Motor drive unit

Abstract

The present invention relates to a motor drive device comprising a first inverter, a second inverter, and a controller. During motor startup, the controller performs DC excitation by supplying a DC excitation current from the first and second inverters to each phase winding of the motor, thereby rotating the motor rotor toward an initial position. After this rotation, the controller performs PWM control of the switching of the first and second inverters so that the rotor rotational speed reaches a target speed. Furthermore, the controller performs DC excitation so that the zero-axis current in each phase winding becomes substantially zero.

Description

Technical Field

[0001] The present invention relates to a motor driving device. The motor has a plurality of phase windings that are in a non-connected state with each other. Background Art

[0002] As a motor for driving a compressor, etc., a permanent magnet synchronous motor (also called a DC brushless motor) having multiple phase windings is used. In addition, the motor that drives the compressor is built into the compressor. Since the interior of the compressor becomes high temperature and high pressure, it is impossible to build in a sensor to detect the rotational position of the motor, that is, the rotor position. Therefore, this type of motor becomes a sensorless drive that infers the rotor position based on the motor winding current that responds to the output of the inverter. In addition, as an example of a permanent magnet synchronous motor, an open-winding motor (Open-Winding Motor) having multiple phase windings that are in a non-connected state is known.

[0003] A motor drive device for driving an open-type winding motor (hereinafter referred to as a motor) includes a first inverter that controls the energization of one end of each phase winding of the motor, and a second inverter that controls the energization of the other end of each phase winding of the motor. The motor is driven by switching these first and second inverters. Specifically, when starting the motor, initial positioning is performed by passing a DC excitation current through a predetermined path from the first and second inverters to each phase winding of the motor, thereby rotating the motor rotor to a predetermined initial position and fixing it at that position. After this positioning, forced commutation is performed by supplying an excitation component current from the first and second inverters to each phase winding, completing the startup. After startup is complete, the current flowing through each phase winding is detected, and the rotor speed and rotor position are detected or estimated based on the detected current. The switching of the first and second inverters is then PWM-controlled so that the rotational speed reaches a target speed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 4906836 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] A unique problem when driving open-coil motors is that zero-axis current, which does not contribute to motor driving, flows as the motor is energized. During initial positioning at startup, as DC excitation current flows through each phase winding, the zero-axis current increases, increasing motor losses.

[0009] An object of an embodiment of the present invention is to provide a motor drive device capable of reducing motor loss during motor startup.

[0010] Means for solving problems

[0011] The motor drive device of claim 1 drives a motor having a plurality of phase windings arranged in a non-connected state, and comprises: a first inverter for controlling energization of one end of each phase winding; a second inverter for controlling energization of the other end of each phase winding; and a controller for rotating the rotor of the motor toward an initial position by supplying DC excitation current from the first and second inverters to the phase windings upon startup of the motor. After this rotation, the controller performs PWM switching control of the first and second inverters so that the rotor rotational speed reaches a target speed. The controller further performs DC excitation to achieve substantially zero zero-axis current in the phase windings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a block diagram showing the structure of one embodiment.

[0013] Figure 2 1 is a flowchart showing control of the controller according to this embodiment.

[0014] Figure 3 This is a diagram showing the phase of DC excitation in this embodiment.

[0015] Figure 4 This is a diagram showing another example of the phase of DC excitation in this embodiment.

[0016] Figure 5 Yes means through Figure 4 Diagram of the path of current flowing due to DC excitation. DETAILED DESCRIPTION

[0017] Hereinafter, a motor drive device according to an embodiment will be described with reference to the drawings.

[0018] like Figure 1 As shown, a three-phase AC power supply 1 is connected to a drive circuit 2 , and the drive circuit 2 is connected to a motor 3 and a controller 4 .

[0019] Motor 3 is a three-phase permanent magnet synchronous motor for driving a compressor having multiple phase windings Lu, Lv, and Lw that are in a non-connected state, that is, a so-called open-winding motor, and includes a stator 41 on which the phase windings Lu, Lv, and Lw are installed, a rotor 42 in which multiple, for example, two, permanent magnets M1 and M2 are embedded, and a rotor shaft 43 that supports the rotor 42.

