Modeling and simulation performance analysis of wind tunnel electric putter control system

In a hypersonic wind tunnel, the motion of the electric putter Y mechanism needs to be controlled synchronously, and the accuracy or control performance of the system's synchronous motion control directly affects the running quality of the wind tunnel. Based on the deviation coupling mechanism of output displacement, the paper puts forward the synchronous control system of the model mechanism electric putter Y mechanism, and establishes the dynamic model of the mechanical system, current control ring, speed control ring and position control ring of the electric putter Y mechanism. A closed-loop synchronous three-ring control system is designed, and performance simulation is carried out. The results show that the system has fast synchronous response speed, high accuracy of synchronous displacement and synchronous speed control, and the system has strong robustness.


Introduction
Wind tunnel is a test device used to simulate the movement of aircraft in the atmosphere, for the model to carry out force test, heat test, wind tunnel field test test, stage separation and multibody separation test. The wind tunnel device has a synchronous control system that supports the synchronous motion of the support mechanism, which has a control accuracy or control performance, which directly affects the operation quality of the wind tunnel. At present, the synchronous control system mainly has the control strategies such as parallel synchronous control, main command reference synchronous control (1) , main-machine synchronous control (2) , and cross-coupling synchronous control, wherein the coupling synchronous control strategy includes the cross-coupled type (3) , the adjacent cross-coupled control (4) , the deviation coupling (5) , and other forms of coupling different control strategies. Parallel control is one of the simplest and direct synchronization control strategies. Its advantage is that the synchronization performance of the system is better in the start-up and stop phase, but the whole system is open-loop control. When one of the subsystems is disturbed in the running process, There will be a great deviation between subsystems, that is, the synchronization performance of the whole system is poor. The master-slave synchronization control strategy takes the output of the master subsystem as the input of the slave subsystem, and any reference input or disturbance loaded on the master subsystem will be reflected and followed by the slave subsystem. However, any disturbance from the subsystem will not be fed back to the master subsystem, so when the load of the slave subsystem changes, the synchronization accuracy between the subsystems can not be guaranteed. The cross-coupling synchronization control strategy is mainly to the output of the subsystems of the velocity or displacement, comparing two synchronization error, and attach it as a reference input signal feedback to each subsystem of control circuit, and its compensation, to reflect any subsystem of load changes, thus make the system get good synchronization control precision. However, the synchronous control strategy for wind tunnel model mechanism is mainly parallel synchronization control strategy. The control method is simple and low cost, and is mainly used in the case of high stiffness of synchronous connection mechanism. In this paper, based on the synchronization accuracy requirement of the electric push rod Y synchronous mechanism system in a wind tunnel, the mathematical model of the mechanism synchronization control system is established by using the cross coupling synchronization control strategy, and the simulation performance of the system is analyzed. In order to realize the synchronous motion of Y mechanism with high precision. 2. Mathematical model of wind tunnel electric putter control system 2.1 Composition of the wind tunnel electric putter control system The structure of the electric putter Y mechanism control system of a wind tunnel model is shown in Figure 1 as a two-axis synchronous control system. The system is a cross-coupled synchronous control system consisting of the active axis PID closed-loop control system and the driven axis PID closed-loop control system. The closed-loop control system consists of PID control regulator, motor driver, servo motor system and its current ring control system, speed ring control system and its detection system, driven Y mechanism and its displacement detection system. The electric putter Y mechanism of the wind tunnel model is shown in Figure 2. Its mathematical models include the load mechanisms such as pushrod-driven load motion, screw nut power drive, screw rotation, and mathematical relationships or equations for permanent magnetic synchronous motor (PMSM) power drive units. The nut, pushrod and other load power parameters such as the pushrod mechanism drive load along the Y direction to make straight motion, and the Y-oriented end moving mechanism of its drive, are converted to the motor output shaft by the ball screw drive, and the equivalent integrated load torque L T and equivalent integrated load rotation L J inertia of the electric putter Y mechanism of the wind tunnel model are respectively.
In the form, h P is the vice-lead of the ball screw nut,  is the positive efficiency of the ball screw nut sub-feed, a F is the power of the pushrod to drive the load mechanism, In the formula, em T is the electromagnetic torque generated by the motor；and m is the mechanical angular velocity of the motor rotor and its connected screw shaft, which is present with the motor's electric angle speed

Dynamic equations of permanent magnetic synchronous motors
The parameters of the permanent magnetic synchronous motor used by the wind tunnel model mechanism are shown in Table 1.  Figure 1 shows the synchronous control system of the electric pushrod Y mechanism, the power drive device is the AC servo permanent magnetic synchronous motor (PMSM) system. In order to simplify the system, the In the formula, q u , q i , and f  , respectively, the stator q -axis voltage, current, and the components on the permanent magnetic chain q -axis; q L is q -axis inductor, n p is motor pole-positive, t k is electromagnetic torque constant.

