Method for electric motor operation, and electric motor

Abstract

The invention relates to a method for electric motor operation (36) of an electric motor (10) as at least one drive element (12) of a vehicle (38), comprising: providing the electric motor (10), which has at least one stator (40) and a rotor (42) that is rotatable with respect thereto; electrically operating (44) the stator (40) by means of an inverter (46) with a three-phase phase current (16) which, in the rotor d-q coordinate system (56) of the rotor (42), corresponds to a d current (Id) for influencing the magnetic flux and to a q current (lq) for controlling the motor torque; during a rotor standstill of the rotor (42), applying (58) at least one d current (Id) for the targeted generation of a heat loss power for heating at least one vehicle component (30), wherein in a first operating state (60) during the rotor standstill, the applied d current (Id) has a temporally alternating trapezoidal shape (66), in particular a rectangular shape (62). The invention also relates to an electric motor (10).

Description

[0001] Methods for electric motor operation and electric motor

[0002] Description introduction

[0003] The invention relates to a method for operating an electric motor according to the preamble of claim 1. Furthermore, the invention relates to an electric motor.

[0004] Permanent magnet synchronous motors (PMSM) are typically controlled with the aim of achieving maximum efficiency, reliability and consistent performance by, among other things, influencing both the magnetic field strength of the motor and the torque through targeted control with phase currents.

[0005] However, PMSM control is also used to generate thermal energy, for example to heat vehicle components, especially in cold environments. For this purpose, it is known to apply a d-current when the rotor is stationary, which generates thermal energy through copper losses, while the q-current is adjusted so that no torque acts on the stationary rotor.

[0006] For example, in DE102021003611A1 it was recognized that applying a d-current in a single polarity when the rotor is stationary can lead to uneven heating, which could cause potential damage or overheating in parts of the power electronics. Therefore, the d-current is applied in a harmonic triangular waveform with alternating positive and negative current values ​​and is accompanied by a zeroing of the q-current when the rotor is stationary, in order to ensure a uniform load and heating of the inverter's high-side and low-side switches.

[0007] The object of the present invention is to increase the power loss when the rotor is at standstill and a given amplitude of the d-current.

[0008] At least one of these problems is solved by a method for operating an electric motor with the features of claim 1. This allows for the generation of greater power loss and thus greater heat output for a given d-current amplitude. The thermal energy required to heat the vehicle component can be provided more quickly. The electric motor can be a permanent magnet synchronous motor (PMSM). The rotor can have permanent magnets. The rotor can be free of active electrical control.

[0009] The electric motor can be the vehicle's sole drive element for generating power to propel the vehicle. The electric motor can be located in the vehicle's electric axle.

[0010] The electric motor can be controlled by a field-oriented control system. The electric motor can have at least three motor phases.

[0011] The vehicle can be a motor vehicle, a truck, or a two-wheeled vehicle.

[0012] Applying the d-current means applying phase currents corresponding to the d-current to the motor phases. During the first operating state, the d-current can have a rectangular shape for at least one period, and a different shape, particularly a trapezoidal shape, either before or after this initial phase. The trapezoidal shape of the d-current can be constant or variable during the first operating state. The d-current can have a first slope in the legs of the trapezoidal shape and, subsequently but still during the first operating state, a second slope in the legs of the trapezoidal shape that differs from the first slope. The slope of the rising leg of the trapezoidal shape can be the same as or different from the slope of the descending leg. The amplitude and / or period of the d-current can be constant or variable during the first operating state.

[0013] In a preferred embodiment of the invention, it is advantageous if the rectangular or trapezoidal shape exhibits alternating negative and positive current values ​​over time. The negative and positive current values ​​can alternate with each other over time.

[0014] In a preferred embodiment of the invention, a q-current is applied in the first operating state such that the motor torque becomes zero. This allows the rotor to remain stationary.

[0015] In a preferred embodiment of the invention, the q-current is applied at zero. Alternatively, the q-current can be different from zero while maintaining a minimum motor torque, particularly in the case of variations in the motor windings.

[0016] In a particular embodiment of the invention, it is advantageous if the DC component of the d-current is zero. The DC component can also have a non-zero value. The DC component can be positive or negative. The d-current can have an offset.

