Electric motor drive unit

Abstract

This invention provides an electric motor drive device that prevents abnormal current from flowing during a fail-safe operation in which the switching elements of the upper or lower arm of all phases are turned on when a short-circuit or open-circuit lock of one phase of the switching elements constituting the inverter is detected, thereby preventing damage to the electric motor, inverter, etc. [Solution] When the processor constituting the control unit detects a short-circuit or open-circuit lock in one phase of the switching elements constituting the inverter, it enters a fail-safe operation that turns on the switching elements of the upper or lower arm of all phases, and then performs a process to break the weld at the neutral point of the stator winding.

Description

Technical Field

[0001] The present invention relates to a drive device for an electric motor.

Background Art

[0002] In recent years, hybrid electric vehicles (HEVs) that can effectively improve the fuel consumption rate (fuel efficiency) of vehicles by using an engine and an electric motor in combination have been widely put into practical use. In addition, electric vehicles (BEVs) that use only an electric motor as a power source and do not emit exhaust gas have also been put into practical use. In hybrid electric vehicles and electric vehicles (electric vehicles) equipped with an electric motor as a power source, an inverter having a plurality of switching elements converts DC power from a high-voltage battery into AC power (for example, three-phase AC) and supplies the AC power to the electric motor, thereby driving the electric motor.

[0003] By the way, for example, when a plurality of switching elements constituting an inverter are short-circuited and fixed or opened and fixed, current cannot be passed correctly, and the sum of the three-phase currents is disrupted, so that unintended torque, that is, abnormal torque is generated.

[0004] Accordingly, for example, Patent Document 1 discloses a technology (permanent magnet synchronous motor drive system) that performs a fail-safe operation of turning on the switching elements of the upper arms or the lower arms of all phases while avoiding short-circuiting of the upper and lower arms of the inverter according to the balance state of the output current of each phase when short-circuit sticking or open sticking of the semiconductor switching elements constituting the inverter is detected.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0006] However, if a short-circuit or open-circuit lock occurs in one phase of the switching elements, turning on the upper or lower arm switching elements for all phases may cause an abnormal current to flow through the electric motor or inverter, potentially leading to damage to the electric motor or inverter.

[0007] The present invention was made to solve the above problems, and aims to provide an electric motor drive device that can prevent abnormal current from flowing during a fail-safe operation in which the switching elements of the upper or lower arm of all phases are turned on when a short-circuit or open-circuit lock of one phase of the switching elements constituting the inverter is detected, thereby preventing damage to the electric motor, inverter, etc. [Means for solving the problem]

[0008] An electric motor drive device according to one aspect of the present invention comprises: an electric motor having a stator in which multiple phase stator windings are connected at a neutral point; an inverter including switching elements and having multiple upper and lower arms corresponding to the multiple phase stator windings, which converts DC power into multiple phase AC power and supplies it to the electric motor by turning the switching elements constituting the upper and lower arms on and off; and a processor which executes a process to control the drive of the inverter by executing a program stored in memory, wherein when the processor detects a short-circuit or open-circuit lock of one phase of the switching elements constituting the inverter, it enters a fail-safe operation that turns on the switching elements of all phases of the upper or lower arm, and then executes a process to break the weld at the neutral point of the stator winding.

[0009] According to one embodiment of the present invention, when a short-circuit or open-circuit lock of one phase of the switching elements constituting the inverter is detected, a fail-safe operation is initiated in which the switching elements of the upper or lower arm of all phases are turned on, after which the weld at the neutral point of the stator winding is broken. This prevents abnormal current from flowing through the electric motor, inverter, etc. [Effects of the Invention]

[0010] According to the present invention, when a short-circuit or open-circuit lock in one phase of the switching elements constituting the inverter is detected, it is possible to prevent abnormal current from flowing during the fail-safe operation in which the switching elements of the upper or lower arm of all phases are turned on, thereby preventing damage to electric motors, inverters, etc. [Brief explanation of the drawing]

[0011] [Figure 1] This diagram shows the configuration of the drive device for an electric motor according to an embodiment. [Figure 2] This figure shows the fracture simulation results of the weld at the neutral point of the stator winding. (a) shows the temperature distribution, and (b) shows the stress distribution. [Figure 3] This is a flowchart showing the processing procedure for fail-safe processing (neutral point fracture processing) by the electric motor drive device according to the embodiment. [Modes for carrying out the invention]

[0012] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference numerals. In addition, in each drawing, the same elements will be denoted by the same reference numerals, and redundant explanations will be omitted.

