METHOD FOR DETERMINING A TARGET VOLUMETRIC FLOW RATE FOR A COOLANT

Abstract

The invention relates to a method for determining a target volumetric flow rate (V) for a coolant that is conducted through a coolant path in order to cool a power converter, wherein: the temperature (T.sub.C) of a DC-link capacitor of the power converter and the temperature (T.sub.K) of the coolant are determined, and a value for the target volumetric flow rate (V) is determined on the basis of the temperature (T.sub.C) of the DC-link capacitor and the temperature (T.sub.K) of the coolant.

Claims

1. A method for determining a target volumetric flow rate (V) for a coolant (180), which is conducted through a coolant path (164) to cool a power converter (110), the method comprising: determining a temperature (TC) of the DC-link capacitor (135) of the power converter (110) and a temperature (TK) of the coolant, and determining a value for the target volumetric flow rate (V) based on the temperature (TC) of the DC-link capacitor and the temperature (TK) of the coolant.

2. The method as claimed in claim 1, wherein the value for the target volumetric flow rate (V) is determined based on a temperature difference (ΔT) between the temperature (TC) of the DC-link capacitor and the temperature (TK) of the coolant and the temperature of the coolant (TK).

3. The method as claimed in claim 1, wherein at least one value of a current is determined in the power converter, and wherein based on the at least one value of the current, an intermediate value (VZ) for the target volumetric flow rate determined from the temperature (TC) of the DC-link capacitor and the temperature of the coolant (TK), on the basis of a characteristic map (K1), is adapted, and used as the value for the target volumetric flow rate (V).

4. The method as claimed in claim 3, wherein (i) a value of a current (IZ) in a DC link of the power converter, iii) a value of a phase current (IP), or both (i) and (ii) are used as the at least one value of the current in the power converter.

5. The method as claimed in claim 1, wherein a time interval (Δt) between two successive determinations of the value for the target volumetric flow rate (V) is predefined as a function of a change of a current in the power converter.

6. The method as claimed in claim 5, wherein upon an increase of the current in the power converter, a longer time interval is predefined than upon a decrease of the current in the power converter.

7. The method as claimed in claim 1, wherein a coolant pump (190) for the coolant (180) is activated based on the determined target volumetric flow rate (V).

8. A processing unit (140), which is configured to carry out all method steps of a method as claimed in claim 1.

9. (canceled)

10. A non-transitory, computer-readable storage medium having a instructions that when executed by a computer cause the computer to determine a target volumetric flow rate (V) for a coolant (180), which is conducted through a coolant path (164) to cool a power converter (110), by: determining a temperature (TC) of the DC-link capacitor (135) of the power converter (110) and a temperature (TK) of the coolant, and determining a value for the target volumetric flow rate (V) based on the temperature (TC) of the DC-link capacitor and the temperature (TK) of the coolant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 schematically shows a power converter, in which a method according to the invention can be carried out.

[0022] FIG. 2 shows the power converter from FIG. 1 in another representation.

[0023] FIG. 3 schematically shows a sequence of a method according to the invention in a preferred embodiment.

DETAILED DESCRIPTION

[0024] A power converter 110, designed by way of example as a B6 bridge, is schematically illustrated in FIG. 1, in which a method according to the invention can be carried out and which is used to activate an electrical machine 100.

[0025] The power converter 110 has two DC voltage terminals 131, 132, which are connected in a typical manner, in addition to a DC-link capacitor 135, designed, for example, as a film capacitor, to, for example, six semiconductor switching elements 120, for example, MOSFETs or IGBTs. A phase (stator winding) of the electrical machine 100 is connected between each two of the semiconductor switching elements 120.

[0026] It is to be noted at this point that the power converter can be operated not only as an inverter, but also as a rectifier, so that the electrical machine is operable overall both as a motor and also as a generator.

[0027] Furthermore, the power converter 110 is connected with its DC voltage terminals 131, 132 to a vehicle electrical system 170, for example in a vehicle. Further components or consumers are in turn typically connected to the vehicle electrical system 170, which are not shown here for the sake of clarity, however.

[0028] During operation of the power converter 110, the individual semiconductor switching elements 120 are activated by means of an activation circuit or an activation unit 150 in a suitable manner to open or close. This is carried out, for example, at a defined clock frequency. In a typical activation, for example, one switch is always closed and the other is open for each branch. A DC voltage U.sub.dc is converted into an AC voltage, so that a phase current I flows in the phases.

