According to many years of experience in research and practice of electromagnetic compatibility , assuming that the cost of solving electromagnetic compatibility problems in the product development stage is 1, then the cost of solving the model development stage may be 10, to solve the cost of mass production It may reach 100, and the cost of solving the problem when it is installed on the spot may be thousands of times or may not be solved. Therefore, the problem of UPS uninterruptible power supply electromagnetic compatibility must be solved in the product development stage.
According to the product characteristics of UPS, the electromagnetic compatibility of UPS mainly includes the following parts: input and output conducted interference of power supply; radiated disturbance of power supply; anti-interference characteristics of UPS. The design methods that meet the requirements of the relevant standards are elaborated below.
1. Suppression of input and output conducted interference For conducted disturbance, three aspects can be considered: interference source, conduction path and direct disturbance suppression.
A. Elimination and reduction of interference sources: In the UPS, there are rectified AC / DC conversion, SPWM inverter DC / AC inverter, PFC high frequency conversion circuit, and DC / DC conversion circuit. It is an important source of harassment in the UPS, especially the transformers, inductors, and high-frequency current loops in it. Therefore, reasonable design of the parameters, processing technology, and layout of the corresponding transformers and inductors in the machine will greatly reduce their harassment. Intensity, reasonable setting of high-frequency current PCB and wiring can also improve UPS disturbance; for the drive circuit in the power converter, the drive resistance can be increased without affecting the efficiency and internal resistance, and the rise of the switching power supply, Falling edge time, thereby reducing the high-frequency harmonic content of voltage and current.
B. Suppression of conduction pathways: Since all conduction interference can only affect the input and output power terminals of the UPS through appropriate space and conductor pathways, reducing transmission pathways as much as possible is also an effective method to reduce UPS uninterrupted power disturbances. For example, install all the interference sources far away from the input and output terminals. The input and output power lines are not routed near the interference source. Strengthen the suppression process at the entrance and exit of the interference source. The other parts are spatially isolated, and the input and output of the power supply are at relatively remote locations in the machine.
C. Direct harassment suppression: If the above method still fails to meet the standard requirements, the corresponding EMI filter devices, such as inductors, high-frequency capacitors, special filters, etc., can be used to effectively reduce the UPS again directly in the input and output circuits. The external conduction interference of the whole machine, the practice shows that as long as the relevant parameters of the filter and the DB value of attenuation are appropriately increased, the conduction disturbance of the UPS can generally be reduced to within the standard limits. Of course, the closer the filter must be installed to the input and output power terminals, the better, because even a few centimeters long wiring will increase interference, and a socket-type filter will be the most ideal choice. In addition, the capacitor in the filter or the added EMI filter capacitor is preferably non-inductive to enhance the filtering effect.
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