DETERMINING VALUES ASSIGNED TO A PHYSICAL QUANTITY OF THE ELECTRIC MOTOR AT DIFFERENT WORKING POINTS OF AN ELECTRIC MOTOR

Description

[0001] The invention relates to a method for determining values ​​of a physical quantity of the electric motor assigned to different operating points of an electric motor.

[0002] It is generally known that an electric motor is operated at a certain speed and is subjected to a certain torque.

[0003] From DE 10 2016 207 333 A1 a method for controlling an electric machine during a pulse start of an internal combustion engine is known.

[0004] From the US 2011 / 163707 A1 The closest state of the art is a method for determining values ​​of a physical quantity of the electric motor, namely the efficiency of the electric motor, which are assigned to different operating points of an electric motor.

[0005] From the CN 108 063 569 B Such a procedure is also known.

[0006] From DE102013204194A1 a control system for a synchronous machine and a method for operating a synchronous machine is known.

[0007] The invention is therefore based on the objective of further developing a method for measuring the efficiency characteristic of an electric motor.

[0008] According to the invention, the problem is solved in the method according to the features specified in claim 1.

[0009] Important features of the invention in the method for determining values ​​of a physical quantity of the electric motor assigned to different operating points of an electric motor, namely of the efficiency of the electric motor, are that In a first process step, the electric motor is operated at a first operating point, in particular at an operating point functioning as a measuring point, for a first period of time t 1 and a first of the values ​​of the physical quantity of the electric motor is recorded and / or determined, and in a second process step, the electric motor is operated at a second operating point, in particular at an operating point functioning as a compensation point, for a second period of time t 2.

[0010] An advantage of this method is that after each measurement point of the characteristic curve of the physical quantity, in particular the efficiency characteristic curve, a compensation operation takes place, thus enabling temperature equalization if a temperature change occurred in the first process step. The target temperature is preferably the temperature that occurs during steady-state operation of the electric motor at its rated point. In this way, the characteristic curve can be measured at a quasi-steady-state temperature according to the invention.

[0011] A disadvantage of the invention is that the second process step takes time, and therefore the total time for measuring the characteristic map can be considerable if many respective first and second process steps have to be carried out.

[0012] In an advantageous embodiment, the first and second process steps are performed for different first and second operating points, respectively. The advantage here is that an entire characteristic curve for the physical quantity can be measured. The second operating points used for compensation are not part of the characteristic curve to be measured, unless a second operating point happens to be identical to a first operating point. In such a specific case, the second operating point can then also be used as a first operating point of the characteristic curve to determine a value of the physical quantity, and no compensation is necessary in this specific case.

[0013] In an advantageous design, after the first and second process steps, in each of the respective process steps For a respective first period of time t 1, the electric motor is operated at a respective first operating point, in particular at an operating point functioning as a respective measuring point, and a respective further value of the physical quantity of the electric motor is recorded and / or determined, and afterwards, for a respective second period of time t 2, the electric motor is operated at a respective second operating point, in particular at an operating point functioning as a respective compensation point.

[0014] The advantage here is that not only a single operating point used to determine a value of the quantity is compensated, but all operating points of a characteristic map used to determine values ​​of the quantity.

[0015] In an advantageous embodiment, the time mean, in particular the arithmetic mean, determined for the time interval formed from the first time period t1 and the second time period t2, corresponds to the speed dependent power loss of the electric motor which occurs during steady-state operation of the electric motor at a third operating point, in particular the rated point speed dependent power loss. An advantage of this is that the temperature change caused by the power loss can be compensated for, and thus the characteristic curve, i.e., all respective first operating points, can be measured at a virtually constant temperature.

[0016] In an advantageous embodiment, the time mean, in particular the arithmetic mean, determined for the time interval formed from the first time period t1 and the second time period t2, corresponds to the loaddependent power loss of the electric motor which occurs during steady-state operation of the electric motor at a third operating point, in particular the rated point load dependent power loss. An advantage of this is that the temperature change caused by the power loss can be compensated for, and thus the characteristic curve, i.e., all respective first operating points, can be measured at a virtually constant temperature.

