Electric motor with a temperature measurement system

Abstract

An electric motor (1) including a stator (3), a rotor (2), and a motor drive system comprising a circuit board (6), a power semiconductor (12) and a temperature measurement system (10) comprising a temperature sensor (13), the circuit board (6) having a first side (11a) and a second side (11b), wherein the power semiconductor (12) and the temperature sensor (13) are arranged on the first side (11a) of the circuit board (6) and thermally connected to the second side (11b) of the circuit board (6) through thermal vias (5a, 5b) extending through the circuit board from the first side to the second side. The temperature measurement system (10) further comprises an insulated metal substrate plate (14) comprising a metal base plate (15), a metal layer (17) and an insulating layer (16) sandwiched between the metal base plate (15) and the metal layer (17), wherein portions of the metal layer (17) are mounted against the second side (11b) of the circuit board (6) overlapping the thermal vias (5a, 5b) and separated by a separation area (18) without metal layer isolating the thermal vias (5a) of the power semiconductor (12) from the thermal vias (5b) of the temperature sensor (13).

Description

[0001] P3083PC00

[0002] ELECTRIC MOTOR WITH A TEMPERATURE MEASUREMENT SYSTEM

[0003] The present invention further relates to an electric motor with a temperature measurement system. The present invention also relates to a method for measuring a temperature, in particular a junction temperature of a power semiconductor device of an inverter.

[0004] It is well known in the art that some of the elements of powerful electric motors generate heat during operation and often need to be cooled to avoid a damage due to overheating. For example, the stator and the power semiconductors of the inverter are often cooled in powerful electric motors. For example, metal-oxide-semiconductor field-effect transistors may be used as power semiconductors in the inverter. In some motor, the electronics required to operate the motor including the inverter is integrated in the motor.

[0005] For some applications, it is useful or even necessary to monitor the temperature of at least some of the heat-generating elements. For example, it may be useful to monitor the temperature of power semiconductors of the inverter.

[0006] In a high voltage inverter, low and high voltage circuitries are galvanically insulated from each other. For example, a control circuitry located in the low voltage side is galvanically insulated from the high voltage power components. In such a case, extensive clearances and creepage distances are to be kept between the low and high voltage circuitries and this in turn makes it difficult to measure the junction temperature of a power semiconductor of the inverter. When a control circuit is located in the high voltage side, at least a functional insulation is required between the temperature sensor and the power semiconductor.

[0007] In view of the foregoing, an object of the invention to provide an electric motor comprising a temperature measurement system for measuring a temperature of a power semiconductor in a reliable, accurate and precise manner. It is also an object of the invention to provide a method for measuring a temperature of a power semiconductor of an electric motor in a reliable, accurate and precise manner.

[0008] It is advantageous to provide an electric motor with a temperature measurement system that is accurate and reliable, yet ensures good separation between high and low voltage components.

[0009] It is advantageous to provide an electric motor with a temperature measurement system that is compact.P3083PC00

[0010] It is advantageous to provide an electric motor with a temperature measurement system that is economical to manufacture.

[0011] Objects of the invention are achieved by an electric motor and method according to the independent claims.

[0012] Disclosed herein is an electric motor including a stator, a rotor, and a motor drive system comprising a circuit board, a power semiconductor and a temperature measurement system comprising a temperature sensor, the circuit board having a first side and a second side, wherein the power semiconductor and the temperature sensor are arranged on the first side of the circuit board and thermally connected to the second side of the circuit board through thermal vias extending through the circuit board from the first side to the second side.

[0013] The temperature measurement system further comprises an insulated metal substrate plate comprising a metal base plate, a metal layer and an insulating layer sandwiched between the metal base plate and the metal layer, wherein portions of the metal layer are mounted against the second side of the circuit board overlapping the thermal vias and separated by a separation area without metal layer isolating the thermal vias of the power semiconductor from the thermal vias of the temperature sensor.

[0014] In an advantageous embodiment, the temperature measurement system is configured to measure a temperature with the temperature sensor and compute a temperature of the power semiconductor using the measured temperature.

[0015] In an advantageous embodiment, the insulated metal substrate plate is mounted on the second side of the circuit board using surface-mount technology.

