Now the United States has a statistics, currently the cheapest electricity supply is wind power, followed by photovoltaic. Last year in Abu Dhabi, the future energy company’s export price in the Middle East was 1.79 cents per kilowatt-hour, which is well below the price for conventional energy.
Domestic implementation of the “photovoltaic leader plan”, north control in Jiangsu Baoying bid price of 0.47 yuan / kwh, side of the average online electricity price is 0.399 yuan. At that time photovoltaic modules were calculated at 2.7 yuan / W, now the module has dropped to 2.2 yuan, 2.3 yuan. According to this trend, whether photovoltaic or wind power, the goal of affordable access to the Internet will soon arrive. The economy of renewable energy is available, but one problem that cannot be solved is its volatility.
The ultimate goal of the energy revolution is that 100% of the world’s energy comes from renewable sources such as solar, wind and hydrogen fuel cells. There are mainly three modes of supply: one is centralized solar power station, wind power station with the new energy storage, the second is chemical storage of large independent energy storage power stations, pumped storage energy, and so on. Third, the user-side regional micro-grid group (virtual power plant) as the framework of the model.
When the cost of new energy storage is lower than that of conventional fossil energy, the model of microgrid and centralized new energy storage will explode. As the key technology of the energy revolution, the microgrid and microgrid cluster control EMS system, the energy storage system BMS,PCS system will be the key to the success of the energy revolution or not.
Key Technology 1-Top level Design of Project
Large-scale energy storage systems have different application scenarios and business models, some energy storage systems are single power network peak-shaving, some are the combination of multi-application scenarios such as peak-shaving, frequency modulation and voltage regulation. According to different items, the configuration of power and battery in large-scale energy storage system is completely different. The objective function of the system should be safe, stable, reliable and economical.
The top-level design of high-power energy storage system is very important, which involves many factors, such as energy storage power configuration, energy storage Pack grouping and energy storage capacity allocation and so on. The average energy storage time for a solar power station is 10 minutes or 20 minutes, or 50 minutes, and the grid is required. For example, Qinghai now requires solar, wind power has 10% of the proportion of energy storage capacity, different places are different. In addition, charge and discharge current size, BMS equilibrium current size, peak-shaving capacity requirements and the time required for primary and secondary FM, between these constraints and the final goal to be achieved to ensure that the entire process design is closed. Ring.
Key Technology 2-Energy Storage system Integration
According to the top-level planning of the energy storage system, the integration of the energy storage system requires all-round control from the core selection at the bottom end to the battery module, the battery package and the battery cluster, and then to the configuration of the energy storage system. It includes the number of BMS time-sharing balanced batteries, the size of equilibrium current, the internal heat management system of container, the working mode of PCS, the sub-level control logic of PCS and the formulation of upper EMS control strategy.
The original energy storage battery is the power battery from the car. The number of electric cores in an electric vehicle is about several hundred, up to 1,000, and the number of cores contained in the high-power energy storage system is tens of thousands or even hundreds of thousands. The biggest problem is its inconsistency. It has a short-board effect, I can manage hundreds of cores, at the same time let tens of thousands, hundreds of thousands of cores to achieve consistency is very difficult.
Key Technology 3–BMS Equalization Technology
High-power energy storage system has a large single capacity, so the top-level design must start with BMS. As soon as possible, I can make a one time selection of all the cores to maintain consistency as far as possible. But after running for a period of time, the electrochemical battery is very sensitive to the reaction of temperature, its inconsistency increases again, the difference comes out again, how to control in this process, and how to find out some of the cores with poor performance. Balance over the cycle of the running process, allowing it to return to consistency. This should be taken into account in the overall control strategy.The high efficiency and low cost of energy storage system one is the cost of system integration, the other is running cost. When the cores are grouped, the inconsistency will be doubled and the difficulty of BMS equalization control will be increased. The large-capacity energy storage system needs to expand the capacity of the parallel core. It is difficult to determine the problem core and the problem Pack, accurately by the means of detecting the parallel core by BMS. If the core is 40 amperes, there will be more strings to be connected in parallel. How to detect at this time, run after a period of time how to carry on the equilibrium, the balance current must match how big, actually this is closely related to your cost.In the process of battery operation, due to the influence of various factors, the attenuation curve of different Pack is inconsistent, thus expanding the internal inconsistency of energy storage system. How to solve this problem? the hardware design of BMS, The on-line equalization strategy must be closely combined with the Pack design and the functional parameters of the whole energy storage system, which can improve the charge and discharge capacity of the energy storage system as a whole and reduce the short-board effect of the system.
