Method for determining a target volume flow rate of a coolant

Abstract

A method for determining a target volume flow (V) of a coolant conducted through a coolant path for cooling a converter, wherein the temperature (T C ) and the temperature of the coolant (T K ), and wherein based on the temperature of the intermediate circuit capacitor (T C ) and the temperature of the coolant (T K ) to determine the value of the target volume flow rate (V).

Description

Technical Field

[0001] The invention relates to a method for determining a target volume flow of a coolant which is conducted through a coolant path for cooling a converter, as well as to a computing unit for carrying out the method and to a computer program for carrying out the method. Background Art

[0002] Electric machines, in particular when used in vehicles, in particular hybrid vehicles or electric vehicles, can be operated with the aid of a converter. In particular, in this case, motor operation and generator operation can be achieved. Due to the heat generated by the power loss in the converter, in particular the power loss of semiconductor switching elements or power semiconductors in the converter, it is expedient to cool such a converter with the aid of a coolant, for example water. Summary of the invention

[0003] According to the invention, a method for determining a target volume flow rate, as well as a computing unit for carrying out the method and a computer program for carrying out the method are proposed. Advantageous embodiments are the subject matter disclosed in the present application.

[0004] The invention relates to a method for determining a target volume flow of a coolant which is guided through a coolant path for cooling a converter. Such a converter can be, in particular, an inverter or a converter. As already mentioned, such a converter usually has semiconductor switching elements, in particular power semiconductors such as MOSFETs or IGBTs, in order to convert a voltage, for example, from a direct voltage to an alternating voltage and vice versa. Depending on the type of electric machine to be controlled by means of the converter and also the converter itself, in particular in the case of high overall power, that is to say high currents, a strong heating of the semiconductor switching elements and thereby the converter can occur due to the corresponding power loss.

[0005] In this case, such an electric machine can be used in particular in a vehicle, in particular a hybrid vehicle or a (purely) electric vehicle.

[0006] Therefore, a cooling device or a cooling option is usually provided in such converters or in general in power electronics. For example, a heat sink can be used for this purpose, on which semiconductor switching elements and, if necessary, other important components are arranged, and along which a coolant is guided in a coolant path in order to dissipate the heat that is generated. The coolant can be a liquid, such as water or a water-glycol mixture. In this case, the heat sink can have cooling fins or the like, which are located in the coolant path in order to be able to dissipate the heat that is generated as efficiently as possible.

[0007] In order to control the corresponding coolant pump in a targeted and as efficient a manner as possible, by means of which the coolant is pumped or guided along the coolant path, it is necessary to know the necessary volume flow of the coolant, i.e. the target volume flow. On the one hand, the converter should not exceed a certain temperature, i.e., it should be protected from overheating, for which a sufficiently high volume flow is required; on the other hand, however, it is also undesirable to provide an unnecessarily high volume flow of the coolant, for which unnecessary energy is required to operate the coolant pump.

[0008] In order to determine a suitable target volume flow, the temperature of the semiconductor switching element or the heat generated thereby and to be dissipated can be determined. A suitable target volume flow can then be determined based on this. However, it has now been shown that the target volume flow of the coolant can also be determined particularly accurately by taking into account the intermediate circuit capacitor of the converter and its temperature.

[0009] Thus, in the proposed method, the temperature of the intermediate circuit capacitor of the converter and the temperature of the coolant are determined. The temperature of the intermediate circuit capacitor can be measured (or modeled) directly at the intermediate circuit capacitor, for example, by means of a corresponding temperature sensor. The temperature of the coolant can be measured (or modeled) at the inlet of the coolant path, for example, by means of a temperature sensor. However, it is also conceivable to measure the temperature of the coolant at other, suitable locations in the coolant circuit, but preferably upstream and in particular in the vicinity of the coolant path of the converter.

[0010] Next, the value of the target volume flow is determined based on the temperature of the intermediate circuit capacitor and the temperature of the coolant. The latter is preferably achieved by first determining the temperature difference between the temperature of the intermediate circuit capacitor and the temperature of the coolant and then determining the value of the target volume flow based on this temperature difference and the temperature of the coolant. Suitably, a coolant pump for the coolant is then controlled or regulated based on the determined target volume flow. The target volume flow for semiconductors, for example, can be a separate function and is therefore independent of the capacitors. However, the target volume flow for the converter or inverter is a maximum function of the capacitors, semiconductors and other temperature models.

[0011] Depending on the temperature difference between the intermediate circuit capacitor, which can be a film capacitor in particular, and the temperature of the coolant, it can be determined particularly easily how high the volume flow of the coolant must or should be in order to actually be able to dissipate the heat to be dissipated. In this case, the temperature difference indicates how much heat is to be dissipated, and the temperature of the coolant indicates how much heat the coolant can still absorb. Thus, already very hot coolant can usually absorb - and dissipate - less heat (per unit volume or mass) than cooler coolant. Correspondingly, the volume flow should be higher in the case of hotter coolant than in the case of cold coolant.