[0029] The power converter 110 and optionally the activation unit 150 can together form a power electronics unit 140 for the electrical machine 100 or can be part of such a power electronics unit. In particular, a measurement of a current or current flow and a voltage in the power converter can also take place.

[0030] In FIG. 2, the power converter 110 from FIG. 1 is shown in another representation, in a sectional view. In particular, a heat sink 160 having a plurality of cooling ribs 161 is additionally shown here, on the surface of which the semiconductor switching elements 120 are arranged or attached (in this view only one semiconductor switching element per phase is visible). A good heat transfer from the semiconductor switches 120 to the heat sink 160 can be achieved by a suitable attachment of the semiconductor switching elements 120 on the heat sink 160. Moreover, the DC-link capacitor 135 is shown, which can also be arranged on the heat sink 160 to enable effective cooling.

[0031] Furthermore, a coolant path 164 is shown, which is delimited, for example, by a suitable housing on the side of the heat sink 160 opposite to the semiconductor switching elements 120, so that in particular the cooling ribs 161 are also located therein. The coolant path 164 has an inlet 162 and an outlet 163, so that coolant, for example, water, which is indicated by arrows 180, can enter through the inlet 162 and can exit again through the outlet 163. In this way, the heat can be emitted from the heat sink 160 to the coolant 180. A coolant pump, which is indicated, for example, by the reference sign 190, can be used to pump the coolant 180.

[0032] Furthermore, a temperature sensor 181 or 182 is respectively attached at both the inlet 162 of the coolant path and also at the DC-link capacitor 135, by which a temperature of the coolant 180 at the inlet 162 of the coolant path and a temperature of the DC-link capacitor 135 can be measured. Further temperature sensors 183 can be provided at the semiconductor switching elements 120.

[0033] A sequence of a method according to the invention in a preferred embodiment is schematically shown in FIG. 3. Firstly, the temperature T.sub.C of the DC-link capacitor and the temperature T.sub.K of the coolant are determined or measured, for example, by means of the temperature sensors mentioned with reference to FIG. 2.

[0034] A temperature difference ΔT can be formed from the temperature T.sub.C and the temperature T.sub.K according to the formula ΔT=T.sub.C−T.sub.K. Based on the temperature difference ΔT and the temperature T.sub.K of the coolant, an intermediate value V.sub.Z of the target volumetric flow rate for the coolant can then be determined on the basis of a characteristic map K.sub.1. For this purpose, the values stored in the characteristic map K.sub.1 can have been determined, for example, on the basis of test measurements and/or simulations. It is also conceivable that the temperature difference is not explicitly determined or calculated, but rather the values stored in the characteristic map directly apply accordingly for the temperatures T.sub.C and T.sub.K.

[0035] Furthermore, a current I.sub.Z in the DC link and/or a phase current I.sub.P is determined or measured by means of corresponding sensors or measuring units. A factor can then be determined in each case on the basis of a respective characteristic curve K.sub.1 or K.sub.2, by means of which the intermediate value V.sub.Z can be adapted, in particular scaled down. It is expedient here to use only one of the two factors, namely in particular the one which results in a higher target volumetric flow rate, to catch any uncertainties. In this way, the target volumetric flow rate V is determined, on the basis of which the coolant pump can be activated.

[0036] As already mentioned, this target volumetric flow rate can be determined regularly, to thus always obtain the presently required value for the target volumetric flow rate, in order to operate the coolant pump efficiently, and possibly also be able to switch it off temporarily. A change or a gradient ΔI.sub.Z or ΔI.sub.P, respectively, can also be determined in this context for the current I.sub.Z in the DC link and/or the phase current I.sub.P. If only one gradient is determined and it is positive, i.e., the current increases, a time interval Δt between two successive determinations of the value for the target volumetric flow rate V can be set to a small value, otherwise to a large value.

[0037] A time interval is expediently predefined here via a time grid of the model used, for example, a call of the function can take place every 100 ms. For example, if a fixed torque and a fixed speed are used for driving, but at two different DC-link voltages, the gradient of the DC-link current changes, so that either less or more heat has to be dissipated. In the case of different signs, the max function engages, i.e., the greater value is used.