion calculation unit 10 is converted from a rotor coordinate system value to U-phase, V-phase, and W-phase values ​​by the second conversion calculation unit 10. An inverter drive unit 11 generates a PWM signal based on the values ​​of each phase obtained by the second conversion calculation unit 10, and the motor drive circuit PM is controlled based on the PWM signal from the inverter drive unit 11.

[0032] In the motor drive control, the rotation speed of the rotor M2 is increased or decreased to a rotation speed corresponding to an external target rotation speed value. In the sensorless deceleration control, the rotation speed of the rotor M2 can be decreased (decelerated) to a predetermined first rotation speed N1.

[0033] The first rotation speed N1 is greater than zero. The first rotation speed N1 is set, for example, to the minimum operable rotation speed under sensorless control in the electric compressor 100. The minimum operable rotation speed is often set to a predetermined value, for example, about 500 rpm to 600 rpm, depending on the characteristics of the motor M, and a rotation speed that matches this predetermined value is set as the first rotation speed N1. Although not particularly limited, in this embodiment, the minimum operable rotation speed is 600 rpm, and the first rotation speed N1 is also set to 600 rpm.

[0034] 4 is a block diagram showing an example of the configuration of the control unit MC when synchronous deceleration control is performed. In synchronous deceleration control, the position of the rotor M2 is not detected, and the rotor M2 is forcibly rotated.

[0035] The control unit MC, which executes synchronous deceleration control, reads and uses stored current values, map data, and the like from the memory unit 6 according to a control example described later. These stored values ​​are provided to a voltage calculation unit 9 via an adder 8 according to a control example described later. A rotation speed setting unit 12 provides the voltage calculation unit 9 with a target rotation speed value that decreases at a constant deceleration rate or a gradually decreasing deceleration rate according to a control example described later until the target rotation speed N2, at which a transition to stop control is initiated, is reached. The voltage calculation unit 9 calculates a voltage value that serves as the basis for a PWM signal based on the current value obtained by the adder 8 and the target rotation speed value obtained by the rotation speed setting unit 12. A second conversion calculation unit 10 converts the calculated value from the rotor coordinate system into U-phase, V-phase, and W-phase values. An inverter drive unit 11 generates a PWM signal based on the values ​​of each phase obtained by the second conversion calculation unit 10, and the motor drive circuit PM is controlled based on the PWM signal from the inverter drive unit 11.

[0036] In the synchronous deceleration control, the rotational speed of the rotor M2 is reduced (decelerated) to a predetermined second rotational speed N2 that is set in advance.

[0037] The second rotation speed N2 is lower than the first rotation speed N1 and greater than zero. In this embodiment, the second rotation speed N2 is set to a value higher than the rotation speed corresponding to the resonance frequency (in other words, the natural frequency) of the vehicle side portion including the portion to which the housing C is fixed in the vehicle. The resonance frequency of the vehicle side portion (the bracket or frame of the vehicle) is often present in a low frequency band of, for example, approximately 1 Hz. Therefore, the second rotation speed N2 is set to a value higher than approximately 60 rpm. Although not particularly limited, in this embodiment, the second rotation speed N2 is set to 120 rpm.

[0038] In synchronous deceleration control, a current detection unit 1 detects each phase current in the same manner as in sensorless control, and a first conversion calculation unit 2 calculates a rotor coordinate system value based on the detected phase current value, and inputs the calculated value to a current calculation unit 3. The current current value of the motor M calculated by the current calculation unit 3 based on the calculation value from the first conversion calculation unit 2 is calculated by an adder 8 together with the current value stored in the storage unit 6, and the current current value is fed back.

