MOTOR-DRIVEN COMPRESSOR

Abstract

A motor-driven compressor (10), comprising: a compression unit (15) configured to compress a fluid; a motor (16) containing three-phase coils (19) and configured to drive the compression unit (15); an inverter circuit (24) with a switching element configured to perform switching to drive the motor (16), wherein the three-phase coils (19) are arranged on an output side of the inverter circuit (24) and connected to the inverter circuit (24); a capacitor (32) arranged on an input side of the inverter circuit (24) and connected in parallel to a DC power supply (31); a controller (25) configured to output three-phase pulse width modulation (PWM) signals to the inverter circuit (24) to control the inverter circuit (24); a temperature estimator configured to estimate the temperature of the capacitor (32); and a rotor position estimator configured to estimate the position of a rotor (18, 30) of the motor (16), wherein the controller (25) is configured to perform a process for determining the current pattern when the temperature of the capacitor (32) estimated by the temperature estimator is less than or equal to a predetermined temperature, the process for determining the current pattern involves selecting a current pattern of the motor (16) from six current patterns according to the position of the rotor (18, 30) estimated by the rotor position estimator, a direct current with a maximum permissible value in the positive or negative direction always flows only through one of the three-phase coils (19) and a direct current in opposite phase with half a maximum value flows through each of the other two of the three-phase coils in each of the six current patterns, the controller (25) is configured to perform a process to determine the maximum allowable value, in order to determine the maximum allowable value based on information from the temperature estimator, the controller (25) is configured to perform a phase angle shifting process to shift a phase angle of one of the three-phase PWM signals generated according to the current pattern selected by the current pattern determination process, and the six current patterns have the same phase angle ranges.

Description

BACKGROUND

[0001] The present disclosure relates to a motor-driven compressor.

[0002] A typical motor-driven compressor includes a compression unit that compresses fluids, a motor that drives the compression unit, an inverter circuit containing a switching element, and a controller that manages the inverter circuit. The switching element performs a switching operation to drive the motor. Three-phase coils are located on the output side of the inverter circuit. That is, the inverter circuit is connected to the three-phase coils. The controller outputs three-phase pulse-width modulation (PWM) signals to the inverter circuit to control it. When the switching element then switches based on the PWM signals output by the controller, a direct current from a DC power supply is converted into an alternating current and fed to the coil of each phase of the motor to drive the motor.

[0003] The input side of the inverter circuit contains a capacitor connected in parallel to the DC power supply. In extremely low temperatures (e.g., 0°C or below), the capacitor's equivalent series resistance (ESR) increases significantly. If current flows through the capacitor when its ESR is at its highest, an overvoltage is generated. If this overvoltage exceeds the voltage rating of the switching element, it can be damaged.

[0004] For example, Japanese patent application JP 2016-32420A describes a phase angle shifting process to shift the phase angle of at least one of the three-phase PWM signals input to the inverter circuit when the capacitor temperature is less than or equal to a predetermined temperature. Specifically, the phase angle of at least one of the PWM signals input to the inverter circuit is shifted to shorten the period during which the polarities of the output voltages of the three phases (U-phase, V-phase, W-phase) output by the inverter circuit are all the same (all high polarity or all low polarity).The current flowing through the capacitor as a result of switching by the switching element based on the PWM signals after the phase angle shift process is greater than the current flowing through the capacitor as a result of switching by the switching element based on the PWM signals before the phase angle shift process. This causes the capacitor to heat up.

[0005] However, the value of the current flowing through each phase changes depending on the position of the rotor. Therefore, the value of the current flowing through the capacitor also changes depending on the rotor's position. Even if the phase angle shifting process is carried out as described in the patent document above, the capacitor may not heat up sufficiently depending on the rotor's position.

[0006] WEI, Yanyu [et al.]: Current Limit Strategy for BLDC Motor Drive With Minimized DC-Link Capacitor. IEEE Transactions on Industry Applications, Vol. 51, 2015, No. 5, pp. 3907-3913. IEEE Xplore [online] describes a current-sampling method to replace a cyclic mode that results in a current limit failure after the elimination of the reverse current.

[0007] DAHONO, PA; SATO, Y.; KATAOKA, T.: Analysis and minimization of ripple components of input current and voltage of PWM inverters. IEEE Transactions on Industry Applications, Vol. 32, 1996, No. 4, pp. 945-950. IEEE Xplore [online] relates to an analysis and minimization of the ripple components of the input current and input voltage of three-phase voltage source PWM inverters. German patent application DE 101 27 670 A1 relates to block commutation. An electric motor is controlled such that the commutation angle is less than 180° and greater than 120°.

[0008] US patent application US 2006 / 0138994A1 describes a current command generation circuit for generating a target current command signal based on a position signal and a predetermined phase angle, wherein the phase angle of the target current command signal is determined by the predetermined phase angle. SUMMARY OF THE REVELATION

[0009] One objective of the present disclosure is to provide a motor-driven compressor that directly heats a condenser regardless of the position of a rotor.

[0010] This summary is intended to present, in simplified form, a selection of concepts that are described in detail below. This summary is neither intended to identify the main features or essential characteristics of the claimed subject matter, nor is it intended to serve as an aid in determining the scope of the claimed subject matter.

[0011] In general terms, a motor-driven compressor is provided. The motor-driven compressor includes a compression unit, a motor, an inverter circuit, a capacitor, a controller, a temperature estimator, and a rotor position estimator. The compression unit is configured to compress a fluid. The motor contains three-phase coils and is configured to drive the compression unit. The inverter circuit contains a switching element configured to perform the switching to drive the motor. The three-phase coils are located on an output side of the inverter circuit and connected to it. The capacitor is located on an input side of the inverter circuit and connected in parallel to a DC power supply. The controller is configured to output three-phase PWM signals to control the inverter circuit.The temperature estimator is configured to estimate the temperature of the capacitor. The rotor position estimator is configured to estimate the position of a motor rotor. The controller is configured to perform a current pattern determination process when the capacitor temperature estimated by the temperature estimator is less than or equal to a predetermined temperature. The current pattern determination process involves selecting a motor current pattern from six available patterns based on the rotor position estimated by the rotor position estimator. The current with a maximum allowable value in either the positive or negative direction always flows through only one of the three-phase coils in each of the six current patterns.The controller is configured to perform a maximum allowable value (MVV) determination process to calculate the maximum allowable value based on information from the temperature estimator. The controller is also configured to perform a phase angle shifting process to shift the phase angle of one of the three-phase PWM signals generated according to the current pattern selected by the MVV determination process. The six current patterns have equal phase angle ranges.

[0012] Further features and aspects will emerge from the following detailed description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a side view of a motor-driven compressor in cross-section according to one embodiment. Fig. Figure 2 is a circuit diagram showing the electrical configuration of the engine-driven compressor. Fig. Figure 3 is a diagram showing the relationship between the currents flowing through a motor and the position of a rotor. Fig. Figure 4 is a diagram showing the relationship between the currents flowing through the motor and the position of the rotor in a heating control mode. Fig. Figure 5 is a table showing the relationship between the position of the rotor and a current pattern of the motor in heating control mode. Fig. Figure 6 is a diagram showing the relationship between the changes in currents flowing through the motor, the changes in the three-phase PWM signals, and the changes in current flowing to a capacitor in a current-energizing pattern where the rotor position is 0°. Fig. Figure 7 is a flowchart showing a control process performed by a controller. Fig. Figure 8 is a diagram showing a current flow at time T1 in Fig. 6 shows. Fig. Figure 9 is a diagram showing the current flow at time T2 in Fig. 6 shows. Fig. 10 is a diagram showing the current flow at time T3 in Fig. 6 shows. Fig. 11 is a diagram showing the current flow at time T4 in Fig. 6 shows. Fig. 12 is a diagram showing the current flow at time T5 in Fig. 6 shows. Fig. 13 is a diagram showing the current flow at time T6 in Fig. 6 shows. Fig. Figure 14 is a diagram showing the relationship between changes in the currents flowing through the motor, changes in the three-phase PWM signals, and changes in the current flowing to the capacitor in a current-energizing pattern where the rotor position is 0° when a controller of a comparison example does not perform a phase angle shift process. Fig. 15 is a schematic diagram showing the current flow at time T11 in Fig. 14 shows. Fig. Figure 16 is a schematic diagram showing the current flow at time T12 in Fig. 14 shows. Fig. 17 is a schematic diagram showing the current flow at time T13 in Fig. 14 shows. Fig. 18 is a schematic diagram showing the current flow at time T14 in Fig. 14 shows. Fig. Figure 19 is a schematic diagram showing the current flow at time T15 in Fig. 14 shows. Fig. 20 is a schematic diagram showing the current flow at time T16 in Fig. 14 shows. Fig. Figure 21 is a diagram showing the relationship between the changes in currents flowing through the motor, the changes in the three-phase PWM signals, and the changes in current flowing to the capacitor in a current-energizing pattern where the rotor position is 30°, according to a comparative example. Fig. 22 is a schematic diagram showing the current flow at time T21 in Fig. 21 shows. Fig. 23 is a schematic diagram showing the current flow at time T22 in Fig. 21 shows. Fig. 24 is a schematic diagram showing the current flow at time T23 in Fig. 21 shows.