[0017] In an advantageous embodiment, each operating point is uniquely assigned a pair of values, wherein each pair represents a value for the rotational speed of the electric motor and a value for the torque of the electric motor. The advantage here is that the operating points are uniquely defined by these two values ​​and are distinguishable from one another.

[0018] In an advantageous embodiment, a function is used to model the speed-dependent power loss whose function value is proportional to the c-th power of the electric motor's speed, where c is greater than zero, in particular greater than 1 and less than 3, and / or a function is used to model the load-dependent power loss whose function value is proportional to the square of the motor current, in particular to the square of the current drawn by the electric motor. The advantage here is that a highly accurate model can be used, thus enabling quasi-stationary measurements.

[0019] In an advantageous embodiment, in the first process step, particularly as the first operating point, the electric motor is loaded with a torque M LP at a rotational speed n LP for the first time period t 1. and afterwards, i.e. in the second process step, in particular as the second operating point, the electric motor is loaded at a speed n CP with a torque M CP during the second time period t 2, whereby the speed n CP and the torque M CP are determined according to: M CP = t 1 + t 2 M N 2 − t 1 M LP 2 t 2 n CP = t 1 + t 2 n N c − t 1 n LP c t 2 c , where n N is the rotational speed at the third operating point, in particular the rated point, and MN is the torque at the third operating point, in particular the rated point, and c is a real number greater than zero, in particular where c is chosen such that for the speed-dependent power loss P V , n ~ nc<This applies, where n is the motor speed. An advantage of this is that for each operating point at which a value of the quantity is determined, a second operating point for thermal compensation can be determined such that the average value of the speed-dependent power loss equals the speed-dependent power loss that occurs at the rated point during steady-state operation.

[0020] In an advantageous embodiment, the torque values ​​assigned to the first operating points are equidistant from one another and / or the speed values ​​assigned to the first operating points are equidistant from one another. The advantage here is that the characteristic map can be densely populated with first operating points, thus enabling the most accurate measurement possible.

[0021] Important features of the device for carrying out the aforementioned method are that the device has a load machine driven by an electric motor and an inverter, wherein the inverter supplies the electric motor.

[0022] An advantage of this is that it allows the characteristic curve to be measured at a quasi-stationary temperature, namely the temperature that occurs during steady-state, and in particular quasi-stationary, operation.

[0023] Further advantages arise from the sub-claims.

[0024] The invention will now be explained in more detail with reference to schematic illustrations: In the Figure 1 A field of operating points is shown for a method according to the invention.

[0025] As in the Figure 1To determine the efficiency characteristic of an inverter-fed electric motor loaded by a load machine, different operating points of the field are approached successively over time.

[0026] The electric motor is preferably a three-phase motor and is powered by a mains-supplied inverter, which regulates it to a target speed n corresponding to the respective operating point. The load machine driven by the electric motor is operated in such a way that the electric motor is subjected to a torque M.

[0027] While the electric motor is operated at this operating point, the temperature changes because speed-dependent and load-dependent power losses occur depending on the operating point.

[0028] In order to remain as close as possible to a desired target temperature during the execution of the procedure, the electric motor is operated at a compensation point 3 after each operating point acting as measuring point 2.

[0029] The target temperature is reached at the beginning of the process by an operating point, in particular the nominal operating point, at which the electric motor is operated at its nominal speed n and loaded with the nominal torque M for such a long time that the target temperature has been reached.

[0030] Each measurement point is assigned a pair of values ​​consisting of rotational speed and torque. The measurement points differ from each other in their pairs of values.

[0031] If a measuring point 2 has such a rotational speed and torque that the temperature rises above the target temperature after a measuring period t 1, a compensation point 3 is subsequently approached, which has a lower total power loss and thus lowers the temperature to the target temperature after a time period t 2.

[0032] Conversely, after a measuring point 2 with lower power loss than at the nominal operating point, a compensation point 3 is approached which has a higher power loss than at the nominal operating point, such that after a time period t 2 the temperature present at the beginning of the measurement at measuring point 2 is restored, i.e. the temperature that occurs at the nominal point in steady-state operation.