[0039] In the stop control (brake control), the controller MC turns all of the IGBTs Q1 to Q6 off (de-energized), and then stops the rotation of the rotor M2 (the orbital orbital motion of the orbiting scroll of the compression mechanism P) by braking control, which controls the drive of predetermined switching elements (hereinafter referred to as braking control elements) among the IGBTs Q1 to Q6 so as to apply a load to the motor M. That is, when the controller MC shifts from the synchronous deceleration control to the stop control as described below, the controller MC first controls the drive of the IGBTs Q1 to Q6 so as to turn all of the IGBTs Q1 to Q6 off by the stop control. This causes the rotor M2 (compression mechanism P) to rotate by inertia. The controller MC applies a load to the motor M by performing the braking control, which controls the drive of the braking control elements while the rotor M2 is rotating by inertia. As a result, a braking force is generated against the inertial rotation of the rotor M2, and the rotation of the rotor M2 stops. The magnitude of the braking force generated by the braking control is determined based on the characteristics of the compression mechanism P and the motor M, the ON period of the braking control element, etc. The specific contents of the stop control will be described in detail later.

[0040] Here, in the control unit MC, the synchronous deceleration control is performed on the condition that a stop command to the motor M is input from outside and the rotation speed of the rotor M2 is equal to or lower than a predetermined first rotation speed N1 (here, the lowest operable rotation speed by sensorless control) and higher than a predetermined second rotation speed N2, and the stop control is performed on the condition that the rotation speed has reached the second rotation speed N2 through the synchronous deceleration control. Then, in the control unit MC, the sensorless deceleration control is performed before the synchronous deceleration control if the rotation speed of the rotor M2 when the stop command to the motor M is input from outside is higher than the first rotation speed N1.

[0041] 5 and 6 are diagrams showing examples of timing charts of the control operation of the control unit MC. Fig. 5 shows an example where the rotation speed when the stop command is input is higher than the first rotation speed N1, and Fig. 6 shows an example where the rotation speed when the stop command is input is equal to or lower than the first rotation speed N1 (lower than the first rotation speed N1 in the figure) and higher than the second rotation speed N2. Note that in Fig. 6, the rotation speed when the stop command is input is specifically lower than the first rotation speed N1, but similar control is performed when the rotation speed when the stop command is input is the same as the first rotation speed N1.

[0042] 5, when the rotation speed at the time of input of the stop command is higher than the first rotation speed N1, the control unit MC first reduces (decels) the rotation speed by sensorless deceleration control. Thereafter, when the rotation speed reaches the first rotation speed N1, the control unit MC shifts to synchronous deceleration control and reduces (decels) the rotation speed by synchronous deceleration control. Furthermore, when the rotation speed reaches the second rotation speed N2, the control unit MC shifts to stop control and stops the rotation of the rotor M2. Therefore, in the operable range of the sensorless control, the control unit MC efficiently reduces the rotation speed with the required torque (current) by sensorless deceleration control, and then shifts to synchronous deceleration control and forcibly reduces the rotation speed by synchronous deceleration control.

[0043] 6, when the rotation speed at the time of input of the stop command is equal to or less than the first rotation speed N1 and higher than the second rotation speed N2, the control unit MC skips the sensorless deceleration control (mode) and executes the synchronous deceleration control without executing the sensorless deceleration control because it is difficult to detect the position of the rotor M2. Then, when the rotation speed reaches the second rotation speed N2, the control unit MC transitions to the stop control and stops the rotation of the rotor M2 (compression mechanism P).

[0044] The control unit MC determines a target current value (command current value) for the synchronous deceleration control, for example, based on the current value X1 in sensorless control immediately before transitioning from sensorless control (motor drive control or sensorless deceleration control) to synchronous deceleration control. That is, as described above, in sensorless control, the control unit MC stores the current current value of the motor M calculated by the current calculation unit 3 and the current rotational value (current rotational speed value) of the rotor M2 calculated by the rotation speed calculation unit 5 in the memory unit 6, and these stored current values ​​and stored rotational values ​​(stored rotational speed values) are updated. Then, when transitioning from sensorless control (motor drive control or sensorless deceleration control) to synchronous deceleration control, the control unit MC performs control to determine a target current value for the synchronous deceleration control based on the immediately preceding (latest) stored current value in the sensorless control stored in the memory unit 6.