[0013] In the drawings and the detailed description, the same reference numbers refer to the same elements. The drawings need not be to scale, and the relative size, proportions, and representation of the elements in the drawings may be exaggerated for clarity, illustration, and convenience. EXECUTIVE FORM OF THE REVELATION

[0014] This description enables a comprehensive understanding of the described processes, apparatus, and / or systems. Modifications and equivalents of the described processes, apparatus, and / or systems are apparent to a person skilled in the art. The procedures are exemplary and can be modified as is apparent to a person skilled in the art, with the exception of work processes that necessarily follow a specific sequence. Descriptions of functions and designs known to a person skilled in the art may be omitted.

[0015] Exemplary embodiments can take various forms and are not limited to the examples described. However, the examples described are thorough and complete and convey the full scope of the disclosure to a person skilled in the art.

[0016] A motor-driven compressor according to one embodiment is now being compared based on the Fig. 1 to 24 described. The motor-driven compressor in the present embodiment is intended, for example, for use in a vehicle air conditioning system.

[0017] As in Fig. As shown in Figure 1, a motor-driven compressor 10 comprises a housing 11. The housing 11 contains an outlet housing 12 and a motor housing 13. The outlet housing part 12 is cylindrical and includes an end wall. The motor housing part 13 is cylindrical and coupled to the outlet housing part 12. The outlet housing part 12 and the motor housing part 13 are made of metal (e.g., aluminum). The motor housing part 13 includes an end wall 13e and a side wall 13a (circumferential wall). The side wall 13a is cylindrical and extends from the periphery of the end wall 13e.

[0018] The motor housing part 13 accommodates a rotating shaft 14. A compression unit 15 and a motor 16 are also housed within the motor housing part 13. The rotation of the rotating shaft 14 drives the compression unit 15, compressing a refrigerant, which is a fluid. The motor 16 rotates the rotating shaft 14 to drive the compression unit 15. The compression unit 15 and the motor 16 are arranged axially adjacent to each other, i.e., in the direction of the axis of rotation of the rotating shaft 14. The motor 16 is located closer to the end wall 13e of the motor housing part 13 than the compression unit 15.

[0019] The compression unit 15, for example, is of a scroll type and contains a worm gear (not shown) that is fixed in the motor housing part 13, and a movable worm gear (not shown) that is arranged opposite the fixed worm gear. The compression unit 15 need not be of a scroll type and could be of a piston type, a vane type, or similar design.

[0020] The motor 16 comprises a cylindrical stator 17 and a rotor 18 located on the inside of the stator 17. The rotor 18 rotates integrally with the rotating shaft 14. The stator 17 surrounds the rotor 18. The rotor 18 encloses a rotor core 18a and a plurality of permanent magnets 18b. The rotor core 18a is attached to the rotating shaft 14, and the permanent magnets 18b are arranged on the rotor core 18a. The stator 17 comprises a cylindrical stator core 17a and coils 19 wound around the stator core 17a. When the coils 19 are energized, the rotor 18 rotates. The rotating shaft 14 rotates integrally with the rotor 18.

[0021] An inlet opening 13h is formed in the side wall 13a. The inlet opening 13h draws refrigerant into the motor housing part 13. The inlet opening 13h is connected to one end of an external refrigerant circuit 20. An outlet opening 12h is formed in the outlet housing part 12. The outlet opening 12h is connected to the other end of the external refrigerant circuit 20.

[0022] The refrigerant is drawn from the external refrigerant circuit 20 through the inlet opening 13h into the motor housing part 13. The compression unit 15 is driven to compress the refrigerant and discharge it from the outlet opening 12h into the external refrigerant circuit 20. The refrigerant then flows through the external refrigerant circuit 20 via a heat exchanger and an expansion valve and returns to the motor housing part 13. The motor-driven compressor 10 and the external refrigerant circuit 20 form a vehicle air conditioning system 21.

[0023] A cylindrical cover 22, comprising an end wall, is coupled to the end wall 13e of the motor housing part 13. The end wall 13e of the motor housing part 13 and the cover 22 define a receiving space 22a. The receiving space 22a accommodates an inverter circuit 24, which drives the motor 16. The compression unit 15, the motor 16, and the inverter circuit 24 are arranged side by side in the axial direction of the rotating shaft 14.

[0024] As in Fig. As shown in Figure 2, the coils 19 of the motor 16 form a three-phase construction with a U-phase coil 19u, a V-phase coil 19v and a W-phase coil 19w. In the present embodiment, the U-phase coil 19u, the V-phase coil 19v and the W-phase coil 19w form a Y-connection.

[0025] Inverter circuit 24 contains the switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2. These switching elements perform the switching to drive motor 16. The switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 are, for example, insulated-gate bipolar transistors (IGBTs as power switching elements). The switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 are connected to the diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2. The diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2 are connected in parallel to the switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2.

[0026] The switching elements Qu1, Qv1, and Qw1 each form an upper arm of a corresponding phase. The switching elements Qu2, Qv2, and Qw2 each form a lower arm of a corresponding phase. The switching elements Qu1 and Qu2 are connected in series via a central point, as are the switching elements Qv1 and Qv2, and Qw1 and Qw2. The gates of the switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 are electrically connected to a controller 25. The collectors of the switching elements Qu1, Qv1, and Qw1 are electrically connected to the positive terminal of a DC power supply 31, which is a vehicle battery. The emitters of the switching elements Qu2, Qv2, and Qw2 are electrically connected to the negative terminal of the DC power supply 31 via corresponding current sensors 41u, 41v, and 41w.The emitters of switching elements Qu1, Qv1, and Qw1 are electrically connected via their respective center points to the U-phase coil 19u, the V-phase coil 19v, and the W-phase coil 19w, respectively. The collectors of switching elements Qu2, Qv2, and Qw2 are also electrically connected via their respective center points to the U-phase coil 19u, the V-phase coil 19v, and the W-phase coil 19w, respectively. Therefore, the coil 19 of each phase of the motor 16 is located at an output side of the inverter circuit 24 and connected to the inverter circuit 24.

[0027] The motor-driven compressor 10 contains a capacitor 32, which is connected in parallel to the DC power supply 31. The capacitor 32 is located on one input side of the inverter circuit 24. The capacitor 32 is, for example, an electrolytic capacitor.

[0028] The motor-driven compressor 10 contains a voltage sensor 33 that detects an input voltage from the DC power supply 31. The voltage sensor 33 is electrically connected to the controller 25 to transmit a measurement result to the controller 25.