[0020] The drive circuit 2 includes a DC power supply 10 that full-wave rectifies and smoothes the three-phase AC voltage of the three-phase AC power supply 1, and outputs the resulting voltage; an inverter (first inverter) 20 that controls the flow of current between the output end of the DC power supply 10 and one end of the phase windings Lu, Lv, and Lw of the open-type motor 1M; and an inverter (second inverter) 30 that controls the flow of current between the output end of the DC power supply 10 and the other end of the phase windings Lu, Lv, and Lw of the open-type motor 1M. A power supply sharing system is employed, in which the DC power supply 10 serves as a common DC power source for the inverters 20 and 30.

[0021] Inverter 20 includes switching elements, such as a series circuit of IGBTs 21 and 22, a series circuit of IGBTs 23 and 24, and a series circuit of IGBTs 25 and 26. IGBTs 21 to 26 are switched on and off to control the flow of current between the interconnection point of IGBTs 21 and 22 and one end of phase winding Lu, the flow of current between the interconnection point of IGBTs 23 and 24 and one end of phase winding Lv, and the flow of current between the interconnection point of IGBTs 25 and 26 and one end of phase winding Lw. Regenerative diodes (also called freewheeling diodes) 21a to 26a are connected in antiparallel to IGBTs 21 to 26.

[0022] Similar to inverter 20, inverter 30 includes switching elements, such as a series circuit of IGBTs 31 and 32, a series circuit of IGBTs 33 and 34, and a series circuit of IGBTs 35 and 36. IGBTs 31 to 36 are switched on and off to control the flow of current between the interconnected point of IGBTs 31 and 32 and the other end of phase winding Lu, the flow of current between the interconnected point of IGBTs 33 and 34 and the other end of phase winding Lv, and the flow of current between the interconnected point of IGBTs 35 and 36 and the other end of phase winding Lw. Regenerative diodes 31a to 36a are connected in antiparallel to IGBTs 31 to 36.

[0023] Inverter 20 is actually a so-called Intelligent Power Module (IPM). This IPM houses a main circuit, consisting of the three series circuits connected in parallel, and peripheral circuits such as the drive circuit for the IGBTs 21 to 26 that drive this main circuit, in a single package. Inverter 30 is also an IPM with the same structure.

[0024] Current sensors 11u, 11v, and 11w are located on the three current lines between the inverter 20 and one end of the phase windings Lu, Lv, and Lw. These current sensors 11u, 11v, and 11w detect the phase currents Iu, Iv, and Iw flowing through the phase windings Lu, Lv, and Lw. The detection signals from these current sensors 11u, 11v, and 11w are transmitted to the controller 4.

[0025] The controller 4 is composed of a microcomputer and its peripheral circuits, performs sensorless vector control on the motor drive by the drive circuit 2 , and includes a rotation speed detection unit 51 , a first control unit 52 , a second control unit 53 , and a third control unit 54 .

[0026] The rotation speed detection unit 51 detects (estimates) the rotation speed (angular speed) of the rotor 42 in the motor 3 based on the phase currents Iu, Iv, and Iw detected by the current sensors 11u, 11v, and 11w.

[0027] When the motor 3 is started, the first control unit 52 performs DC excitation by supplying DC excitation currents Idu, Idv, and Idw from the inverters 20 and 30 to the phase windings Lu, Lv, and Lw of the motor 3 via a predetermined path, thereby performing initial positioning of the rotor 42 of the motor 3 to a predetermined initial position (predetermined rotational mechanical angle). Specifically, when the motor 3 is started, the first control unit 52 performs DC excitation to bring the zero-axis current (also called zero-phase current) Iz in the phase windings Lu, Lv, and Lw to nearly zero. The DC excitation currents Idu, Idv, and Idw used for this DC excitation are equal to the phase currents Iu, Iv, and Iw flowing through the phase windings Lu, Lv, and Lw through PWM control (described later) by the second control unit 53, at the phases at which the zero-axis current Iz of the phase windings Lu, Lv, and Lw is nearly zero. The phase currents Iu, Iv, and Iw at the phase where the zero-axis current Iz is substantially zero are the phase currents Iu, Iv, and Iw at which one phase current reaches zero while the positive and negative currents of the remaining two phases have substantially the same value. Taking the electrical angle at which any phase current reaches its maximum value as a reference of 0 degrees, the electrical angles at which one phase current reaches zero while the positive and negative currents of the remaining two phases have substantially the same value are 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees. Hereinafter, expressions regarding phase refer to electrical angles using this reference.

