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Special power supply can be subdivided into shore power supply, security power supply, high-voltage power supply, medical power supply, military power supply, aerospace power supply, laser power supply and other special power supply.
Special power supply is a special kind of power supply. The so-called special is mainly because the technical index requirements for measuring the power supply are different from the common power supply. It is mainly that the output voltage is particularly high, the output current is particularly large, or the requirements for stability, dynamic response and ripple are particularly high, or the output voltage or current of the power supply is pulse or other requirements. This makes the design and production of this kind of power supply have more special and even more stringent requirements than ordinary power supply. Special power supply is generally designed for special load or occasion requirements, and it is widely used. It mainly includes electroplating and electrolysis, anodizing, induction heating, medical equipment, power operation, power test, environmental protection and dust removal, air purification, food sterilization, laser infrared, photoelectric display, etc. In national defense and military affairs, special power supply is more irreplaceable than ordinary power supply. It is mainly used for radar navigation, high-energy physics, plasma physics and nuclear technology research.
1. High voltage power supply for radar transmitter
In modern radar transmitters, traveling wave tube (TWT) takes a large proportion as microwave power amplification device. As a high-power part, its reliability and technical indicators have a direct impact on the radar transmitter and even the whole radar. The high voltage power supply (system) supporting TWT is more important. As a high-frequency and high-efficiency power electronic technology, switching power supply technology has developed with the continuous renewal of electronic components and products and the renewal of high-power devices. The high-voltage switching power supply for radar TWT can adopt the full bridge resonant PWM modulation mode. The high-power switching device adopts advanced IGBT module and advanced and reliable driving circuit, which makes the overall performance and stability of the power supply good, and has various protection functions.
Working principle: through the power grid filter, 50Hz three-phase 380V is rectified and filtered to obtain more than 500 V DC voltage, which is supplied to the series resonant converter. Since the output of the power supply is up to 20kV, in order to reduce the design difficulty of the transformer, reduce the withstand voltage value of the high-voltage rectifier diode and improve the reliability of the power supply, the two secondary of the transformer are used for full bridge rectification respectively, and then superimposed output. The full bridge converter consists of four IGBTs, a high frequency transformer and rectifier circuit. The control circuit provides two pairs of mutually insulated pulses with a phase difference of 180 ° to the IGBT drive circuit to control the on-off of IGBT. The DC voltage is transformed into an alternating 20kHz pulse voltage, and the voltage of tens of kV is obtained through transformer, full bridge rectifier and filter circuit.
2. High power high voltage power supply for electron beam welder
Electron beam welding is widely used in many industries, such as aerospace, atomic energy, national defense and military industry, automobile, electrical and electrical instruments, because it has the advantages of no electrode, difficult oxidation, good process repeatability and small thermal deformation. The basic principle of electron beam welding is that the cathode in the electron gun emits electrons due to direct or indirect heating. Under the acceleration of high-voltage electrostatic field, the electron can form an electron beam with high energy density through the focusing of electromagnetic field. This electron beam is used to bombard the workpiece, and the huge dynamic energy is converted into heat to melt the workpiece at the welding place and form a molten pool, So as to realize the welding of the workpiece.
High voltage power supply is one of the key technologies of the equipment. It mainly provides acceleration voltage for the electron gun. Its performance directly determines the electron beam welding process and welding quality. Compared with other types of high-voltage power supply, the high-voltage power supply for electron beam welding machine has different technical characteristics. The technical requirements are mainly ripple coefficient and stability. The ripple coefficient is required to be less than 1%, the stability is ± 1%, even the ripple coefficient is less than 0.5%, the stability is ± 0.5%, and the repeatability is required to be less than 0.5%. The above requirements are determined according to the electron beam spot and welding process. The operation of high-voltage power supply for electron beam welding machine must be interlocked with relevant systems, mainly including vacuum interlock, cathode interlock, gate valve interlock, focusing interlock, etc., to ensure equipment and personal safety. The high voltage power supply must comply with EMC standard and have soft start function to prevent the impact of sudden closing on the power supply.
Due to its high power (up to 30kW), high output voltage (150kV) and high working frequency (20kHz), this power supply has high requirements for stability accuracy, ripple and voltage regulation rate. The advanced three-phase fully controlled rectifier technology and high-power high-frequency inverter are selected, and the new power device IGBT is used as the power switch. The three-phase fully controlled rectifier and inverter adopt independent control boards respectively, and the IGBT drive adopts an imported thick film drive circuit, plus a filter circuit composed of an input power grid filter, a flat wave reactor and a capacitor. The power conversion part of the power supply has advanced technology and good power conversion.
High voltage part: the magnetic core of high-voltage transformer adopts the latest amorphous materials, adopts unique high-frequency and high-voltage winding process, and the double high-voltage transformers work together. Advanced rectification, reasonable voltage doubling circuit and high-voltage voltage equalizing technology ensure the stability and reliability of the high-voltage part of the high-voltage power supply. The feedback and high-voltage indication signals are directly sampled by the high-voltage output end with a precision voltage divider to ensure that the power supply has high voltage stabilizing accuracy, voltage adjustment rate and accurate and reliable high-voltage measurement accuracy. Reasonable high-voltage filtering technology is adopted to ensure that the power supply has good ripple. The high-pressure part is placed in an oil tank.
3. High voltage pulse power supply
In radar navigation equipment, the transmitting part generally needs a high-voltage, narrow pulse and high-power pulse source with different repetition rates. This high-power pulse source generally raises the municipal power to thousands of volts to tens of thousands of volts DC high voltage through a high-voltage power supply, and then a modulator modulates the DC high voltage into a pulse source with the required pulse width and frequency for the use of the transmitting tube.
The pulse source is mainly composed of high-voltage power supply and modulator. The high-voltage power supply adopts switching regulated power supply, and the modulator adopts solid-state modulator of semiconductor devices.
The trigger pulse given by the user is a TTL level signal. An interface circuit shall be added before input to the isolation transformer. This interface circuit is used to pre amplify the TTL pulse signal and match with the isolation transformer. In order to achieve the purpose of isolation, the user can provide the power supply of the interface circuit, and the manufacturer only needs to put forward the power demand and design the corresponding transformation and filter circuit in the circuit.
The trigger pulse is isolated by the pulse transformer, shaped by the preset pulse, and the power is amplified to trigger the operation of the modulation board and the tail cutting board. The excitation pulse generated by the preset is isolated by the transformer to drive each FET of the modulation board. At this time, the modulation board turns on the high-voltage power supply and sends it to the anode of the microwave triode. The cathode electrons of the microwave triode begin to emit. The microwave triode amplifies the low-power high-frequency signal sent to the input end into a high-power high-frequency signal. When the pulse ends, the truncated pulse generated by the preset triggers the truncated plate. After the truncated plate is turned on, the distributed capacitance of the microwave triode is released, so a good pulse trailing edge can be obtained.
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