[0029] The controller 25 controls a drive voltage of the motor 16 by pulse width modulation. Specifically, the controller 25 generates three-phase pulse width modulation (PWM) signals from a high-frequency triangular wave signal, referred to as the carrier wave signal, and a voltage command signal that assigns a voltage. The PWM signal, which is a square wave signal that has undergone pulse width modulation, controls an output voltage of the inverter circuit 24. The three-phase PWM signals each contain a predetermined phase angle and a predetermined duty cycle. Furthermore, the controller 25 sends the generated three-phase PWM signals to the switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 to control the switching (on / off control) of these switching elements. The controller 25 is therefore a controller that sends the three-phase PWM signals to the inverter circuit 24 in order to control the inverter circuit 24.The controller 25 or its components can be circuits containing: 1) one or more processors running a computer program (software); 2) one or more dedicated hardware circuits, such as an application-specific integrated circuit (ASIC), executing at least some of the various types of processes; or 3) a combination thereof. A processor contains a CPU and memory, such as RAM or ROM. The memory stores program code or instructions configured to execute a process with the CPU. The memory, which is a computer-readable medium, can be any available medium accessible to a general-purpose or dedicated computer.

[0030] The controller 25 controls the inverter circuit 24 to convert the direct current from the DC power supply 31 into alternating current. The switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 each perform a switching operation to convert the direct current from the DC power supply 31 into alternating current. The alternating current is then supplied to the motor 16 to drive the motor 16.

[0031] Controller 25 is electrically connected to an electronic climate control unit (ECU) that controls the entire vehicle climate control system 21. The climate control ECU 26 is configured to receive a passenger compartment temperature, a previously set temperature, or similar information and, based on these parameters, transmits information regarding a target engine speed 16 to controller 25. Furthermore, the climate control ECU 26 transmits various types of commands to controller 25, such as an activation command for engine 16 and a deactivation command for engine 16.

[0032] The controller 25 is configured to control the rotation of the motor 16 by estimating the position θ of the rotor 18 of the motor 16 based on the current flowing from the inverter circuit 24 to the motor 16, without using a rotation angle sensor such as a resolver to detect the position θ of the rotor 18 of the motor 16. The motor-driven compressor 10 of the present embodiment performs position sensorless control, which controls the rotation of the motor 16 based on the position θ of the rotor 18 estimated by the controller 25. Thus, the controller 25 also serves as a rotor position estimator, estimating the position θ of the rotor 18 of the motor 16.

[0033] In particular, the controller 25 prestores a rotor position estimation program for estimating the position θ of the rotor 18 from a U-phase current Iu, a V-phase current Iv, and a W-phase current Iw flowing through the motor 16 and detected by the current sensors 41u, 41v, and 41w, and the input voltage detected by the voltage sensor 33. The controller 25 estimates the position θ of the rotor 18 based on the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw flowing through the motor 16 and detected by the current sensors 41u, 41v, and 41w, the input voltage detected by the voltage sensor 33, and the rotor position estimation program.

[0034] The controller 25 converts the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw into a d-axis current (excitation component current) and a q-axis current (torque component current), based on the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw flowing through the motor 16 and detected by the current sensors 41u, 41v, and 41w, as well as the estimated position θ of the rotor 18. The d-axis current (excitation component current) is a current vector component of the current flowing through the motor 16, acting in the same direction as the magnetic flux generated by the permanent magnets 18b. The q-axis current (torque component current) is a current vector component of the current flowing through the motor 16, acting in a direction perpendicular to the d-axis.

[0035] The controller 25 controls the on / off switching of the switching elements Qu1, Qu2, Qv1, Qv2, Qw1 and Qw2 based on the U-phase current Iu, the V-phase current Iv and the W-phase current Iw flowing through the motor 16 and detected by the current sensors 41u, 41v and 41w, such that the d-axis current (excitation component current) and the q-axis current (torque component current) at the motor 16 are equal to the setpoint values. In this way, the motor 16 is rotated at the target speed transmitted by the air conditioning control unit 26.

[0036] Fig. Figure 3 shows the relationship between the current flowing through the motor 16 and the position θ of the rotor 18. Fig. Figure 3 shows the waveform of the U-phase current Iu by the solid line, the waveform of the V-phase current Iv by the single dashed line, and the waveform of the W-phase current Iw by the double dashed line. As in Fig. As shown in Figure 3, the waveforms of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw are formed by sinusoidal waves whose phase angles are offset by 120° from each other. The ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw satisfies the ratio Iu + Iv + Iw = 0, regardless of the position θ of the rotor 18.

[0037] In the present embodiment, for example, if Iu : Iv : Iw = +1 : -0.5 : -0.5 is satisfied, the position θ of rotor 18 is 0°. If, for example, Iu : Iv : Iw = +√3 / 2 : 0 : -√3 / 2 is satisfied, the position θ of rotor 18 is 30°. If, for example, Iu : Iv : Iw = +0.5 : +0.5 : -1 is satisfied, the position θ of rotor 18 is, for example, 60°.

[0038] As in Fig. As shown in Figure 2, the motor-driven compressor 10 contains a temperature sensor 34. The temperature sensor 34 is electrically connected to the controller 25. The temperature sensor 34 detects, for example, the temperature to estimate the temperature of the capacitor 32. In particular, the temperature sensor 34 detects the temperature of a substrate on which the capacitor 32 is mounted. Information regarding the temperature detected by the temperature sensor 34 is transmitted to the controller 25.

[0039] The controller 25 stores a temperature estimation program in advance to estimate the temperature of the capacitor 32 based on information transmitted by the temperature sensor 34. Accordingly, the controller 25 estimates the temperature of the capacitor 32 based on the temperature estimation program and the temperature detected by the temperature sensor 34. Therefore, the temperature sensor 34 and the controller 25 act as a temperature estimator, estimating the temperature of the capacitor 32.

[0040] Furthermore, the controller 25 stores a program in advance to execute a process for determining a maximum permissible value, specifically to calculate the maximum permissible motor current (maximum allowable value) based on information about the estimated temperature of the capacitor 32. In particular, the controller 25 stores a calculation program in advance to calculate the maximum permissible motor current. The maximum permissible motor current is the maximum current that will not damage the switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 when the overvoltage is generated by the equivalent series resistance (ESR) of the capacitor 32.In other words, a situation in which the switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 are damaged by an overvoltage generated by the equivalent series resistance (ESR) of capacitor 32 can be avoided if the current flowing through motor 16 is less than or equal to the maximum permissible motor current. Controller 25 calculates the maximum permissible motor current based on the estimated temperature of capacitor 32 and the previously stored calculation program. Controller 25 then controls inverter circuit 24 so that the current flowing through motor 16 is less than or equal to the calculated maximum permissible motor current.

[0041] The controller 25 stores a pre-programmed program to execute a heating control mode for heating the capacitor 32 by controlling the inverter circuit 24 to supply the motor 16 with direct current when the estimated temperature of the capacitor 32 is less than or equal to a predetermined temperature. The controller 25 also stores a pre-programmed program to execute a normal control mode for controlling the inverter circuit 24 to supply the motor 16 with alternating current when the estimated temperature of the capacitor 32 is higher than the predetermined temperature. Therefore, the controller 25 is configured to switch between the heating control mode and the normal control mode based on the estimated temperature of the capacitor 32.

[0042] The controller 25 stores a program in advance for executing a process to determine the current pattern in order to determine a current pattern for the motor 16 by selecting one of six current patterns according to the estimated position θ of the rotor 18 in the heating control mode. In each of the six current patterns, the motor current flows continuously through only one of the three-phase coils 19 at the maximum permissible value in either the positive or negative direction.

[0043] Fig. Figure 4 shows the relationship between the current flowing through motor 16 and the position θ of rotor 18 in heating control mode. Furthermore, it shows Fig. 5 the relationship of the position θ of the rotor 18 and the current patterns to the motor 16 in the heating control mode.

[0044] As in Fig. 4 and Fig. As shown in Figure 5, in heating control mode, when the estimated position θ of the rotor 18 lies within a predetermined range (e.g., 330° < θ ≤ 360°, 0° ≤ θ ≤ 30°), the controller 25 determines the current pattern in the process of determining the current pattern so that the position θ of the rotor 18 becomes 0°. The current pattern at which the position θ of the rotor 18 becomes 0° refers to a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw corresponding to Iu : Iv : Iw = +1 : -0.5 : -0.5. That is, in the current pattern in which the position θ of the rotor 18 becomes 0°, the value of the U-phase current Iu, which is the current flowing through one of the three-phase coils 19, is always the maximum permissible motor current value in the positive direction.

