Designing a lithium-based battery backup system for a Telecom or Data Center application presents new and different challenges.
Designing a lithium-based battery backup system for a Telecom or Data Center application presents new and different challenges compared to a traditional VRLA design. Balancing the flow of energy in and out of the battery bank is a critical design parameter. Designers must ensure that power is available under all conditions and optimize the performance of the batteries at the same time. There are 3 main issues designers encounter when designing lithium battery-based systems.
This article presents 3 common issues designers face when making the shift to lithium, and how Green Cubes has developed a patent pending Energy Balance Technology (EBT) to solve these challenges, reduce costs and optimize the use of lithium-ion batteries in UPS applications.
Recently designers of telecom and data centers have begun to strongly consider Lithium batteries for their new installations, and to retrofit their existing UPS installations. There are many key advantages to using lithium batteries, specifically cost, life, space savings, and improved performance. Designing a lithium battery-based backup power system for a Telecom rack, Data Center, or other IT infrastructure is quite different than traditional VRLA system design.
To fully experience the advantages that lithium has, designers must consider that they operate a bit differently than traditional VRLA systems. There are 3 main issues, Green Cubes Technologies has encountered. In response to these issues Green Cubes has developed and deployed patent pending Energy Balance Technology (EBT) in their Telecom and Data Center Power supplies and UPS systems. Find out what these issues are, and how EBT helps solve them.
1. Using cable length and bus bar oversizing to ensure equal current draw from all batteries
When multiple batteries are placed in parallel, the designer must work to control the current that is drawn from each battery pack during a discharge event. Under normal operation, the rectifiers control the voltage on the DC bus, but during a discharge event, the voltage on the bus can drop. This voltage drop is called droop and can cause equipment to shut down prematurely. Voltage droop is directly related to current, since Voltage equals Current times Resistance (V=I*R). The current drawn from the battery system can be anywhere from tens to thousands of amps. To equally distribute the current to each battery bank, designers often use cables of equal length to ensure the resistance, therefore voltage drop from each bank to the bus bars is equal, in theory. In practice, each battery bank has an internal resistance that is influenced by a number of factors such as temperature, age, and cycles. The internal resistance of each bank is not equal and will cause unequal current to be sourced from each bank during a discharge event.
In a lithium system, distributing current equally among packs is even more important. Lithium battery packs all contain a Battery Management System (BMS) that monitors critical parameters of the battery, including current, voltage, temperature, and others. When a parameter is measured to exceed a safe limit, the BMS will disable the output of the battery until the fault is cleared. In the case that the current is not equally distributed to the lithium batteries in the bank, one pack may exceed the safe current discharge limit, and the battery will disable the output. This will then shift the current to other batteries, potentially causing a cascading effect of batteries shutting off their outputs due to over- current limits. This can bring down an entire lithium battery bank, and then the system during a critical discharge event.
Green Cubes has developed patent-pending Energy Balance Technology in all lithium battery packs intended for UPS power systems. This technology communicates between all the batteries and automatically equalizes the discharge current across all of the batteries. This current distribution is actively managed at each battery and compensates automatically for unequal battery cable lengths, different battery internal resistances, and changes in load current. This technology also compensates for different States of Charge (SOC) and States of Health (SOH) across the entire UPS. Additionally, this technology eliminates the possibility of a cascading over current fault as the battery will only deliver up to its max current and then automatically limit its current without disconnecting.
2. Failing to control charge on each pack, and prevent over-charging
In a traditional VRLA battery bank, the charger periodically does an equalize charge to ensure all of the batteries are at the same SOC. This is accomplished by over charging the VRLA’s for a short period of time and is designed to remove sulfate crystals from the lead plates. This cleans the plates and allows for better interaction between the acid and the lead.
Over-charging lithium batteries can create severe damage. Over-charging can cause irreversible damage, excessive heat, internal shorts, cell venting, and thermal runaway. These are the primary reasons that a BMS is required in all lithium batteries. The BMS will monitor the voltage and current going into the cells and prevent overcharging. If either the current or voltage exceeds safe levels, in an over charge event, the BMS will disable the battery output and disconnect the battery from the system.
In a large battery installation, the difference in cable lengths, combined with different internal resistances (from different SOC, temperature, or SOH) in each battery will cause the current and voltage delivered to each battery during charging to differ. Some batteries will reach fully charged before other batteries, causing their BMS to disconnect the pack from the system. This can cause other batteries to receive excessive current during the critical taper charge. Additionally, batteries with a lower internal resistance will receive more current than batteries with a higher internal resistance, causing an additional imbalance of charge, heat generation, and ageing effects.
Green Cubes Energy Balance Technology also controls current into each battery, optimizing the charging of each battery and enabling battery-to-battery balancing. Through communication with the other batteries and the system controller, each battery can control exactly the right amount of current and voltage to charge the most efficiently and stop the charge precisely at full charge. Since each battery can regulate its own charge current, the system operates more efficiently, safely, and optimizes the lifetime of the batteries.
3. Attempt to integrate Packs, Rectifiers, Controllers and Management software from different vendors
In the technology world, standard interfaces are commonplace. API’s, standardized connectors, and Industry Trade Group standards allow all sorts of different equipment to communicate and work well with each other. The same is not true (yet!) for lithium batteries and UPS systems. There are several different power system solution providers on the market, each with advantages and disadvantages. Often, designers want to use different components in their systems and integrate them through software and hardware to create an optimal solution. Sometimes this is very straight forward, but often integrating these components is very difficult, if not impossible. Different protocols, implementations, data sets, and connectors require customization to make it all work together. This can take a lot of time and resources to sort out.
Green Cubes provides complete UPS power systems. EBT has been developed to work with the entire power system. This includes power rectifiers, lithium battery packs, and intelligent system controllers. All of these components can be controlled from a single location, either locally at the UPS or remotely via SNMP v3 or through our remote-control software. Green Cubes is unique in the fact that all the components have been designed and tested by the same engineering group and work seamlessly together. This eliminates the integration work during installation and allows your IT professionals to concentrate on what matters: operating the best Telecom, Data Center, or IT infrastructure possible.
These are the common issues designers encounter when designing a new lithium-based UPS system. Green Cubes Energy Balance Technology was developed to eliminate the problem and improve the performance of lithium battery UPS systems.