[0028] The second control unit 53 rotates the rotor 42 to the initial position by the above-mentioned DC excitation, and then completes the startup of the motor 3 by supplying forced commutation of the excitation component current (d-axis current) from the inverters 20 and 30 to the phase windings Lu, Lv, and Lw, thereby rotating the rotor 42 of the motor 3.

[0029] After the startup of the motor 3 based on the above-mentioned forced commutation is completed, the third control unit 54 performs PWM control (pulse width modulation control) on the switches of the inverters 20 and 30 so that the rotation speed of the rotor 42 detected by the rotation speed detection unit 51 becomes the target speed instructed from the outside.

[0030] Figure 2 The flowchart shows the control executed by the controller 4. Steps S1, S2, ... in the flowchart are simply referred to as S1, S2, ...

[0031] When the motor 3 is started ("YES" in S1), the controller 4 performs DC excitation at a phase where the zero-axis current Iz in the phase windings Lu, Lv, and Lw becomes substantially zero, in order to rotate the rotor 42 of the motor 3 to a predetermined initial position (S2). Specifically, the controller 4 controls the switches of the inverters 20 and 30 so that no DC excitation current flows through one phase winding, a DC excitation current in one direction flows through another phase winding, and a DC excitation current in the other direction flows through the remaining phase winding.

[0032] After the rotor 42 is rotated to its initial position by this DC excitation, the controller 4 supplies excitation component current from the inverters 20 and 30 to the phase windings Lu, Lv, and Lw through forced commutation (S3), thereby rotating the rotor 42 of the motor 3 and completing the startup of the motor 3. After the startup is completed, the controller 4 performs PWM control (pulse width modulation control) on the switches of the inverters 20 and 30 so that the rotational speed of the rotor 42 detected by the rotational speed detection unit 51 reaches the target speed (S4).

[0033] like Figure 3 As shown in FIG, the phase currents Iu, Iv, and Iw flowing through the phase windings Lu, Lv, and Lw in operation are shifted 120 degrees in phase. The solid line represents the phase current Iu, the dotted line represents the phase current Iv, the single-dot chain line represents the phase current Iw, and the double-dot chain line represents the zero-axis current Iz. Figure 3 In the figure, the electrical angle at which the U-phase phase current Iu reaches its maximum value is represented as a reference of 0 degrees. The zero-axis current Iz changes in a sinusoidal wave with a period three times that of each phase current, and each cycle of the phase current includes six zero-crossing points. The phases of these zero-crossing points are 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees. In each of these phases, a power-on mode is formed in which one phase current becomes zero and the remaining two phase currents have the same value on the positive and negative sides. That is, the switching elements of the inverters 20 and 30 connected to one phase winding are disconnected, the upper switching element of the inverter 20 connected to the other phase winding is turned on, and the lower switching element of the inverter 30 is turned on, and the upper switching element of the inverter 30 connected to the remaining phase winding is turned on, and the lower switching element of the inverter 20 is turned on.

[0034] The DC excitation currents Idu, Idv, and Idw for DC excitation are equal to the phase currents Iu, Iv, and Iw flowing through the phase windings Lu, Lv, and Lw, where one of the phase currents Iu, Iv, and Iw becomes zero and the remaining two phase currents have the same value on the positive and negative sides, for example, at a phase of 30 degrees. At this 30-degree phase, the DC excitation current Idv becomes zero and the DC excitation currents Idu and Idw have the same value on the positive and negative sides. Figure 1 The paths along which the DC excitation currents Idu and Idw flow are indicated by dotted arrows.