[0016] In an advantageous embodiment, the power semiconductor comprises or consists of a metal-oxide-semiconductor field-effect transistor.

[0017] In an advantageous embodiment, the temperature of the power semiconductor is a junction temperature.

[0018] In an advantageous embodiment, the metal base plate is made of aluminium, copper or stainless steel.

[0019] In an advantageous embodiment, the metal base plate has a thickness between 0.5 mm and 5 mm, preferably between 0.8 mm and 3.2 mm, for instance between 1 mm and 3 mm.P3083PC00

[0020] In an advantageous embodiment, the metal layer is made of copper.

[0021] In an advantageous embodiment, the metal layer has a thickness between 10 pm and 500 pm, preferably between 20 pm and 100 pm.

[0022] In an advantageous embodiment, the insulating layer is made of an electrically insulating material selected from any one or more of a polymer, a ceramic filled polymer, an epoxy, a glass-reinforced epoxy laminate material, or a polyimide.

[0023] In an advantageous embodiment, the insulating layer has a thickness between 0.05 mm and 0.20 mm.

[0024] In an advantageous embodiment, the insulated metal substrate plate is mounted against a heat sink of the electric motor, the motor comprising a liquid cooling circuit in contact with the heat sink.

[0025] In an advantageous embodiment, the electric motor comprises a liquid cooling circuit configured to cool the insulated metal substrate plate through a direct contact of a coolant with the metal base plate.

[0026] In an advantageous embodiment, a distance separating the power semiconductor and the temperature sensor is in a range of 3 mm to 20 mm, preferably in a range of 5 mm to 10 mm.

[0027] Also disclosed herein is a method for measuring a temperature of a power semiconductor of a motor drive system of an electric motor, the method comprising the steps of

[0028] providing an electric motor according to any preceding embodiment;

[0029] measuring a temperature using the temperature sensor;

[0030] calculating a temperature of the power semiconductor from the measured temperature and a dissipated power of the of the power semiconductor.

[0031] In an advantageous embodiment, the method further comprises the steps of

[0032] measuring one or more further parameters selected of a current, a voltage and a frequency;

[0033] calculating the dissipated power of the power semiconductor from the measured one or more further parameters.P3083PC00

[0034] Further objects and advantageous features of the invention will be apparent from the claims, from the detailed description, and annexed drawings, in which:

[0035] Figure 1 is a perspective view of an electric motor according to a first embodiment of the invention;

[0036] Figures 2a and 2b are exploded perspective views of a base portion of a stator housing and a motor drive system housing of an electric motor according to the first embodiment of the invention;

[0037] Figure 3a is a cross-sectional view of an electric motor according to the first embodiment of the invention.

[0038] Figure 3b is a perspective cross-sectional view of a portion of an electric motor according to the first embodiment of the invention.

[0039] Figure 4 is a perspective view of a motor drive system housing of an electric motor according to the first embodiment of the invention;

[0040] Figure 5 is a perspective view of a motor drive system housing of an electric motor according to a variant of the first embodiment of the invention;

[0041] Figure 6 is a perspective view of a stator and stator housing of an electric motor according to the first embodiment of the invention;

[0042] Figure 7 is a perspective view of an electric motor according to a second embodiment of the invention;

[0043] Figure 8 is a perspective cross-sectional view of an electric motor according to the second embodiment of the invention;

[0044] Figure 9 is a schematic cross-sectional view of a portion of a motor drive system according to an embodiment of the invention;

[0045] Figure 10a is a perspective view of a circuit board and electronic components of a motor drive system of an electric motor according to the first embodiment of the invention;

[0046] Figure 10b is a perspective view of the circuit board of figure 10b from an opposite side.P3083PC00

[0047] Referring to the figures, an electric motor 1 according to embodiments of the invention comprises a rotor 2, a stator 3, a motor drive system and a housing 20 in which the rotor, stator and motor drive system are mounted.

[0048] The electric motor 1 further comprises a cooling system 4 including a cooling channel 9 formed within the housing 20, a cooling liquid received in and flowing through the cooling channel.