[0012] In this case, the target volume flow can be determined based on the temperature difference between the temperature of the intermediate circuit capacitor and the temperature of the coolant on the one hand and the temperature of the coolant on the other hand, in particular, based on a characteristic map. At this characteristic map, suitable values ​​for the target volume flow can be registered for different values ​​of the two variables mentioned, for example. These values ​​can have been determined beforehand within the framework of test measurements and / or simulations.

[0013] It is now particularly preferred that at least one value of the current in the converter is determined. Then, depending on the temperature of the intermediate circuit capacitor and the temperature of the coolant (or the temperature difference and the temperature of the coolant), an intermediate value of the target volume flow can first be determined or ascertained, in particular on the basis of the aforementioned characteristic map, which intermediate value is then adapted, in particular scaled, based on the at least one value of the current and then used as the value of the target volume flow.

[0014] Here, in particular, the value of the current in the intermediate circuit of the converter and / or the value of the phase current are considered as the at least one value of the current in the converter. Both the current in the intermediate circuit and the phase current are parameters that characterize the current operating state of the converter, in particular with respect to the current power loss and the heat generated and to be dissipated thereby. However, this also applies in particular to the future development of the heat generated and to be dissipated. That is, if the current is only small, it can be assumed that the heat generated and to be dissipated will be reduced. Thus, the target volume flow rate can also be selected to be smaller. Correspondingly, in the case of high currents, the target volume flow rate can be selected to be higher or not so small. By this, the efficiency of cooling can be further improved until the goal of completely shutting down the coolant pump at least temporarily, for example when the converter is not working, and thus saving energy and reducing emissions is achieved.

[0015] The target volume flow or its current value is expediently determined repeatedly, in particular regularly, at specific time intervals. In this case, it is then preferred that the time interval between two consecutive determinations of the value of the target volume flow is specified as a function of the change in the current in the converter. In particular, one of the two above-mentioned currents, i.e. the current in the intermediate circuit or the phase current, can be used as the current in the converter. It is also conceivable to use two currents, wherein both can then be taken into account and one of them can be selected depending on the situation.

[0016] In this case, it is expedient to specify a longer time interval when the current in the converter is increased (i.e. a positive gradient) than when the current in the converter is reduced (i.e. a negative gradient). In this way, it is possible to avoid, for example, afterheating when possible adverse thermal effects occur. Heating is usually slightly faster than cooling, so a distinction should be made between the two. In order not to cause too strong afterheating effects, the volume flow is expediently changed slowly during cooling, while a relatively rapid high volume flow should be required during heating.

[0017] A computing unit according to the invention, for example a control unit of a motor vehicle or a control unit or a power electronics unit of an electric machine, is set up, in particular by means of programming, to carry out the method according to the invention.

[0018] In particular, when the implementing control device is also used for other tasks and is therefore always present, the implementation of the method according to the invention in the form of a computer program or computer program product with program code for executing all method steps is also advantageous, since this results in particularly low costs. In particular, suitable data carriers for providing the computer program are magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs and others. It is also possible to download the program via a computer network (Internet, intranet, etc.).

[0019] Further advantages and embodiments of the invention are apparent from the description and the accompanying drawings.

[0020] The invention is schematically illustrated in the drawings based on exemplary embodiments and is described below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A converter is schematically shown in which the method according to the invention can be carried out.

[0022] Figure 2 Shows Figure 1 Another converter shown in FIG.

[0023] Figure 3The sequence of the method according to the invention in a preferred embodiment is schematically shown. DETAILED DESCRIPTION

[0024] exist Figure 1 Schematically shown in FIG. 1 is a converter 110 , which is designed as a B6 bridge by way of example, in which the method according to the invention can be carried out and which is used to control the electric machine 100 .

[0025] The converter 110 has two DC voltage terminals 131, 132, which are connected in a conventional manner to, for example, six semiconductor switching elements 120, for example MOSFETs or IGBTs, in addition to an intermediate circuit capacitor 135, which is designed, for example, as a film capacitor. The phases (stator windings) of the electric machine 100 are connected between two of these semiconductor switching elements 120, respectively.

[0026] At this point it should be pointed out that the converter can be operated both as an inverter and as a rectifier, so that the electrical machine as a whole can be operated both as a motor and as a generator.

[0027] The converter 110 is also connected to an onboard power supply 170, for example an onboard power supply in a vehicle, with its DC voltage terminals 131, 132. Further components or consumers are usually connected to the onboard power supply 170, but are not shown here for the sake of clarity.

[0028] During operation of the converter 110, the individual semiconductor switching elements 120 are now controlled in a suitable manner by means of a control circuit or a control unit 150 to open or close. This is achieved, for example, using a specific clock frequency. In the case of conventional control, for example, one switch is always closed and another switch is opened for each branch. In this case, the DC voltage U dc is converted into an alternating voltage so that a phase current I flows in the phase.

[0029] In this case, the converter 110 and optionally the control unit 150 may together form a power electronics unit 140 for the electric machine 100 or may be part of such a power electronics unit. In particular, the current or the current flowing in the converter and the voltage may also be measured.

