Dual inverter system

Abstract

To provide a technique for preventing a rush current from flowing through a snubber capacitor.SOLUTION: A dual inverter system for an open-winding motor includes a motor, first and second inverters, positive and negative switch circuits disposed between the second inverter and a battery, and a control device capable of switching a drive mode of the motor between a single mode in which the two switch circuits are opened and only the first inverter is subjected to switching control and a dual mode in which the two switch circuits are closed and the first and second inverters are subjected to switching control. When the drive mode of the motor is switched from the single mode to the dual mode, the control device performs precharging of the snubber capacitor by closing only the negative electrode switch circuit in a state where the positive electrode switch circuit is opened.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed herein relates to a dual inverter system for an open winding motor. [Background technology]

[0002] Patent Document 1 describes a dual inverter system for an open-winding motor. The dual inverter system includes a first inverter connected to one end of each of multiple layers of windings, and a second inverter connected to the other end of each of the multiple layers of windings. The dual inverter system is configured to be able to switch the motor drive mode between a single mode in which a switch circuit disposed between the second inverter and a battery is opened and the motor is driven using only the first inverter, and a dual mode in which the switch circuit is closed and the motor is driven using both the first and second inverters. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-162287 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described dual inverter system, a snubber circuit having a snubber capacitor may be provided for each inverter to suppress surge voltages generated by inverter switching. In this case, when the motor drive mode is switched from single mode to dual mode, an inrush current may flow from the battery to the snubber capacitor provided in the second inverter. This may cause an unintended excessive current (so-called inrush current) to flow in a switch circuit located between the battery and the snubber capacitor. This specification provides a technology that can prevent inrush current from flowing to the snubber capacitor in the above-described dual inverter system. [Means for solving the problem]

[0005] The technology disclosed in this specification relates to a dual inverter system including an open-winding motor with multi-phase windings, a first inverter having a positive terminal and a negative terminal connected to a battery and a plurality of AC terminals connected to one end of each of the multi-phase windings, a second inverter having a positive terminal and a negative terminal connected to the battery and a plurality of AC terminals connected to the other end of each of the multi-phase windings, a positive switch circuit disposed between the positive terminal of the second inverter and the positive terminal of the battery, a negative switch circuit disposed between the negative terminal of the second inverter and the negative terminal of the battery, and a control device capable of switching the drive mode of the motor between a single mode in which the positive switch circuit and the negative switch circuit are opened and only the first inverter is switched to drive the motor, and a dual mode in which the positive switch circuit and the negative switch circuit are closed and both the first inverter and the second inverter are switched to drive the motor. The second inverter has a snubber circuit electrically connecting the positive terminal and the negative terminal and including a snubber capacitor. When switching the drive mode of the motor from the single mode to the dual mode, the control device precharges the snubber capacitor by closing only the negative switch circuit while keeping the positive switch circuit open.

[0006] In the dual inverter system described above, when the motor drive mode is switched from single mode to dual mode, the snubber capacitor is precharged by closing only the negative switch circuit while leaving the positive switch circuit open. At this time, precharge current from the battery is supplied to the snubber capacitor through the motor winding. This prevents a sudden increase in precharge current from occurring due to the inductance of the winding, preventing an inrush current from flowing through the snubber capacitor. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block circuit diagram showing the configuration of a dual inverter system. [Figure 2] Figure 2(a) is a diagram showing the current flow when the motor is in single mode. Figure 2(b) is a diagram showing the current flow when the motor is in dual mode. In Figures 2(a) and 2(b), switching elements that are on are marked "ON." [Figure 3] Figure 3(a) shows the current flow during snubber capacitor pre-charging. Figure 3(b) shows a time chart for switching the motor drive mode in a dual inverter system. In Figure 3(a), the switching elements that are on are marked "ON." DETAILED DESCRIPTION OF THE INVENTION

[0008] A dual inverter system for an open winding motor according to an embodiment will now be described with reference to the drawings.