[0033] According to the invention, the compensation point 3 is selected such that after a time period t 2 the temperature that sets in at the nominal point during steady-state operation is reached if the measuring point 2 was previously approached for a time period t 1.

[0034] According to the invention, after the electric motor has been operated at measuring point 2 for a period of time t1, the electric motor is operated at compensation point 3 for a period of time t2, so that the average value of the speed-dependent power loss formed over the total time t1 + t2 is PV,n the speed-dependent power loss PV,n,N at nominal point 1 is the same and that the mean value of the load-dependent power loss is P V , M The load-dependent power loss at the nominal point is equal over the total time t 1 + t 2.

[0035] Because the sum of the speed-dependent power losses PV,n and the load-dependent power loss PV , M This is essentially equal to the total power loss of the electric motor.

[0036] Preferably, this applies to the mean value of the speed-dependent power loss. P V , n , N = 1 t 1 + t 2 ⋅ t 1 ⋅ P V , n , LP + t 2 ⋅ P V , n , CP and for the average value of the load-dependent power loss P V , M , N = 1 t 1 + t 2 ⋅ t 1 ⋅ P V , M , LP + t 2 ⋅ P V , M , CP where the measurement duration t 1 is maintained at measurement point 2, where the measurement duration t 2 is maintained at compensation point 3, where P V , M,LP the load-dependent power loss at measuring point 2 is, where PV,M,CP the load-dependent power loss at compensation point 3 is, where PV,n,LP the speed-dependent power loss at measuring point 2 is, where PV,n,CP the speed-dependent power loss at compensation point 3 is, where PV,M,N the load-dependent power loss at the nominal point is and PV,n,N The speed-dependent power loss at the rated point is...

[0037] The nominal point is an operating point specified by the manufacturer of the electric motor, which is not located at the edge of the field, as otherwise no suitable compensation points 3 can be determined.

[0038] In a preferred embodiment, a compensation point is determined from a measuring point 2, to which a torque M LP and a rotational speed n LP are assigned, which has a torque M CP and a rotational speed n CP, which are determined according to M CP = t 1 + t 2 M N 2 − t 1 M LP 2 t 2 n CP = t 1 + t 2 n N c − t 1 n LP c t 2 c where nN is the rotational speed at the rated point and MN is the torque at the rated point, and c is a real number greater than zero. Preferably, c is chosen such that the speed-dependent power loss is... PV,n ~nc< applies, where n is the speed of the motor.

[0039] With the method according to the invention, the value of a physical quantity, such as efficiency, can be determined for each measuring point. Therefore, the time period t1 is selected such that the determination of the value of this physical quantity is achieved with sufficient accuracy. For example, a time period between 10 and 100 seconds is chosen as t1. The time period t2 is selected such that the radicand in the above formulas is greater than zero, whereby the time period t2 is chosen to be as similar as possible to t1. Preferably, the two time periods are equal, such that t1 = t2.

[0040] Preferably, the rotational speeds of measuring points 2 in the field are equidistantly distributed and the torques of measuring points 2 are also equidistantly distributed.

[0041] Furthermore, the following applies preferentially to the load-dependent power loss: PV,M ~I 2< , where I is the motor current, in particular where for the current I ~M applies, where M is the torque of the motor.

[0042] In a preferred embodiment, a compensation point is determined from a measuring point 2, to which a torque M LP and thus a current I LP and a rotational speed n LP are assigned, which has a torque M CP and thus a current I CP and a rotational speed n CP, which are determined according to I CP = t 1 + t 2 I N 2 − t 1 I LP 2 t 2 n CP = t 1 + t 2 n N c − t 1 n LP c t 2 c where nN is the rotational speed at the rated point and IN is the current at the rated point, and c is a real number greater than zero. Preferably, c is chosen such that the speed-dependent power loss is... P V , n ~ nc< applies, where n is the speed of the motor. Reference symbol list

[0043] P Power, especially power loss n Speed ​​M Torque 1 Nominal point 2 Measuring point 3 Compensation point

