Research And Application Of A Novel Cascade Adjustable Speed System

Application quantity of fan and water pump is numerous, its electricity consumption is huge, and it has the serious throttle loss in different sections of the national economy. Therefore, power saving effect of speed adjusting operation of fan and water pump is very obvious; the average energy saving electric quantity is approximately 30%. AC Speed Regulation application is mostly frequency control at present, but high-voltage frequency converting system is limited in actual use because of technology and harmonic pollution. Cascade Speed Control is a kind of reasonable scheme as fan and water pump etc.Basic principle of the domestic and foreign traditional cascade speed control and its advantages and disadvantages have been analyzed in the article, although the efficiency has been enhanced, power factor is low and the volume is huge. Based on this, inner-feeding motor has been used in the article. Senseless slip power's cycle has been prevented effectively in induction motor, rectifier, inverter transformer and power network. Power factor has been enhanced, not only device volume and production cost has been reduced, but also system power factor has been enhanced.In main circuit's designing, traditional thyristor active inverter has been replaced of PWM rectification technology. With the help of instantaneous reactive power theory, the principle that PWM rectification technology can enhance cascade speed control system power factor has been analyzed. The technology has enhanced system power factor and reduced line side harmonic content. Parameters of main power devices which include diode, IGBT, capacitor, inductance and buffer snubber circuit have been calculated in main circuit in the article.DSP control panel has been used to carry out digital double closed loop control in chopper of internal feedback chopper cascade speed control system, namely current and speed double closed loop control; current regulator, speed regulator and related hardware realization circuit have been designed. PLC has been used in process control.The system has been debugged and the massive experiments have been done in the laboratory, and adjustable-speed function has been realized. Developed internal feedback chopper cascade speed control system has been used in practical industrial field, the whole series-wound timing system can operate successfully. But there are some questions in speed control, through the analysis, the corresponding solution has been proposed.