[0013] First, the configuration of the electric motor drive device 1 according to this embodiment will be described using Figure 1. Figure 1 shows the configuration of the electric motor drive unit 1.

[0014] The electric motor 10 is, for example, a three-phase AC type AC synchronous motor (three-phase AC motor) and serves as the driving force source for an electric vehicle. The electric motor 10 is also a permanent magnet type synchronous motor (PM synchronous motor) that uses permanent magnets in the rotor (not shown) and stator windings (armature windings) 11 in the stator. The stator windings 11 (three-phase wires) of multiple phases (three phases in this embodiment: U phase, V phase, W phase) that constitute the stator of the electric motor 10 are connected (welded) at one end at the neutral point 110.

[0015] A temperature sensor 53 is attached to the stator winding 11 of the electric motor 10 to detect the temperature of the stator winding 11. The temperature sensor 53 is connected to a control unit 50 (hereinafter referred to as "CU50"), which will be described later, and an electrical signal (for example, voltage) corresponding to the temperature of the stator winding 11 is input to the CU50.

[0016] The electric motor 10 is, for example, an oil-cooled (liquid-cooled) electric motor that is cooled by oil (equivalent to a coolant). In the electric motor 10, oil (coolant) pressurized by the electric oil pump 41 is supplied directly to the stator from the nozzle 45 for cooling.

[0017] Therefore, the electric motor 10 is provided with an oil jet (oil supply) device 40 that injects oil toward the stator winding 11 (particularly the neutral point 110). The oil jet device 40, for example, pressurizes the oil stored in the oil pan 42 using an electric oil pump 41, pumps it through an oil passage (hydraulic circuit) 43 to a nozzle 45, and injects it from the nozzle 45 toward the stator winding 11 (particularly the neutral point 110). Alternatively, an on / off valve 44 (solenoid valve) for switching the operation of the oil jet may be interposed in the oil passage (hydraulic circuit) 43. The drive of the electric oil pump 41 (and the on / off valve 44) (i.e., the supply and stopping of oil) is controlled by a CU 50, which will be described later (details will be described later).

[0018] The oil jet device 40 is equipped with an oil temperature sensor 54 that detects the temperature of oil (oil temperature). The oil temperature sensor 54 is connected to the CU 50, and an electrical signal (e.g., voltage) corresponding to the oil temperature is input to the CU 50.

[0019] The inverter 20 includes switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS, and has a plurality of (three-phase) upper arms 21U, 21V, 21W and lower arms 22U, 22V, 22W corresponding to the multi-phase (three-phase in the present embodiment) stator windings 11 (three-phase lines). By complementarily turning on and off the switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS that constitute the upper arms 21U, 21V, 21W and lower arms 22U, 22V, 22W, the inverter converts the DC power of the high-voltage battery 30 into multi-phase (three-phase) AC power and supplies it to the electric motor 10 (that is, drives the electric motor 10).

[0020] More specifically, the inverter 20 has three-phase upper and lower arms (21U and 22U, 21V and 22V, 21W and 22W) each formed by a pair of switching elements (21US and 22US, 21VS and 22VS, 21WS and 22WS) connected in series, and the connection points (connection nodes) of the upper and lower arms of each phase (21U and 22U, 21V and 22V, 21W and 22W) are respectively connected to the stator windings 11U, 11V, 11W of the corresponding phase.

[0021] That is, the inverter 20 has upper arms 21U, 21V, 21W and lower arms 22U, 22V, 22W corresponding to the three-phase lines of the electric motor 10. The U-phase upper arm 21U and lower arm 22U are connected in series, and their connection point (connection node) is connected to the other end of the U-phase stator winding 11U of the electric motor 10.

