As everyone knows, electrical automation technology is the synthesis of the world's most active, the most energetic, most developing prospect of comprehensive discipline with many of the new and high technology. Its application range is very wide, almost penetrated into all sectors of the national economy, with the development of science and technology of China, electrical automation technology have also improved. The following for electrical automation in power engineering some technical problems are discussed.
1 full controlled power electronic switch gradually replace the half controlled thyristor
Thyristor appeared at the end of the 50's tube marks a new era of motion control. It is the first generation of electronic power devices, in our country is still widely used in DC and AC drive control system. With the rise of AC variable frequency technology, appeared in succession of full control type devices -- CTR, GTO, P-MOSEFT etc.. This is the second generation of power electronic devices. Because the current / present can produce voltage ration and switching time of different devices, a variety of different application range.
The two breakdown phenomena of GTR and its safe operating area affected by various parameters which influence and change and small heat capacity, low ability of flow problems, make people put main energy in according to the different characteristics of designed circuit and protection suitable driving circuit, which makes the circuit more complex, difficult to master.
GTO is a high voltage device with gate turn off, its main disadvantage is the turn off gain low, generally 4 ~ 5, which requires a very large off the drive circuit, and the voltage drop of it than the ordinary thyristor high, about Zv ~ 4.5V, open di/dt and turn off of the dv/dt is also limited to another reason for GTO to promote the use of, the former is about 500A/us, which is about 500V/us, which requires a large absorption circuit.
Because GIR, GTO bipolar full controlled devices must have the control current is larger, so that the gate control circuit is very large, so as to promote all plant of a new generation with high input impedance of the MOS structure of power semiconductor devices. Power MOSFET is a voltage drive device, basically does not require stable driving current, driving circuit only needs to provide the capacitive charging current in the device is opened, and turn off the discharge current can be provided, thus driving circuit is very simple. Switch time it very fast, safe operating area is very stable, but the on state voltage drop along with the increase of rated voltage P-MOSFET and increase, caused great difficulties which give manufacturing high voltage P-MOSFET.
IGBT is a product of P-MOSFET technology based on MOSFET hybrid devices, it has high input impedance, high speed characteristics and GTR high current density characteristics. Its switch speed is lower than that of P-MOSFET, but faster than GTR; the on state voltage drop and GTR to about 1.5V ~ 3.5V, is much smaller than P-MOSFET, the turn off current decreased storage time and time for a 04us and 0.2us is 0.2us ~ 1.5us, so it has higher operating frequency, it has a wide and the stability safety working area, high efficiency, has the advantages of simple driving circuit.
MOS controlled thyristor (MCT) is a kind of single cell in its integrated of thyristor in MOSFET, to control the thyristor turn-on and turn off using the MOS gate, having a low on state voltage of the thyristor drop, but the current density is far higher IGBT and GTR, the switching frequency at the theory can be made of thousands of volts of blocking voltage and tens of kHz, and its off gain high.
IGBT and MGT of this kind of complex power electronic devices can be called the third generation device. In the composition of the device at the same time, the module that converter, half bridge or full bridge arms in combination devices also has entered a practical large-scale production. Based on the modular and complex ideas Bu, its development is the power integrated circuit PIC (Powerl, lntegratcdCirrrrcute), in PIC, not only the devices in the main circuit, and driving circuit, an overvoltage and overcurrent protection, current detection or automatic temperature control function are integrated together, form a whole, this can be regarded as the fourth generation of power electronic devices.
The 2 converter circuit development from low frequency to high frequency direction
With the development of power electronic device update, converter circuit composed of it must update. Application of thyristor DC transmission, converter is the main phase controlled rectifier, and AC frequency conversion ship is handed in has been a cycloconverter. When the power electronic devices to the second generation, more is the use of PWM converter. Using PWM method, and improve the power factor, reduce the effect of harmonic on electric gang, solved the torque ripple of the motor in the low frequency region.
But the torque ripple effect of harmonic components of voltage, current of inverter in PWM generation of the rotor, the motor winding vibration and noise. In order to solve this problem, one method is to increase the switching frequency, which exceeds the range of the human ear can feel, but the power electronic devices in high voltage and large current in the case of turn-on or turn off, switch loss is very large. The loss of the switch limits the operating frequency of the inverter to improve.
In 1986 American University of Wisconsin professor Divan proposed the resonant DC link inverter. The traditional inverter is hanging in the DC link stability, power electronic devices are in the high voltage conversion 'hard switch', the switching loss is bigger, limit switch in frequency increase. And the harmonic taking type DC link inverter is put through a resonant inverter Hang Road Zero in high frequency oscillation, the power electronic devices to switch at zero voltage or zero current, that work in the so-called 'soft switch' state, so that the switching loss is reduced to zero. In this way, can make the inverter size reduction, reduce costs, may also make the inverter in high power integrated. Therefore,