[0045] In heating control mode, when the estimated position θ of rotor 18 lies within a predetermined range (e.g., 30° < θ ≤ 90°), the controller 25 determines the current pattern through the current pattern determination process, such that the position θ of rotor 18 becomes 60°. The current pattern at which the position θ of rotor 18 becomes 60° corresponds to a situation where the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw is Iu : Iv : Iw = +0.5 : +0.5 : -1. That is, in the current pattern in which the position θ of the rotor 18 becomes 60°, the value of the W-phase current Iw, which is the current flowing through one of the three-phase coils 19, is always equal to the maximum permissible motor current value in the negative direction.

[0046] In heating control mode, when the estimated position θ of rotor 18 lies within a predetermined range (e.g., 90° < θ ≤ 150°), the controller 25 determines the current pattern through the current pattern determination process, such that the position θ of rotor 18 becomes 120°. The current pattern at which the position θ of rotor 18 becomes 120° is related to a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw corresponding to Iu : Iv : Iw = -0.5 : +1 : -0.5. That is, in the current pattern in which the position θ of the rotor 18 becomes 120°, the value of the V-phase current Iv, which is the current flowing through one of the three-phase coils 19, is always equal to the maximum permissible motor current value in the positive direction.

[0047] In heating control mode, when the estimated position θ of rotor 18 lies within a predetermined range (e.g., 150° < θ ≤ 210°), the controller 25 determines the current pattern through the current pattern determination process, such that the position θ of rotor 18 becomes 180°. The current pattern at which the position θ of rotor 18 becomes 180° is related to a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw corresponding to Iu : Iv : Iw = -1 : +0.5 : +0.5. That is, in the current pattern in which the position θ of the rotor 18 becomes 180°, the value of the U-phase current Iu, which is the current flowing through one of the three-phase coils 19, is always equal to the maximum permissible motor current value in the negative direction.

[0048] In heating control mode, when the estimated position θ of rotor 18 lies within a predetermined range (e.g., 210° < θ ≤ 270°), the controller 25 determines the current pattern through the current pattern determination process, such that the position θ of rotor 18 becomes 240°. The current pattern at which the position θ of rotor 18 becomes 240° is related to a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw corresponding to Iu : Iv : Iw = -0.5 : -0.5 : +1. That is, in the current pattern in which the position θ of the rotor 18 becomes 240°, the value of the W-phase current Iw, which is the current flowing through one of the three-phase coils 19, is always equal to the maximum permissible motor current value in the positive direction.

[0049] In heating control mode, when the estimated position θ of rotor 18 lies within a predetermined range (e.g., 270° < θ ≤ 330°), the controller 25 determines the current pattern through the current pattern determination process, such that the position θ of rotor 18 becomes 300°. The current pattern at which the position θ of rotor 18 becomes 300° is related to a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw corresponding to Iu : Iv : Iw = +0.5 : -1 : +0.5. That is, in the current pattern in which the position θ of the rotor 18 becomes 300°, the value of the V-phase current Iv, which is the current flowing through one of the three-phase coils 19, is always equal to the maximum permissible motor current value in the negative direction.

[0050] In this way, during the process of determining the current pattern, the controller 25 selects one of the six current patterns, which differ from each other by 60°, according to the estimated position θ of the rotor 18. Each current pattern has a phase angle range of 60°. The six current patterns have identical phase angle ranges. The term "phase angle range of the current pattern" refers to a phase angle range of the rotor 18 that corresponds to the selected current pattern. During the process of determining the current pattern, the controller 25 selects the one of the six current patterns whose corresponding position is closest to the estimated position θ of the rotor 18.

[0051] Furthermore, the controller 25 stores a program in advance to execute a phase angle shift process in heating control mode to shift the phase angle of one of the three-phase PWM signals generated according to the current pattern selected by the current pattern determination process.

[0052] Fig. Figure 6 shows the relationship between changes in the currents flowing through the motor 16, changes in the three-phase PWM signals, and changes in the current flowing to the capacitor 32 in the current pattern where the position θ of the rotor 18 becomes 0°. Fig. For example, with a high U-phase PWM signal, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. When the U-phase PWM signal is low, switching element Qu1 of the U-phase upper arm is OFF and switching element Qu2 of the U-phase lower arm is ON. Similarly, with a high V-phase PWM signal, switching element Qv1 of the V-phase upper arm is ON and switching element Qv2 of the V-phase lower arm is OFF. When the V-phase PWM signal is low, switching element Qv1 of the V-phase upper arm is OFF and switching element Qv2 of the V-phase lower arm is ON. Furthermore, when the W-phase PWM signal is high, switching element Qw1 of the W-phase upper arm is ON and switching element Qw2 of the W-phase lower arm is OFF. When the W-phase PWM signal is low, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON.

[0053] As in Fig. As shown in Figure 6, in the present embodiment, the controller 25 shifts the phase angle of the V-phase PWM signal to shorten the time during which the output voltages of the three phases (U-phase, V-phase, and W-phase) output by the inverter circuit 24 each have the same polarity (all high polarity or all low polarity). Specifically, after the phase angle shift process, the phase angle of the V-phase PWM signal waveform is offset by 180° relative to the phase angles of the U- and W-phase PWM signal waveforms. In the present embodiment, the controller 25 thus shifts the phase angle of the waveform of the V-phase PWM signal, which is one of the three-phase PWM signals generated according to the current pattern selected by the process for determining the current pattern, by 180° from the phase angles of the waveforms of the U-phase and W-phase PWM signals during the phase angle shift process.

[0054] In Fig. Figure 6 shows the waveform of the V-phase PWM signal before the phase angle shift process by the double-dashed line and the waveform of the V-phase PWM signal after the phase angle shift process by the solid line. Fig. Section 6 compares the waveforms of the three-phase PWM signals before the phase angle shift process with the waveforms of the three-phase PWM signals after the phase angle shift process. As in Fig. As shown in Figure 6, after the phase angle shift process, the period in which the three-phase PWM signals are all high or low is shortened.

[0055] The controller 25 stores a control program in advance to perform control on the inverter circuit 24 in order to output the three-phase PWM signals with phase angles following the phase angle shift process to the inverter circuit 24 and to supply the motor 16 with a direct current in the current pattern selected by the process for determining the current pattern.

[0056] The functionality of the present embodiment will now be described.

[0057] As in Fig. As shown in Figure 7, in step S11, the controller 25 estimates the temperature of the capacitor 32 based on the information transmitted by the temperature sensor 34. Then, in step S12, the controller 25 determines whether the estimated temperature of the capacitor 32 is less than or equal to a predetermined temperature. If the controller 25 determines that the temperature of the capacitor 32 is not less than or equal to the predetermined temperature in step S12, the controller proceeds to step S13. In step S13, the controller 25 switches to normal control mode to control the inverter circuit 24 and supply the motor 16 with alternating current.

[0058] In a case where the controller 25 determines that the temperature of the capacitor 32 is less than or equal to the predetermined temperature in step 12, the controller 25 proceeds to step S14 and switches to the heating control mode. In step S14, the controller 25 estimates the position θ of the rotor 18. Then, in step S15, the controller 25 performs the current pattern determination process to select the current pattern of the motor 16 according to the position θ of the rotor 18. For example, if the estimated position θ of the rotor 18 is 30°, the controller 25 selects the current pattern in which the position θ of the rotor 18 becomes 0° during the current pattern determination process.

[0059] Subsequently, in step S16, the controller 25 performs the process of determining the maximum permissible value to calculate the maximum permissible motor current. In step S17, the controller 25 generates the three-phase PWM signals according to the current pattern selected during the current pattern determination process. For example, if the current pattern selected during current pattern determination is one in which the rotor position θ 18 becomes 0°, the controller 25 generates the three-phase PWM signals so that the rotor position θ becomes 180°.

[0060] In step 18, the controller 25 performs the phase angle shift process to shift the phase angle of one of the generated three-phase PWM signals. For example, the controller 25 performs the phase angle shift process to shift the phase angle of the V-phase PWM signal and outputs the three-phase PWM signals with the phase angles after the phase angle shift process to the inverter circuit 24.

