For the high-speed linear motor, the stability of control is very sensitive to speed measurement errors, so high-precision and real-time position and speed measurement system is crucial for the stable operation of high-speed linear motors. The current position and speed measurement methods applied to maglev trains and electromagnetic catapults can only meet the requirements of position and speed detection at speeds below 600km/h. However,it is not yet clear for speeds above 1000km/h with these methods. Optical encoders have the advantages of fast response frequency and high measurement accuracy, and are widely used for position and speed measurement for rotating motors. Its applications in linear electric fields are mainly concentrated in the field of small machining machines. In the field of large-scale linear motor applications, the operating environment of the system is complex, and lasers are prone to interference. Therefore, there is still limited research on the application of optoelectronic encoders in this field. In this paper, a laser array-based position and speed measurement system for high-speed linear motor control systems is proposed. By closed-loop joint hardware-in-the-loop simulation with motor control system, it accurately measures the position and speed of the rotator and the motor system operates well in the high-speed section.
Firstly, according to the mathematical model of a high-speed linear motor, the normalized thrust F_e/F_emax of the motor was calculated as a function of the speed measurement error δ at different speeds. Then, the impact of grating ruler vibration and yaw on speed measurement error is analyzed. The constraints condition for grating ruler and sensor spot diameter is derived. The position and speed measurement algorithm are given. In order to realize high precision speed measurement in all speed range, traditional T method and tracking differentiator are used.
Secondly, a hardware-in-the-loop simulation system for position and speed measurement was constructed based on the developed collector, pulse generator, multi-channel simulator, and controller. A mathematical model of the encoder and laser sensor array was established in the pulse generator. Pulse signals were generated based on the given position information to drive the laser, simulating the optical pulse signals generated by the encoder at different speeds. Based on the detected optical pulse signals, the position and speed of the rotor were calculated. The measurement error is quantified by comparing the data results of the given position/speed with the detected position/speed. Finally, a closed-loop joint hardware-in-the-loop simulation was conducted with the motor control system.
The experiment shows that the pulse wave after filter is good and can meet the requirements of position and speed detection at highest design speed. Simulation results show that the speed measurement error is basically stable at 0.5m/s, with a maximum value of 0.6m/s in all speed range by comparing the reference speed and position curve and measurement results. The speed measurement error can meet the error requirements of the motor control system in the full speed range. From the closed-loop joint hardware-in-the-loop simulation, it can be seen that the motor operates stably and the thrust remains basically unchanged in the entire process.
The following conclusions can be drawn from the simulation analysis: The hardware-in-the-loop simulation system for position and speed measurement based on the developed distributed acquisition equipment, pulse generator, laser generator, multi-channel simulator, and system controller has a high degree of compatibility with the actual system. It can perform hardware-in-the-loop simulation experiments on different position and speed detection algorithms, extract and analyze simulation results data at any time to quantify speed measurement errors At the same time, hardware-in-the-loop simulation was conducted with the motor control system based on RT-LAB, verifying the effectiveness of the position and speed measurement system topology network and speed measurement algorithm. The system has high integration and strong applicability, which is beneficial for improving research on position and speed algorithms, fault detection and analysis methods, and redundant control strategy. It has high guiding significance and reference value for engineering practice.
Based on the constructed hardware-in-the-loop simulation system, the fault diagnosis and fault-tolerant control algorithms, speed sensorless control method for segmented linear induction motors will be researched in the future work.