[0049] The motor drive system comprises a circuit board 6 and electronic components mounted on the circuit board including at least one inverter comprising a power semiconductor 12. The inverter supplies a drive current to an electrical phase of the electric motor, whereby a motor with a plurality of phases has a corresponding plurality of inverters.

[0050] The power semiconductor of the inverter may for instance be in the form of a bipolar transistor, an insulated-gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET), e.g., based on Si, SiC or GaN, or a high-electron-mobility transistor (HEMT), e.g., based on GaN as perse well known in the art of inverters for electric motors.

[0051] In certain embodiments, the electric motor 1 may be a high voltage electric motor with a nominal DC voltage above 850 V, in particular above 1000 V and in particular above 1500 V.

[0052] The housing 20 comprises a stator housing section 21 in which the stator 3 is lodged, and a drive system housing section 25 in which the circuit board 6, with the electronic components including the power semiconductors 12, of the motor drive system is lodged. The drive system housing section 25 is advantageously positioned at an axial end stator housing section 21, such that the circuit board 6 of the motor drive system is positioned adjacent an axial end of the stator 3, the axial direction being defined herein as the direction of the axis of rotation of the rotor 2. The mounting of the motor drive system over an axial end of the stator 3 advantageously provides for a compact configuration and allows for efficient cooling of both the stator and motor drive system electronic components as will be described in more detail hereinbelow.

[0053] The stator housing section 21 comprises a circumferential wall 22a surrounding and in contact with the stator 3. The circumferential wall also bounds, on a side opposite to the side in contact with the stator, the cooling channel 9 such that heat produced in the stator is mainly evacuated by conduction through the circumferential wall 22a into the cooling fluid flowing in the cooling channel. The circumferential wall 22a may continue via a bend into an end wall 23 against which an axial end of the stator 3 is seated.P3083PC00

[0054] The drive system housing section 25 comprises a base wall 26 positioned axially between the stator 3 and the circuit board 6 with electronic components of the motor drive system. The base wall 26 also has a portion that bounds, on a side opposite to the side in contact with the motor drive system, the cooling channel 9 such that heat produced in the motor drive system, and more particularly heat produced by the power semiconductors of the motor drive system, is mainly evacuated by conduction through the base wall 26 into the cooling fluid flowing in the cooling channel 9.

[0055] The cooling channel 9 is thus bounded by wall portions that include portions of the circumferential wall 22a surrounding the stator 3 and of the base wall 26 on which the motor drive system is mounted such that the cooling liquid flowing in the cooling channel serves to concomitantly cool both the stator and the motor drive system. An outer circumferential wall 22b of the stator housing section 21 bounds and closes an outer radial side of the cooling channel.

[0056] In the illustrated embodiment, the stator housing section 21 and drive system housing section 25 are separate parts assembled and fixed together. Seals 33a, 33b may be mounted in the interface between the stator housing section 21 and drive system housing section 25 to ensure sealing of the cooling channel 9 and prevent leakage of liquid out of the cooling channel at the interface between the housing sections 21, 25.

[0057] However, in variants, it is possible to form the stator housing section 21 and drive system housing section 25 as a single integrally formed part, for instance by additive manufacturing techniques such as 3D printing techniques. The cooling channel 9 in such variants may therefore be bounded by the housing walls without a sealing interface.

[0058] The housing 20 may comprise other parts that fit onto the stator housing section 21, such as a cap 24 covering an opposite end of the stator 3 to the end where the drive system housing section 25 is positioned.

[0059] It may be noted that an output shaft 29 of the rotor 2 may extend axially out of one side of the motor as in the illustrated embodiments, or may extend out of both sides of the motor (embodiment not shown). For instance, in the latter variant, the cap may be provided with an orifice through which the rotor shaft extends.1

[0060] P3083PC00

[0061] The motor drive system may be positioned on a side of the stator 3 through which the rotor output shaft 29 extends as in the first embodiment illustrated in figures 1-6. In this embodiment, the circuit board 6 comprises a hole 30 to allow the rotor shaft to extend therethrough.