[0030] exist Figure 2 The cross-sectional view shows Figure 11 shows a converter 110 in another illustration. In particular, a heat sink 160 with a plurality of cooling fins 161 is additionally shown here, on the surface of which semiconductor switching elements 120 are arranged or mounted (in this view, only one semiconductor switching element per phase can be seen). By suitable connection of these semiconductor switching elements 120 on the heat sink 160, a good heat transfer from the semiconductor switch 120 to the heat sink 160 can be achieved. An intermediate circuit capacitor 135 is also shown, which can also be arranged on the heat sink 160 in order to enable effective cooling.

[0031] Also shown is a coolant path 164, which is delimited, for example, by a suitable housing on the side of the heat sink 160 opposite the semiconductor switching elements 120, so that in particular the cooling fins 161 are also located in the coolant path. The coolant path 164 has an inlet 162 and an outlet 163, so that a coolant, for example water, indicated by an arrow 180 can flow in through the inlet 162 and out again through the outlet 163. In this way, heat can be released from the heat sink 160 to the coolant 180. In order to pump the coolant 180, a coolant pump can be used, which is exemplarily indicated by the reference numeral 190.

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

[0033] exist Figure 3 In the figure, the process of the method according to the present invention in a preferred embodiment is schematically shown. First, for example, with the help of reference Figure 2 The temperature sensor mentioned determines or measures the temperature T of the intermediate circuit capacitor. C and the coolant temperature T K .

[0034] Next, according to the temperature T C and temperature T K , we can use the formula ΔT = T C -T K Next, based on the temperature difference ΔT and the temperature T of the coolant, K The intermediate value of the target volume flow rate of the coolant can be determined or found out based on the comprehensive characteristic curve K1. For this purpose, the value stored in the characteristic map K1 may have been determined, for example, based on test measurements and / or simulations. It is also conceivable that the temperature difference is not determined or calculated explicitly, but that the value stored in the characteristic map is directly regarded as the temperature T C and T K .

[0035] Furthermore, the current l in the intermediate circuit is determined or measured by means of corresponding sensors or measuring devices. Z and / or phase current l P Then, factors can be determined according to the corresponding comprehensive characteristic curves K1 or K2, with the help of which the intermediate values ​​can be An adaptation, in particular a reduction, is carried out. It is expedient here to use only one of the two factors, in particular the factor that leads to a higher target volume flow, in order to compensate for possible uncertainties. The target volume flow is then obtained in this way. The coolant pump can be actuated as a function of the target volume flow.

[0036] As already mentioned, the target volume flow can be determined regularly in order to always obtain the currently required value of the target volume flow in order to operate the coolant pump efficiently and also to be able to temporarily switch off the coolant pump if possible. Z and / or phase current l P Determine the change or gradient ΔI Z or ΔI P If, in the case of only one determined gradient, this gradient is positive, ie the current is increasing, then two consecutive determinations of the target volume flow can be combined. The time interval Δt between the values ​​of is set to a small value, otherwise to a large value. The time interval is expediently specified by the time grid of the model used, for example the function can be called every 100 ms. If, for example, a fixed torque and a fixed speed are used, but two different intermediate circuit voltages are used, the gradient of the intermediate circuit current changes, so that less or more heat must be dissipated. In the case of different signs, the max function is used, that is to say the larger value.

Claims

1. A method for determining a target volume flow rate of a coolant (180) guided through a coolant path (164) for cooling a converter (110) method, The temperature (T C ) and the temperature of the coolant (T K ), where the temperature of the intermediate circuit capacitor (T C ) and the temperature of the coolant (T K ) to determine the target volume flow The value of where the temperature of the intermediate circuit capacitor (T C ) and the temperature of the coolant (T K ) and the temperature of the coolant (T K ) to determine the target volume flow The value of wherein at least one value of the current in the converter is determined, and wherein based on the at least one value of the current, a temperature (T C ) and the temperature of the coolant (T K ) is the median value of the target volume flow rate determined by is adapted and is used as the target volume flow The value of Based on the determined target volume flow To operate a coolant pump (190) for the coolant (180).

2. The method according to claim 1, wherein the determined intermediate value of the target volume flow rate is scaled and used as the target volume flow The value of .

3. The method according to claim 1, wherein the current (l Z ) and / or phase current (l P ) as the at least one value of the current in the converter.

4. The method according to any one of the preceding claims 1 to 3, wherein the target volume flow rate is determined twice in succession according to a change in the current in the current transformer. The time interval (Δt) of the values ​​of . 5 . The method as claimed in claim 4 , wherein a longer time interval is specified when the current in the converter increases than when the current in the converter decreases.

6. A computing unit (140) which is configured to carry out all method steps of the method according to any of the preceding claims.

7. A computer program product having a computer program which, when executed on a computing unit (140), causes the computing unit (140) to carry out all method steps of the method according to any one of claims 1 to 5.

8. A machine-readable storage medium having a computer program stored thereon, which, when executed on a computing unit (140), causes the computing unit (140) to perform all method steps of the method according to any one of claims 1 to 5.

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