[0061] Fig. Figure 8 shows the current flow at time T1 in Fig. 6. At time T1, the U-phase PWM signal is high, the V-phase PWM signal is low, and the W-phase PWM signal is switching from high to low. As shown in Fig. As shown in Figure 8, the U-phase PWM signal is high at time T1. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as indicated by arrow R1 in Figure 8, the current flows. Fig. Figure 8 shows the current discharged from capacitor 32 through switching element Qu1 to motor 16 as the U-phase current Iu. Here, the DC power supply 31 contains an inductance component. Accordingly, as indicated by arrow R1b, the current from the DC power supply 31 continues to flow as the U-phase current Iu. In this case, in the current pattern where the position θ of rotor 18 becomes 0°, the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw is Iu : Iv : Iw = +1 : -0.5 : -0.5. Thus, the value of the current discharged from capacitor 32, which flows as the U-phase current Iu, is at its maximum. Consequently, the current discharged from capacitor 32 is increased. This causes capacitor 32 to heat up.

[0062] Furthermore, at time T1 the V-phase PWM signal is low. Therefore, switching element Qv1 of the V-phase upper arm is OFF and switching element Qv2 of the V-phase lower arm is ON. Accordingly, current flows as shown by arrow R1c in Fig. As shown in Figure 8, the V-phase current Iv flows through switching element Qv2 towards the DC network 31 and the capacitor 32. Furthermore, at time T1, the W-phase PWM signal is low. Thus, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON. Accordingly, as indicated by arrow R1d in Fig. 8 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0063] Fig. Figure 9 illustrates the current flow at time T2 in Fig. 6. At time T2, the W-phase PWM signal is low, the U-phase PWM signal switches from high to low, and the V-phase PWM signal switches from low to high. At time T2, the V-phase PWM signal is high. Thus, switching element Qv1 of the V-phase upper arm is ON, and switching element Qv2 of the V-phase lower arm is OFF. Accordingly, as indicated by arrow R2a in Fig. As shown in 9, the V-phase current Iv flows through the switching element Qv1 and as a return current to capacitor 32. In this case too, as indicated by arrow R2b in Fig. Figure 9 shows current from the DC power supply 31 to the capacitor 32, charging the capacitor 32. This heats up the capacitor 32.

[0064] Furthermore, at time T2 the U-phase PWM signal is low. Thus, switching element Qu1 of the U-phase upper arm is OFF and switching element Qu2 of the U-phase lower arm is ON. Accordingly, as indicated by arrow R2c in Fig. Figure 9 shows the current from the DC power supply 31 and the capacitor 32 through the switching element Qu2 and to the motor 16 as the U-phase current Iu. Furthermore, the W-phase PWM signal is low. Thus, the switching element Qw1 of the W-phase upper arm is OFF and the switching element Qw2 of the W-phase lower arm is ON. Accordingly, current flows as indicated by arrow R2d in Fig. Figure 9 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0065] Fig. Figure 10 shows the current flow at time T3 in Fig. 6. Time T3 is reached when a predetermined period has elapsed from time T2 without changing the high-low ratio of the three-phase PWM signals at time T2. As in Fig. As shown in Figure 10, capacitor 32 is fully charged at time T3, when the predetermined time interval from time T2 has elapsed. Thus, the V-phase current Iv flows through the switching element Qv1 as a return current to the DC power supply 31 and not to capacitor 32, as indicated by arrow R3a in Figure 10. Fig. 10 shown.

[0066] Fig. Figure 11 shows the current flow at time T4 in Fig. 6. At time T4, the V-phase PWM signal is high, the W-phase PWM signal is low, and the U-phase PWM signal is switching from low to high. As shown in Fig. As shown in Figure 11, the U-phase PWM signal is high at time T4. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as shown by arrow R4a, the current discharged from capacitor 32 flows through switching element Qu1 and to motor 16 as U-phase current Iu.

[0067] Furthermore, at time T4 the V-phase PWM signal is high. Therefore, switching element Qv1 of the V-phase upper arm is ON and switching element Qv2 of the V-phase lower arm is OFF. Accordingly, as indicated by arrow R4b in Fig. Figure 11 shows the V-phase current Iv through the switching element Qv1 as a return current to capacitor 32. Consequently, the value of the current discharged from capacitor 32 to motor 16 as U-phase current Iu is obtained by subtracting the value of the V-phase current Iv flowing to capacitor 32 as a return current. Additionally, the DC power supply 31 contains an inductance component. Accordingly, the current flows as shown by arrow R4c in Fig. Figure 11 shows the current flowing from capacitor 32 to the DC power supply 31. The current is also discharged from capacitor 32 to the DC power supply 31. This causes capacitor 32 to heat up.

[0068] Furthermore, at time T4 the W-phase PWM signal is low. Therefore, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON. Accordingly, as indicated by arrow R4d in Fig. 11 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0069] Fig. Figure 12 illustrates the current flow at time T5 in Fig. 6. At time T5, the U-phase PWM signal is high, the V-phase PWM signal switches from high to low, and the W-phase PWM signal switches from low to high. As shown in Fig. As shown in Figure 12, the U-phase PWM signal is high at time T6. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as indicated by arrow R5a in Figure 12, the signal flows. Fig. Figure 12 shows the current discharged from capacitor 32 through the switching element Qu1 and to the motor 16 as U-phase current Iu.

[0070] Furthermore, the W-PWM signal is high at time T5. Therefore, switching element Qw1 of the W-phase upper arm is ON and switching element Qw2 of the W-phase lower arm is OFF. Accordingly, the current flows as shown by arrow R5b in Fig. Figure 12 shows the W-phase current Iw as a return current through the switching element Qw1 to capacitor 32. Consequently, the value of the current discharged from capacitor 32 to motor 16 as U-phase current Iu is obtained by subtracting the value of the W-phase current Iw flowing to capacitor 32 as a return current. Additionally, the DC power supply 31 contains an inductance component. Accordingly, the current flows as shown by arrow R5c in Fig. Figure 12 shows the current flowing from capacitor 32 towards the DC power supply 31. Thus, the current is also discharged from capacitor 32 to the DC power supply 31. This causes capacitor 32 to heat up.

[0071] Furthermore, at time T5 the V-phase PWM signal is low. Therefore, switching element Qv1 of the V-phase upper arm is OFF and switching element Qv2 of the V-phase lower arm is ON. Accordingly, as indicated by arrow R5d in Fig. Figure 12 shows the V-phase current Iv through the switching element Qv2 and to the DC supply 31 and to the capacitor 32.

[0072] Fig. Figure 13 shows the current flow at time T6 in Fig. 6. Time T6 is reached when a predetermined period has elapsed from time T5 without the high-low ratio of the three-phase PWM signals having changed at time T5. As in Fig. As shown in Figure 13, the capacitor 32 stops discharging at time T5, when the predetermined time interval from time T6 has elapsed, and the current from the DC supply 31 flows through the switching element Qu1 and to the motor 16 as U-phase current Iu, as indicated by arrow R6a in Figure 13. Fig. Figure 13 shows the current flowing from the DC power supply 31 to the capacitor 32, charging it. As described above, the current in Fig. The current flow shown in 8 to 13 is repeated to heat the capacitor 32.

[0073] As in Fig. As shown in Figure 7, in step S19, the controller 25 estimates the temperature of the capacitor 32 based on the information transmitted by the temperature sensor 34. Then, in step S20, the controller 25 determines whether the estimated temperature of the capacitor 32 has exceeded a predetermined temperature. If the controller 25 determines that the temperature of the capacitor 32 has not exceeded the predetermined temperature in step S20, the controller 25 proceeds to step S16. If the controller 25 determines that the temperature of the capacitor 32 has exceeded the predetermined temperature in step S20, the controller 25 proceeds to step S13 and switches from heating control mode to normal control mode.