[0045] Specifically, the control unit MC having the configuration shown in FIG. 4 reads the current value (previous current value X1) stored in the memory unit 6 as the target current value for synchronous deceleration control, and provides it to the voltage calculation unit 9 via the adder 8. That is, the control unit MC uses, for example, the previous current value X1 as the target current value for synchronous deceleration control without correction (100%). In this case, as shown by the solid lines in FIGS. 5 and 6, the phase current value remains constant during synchronous deceleration control. When the pressure difference between the refrigerant suction pressure region (Ps) and discharge pressure region (Pd) is large, the rotation speed decreases, making it difficult to maintain the differential pressure state. The discharge pressure (Pd) and suction pressure (Ps) tend to equalize, but the transition time until the pressure equalization condition is reached varies depending on factors related to the control of the automotive air conditioner (e.g., the air volume in the condenser unit and the solenoid valve opening of the expansion valve). If the target current value (command current value) is lower than the immediately preceding current value X1, the output torque from the motor M may be overwhelmed by the load torque acting on the motor M due to the pressure difference, which may result in a breakdown of the synchronous deceleration control. In this case, the rotor M2 may not follow the synchronous deceleration control, causing micro-vibrations or the rotor M2 to stop due to being overwhelmed by the load torque. Therefore, the control unit MC sets the target current value during synchronous deceleration control so that it does not become lower than the immediately preceding current value X1.

[0046] That is, the controller MC may not use the linear current value X1 as the target current value in the synchronous deceleration control, but may use a value obtained by incrementally correcting (100% + α%) the previous current value X1 as the target current value in the synchronous deceleration control (X1 × 120% in the figure). In this case, the phase current value becomes a constant value higher than the previous current value X1, as indicated by the dashed-dotted lines in FIGS. 5 and 6 . By setting the target current value in the synchronous deceleration control higher than the current value X1 in the previous sensorless control, stable synchronous deceleration control is achieved. That is, the controller MC can ensure that the motor M can adequately follow the current even when affected by disturbances due to pressure conditions or refrigerant return conditions in the automotive air conditioner, thereby achieving stable deceleration control through synchronous control. When the target current value is set higher than the previous current value X1, the incremental correction rate (α value) is set so that the target current value is lower than the overload protection threshold of the motor M or the startup current of the motor M. This prevents shortened lifespans and excessive losses in inverter components such as IGBTs.

[0047] In both the case without correction (solid line in FIG. 5) and the case with correction (dashed dotted line in FIG. 5), the controller MC fixes the target current value in the synchronous deceleration control to a predetermined value equal to or greater than the immediately preceding current value X1, but this is not limited to this. That is, the controller MC may change the target current value in the synchronous deceleration control. In this case, the controller MC determines the target current value in the synchronous deceleration control based on the pressure value Ps in the suction pressure region and the pressure value Pd in ​​the discharge pressure region of the compression mechanism P when the synchronous deceleration control is being executed, and changes the determined target current value in accordance with changes in the pressure values ​​(Ps, Pd).