[0022] Similarly, the upper arm 21V and the lower arm 22V of the V phase are connected in series, and the connection point (connection node) thereof is connected to the other end of the V-phase stator winding 11V of the electric motor 10. Further, the upper arm 21W and the lower arm 22W of the W phase are connected in series, and the connection point (connection node) thereof is connected to the other end of the W-phase stator winding 11W of the electric motor 10.

[0023] Each of the upper arms 21U, 21V, 21W and each of the lower arms 22U, 22V, 22W has switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS, and freewheeling diodes 21UD, 21VD, 21WD, 22UD, 22VD, 22WD connected in antiparallel to the switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS. As the switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS, for example, IGBTs, MOSFETs or the like are used. Each of the switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS is complementarily turned on and off by a switching signal from the CU50. That is, the driving of the inverter 20 is controlled by the CU50.

[0024] The CU50 controls the electric motor 10 by performing switching control of the inverter 20 (that is, controlling the driving of the inverter 20). In addition, the CU50 controls the operation and stop of the oil jet device 40 (that is, the supply and stop of oil to the stator) by controlling the driving of the electric oil pump 41 (and / or the on-off valve 44). The details will be described later.

[0025] The CU50 is connected with the aforementioned temperature sensor 53 that detects the temperature of the stator winding 11, and an oil temperature sensor 54 that detects the temperature of oil (cooling oil).

[0026] The CU50 is configured to include a microprocessor 51 (equivalent to a processor) that performs calculations, an EEPROM 52 (equivalent to memory) that stores programs for causing the microprocessor 51 to execute various processes, a RAM that stores various data such as calculation results, a backup RAM that holds the contents of the stored data, and an input / output interface (I / F).

[0027] In particular, the control unit 50 (processor 51) has a function to prevent damage to the electric motor 10, inverter 20, etc., by detecting a short-circuit or open-circuit lock in one phase of the switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS that constitute the inverter 20, and turning on the switching elements 21US, 21VS, 21WS, or 22US, 22VS, 22WS of the upper arm 21U, 21V, 22V, 21W or the lower arm 22U, 22V, 22W, while avoiding a short circuit in the upper arm 21U, 21V, 21W or the lower arm 22U, 22V, 22W of the inverter 20. In the CU 50, this function is realized by the execution of a program stored in the EEPROM 52 or the like (memory) by the microprocessor 51 (hereinafter sometimes simply referred to as "processor 51").

[0028] Therefore, when the processor 51 constituting the CU50 detects a one-phase short-circuit or one-phase open-circuit fixation of the switching elements 21US, 21VS, 21WS, 22US, 22VS, and 22WS constituting the inverter 20, it avoids short-circuiting the upper and lower arms (21U and 22U, 21V and 22V, 21W and 22W) of the inverter 20, while simultaneously controlling the switching elements 21US, 21VS, 21WS, or the switching elements 21US, 21VS, 21WS of the upper arms 21U, 21V, 21W or the lower arms 22U, 22V, 22W of all phases. After entering failsafe mode by turning on 22US, 22VS, and 22WS (for example, if one phase of the upper arm 21U, 21V, and 21W is stuck in an open circuit, all of the lower arm 22U, 22V, and 22W are turned on; if one phase of the upper arm 21U, 21V, and 21W is stuck in a short circuit, all of the upper arm 21U, 21V, and 21W are turned on, and all of the lower arm 22U, 22V, and 22W are turned off, etc.), the process of breaking the weld at the neutral point 110 of the stator winding 11 is performed.

[0029] In other words, when CU50 detects a short-circuit or open-circuit lock in one phase of the switching elements 21US, 21VS, 21WS, 22US, 22VS, and 22WS that constitute the inverter 20, it enters a fail-safe operation that turns on the switching elements 21US, 21VS, 21WS, or 22US, 22VS, and 22WS of the upper arm 21U, 21V, 22V, and 21W, while avoiding a short circuit in the upper arm 21U, 21V, 21W or the lower arm 21US, 21VS, 21WS, or 22US, 22VS, and 22WS of all phases, and then breaks the weld at the neutral point 110 of the stator winding 11. The same applies hereafter.

