Method for operating an electric motor, and electric motor

Abstract

The invention relates to a method for operating (10) an electric motor (12), involving: providing the electric motor (12) comprising motor windings; providing a current controller (14) which outputs, in each case in relation to at least one coordinate direction (18) in a rotating electrical coordinate system (16) of the electric motor (12), an output voltage (U a ), which is limited to a maximum output voltage (U a , m ), on the basis of a target current (I s ); providing an inverter (22) for outputting phase voltages (U p ) on the motor windings in order to set a phase current (I p ) in the motor windings at least on the basis of the output voltage (U a ); calculating (24) at least one voltage reserve value (U r ) for the output voltage (U a ) on the basis of the maximum output voltage (U a,m ) and the output voltage (U a ); calculating (25) the maximum rate of change (R) of the target current (I s ) on the basis of the at least one voltage reserve value (U r ); and limiting (28) the target current gradient (formula (I)) of the target current (I s ) provided to the current controller (14) to the maximum rate of change (R). The invention also relates to an electric motor (12). AA%%%Figure 1

Description

[0001] P241740

[0002] -1-

[0003] Methods for operating an electric motor and electric motor

[0004] Description introduction

[0005] The invention relates to a method for operating an electric motor according to claim 1. Furthermore, the invention relates to an electric motor.

[0006] German patent DE 10 2018 127 709 A1 describes a method for limiting the control values ​​in the field-oriented current control of permanent magnet synchronous machines to ensure stable operation near the voltage limit. In this method, the control values ​​of the voltage components are set based on their current effect, depending on the operating point.

[0007] The object of the present invention is to improve the control of the electric motor and to operate the electric motor more cost-effectively and efficiently.

[0008] At least one of these problems is solved by a method for operating an electric motor with the features according to claim 1. This allows the electric motor's control system to reliably and accurately set the target current. The stability of the electric motor's control system can be increased. The electric motor can be operated more reliably and efficiently. The current controller can operate with more precise and accurate inputs. The motor parameters can be calculated based on more accurate and correct operating points of the electric motor.

[0009] The electric motor can be located in a vehicle. The electric motor can provide drive power to propel the vehicle. The electric motor can be a permanent magnet synchronous motor or a separately excited synchronous motor. The electric motor can have a stator and a rotor that rotates relative to the stator. The electric motor can have three motor phases, each with a phase voltage applied for operation.

[0010] The rotating electrical coordinate system can specify the electrical quantities in the rotor-fixed dq coordinate system. The electrical quantities in the rotating coordinate system can be calculated from the quantities of the stator-fixed coordinate system by Park transformation. P241740

[0011] -2- The phase currents can flow into the motor windings of the electric motor to operate it. The current controller can output the voltage to the inverter.

[0012] By limiting the target current gradient, exceeding the target current gradient beyond the maximum rate of change can be prevented. This prevents excessive demands on current dynamics that cannot be met due to the maximum output voltage.

[0013] The maximum output voltage can depend on the input voltage applied to the inverter. The input voltage can be a DC voltage. The maximum output voltage can be calculated from the known input voltage.

[0014] The described limitation of the target current gradient to the maximum rate of change can be implemented specifically for a coordinate direction of the rotating coordinate system. In this case, for example, the target current, the target current gradient, the output voltage, the maximum output voltage, and the maximum rate of change are specific to the respective coordinate direction, such as the d-direction or the q-direction. The described limitation of the target current gradient to the maximum rate of change can be implemented for all coordinate directions of the rotating coordinate system.

[0015] The described limitation of the set current gradient to the maximum rate of change can be implemented specifically for a given sign direction. In this case, for example, the set current gradient, the output voltage, the maximum output voltage, and the maximum rate of change are specific to the respective sign direction, such as positive or negative. The described limitation of the set current gradient to the maximum rate of change can be implemented for all sign directions.