[0074] Fig. Figure 14 shows a comparative example where the controller 25 does not perform the phase angle shift process. More precisely, it shows Fig. 14 the relationship between the changes in the currents flowing through the motor 16, the changes in the three-phase PWM signals, and the changes in the current flowing to the capacitor 32 in the current pattern where the position θ of the rotor 18 becomes 0°. As in Fig. As shown in Figure 14, the controller 25 in the comparison example does not perform the phase angle shift process. Therefore, the period in which the three-phase PWM signals are all high or all low is longer than in a case where the phase angle shift process is performed.

[0075] Fig. Figure 15 shows the current flow at time T11 in Fig. 14. At time T11, the U-phase PWM signal is high, and the V- and W-phase PWM signals are each switched from high to low. As in Fig. As shown in Figure 15, the U-phase PWM signal is high at time T11. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as indicated by arrow R11a in Fig. Figure 15 shows the current discharged from capacitor 32 through the switching element Qu1 and to the motor 16 as the U-phase current Iu. In this case, in the current flow pattern where the position θ of the rotor 18 becomes 0°, the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw is Iu : Iv : Iw = +1 : -0.5 : -0.5. Thus, the value of the current discharged from capacitor 32, which flows as the U-phase current Iu, is greatest. Accordingly, the current discharged from capacitor 32 is increased. This causes capacitor 32 to heat up.

[0076] Furthermore, at time T11 the V-phase PWM signal is low. Therefore, switching element Qv1 of the V-phase upper arm is OFF and switching element Qv2 of the V-phase lower arm is ON. Accordingly, as indicated by arrow R11b in Fig. As shown in Figure 15, the V-phase current Iv flows through switching element Qv2 towards the DC network 31 and capacitor 32. Furthermore, at time T11, the W-phase PWM signal is low. Thus, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON. Accordingly, as indicated by arrow R11c, Fig. 15 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0077] Fig. Figure 16 shows the current flow at time T12 in Fig. 14. At time T12, the V-phase PWM signal and the W-phase PWM signal are low, and the U-phase PWM signal switches from high to low. As shown in Fig. As shown in Figure 16, at time T12 all three-phase PWM signals are low. Thus, the switching elements Qu1, Qv1, and Qw1 of the upper arms are OFF, and the switching elements Qu2, Qv2, and Qw2 of the lower arms are ON. Accordingly, the V-phase current Iv flowing through switching element Qv2, which is in Fig. 16 is represented by arrow R12a, and the W-phase current Iw flowing through the switching element Qw2, which is in Fig. 16 is represented by arrow R12b, through the switching element Qu2 to the motor 16 as U-phase current Iu, which in Fig. 16 is represented by arrow R12c. Furthermore, as shown by arrow R12d in Fig. Figure 16 shows the current from the DC power supply 31 flowing to the capacitor 32 and charging it. This heats up the capacitor 32.

[0078] Fig. Figure 17 shows the current flow at time T13 in Fig. 14. Time T13 is reached when a predetermined period has elapsed from time T12 without the high-low ratio of the three-phase PWM signals having changed at time T12. As in Fig. As shown in Figure 17, capacitor 32 is fully charged at time T13, when the predetermined time interval from time T12 has elapsed. Therefore, no current flows from the DC power supply 31 to capacitor 32.

[0079] Fig. Figure 18 shows the current flow at time T14 in Fig. 14. At time T14, the V-phase PWM signal and the W-phase PWM signal are low, and the U-phase PWM signal switches from low to high. As in Fig. As shown in Figure 18, the U-phase PWM signal is high at time T14. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as indicated by arrow R13a in Fig. Figure 18 shows the current discharged from capacitor 32 through the switching element Qu1 and to the motor 16 as a U-phase current Iu. This heats and warms the capacitor 32.

[0080] Furthermore, at time T14 the V-phase PWM signal is low. Therefore, switching element Qv1 of the V-phase upper arm is OFF and switching element Qv2 of the V-phase lower arm is ON. Accordingly, as indicated by arrow R13b in Fig. As shown in Figure 18, the V-phase current Iv flows through switching element Qv2 towards the DC network 31 and capacitor 32. Furthermore, at time T14, the W-phase PWM signal is low. Thus, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON. Accordingly, as indicated by arrow R13c, Fig. 18 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0081] Fig. Figure 19 shows the current flow at time T15 in Fig. 14. At time T15, the U-phase PWM signal is high, and the V-phase PWM and W-phase PWM signals are switched from low to high. As in Fig. As shown in Figure 19, at time T15 all three-phase PWM signals are high. Thus, the switching elements Qu1, Qv1, and Qw1 of the upper arms are ON, and the switching elements Qu2, Qv2, and Qw2 of the lower arms are OFF. Accordingly, the V-phase current Iv flowing through switching element Qv1, which is in Fig. 19 is represented by arrow R14a, and the W-phase current Iw flowing through the switching element Qw1, which is in Fig. 19 is represented by arrow R14b, through the switching element Qu1 to the motor 16 as U-phase current Iu, which in Fig. 19 is represented by arrow R14c. Furthermore, as shown by arrow R14d in Fig. Figure 19 shows current flowing from the DC power supply 31 to the capacitor 32, charging it. This heats up the capacitor 32.

[0082] Fig. Figure 20 shows the current flow at time T16 in Fig. 14. Time T16 is the time at which a predetermined period has elapsed since time T15 without the high-low ratio of the three-phase PWM signals having changed at time T15. As in Fig. As shown in Figure 20, capacitor 32 is fully charged at time T16, when the predetermined time interval from time T15 has elapsed. Therefore, no current flows from the DC power supply 31 to capacitor 32.

[0083] In the comparative example in Fig. In equations 14 to 20, the three-phase PWM signals are all high or low during the period from time T12 to time T13 and during the period from time T15 to time T16. During these periods, the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw do not contribute to charging or discharging capacitor 32. In the comparative example of the Fig. From 14 to 20, the phase angle shift is not performed. If the phase angle shift process is not carried out, the period in which the three-phase PWM signals are all high or low is lengthened. This extends the time in which none of the U-phase currents Iu, the V-phase currents Iv, and the W-phase currents Iw contribute to charging or discharging capacitor 32. In this way, in a case where the phase angle shift process is not carried out, as in the one described in the Fig. In the comparative example shown in Figures 14 to 20, the charge or discharge quantity of the capacitor 32 is small. Therefore, the capacitor 32 is difficult to heat up compared to the present embodiment.

[0084] In the present embodiment, the controller 25, in heating control mode, executes the phase angle shift process such that the V-phase current Iv flows through the switching element Qv1 and as a feed-in current to the capacitor 32 from time T2 to time T3. This increases the charging or discharging rate of the capacitor 32 from the time when the phase angle shift process is not being carried out. This causes the capacitor 32 to heat up slightly.

[0085] As a further comparative example, Fig. 21 the relationship between changes in the currents flowing through the motor 16, changes in the three-phase PWM signals and changes in the current flowing to the capacitor 32 in the current pattern where the position θ of the rotor 18 becomes 30°. In this comparative example, as in Fig. Figure 21 shows that the phase angle of the V-phase PWM signal is shifted to shorten the time interval during which the output voltages of the three phases (U-phase, V-phase, and W-phase) output by the inverter circuit 24 each have the same polarity (all high-polarity or all low-polarity). Specifically, after the phase angle shifting process, the phase angle of the V-phase PWM signal waveform is shifted by 180° relative to the phase angles of the U- and W-phase PWM signal waveforms.

[0086] Fig. 22 shows the current flow at time T21 in Fig. 21. At time T21, the U-phase PWM signal is high, the V-phase PWM signal is low, and the W-phase PWM signal is switching from high to low. As in Fig. As shown in Figure 22, the U-phase PWM signal is high at time T21. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as indicated by arrow R21a, the current flows Fig. Figure 22 shows the current discharged from capacitor 32 through the switching element Qu1 and to the motor 16 as a U-phase current Iu. This heats and warms the capacitor 32.

