Why are HVDC power systems different from other power supply systems?
1. The reliability of the high-voltage DC power supply system is greatly improved - the main purpose of applying the high-voltage DC power supply technology is to improve the safety of the system.
2. The efficiency of high-voltage DC power supply system is greatly improved - the UPS hosts that are widely used at present are all online double conversion type. When the load rate is greater than 50%, the conversion efficiency is similar to that of switching power supply.
3. The input parameters of the high-voltage DC power supply system are greatly improved. The field test found that the commonly used 12-pulse online double-conversion UPS host, after adding 11 filters, its input power factor is usually 0.8 to 0.9, and the maximum is only 0.8 to 0.9. 0.95, the input current harmonic content is usually around 7.5%.
4. High-voltage DC power supply system, the load capacity is greatly improved - the load capacity of the UPS system is restricted by two factors. One is the power factor of the load. Taking a certain type of host of a large domestic UPS manufacturer as an example, the output power factor When it is 0.5 (capacitive), its maximum allowable load rate is only 50%; the second is the current crest factor of the load, usually the design crest factor of the UPS host is 3, if the current crest factor of the load is greater than 3, the UPS host will drop. can be used.
5. High-voltage DC power supply system, small transmission voltage drop - DC cable lines do not have the trouble of capacitive current in AC cable lines, no magnetic induction loss and dielectric loss, basically only core wire resistance loss, relatively low insulation voltage, DC transmission technology It is more suitable for long-distance transmission, and meets the current national requirements for energy conservation, consumption reduction and environmental protection. It belongs to a green and environmentally friendly power supply scheme.
Of course, there are also problems in DC transmission, such as high cost of converter station, poor overload capacity, large capacity of reactive power compensation equipment, converter station itself is a large source of harmonics, difficult production of DC high voltage circuit breakers and high cost.
