Fully online battery discharge safety and energy-saving technology

The quality of communication backup batteries is an important guarantee for the uninterrupted power supply of the communication network, the power supply guarantee of the entire communication power supply equipment, and the last line of defense to ensure the normal operation of the communication network. According to the battery characteristics and maintenance requirements, the battery discharge capacity test is indispensable. This paper discusses the advantages and disadvantages of the two current battery discharge capacity test technologies, and provides an innovative full-online battery discharge safety and energy-saving technology, which is a useful exploration to solve the safety hazards of battery discharge testing in the industry for decades.

1. Analysis of current battery discharge technology

1.1 Technical analysis of offline discharge method
(1) After one group of batteries is disconnected from the system, once the city power is interrupted, the system backup battery power supply time is significantly shortened. Moreover, it is not clear whether the other group of online batteries has quality problems at this time. This discharge method has a high risk of accidents. If this method is used for discharge, it is recommended to enable the generator set in advance and ensure that the generator set, switching power supply and other equipment can operate normally to ensure safety;

(2) There is a large voltage difference between the battery group after the offline discharge and the online battery group. If the operation is improper, the switching power supply and the online battery group will charge the battery group after the offline discharge with a large current, generating huge sparks, which is prone to safety accidents. To discharge in this way, a whole set of intelligent chargers is required. The offline battery pack is first charged and restored before being connected in parallel to the system to solve the sparking problem. This will keep the system in a single-group power supply state for a longer period of time, which has a high risk of accidents. In addition, the rectifier output is adjusted to be equal to the voltage of the discharged battery pack before the connection is restored. The above operations must be performed with caution;

(3) When operating this discharge method, both the positive and negative poles of the battery pack must be disconnected. In particular, special care must be taken when disconnecting the negative pole of the battery pack. Improper operation will cause the negative pole to short-circuit, which will cause system power supply interruption and communication accidents;

(4) This method consumes the battery in the form of heat through a dummy load, which wastes electricity and affects the operating environment of the equipment in the computer room. Maintenance personnel are required to guard at all times to prevent accidents caused by high temperature.

1.2 Technical analysis of online evaluation discharge method
(1) Adjust the rectifier output voltage to the protection low voltage value (such as 46V) so that all backup battery packs can directly discharge to the actual load to the rectifier output voltage protection setting value. Since most of the battery configurations of the existing network system equipment have a backup power supply time of 1 to 4 hours and a large discharge current, the voltage drop from the battery group to the equipment power supply circuit and the low-voltage working threshold of the equipment should be considered, as well as the safety of the system power supply. The online evaluation discharge does not allow the rectifier output voltage to be adjusted too low (such as 46V), the discharge depth is limited, and it is difficult to grasp the discharge time of the actual load. It is difficult to accurately evaluate the battery capacity, and there are uncertain factors in the battery performance test, so it is difficult to achieve the expected maintenance effect for the discharge test purpose of maintaining the activity of the battery group;

(2) If both groups of batteries have quality problems such as loss of capacity, undercapacity, and backwardness, when they are discharged to the rectifier output protection value, it is not easy for maintenance personnel to discover it in time. At this time, the backup battery capacity may be almost gone, which poses a high risk. In this case, this discharge method is less safe than the offline discharge method;

(3) Due to the limited discharge depth, the purpose of the discharge test to maintain the activity of the battery group cannot be achieved. More importantly, in the practice of full-capacity discharge, we often find that some battery groups perform normally in the early stage of discharge, but in the middle and late stages, some backward batteries begin to gradually expose themselves. This part of the lagging monomers was not discovered because the depth of this discharge method was not enough. Therefore, we call this discharge method an online evaluation method. It can only roughly evaluate the performance of the battery group, or detect the length of time that this battery group can discharge to this protection voltage, but cannot further check how long it can discharge beyond this time;

(4) The discharge current of the batteries between groups is unbalanced. Each group of batteries will naturally share the load current of the system to discharge according to its own situation. The lagging battery group has a large internal resistance and a small shared current, while the healthy battery group has a low internal resistance and a large shared current. As a result, some lagging batteries cannot be exposed because the discharge current is not large enough, and we cannot achieve the purpose of our discharge performance quality inspection.

In summary, under the requirement that the central computer room battery must be regularly tested for capacity, the two current capacity testing methods have their own characteristics and disadvantages. Although the offline discharge method can achieve the purpose of battery capacity testing, the workload is too large and the system safety is low. Although the online evaluation discharge method has a relatively small workload, the system safety is low and it cannot achieve the purpose of battery capacity testing. There are great potential safety hazards. Therefore, the current battery capacity testing method must be reformed. We will now introduce a new and scientific capacity testing technology - full online discharge technology, so that the battery discharge capacity test can achieve the expected maintenance quality detection effect. The battery discharge maintenance operation is simple and safe, which improves the maintenance work efficiency and is easy to be effectively implemented.

