The DC power supply has positive and negative electrodes. The potential of the positive electrode is high and the potential of the negative electrode is low. When the two electrodes are connected with the circuit, it can maintain a constant potential difference between the two ends of the circuit, thus forming a current from the positive electrode to the negative electrode in the external circuit.DC power supply is an energy conversion device, which converts other forms of energy into electrical energy supply circuit to maintain the steady flow of current.[1]
Fundamentals
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The steady water flow cannot be maintained by the difference of water level alone, but it can be maintained by a certain water level difference with the help of the pump to continuously send water from the low to the high.Similarly, the electrostatic field generated by the charge alone cannot maintain a steady current, but with the help of DC power supply, the non electrostatic effect (referred to as“Non electrostatic force”）Make the positive charge return from the negative electrode with lower potential to the positive electrode with higher potential through the power supply to maintain the potential difference between the two electrodes, so as to form a stable current.
The non electrostatic force in the DC power supply points from the negative pole to the positive pole.When the DC power supply is connected to the external circuit, the current from the positive pole to the negative pole is formed outside the power supply (external circuit) due to the push of the electric field force.In the power supply (internal circuit), the effect of non electrostatic force makes the current flow from the negative pole to the positive pole, thus making the charge flow form a closed cycle.
An important characteristic of the power supply itself is the electromotive force of the power supply, which is equal to the work done by the non electrostatic force when the unit positive charge moves from the negative pole to the positive pole through the power supply.
When the internal resistance of the power supply can be ignored, it can be considered that the electromotive force of the power supply is approximately equal to the potential difference or voltage between the two poles of the power supply.
In order to obtain higher DC voltage, DC power supplies are often used in series. At this time, the total electromotive force is the sum of the electromotive forces of each power supply, and the total internal resistance is also the sum of the resistances within each power supply.Due to the increase of internal resistance, it can only be used for circuits with low current intensity.In order to obtain greater current intensity, DC power sources with equal electromotive force can be used in parallel. At this time, the total electromotive force is the electromotive force of a single power source, and the total internal resistance is the parallel value of the resistance in each power source.
There are many types of DC power supply. In different types of DC power supply, the nature of non electrostatic power is different, and the process of energy conversion is also different.In chemical batteries (such as dry cells, batteries, etc.), non electrostatic force is a chemical action associated with the dissolution and deposition of ions. When a chemical battery discharges, chemical energy is converted into electrical energy and joule heat. In thermoelectric power sources (such as metal thermocouples, semiconductor thermocouples), non electrostatic force is a diffusion action associated with temperature difference and electron concentration difference,When the thermoelectric power supply supplies power to the external circuit, the thermal energy is partially converted into electrical energy.stayDC generatorMedium, non electrostatic force iselectromagnetic inductionFunction, when the DC generator supplies power,mechanical energyConvert toelectric energyAndJoule heat。In a photocell, the non electrostatic force isPhotovoltaic effectWhen the photocell is powered, the light energy is converted into electric energy and joule heat.[1]
Technical indicators
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The technical indicators of DC power supply can be divided into two types: one is characteristic indicators, including allowable input voltage, output voltage, output current and output voltage regulation range;The other is the quality index, which is used to measure the stability of the output DC voltage, including the voltage stabilizing coefficient (or voltage regulation rate), output resistance (or current regulation rate), and ripple voltage (ambient and random drift).
1) Voltage stabilization coefficient andVoltage regulation rate: The voltage stabilizing coefficient refers to the relative change of output voltage caused by the relative change of input voltage when the load current and ambient temperature remain unchanged.The voltage regulation rate refers to the relative change of output voltage when the relative change of input voltage is ± 10%. The voltage stabilizing coefficient and voltage regulation rate both indicate the impact of input voltage change on output voltage, so only one of them needs to be tested.
2) Output resistance andCurrent regulation rate: The output resistance is the same as the output resistance of the amplifier, and its value is the absolute value of the ratio of the output voltage change to the output current change when the input voltage is constant.Current regulation rate: the relative change value of output voltage generated when the output current changes from 0 to the maximum value.Both the output resistance and the current regulation rate indicate the impact of load current changes on the output voltage, so only one of them needs to be tested.
3）Ripple voltage: AC voltage component superimposed on output voltage.The peak and peak values observed with an oscilloscope are generally in the order of millivolts.Also availableAC millivoltmeterThe effective value is measured, but the ripple is not a sine wave, so there is a certain error.[1]
application
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The space industry bears a special national mission.The space communication system has the characteristics of specificity and confidentiality, especially high timeliness requirements.The reliability of the communication power supply is the primary consideration of the aerospace communication department and an important guarantee for the safe operation of the communication system.At present, communication bureaus (stations) of the space system generally adoptUPS systemAs the main power supply of IT equipment, it overcomes the system interruption caused by mains power interruption.However, the failures of UPS itself and even the parallel redundant system have led to network communication accidents from time to time, which have caused great social impact and considerable economic losses.