[0017] In an advantageous embodiment of the invention, the inverter comprises a three-phase bridge circuit with a high-side switch and a low-side switch for each motor phase. The switches can be semiconductor components, in particular transistors, for example field-effect transistors or IGBTs (Insulated Gate Bipolar Transistors).

[0018] A preferred embodiment of the invention is advantageous in which the d-current is generated in the first operating state by alternately switching the high-side and low-side switches of at least one motor phase. Preferably, the d-current is generated in the first operating state by alternately switching the high-side and low-side switches of all three motor phases. This allows for a more even thermal load on the switches. Both the high-side and low-side switches are subjected to stress. One-sided thermal stress is avoided.

[0019] In a preferred embodiment of the invention, the period of the rectangular or trapezoidal shape is selected depending on a temperature time constant of the high-side switches and / or low-side switches. This prevents the switches from overheating.

[0020] In a specific embodiment of the invention, it is advantageous if at least one slope of the legs of the trapezoidal d-flow is selected depending on the required heat loss capacity. This allows the required heat loss capacity to be adjusted as needed.

[0021] Furthermore, within the scope of the invention, an electric motor with the features according to claim 10 is proposed to solve at least one of the previously specified problems.

[0022] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustrations.

[0023] Character description

[0024] The invention is described in detail below with reference to the figures. Figure 1 shows a method for generating waste heat from an electric motor.

[0025] Figure 2: A method for operating an electric motor in a special embodiment of the invention.

[0026] Figure 3: A d-current of a method for operating an electric motor in a further special embodiment of the invention.

[0027] Figure 4: A d-current of a method for operating an electric motor in a further special embodiment of the invention.

[0028] Figure 1 shows a method for generating waste heat from an electric motor. The method for generating waste heat uses an electric motor 10, preferably a permanent magnet synchronous motor (PMSM), which is in particular a drive element 12 of a vehicle. A power electronics unit 14, comprising an inverter, supplies the electric motor 10 with a three-phase current 16. The power electronics unit 14 is controlled by a control signal 18 from a control unit 20. The control unit 20 receives a rotor position signal 22 from a position sensor of the electric motor 10 and exchanges control data 24 with a thermal control system 26.The heat control system 26 transfers the heat energy generated by the electric motor 10 as waste heat 28 to a coolant, which transfers the heat energy to vehicle components 30, here a vehicle interior 32 for heating and to a vehicle battery 34 to achieve a required minimum operating temperature.

[0029] Figure 2 shows a method for operating an electric motor in a specific embodiment of the invention. The method for operating an electric motor 36 is applied to an electric motor 10 used as a drive element 12 of a vehicle 38. The electric motor 10 comprises a stator 40 and a rotor 42 rotatable relative to it. The electric motor 10 is preferably a permanent magnet synchronous motor, which is electrically controlled by a power electronics unit 14 with a three-phase phase current 16 via an electrical drive 44 with field-oriented control. The power electronics unit 14 has an inverter 46 with a three-phase bridge circuit 48, each with a high-side switch 50 and a low-side switch 52 for a respective motor phase 54. The three-phase phase current 16 of the stator 40 corresponds, in a dq coordinate system 56 of the rotor 42, to a d-current Id for influencing the magnetic flux and a q-current Iq for controlling a motor torque.The d-current Id is generated in the first operating state 60 when the rotor is at standstill, i.e., when the rotor speed is zero, by alternately switching the highside switch 50 and lowside switch 52 of at least one motor phase 54.

[0030] During the rotor standstill of rotor 42, at least one d-current Id is imprinted 58 to generate heat loss for heating at least one vehicle component. In the first operating state 60 during the rotor standstill, the imprinted d-current Id exhibits a trapezoidal shape that alternates over time.

[0031] Figure 3 shows a d-current of a method for operating an electric motor in a further specific embodiment of the invention. The d-current Id has a time-alternating rectangular shape 62 with negative and positive current values ​​64 that alternate over time. The RMS value of the d-current Id with amplitude A is equal to the value of the amplitude A. This allows the heat loss to be increased and the generation of heat loss to be accelerated.

[0032] The period D of the rectangular shape 62 is preferably chosen depending on a temperature time constant of the high-side switches and / or low-side switches.