[0062] In another embodiment, the motor drive system may be positioned on a side of the stator 3 through which the rotor output shaft 29 does not extend as illustrated in figures 7 and 8. In this embodiment, the circuit board 6 does not require a hole and the motor drive system may comprise a position sensor 36 mounted on the circuit board facing an axial end of the rotor shaft to detect the angular position and speed of the rotor.

[0063] In the second embodiment, an advantage of mounting the motor drive system on a side without the output shaft is the easy access to the drive system electronic components which can be repaired or replaced easily.

[0064] The cooling system 4 comprises an inlet 31 and an outlet 32 fluidly connected to the cooling channel 9.

[0065] The cooling channel 9 has an axially extending portion 9a and a radially extending portion 9b, wherein the axial portion 9a is extends along the circumferential wall 22a and the radial portion 9b extends over the base wall 26

[0066] The axial portion 9a preferably overlaps the stator 3 over a length al of more than 50% of an axial length a2 of the stator 3.

[0067] The radial portion 9b may be extend radially over a distance r1 such that the radial portion overlaps the stator 3 and serves to cool electronic components of the motor drive system positioned within the circumference of the motor which is dependent on the stator diameter.

[0068] In the illustrated embodiments, the cooling channel 9 substantially completely surrounds the stator 3, except for a separating wall 34b between the inlet 31 and outlet 32. The inlet and the outlet comprise an inlet mouth and an outlet mouth, respectively. The inlet and outlet mouths may be formed through the base wall 26 of the drive system housing section 25 as illustrated in figures 1-6 or through the outer circumferential wall 22 as illustrated in figures 7 and 8. The inlet and outlet mouths may be arranged adjacent each other, whereby a separating wall 34a, 34b is formed in the cooling channel 9 between the inlet and outlet mouths to ensure a flow of coolant liquid from the inlet mouth, around the circumference of the stator, to the outlet mouth.P3083PC00

[0069] The axial portion 9a and the radial portion 9b of the cooling channel 9 may form together an essentially single unconstricted channel as in the embodiment of figures 1-6, or may form constricted portions interconnected fluidly by a restricted fluid interconnection passage 9c. The restricted fluid interconnection passage 9c allows to have a single coolant liquid circuit (with a single inlet and single outlet) in the electric motor, yet separate the bulk of the hydrodynamique coolant liquid flow around the stator from the bulk of the hydrodynamique coolant liquid flow over the base wall 26 of the motor drive system. The partially separated coolant liquid flows allows to better adjust and optimize coolant flows for evacuating heat from the motor drive system and stator according to the configuration of the motor and the heat generated by the respective motor drive system and stator.

[0070] A main source of heat generated in the motor drive system is by the power semiconductors 12. The power semiconductors are positioned on the circuit board 6, preferably axially aligned with or overlapping the cooling channel 9, in particular the radial portion 9b of the cooling channel. The heat conduction path between the power semiconductors 12 and the coolant liquid may thus be advantageously very short.

[0071] Heat transfer between the material, for instance metal, of the wall portions 22a, 26 bounding the cooling channel 9 and the coolant liquid may be increased by providing heat transfer enhancement structures 35 such as ribs, pillars, fins, indents, troughs or other protuberant or structures on the wall portions in the cooling channel 9. In an advantageous embodiment, the base wall 26 of the drive system housing section 25 comprises at least one heat transfer enhancement structure 35 in the cooling channel 9. The base wall 26 of the drive system housing section 25 may comprise a plurality of heat transfer enhancement structure 35 in the cooling channel 9 of the same type or of different types. Advantageously, heat transfer enhancement structures 35 may be placed in thermal contact with the power semiconductors, through a stack of material layers, said stack of layers being thermally conductive but electrically insulated.

[0072] In a preferred embodiment, the electric motor 1 further comprises a temperature measurement system 10 comprising a temperature sensor 13.

[0073] The circuit board 6 has a first side 11a and a second side 11b. The power semiconductor 12 and the temperature sensor 13 of the temperature measurement system 10 are arranged on the first side 11a of the circuit board 6.P3083PC00

[0074] In an advantageous embodiment, the temperature sensor 13 comprises or consists of a Negative Temperature Coefficient (NTC) thermistor, a thermocouple, a PT100, a PT1000 or a p-n junction temperature sensor.