[0030] As a result, each of the three phase stator windings 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W) becomes disconnected (non-conductive), preventing abnormal current from flowing. Note that, for detecting single-phase short-circuiting or single-phase open-circuiting of the switching elements 21US, 21VS, 21WS, 22US, 22VS, and 22WS, known methods, such as a method based on the imbalance of the sum of the three phase currents (the unbalanced state of the currents in each phase), can be used.

[0031] At that time, the processor 51 of the CU50 performs a process to apply thermal stress to the weld at the neutral point 110 to fracture (break) the weld. More specifically, after entering fail-safe operation, the processor 51 of the CU50 temporarily stops the operation of the electric oil pump 41 (or temporarily closes the on / off valve 44) and stops the supply of oil (cooling oil). Then, when the temperature of the stator winding 11 rises and the temperature difference between the temperature of the stator winding 11 and the temperature of the oil (cooling oil) becomes greater than or equal to a predetermined temperature (for example, 160°C), the electric oil pump 41 is restarted (or the on / off valve 44 is opened) and the process of injecting oil (cooling oil) into the weld at the neutral point 110 is performed.

[0032] More specifically, if one end of each of the three phase stator windings 11 is welded (connected) to each other via the neutral wire 110, that is, if the welds of the U-phase wire 11U and the neutral wire 110, the V-phase wire 11V and the neutral wire 110, and the W-phase wire 11W and the neutral wire 110 are each individually spaced apart (the welds are divided into three locations), then the oil (cooling oil) is sprayed onto either one (one side) of the stator windings 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W) and the neutral wire 110 at each weld. In other words, the nozzle 45 is positioned so that the oil is applied to either one (one side). As a result, the welded portion of the neutral point (neutral wire) 110 is fractured due to thermal stress caused by the temperature difference between each stator winding 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W) and the neutral wire 110.

[0033] Furthermore, if one end of each of the three phase stator windings 11 (the U-phase wire 11U, V-phase wire 11V, and W-phase wire 11W that constitute the three phases) is welded (connected) in a single location, oil (cooling oil) is sprayed onto the stator windings 11 located at both ends of the weld, or onto the stator winding 11 located in the center. In other words, the nozzle 45 is positioned so that oil is applied to the stator windings 11 at both ends or in the center of the weld. As a result, the weld of the neutral wire (neutral point) 110 is fractured due to thermal stress caused by the temperature difference between each stator winding 11 (U-phase wire 11U, V-phase wire 11V, and W-phase wire 11W).

[0034] Figure 2 shows the fracture simulation results of the weld at the neutral point 110 of the stator winding 11. (a) shows the temperature distribution, and (b) shows the stress distribution. The simulation utilized the Thermal Analysis (ATH) method. The models of the stator winding 11 (e.g., U-phase wire 11U), the neutral wire 110, and the weld were integrated, and the base ends of the stator winding 11 (e.g., U-phase wire 11U) and the neutral wire 110 were fully constrained. When the stator winding 11 (e.g., U-phase wire 11U) was set to 200°C and the neutral wire 110 to 40°C, it was confirmed that the von Mises stress inside the weld exceeded 195 MPa, and that the weld could fracture due to thermal stress. Therefore, for example, if the oil temperature is 60°C, raising the temperature of the stator winding 11 to 220°C (<heat resistance temperature) will result in a temperature difference of 160°C, which can cause the weld at the neutral point 110 to break due to thermal stress.

[0035] Next, the operation of the electric motor drive unit 1 will be explained with reference to Figure 3. Figure 3 is a flowchart showing the fail-safe processing (neutral point fracture processing) procedure performed by the electric motor drive unit 1. This processing is mainly performed repeatedly at predetermined timings by the microprocessor 51 that constitutes the CU50.

