Simulation on Operating Characteristics of Shunt DC Motor

By comparing the literature at home and abroad, according to the working process and principle of shunt excited DC motor, the working characteristics and mechanical characteristics of the motor are analyzed by Simulink software. Among them, the working characteristics cover the speed characteristics and torque characteristics, and the mechanical characteristics include the inherent mechanical characteristics and artificial mechanical characteristics. The working characteristics of motor speed and torque are analyzed when the magnetic flux and armature resistance are changed. At the same time, the effects of changing the armature voltage, armature resistance and series resistance on the inherent and artificial characteristics of the motor, and the suggestions for starting the motor are given.


Introduction
Control problem of field weakening for a separately excited DC motor system, is tackled in Zuo Z.Liu's paper.A novel constant power field weakening controller, based on nonlinear load-adaptive multi-input multi-output (MIMO) linearization technique, is developed to achieve high-performance speed tracking through rejecting load disturbance [1].Hu Hao [2] analyses the mechanical characteristics of the separately or shunt exited DC motor, and theirs difference was drawn by comparing in the paper,the accurate and reliable data was measured,and the procedure will completely meet the practical application in engineering.Bingwen Yang,etc, [3] discussed the mechanical characteristics of the separately and shunting exited DC motor,and their difference was drawn by comparing: the no-load speed is constant and independent of the voltage U, the slope of the torque speed curves decreases with increasing U,It offers the theoretical foundationr;Shuangcheng Deng,Lipei Jiang,etc.[4] introduced the dynamic mathematical model of shunt-excited DC motors in paper ,and its corresponding transient-process simulation model was set up based on Lab view software.mainlysimulating the direct start-up process with series resistance in the armature circuit.the simulation results show that the model is reliable for shunt-excited DC motors.According to the dynamic mathematical model of shunt excitation DC motor, Deng Jianguo, Rui Yu,etc, [5,6] using a dynamic simulation tool Simulink establishing model of the transient process.Chunyu Xin [7] introduces the two different kinds of speed regulation methods of shunt excited DC motor, which are not suitable for all types of loads.The excitation winding of shunt excited DC motor is parallel with the armature winding, The voltage at both ends of the shunt winding is the one at both ends of the armature, but the excitation winding is wound with a thin wire, and the number of turns are many, so it has a large resistance, so that the excitation current through it is small.The mechanical characteristics of shunt motor are relatively hard, the initial starting torque is relatively large, the speed quickly rises to the rated speed, after that, the speed no longer continues to rise, the torque also rapidly decreases, and remains stable at a level.The circuit diagram of shunt excited DC motor is shown as Fig. 1.

Figure 1. Circuit diagram of shunt excited DC motor
The excitation winding of a shunt DC motor is in parallel with the armature winding, and the relationship among the power supply voltage, armature voltage and excitation voltage as well as the one among the load current, armature current and excitation current are shown as in ( 1) :

Simulation of Working Characteristics of Shunt Excited DC Motor
The operating characteristics of shunt ecited DC motor(short form:DCmotor,the same below) includes revolution characteristics and torque characteristics.

Revolution Chericteristics
,the revolution characteristics of shunt excited DC motor are expressed as in (2) : Where, n is the motor speed, U is the power supply voltage, a R is the armature resistance, a I is armature current, e C is the electromotive force constant,  is the magnetic pole magnetic flux, and the electromotive force constant is as in (3) : Where, p is the number of poles, a is the number of parallel branches of armature winding, single stack winding ap = , single wave winding 1 a = , and the N is total number of armature winding conductors.According to the mathematical model of speed characteristic of DC motor, the Matalb program was written to draw the speed characteristic curve, and the motor speed characteristic curve under the changing magnetic flux and armature internal resistance were obtained respectively, as shown in Fig. 2 and Fig. 3.
As can be seen from Fig. 2, with the increase of armature current, when the magnetic flux increases, the RPM decreases gradually as the current increases.When the armature resistance increases, the speed also tends to decrease.But the change is not obvious.This shows that the magnetic flux has a great influence on the motor speed.