[0016] In a preferred embodiment of the invention, it is advantageous if the target current is calculated by a feedforward control system as a function of a preset current. The preset current can be predetermined based on a requested motor power and motor parameters of the electric motor, for example, inductances, ohmic resistances, and other parameters.

[0017] In a preferred embodiment of the invention, the maximum rate of change is calculated as a function of the current difference between the setpoint current and the target current. The setpoint current can be set in the static case and / or at P241740

[0018] -3-The absence of intervention by the limit, even in the dynamic case, corresponds to the target current supplied to the current controller.

[0019] In an advantageous embodiment of the invention, the voltage reserve value is calculated as the voltage difference between the maximum output voltage and the steady-state output voltage. The voltage reserve value can be calculated as the voltage difference between the maximum output voltage and the steady-state output voltage component.

[0020] The steady-state output voltage component can be formed depending on decoupling components that compensate for the inductive coupling between the coordinate directions and the resistance components that compensate for the ohmic resistances in the motor windings. The steady-state output voltage component can be the portion of the output voltage required to maintain the set current.

[0021] In a preferred embodiment of the invention, the voltage reserve value includes a positive voltage reserve value, which is calculated as the voltage difference between the positive maximum output voltage and the output voltage.

[0022] In a particular embodiment of the invention, it is advantageous if the voltage reserve value includes a negative voltage reserve value, which is calculated as the voltage difference between the negative maximum output voltage and the output voltage.

[0023] In a preferred embodiment of the invention, it is advantageous if the maximum rate of change comprises a maximum positive rate of change component and a maximum negative rate of change component. The maximum positive rate of change component can be calculated depending on the positive voltage reserve value, and / or the maximum negative rate of change component can be calculated depending on the negative voltage reserve value. The limiting of the target current gradient can comprise limiting a positive target current gradient and / or a negative target current gradient. The positive target current gradient can be limited depending on the maximum positive rate of change component. The negative target current gradient can be limited depending on the maximum negative rate of change component.

[0024] In a preferred embodiment of the invention, it is advantageous if the maximum rate of change is calculated as a function of the motor parameters of the electric motor. P241740

[0025] -4- Motor parameters may include inductances and / or ohmic resistances of the electric motor.

[0026] In an advantageous embodiment of the invention, the motor parameters are calculated based on the target current, which is limited, in particular, by the limiting factor. The motor parameter values ​​can be calculated from the target current using a lookup table.

[0027] 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.

[0028] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustration.

[0029] Character description

[0030] The invention is described in detail below with reference to the illustration.

[0031] The figure shows a method for operating an electric motor in a special embodiment of the invention. The method for operating 10 an electric motor 12 comprises providing the electric motor 12 with motor windings. Furthermore, a current controller 14 is provided which, with respect to at least one coordinate direction 18 of a rotating electrical dq coordinate system 16 of the electric motor 12, adjusts the current based on a set current I. s an output voltage U a outputs, which is limited to a maximum output voltage U a,m is restricted with respect to the coordinate direction 18. For example, the current controller 14 can be adjusted with respect to the q-direction depending on a set current I. s an output voltage U a output voltages that are limited to a maximum output voltage U a,mis limited. The current controller 14 can additionally or alternatively be adjusted with respect to the d-direction depending on a set current I. s an output voltage U a output voltages that are limited to a maximum output voltage U a,m is limited.

[0032] If the electric motor 12 is a separately excited synchronous motor, an excitation direction is available as a further coordinate direction 18. The current controller 14 can additionally or alternatively be configured with respect to the excitation direction depending on a set current I. s aP241740

[0033] -5- Output voltage U a output voltages that are limited to a maximum output voltage U a,m is limited with regard to the direction of transmission.

