The hottest new rectifier for communication

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Abstract: This paper introduces the circuit composition and technical characteristics of a new communication rectifier, and gives the main circuit structure and technical indicators

key words: rectifier; Zero voltage; Single ended active clamping

1 introduction

with the prosperity of the telecommunications market, as the heart of the communication network, power supply equipment and monitoring system are more and more important, and their requirements are higher and higher. For users, the new generation of rectifier equipment should have the following characteristics:

1) high efficiency

2) good dynamic response

3) small size, light weight, easy to carry

4) high reliability and easy replacement

build more than 10 high-level new materials research institutes to support the development of materials in key fields 5) high power factor and low EMI

6) high intelligence

in response to the above requirements, Xi'an Pusheng Telecom Co., Ltd. has developed a new generation of switching rectifier equipment. Now I will make a brief introduction to its main parts

2 circuit composition

the whole circuit block diagram is shown in Figure 1. The input voltage is single-phase 154 ~ 275v 50Hz. Through the protection circuit, rectifier circuit and power factor correction circuit, a DC voltage of about 400V is obtained and sent to the switch circuit. At the same time, the auxiliary power takes out energy from behind the filter circuit

Figure 1 circuit block diagram

the switching circuit converts the 400V DC into a square wave with a frequency of about 100kHz and an adjustable pulse width. After the main transformer depressurizes, an AC square wave sequence is obtained, and then through the rectification and filtering of the output part, 54.0v DC is obtained

the voltage and current error amplifier will take out the voltage and current signals proportional to the output from the output part, compare them with their respective reference values to obtain the error signal, and send it to the pulse width modulation circuit. The error signal determines the duty cycle of the switch to achieve voltage stabilization

the control of the whole machine is completed by the built-in CPU

3 main circuit structure

3.1 input circuit

as shown in Figure 2, the input circuit adopts multistage filtering to meet the requirements of electromagnetic compatibility. At the moment when AC is added, the main relay K will not close immediately, but will act after a period of time to reduce surge

Figure 2 AC input part

3.2 power factor correction circuit

the efficiency of rectifier is directly related to the reliability, volume and weight of equipment. Improving efficiency is the most positive way to improve reliability. A typical rectifier consists of an ac/dc converter (usually a diode bridge), a power factor correction part, and an isolated dc/dc converter. In order to provide power factor correction in single-phase applications, the input current must follow the input AC voltage. Common topologies include boost, buck boost, zeta and Cuk circuits. For ac280v input, the maximum switching voltage in boost circuit is 440V, while it is much higher in buck boost, zeta and Cuk circuits. The high switching voltage makes it difficult to choose the appropriate switching devices. Common switching devices include GTR, MOSFET and IGBT. Although the saturation voltage of GTR is low, the switching speed is slow. Power MOSFET has high speed, but large body resistance and large saturation voltage drop. IGBT has a low turn-on voltage drop relative to power MOSFET. Due to the current tailing phenomenon and large switching loss, it is not suitable for high frequency (about 100kHz). Considering comprehensively, it is more suitable to choose power MOSFET as switching device and boost circuit as power factor correction circuit. At the same time, because the output voltage of the boost circuit is always higher than the input voltage, it is very ideal to use the boost circuit for voltage pre stabilization in areas with large voltage fluctuations

as shown in Figure 3, the main components of power factor correction (PFC) circuit are boost choke, boost diode and switch tube. Its basic principle is: when the switch is on, the current flows through the boost choke and the switch, and the energy is stored in the boost choke; When the switch is disconnected, the energy stored in the boost choke attempts to keep the current flowing, causing the drain voltage of the switch to rise rapidly. Once this voltage exceeds the voltage on the energy storage capacitor, the current flows through the diode, thereby transferring the stored energy from the boost choke to C1. In order to improve the conversion efficiency of PFC and reduce electromagnetic interference, zero voltage PFC circuit is adopted