Claims

1. Method for determining values of a physical variable of an electric motor, specifically the efficiency of the electric motor, that are assigned to different working points of the electric motor, wherein, in a first method step, the electric motor is operated for a first length of time t1 at a first working point, in particular at a working point acting as a measurement point (2), the power loss is determined, and a first of the values of the physical variable of the electric motor is determined, and in a second method step, the electric motor is operated for a second length of time t2 at a second working point, in particular at a working point acting as a compensation point (3), the power loss is determined, and a second of the values of the physical variable of the electric motor is determined, characterised in that the time average, in particular the arithmetic average, determined for the time period formed of the first length of time t1 and the second length of time t2, of the power loss of the electric motor is equal to the power loss that is determined and occurs at a third working point, in particular the nominal working point (1), while the electric motor is in steady-state mode, wherein the first method step and the second method step are repeated for each further working point using associated lengths of time t1 and t2, wherein the time average, in particular the arithmetic average, determined for the time period formed of each first length of time t1 and each second length of time t2, of the power loss of the electric motor is equal to the power loss that is determined and occurs at a third working point, in particular the nominal working point (1), while the electric motor is in steady-state mode.

2. Method according to claim 1, characterised in that the first and second method steps are carried out for every other first and second working point.

3. Method according to any of the preceding claims, characterised in that thereafter, in associated method steps, in each case - the electric motor is operated for an associated first length of time t1 at an associated first working point, in particular at a working point acting as an associated measurement point (2), and an associated further value of the values of the physical variable of the electric motor is detected and / or determined, - and then the electric motor is operated for an associated second length of time t2 at an associated second working point, in particular at a working point acting as an associated compensation point (3).

4. Method according to any of the preceding claims, characterised in that the time average, in particular the arithmetic average, determined for the time period formed of the first length of time t1 and the second length of time t2, of the speed-dependent power loss of the electric motor is equal to the speed-dependent power loss that occurs at a third working point, in particular the nominal working point (1), while the electric motor is in steady-state mode.

5. Method according to any of the preceding claims, characterised in that the time average, in particular the arithmetic average, determined for the time period formed of the first length of time t1 and the second length of time t2, of the load-dependent power loss of the electric motor is equal to the load-dependent power loss that occurs at a third working point, in particular the nominal working point (1), while the electric motor is in steady-state mode.

6. Method according to any of the preceding claims, characterised in that each of the working points is assigned, in particular unambiguously assigned, an associated two-tuple, each two-tuple having a particular value of the speed of the electric motor and a particular value of the torque of the electric motor.

7. Method according to any of the preceding claims, characterised in that to model the speed-dependent power loss, a function is used of which the function value is proportional to the cth power of the speed of the electric motor, where c is greater than zero, in particular greater than 1 and less than 3, and / or in that to model the load-dependent power loss, a function is used of which the function value is proportional to the square of the motor current, i.e. in particular to the square of the current consumed by the electric motor.

8. Method according to any of the preceding claims, characterised in that in the first method step, in particular as a first working point, the electric motor is loaded with a torque MLP for a first length of time t1 at a speed nLP, and in that thereafter, i.e. in the second method step, in particular as a second working point, the electric motor is loaded with a torque MCP for a second length of time t2 at a speed nCP, the speed nCP and the torque mCP being determined in accordance with: M CP = t 1 + t 2 M N 2 − t 1 M LP 2 t 2 n CP = t 1 + t 2 n N c − t 1 n LP c t 2 c where nN is the speed at the third working point, in particular the nominal working point (1), MN is the torque at the third working point, in particular the nominal working point (1), and c is a real number greater than zero, c in particular being selected such that PV,n~nc applies to the speed-dependent power loss, where n is the speed of the motor.

9. Method according to any of the preceding claims, characterised in that the torque values assigned to the first working points are equidistant from one another, and / or in that the speed values assigned to the first working points are equidistant from one another.

10. Device for carrying out a method according to any of the preceding claims, characterised in that the device has a load machine, which is driven by the electric motor, and a converter, wherein the converter feeds the electric motor.