[0087] Furthermore, at time T21 the V-phase PWM signal is low. Therefore, switching element Qv1 of the V-phase upper arm is OFF and switching element Qv2 of the V-phase lower arm is ON. Accordingly, as indicated by arrow R21b in Fig. Figure 22 shows the V-phase current Iv flowing through switching element Qv2 towards the DC network 31 and capacitor 32. Furthermore, at time T21, the W-phase PWM signal is low. Thus, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON. Accordingly, as indicated by arrow R21c, Fig. 22 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0088] Fig. 23 shows the current flow at time T22 in Fig. 21. At time T22, the U-phase PWM signal is high, the W-phase PWM signal is low, and the V-phase PWM signal is switching from low to high. As in Fig. As shown in Figure 23, the U-phase PWM signal is high at time T22. Therefore, switching element Qu1 of the U-phase upper arm is ON and switching element Qu2 of the U-phase lower arm is OFF. Accordingly, as indicated by arrow R22a, the current flows Fig. Figure 23 shows the current discharged from the capacitor 32 through the switching element Qu1 and to the motor 16 as U-phase current Iu.

[0089] Furthermore, at time T22 the V-phase PWM signal is high. Therefore, switching element Qv1 of the V-phase upper arm is ON and switching element Qv2 of the V-phase lower arm is OFF. Accordingly, as indicated by arrow R22b in Fig. Figure 23 shows the V-phase current Iv through the switching element Qv1 as a return current to capacitor 32. Consequently, the value of the current discharged from capacitor 32 to motor 16 as U-phase current Iu is obtained by subtracting the value of the V-phase current Iv flowing to capacitor 32 as a return current. This heats up capacitor 32.

[0090] Furthermore, at time T22 the W-PWM signal is low. Therefore, switching element Qw1 of the W-phase upper arm is OFF and switching element Qw2 of the W-phase lower arm is ON. Accordingly, current flows as shown by arrow R22c in Fig. 23 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0091] Fig. 24 shows the current flow at time T23 in Fig. 21. At time T23, the V-phase PWM signal is high, the W-phase PWM signal is low, and the U-phase PWM signal is switching from high to low. As in Fig. As shown in Figure 24, the V-phase PWM signal is high at time T23. Therefore, switching element Qv1 of the V-phase upper arm is ON and switching element Qv2 of the V-phase lower arm is OFF. Accordingly, as indicated by arrow R23a in Fig. Figure 24 shows the V-phase current Iv through the switching element Qv1 and as a return current to the capacitor 32. This heats up the capacitor 32.

[0092] Furthermore, at time T23 the U-phase PWM signal is low. Thus, switching element Qu1 of the U-phase upper arm is OFF and switching element Qu2 of the U-phase lower arm is ON. Accordingly, as indicated by arrow R23b, Fig. Figure 24 shows the current from the DC power supply 31 and the capacitor 32 through the switching element Qu2 to the motor 16 as the U-phase current Iu. Furthermore, the W-phase PWM signal is low. Thus, the switching element Qw1 of the W-phase upper arm is OFF and the switching element Qw2 of the W-phase lower arm is ON. Accordingly, as indicated by arrow R23c, the current flows Fig. 24 shows the W-phase current Iw through the switching element Qw2 to the DC supply 31 and to the capacitor 32.

[0093] In the same way as the comparative example in the Fig.In the current pattern where the position θ of rotor 18 becomes 30°, the ratio of the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw is Iu : Iv : Iw = +√3 / 2 : 0 : -√3 / 2. In this comparative example, the phase angle of the V-phase PWM signal, which has the minimum current value, is shifted. In this case, at time T23, the V-phase current Iv flows through the switching element Qv1 and as a feed-in current to capacitor 32. However, the value of the feed-in current through capacitor 32 is small because the value of the V-phase current Iv is at its minimum. Consequently, the heat generated by capacitor 32 is low. Therefore, it is difficult to heat capacitor 32 compared to the present implementation.In this way, the inventors discovered that when the phase angle of the PWM signal is shifted to the minimum current value, the current flowing as feedback current from the coil 19 of the shifted phase to the capacitor 32 is small. Consequently, the heat generated by the capacitor 32 is also low. Thus, the capacitor 32 is difficult to heat up compared to the existing embodiment.

[0094] In the present embodiment, the controller 25 performs the current pattern determination process. Even if the estimated position θ of the rotor 18 corresponds to the position where the current value of one of the three phases is at its minimum (e.g., θ = 30°), the current pattern of the motor 16 will be the current pattern corresponding to the position θ of the rotor 18 where only one of the three phases is always at the maximum permissible motor current value in either the positive or negative direction. Furthermore, the controller 25 performs the phase angle shifting process to shift the phase angle of one of the three-phase PWM signals generated according to the current pattern selected by the current pattern determination process.Therefore, among the three PWM signals generated when the rotor 18 is at position θ where one of the current values ​​is minimal, the phase angle of the PWM signal at which the current value is minimal is never shifted. Furthermore, the controller 25 outputs the three-phase PWM signals with the phase angles after the phase angle shifting process to the inverter circuit 24 and supplies the motor 16 with a DC current in the current pattern selected by the process for determining the current pattern. This increases the current flowing as regenerative current from the coil 19 to the capacitor 32, slightly heating the capacitor 32. Therefore, the capacitor 32 is slightly heated regardless of the position θ of the rotor 18.

[0095] The above embodiment achieves the following advantages.

[0096] (1) The controller 25 performs the current pattern determination process when the estimated temperature of the capacitor 32 is less than or equal to a predetermined temperature. The current pattern determination process involves selecting the current pattern of the motor 16 from the six current patterns according to the estimated position θ of the rotor 18. In each of the six current patterns, the current of the maximum allowable motor current value always flows in the positive or negative direction through only one of the three-phase coils 19. In addition, the controller 25 performs the maximum allowable value determination process to determine the maximum allowable motor current value based on the information about the estimated temperature of the capacitor 32.Furthermore, the controller 25 performs the phase angle shifting process to shift the phase angle of one of the three-phase PWM signals generated according to the current pattern selected by the process for determining the current pattern. The six excitation patterns have equal phase angle ranges. Thus, among the three PWM signals generated when the position θ of the rotor 18 is such that one of the current values ​​is minimal, the phase angle of the PWM signal at which the current value is minimal is never shifted. This increases the current flowing as regenerative current from the inductor 19 to the capacitor 32. Consequently, the capacitor 32 heats up slightly. As a result, the capacitor 32 heats up slightly regardless of the position θ of the rotor 18.

[0097] (2) When determining the current pattern, the controller 25 selects from the six current patterns one whose corresponding position is closest to the estimated position θ of the rotor 18. More precisely, the six current patterns each correspond to six positions of the rotor 18. The position of the rotor 18 that corresponds to the current pattern selected by the current pattern determination process is the one that is closest to the position of the rotor 18 estimated by the controller 25 from among the six positions of the rotor 18. This prevents the rotor 18 from being over-rotated when the controller 25 controls the inverter circuit 24 to supply the motor 16 with a direct current in the current pattern selected by the current pattern determination process. Accordingly, no noise is generated at the compression unit 15 due to over-rotation of the rotor 18.

[0098] (3) In phase angle shifting, the controller 25 shifts the phase angle of the waveform of the V-phase PWM signal, which is one of the three-phase PWM signals generated according to the current pattern selected by the process for determining the current pattern, by 180° from the phase angles of the waveforms of the U-phase and W-phase PWM signals. This increases the period during which the current flows through the capacitor 32. Thus, the capacitor 32 heats up further quickly and easily.

[0099] (4) If the estimated temperature of the capacitor 32 is less than or equal to a predetermined temperature, the capacitor 32 is slightly heated. This accelerates the initiation of the control at the inverter circuit 24, which is carried out by the controller 25 in normal control mode.

[0100] The above embodiment can be modified as described below. The above embodiment and the following modified examples can be combined as long as the combined modifications remain technically consistent.

[0101] In this embodiment, the controller 25 can select a current pattern that does not correspond to the estimated position θ of the rotor 18 when determining the current pattern. More precisely, if the estimated position θ of the rotor 18 is 30°, the controller 25 can, for example, select a current pattern that corresponds to the position θ of the rotor 18 when determining the current pattern at 120°, instead of the current pattern where the position θ of the rotor 18 becomes 0°.