Figure 3 PFC circuit principle

3.3 main conversion circuit

dc/dc conversion. The commonly used topology includes full bridge structure and double forward structure. The full bridge structure has large output power and high transformer utilization, but there are hidden dangers of transformer magnetic bias and power tube direct connection. Double forward structure has attracted much attention because of its high reliability and no through problem. It is a highly respected circuit structure, but it has the problem of low utilization of transformer

in order to improve efficiency, single ended active clamping and zero voltage switching technology are used in the new rectifier. In the single ended active clamping circuit, the active devices are used to reset the conventional single ended forward transformer, which makes the transformer work in the first and third quadrants, and improves the utilization of the transformer. At the same time, because it is a single ended circuit, it avoids the problem of ensuring that the electronic tensile test motor can move directly according to the instructions of the control software, and ensures the high reliability of the whole machine. The switch tube works in the zero voltage state, which greatly reduces the switching loss of the switching device, and also reduces the electromagnetic interference. The main conversion circuit is shown in Figure 4

Figure 4 main conversion circuit

3.4 parameters of power module

input voltage rated voltage 220V 50Hz

working voltage 150 ~ 280v

output voltage average charge 56.4v

floating charge 54.0v (adjustable)

current limiting protection 55A (adjustable)

undervoltage alarm 47v

voltage regulation rate is better than 0.1%

load regulation rate is better than 0.5%

peak peak to peak ripple voltage 150mV

power factor 0.99

efficiency 90%

volume 133mm 245mm 350mm

4 circuit design features

the rectifier adopts a high-efficiency design, greatly reduces the calorific value, and designs a special air duct, using a high-performance temperature controlled brushless DC fan to force air cooling, The lower temperature rise of the whole machine is ensured. At the same time, when the CPU detects that the temperature rise of the radiator exceeds the set value, the output current limiting point decreases. In addition, it also has short-circuit, overvoltage, overheating, volt second product protection, fan failure and other protection functions

the AC input and DC output of the rectifier are equipped with high-performance hydraulic electromagnetic circuit breakers. On the one hand, they can be used as input and output overcurrent protection. On the other hand, in the use of the system, a unit can be easily cut out and put into operation, which is easy to replace without affecting the stability of the system

in the rectifier, the built-in CPU completes the control of the whole machine uniformly, which has extremely high intelligence

the average charging voltage, floating charging voltage, output current limiting point, high voltage alarm point and overvoltage protection point of the rectifier can be set by the panel and displayed by LCD. In addition, the CPU completes the equalizing charge, floating charge, test state, and on-off control

output voltage, current value, software version number, module address code, input AC voltage, radiator temperature and other information can be displayed on the LCD. In addition, it has a unique test function. Using this function, it is convenient to test the protection function and protection value of each unit in the rack. The second standard is not to damage the operation of the system. The communication interface can be used to communicate with the upper computer, and it has the functions of remote charging and shutdown

a complete rack system can be formed by connecting multiple machines in parallel with AC and DC screens. The modules in the rack operate in parallel, and a reasonable current sharing circuit is conducive to the improvement of system reliability. The current sharing circuit compares the output currents of several modules, and automatically establishes one as the main module, while the other modules automatically track this module to make the module in the current sharing state. If the non main module fails, it will automatically exit the system; If the main module fails, it will exit the system first, and then automatically establish one of the remaining modules as the main module, and the other modules will be compared with it. In this way, the main module can be selected automatically, and the failure of any module will not affect the work of the system. The current sharing circuit is realized by the internal hardware of the module, which has nothing to do with the system monitor. If the monitor is turned off or even removed, the system can still work with current sharing, which improves the reliability of the system

the rack system can be connected to two lines of mains power and can charge two sets of batteries. The system controller adopts the operation mode of large screen LCD Chinese character menu, which can monitor the voltage, current, frequency of AC mains power, output current of rack, battery charging current and main shunt current, and has complete three remote functions. The system is highly intelligent

5 conclusion

due to the adoption of new technologies and devices, the rectifier has reached a higher technical index. Its efficiency is 90%, the input voltage range is 150 ~ 280v, the peak peak ripple voltage is 150mV, and the power factor is 0.99. Built in CPU makes it extremely intelligent. It is an ideal rectifier equipment for communication according to experts' calculation

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