Motion control has obvious period characteristics, it is a combination of a variety of high-tech, used to push industrial automation, office automation and home automation to a higher stage. At present, motion control is mainly composed of three parts: variable frequency drive (VFD), motor and controller.
VFD local
The center of VFD is power electronics and control methods.
1) Power electronic devices Power electronic devices are in the circuit to play an on-off role and complete a variety of conversion devices, VFD is the installation of this converter, so it is carried out with the development of inverter parts, the quality of inverter components depends on its on-off ability, accept on-off current and rated voltage; The size of the loss in the on-off process, such as saturation voltage drop and switching loss, determines the efficiency and volume of the VFD; Switching losses are related to the switching frequency; The switching frequency is related to noise, but also to the output voltage and current waveform. That is to say, power electronic devices should be carried out in the direction of high voltage, large current, high switching frequency and small on-voltage drop. Thyristor is a semi-controlled device, belonging to the first generation of products, but low modulation frequency, complex control, low efficiency, large capacity, high voltage, long history, whether used as rectification or inverter, is relatively mature.
Fully controlled devices GTO thyristors and BJTs, whether it is assembling DC choppers or assembling VFDs, GTO thyristors have a monopoly on the application of electric locomotives. This is also a serious scientific research topic organized to tackle during the "Eighth Five-Year Plan" period in China. However, the use of GTO thyristor VFDs for other centers is controversial because the off-current gain of GTO thyristors is too small, overcurrent maintenance is difficult, and the modulation frequency is low. DC choppers and PWMVFDs assembled with BJTs are very popular, but the output voltage does not exceed 460V and the capacity does not exceed 400kW. BJT is a current drive, large power consumption, low modulation frequency, and large noise, which is not as simple and reliable as the voltage drive of MOSFET. But the latter has a smaller capacity and a lower output voltage, and there are not many competitive products in the market.
In motion control, the new generation of power electronics devices are IGBT and MCT: the former is MOS driving BJT, the advantage is that the capacity and voltage have surpassed BJT, and there is a tendency to replace it; The latter MOS drives thyristors and theoretically has the advantages of both. These two new devices have mature products, IGBT has been carried out to the fourth generation, and at present, foreign countries are transferring the consumption process of microelectronics to power electronics, so that application-specific integrated circuits () are produced. The intelligent device that combines the driving circuit and maintenance circuit of the IGBT is called IPM, and the switching power supply is combined with the IPM, which makes VFD more reliable, once became the leading product of speed regulation, will replace DC speed regulation, and the 21st century will be the period of AC speed regulation.
2) Control method VFD adopts different control methods and has different speed adjustment performance, characteristics and uses. Control methods are broadly divided into open-loop and closed-loop control. Open-loop control includes U/f (voltage and frequency) proportional control method; The closed loop includes slip frequency control and various vector controls. From the perspective of development history, it is also from open loop to closed loop. The usual vector control is comparable to the armature current control of DC motors. Now the AC motor parameters can be directly stopped direct torque control, which is convenient and accurate, and the control accuracy is high.