[0048] Specifically, when there is a pressure difference between the suction pressure region and the discharge pressure region of the refrigerant, the required torque and target current value required to rotate the motor M are confirmed in advance through experiments or the like for each differential pressure value. Reference data (e.g., table data, map data, etc.) associating the differential pressure value, the required torque, and the target current value is stored in advance in the storage unit 6. When the synchronous deceleration control is started, the control unit MC extracts from the reference data the target current value corresponding to the current differential pressure value based on a signal indicating the pressure values ​​(Ps, Pd) detected by the electric compressor 100 or a pressure sensor on the vehicle side, thereby determining the target current value. Since the differential pressure value gradually decreases during the deceleration control, the control unit MC changes the target current value in response to the change (decrease) in the differential pressure during the synchronous deceleration control. The control unit MC then provides the determined target current value from the adder 8 to the voltage calculation unit 9. The target current value is determined, for example, at predetermined control intervals. As a result, the target current value (command current value) in synchronous deceleration control is changed so as to decrease in response to a decrease in the differential pressure, and the phase current value decreases as shown by the two-dot chain lines in Figures 5 and 6. As a result, compared to control in which the target current value is fixed at a constant value (as shown by the solid and dashed dotted lines in Figure 5), a torque sufficient to rotate the motor M is output, thereby reducing unnecessary load on the electric compressor 100, such as excessive motor heat generation and IGBT overheating, more effectively reducing power consumption, and more reliably ensuring the life of inverter components such as the IGBT. Note that the target current value may be determined by calculating the target current value at each predetermined control period based on a regression equation that shows the relationship between the load torque (target current value) of the electric compressor and the differential pressure, rather than by extraction from reference data.

[0049] The control unit MC also executes control to determine a target rotational speed (also referred to as a speed command value or a target rotational speed value) in the synchronous deceleration control. Specifically, a rotational speed setting unit 12 (see FIG. 4) of the control unit MC provides the voltage calculation unit 9 with a target rotational speed that decreases at a predetermined (constant) deceleration rate that is set in advance and stored internally, until the target rotational speed reaches a second rotational speed N2 that is set to transition to stop control.

[0050] FIG. 7 is a conceptual diagram showing an example of a change in the target rotational speed (speed command value) due to synchronous deceleration control. In synchronous deceleration control, the control unit MC (rotational speed setting unit 12) reduces (decels) the rotational speed in a linear deceleration pattern with a constant deceleration rate, for example, as shown by the solid line in FIG. 7. That is, the rotational speed setting unit 12 provides the voltage calculation unit 9 with a target rotational speed (speed command value) that is reduced (decels) in a linear deceleration pattern with a constant deceleration rate until the second rotational speed N2 is reached. As a result, as shown in FIGS. 5 and 6, the rotational speed decreases at a constant deceleration rate from the first rotational speed N1 to the second rotational speed N2. Data related to the deceleration rate is set in advance and stored in the storage unit 6.

[0051] However, the deceleration pattern is not limited to a linear deceleration pattern. For example, in the synchronous deceleration control, the control unit MC (rotation speed setting unit 12) may reduce (deceler) the rotation speed using a curved deceleration pattern in which the deceleration gradually decreases, as shown by the dashed line in FIG. 7 . The gradually decreasing deceleration data is preset and stored in the memory unit. That is, a linear constant deceleration or a one-time delay speed command value is used as the target rotation speed in the synchronous deceleration control. Referring to FIG. 7 , when the time Tb until the synchronous deceleration control ends (i.e., the duration Tb of the synchronous deceleration control) is the same, the curved deceleration pattern (dashed line) causes the rotation speed to reach the second rotation speed N2 earlier than the linear deceleration pattern (solid line) and maintains the low-speed operating state for a longer period than the linear deceleration pattern. Therefore, the curved deceleration pattern can mitigate the reverse rotation caused by the pressure difference between the suction pressure region and the discharge pressure region, and reduce the movement of the electric compressor 100 itself and the reaction movement to the electric compressor 100 due to deceleration, resulting in a quieter stop.

[0052] When the deceleration is constant, the smaller the deceleration value, the longer the time Tb until the synchronous deceleration control is terminated. When the deceleration gradually decreases, the smaller the initial deceleration amount, the longer the time Tb until the synchronous deceleration control is terminated. In the above example, the time Tb until the synchronous deceleration control is terminated is fixed to a predetermined value (time) determined by the preset deceleration of the linear deceleration pattern or the curved deceleration pattern.