Torque Characteristic
The torque characteristics motor can be expressed as in (4) [3]: In the formula, e T is electromagnetic torque, T C is the torque constant, both are related to the motor structure.The torque constant is given as in (5) : If armature reaction is ignored, the torque is a straight line through centre point.
According to the mathematical model above, the torque characteristic curve Matlab program was written to obtain the torque characteristic curve, as shown in Figure 4.
It can be seen that the electromagnetic torque of shunt excited DC motor increases with the increase of armature current and magnetic flux, showing a linear change.

Mechanical Charecteristic
Mechanical characteristics refers to the relationship between the motor speed n and torque T when the armature voltage, excitation current and total resistance of the armature circuit are unchanged.It can be divided into inherent mechanical properties and artificial mechanical properties.

Inherent Mechanical Characteristic
The relation between speed and torque of mechanical characteristics can be expressed as in (8) [7] : Inherent mechanical characteristics refers to the motor's armature operating voltage and excitation flux are constant values, and the armature circuit is not string into the additional resistance, therefore, j R =0.

Factitious Mechanical Characteristic
Artificial mechanical characteristics are the one obtained by changing the motor circuit parameters or armature voltage artificially, generally changing only one parameter among the voltage, magnetic flux, additional resistance or armature resistance.Only the two parameters of voltage and resistance are analyzed in paper.Artificial mechanical properties of changing armature voltage.According to formula (8), the program is implemented as shown in Figure 5. Shown as Fig. 5.It can be seen that the power supply voltage is gradually reduced, and the ideal noload speed gradually decreases, but the change from no-load to full load is not large, and this characteristic is displayed as a hard mechanical characteristic.Thus, the DC motor has excellent speed regulation characteristics.When the magnetic passing is weakened, if the load torque is unchanged, the motor current will be greatly increased and overload seriously; When the theoretical speed of the motor approaches infinity or rises to exceed the allowable value of mechanical strength, it will produce a "flying car" phenomenon.Therefore, the excitation current must be added when the DC motor starts, and the excitation circuit is not allowed to be disconnected or the excitation current is 0 during operation.Artificial mechanical properties of changing armature resistance.It shows the mechanical characteristic curve of shunt DC motor when the armature resistance is changed.As shown in the figure 6, the absolute slope of the curve gradually increases and the speed decreases, making the characteristics gradually softer, but the ideal no-load speed of the motor remains unchanged.Artificial mechanical properties altering series resistance.Shown as Fig. 7, when resistance increasing, the absolute slope of the curve gradually increases, and the speed decreases,making the characteristics gradually softer, but the ideal no-load speed of the motor remains unchanged.Compared with the inherent mechanical characteristic curve, the ideal no-load speed is unchanged, but the speed drop increases, and the bigger the series resistance, the softer the characteristic becomes.

Conclusion
Through the analysis of the characteristics of shunt excitation DC motor, the conclusions are as follows: a) The speed of shunt DC motor decreases slightly with the increase of armature current, does rapidly with the increase of magnetic flux, and slightly with the increase of armature resistance.b)The electromagnetic torque of shunt DC motor increases with the increase of armature current and magnetic flux.c) When the armature voltage is changed, the ideal no-load speed gradually decreases, the no-load to full load defense interval is not large, and the characteristic curve stiffens.d) excitation current should be added when the motor starts.e) When the resistance is attached in series, the absolute value of the slope of the curve becomes larger and the characteristic curve becomes softer with the increase of the resistance,the speed decreases,so does the armature resistance increase.Therefor,if make the speed increase,decrease the resistance of armature and series resistance;If make the torque increase,then increase the resistance when the vehicle is uphill or heavy load.

Acknowledgment
Thanks for all the Chinese and foreign authors who provided the documents and other material.Jinku Li,SanYa College,item No: SYJKCP2023090; Haizhi Guo, item No: Hnjg2023-109;HaoLi,the corresponding author total number of armature winding conductors N =400, number of parallel branches a =1, Setting the three-stage magnetic flux a f =  = [0.0064,0.0122,0.0164].

Figure 2 .Figure 3 .
Figure 2. Speed characteristic curve of shunt excited DC motor with changing magnetic flux sloping curve.This shows that increasing the load of the motor will reduce the speed.

Figure 4 .
Figure 4. Torque characteristic curve of motor

R
is the series resistance outside the armature circuit.

Figure 5 .Figure 6 .Figure 7 .
Figure 5. Mechanical characteristic curve of shunt DC motor when the armature voltage changed Figure 6.Mechanical characteristic curve of shunt DC motor with changing