Research On Modeling And Control Technique Of Power Quality Of Spot Welding Machine Cluster

AC spot welding machine is widely used as a kind of power load. Some noticeable power quality problems are caused by AC spot welding machine, such as voltage fluctuate and flicker, harmonic aberrance, and three phase unbalance etc. The thesis takes all the spot welding machines under the management point as a whole, and defines the concept of spot welding machine cluster. Spot welding machine cluster is a typical three phase unbalanced load. The thesis researches on the working principle, power quality problems and the management method of spot welding machine cluster.Load model of spot welding machine cluster based on Least Squares Support Vector Machine (LS-SVM) is put forward. Active power model and reactive power model of spot welding machine cluster can be get according to testing data using the modeling method with better generalization ability. In order to improve the fitting speed and precision, the load model of spot welding machine cluster based on Least Squares Support Vector Machine using Bayesian evidence framework (BLS-SVM) is put forward. The simulation results indicate the modeling method based on BLS-SVM can realize better fitting effect than LS-SVM. For the practice application of the load model, pruning method is used to get the simplified model of LS-SVM and BLS-SVM. Furthermore, a kind of power quality model of spot welding machine cluster is put forward, which can reflect voltage fluctuate and flicker, harmonic, and three phase unbalance of spot welding machine cluster at the same time. The applicability and validity of the model is proved by the simulation result.Facing to the compensation of three phase unbalanced load such as spot welding machine cluster, Static var compensator (SVC) with the ability of controlling single phase is applied. The working principle and characters of SVC (Thyristor Controlled Reactor+Thyristor Switching Capacitor, TCR+TSC) is introduced. And the engineering design method of compensation for spot welding machine cluster is researched on. TSC branch and compensation capacity are designed with emphasis. In the compensation of spot welding machine cluster, the influence of 3th harmonic and var fluctuation should be considered as an emphasis when designing passive filter branch. The most suitable design method of compensation for spot welding machine cluster is proposed by means of simulation.Because of the voltage aberrance and three phase unbalance, p-q and ip-iq based on instantaneous reactive power theory may cause obvious error in the detecting of reactive power and negative component. The method of compensation based on synchronous symmetrical component for unbalanced load is introduced in the thesis. With positive sequence voltage synchronous coordinate, the method uses rolling symmetrical component method to obtain compensator admittance directly. This method can realize better compensation effect because the three phase voltage extraction method can remove the interference of net voltage distortion effectively and rolling symmetrical component method can remove the influence of current harmonics.SVC is a kind of D-FACTStechnology facing to the compensation of power load, and the design level of controller is critical point to realize good compensation effect. Aiming at the power quality characteristics of spot welding machine cluster, a kind of compound control strategy is brought forward. The strategy can not only realize comprehensive compensation of negative sequence and reactive in faster response speed, but also can improve the accuracy of var compensation. Robust PID controller based on H∞control theory is researched in the thesis. Simulation results show that robust PID control system has significant advantages in overshoot, accommodation time and the ability of anti-interference. So robust PID controller of SVC is raised to realize precise of phase difference and perform better ability of anti-interference.The simulation model of SVC system in the compensation of spot welding machine cluster is built, and the compensation effect is analyzed. At the end, the experiment is done. Frock of spot welding machine cluster is put up and experimental prototype is made. The results of simulation and experiment demonstrate that the SVC device designed in the thesis can resolve the power quality problems of spot welding machine cluster such as reactive power, unbalance and harmonics.