[0053] If the synchronous deceleration control is terminated in a short time when the differential pressure between the pressure value Pd in ​​the discharge pressure region and the pressure value Ps in the suction pressure region is relatively high, it may be difficult to sufficiently suppress the occurrence of movements (behaviors) including reverse rotation and vibrations during stoppage (after reaching the second rotation speed N2). Therefore, the longer the time Tb until the synchronous deceleration control is terminated, the better. In the above control example, the time Tb until the synchronous deceleration control is terminated is a fixed value. However, this is not limited to this, and the time Tb may be configured to be variable depending on the differential pressure. In other words, the control unit MC may determine the time Tb until the synchronous deceleration control is terminated based on the pressure value Ps in the suction pressure region and the pressure value Pd in ​​the discharge pressure region of the compression mechanism P immediately before the transition from sensorless control to synchronous deceleration control.

[0054] Specifically, when there is a pressure difference between the suction pressure region and the discharge pressure region of the refrigerant, the optimal duration Tb of the synchronous deceleration control is confirmed in advance through experiments or the like for each differential pressure value. Log data of the differential pressure value based on pressure values ​​(Ps, Pd) from the pressure sensor is stored in the memory unit 6. Reference data (table data, map data, etc.) associating the differential pressure value with the duration is also stored in the memory unit 6. When the control unit MC transitions to the synchronous deceleration control, it determines the duration by extracting from the reference data the duration corresponding to the differential pressure value immediately before the transition. As a result, when the differential pressure value immediately before the transition is relatively low (see FIG. 7 ), the duration Tb of the synchronous deceleration control is shorter than that shown in FIG. 8 , which shows an example of a case where the differential pressure is high. This reduces unnecessary operation and allows for a prompt transition to stop control. When the differential pressure immediately before the transition is relatively high (see FIG. 8 ), the duration Tb of the synchronous deceleration control is longer than that shown in FIG. 7 , which reliably reduces reverse rotation and vibration after the second rotation speed N2 is reached.

[0055] Returning to FIGS. 5 and 6, when the rotation speed reaches the second rotation speed N2 through the above-described synchronous deceleration control, the control unit MC finally executes the stop control.

[0056] Specifically, the control unit MC drives all IGBTs Q1 to Q6 to the OFF state, and then performs the braking control by simultaneously turning on (also referred to as the Hi state) all low-side devices or all high-side devices (in FIGS. 5 and 6, the low-side devices IGBTs (Q2, Q4, Q6)). In the braking control of the stop control, if the detected current value detected by the current detection unit 1 is higher than a predetermined first threshold, the control unit MC turns off all IGBTs Q1 to Q6. In addition, in the braking control, if the detected current value is lower than the first threshold, the control unit MC adjusts the drive pattern of the braking control devices so that the detected current value does not exceed a predetermined second threshold that is lower than the first threshold. Although not particularly limited, the braking control devices serving as the predetermined switching devices whose drive pattern is to be adjusted are all low-side devices IGBTs (Q2, Q4, Q6).

[0057] In this embodiment, the first threshold is set to a value lower than the current value that may damage the IGBT, for example, a value equivalent to an abnormal current value that may occur when an overload occurs in the motor M. The second threshold is set to a peak value of a startup current that occurs at startup in the motor drive control. Because a current of the second threshold flows through the motor drive circuit PM at startup, IGBTs Q1 to Q6 that are tolerant to a current of the second threshold are selected. Furthermore, the second threshold is higher than the rated current value that flows through the motor drive circuit PM during the motor drive control after startup. In other words, the relationship: first threshold > second threshold > rated current value is established.