[0075] The power semiconductor 12 and the temperature sensor 13 are preferably mounted onto the first side 11a of the circuit board 6 using surface-mount technology (SMT), i.e., these components are Surface Mount Devices (SMD).

[0076] The distance between the power semiconductor 12 and the temperature sensor 13 corresponds to a creepage distance Lc and is selected to be sufficiently large depending on the voltage between the power semiconductor 12 and the temperature sensor 13 and on the conductivity of the circuit board 6.

[0077] The power semiconductor 12 and the temperature sensor 13 are thermally connected to the second side 11 b of the circuit board 6 through thermal vias 5a, 5b extending through the circuit board from the first side 11 a to the second side 11b. The thermal vias may be made of metal tracks similar to the tracks formed on the circuit board for electrical conduction and interconnection of electrical components.

[0078] The temperature measurement system 10 further comprises an insulated metal substrate plate 14 comprising a metal base plate 15, a metal layer 17 and an insulating layer 16 between the metal base plate 15 and the metal layer 17.

[0079] In embodiments, the metal base plate 15 may be made of aluminium, copper or stainless steel. In embodiments, the metal base plate 15 has a thickness between 0.5 mm and 5 mm, preferably between 0.8 mm and 3.2 mm, for instance between 1 mm and 3 mm.

[0080] The metal layer 17 is preferably made of copper, but in variants other metals such as silver or gold may be used. In embodiments, the metal layer 17 has a thickness between 10 pm and 500 pm, preferably between 20 pm and 100 pm.

[0081] The insulating layer 16 is made of an electrically insulating material, e.g., a dielectric, such as a polymer, ceramic filled polymer, an epoxy, a glass-reinforced epoxy laminate material, in particular FR-4, or a polyimide, in particular Kapton®. The insulating layer 16 may have a thickness between 0.05 mm and 0.20 mm. The thermal resistance through the insulating layer 16 is relatively low even if its material has a relatively poor thermal conductivity because the insulating layer 16 may be relatively thin. Obviously, the thickness of the insulating layer 16 could be increased if new materials with higher thermal conductivity become available.P3083PC00

[0082] The insulated metal substrate plate 14 is mounted on the second side 11b of the circuit board 6 using SMT, which may comprise soldering, welding or sintering, in particular pressureless sintering. The insulated metal substrate plate 14 has a surface area and shape configured to extend between and overlap both the thermal vias 5a of the electronic component 12 and the thermal vias 5b of the temperature sensor 13. The metal layer 17 comprises a portion which overlaps the thermal vias 5a of the power semiconductor 12, and a portion which overlaps the thermal vias 5b of the temperature sensor 13, the portions being separated by a separation area 18 without metal layer such that the portions are electrically isolated from each other. The separation area 18 between power semiconductor 12 and the temperature sensor 13 electrically isolates the thermal vias 5a of the power semiconductor 12 from the thermal vias 5b of the temperature sensor 13. The insulated metal substrate plate 14 may be manufactured with a continuous metal layer 17 which is then etched over the separation area 18 to remove the metal layer from the separation area.

[0083] Thus, the power semiconductor 12 and the temperature sensor 13 are electrically insulated by the insulating layer 16. At the same time, the thermal resistance between the power semiconductor 12 and the temperature sensor 13 is relatively low because of the metal base plate 15.

[0084] In advantageous embodiments, the distance Lc separating the power semiconductor 12 and the temperature sensor 13 is in a range of 3 mm to 20 mm, preferably in a range from 5 mm to 10 mm. This distance Lc allows on the one hand a sufficient electrical separation between the high voltage power semiconductor 12 and the low voltage temperature sensor 13, while ensuring a sufficiently short thermal conduction path through the metal base 15 of the insulated metal substrate plate 14 between the power semiconductor 12 and the temperature sensor 13 for accurate temperature estimation of the power semiconductor.

[0085] In the illustrated embodiments, the motor drive system comprises three insulated metal substrate plates 14, each comprising one temperature sensor 13 and two power semiconductors 12. According to the invention, several inverters each supplying one electrical phase of the electric motor may have separate IMS plates and temperature sensors. In an alternative embodiment according to the invention, several inverters may share an IMS plate with a temperature sensor.

