Motion control has a significant period characteristic, it is a combination of a variety of high-tech to push industrial automation, office automation and home automation to a higher stage. At present, the motion control is mainly composed of three parts: inverter, motor and controller.
1. VFD local
The center of the VFD is the power electronics and the control method.
1) Power electronic equipmentPower electronic equipment is the equipment that plays the role of on-off in the circuit and completes various conversions, VFD is the device of this conversion, so it is unfolded with the development of inverter equipment, and the quality of inverter equipment depends on its on-off ability, and accepts the current and additional voltage that are on-off; In the on-off process, the size of the loss, such as saturation pressure 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, and is related to the output voltage and current waveform. That is to say, power electronic equipment should be deployed in the direction of high voltage, high current, high switching frequency and small conduction voltage drop. The thyristor is a semi-control device, which belongs to the first generation of products, but the modulation frequency is low, the control is complex, the efficiency is low, the capacity is large, the voltage is high, and the history is long, whether it is used as a rectifier or as an inverter, it is relatively sophisticated.
The full control equipment GTO thyristor and BJT, whether it is assembled DC chopper or assembled VFD, the use of GTO thyristor in electric locomotive has a monopoly. This is also a serious scientific research topic that China has arranged to tackle during the Eighth Five-Year Plan period. However, the use of GTO thyristor VFD for other centers is controversial because the turn-off current gain of the GTO thyristor is too small, overcurrent protection is difficult, and the modulation frequency is low. DC choppers and PWMVFDs assembled with BJT are very popular, but the output voltage does not exceed 460V and the capacity does not exceed 400kW. BJT is a current drive, with high power consumption, low modulation frequency, and high noise, which is not as simple and reliable as the voltage drive of MOSFET. However, 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 are IGBT and MCT: the former is MOS-driven BJT, which has the advantage of surpassing BJT in capacity and voltage, and has a tendency to replace it; The latter MOS drives thyristors and theoretically has the advantages of both. These two new types of equipment have sophisticated products, IGBT has been developed to the fourth generation, and now foreign countries are transferring the consumption process of microelectronics to power electronics, so the production of application-specific integrated circuits (). The intelligent equipment that combines the drive circuit and the protection circuit of the IGBT is called IPM, and the IPM that combines the switching power supply, so that the VFD is more reliable, and it has become the leading product of speed regulation in the past, which will replace the DC speed regulation, and the 21st century will be the period of communication speed regulation.
2) Control methodVFD adopts different control methods, with different speed adjustment functions, characteristics and uses. The control method is roughly divided into open-loop and closed-loop control. Open-loop control includes U/f (voltage and frequency) proportional control; The closed loop includes slip frequency manipulation and various vector manipulations. From the perspective of development history, it is also from open-loop to closed-loop. The usual vector manipulation is comparable to the armature current manipulation of a DC motor. Now the communication motor parameters can directly stop the direct torque control, which is convenient and accurate, and the control accuracy is high.
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