[0058] The adjustment of the drive patterns of all low-side IGBTs (Q2, Q4, Q6) during the braking control is performed by periodically changing the duty ratio, which indicates the proportion of time that all low-side IGBTs (Q2, Q4, Q6) are in an on-state during a predetermined period T. More specifically, at the start of the braking control, the controller MC turns all low-side IGBTs (Q2, Q4, Q6) on for a period based on a predetermined initial duty ratio. Then, if the detected current value is lower than a second threshold, the controller MC increases the duty ratio by a predetermined percentage. If the detected current value is higher than the second threshold, the controller MC maintains the duty ratio or decreases the duty ratio by a predetermined percentage. This duty ratio adjustment is performed periodically, and the duty ratio eventually reaches 100%, maximizing the braking force. Even when the braking force reaches its maximum, the vehicle may coast in a forward rotation state. Therefore, the controller MC maintains this state for a predetermined time after the maximum braking force is reached to reliably stop the coasting rotation. More specifically, although not particularly limited, the control unit MC executes zero vector energization as the braking control, which simultaneously and intermittently turns on all the low-side device IGBTs (Q2, Q4, Q6). That is, this zero vector energization is not maintained during the braking control, but is released (turned off) for a period (time) corresponding to the duty ratio at every predetermined period.

[0059] Next, the overall flow of the control operation of the control unit MC will be described with reference to Fig. 9. Fig. 9 is a flow chart for explaining the overall flow of the control operation by the control unit MC.

[0060] When a stop command for the motor M is input to the control unit MC from an external device (reception of the motor stop command), the control unit MC starts control to stop the rotation of the rotor M2 (STEP 1). First, at the time of input (reception) of the stop command, that is, when the rotor M2 is currently rotating, it determines whether or not it is equal to or less than the first rotation speed N1 (STEP 2). The control unit MC also measures the elapsed time Tc since the stop command was input. If the rotation speed is higher than the first rotation speed N1 (NO) in STEP 2, the control unit MC transitions to sensorless deceleration control (STEP 3) and continues to execute the sensorless deceleration control in the sensorless control mode until the rotation speed reaches the first rotation speed (STEP 2: YES). If the rotation speed is equal to or less than the first rotation speed N1 (YES) in STEP 2, the control unit MC determines whether the rotation speed is higher than the second rotation speed N2 (STEP 4). If the rotation speed is equal to or less than the second rotation speed N2 (NO), the control unit MC skips the synchronous deceleration control and transitions to stop control, starting the stop control (STEP 8). On the other hand, if the rotation speed is greater than the second rotation speed N2 in STEP 4 (YES), the control unit MC transitions to synchronous deceleration control and starts the synchronous deceleration control (STEP 5). In the synchronous deceleration control, the control unit MC determines or changes the target current value and the target rotation speed value according to the control example described above (STEP 6). In the synchronous deceleration control, the control unit MC determines whether at least one of Condition 1, that is, that the rotation speed is equal to or less than the second rotation speed N2, and Condition 2, that is, that the elapsed time Tc from the stop command is equal to or greater than a predetermined elapsed time threshold Tc1, is satisfied (STEP 7). If at least one of Conditions 1 and 2 is not satisfied in STEP 7 (NO), that is, if the rotation speed is higher than the second rotation speed N2 (Condition 1 is not satisfied) and the elapsed time Tc from the stop command is shorter than the elapsed time threshold Tc1 (Condition 2 is not satisfied), the control unit MC continues the synchronous deceleration control. On the other hand, if at least one of Condition 1 and Condition 2 is satisfied in STEP 7 (YES), that is, if the rotation speed is equal to or greater than the second rotation speed N2 (Condition 1 is satisfied), if the elapsed time Tc from the stop command is equal to or greater than the elapsed time threshold Tc1 (Condition 2 is satisfied), or if either Condition 1 or Condition 2 is satisfied, the control unit MC shifts to stop control and executes the stop control (STEP 8). The control unit MC measures the time since the shift to stop control, that is, the duration Td of the stop control.Then, the control unit MC determines whether the duration Td of the stop control is equal to or longer than a predetermined duration threshold Td1 (STEP 9). If the duration Td of the stop control is shorter than the duration threshold Td1 (NO) in STEP 9, the control unit MC continues the stop control. On the other hand, if the duration Td of the stop control reaches the duration threshold Td1 (YES in STEP 9), the maximum braking force state has elapsed for a sufficient period of time, and the inertial rotation has been reliably stopped. At this time, the control unit MC ends the braking control, all IGBTs Q1 to Q6 are turned off, and the control unit MC ends the stop control (STEP 10). This ends the control by the control unit MC to stop the rotation of the rotor M2 (STEP 11).