2. Analysis of full online discharge technology

Full online discharge technology refers to the battery pack under test being connected in series with the full online discharge test equipment of the battery pack to increase the online power supply voltage, and automatically control the output with constant current or constant power, so that the battery pack under test can supply power to the online load equipment, realize the constant current discharge test or constant power discharge test of the battery pack under test, and achieve the effect of safe energy-saving maintenance.

The system technical schematic diagram is shown in Figure 1.

Figure 1 Working principle diagram of battery full online discharge equipment

The principle of discharge technology is shown in Figure 2. Analysis of the full online discharge principle of the battery group under test: As shown in Figure 2, the full online discharge equipment of the battery group under test is connected in series with the positive electrode of the battery group under test, so that the voltage of the branch where the battery group under test is located is slightly higher than the rectifier output or the voltage of another group of batteries, so that the battery group can discharge the actual load. During the discharge process, the voltage of the battery group under test changes (gradually decreases) as the discharge time changes (extends). The full online discharge equipment is used to perform automatic voltage compensation adjustment to ensure that the battery group under test always maintains a constant current or constant power for discharge. When the battery group discharge termination voltage, capacity, time and single cell voltage reach the discharge threshold value we expect, the discharge test is completed. The purpose of the online discharge test of the battery group and the expected maintenance effect are achieved. The working principle of full online discharge is shown in Figure 3.

Figure 2 Fully online discharge principle

Figure 3 Online discharge working principle diagram

2.1 After the online discharge is completed, the online charging and equipotential connection are automatically completed
. After the discharge test of the battery group under test is completed, the battery group full online discharge equipment automatically enters the charging program, guides the rectification output of the online switching power supply, and automatically performs current limiting charging on the battery group under test through the charging and equipotential control protection circuit of the full online discharge test equipment, and automatically completes the online equipotential connection. According to the operation requirements prompted by the full online discharge test equipment system, after restoring the normal connection of the system, the full online discharge test equipment exits the service, completing the whole process of ending the full online discharge of the battery group, charging and restoring the normal connection of the equipotential. Another group of batteries undergoes online discharge capacity testing in the same way. As shown in Figure 4.

Figure 4 Working principle diagram of online charging automatic control equipotential connection

2.2 Online Discharge "Seamless Connection" Technology
To ensure the safety of battery discharge testing, the battery pack full online discharge equipment is required to be seamlessly connected when connected in series to the positive electrode of the battery pack, as shown in Figure 5.

Figure 5: Wiring diagram for online discharge capacity test

For seamless connection operation of online discharge test of battery pack, the connection of "equipment" should comply with the principle of "connect three first, then remove one", that is, connect power lines L1, L2, L3 first, then remove the original power line L5; when "equipment" completes the test and exits the service, the principle of "connect one first, then remove three" should be followed, that is, connect the original power line L5 first, then remove the power lines L1, L2, L3.

3. Comparative analysis between online discharge technology and current discharge technology

3.1 Comparative analysis with offline discharge technology
(1) The discharge process guarantees the battery pack's backup power to the maximum extent, minimizing the risk of system paralysis caused by discharge testing;
(2) The battery pack can automatically charge and recover after discharge, overcoming the difficulty of operating the equal potential access system after offline discharge and potential safety issues;
(3) The electric energy stored in the battery pack is utilized to the maximum extent, overcoming the waste of energy in offline discharge, with basically no heat generation, no high temperature risk, and no impact on the ambient temperature of the computer room;
(4) Seamless connection operations are performed only at the positive pole of the battery pack, avoiding the risk of short circuit caused by improper operation of offline discharge;
(5) Once the device is connected in series to the positive pole of the battery pack and the relevant discharge parameters are set, all discharge and charging work is automatically completed, and maintenance personnel can perform other work, reducing work intensity and improving work efficiency.

3.2 Comparative analysis with online evaluation discharge technology
(1) The full online discharge method can achieve the purpose of deep discharge to maintain battery activity and detect lagging batteries, and fully grasp the remaining capacity and backup power supply time of the battery pack;
(2) During the discharge process, the battery pack backup power is guaranteed to the maximum extent, minimizing the risk of system paralysis caused by capacity testing;
(3) The full online discharge method can realize group discharge of each group of batteries with the same current, and any lagging single cell can be exposed, overcoming the limitations of online evaluation discharge;
(4) Once the full online discharge equipment is connected in series to the positive electrode of the battery pack and the relevant discharge parameters are set, all discharge and charging work is automatically completed, and maintenance personnel can carry out other work, reducing work intensity and improving work efficiency.