[0086] In advantageous embodiments, the metal base plate 15 of the insulated metal substrate plate 14 is positioned against a heatsink 8 via an electrically conductive or non-conductive thermal interface layer 7.P3083PC00

[0087] The heatsink 8 may form part of a housing 20 of the electric motor 1 cooled by a liquid coolant as described hereinabove. In particular, the heatsink 8 may be formed by base wall 26 of the drive system housing section 25.

[0088] In the illustrated embodiments, the insulated metal substrate plate 14 is positioned against the base wall 26 of the drive system housing section 25 via a thermal interface layer 7.

[0089] The temperature measurement system 10 described herein may be also be used in an electric motor with a conventional cooling system or without a cooling of the power electronics. In a variant, a liquid cooling circuit of an electric motor is configured to cool the insulated metal substrate plate 14 through a direct contact of a coolant with the metal base plate 15.

[0090] The temperature measurement system 10 is configured to indirectly measure a temperature of the power semiconductor 12, namely, to measure a temperature with the temperature sensor 13 which is thermally coupled with the power semiconductor 12 via the insulated metal substrate plate 14 and calculate the temperature of the power semiconductor 12 using the measured temperature. The calculation of the temperature of the power semiconductor 12 is based on a thermal model, which has as input at least the measured temperature and the dissipated power of the power semiconductor 12.

[0091] The dissipated power of the power semiconductor 12 may depend on one or more variables, such as a voltage, a current or a frequency. In such a case, the dissipated power of the power semiconductor 12 is calculated from the measured one or more variables. The calculation of dissipated power of power semiconductors is known in the art, in particular for a power semiconductor, such as an IGBT or a MOSFET.

[0092] In the example of a MOSFET, the dissipated power Pdiss can be calculated by a sum of conduction losses Pcond and switching losses Psw.

[0093] Pdiss = Pcond + Psw.

[0094] The conduction losses Pcond can be obtained by

[0095] Pcond = Rds(on) * lrms*2,

[0096] where the Rds(on) is the drain source on-resistance and Irms is the effective current, i.e., the rms value of the MOSFET on-state current. The switching losses are a product of the switching energies and the switching frequency f.

[0097] Psw = (Eon + Eoff) * f,P3083PC00

[0098] where Eon is the turn on switching energy loss and Eoff is the turn off switching energy loss. More detailed equations taking into account further effects may be derived for the calculation of the dissipated power of a MOSFET.

[0099] In the simplest thermal model, the junction temperature Tcalc of the power semiconductor 12 is calculated using the equation 1:

[0100] Tcalc = Tmeas + Pdiss * Rth,

[0101] wherein Tmeas is the measured temperature obtained by the temperature sensor 13, Pdiss is the dissipated power of the power semiconductor 12, and Rth is the thermal resistance between the power semiconductor 12 and the metal base plate 15. The thermal resistance Rth can be determined by a measurement and / or computer simulation. In this model, heat transfer from power semiconductor 12 to the temperature sensor 13 via the circuit board 6 is neglected.P3083PC00