The first is the accuracy of the SOC estimation of the electric core level. It includes the self-correction when the change rate of the core voltage is less than the BMS voltage acquisition accuracy and the self-correction after the SOC error calibration.
The second is the accuracy of the SOH estimation of the electric core level. Real-time and fast determination of the SOH of each core is an important guide to the equilibrium strategy, which can provide data support for on-line maintenance and core replacement of the system. Including the core equalization in BMU, the core equalization across BMU, the balance between battery clusters, the optimal equalization strategy for the overall core voltage and SOC,SOH core temperature is worked out.
At present, our country’s energy storage system, microgrid system is the most lack of more thorough system integrator, this is a system engineering, not I buy a manufacturer to do BMS for me, this needs us all to work together.
Key Technology 4–PCS multilevel VF parallel Technology
The traditional PQ control mode is not enough to reflect the flexible, fast and stable power characteristics of the energy storage system. It is difficult for the traditional VF control mode to realize multi-machine parallel connection, and the expansion of voltage source capacity and support capacity is limited. For large-scale energy storage systems, PCS multi-stage V / F parallel technology has been an urgent problem for the industry. PPCs multi-stage V / F parallel technology can greatly reduce the system cost, simplify the system design, and improve the instantaneous response ability of the system.
Key Technology 5–PCS Seamless switching Technology
PCS is connected to the grid in the form of V / F, providing primary frequency modulation, voltage regulation and other power auxiliary services to the power grid. In the case of power network failure, it does not need to switch between PQ and VF directly into the operation mode of the isolated network, and provides the voltage and frequency set value (reference), for the isolated network, thus ensuring the uninterrupted power supply of the important load. The use of this technology can make the PCS system replace the traditional UPS system, and provide power auxiliary services such as primary frequency modulation, secondary frequency modulation and reactive power regulation, which can not be realized by the traditional UPS system.
The technology can be widely used in data centers and customers with high power quality requirements, and plays an important role in improving the reliability of microgrid power supply.
Key Technology 6-Intelligent Energy Management system EMS
The intelligent EMS system can prejudge the running state of the future system, and adjust the control strategy in advance so as to make the system self-optimizing continuously. The following three points must be followed:
We are already running a power station in which EMS can modify the energy storage system online by artificial intelligence algorithm based on the data collected by the battery BMS, the actual and forecast data of photovoltaic power generation and the dispatching instructions of the power grid. When the data is different every day, the PCS mode can be freely switched. If the frequency modulation phase is switched to V / F mode, if the PQ source mode is used in the general phase, all the working conditions are constantly switched according to the actual situation in the field, so as to ensure the maximum cycle life of the battery under various working conditions.
Key Technology 7-coordinated Control of “New Energy Storage”
Through different EMS control strategies, “new energy storage” can participate in power network frequency modulation, peak shaving, and can predict the output of new energy generation 24 hours in advance, and the prediction precision can reach more than 85%. It is higher than the regulation performance of conventional units such as thermal power plant. With the realization of this technology, photovoltaic and wind energy storage systems will be transformed into a controllable energy source. As the cost of new energy sources and energy storage systems decreases continuously, the new energy will completely replace fossil energy and eventually realize the energy revolution. And this one can be operated remotely.
Key Technology 8-Microgrid and Cluster Control of Microgrid
The development trend in the future is to take microgrid as the unit and microgrid cluster as the regional power supply mode. The large power grid will gradually fall back to the status of backup power supply. As a result, the virtual power plant, big data dispatching platform in cloud and various artificial intelligence algorithms, big data mining technology will become a development trend of micro-grid and micro-grid cluster EMS.
Key Technologies 9-Regional Energy Management platform (Regional Autonomy)
The relationship between distributed generation and large power grid has changed from one-sided dependence to cooperation and mutual win-win. The regional energy management platform can control the operation of multiple microgrids and establish the bidding mechanism among multiple microgrids. In the future, through cloud computing, we will dispatch these decentralized distributed power sources, whether photovoltaic, wind or storage power stations, in a unified manner. This is one of the directions of our research.
