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EP-4285483-B1 - DETERMINING VALUES OF A PHYSICAL PARAMETER OF AN ELECTRIC MOTOR ASSIGNED TO DIFFERENT OPERATING POINTS OF THE ELECTRIC MOTOR

EP4285483B1EP 4285483 B1EP4285483 B1EP 4285483B1EP-4285483-B1

Inventors

  • KRÄMER, Andre

Dates

Publication Date
20260513
Application Date
20211208

Claims (10)

  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 t 1 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 t 2 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 t 1 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 t 2 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 M LP for a first length of time t 1 at a speed n LP , 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 M CP for a second length of time t 2 at a speed n CP , the speed n CP and the torque m CP 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 n N is the speed at the third working point, in particular the nominal working point (1), M N 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 P V,n ~n c 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.

Description

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. It is generally known that an electric motor is operated at a certain speed and is subjected to a certain torque. From the DE 10 2016 207 333 A1 is a known method for controlling an electric machine during a pulse start of an internal combustion engine. From theUS 2011/163707 A1The 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. From theCN 108 063 569 BSuch a procedure is also known. From the DE102013204194A1 A control system for a synchronous machine and a method for operating a synchronous machine are known. The invention is therefore based on the objective of further developing a method for measuring the efficiency characteristic of an electric motor. According to the invention, the problem is solved in the method according to the features specified in claim 1. Important features of the invention in the method for determining values of a physical quantity of the electric motor, namely the efficiency of the electric motor, assigned to different operating points of an 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 for a second period of time t 2 at a second operating point, in particular at an operating point acting as a compensation point. 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. 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. 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 operation 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 considered a first operating point of the characteristic curve. Determining a value of the physical quantity can be used, and in this particular special case, no compensation is necessary. In an advantageous design, after the first and second process steps, in each of the respective process steps For a respective first time period 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 acting as a respective compensation point. 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. In an advantageous embodiment, the time-averaged value, in particular the arithmetic mean, of the speed- dependent power loss of the electric motor, 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 that occurs during steady-state operation of the electric motor at a third operating point, in particular the rated point. It is advantageous that the change in temperature 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. In an advantageous embodiment, the time-averaged value, in particular the arithmetic mean, of the load- dependent power loss of the electric motor, determined for the time interval formed from