[0033] Figure 4 shows a d-current of a method for operating an electric motor in a further specific embodiment of the invention. The d-current Id has a time-alternating trapezoidal shape 66 with negative and positive current values ​​64 that alternate over time. The RMS value of the d-current Id is smaller than the value of the amplitude A of the d-current Id and greater than the value that is present in a triangular form of the d-current Id.

[0034] The slope 68 of the legs 70 of the trapezoidal shape 66 of the d-flow Id is selected depending on the required heat loss capacity. The advantage of the trapezoidal shape 66 lies in a more stable rotor behavior when the d-flow Id increases continuously, especially when there are deviations in the rotor angle of the d-axis.

[0035] Reference symbol list

[0036] 10 Electric motor

[0037] 12 Drive element

[0038] 14 Power Electronics

[0039] 16 phase current

[0040] 18 Control signal

[0041] 20 Control unit

[0042] 22 Rotor position signal

[0043] 24 control data

[0044] 26 Heat control system

[0045] 28 Waste heat

[0046] 30 vehicle components

[0047] 32 Vehicle interior

[0048] 34 Vehicle battery

[0049] 36 methods for operating an electric motor

[0050] 38 vehicles

[0051] 40 Stator

[0052] 42 Rotor

[0053] 44 electrical operation

[0054] 46 inverters

[0055] 48 Bridge circuit

[0056] 50 Highside switches

[0057] 52 Lowside switches

[0058] 54 Engine phase

[0059] 56 dq coordinate system

[0060] 58 embossing

[0061] 60 first operating state

[0062] 62 Rectangular shape 64 Current values

[0063] 66 T trapezoidal shape

[0064] 68 gradient

[0065] 70 thighs

[0066] A Amplitude

[0067] D Period

[0068] Id d-current

[0069] Iq q-current

Claims

Patent claims 1. Method for operating an electric motor (36) of an electric motor (10) as at least one drive element (12) of a vehicle (38), comprising Providing the electric motor (10), which has at least one stator (40) and a rotor (42) rotatable relative to it, electrical operation (44) of the stator (40) via an inverter (46) with a three-phase phase current (16), which in the rotor-fixed dq coordinate system (56) of the rotor (42) corresponds to a d-current (Id) for influencing the magnetic flux and a q-current (Iq) for controlling the motor torque, imprinting (58) at least one d-current (Id) during a rotor standstill of the rotor (42) for the targeted generation of heat loss for heating at least one vehicle component (30), characterized in that in a first operating state (60) during the rotor standstill the imprinted d-current (Id) has a temporally alternating trapezoidal shape (66), in particular rectangular shape (62).

2. Method for operating an electric motor (36) according to claim 1, characterized in that the rectangular or trapezoidal shape (66) has alternating negative and positive current values ​​(64) over time.

3. Method for operating an electric motor (36) according to claim 1 or 2, characterized in that in the first operating state (60) a q-current (Iq) is applied such that the motor torque becomes zero.

4. Method for operating an electric motor (36) according to one of the preceding claims, characterized in that the q-current (Iq) is applied to zero.

5. Method for operating an electric motor (36) according to one of the preceding claims, characterized in that the DC component of the d-current (Id) is zero.

6. Method for operating an electric motor (36) according to one of the preceding claims, characterized in that the inverter (46) has a three-phase Bridge circuit (48) with a highside switch (50) and lowside switch (52) of a respective motor phase (54).

7. Method for operating an electric motor (36) according to claim 6, characterized in that the d-current (Id) is generated in the first operating state (60) by alternating switching of the highside and lowside switch (52) of at least one motor phase (54).

8. Method for electric motor operation (36) according to claim 6 or 7, characterized in that the period (D) of the rectangular shape (62) or trapezoidal shape (66) is selected depending on a temperature time constant of the highside switches (50) and / or lowside switches (52).

9. Method for electric motor operation (36) according to one of the preceding claims, characterized in that at least one slope (68) of the legs (70) in the trapezoidal shape (66) of the d-current (Id) is selected depending on the required heat loss power.

10. Electric motor (10) as at least one drive element (12) of a vehicle (38), comprising at least one stator (40) and a rotor (42) rotatable relative to the stator, wherein the electric motor (10) is configured to be operated using a method for electric motor operation (36) according to one of the preceding claims.

Images