[0036] In step S100, a determination is made as to whether or not a single-phase short-circuit lock or single-phase open-circuit lock has been detected in the switching elements 21US, 21VS, 21WS, 22US, 22VS, and 22WS that constitute the inverter 20. If no single-phase short-circuit lock or single-phase open-circuit lock is detected, the process is temporarily exited. On the other hand, if a single-phase short-circuit lock or single-phase open-circuit lock is detected, the process proceeds to step S102.

[0037] In step S102, the switching elements 21US, 21VS, 21WS, 22US, 22VS, 22WS of the upper arm 21U, 21V, 21W or the lower arm 22U, 22V, 22W are turned on (i.e., a fail-safe operation is performed) while avoiding a short circuit between the upper and lower arms of the inverter 20 (21U and 22U, 21V and 21W, 21W and 21W).

[0038] Next, in step S104, the electric oil pump 41 is temporarily stopped (or the on / off valve 44 is temporarily closed). As a result, the oil supply is stopped and the temperature of the stator winding 11 rises.

[0039] Then, in step S106, a determination is made as to whether the temperature difference between the temperature of the stator winding 11 and the temperature of the oil (coolant) has reached a predetermined temperature (for example, 160°C). If the temperature difference has not reached the predetermined temperature, the process moves to step S104, and the processes described in steps S104 to S106 are repeated until the temperature difference reaches the predetermined temperature. On the other hand, if the temperature difference reaches the predetermined temperature, the process moves to step S108.

[0040] In step S108, the electric oil pump 41 is restarted (or the on / off valve 44 is reactivated), and oil (cooling oil) is injected into the weld at the neutral point 110 of the stator winding 11. The method of injecting oil (cooling oil) into the weld at the neutral point 110 of the stator winding 11 is as described above, so a detailed explanation is omitted here. Then, the weld at the neutral point 110 is fractured due to thermal stress caused by the temperature difference between the two. After that, the process is exited.

[0041] As described in detail above, according to this embodiment, when a single-phase short-circuit or single-phase open-circuit lock is detected in the switching elements 21US, 21VS, 21WS, 22US, 22VS, and 22WS constituting the inverter 20, a fail-safe operation is entered in which the switching elements 21US, 21VS, 21WS, 22US, 22VS, and 22WS of all phases of the upper arm 21U, 21V, and 21W or the lower arm 22U, 22V, and 22W are turned on while avoiding a short circuit of the upper arm (21U and 22U, 21V and 22V, 21W and 22W) of the inverter 20. After this, the welded portion of the neutral point 110 of the stator winding 11 is broken. Therefore, it is possible to prevent abnormal current from flowing to the electric motor 10, inverter 20, etc. As a result, it is possible to prevent abnormal current from flowing during fail-safe operation and prevent damage to the electric motor 10, inverter 20, etc.

[0042] In particular, according to this embodiment, after entering fail-safe mode, the electric oil pump 41 is temporarily stopped (or the on / off valve 44 is temporarily closed), the temperature of the stator winding 11 rises, and when the temperature difference between the temperature of the stator winding 11 and the temperature of the oil (cooling oil) exceeds a predetermined temperature (for example, 160°C), the electric oil pump 41 is restarted (or the on / off valve 44 is reopened), and oil (cooling oil) is injected into the weld of the neutral point 110. As a result, the weld of the neutral point 110 can be fractured by thermal stress caused by the temperature difference between the stator winding 11 and the neutral point (neutral wire) 110. Furthermore, the weld of the neutral point 110 can be fractured without adding any new dedicated parts (for example, a pilot fuse).

[0043] According to this embodiment, when one end of each of the three phase stator windings 11 is welded (connected) to each other via a neutral wire 110, that is, when the welds between the U-phase wire 11U and the neutral wire 110, the V-phase wire 11V and the neutral wire 110, and the W-phase wire 11W and the neutral wire 110 are each separately spaced apart, oil (cooling oil) is sprayed onto either one (one side) of the stator windings 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W) and the neutral wire 110 at each weld. As a result, a temperature difference can be created between each of the stator windings 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W) and the neutral wire 110, and the thermal stress caused by this temperature difference can cause the weld at the neutral point (neutral wire) 110 to break.

