Research On Key Techniques Of Vector Variable Frequency Controlled Electric Actuator

Developing a high performance vector variable frequency controlled electric actuator and researching on its key techniques is very important to enhance the performance of domestic process controlled instrument. Aiming at the reality of huge gap between domestic and overseas’ advanced production, a high performance vector variable frequency controlled electric actuator is oriented in this paper. The key techniques of sensorless control, motor parameter identification, dead-time compensation, positioning and torque detection are researched in theory, and more over corresponding experiments and analysis are performed in details as well.The motor parameters are identified in offline by equivalent circuit method. On the basis of analyzing the shortcoming, a new approach which can identify parameters in standstill is proposed. The motor model can be divided into two parallel submodules by the frequency of injected voltage. The motor parameters are identified both in high frequency and low frequency respectively, and consequently all the parameters are obtained. The algorithm is induced and experiments are performed. The Experimental results show that a good current decouple property is obtained by the proposed approach, so the accuracy of identification is proved. And more important, the parameters can be identified at standstill so a wider application circumstances is got compared to the equivalent circuit method.The dead-time of inverter will cause current distortion in low frequency and affects the low speed performance of electric actuators. Aimed at this problem a simple and effective compensation approach is proposed. Firstly, the zero-crossings of the current is detected indirectly by calculate the current vector angle, so error compensation caused by multiple zero-crossings which induced by the noise can be avoided. And then the theoretical step compensation voltage near zero-crossings is linearized which can eliminate error further. The verification experimental results demonstrated that the compensated current waves have nice sinusoidal performance and the current wave near zero-crossings is obviously improved. So the compensation performance is better than conventional method, and moreover, the method is simple and effective.The conventional positioning method including speed regulation and position regulation will cause high current shock. Aimed at the problem an approach that could automatically generate reference speed curve for positioning is proposed. The electric actuator can operated in low speed both at starting part and halting part, so the soft start up and soft halting is achieved. This will reduce current shock and enlarger the life as well as the accuracy of electric actuators. Moreover, different positioning curves can be generated corresponding to the target position so adaptive property is provided. Experiments with different position and different load on two different power electric actuators are performed and compared to conventional method. The Experimental results show that the proposed approach has the property of low current shock, high accuracy and rigid adaptive.An approach of detecting the torque of electric actuator by software is proposed to fulfill torque protection and solving the problem of strict installation requirement and high cost of sensor. The torque is calculated by detecting the stator flux and actual transmission ratio between motor and mechanical which is achieved by curve-fitting. Moreover, in the stator flux calculation part the offset in current sampling is compensated by PI regulator and the divergence of integration is eliminated, consequently, an accuracy stator flux is obtained. The Experimental results show that an accuracy output torque can be obtained by the proposed approach.A vector variable frequency controlled electric actuator is developed and the hardware circuit as well as the software is designed. Experiments of step speed and reverse speed are performed in field. The performance between vector variable frequency controlled electric actuator and domestic as well as overseas’electric actuator is compared. The Experimental results show that the speed range could reach between 2Hz and 100Hz, the accuracy could reach 0.2%, the dead-band could reach 0.1% and the torque detection accuracy could reach 7%, the performance indices are better than overseas’electric actuator, so it lays a solid foundation for realizing the industrialization of this new type electric actuator.