[0061] In the electric compressor 100 according to this embodiment, the controller MC executes synchronous deceleration control, which reduces the rotational speed of the rotor M2 through forced synchronous control using a current of a predetermined target current value, when a stop command is input from an external device to the motor M and the rotational speed of the rotor M2 is equal to or lower than a predetermined first rotational speed N1 and higher than a predetermined second rotational speed N2. Therefore, for example, by simply presetting the first rotational speed N1 to a value equal to the minimum operable rotational speed under sensorless control, even if the rotational speed of the rotor M2 at the time of input of the stop command is lower than the minimum operable rotational speed under sensorless control, the rotor M2 does not rotate by inertia, but the rotational speed of the rotor M2 is reduced (decelerated) through synchronous deceleration control. As a result, quieter operation during shutdown is achieved than in the past. Furthermore, after the rotational speed reaches the second rotational speed N2 through synchronous deceleration control, the controller MC stops the rotation of the rotor M2 through stop control. This quickly prevents or suppresses reverse rotation of the rotor M2 (compression mechanism P) and the generation of abnormal noise due to this reverse rotation. In this way, the electric compressor 100 is provided that can improve quietness compared to conventional electric compressors after an external command to stop operation is input. That is, the rotor M2 is decelerated by the synchronous deceleration control to a low rotation speed range where it is difficult to estimate the position of the rotor M2 and deceleration by sensorless control is not possible, and reverse rotation is prevented by the stop control, so that noise (NVH) when stopped is improved, thereby providing a comfortable environment for the entire vehicle.

[0062] In this embodiment, when the rotation speed at the time of input of the stop command is higher than the first rotation speed N1, the control unit MC executes the sensorless deceleration control before the synchronous deceleration control. Therefore, in the operable range of the sensorless control, the control unit MC efficiently reduces the rotation speed with the required torque (current) by the sensorless deceleration control, thereby suppressing power consumption.

[0063] In this embodiment, the second rotation speed N2, which is the rotation speed at which the synchronous deceleration control is switched to the stop control, is set to a value higher than the rotation speed corresponding to the resonant frequency of the vehicle-side portion, including the portion of the vehicle to which the housing C of the electric compressor 100 is fixed. This allows the electric compressor 100 to drive the motor M in the synchronous deceleration control within an operating range (first rotation speed N1 to second rotation speed N2) that avoids the rotation speed corresponding to the resonant frequency of the vehicle-side portion (the vehicle bracket or frame). This more reliably suppresses the generation of vibration and noise in the low rotation speed range, thereby creating a more comfortable environment for the vehicle as a whole. Specifically, for example, if the second rotation speed N2 is zero, the rotation speed of the rotor M2 may pass through the rotation speed corresponding to the resonant frequency of the vehicle-side portion during the synchronous deceleration control, which may result in the generation of low-frequency noise and vibration during the synchronous deceleration control. In this regard, the electric compressor 100 of this embodiment is configured to operate within an operating range that avoids the rotation speed corresponding to the resonant frequency of the vehicle-side portion.

[0064] In this embodiment, the braking control elements as the specified switching elements to be subjected to the adjustment of the drive pattern are all low-side elements IGBT (Q2, Q4, Q6), but this is not limited thereto and may be all high-side elements IGBT (Q1, Q3, Q5).

