In bad environment, the speed sensor in power transmission system will fail, which results in low switching frequency limitation in low speed operation. At this time, the traditional direct torque control system is used to search the optimal motor parameter control point from a single point, and there is a high torque ripple. Therefore, a torque controller based on improved genetic tabu algorithm is proposed. The controller controls the motor’s torque, speed and angle through the torque control system based on DSP, and gives the torque control instructions based on the improved genetic tabu algorithm control scheme to realize the accurate control of the power transmission system’s torque. The speed controller adopts the improved genetic tabu algorithm PID controller to improve the torque control performance of the electric drive system. Tabu search method is used as mutation operator of genetic algorithm to avoid overshoot of PID speed controller in electric drive torque control system, which makes the torque controller keep stable torque ripple under low speed operation and enhance the stability of electric drive system. The experimental results show that the method can effectively optimize the torque performance of power transmission system and obtain stable torque waveform. With the large-scale construction of high-speed and heavy-haul trunk railway network, large-scale electric drive system is widely used in the field of electric locomotive driving. In harsh environment, the power transmission system of torque control and the speed sensor will fail, which will be limited by low switching frequency under low speed operation, resulting in the danger of sudden stop of locomotive power [1?2]. Therefore, it is of great significance to optimize the direct torque controller in the power transmission system and improve the operation efficiency of the transmission system. However, the low switching frequency restriction leads to the high torque ripple in traditional direct torque control system [3?5]. At present, there are many problems in the design of torque controller, such as the torque control method based on space vector modulation proposed in reference [6]. It can complete the torque control by reducing the fixed switching frequency of the torque ripple at low speed. However, this method requires high stability of the torque ripple and has some limitations.
Literature [7] divides the original system into three parts to obtain more voltage vectors, and precisely controls the torque through a multi-stage hysteresis structure. However, it needs a lot of calculation and the control efficiency is low. Document [8] combines direct torque control and DTC? SVM method. In the initial stage, DTC? SVM method is used to enhance the dynamic response performance, while DTC? SVM method is used to reduce the torque ripple in the steady state. However, this method has the problem of high energy consumption. In order to solve the above problems, a torque controller optimized by improved genetic tabu algorithm is proposed. The controller uses a DSP chip to control the motor’s torque, speed and angle.
Based on the improved genetic tabu algorithm control scheme, the torque control instructions are given, and the precise control of the power transmission system’s torque is realized. Torque control system contains more harmonic and pulsation factors, and the accuracy of speed estimation is low. In order to improve dynamic response efficiency, speed estimation should be enhanced. The torque control circuit module based on DSP (Digital Signal Processor) chip can control the motor torque quickly and accurately. By controlling the motor’s torque, speed and angle, the circuit module gives the torque control instructions based on the improved genetic tabu algorithm control scheme, and achieves the effective control of the power transmission system’s torque. The hardware structure of the torque control system based on DSP is shown in Figure 1, which mainly includes the main circuit hardware module and the control circuit hardware module. The main circuit hardware module is composed of uncontrolled rectifier circuit and IPM intelligent three-phase inverter bridge power module. The uncontrolled rectifier circuit can convert the input three-phase AC into DC, and use DC as the power supply for AC speed regulation. IPM Intelligent Three-phase Inverter Bridge Power Module can convert DC voltage into controllable voltage for power transmission system operation. If there is a fault, the power module can cut off the three-phase inverter bridge independently and quickly to ensure the smooth operation of the transmission system.
Digital signal processing chip (DSP) TMS320F240 is the core operation module of power transmission system. Its core has high operation performance and reliability. The designed torque control system is used as the arithmetic module to realize the torque control. The event manager in the chip of TMS320F240 can provide a high-speed and efficient control method for power transmission system. This high-speed real-time operation performance is based on the torque current and speed information provided by the current detection and speed detection module, and the precise control of the torque is achieved by improving the genetic tabu algorithm.
As the key operation module of the torque control system, the TMS320F240 chip can better realize the dynamic and static performance of the torque control system. The signal processing circuit of the current and speed sensor performs differential processing and isolation protection for the motor signal and the encoder encoder signal in the electric drive system, thermostatic element so as to ensure that the sensor signal of the motor and the encoder can be transformed into the signal recognized by the DSP chip. The DSP chip is a high-efficiency microprocessor, which can control the torque, speed and angle of the power transmission system, ensure that the transmission system runs according to the set instructions, and greatly improve the performance of the system. Based on the above analysis of the torque control circuit structure, the torque control system as shown in Figure 2 is modeled.
In the structure of the torque control system given above, the speed regulator can realize the closed-loop speed, and its output is the given value of the electromagnetic torque of the motor; the voltage source inverter sets a reasonable voltage based on the electromagnetic torque value of the motor, and acts on the voltage of the induction motor, thus driving the operation of the overall drive system. The speed regulator is realized by PID controller based on Improved Genetic Tabu algorithm. According to the requirement of torque control of electric drive system and the fluctuation of response curve, the rising time is regarded as the speed index of predicting motor. Through acceleration based on the original soft start device, the output and speed error of the controller in the PID speed regulator are included in the objective function. The objective function optimizes the parameters. Good torque control performance of electric drive system.