Control model of electric pushrod drive Y mechanism
The system shown in Figure 1 is a two-axis synchronous control system, and the structure of each axis system is identical, so only one of the axis systems needs to be used to establish its control structure model.
Take the Laplace transform of equations (4) and (5) to draw the open-loop control system of the electric push rod control system, as shown in figure 3.
In the formula, pwm T is the time constant of the inverter power supply, an pwm K is the inverter magnification factor.
The establishment of an electric pushrod single-axis control system for three-ring control, such as current, speed and position, is shown in Figure 4. In the figure, In the formula, p K is the proportional adjustment parameter of the current ring or speed ring, and i T is the integral time adjustment parameter of the current ring or speed ring. The position ring regulator of the electric pushrod single-axis control system is used with PID regulator, which has a transfer function of In the formula, w K is the proportional adjustment parameter, wi T is the integral time adjustment parameter, and wd T is the differential time adjustment parameter.
3. Simulation performance analysis of the synchronous control system of electric putter

Simulation performance analysis of current ring control
The performance of the electric putter control system of the wind tunnel model depends on the vector control strategy of the permanent magnetic synchronous motor. In the final analysis, the control of the motor stator current, high-performance electromechanical servo system performance depends on the optimal performance of each ring, and the performance of the outer ring depends on whether the inner ring performance is optimal. Therefore, the current ring occupies an important position in the whole electromechanical position servo system, which is the key to improve its response speed, control accuracy, and improve the performance of the system. The permanent magnetic synchronous servo motor uses the voltage inverter as the control object of the current ring, and its transfer function is shown in the equation (6). Because its current feedback signal contains a large number of harmonic components affecting the stability of the system, the harmonic component is filtered by adding inertia (filtering) in current feedback, and the inertia link of the time constant equal is set at the given input of the current ring to compensate for the time delay caused by the filtering link, and its transfer function is If the control system meets the conditions: 1) the current ring response speed is fast enough, the cross feedback item n f p  in Figure 5 In the formula, pass gain of the current ring. The closed-loop system of the current ring is compared with the second-order system in the standard form, and the system is parameterised with the second-order optimal law (the optimal damping ratio is 0.707). That is, the optimal damping ratio of the current ring system is 0.707, then the formula (11)    In the absence of a regulator, the speed ring is unstable and needs to be comprehensively corrected, with PI regulator (7) to turn the speed ring into a type I system, with the open loop transfer function is In the formula, is the open-loop gain of the speed ring.
By phase margin 30 The outer ring of the wind tunnel electric pushrod synchronous control system is the position ring. The control object sits on the position ring, which includes the speed ring and the end of the pushrod ited, the Y-toward mechanism, which is adjusted by PID to form a 5th-order   Figure 7 is a step response graph for the output of the driven axis Y2, which is suddenly disturbed by the load. Figure 7(a) is the step response performance graph for the active axis, and Figure 7(b) is the step response performance graph for the driven axis. Comparing 2 graphs shows that the synchronization error of the system is compensated and has good dynamic response performance. Figure 7(c) is the synchronous error response curve of the system used for disturbance action, the maximum dynamic error is not more than 0.6mm, indicating that the dynamic error of the system is small, less than 1.2mm required by the system, and the steady-state error is zero, and has good anti-jamming ability.
(2) Simulation performance analysis of speed synchronous control of electric putter system When the wind tunnel model body electric putter system is given a reference speed of 300mm/s, when the system reaches a steady state, that is, when the simulation time is 0.15s, the active axis Y1 suddenly applies a interference load of 50N size, the step response curve of the active axis Y1 and the derived axis Y2 output speed and its synchronous control error response curve are shown in

Conclusions
(1) The synchronous control system of wind tunnel electric putter based on the deviation coupling mechanism of output displacement is proposed, and the structure and composition of the synchronous control system are introduced.
(2) For the wind tunnel model electric putter Y mechanism synchronous control system, the pushrod mechanical system, current control ring, speed control ring and position control ring, respectively, to establish a dynamic mathematical model; (3) The three-ring synchronous control system of the electric putter Y mechanism of the wind tunnel model was adjusted, and the three-ring synchronous control system of the electric putter Y mechanism with excellent dynamic performance was designed.
(4) The performance simulation results of the electric putter Y mechanism synchronous control system of the wind tunnel model are analyzed, and the results show that the system has fast synchronous response speed, high synchronous control displacement and speed accuracy, and the system has strong robustness.