Key Technologies of Lifepo4 Battery Energy Storage System

Regarding the most important issue of battery energy storage, the first issue is safety; the second is life, and then high efficiency.

For energy storage systems, the first thing to consider at present is safety, and then efficiency. Adhering to efficiency, the rate of transformers and life, and the problem of energy utilization after the battery declines. Maybe this problem is not quantified in many cases. Indicators to describe it, but it should be very important for energy storage. We hope that through several things, we can solve the problem of safe life and high efficiency. A standardized energy storage system, a combing analysis system of battery status, and energy storage systems are very used in electric vehicles and public transportation systems.

The use of energy storage systems, node controllers and smart distribution boxes that everyone is currently using improves the overall economy and stability of the system, enhances the core value of the system integrator, and can be connected to the back-end cloud platform friendly.

This is a centralized energy dispatch system. This hierarchical structure has been explained very clearly in the morning, and we can achieve long-term optimized scheduling of multi-energy storage power stations and microgrids through multi-node controllers.

Now it is made into a standard intelligent power distribution cabinet. This is the basic feature of the power distribution cabinet. It contains a variety of functions, such as charging and discharging functions, automatic protection and interface functions. This is standard equipment.

The node controller realizes the core equipment of local energy management, the main data collection function, monitoring, storage, management strategy execution and uploading. There is a problem in this, which requires serious in-depth research. Regarding the data sampling rate and the time of data sampling when data is uploaded, the analysis of battery data in the background of the battery is implemented, and the maintenance of the battery is turned into intelligent maintenance. We are also Do some work, how large is the number of samples, or how fast is the storage speed, to fully describe the current state of the battery.

If I drive an electric car, you will find that the state of many electric cars will often change and jump. In fact, energy storage faces the same problem in the application of energy storage in the power system. We hope to solve it through data. Here we have a BMS sample quantity that is suitable.

Let me talk about flexible energy storage. Everyone says that I can do it 6,000 times, and it can be used a thousand times in a car. It’s hard to tell. Now you can help it to implement an energy storage system, which claims to do it 5,000 times. Facts How much is the utilization rate of the battery? Because the battery itself has a big problem. The decline of the battery is random during the decline. The decline of each battery is different, and the difference of the single battery becomes larger and larger. The inconsistency of changes in battery decay among manufacturers is also different. How much the battery can be used and the energy is available, which is a problem that requires careful analysis. For example, when electric vehicles are used, from 10 to 90% are in use, and to a certain extent, only 60% to 70% can be used. This poses a big challenge to energy storage.

Can we use it in groups according to the law of decay, and make a compromise. In the end, choose what is suitable to get better performance and better efficiency. We hope to group it according to the law of lifepo4 battery decay. Is 20 as a node? It is more appropriate or 40 is more appropriate, there is a balance optimization between efficiency and power electronics. So we do something about flexible energy storage, which is also one of our projects to do this. Of course, there is still a better place that can be used in cascades. I think the use of cascades in the past two years has a certain value, but whether it is worth using in the future, we still need to think about the efficiency of charging and discharging and the price of batteries once they drop. There are some problems with echelon utilization. Flexible grouping can solve big problems. The other is highly modular, which reduces the cost of the entire system. The biggest one can increase utilization.

Like the lifepo4 battery used in a car after three years, the decline is less than 8%, and the utilization rate is only 60%. It is caused by the difference. If you make 5 groups, the utilization rate can reach 70%, which can increase the utilization rate. Stringing battery modules together can also improve battery utilization. After maintenance, energy storage increases by 33%.

Looking at this example, after balancing, it can increase by 7%. After flexible grouping, I can increase it by 3.5%. Doing equalization can increase by 7%. Flexible grouping can bring a benefit. In fact, the reason is that different manufacturers have different battery decline trajectories. You need to know in advance what the set of batteries will become or what the parameter distribution is, and then you can make a targeted optimization.

This is a scheme adopted, module full power independent current control, which is not suitable for high-power applications.

Part of the power of the module is controlled by independent current. This circuit is suitable for medium and high voltage and repeated use. This is the solution for MMC battery energy storage suitable for high voltage and high power.

In addition, regarding battery status analysis. I have always said that the battery capacity is inconsistent, the decline is random, the battery age is inconsistent, the capacity and internal resistance are greatly reduced, and this parameter is used for characterization, and everyone uses the more one is capacity and internal resistance. If you want to find a way to maintain consistency, you need to evaluate the SOC difference of each battery, how to evaluate the SOC of this single cell, and then you can say how the battery is inconsistent and how much the maximum power can differ. The battery is maintained through the SOC, how does a single SOC come from? The current practice is to put the BMS on the battery system and estimate the SOC online in real time. We want to describe it in another way. We hope to run the sampled data to the background. We analyze the SOC and the battery through the background data. SOH, optimize the battery on this basis. Therefore, we hope that through car battery data, not big data, it is a data platform that expands the estimation model of SOH through machine learning and mining, and provides management strategies for the full charge and discharge of the battery system based on the estimation results.

After the data comes up, there is another advantage, I can make an early warning of the battery health status. Battery fires still happen frequently, and the energy storage system must be used as a safety. We hope to establish real-time information and mid- to long-term early warning through background data analysis, find an online early warning method for short-time and long-term security risks, and finally improve the safety and reliability of the entire system.

In this way, I can greatly achieve several aspects, one is to improve the energy utilization of the system, the second is to extend the battery life, and the third is to ensure safety. This energy storage system can work reliably.

How much data is needed to pass up to meet my requirements? I need to find the smallest pole that meets the battery operating state. These data can support the subsequent analysis. The data cannot be too large. Sending a large amount of data is actually very large for the entire network. A load. For tens of milliseconds, you take the voltage and current of each battery, and you pass it to the background. This is not achievable. We have now found a way. We can tell you what sampling frequency should be and what characteristic data you need to transmit , We make a simple compression of these data, and then send it to the network. The battery curve parameter is one millisecond, which is enough to meet the needs of battery evaluation. We record very, very little data.

The last one, we say BMS, the cost of energy storage has become more important than the cost of batteries. If you add all the functions to the BMS, you will not be able to reduce the cost of this BMS. Since we can send the data, we can have a powerful analysis platform behind. I can simplify it in front, and only data sampling or simple protection in front. To do a very simple SOC calculation, other data are sent from the background. This is what we are doing now. The entire state estimation and the sampling of the BMS below are passed through the energy storage node controller and finally transmitted to the network for energy storage. The node controller will have a certain algorithm, the following is basically detection and equalization. The final calculation is performed on the background network. This is the entire system architecture.

Let's look at the bottom layer that is effective and simple, which is equalization, low voltage acquisition and equalization acquisition to current acquisition. The energy storage node controller tells the next what to do, including the SOC doing it here once, and the background doing it again. This is the smart sensor, battery management unit, and smart node controller that we are already doing, which greatly reduces the cost of portable power station