[0009] As shown in Fig. 1, the dual inverter system 100 includes a motor 10, a first inverter 20, a second inverter 30, a positive pole switch circuit 40p, a negative pole switch circuit 40n, and a control device 50. The dual inverter system 100 is mounted on, for example, a vehicle, and can drive wheels using the motor 10. The vehicle referred to here includes, for example, a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc. The dual inverter system 100 is connected to a high-voltage battery 60 mounted on the vehicle. The dual inverter system 100 controls the power supplied from the battery 60 to the motor 10.

[0010] The battery 60 has one or more secondary battery cells and is configured to be chargeable and dischargeable. The secondary battery cells are not particularly limited, but may be, for example, lithium ion battery cells or all-solid-state battery cells.

[0011] The motor 10 is an open-winding motor with multiple phase windings that are not connected to each other. The motor 10 is a three-phase AC motor, and the multiple phase windings include a U-phase winding 12, a V-phase winding 14, and a W-phase winding 16. One end 12a, 14a, 16a of each winding 12, 14, 16 of the motor 10 is connected to a battery 60 via a first inverter 20. The other end 12b, 14b, 16b of each winding 12, 14, 16 of the motor 10 is connected to the battery 60 via a second inverter 30.

[0012] A capacitor 48 is disposed between the first inverter 20, the second inverter 30 and the battery 60.

[0013] The first inverter 20 has a positive terminal 20p, a negative terminal 20n, and three AC terminals 20u, 20v, and 20w. The positive terminal 20p is connected to the positive terminal 60p of the battery 60, and the negative terminal 20n is connected to the negative terminal 60n of the battery 60. The three AC terminals 20u, 20v, and 20w are connected to one end 12a, 14a, and 16a of each winding 12, 14, and 16 of the motor 10. The subscripts "u," "v," and "w" in the symbols of the inverters 20 and 30 refer to the U phase, V phase, and W phase of the three-phase AC, respectively.

[0014] The first inverter 20 has three switching circuits 21u, 21v, and 21w. The three switching circuits 21u, 21v, and 21w are connected in parallel to one another. Each of the switching circuits 21u, 21v, and 21w has two switching elements 22 connected in series. One of the two switching elements 22 is an upper arm switching element located on a high potential side, and the other of the two switching elements 22 is a lower arm switching element located on a low potential side. Each of the switching circuits 21u, 21v, and 21w is connected to an AC terminal 20u, 20v, or 20w at a midpoint between the two switching elements 22. Each of the switching elements 22 may be, but is not limited to, a metal-oxide-semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT).

[0015] The first inverter 20 has a plurality of snubber circuits 24. Each snubber circuit 24 is connected in parallel to a corresponding one of the three switching circuits 21u, 21v, and 21w. Each snubber circuit 24 has a snubber capacitor 26 and a resistor 28. The snubber capacitor 26 and the resistor 28 are connected in series. The resistor 28 is arranged on the higher potential side than the snubber capacitor 26.

[0016] The second inverter 30 has a configuration similar to that of the first inverter 20. That is, the second inverter 30 also has a positive terminal 30p, a negative terminal 30n, and three AC terminals 30u, 30v, and 30w. The positive terminal 30p is connected to the positive terminal 60p of the battery 60, and the negative terminal 30n is connected to the negative terminal 60n of the battery 60. The three AC terminals 30u, 30v, and 30w are connected to the other terminals 12b, 14b, and 16b of the windings 12, 14, and 16 of the motor 10. However, a positive switch circuit 40p is interposed between the positive terminal 30p of the second inverter 30 and the positive terminal 60p of the battery 60. Furthermore, a negative switch circuit 40n is interposed between the negative terminal 30n of the second inverter 30 and the negative terminal 60n of the battery 60.

[0017] The second inverter 30 has three switching circuits 31u, 31v, and 31w. The three switching circuits 31u, 31v, and 31w are connected in parallel to one another. Each of the switching circuits 31u, 31v, and 31w has two switching elements 32 connected in series. One of the two switching elements 32 is an upper arm switching element located on a high potential side, and the other of the two switching elements 32 is a lower arm switching element located on a low potential side. Each of the switching circuits 31u, 31v, and 31w is connected to an AC terminal 30u, 30v, and 30w at the midpoint between the two switching elements 32. Each of the switching elements 32 may be, but is not limited to, a MOSFET or an IGBT.