[0065] In the present embodiment, the controller MC performs zero vector energization to simultaneously and intermittently turn on all of the low-side IGBTs (Q2, Q4, Q6) or all of the high-side IGBTs (Q1, Q3, Q5) during the stop control. However, this is not limiting. For example, the controller MC may (1) intermittently drive one IGBT among the high-side IGBTs (Q1, Q3, Q5) and one IGBT among the low-side IGBTs (Q2, Q4, Q6) to the on state, (2) intermittently drive two IGBTs among the high-side IGBTs (Q1, Q3, Q5) and one IGBT among the low-side IGBTs (Q2, Q4, Q6) to the on state, or (3) intermittently drive one IGBT among the high-side IGBTs (Q1, Q3, Q5) and two IGBTs among the low-side IGBTs (Q2, Q4, Q6) to the on state. In these cases, the IGBT to be driven is determined so that the high-side element and the low-side element of the same phase are not simultaneously turned on.

[0066] The above describes the embodiments of the present invention and their modifications. However, the present invention is not limited to the above-described embodiments and modifications, and it goes without saying that further modifications and changes are possible based on the technical concept of the present invention. [Explanation of symbols]

[0067] B... DC power supply, C... housing, IGBT (Q1 to Q6)... multiple switching elements, M... motor, M2... rotor, MC... control unit, N1... first rotation speed, N2... second rotation speed, P... compression mechanism, Pd... pressure value in suction pressure region, Ps... pressure value in discharge pressure region, PM... motor drive circuit, 100... electric compressor

Claims

1. 1. An electric compressor comprising: a compression mechanism that compresses and discharges a refrigerant; a motor that drives the compression mechanism; a motor drive circuit that is connected between the motor and a DC power supply and has a plurality of switching elements; and a control unit that controls drive of the motor, including sensorless control that increases or decreases the rotation speed of the rotor while estimating a position of a rotor of the motor based on a current value of a current flowing from the motor drive circuit to the motor, The control unit a synchronous deceleration control that is performed when a stop command to the motor is input from outside and the rotation speed of the rotor is equal to or less than a predetermined first rotation speed and higher than a predetermined second rotation speed, and that reduces the rotation speed by forced synchronous control using a current of a predetermined target current value; and stop control, which is performed on the condition that the rotation speed has reached the second rotation speed by the synchronous deceleration control, and which stops the rotation of the rotor by braking control that controls drive of a predetermined one of the plurality of switching elements so as to apply a load to the motor.

2. 2. The electric compressor according to claim 1, wherein, when the rotation speed when the stop command is input from outside is higher than the first rotation speed, the control unit executes, before the synchronous deceleration control, sensorless deceleration control to reduce the rotation speed until it reaches the first rotation speed through the sensorless control.

3. a housing that houses the compression mechanism, the motor, the drive circuit, and the control unit and is fixed to the vehicle; 3. The electric compressor according to claim 1, wherein the second rotational speed is set to a value higher than a rotational speed corresponding to a resonance frequency of a vehicle-side portion including a portion of the vehicle to which the housing is fixed.

4. 4. The electric compressor according to claim 1, wherein the control unit determines the target current value in the synchronous deceleration control based on the current value in the sensorless control immediately before transition from the sensorless control to the synchronous deceleration control.

5. 4. The electric compressor according to claim 1, wherein the control unit determines the target current value in the synchronous deceleration control based on a pressure value in a suction pressure region and a pressure value in a discharge pressure region of the compression mechanism when the synchronous deceleration control is being executed, and changes the determined target current value in accordance with a change in the pressure values.

6. 6. The electric compressor according to claim 1, wherein the control unit, in the synchronous deceleration control, reduces the rotation speed using a linear deceleration pattern in which deceleration is constant or a curved deceleration pattern in which deceleration gradually decreases.

7. 7. The electric compressor according to claim 6, wherein the control unit determines a time until the synchronous deceleration control is terminated based on a pressure value in a suction pressure region and a pressure value in a discharge pressure region of the compression mechanism immediately before transition from the sensorless control to the synchronous deceleration control.

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