[0035] The DC excitation current Idu flows from the positive side output terminal (+) of the DC power supply unit 10 through the IGBT21 on the upper side of the inverter 20 to one end of the phase winding Lu by turning on the IGBT21 on the upper side of the inverter 20 and the IGBT32 on the lower side of the inverter 30, and flows from the other end of the phase winding Lu through the IGBT32 on the lower side of the inverter 30 to the negative side output terminal (-) of the DC power supply unit 10.

[0036] The DC excitation current Idw flows from the positive side output terminal (+) of the DC power supply unit 10 through the IGBT35 on the upper side of the inverter 30 to the other end of the phase winding Lw by turning on the IGBT35 on the upper side of the inverter 30 and the IGBT26 on the lower side of the inverter 20, and flows from one end of the phase winding Lw through the IGBT26 on the lower side of the inverter 20 to the negative side output terminal (-) of the DC power supply unit 10.

[0037] Since the DC excitation current Idv is zero and the DC excitation currents Idu and Idw are balanced at the same value on the positive and negative sides, the zero-axis current Iz flowing from the negative output terminal (-) of the DC power supply unit 10 through the inverters 20 and 30 to the phase windings Lu, Lv, and Lw is zero. Since the zero-axis current Iz is zero, motor losses during DC excitation can be reduced.

[0038] Assume that Figure 4 As shown in FIG. 1 , when DC excitation is performed at a phase of 45 degrees, the DC excitation current Idv becomes a value deviated from zero to the positive side, and the DC excitation currents Idu and Idw become values ​​different from each other on the positive side and the negative side. Figure 5 The dotted arrows in FIG. 5 indicate the paths along which the DC excitation currents Idu, Idv, and Idw flow.

[0039] The DC excitation current Idu flows from the positive side output terminal (+) of the DC power supply unit 10 through the IGBT21 on the upper side of the inverter 20 to one end of the phase winding Lu by turning on the IGBT21 on the upper side of the inverter 20 and the IGBT32 on the lower side of the inverter 30, and flows from the other end of the phase winding Lu through the IGBT32 on the lower side of the inverter 30 to the negative side output terminal (-) of the DC power supply unit 10.

[0040] The DC excitation current Idv flows from the positive side output terminal (+) of the DC power supply unit 10 through the IGBT25 on the upper side of the inverter 20 to one end of the phase winding Lv by turning on the IGBT25 on the upper side of the inverter 20 and the IGBT34 on the lower side of the inverter 30, and flows from the other end of the phase winding Lv through the IGBT34 on the lower side of the inverter 30 to the negative side output terminal (-) of the DC power supply unit 10.

[0041] The DC excitation current Idw flows from the positive output terminal (+) of the DC power supply 10 through the upper IGBT 35 of the inverter 30 and the lower IGBT 26 of the inverter 20, to the other end of the phase winding Lw. It then flows from one end of the phase winding Lw through the lower IGBT 26 of the inverter 20 to the negative output terminal (-) of the DC power supply 10. Furthermore, the current component Idw' of the DC excitation current Idw that passes through the switching element 26, which is larger than the combined component of the DC excitation currents Idu and Idv, becomes the zero-axis current Iz, which flows through the regenerative diode 36a of the lower IGBT 36 of the inverter 30 and flows to the phase winding Lw. During this energization, the zero-axis current Iz increases, thereby increasing motor losses. This disadvantage can be eliminated in the present embodiment.

[0042] Furthermore, the phases at which one of the phase currents Iu, Iv, and Iw reaches zero while the remaining two phase currents have substantially the same value on the positive and negative sides are not limited to 30 degrees, but also include 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees. At a phase of 90 degrees, the DC excitation current Idu reaches zero, and the DC excitation currents Idv and Idw balance with substantially the same value on the positive and negative sides. At a phase of 150 degrees, the DC excitation current Idw reaches zero, and the DC excitation currents Idv and Idu balance with substantially the same value on the positive and negative sides. DC excitation can be performed at any of these phases of 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees.

