In which fields are UPS power supplies widely used?
UPS power supply system equipment is the first type of information equipment, mainly used in the security protection of computer information systems, communication systems, mobile data network centers, etc. In the big data industry, big data industry, road transportation, financial industry industry chain, aerospace industry chain, etc. As an important peripheral equipment of computer information system, communication system and data network center, uninterruptible power supply plays a very important role in protecting computer data, ensuring the stability of power grid voltage and frequency, improving the quality of power grid, and preventing instantaneous power failure and unexpected power failure from causing harm to users. role.
The second type of industrial power UPS power supply system equipment is mainly used in the fields of electric power, steel, non-ferrous metals, coal, petrochemical, construction, medicine, automobile, food, military and other fields in the industrial power equipment industry, ensuring that all power automation industrial system equipment, remote The reliability of industrial automation power supply for AC and DC uninterruptible power supply equipment such as executive system equipment, high-voltage circuit breaker connection, relay protection, automatic devices, and signal devices. Industrial-grade uninterruptible power supplies are high-end products among uninterruptible power supplies. It involves power electronics technology for high-power (maybe megawatt-level) energy conversion, digital control system, AC series redundancy technology, active pulse current suppression technology, high-power product production technology, etc. Obviously, ordinary power supply companies cannot enter this industry. Only companies with high-power power electronics technology and a series of product development, manufacturing and service capabilities, and accumulated corresponding industrial production and application experience, can do a good job in the design of industrial uninterruptible power supply systems , Manufacturing and sales of market services.
At present, there are four schemes for large-scale UPS input harmonic current suppression
plan 1.
6-pulse UPS+active high-order harmonic filter, input current high-order harmonics <5% (rated load), input power factor 0.95. This arrangement makes the input indicator very good, but its technology is immature, and there are problems such as error compensation, overcompensation, etc., which cause such as false tripping or damage of the main input switch. The defects of the THM active harmonic filter technology are Common
a) There is a problem of “false compensation”: because the compensation response speed exceeds 40ms, there is a potential safety hazard of “false compensation”. For example, when performing cutting/commissioning operations on the input power supply, or performing heavy-duty cutting/commissioning operations on the upstream and downstream sides of the UPS input, it is easy to cause “deviation compensation”. The light came on, causing a “sudden change” in the ups power input harmonic current. When it is more serious, it will cause “false tripping” of the UPS input switch.
b) Low reliability: For the uninterruptible power supply with 6 pulses + active filter, the failure rate is high, because the power drive tube of its rectifier and converter is an IGBT tube. On the contrary, for 12-pulse + passive filter UPS, highly reliable inductors and capacitors are used in its filters.
c) Reduce system efficiency and increase operating costs: the system efficiency of active filters is about 93%. In the 400KVA UPS parallel connection, under the condition of full charging and 33% input high-order harmonic current compensation, if the electricity fee is paid at 0.8 yuan per KW*hr=, the operating expenses paid within one year are as follows
400KVA*0.07/3=9.3KVA; the annual electricity consumption is 65407KW.Hr, and the increased electricity fee is 65407X0.8 yuan=52,000 yuan.
d) Adding an active filter is extremely expensive: the nominal input current of an active filter 200 kVA UPS is 303 amps;
Harmonic current estimation: 0.33*303A=100A,
If the input harmonic current content is less than 5%, the compensation current must be calculated as at least: 100A;
Actual Configuration: A set of 100 amp active filters. According to the current estimate of 1500-2000 yuan for the ampere, the total cost will increase by 150,000-200,000 yuan, and the cost of the 6-pulse 200KVA UPS will increase by about 60%-80%.
Scenario 2
Adopt 6-pulse uninterruptible power supply + 5th harmonic filter. If the uninterruptible power supply rectifier is a three-phase fully-controlled bridge-type 6-pulse rectifier, the harmonics generated by the rectifier account for nearly 25-33% of all harmonics, and after adding a 5th harmonic filter, the harmonics are reduced to below 10%. The input power factor is 0.9, which can partially reduce the harm of harmonic current to the power grid. With this configuration, the input current harmonics are still relatively large, and the generator capacity ratio is required to be greater than 1: 2, and there is a hidden danger of abnormal increase in generator output.
Option 3
The fake 12-pulse scheme using a phase-shifting transformer + 6-pulse rectifier is composed of two 6-pulse rectifier ups:
a) A standard 6-pulse rectifier
b) A phase-shifted 30-degree transformer + 6-pulse rectifier
Configured fake 12-pulse rectifier UPS. On the surface, the harmonics of the full load input current appear to be 10%. This configuration has a serious single point of failure. When the uninterruptible power supply fails, the input harmonic current of the system increases sharply, seriously endangering the safety of the power supply system.
Main disadvantages:
1). Cutting corners and materials of the original device, a whole set of equipment is missing.
2). If the rectifier of a UPS fails, it will be transformed into a 6-pulse UPS, and the harmonic content will increase sharply.
3). And the control of the DC bus line is an open-loop control system. The input current sharing cannot be very good. The harmonic current at light load will still be very large.
4). System expansion will be extremely difficult
5). The phase-shifting transformer installed is not the original product, and the match with the original system will not be very good.
6). The floor area will be relatively large
7). The performance is 12-15%, which is not as good as the 12-pulse UPS.
Option 4
Adopt 12-pulse uninterruptible power supply + 11-order harmonic filter. If the uninterruptible power supply rectifier is a three-phase fully-controlled bridge-type 12-pulse rectifier, after adding an 11th-order harmonic filter, it can be reduced to below 4.5%, which can basically completely eliminate the harm of the harmonic current content to the power grid, and the price ratio is The source filter is much lower.
12-pulse UPS+11th harmonic filter is adopted, the input current harmonic is 4.5% (rated load), and the input power factor is 0.95. This type of configuration is a complete and reliable solution for the UPS power supply industry, and requires a generator volume of 1: 1.4.
Based on the above analysis, a harmonic elimination scheme of 12-pulse rectifier + 11th-order harmonic filter with good performance, high reliability, stable and reliable performance, and good cost performance is recommended in practice.
Post time: Apr-13-2023