[0034] The target current I s in the respective coordinate direction 18 depends on a specified current I v calculated by a feedforward control 20. The setpoint current I vDepending on the required motor power and motor parameters P of the electric motor 12, such as inductances, ohmic resistances, and others, the motor output can be specified. Furthermore, an inverter 22 is provided to output phase voltages U. p at the motor windings for setting a phase current I p in the motor windings at least dependent on the output voltage U a The electric motor 12 can comprise three motor phases 23, each of which has a phase voltage U for operating the electric motor 12. p is pending.

[0035] The maximum output voltage U a,m is dependent on an input voltage U applied to the inverter 22 e , which is a DC voltage. The maximum output voltage U a,m can be derived from the known input voltage U e will be calculated.

[0036] Furthermore, a calculation is performed for at least one voltage reserve value U.r to the output voltage U a depending on the maximum output voltage U a,m and the output voltage U a , in particular a stationary output voltage component U a,s the output voltage U a The steady-state output voltage component is formed depending on decoupling components that compensate for the inductive couplings between the coordinate directions 18 and resistance components that compensate for the ohmic resistances in the motor windings. The steady-state output voltage component U a,s can the proportion of the output voltage U a be the one that maintains the target current I s is required.

[0037] The voltage reserve value U r is defined as the voltage difference between the maximum output voltage U a,m and the output voltage U a , here the stationary output voltage component U a,s , calculated. The voltage reserve value U rincludes a positive voltage reserve value U r p and a negative voltage reserve value U r n The positive voltage reserve value U r,p is defined as the voltage difference between the positive maximum output voltage U a,m and the stationary output voltage component U a,s and the negative voltage reserve value U r,n as a voltage difference between the negative maximum output voltage U a,m and the stationary output voltage component U a,s calculated.P241740

[0038] -6- From the positive voltage reserve value U r,p and the negative voltage reserve value U r,n as well as from motor parameters P of the electric motor 12 and a current difference ΔI between the set current I v and the target current I sWith respect to the respective coordinate direction 18, a maximum rate of change R is calculated coordinate-related using a calculation 25. The maximum rate of change R includes a maximum positive rate of change component R. p and a maximum negative rate-of-change component R n , where the maximum positive rate of change component R p with regard to the voltage reserve value U r depending on the positive voltage reserve value U r,p and the maximum negative rate of change component R n with regard to the voltage reserve value U r depending on the negative voltage reserve value U r,n is calculated.

[0039] The calculation 25 can determine a respective maximum positive rate of change component R for each coordinate direction 18, i.e., the d-direction, the q-direction, and the excitation direction. p and maximum negative rate of change component R ncalculate, which results in a total of six maximum rate-of-change component fractions of the rate of change R.

[0040] The motor parameters P can be determined using a lookup table 26 depending on the target current I. s will be calculated.

[0041] Furthermore, a limitation of the target current gradient is applied. dI / dt of the target current I s with respect to the respective coordinate direction 18, the associated maximum rate of change R. For the positive target current gradient ( dI / dt ) p especially with regard to the q-direction, the limitation 28 applies

[0042] dl

[0043]

[0044] and accordingly for the negative target current gradient ( dI / dt ) n

[0045] O < R n-

[0046] The target current gradients are also affected. dI / dtThe d-direction and the excitation direction are limited with a corresponding maximum rate of change R, whereby the respective positive target current gradient is determined by the smaller of the two maximum positive rate of change components R. p the d-direction and the excitation direction are limited, and the respective negative target current gradient is determined by the larger of the two maximum negative P241740

[0047] -7- Rate of change components R n The d-direction and the excitation direction are limited to account for coupling effects between these two coordinate directions 18. The current controller 14 calculates the set current I depending on this limited set current. s and the motor parameters P from lookup table 26, the output voltage U a with respect to the coordinate direction 18 for the inverter 22.P241740

