DE102020208845A1 - Method of operating a refrigeration system, control unit - Google Patents

Abstract

The invention relates to a method for operating a cooling system, which is used to cool at least one component in a vehicle using a circulating coolant, in which derating is carried out to maintain a maximum cooling capacity of the cooling system. According to the invention, the point in time of the derating is determined on the basis of a model that takes into account the physical relationships between the coolant temperature and the component temperature. The invention also relates to a control unit for carrying out the method.

Description

The invention relates to a method for operating a cooling system with the features of the preamble of claim 1. The cooling system can in particular be a cooling system of a vehicle that can be operated electrically and/or by means of a combustible or fuel.

In addition, the invention relates to a control unit for carrying out the method.

State of the art

Cooling systems in vehicles are used to remove heat or waste heat that arises from the operation of a wide variety of components. In a fuel cell vehicle, for example, the operation of the fuel cells generates not only electrical energy but also heat that has to be dissipated. The same applies analogously to the operation of an electric motor or an internal combustion engine of a vehicle.

To cool the cooling system, these are connected not only to at least one heat source, but also to at least one heat sink. In this way, a refrigeration cycle with a circulating coolant can be formed. At the same time, the cooling system can be used not only for cooling but also for heating a component and/or a working medium. The term "cooling system" therefore actually describes a system for temperature control. If a cooling system is discussed below, this term is therefore understood to mean a temperature control system.

In order to effectively dissipate heat, the performance of a cooling system must be adapted to the current cooling requirement. It should be noted that the cooling capacity has an upper limit. If the temperature of a component to be cooled cannot be kept below a maximum limit with maximum cooling performance, the component can be damaged due to overheating or even be completely destroyed. Therefore, in this case, the performance of the system must be limited (“derating”), which is achieved by reducing the heat input into the system.

In order to determine the point in time when derating is to be carried out, the temperature of the cooling system is measured at a specific point and compared with a limit value in the prior art. If the limit value is reached, the heat input into the system is reduced, for example by reducing the power of an electrical machine that is to be cooled and is connected to the cooling system. In this way, the temperature in the cooling system can be reduced. Due to the inertia of the system, however, there is a risk that the target will be overshot and thus sufficient cooling will no longer be achieved for the at least one component to be cooled. This can therefore be damaged. Due to the inertia of the system, it can also happen that--particularly in the case of a particularly high component output--there is a delay in recognizing the warming-up of the coolant. It is true that one or more adjustments can be made so that the system settles around the limit value. However, this takes time and can also be at the expense of the component to be cooled.

Since the cooling requirement can vary greatly from component to component, a vehicle often has several cooling systems that are operated at different temperature levels. The temperature limit values of these cooling systems also differ accordingly. Compliance with these limit values must be monitored during operation of these cooling systems.

The invention is therefore based on the object of specifying a method for operating a cooling system which helps to avoid the problems mentioned above. In particular, as stable a state of equilibrium as possible should be achieved in the cooling system.

To solve the problem, the method with the features of claim 1 is proposed. Advantageous developments of the method according to the invention can be found in the dependent claims. In addition, a control unit for carrying out the method is specified.

Disclosure of Invention

In the proposed method for operating a cooling system, which is used to cool at least one component in a vehicle using a circulating coolant, derating is carried out to maintain a maximum cooling capacity of the cooling system. According to the invention, the point in time of the derating is determined on the basis of a model that takes into account the physical relationships between the coolant temperature and the component temperature.

The proposed model-based approach has the advantage over the conventional approach described above that taking into account the physical relationships between the coolant temperature and the component temperature enables the component temperature to be precisely adjusted to a predetermined maximum limit value. That means an over oscillate and/or transient around a maximum permissible component temperature is avoided. The performance of the component does not need to be repeatedly adjusted, so both the operation of the component and the operation of the cooling system are stabilized.

The proposed model-based approach takes into account the underlying problem that during the operation of the cooling system, the increase in coolant temperature and component temperature is not equal. This knowledge is not taken into account if the derating according to the conventional approach is based solely on the coolant temperature.

At least one physical equation is preferably used to describe the physical relationships between the coolant temperature and the component temperature. This is then used as a basis for the model. The use of a physical equation has the advantage that the method can be carried out with the aid of a computer. Because the physical equation does not change, only the input variables to be used in the equation.

Furthermore, a predefined maximum permissible component temperature is preferably used as the input variable. This means that in the present case a target or target variable is used as the input variable. With the help of the model or the physical equation, the required performance of the component can then be determined and, if necessary, adjusted accordingly.

Furthermore, it is proposed that the heat input into the cooling system, which is required to maintain the maximum permissible component temperature at the maximum cooling capacity of the cooling system, is determined with the aid of the model. The determined heat input can then be used as a reference value, so that a comparison with the current heat input into the cooling system is possible.

In a development of the invention, it is therefore proposed that the current heat input into the cooling system is determined. For this purpose, the current component temperature is preferably measured or modeled. Knowing the current component temperature or its gradient and knowing the performance of the component, the coolant temperature and the coolant mass flow, the current heat input into the cooling system can then be determined.

Due to the fact that not only the current component temperature is taken into account when determining the current heat input into the cooling system, but also the temperature gradient or the temperature curve, a derating strategy can be selected which may represent a less severe intervention in the system and/or first take effect at a later date. Because the temperature gradient or temperature profile is more meaningful than a single temperature reading.

Furthermore, it is proposed that the derating strategy be adapted to the current operating mode of the vehicle. Known operating modes of a vehicle are, for example, "comfort mode", "eco mode" or "sport mode". Depending on the vehicle's current operating mode, the timing of the derating can then be postponed and/or the severity of the intervention can be adjusted.