As a simple and reliable technology, 240V high-voltage DC power supply system (HVDC) reduces power conversion links, improves power supply reliability and efficiency, and has attracted extensive attention in the industry.Aerospace communication departments should actively track the development and change of power technology, pay attention to the exploration results in application practice, convert new technologies into new applications, and improve the reliability level of aerospace communication systems.
Advantages of 240V high-voltage DC power supply system
The 240V high-voltage DC power supply system has the advantages of mature technology, high reliability, simple maintenance and operation, high conversion efficiency, simple online expansion, etc. The communication industry has been discussing the use of high-voltage DC system to replaceUPS system。
The 240V high-voltage DC power supply system has obvious technical and price advantages, and can be popularized on the premise of using existing IT equipment, so it has been widely valued and supported by departments at all levels.
1. Simple system structure
Principle, architecture and − 48V of traditional communication bureaus (stations)DC power supply systemThe availability and reliability of the latter have been tested by decades of operation.Therefore, the system is easy to maintain and less dependent on manufacturers;High load rate and easy to expand;High operation efficiency;DC bus is the common junction of battery pack, rectifier and load, with high system reliability.
2. Simple power supply and distribution
The figure shows the 240V high-voltage DC power supply system.
It can be seen from the figure that the battery pack forms an output bus at the general output panel through the fuse and the output end of the rectifier module. The system has two outputs (A and B), and the power distribution is through the array cabinet to meet the needs of dual power servers, while the single power server only uses A or B circuits.
The system uses two cables (positive and negative) to supply power from the power supply end to the equipment end in suspension mode;The whole system rack shell is electrically connected to the floor equipotential body.
3. Reduced system investment
According to the statistics of China Telecom Jiangsu Yancheng BranchUPS systemThe use of 240V high-voltage DC power supply system can save more than 40% of investment on average, and save 20%~30% of electricity on average throughout the life cycle
Feasibility analysis of HVDC application
With the progress of power technology, the power module of IT equipment has already been adoptedHigh frequency switching power supply。In this way, 240V high-voltage DC system power supply becomes possible.
1. Availability of 240V HVDC
The figure shows the equivalent diagram at the AC power inlet of the IT equipment power module.
It can be seen from the figure that under the traditional working environment, Ui between AB is the nominal 220V AC;After full bridge rectification, Uo between CDs will obtain 198-308V DC (depending on the load rate and whether PFC - power factor correction circuit is available).
The fluctuation of mains voltage will cause the fluctuation of rectifier voltage.According to GB/T 12325-2003 Power Quality - Allowable Deviation of Supply Voltage, the voltage deviation is − 10% and+7% of the nominal voltage, that is, 198~235.4V, and the corresponding rectification voltage Uo is 178.2~329.6V.It can be seen that the working voltage range between IT equipment CDs is wide.
When the IT equipment directly uses DC power supply, such as A terminal+, B terminal -, Ui is DC270V (floating charge voltage), it will make diodes 2 and 4 turn on for a long time, and the other two diodes 1 and 3 turn off for a long time.Diodes 2 and 4 are equivalent to conductors, and Uo between CDs is about 270V DC.The conclusion is that the IT equipment is fully equivalent under the condition of AC220V or DC270V.
2. Output voltage analysis of HVDC under various states
According to the requirements of YD/T 2378-2011 240V DC Power Supply System for Communication, the system shall adopt lead-acid battery pack and have battery management capability.Lead acid batteryThe voltage range of the battery pack is determined by its characteristics, and whether it is within the tolerance range of IT equipment is a key factor in usability research.Taking a domestic brand battery as an example, the output voltage under various states is analyzed.
1) Float charging status.Requirements of YD/T 2378-2011 240V DC Power Supply System for Communication, 240VHigh voltage DC power supplyThe output voltage range of is 204~288V, and the maximum allowable voltage drop in the whole process is 12V, that is, the voltage bearing range of IT equipment is 192~288V.Under normal conditions, the floating charge voltage of the brand's 240V battery pack is 270V, which meets the voltage requirements of IT equipment.
2) Discharge state.In case of long-term power failure without backup means,Battery packThe termination (protection) voltage of discharge is 222V, which is higher than the lower limit (204V) of operating voltage of IT equipment.Of course, modern communication bureaus (stations) should (all) have the capability of backup power supply and fast connection.
3) Equally charged state.The average charging voltage of the brand 240V battery pack is 282V, which is lower than the upper limit of IT equipment working voltage (288V).
From the above parameter analysis, it can be concluded that the output voltage of the 240V high-voltage DC power supply system under various states can meet the working needs of IT equipment, and there is a certain safety margin.
3. Established a perfect standard system
China has successively issued YDB 037-2009 Technical Requirements for 240V DC Power Supply System for Communication, YD/T 2378-2011 240V DC Power Supply System for Communication, YD/T 2555-2013 Distribution Equipment for 240V DC Power Supply System for Communication, YD/T 2556-2013 Technical Requirements for Application and Maintenance of 240V DC Power Supply System for Communication, YD 5210-2014 Engineering Technical Specifications for 240V DC Power Supply SystemAnd other systematic standards to promote the application and gradual replacement of 240V high-voltage DC power supply systemUPS power supplyThe system has laid a solid foundation.[2]