[0102] In this embodiment, if the estimated position θ of rotor 18 is, for example, 330° ≤ θ ≤ 360° and 0° ≤ θ < 30°, the controller 25 can select a current flow pattern in which the position θ of rotor 18 becomes 0° during the process of determining the current flow pattern in heating control mode. If the estimated position θ of rotor 18 is, for example, 30° ≤ θ < 90°, the controller 25 can select a current flow pattern in which the position θ of rotor 18 becomes 60° during the process of determining the current flow pattern in heating control mode. If the estimated position θ of rotor 18 is, for example, 90° ≤ θ < 150°, the controller 25 can select a current flow pattern in which the position θ of rotor 18 becomes 120° during the process of determining the current flow pattern of the heating control mode.If the estimated position θ of the rotor 18 is 150° ≤ θ < 210°, the controller 25 can select a current flow pattern in which the position θ of the rotor 18 becomes 180° during the process of determining the current flow pattern for the heating control mode. If the estimated position θ of the rotor 18 is, for example, 210° ≤ θ < 270°, the controller 25 can select a current flow pattern in which the position θ of the rotor 18 becomes 240° during the process of determining the current flow pattern for the heating control mode. If the estimated position θ of the rotor 18 is, for example, 270° ≤ θ < 330°, the controller 25 can select a current flow pattern in which the position θ of the rotor 18 becomes 300° during the process of determining the current flow pattern for the heating control mode.

[0103] In this embodiment, the controller 25 can, for example, shift the phase angle of the U-phase PWM signal instead of the phase angle of the V-phase PWM signal when performing a phase angle shift. Furthermore, the controller 25 can, for example, shift the phase angle of the W-phase PWM signal instead of the phase angle of the V-phase PWM signal when performing a phase angle shift.

[0104] In this embodiment, the phase angle of the V-phase PWM signal waveform does not need to be shifted by 180° relative to the phase angles of the U- and W-phase PWM signals during phase angle shifting. During phase angle shifting, the phase angle of the V-phase PWM signal waveform can be shifted arbitrarily relative to the phase angles of the U- and W-phase PWM signals, as long as the time interval during which the polarities of the output voltages of the three phases (U-phase, V-phase, and W-phase) output by inverter circuit 24 are all the same (all high polarity or all low polarity) is shortened.

[0105] In this embodiment, the phase angle ranges of the excitation patterns do not need to be 60°. The phase angle ranges of the excitation patterns can be set in any way, as long as the phase angle ranges are substantially the same.

[0106] In this embodiment, the capacitor 32 can be, for example, a film capacitor.

[0107] In this embodiment, the temperature sensor 34 does not need to detect the temperature of the substrate on which the capacitor 32 is mounted and can detect (estimate) the temperature of the capacitor 32. In this case, the controller 25 does not need to prestore the temperature estimation program for estimating the temperature of the capacitor 32 based on the temperature information transmitted by the temperature sensor 34. Furthermore, the temperature sensor 34 acts as a temperature estimator, estimating the temperature of the capacitor 32.

[0108] In this embodiment, the controller 25 performs position sensorless control, which controls the rotation of the motor 16 based on the estimated position θ of the rotor 18. Alternatively, the controller 25 can control the rotation of the motor 16 by estimating the position θ of the rotor 18 using a speed sensor, e.g., a resolver.

[0109] In this embodiment, the motor-driven compressor 10 can be configured, for example, such that the inverter circuit 24 is arranged radially outwards from the rotating shaft 14 with respect to the housing 11. In other words, the compression unit 15, the motor 16, and the inverter circuit 24 do not have to be arranged side by side in the same direction as the axis of rotation of the rotating shaft 14.

[0110] In this embodiment, the motor-driven compressor 10 forms the vehicle air conditioning system 21. Alternatively, the motor-driven compressor 10 can be installed in a fuel cell vehicle and compress the air supplied to the fuel cell in the compression unit 15.

[0111] The examples above may be modified in form and detail without altering the spirit and scope of the claims and their equivalents. The examples serve only for description and not for limitation. Descriptions of features in each example are to be understood as applicable to similar features or aspects in other examples. Suitable results may be achieved by performing the sequences in a different order and / or by combining components differently in a described system, architecture, device, or circuit and / or by replacing or supplementing them with other components or their equivalents. The scope of disclosure is not defined by the detailed description but by the claims and their equivalents. All deviations within the scope of the claims and their equivalents are included in the disclosure.

Claims

[1] A motor-driven compressor (10), comprising: a compression unit (15) configured to compress a fluid; a motor (16) containing three-phase coils (19) and configured to drive the compression unit (15); an inverter circuit (24) with a switching element configured to perform switching to drive the motor (16), wherein the three-phase coils (19) are arranged on an output side of the inverter circuit (24) and connected to the inverter circuit (24); a capacitor (32) arranged on an input side of the inverter circuit (24) and connected in parallel to a DC power supply (31); a controller (25) configured to output three-phase pulse width modulation (PWM) signals to the inverter circuit (24) to control the inverter circuit (24); a temperature estimator configured to estimate the temperature of the capacitor (32); and a rotor position estimator configured to estimate the position of a rotor (18, 30) of the motor (16), wherein the controller (25) is configured to perform a process for determining the current pattern when the temperature of the capacitor (32) estimated by the temperature estimator is less than or equal to a predetermined temperature, the process for determining the current pattern involves selecting a current pattern of the motor (16) from six current patterns according to the position of the rotor (18, 30) estimated by the rotor position estimator, a direct current with a maximum permissible value in the positive or negative direction always flows only through one of the three-phase coils (19) and a direct current in opposite phase with half a maximum value flows through each of the other two of the three-phase coils in each of the six current patterns, the controller (25) is configured to perform a process to determine the maximum allowable value, in order to determine the maximum allowable value based on information from the temperature estimator, the controller (25) is configured to perform a phase angle shifting process to shift a phase angle of one of the three-phase PWM signals generated according to the current pattern selected by the current pattern determination process, and the six current patterns have the same phase angle ranges. [2] The motor-driven compressor (10) according to claim 1, wherein the six current patterns each correspond to six positions of the rotor (18, 30) and the controller (25) is configured to select from the six current patterns the current pattern whose corresponding position is closest to the position of the rotor (18, 30) estimated by the rotor position estimator in the process of determining the current pattern. [3] The motor-driven compressor (10) according to claim 1 or 2, wherein the controller (25) is configured in the phase angle shifting process to shift the phase angle of one of the three-phase PWM signals generated according to the current pattern selected in the process for determining the current pattern by 180° from the phase angles of the other PWM signals. [4] The motor-driven compressor (10) according to any one of claims 1 to 3, wherein the rotor position estimator is configured to estimate a position θ of the rotor (18, 30) of the motor (16), the currents flowing through the three-phase coils (19) are each a U-phase current Iu, a V-phase current Iv and a W-phase current Iw, where the six current patterns each a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv and the W-phase current Iw corresponding to Iu : Iv : Iw = +1 : -0.5 : -0.5 is when the estimated position θ of the rotor (18, 30) 18 is in a range of 330° < θ ≤ 360°, 0° ≤ θ ≤ 30°; a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv and the W-phase current Iw corresponding to Iu : Iv : Iw = +0.5 : +0.5 : -1 is when the estimated position θ of the rotor (18, 30) 18 is in a range of 30° < θ ≤ 90°; a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv and the W-phase current Iw corresponding to Iu : Iv : Iw = - 0.5 : +1 : -0.5 is when the estimated position θ of the rotor (18, 30) 18 is in a range of 90° < θ ≤ 150°; a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv and the W-phase current Iw corresponding to Iu : Iv : Iw = -1 : +0.5 : +0.5 is when the estimated position θ of the rotor (18, 30) 18 is in a range of 150° < θ ≤ 210°; a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv and the W-phase current Iw corresponding to Iu : Iv : Iw = - 0.5 : -0.5 : +1 is when the estimated position θ of the rotor (18, 30) 18 is in a range of 210° < θ ≤ 270°; a current pattern with the ratio of the U-phase current Iu, the V-phase current Iv and the W-phase current Iw corresponding to Iu : Iv : Iw = +0.5 : -1 : +0.5 is when the estimated position θ of the rotor (18, 30) 18 is in a range of 270° < θ ≤ 330°.

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