In addition, a control unit is specified which is set up to carry out the method according to the invention described above. In particular, the physical relationships between the coolant temperature and the component temperature can be stored in the control unit, preferably in the form of at least one physical equation. With the help of the control unit, the required cooling power to maintain the maximum permissible component temperature and/or the current heat input into the cooling system can then be determined.

Advantageously, several derating strategies are stored in the control unit, which allow the derating to be adapted to a specific operating mode, such as “comfort mode”, “eco mode” or “sport mode” of the vehicle.

• 1 ein Blockdiagramm zur Darstellung des Ablaufs des erfindungsgemäßen Verfahrens,
• 2 a) ein Diagramm zur Darstellung der Kühlmittel- und der Komponententemperatur über die Zeit und b) ein Diagramm zur Darstellung der Leistung über die Zeit, wenn ein Derating nach dem erfindungsgemäßen Verfahren durchgeführt wird, und
• 3 a) ein Diagramm zur Darstellung der Kühlmittel- und der Komponententemperatur über die Zeit und b) ein Diagramm zur Darstellung der Leistung über die Zeit, wenn ein Derating nach dem eingangs beschriebenen konventionellen Verfahren durchgeführt wird.

The invention is explained in more detail below with reference to the accompanying drawings. These show:

• 1 a block diagram to show the sequence of the method according to the invention,
• 2 a) a diagram showing the coolant temperature and the component temperature over time and b) a diagram showing the power over time when derating is carried out according to the method according to the invention, and
• 3 a) a diagram showing the coolant temperature and the component temperature over time and b) a diagram showing the power over time when derating is carried out according to the conventional method described at the outset.

Detailed description of the drawings

Using the block diagram of 1 is an example of the process of an inventive procedure described. The physical model on which the method is based is given here as black box 1. By entering specific signals or input variables, a target variable can be determined with the aid of the model, this being the maximum component power P _Kom,max . The maximum component power P _Kom,max specifies the power that does not lead to an overload of the cooling system. If _{PCom,max exceeds} the current power, derating must be carried out or the power of the component must be adjusted accordingly.

In order to _{arrive at P Kom,max} as the target variable, the current component temperature T _Kom,akt is first measured or modeled. Based on the current component temperature T _Kom,akt , a trajectory is created with the maximum permissible component temperature T _Kom,max as the target value. A PT1 filter 2 is used here for this purpose. _{The current coolant temperature T Küh,akt and the maximum coolant temperature T Küh,max,} which is assumed to be known, are included as additional input variables in the physical model (Black Box 1). On the basis of these variables and the maximum cooling capacity of the cooling system, the maximum component capacity P _Kom,max can then be determined with the aid of the physical model.

Based on 2a) and 2 B) as well as the 3a) and 3b) the advantages of the method according to the invention compared to the conventional method are described below.

the 2a) and 2 B) show typical curves when carrying out the method according to the invention. The upper diagram shows the curves of the component _{temperature T Kom,akt} and the coolant temperature T _Küh,akt. Also entered is the maximum permissible component temperature T _Kom,max .- The diagram below shows the course of the maximum component power P _Kom,max .

With model-based derating according to the 2a) and 2 B) Due to the consideration of the physical relationship between the coolant temperature T _Küh,akt and the component _{temperature T Kom,akt} the component _{temperature T Kom,akt} can be controlled exactly to the limit value T _Kom,max. This means that the limit value is not exceeded or that overshooting and transient effects around the limit value are avoided. Because even before the limit value T _Kom,max is reached, the limitation of the component power P _Kom,max associated with the derating begins.

the 3a) and 3b) show, in contrast, typical curves when the conventional method is carried out. The upper diagram again shows the curves of the component _{temperature T Kom,akt} and the coolant temperature T _Küh,akt. Also entered here is the maximum permissible coolant temperature T _Küh,max. . The diagram below shows the course of the maximum component power P _Kom,max .

With normal derating according to the 3a) and 3b) the physical relationship between the coolant temperature T _Küh,akt and the component _{temperature T Kom,akt is} not taken into account. Instead, only the coolant temperature is looked at. If this reaches the maximum permissible coolant temperature T _Küh,max , the derating process is initiated. However, the increase in coolant temperature T _Küh,akt and the increase in component _{temperature T Kom,akt} are not the same, so that there is an overshoot and a transient with respect to _{component temperature T Kom,akt} and component power P _Kom,max there is a power P _{Kom,max that} is required to maintain the maximum permissible coolant temperature T _Küh,max.

Claims (7)

Method for operating a cooling system, which is used to cool at least one component in a vehicle using a circulating coolant, in which derating is carried out to maintain a maximum cooling capacity of the cooling system, characterized in that the point in time of the derating is determined on the basis of a model , which takes into account the physical relationships between the coolant temperature and the component temperature. procedure after claim 1 , characterized in that at least one physical equation is used to describe the physical relationships between the coolant temperature and the component temperature on which the model is based. procedure after claim 1 or 2 , characterized in that a predetermined maximum permissible component temperature is used as an input variable. Method according to one of the preceding claims, characterized in that the heat input into the cooling system which is required to maintain the maximum permissible component temperature at maximum cooling capacity of the cooling system is determined with the aid of the model. Method according to one of the preceding claims, characterized in that the current component temperature is measured or modeled and, knowing the current com ponent temperature or its gradient as well as knowledge of the performance of the component, the coolant temperature and the coolant mass flow of the current heat input into the cooling system is determined. Method according to one of the preceding claims, characterized in that the derating strategy is adapted to the current operating mode of the vehicle. Control unit set up to carry out a method according to one of the preceding claims.

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