In order to solve the problem of chromosome similarity and mutation probability in crossover algorithm of genetic algorithm, which causes the algorithm to fall into local optimal solution too early, tabu search method is regarded as mutation operator of genetic algorithm, which can avoid the overshoot problem of PID speed controller in electric drive torque control system, and make the torque controller keep stable torque ripple under low speed operation, so as to ensure electric drive. The system runs smoothly.
In the formula, I denotes the number of parameters, setting the number of parameters of the PID speed controller is 9, and the range of value [R] is [0,20]. Considering the absolute error time integral performance index as the minimum objective function of parameter selection, satisfactory dynamic characteristic parameters can be obtained. The output of the controller in the PID speed controller is included in the objective function. The objective function optimizes the parameters to avoid too high operation energy. In [J=w1 e(t) w2 u 2(t)dt w3.t u](2), e(t) is the error of the torque control system; u(t) is the output of the torque PID speed regulator, [tu] is the rising time, [w1], [w2], [w3] is the weight. In the formula, [w3] is the weight and [w4? W1], [ey (t) = y (t) – y (t – 1)], [y (t)] is the output of the PID speed regulator. Here we take [w1 = 0.999,] [w2 = 0.011,] [w3 = 1.96,] [w4 = 148]. Since the size of population is the premise of genetic algorithm, it is necessary to deal with the size of population first. When it is too small, the diversity of the population will be affected, and the range of optimum selection will be narrowed, which will lead to the early end of the collection work; when it is too large, more work will be needed to calculate, which will weaken the role of improving genetic tabu algorithm. Usually, when the initial population is relatively large, many solutions can be solved simultaneously, and the global optimal solution can be obtained easily. The population size is 2 times the encoding length, which is expressed as [n=2 * l=180]. By selecting different crossover probability [pc], the operation and function of genetic tabu algorithm can be improved. According to specific needs, [pc] itself can change at any time. [pc = PC1 (pc1-pc2) (f’-favg) fmax-favg, f’> favgpc1, F’setting [pc1 = 0.9], [pc2 = 0.6]. In formula 4, [fmax] denotes the maximum fitness of the population, [favg] denotes the average fitness of the population, [f’] denotes the greater fitness of two crossed individuals, and [f] denotes the fitness of the mutated individuals. Tabu lookup technique is used as mutation operator of genetic algorithm to make up for the deficiency of genetic algorithm.
It can optimize the speed controller of PID and avoid overshoot of torque. After completing the above settings, the genetic algorithm operation process as shown in Figure 3 is used to complete the search of the optimal control results of the PID speed regulator, which makes the torque controller maintain stable torque ripple and enhance the stability of the power transmission system at low speed. The initialization function of the system is implemented in gon2013_open function, which is composed of data structure development and equipment initialization.
In order to verify the performance of the method, a simulation model based on MATLAB/Simulink is built to simulate and analyze the selected 9 kW 8/6 pole power transmission system. The simulation circuit voltage is 150 V and the reference current is 10 A. Fig. 4 and Fig. 5 show the simulation waveforms of space vector modulation method and this method when the motor speed is 100 r/min and the load torque changes from 0.4 s to 3 N.m. From the analysis of Fig. 4 and Fig.
5, it can be concluded that when the load changes suddenly, the rotational speed drops to 92 r/min instantaneously and reaches steady state again through 0.
13 s. When the load of the power transmission system fluctuates instantaneously, the speed drops to 94 r/min and reaches steady state again after 0.02 s. The main reason is that this method greatly improves the control accuracy and efficiency, the response speed of the power transmission system is significantly improved, the performance of the system against adverse environmental interference is enhanced, and the steady state error of the system is reduced. As shown in Fig. 6, under the premise of running speed of 1 000 r/min, the torque diagrams synthesized by the two methods show a downward trend and an increase in average torque compared with the discrete space vector modulation method. In this paper, a torque controller based on improved genetic tabu algorithm is proposed. The controller controls the motor’s torque, speed and angle through the torque control system based on DSP. The torque control instructions are given based on the improved genetic tabu algorithm control scheme, and the accurate control of the power transmission system’s torque is realized. The speed controller adopts the improved genetic tabu algorithm PID controller to improve the torque control performance of the electric drive system. Tabu search method is used as mutation operator of genetic algorithm to avoid overshoot of PID speed controller in electric drive torque control system, which makes the torque controller keep stable torque ripple under low speed operation and enhance the stability of electric drive system. The experimental results show that the method can effectively optimize the torque performance of power transmission system and obtain stable torque waveform.