[0048] -8- List of reference symbols

[0049] 10 procedures for operation

[0050] 12 Electric motor

[0051] 14 current regulators

[0052] 16 dq coordinate system

[0053] 18 Coordinate direction

[0054] 20 Feedforward control

[0055] 22 inverters

[0056] 23 Motor phase

[0057] 24 Calculation

[0058] 25 Calculation

[0059] 26 Lookup table

[0060] 28 Limit

[0061] I p Phase current

[0062] I s Target current

[0063] I v Target current

[0064] P Motor parameters

[0065] R maximum rate of change

[0066] R n maximum negative rate of change component R p maximum positive rate of change component U a Output voltage

[0067] U e Input voltage

[0068] U p Phase voltage

[0069] U r Voltage reserve value

[0070] U a,m maximum output voltage

[0071] U a,s stationary output voltage component U r,n negative voltage reserve value

[0072] U r,p positive voltage reserve value

[0073] ΔI Current difference

[0074] dI / dt Target current gradient

Claims

P241740 -9- Patent claims 1. Method for operating (10) an electric motor (12), comprising Providing the electric motor (12) comprising motor windings, providing a current controller (14) which is dependent on a set current (I) with respect to at least one coordinate direction (18) of a rotating electrical coordinate system (16) of the electric motor (12). s ) one limited to a maximum output voltage (U a,m ) limited output voltage (U a ) outputs, providing an inverter (22) for outputting phase voltages (U p ) on the motor windings to adjust a phase current (I p ) in the motor windings at least dependent on the output voltage (U a ), calculation (24) of at least one voltage reserve value (U r ) to the output voltage (U a ) depending on the maximum output voltage (U a,m ) and the output voltage (Ua ), Calculation (25) of a maximum rate of change (R) of the target current (I) s ) depending on at least one voltage reserve value (U) r ) and Limitation (28) of a target current gradient ( dI / dt ) of the set current supplied to the current controller (14) (I s ) on the maximum rate of change (R).

2. Method for operation (10) according to claim 1, characterized in that the target current (I s ) depending on a specified current (I v ) is calculated by a feedforward control (20).

3. Method for operation (10) according to claim 1 or 2, characterized in that the maximum rate of change (R) depends on a current difference (ΔI) between the set current (I) v ) and the target current (I s ) is calculated.

4. Method for operation (10) according to one of the preceding claims, characterized in that the voltage reserve value (U) r) as the voltage difference between the maximum output voltage (U am ) and the output voltage (U a ) is calculated.

5. Method for operation (10) according to claim 4, characterized in that the voltage reserve value (U) r ) a positive voltage reserve value (U rp ) includes, P241740 -10- which is the voltage difference between the positive maximum output voltage and the output voltage (U a ) is calculated.

6. Method for operation (10) according to claim 4 or 5, characterized in that the voltage reserve value (U) r ) a negative voltage reserve value (U r n ) includes, which is the voltage difference between the negative maximum output voltage (U) a m ) and the output voltage (U a ) is calculated.

7. Method for operation (10) according to claims 5 and 6, characterized in that the maximum rate of change (R) has a maximum positive rate of change component (R). p ) and a maximum negative rate-of-change component (R n ) includes, where the maximum positive rate-of-change component (R) p ) depending on the positive voltage reserve value (U) r p ) and the maximum negative rate-of-change component (R n ) depending on the negative voltage reserve value (U r n ) is calculated.

8. Method for operation (10) according to claim 7, characterized in that the target current gradient ( dI / dt ) a positive target current gradient ( dI / dt ) p and a negative setpoint gradient ( dI / dt ) n includes and the limitation (28) of the positive setpoint gradient ( dI / dt ) p on the maximum positive rate of change component (Rp )and the limitation (28) of the negative target current gradient ( dI / dt ) n on the maximum negative rate of change component (R n ).

9. Method for operation (10) according to one of the preceding claims, characterized in that the maximum rate of change (R) is calculated depending on motor parameters (P) of the electric motor (12).

10. Electric motor (12) with a stator and a rotor rotatable relative to the stator and operable by a method for operation (10) according to one of the preceding claims.

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