How to calculate the temperature field of hub motor? Five calculation methods

The temperature field calculation of hub motor is to calculate the temperature rise of some key parts in the hub motor and analyze the overall temperature distribution. It is an essential link in the design of hub motor. Let's sum up the following methods of calculating the global wind field.

 

1. Simplified formula method

 

The simplified formula method is simple and fast, and is generally used by hub motor manufacturers to calculate and estimate the average temperature of core and winding. It assumes that there is no heat exchange between the effective part and the end of the winding, and the heat dissipation coefficient used is mostly empirical value or experimental value, so the calculation result is close to the actual value. However, this method can only estimate the overall average temperature rise of the core and winding, ignoring some mechanical losses and eddy current losses, so the calculation results are relatively rough.

 

2. Equivalent thermal path method

 

(1) The equivalent thermal path method combines the mature circuit theory with the thermal circuit method to calculate the thermal path. It is based on many assumptions, including replacing the real heat source with the centralized equivalent heat source, replacing the real thermal resistance with the centralized equivalent thermal resistance, and transforming the temperature field into the equivalent heat path calculation with centralized parameters.

 

(2) The equivalent thermal path method has the advantages of simple calculation and small workload, and can obtain the average temperature of core and winding by calculation. However, the traditional equivalent thermal path method can only get the average temperature of the core and winding, and it is powerless for the distribution of component temperature and the location and value of hot spots. It is generally used to guide the design, manufacture and condition detection of hub motor.

 

3. Equivalent thermal network method

 

(1) Based on graph theory, equivalent thermal network method is a method of thermal field analysis using topological structure of network. According to the structure of the calculation object, the required solution area is divided and scattered. In addition, the heat source is regarded as a point by using the method of local centralized parameters, and the heat flow is concentrated through the branches, thus forming an equivalent network, and calculating the relevant parameters of each node and branch, including the treatment of loss, thermal resistance and boundary conditions, so as to establish the physical model. According to the physical model and Kirchhoff's law of heat flow, the temperature equations are listed and solved by computer with reasonable algorithm.

 

(2) Because the physical concept of the equivalent thermal network method is clear, and the requirements of computer hardware resources are low. Therefore, this method is widely used in hub motor design and condition monitoring.

 

4. Finite element analysis method

 

(1) The finite element analysis method uses the method of mathematical discretization to divide the model into several small unit modules, so that the macro problem of the temperature field is transformed into a micro problem, and then the temperature rise of each point of the hub motor model is calculated.

 

(2) The finite element method has the advantages of flexible element selection, high calculation accuracy and good boundary adaptability. Moreover, the temperature distribution and temperature rise position of the hub motor model can be obtained by using the finite element method, so it is widely used at present. However, due to its large amount of calculation, complex and difficult boundary treatment, high requirements for the computer and long calculation time, it is more used in the design and manufacturing process of hub motor.

 

5. Parameter identification method

 

(1) The parameter identification method is to identify the resistance of the stator and rotor windings of the hub motor in normal operation through parameter identification and technology. According to the linear relationship between the metal material selected by the resistance and its temperature in a certain range, the approximate temperature of the stator and rotor winding is deduced. The key point is how to derive the identification algorithm of winding resistance.

 

(2) Because of its simplicity and practicality, this method is generally used to monitor and calculate the stator and rotor temperature of hub motor. However, it can only get the average temperature of one phase winding on the stator and rotor of hub motor in steady state.

 

The above is about how to calculate the temperature field of hub motor. From the above five methods, each method has its own advantages and disadvantages. The simple formula method only estimates the temperature rise of core and winding. The accuracy of equivalent thermal path method is low, and the value of temperature field can not be accurately obtained. The parameter calculation method is more suitable for temperature detection. Although the calculation accuracy of the finite element method is high, it depends on the computer and is time-consuming, so it is more suitable for the design and manufacture of hub motor.