[0018] The second inverter 30 has a plurality of snubber circuits 34. Each snubber circuit 34 is connected in parallel to a corresponding one of the three switching circuits 31u, 31v, and 31w. Each snubber circuit 34 has a snubber capacitor 36 and a resistor 38.

[0019] The positive switch circuit 40p has two switching elements S1 and S2 connected in series. While not particularly limited, each of the switching elements S1 and S2 may be a reverse conducting IGBT (RC-IGBT) with a built-in freewheeling diode or a MOSFET with a body diode formed between the source and drain. The two switching elements S1 and S2 are connected so that the rectification directions of the built-in diodes are opposite. The switching element S1 is located on the positive terminal 30p side of the battery 60, and the switching element S2 is located on the second inverter 30 side.

[0020] When both switching elements S1 and S2 are on, conduction occurs between the positive electrode 60p of the battery 60 and the positive terminal 30p of the second inverter 30. In this case, the positive switch circuit 40p is said to be closed in this specification. On the other hand, when at least switching element S2 is off, current flow from the battery 60 to the second inverter 30 is cut off. In this case, the positive switch circuit 40p is said to be open in this specification.

[0021] The negative switch circuit 40n has a switching element S3. Although not particularly limited, the switching element S3 may be an RC-IGBT with a built-in freewheeling diode or a MOSFET with a body diode formed between the source and drain.

[0022] When the switching element S3 is on, conduction occurs between the negative electrode 60n of the battery 60 and the negative terminal 30n of the second inverter 30. In this case, the negative switch circuit 40n is said to be closed in this specification. On the other hand, when the switching element S3 is off, current flow from the battery 60 to the second inverter 30 is cut off. In this case, the negative switch circuit 40n is said to be open in this specification.

[0023] The control device 50 controls the positive switch circuit 40p and the negative switch circuit 40n, and can switch the drive mode of the motor 10 between a single mode and a dual mode.

[0024] Referring to FIG. 2, the single mode and dual mode drive modes of the motor 10 will be described. The control device 50 is not shown in FIG. 2. FIG. 2(a) shows an example of current flow when the drive mode is single mode, indicated by thick arrows. In single mode, the motor 10 is driven using only the first inverter 20. In this case, as shown in FIG. 2(a), the control device 50 opens the positive pole switch circuit 40p and the negative pole switch circuit 40n. The control device 50 also maintains all upper arm switching elements of the multiple switching elements 32 of the second inverter 30 on and all lower arm switching elements off. Alternatively, all lower arm switching elements of the multiple switching elements 32 of the second inverter 30 may be maintained on and all upper arm switching elements off. As a result, the multiple layers of windings 12, 14, and 16 of the second inverter 30 are connected to each other, forming a neutral point for the motor 10. In this state, the control device 50 selectively turns on and off each switching element 22 of the first inverter 20. Thus, in the single mode, the motor 10 is driven only by the first inverter 20 as a motor having a neutral point.

[0025] FIG. 2(b) shows an example of current flow when the drive mode is dual mode, indicated by thick arrows. In dual mode, the motor 10 is driven using both the first inverter 20 and the second inverter 30. In this case, as shown in FIG. 2(b), the control device 50 closes the positive switch circuit 40p and the negative switch circuit 40n. In this state, the control device 50 selectively turns on and off each switching element 22 of the first inverter 20 and each switching element 32 of the second inverter 30. At this time, between the first inverter 20 and the second inverter 30, switching circuits of the same phase (e.g., 21u, 31u) are driven in opposite phases. As a result, a voltage approximately 1.73 times higher than in single mode is applied to the motor 10, and the motor 10 operates at high output. Thus, in dual mode, the motor 10 is driven by both the first inverter 20 and the second inverter 30.