[0043] Furthermore, motor losses are proportional to the magnitude of the zero-axis current. Furthermore, the zero-axis current changes in a roughly sinusoidal manner at a frequency three times that of the normal sinusoidal motor drive cycle. Therefore, the state in which the zero-axis current is zero achieves maximum efficiency, but even by energizing at a phase near zero, the motor efficiency can be substantially improved. Therefore, even if the zero-axis current is not completely zero, the motor efficiency can be improved by outputting PWM control at phases near 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees, for example, within a range of ±5 degrees. During energization at these phases, the DC excitation current Idu is almost zero, and the DC excitation currents Idv and Idw are almost identical on the positive and negative sides. Although a small amount of zero-axis current Iz is generated, its value is small, resulting in minimal losses and a minimal reduction in motor efficiency.

[0044] In addition, the above-mentioned embodiments and modifications are provided as examples and are not intended to limit the scope of the invention. These new embodiments and modifications can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the invention. These embodiments and modifications are included in the scope and spirit of the invention and are included in the invention described in the patent claims and their equivalents.

[0045] Explanation of symbols

[0046] 1. 3-phase AC power supply; 2: Drive circuit; 3: Open-winding motor; 4: Controller; 10: DC power supply unit; 20: Inverter (first inverter); 30: Inverter (second inverter); 41: Stator; 42: Rotor; Lu, Lv, Lw: Phase windings.

Claims

1. A motor driving device for driving a motor in which a plurality of phase windings are arranged in a non-connected state, characterized in that: have: a first inverter for controlling the energization of one end of each phase winding; a second inverter for controlling the energization of the other ends of the respective phase windings; and a controller that, when the motor is started, supplies DC excitation current from the first inverter and the second inverter to the respective phase windings to rotate the rotor of the motor toward an initial position, and then, after the rotation, performs PWM control on the switches of the first inverter and the second inverter so that the rotation speed of the rotor reaches a target speed. The controller performs the DC excitation so that the zero-axis current in the phase winding becomes zero.

2. The motor drive device according to claim 1, wherein: The DC excitation currents are a plurality of DC excitation currents equal to the phase currents of the phases at which the zero-axis current in the phase windings becomes zero, among the phase currents flowing in the phase windings by the PWM control.

3. The motor drive device according to claim 1, wherein: The DC excitation current is equal to a phase current of a phase in which one of the phase currents flowing through the phase windings becomes zero and the remaining phase currents have the same value on the positive side and the negative side.

4. The motor drive device according to claim 1, wherein: The above-mentioned phase windings are 3 phase windings. The controller controls the switches of the first inverter and the second inverter so that no DC excitation current flows through one of the three phase windings, a DC excitation current in one direction flows through another phase winding, and a DC excitation current in the other direction flows through the remaining phase winding.

5. The motor drive device according to claim 3, wherein: The above-mentioned phase windings are 3 phase windings. The DC excitation current is three DC excitation currents equal to three phase currents of the three phase currents flowing in the above-mentioned phase windings by the above-mentioned PWM control, in which one phase current becomes zero and the remaining two phase currents have the same value on the positive side and the negative side.

6. The motor drive device according to claim 4, wherein: The phases at which the one phase current becomes zero and the remaining two phase currents have the same value on the positive side and the negative side are 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees.

7. The motor drive device according to claim 1, wherein: The above controller is, When the motor is started, the rotor of the motor rotates to an initial position by supplying DC excitation current from the first inverter and the second inverter to the respective phase windings. After this rotation, the first inverter and the second inverter supply excitation component current to the respective phase windings through forced commutation, thereby rotating the rotor and completing the starting of the motor. After the startup is completed, the rotational speed of the rotor is detected based on the respective phase currents flowing in the respective phase windings, and the switches of the first inverter and the second inverter are PWM controlled so that the detected rotational speed becomes the target speed.

Images