[0044] On the other hand, according to this embodiment, when one end of each of the three phase stator windings 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W) is welded (connected) in a single location, oil (cooling oil) is sprayed onto the stator windings 11 located at both ends of the welded area, or onto the stator winding 11 located in the center. As a result, a temperature difference can be created between each of the stator windings 11 (U-phase wire 11U, V-phase wire 11V, W-phase wire 11W), and the welded area at the neutral point 110 can be fractured by the thermal stress caused by this temperature difference.

[0045] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, in the above embodiments, the present invention was described using the case where it is applied to a permanent magnet synchronous motor (PM synchronous motor) as an example, but it can also be applied to other types of electric motors, such as AC induction motors (IM motors). Furthermore, the present invention can be applied to electric vehicles that use electric motors as a driving force source, including battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell electric vehicles (FCEVs). Moreover, it may be applied to electric vehicles equipped with multiple electric motors.

[0046] In the above embodiment, a three-phase electric motor 10 and inverter 20 were used, but the number of phases of the electric motor and inverter is not limited to three phases.

[0047] Furthermore, the dimensions, materials, and other specific numerical values ​​shown in the above embodiments are illustrative examples to facilitate understanding of the present invention and do not limit the present invention unless otherwise specified. [Explanation of symbols]

[0048] 1. Drive system for electric motor 10 Electric motors 11 Stator windings 110 Neutral point (neutral wire) 11U U phase line 11V V phase line 11W W phase wire 20 Inverters 21U, 21V, 21W Upper Arm 22U, 22V, 22W, bottom arm 21US, 21VS, 21WS, 22US, 22VS, 22WS switching elements 21UD, 21VD, 21WD, 22UD, 22VD, 22WD Diode 30 High-Voltage Batteries 40 Oil jet device 41 Electric oil pump 42 Oil pan 43 Oil road 44 On / Off Valve 45 nozzles 50 CU (Control Unit) 51 Microprocessors (Processors) 52 memory 53 Temperature Sensor 54 Oil temperature sensor

Claims

1. An electric motor having a stator in which multiple phase stator windings are connected at a neutral point, An inverter that includes switching elements and has a plurality of upper and lower arms corresponding to the plurality of phase stator windings, and converts DC power into plurality of phase AC power and supplies it to the electric motor by turning the switching elements constituting the upper and lower arms on and off, The system includes a processor that performs a process to control the drive of the inverter by executing a program stored in memory, The electric motor drive device is characterized in that, when the processor detects a short-circuit or open-circuit lock in one phase of the switching elements constituting the inverter, it enters a fail-safe operation that turns on the switching elements of the upper or lower arm of all phases, and then performs a process of breaking the weld at the neutral point of the stator winding.

2. The electric motor drive device according to claim 1, characterized in that the processor performs a process of applying thermal stress to the welded portion of the neutral point to break the welded portion.

3. The electric motor is a liquid-cooled electric motor in which a coolant pressurized by an electric oil pump is supplied to the stator for cooling. The electric motor drive device according to claim 2, characterized in that the processor, after entering the fail-safe operation, temporarily stops the supply of the coolant, and when the temperature difference between the temperature of the stator winding and the temperature of the coolant becomes above a predetermined temperature, resumes the supply of the coolant and performs the process of spraying the coolant onto the weld portion of the neutral point.

4. The ends of each of the aforementioned multi-phase stator windings are welded to each other spaced apart via a neutral wire. The electric motor drive device according to claim 3, characterized in that the coolant is injected into either the stator winding or the neutral wire at the welded joint between each end of the multiple phase stator winding and the neutral wire.

5. The aforementioned multiple phases are three phases, The ends of each of the three phase stator windings are lined up and welded together at one point. The electric motor drive device according to claim 3, characterized in that the coolant is sprayed onto the stator windings located at both ends of the welded portion or onto the stator winding located in the center.

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