[0026] As described above, when the drive mode of the motor 10 switches from the single mode to the dual mode, the positive switch circuit 40p and the negative switch circuit 40n are closed, and the positive terminal 30p and the negative terminal 30n of the second inverter 30 are connected to the battery 60. This may cause an inrush current to flow from the battery 60 to each snubber capacitor 36 provided in the second inverter 30. In this case, an unintended excessive current (so-called inrush current) may flow to the switch circuits 40p, 40n located between the battery 60 and the snubber capacitors 36.

[0027] 3(a) and 3(b), in the dual inverter system 100 of this embodiment, when the control device 50 switches the drive mode of the motor 10 from single mode to dual mode, it closes only the negative switch circuit 40n while leaving the positive switch circuit 40p open. This causes each snubber capacitor 36 to be precharged. At this time, a precharge current from the battery 60 is supplied to each snubber capacitor 36 of the second inverter 30 through the windings 12, 14, and 16 of the motor 10. As a result, a sudden increase in the precharge current is suppressed by the inductance of the windings 12, 14, and 16, preventing an inrush current from flowing through the snubber capacitor 36.

[0028] That is, as shown in FIG. 3(b), in single mode, a voltage is applied from the first inverter 20 to each of the windings 12, 14, and 16 of the motor 10. Then, while the motor remains in single mode, only the negative switch circuit 40n is closed (i.e., the switching element S3 shown in FIG. 3(b) is turned on), and a voltage is applied to each of the windings 12, 14, and 16 of the motor 10. The applied voltage is used to control the motor 10 and to precharge each of the snubber capacitors 36 of the second inverter 30. Each snubber capacitor voltage Vc is charged from the battery 60 via each of the windings 12, 14, and 16, and slowly rises to a level equivalent to the battery voltage Vb. This suppresses inrush current to the snubber capacitor 36. That is, the inrush current does not affect the switch circuits 40p and 40n. After the snubber capacitor 36 is precharged, the positive switch circuit 40p is closed (that is, the switching element S2 is turned on), and the motor 10 is driven in the dual mode.

[0029] In this embodiment, snubber circuits 24, 34 are provided in each inverter 20, 30. This makes it possible to suppress surge voltages. Therefore, it is not necessary to employ large elements for the switching elements 22, 32 of each inverter 20, 30 as a countermeasure against surge voltages. Furthermore, small elements with relatively small allowable currents can be employed for the switching elements S1, S2, S3 in the positive switch circuit 40p and the negative switch circuit 40n. This makes it possible to prevent the dual inverter system 100 from becoming larger due to surge voltages. [Explanation of symbols]

[0030] 10: motor, 12, 14, 16: winding, 20: first inverter, 20p: positive pole terminal, 20n: negative pole terminal, 20u, 20v, 20w: AC terminal, 24: snubber circuit, 26: snubber capacitor, 30: second inverter, 30p: positive pole terminal, 30n: negative pole terminal, 30u, 30v, 30w: AC terminal, 34: snubber circuit, 36: snubber capacitor, 40p: positive pole switch circuit, 40n: negative pole switch circuit, 50: control device, 60: battery, 60p: positive pole, 60n: negative pole

Claims

[Claim 1] an open winding motor having multiple phase windings; a first inverter having a positive terminal and a negative terminal connected to a battery and a plurality of AC terminals connected to respective ends of the plurality of phase windings; a second inverter having a positive terminal and a negative terminal connected to the battery and a plurality of AC terminals connected to the other ends of the plurality of phase windings; a positive switch circuit disposed between the positive terminal of the second inverter and the positive terminal of the battery; a negative switch circuit disposed between the negative terminal of the second inverter and the negative terminal of the battery; a control device capable of switching a drive mode of the motor between a single mode in which the positive switch circuit and the negative switch circuit are opened and only the first inverter is switched to drive the motor, and a dual mode in which the positive switch circuit and the negative switch circuit are closed and both the first inverter and the second inverter are switched to drive the motor; Equipped with the second inverter has a snubber circuit electrically connected between the positive terminal and the negative terminal and provided with a snubber capacitor; When switching the drive mode of the motor from the single mode to the dual mode, the control device closes only the negative switch circuit while keeping the positive switch circuit open, thereby precharging the snubber capacitor. Dual inverter system.

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