[0102] List of features illustrated

[0103] Electric motor 1

[0104] Rotor 2

[0105] Output shaft 29

[0106] Stator 3

[0107] Housing 20

[0108] Stator housing section 21

[0109] Circumferential wall 22a

[0110] Outer circumferential wall 22b End wall 23

[0111] Cap 24

[0112] Fixing elements 28a

[0113] Drive system housing section 25

[0114] Base wall 26

[0115] Fixing elements 28b

[0116] Cooling system 4

[0117] Thermal interface layer 7

[0118] Heatsink 8

[0119] Cooling channel 9

[0120] Axial portion 9a

[0121] Radial portion 9b

[0122] Connection portion 9c

[0123] Inlet 31

[0124] Outlet 32

[0125] Sealing

[0126] Inner sealing 33a

[0127] Outer sealing 33b

[0128] Separating wall 34a, 34b

[0129] Heat transfer enhancement structure 35 e.g. ribs, pillars, trough

[0130] Motor drive system

[0131] Circuit board 6

[0132] First side 11a

[0133] Second side 11b

[0134] Electronic componentsP3083PC00

[0135] Power semiconductor 12 Temperature measurement system 10

[0136] Temperature sensor 13 Thermal vias 5a, 5b

[0137] Insulated metal substrate plate 14

[0138] Metal base plate 15 Insulating layer 16

[0139] Metal layer 17

[0140] copper

[0141] Separation area 18 Surface-mount connection 19 Computing means

[0142] Creepage distance Lc

Claims

P3083PC00CLAIMS1. An electric motor (1) including a stator (3), a rotor (2), and a motor drive system comprising a circuit board (6), a power semiconductor (12) and a temperature measurement system (10) comprising a temperature sensor (13), the circuit board (6) having a first side (11a) and a second side (11b), wherein the power semiconductor (12) and the temperature sensor (13) are arranged on the first side (11a) of the circuit board (6) and thermally connected to the second side (11b) of the circuit board (6) through thermal vias (5a, 5b) extending through the circuit board from the first side to the second side, the temperature measurement system (10) further comprising an insulated metal substrate plate (14) comprising a metal base plate (15), a metal layer (17) and an insulating layer (16) sandwiched between the metal base plate (15) and the metal layer (17), wherein portions of the metal layer (17) are mounted against the second side (11b) of the circuit board (6) overlapping the thermal vias (5a, 5b) and separated by a separation area (18) without metal layer isolating the thermal vias (5a) of the power semiconductor (12) from the thermal vias (5b) of the temperature sensor (13).

2. The electric motor according to claim 1 , wherein the temperature measurement system (10) is configured to measure a temperature with the temperature sensor (13) and compute a temperature of the power semiconductor (12) using the measured temperature.

3. The electric motor according to any preceding claim 1 or 2, wherein the insulated metal substrate plate (14) is mounted on the second side (11b) of the circuit board (6) using surfacemount technology.

4. The electric motor according to any preceding claim 1-3, wherein the power semiconductor (12) comprises or consists of a metal-oxide-semiconductor field-effect transistor.

5. The electric motor according to any preceding claim 1-4, wherein the temperature of the power semiconductor (12) is a junction temperature.

6. The electric motor according to any preceding claim 1-5, wherein the metal base plate (15) is made of aluminium, copper or stainless steel.

7. The electric motor according to any preceding claim 1-6, wherein the metal base plate (15) has a thickness between 0.5 mm and 5 mm, preferably between 0.8 mm and 3.2 mm, for instance between 1 mm and 3 mm.P3083PC008. The electric motor according to any preceding claim 1-7, wherein the metal layer (17) is made of copper.

9. The electric motor according to any preceding claim 1-8, wherein the metal layer (17) has a thickness between 10 pm and 500 pm, preferably between 20 pm and 100 pm.

10. The electric motor according to any preceding claim 1-9, wherein the insulating layer (16) is made of an electrically insulating material selected from any one or more of a polymer, a ceramic filled polymer, an epoxy, a glass-reinforced epoxy laminate material, ora polyimide.

11. The electric motor according to any preceding claim 1-10, wherein the insulating layer (16) has a thickness between 0.05 mm and 0.20 mm.

12. The electric motor according to any preceding claim 1-11, wherein the insulated metal substrate plate (14) is mounted against a heat sink (8) of the electric motor, the motor comprising a liquid cooling circuit in contact with the heat sink.

13. The electric motor according to any one of claims 1-8, comprising a liquid cooling circuit configured to cool the insulated metal substrate plate (14) through a direct contact of a coolant with the metal base plate (15).

14. The electric motor according to any preceding claim 1-13 wherein a distance (Lc) separating the power semiconductor (12) and the temperature sensor (13) is in a range of 3 mm to 20 mm, preferably in a range of 5 mm to 10 mm.

15. A method for measuring a temperature of a power semiconductor of a motor drive system of an electric motor, the method comprising the steps ofproviding an electric motor according to any preceding claim;measuring a temperature using the temperature sensor (13);calculating a temperature of the power semiconductor (12) from the measured temperature and a dissipated power of the of the power semiconductor (12).

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