Application types and characteristics of microgrid projects
1. The concept of microgrid
Microgrid is a concept relative to the traditional large power grid. It refers to a network composed of multiple distributed power sources and their related loads according to a certain topological structure. It is an effective way to realize an active distribution network, transforming traditional power grids into smart grids. transition.
The microgrid involves the six major areas of power generation, energy storage, distribution, electricity consumption, dispatching, and communications. It can work in both grid-connected and isolated grid modes, and has a high degree of reliability and stability.
2. Application of microgrid
The application market of microgrid is mainly divided into the following four aspects: 1. Home microgrid: This market application is still relatively limited in China, and most microgrids integrate optical storage and charging. 2. Industrial park microgrid: This area is widely used. 3. Island microgrid: Develop photovoltaic and wind power generation on islands to solve the problem of island power stability and safety. 4. Microgrid in remote/no power areas: Build a micro multi-energy complementary grid to solve the problem of no power supply in remote areas.
The microgrid can operate on the grid or on an island. The entire system is designed to be plug-and-play, improving power supply flexibility and reliability. The energy storage microgrid can also be used as a backup power supply, using its black start function; in addition, it can Participate in the regulation of the main network through the local energy management system.
3. Types of microgrids
(1) Communication micronet
AC microgrid is mainly a coupling technology of distributed energy through AC bus, which connects wind power generation, diesel power generation, photovoltaic and energy storage to the system. Finally, the entire system is connected to the large power grid through intelligent distribution cabinets to form a simple AC Micronet. The application of this kind of AC microgrid is very typical in current microgrid energy storage applications or projects, and the technology is relatively mature and the application is very flexible. As with all energy storage microgrid technologies, it is relatively easy for equipment suppliers or system integrators to achieve system integration.
This type of AC microgrid is more suitable for island microgrids. Because in relatively wide areas of the island, photovoltaics can be used to supplement energy, and coupled with an energy storage system, when the load cannot be consumed completely, the remaining electricity can be stored first and then power the load at night. When the entire system cannot generate electricity on rainy days, you can consider adding a diesel generator to use it as a backup power source.
Characteristics of AC microgrid: 1. The system design of AC microgrid can support grid-connected operation or off-grid operation. 2. The entire system has a wide access power range and a flexible design, and can be connected to photovoltaic energy, wind power, supercapacitors and other types of energy storage battery systems. 3. Support the application of ladder batteries. The batteries can be connected to multiple branches to reduce parallel connection of battery packs. 4. The entire AC system microgrid can be made into a container design that integrates photovoltaics, energy storage, and batteries. In situations where the capacity is relatively small, the energy storage battery occupies a relatively large area. If the system device is placed in a specific area and there is no space, a container can be placed outdoors and packaged as a whole.
The key technologies of communication microgrid: 1. Microgrid energy management strategy, by managing the operating status of the load in the microgrid, ensures the economical and reliable operation of the microgrid. To form a microgrid, energy management, scheduling and policy control are indispensable in the background. 2. On-grid and off-grid seamless switching technology ensures the reliability of power supply for important loads in the microgrid and plays an important role in the safe and reliable operation of the large power grid. 3. VSG function increases system inertia and maintains the stability of system voltage and frequency.
(2) DC microgrid
DC microgrids are mainly used in electric vehicle charging stations, industrial and commercial parks and some emergency power supply situations. The system composition mainly considers two points: 1. Maximizing the role of photovoltaics. Because the photovoltaic and energy storage sectors are indispensable in the microgrid, and energy storage is the core component of the entire microgrid equipment. Photovoltaic power generation is generally DC power. The DC power generated by photovoltaics is integrated into the DC bus through an intermediate device, and the battery is connected to the system through the DC converter in the middle. In this way, photovoltaic power generation does not need to be inverted and then rectified back to charge the battery. The entire The conversion efficiency of the system will be very high. 2. At present, the charging technology of electric vehicles mainly uses AC charging piles or DC charging piles. The energy of such charging piles comes from alternating current. A DC microgrid is built to flow the energy through DC charging DC conversion to directly charge electric vehicles. The maximum Improve the conversion efficiency and utilization efficiency of the system. The entire system is connected to the grid through the energy storage converter, which plays a complementary role. When the photovoltaic energy is insufficient or load power supply, DC source and other similar loads need power supply, power can be drawn from the grid; when the photovoltaic power consumption is not enough. When finished, you can use the remaining power to connect to the Internet.
Characteristics of DC microgrid: 1. DC microgrid adopts DC bus coupling technology to reduce AC to DC conversion losses. 2. Make full use of photovoltaic power generation to achieve power balance in the microgrid system. 3. Minimize the power distribution capacity on the grid side, because many loads draw power from the grid when power is supplied, and the transformer configuration capacity on the grid side will be very large. If there are many DC loads, DC microgrid can be used to solve the problem. 4. As a simple emergency power supply, this emergency power supply cannot achieve seamless power supply switching like a conventional UPS, but the switching delay can be controlled within 15 milliseconds.
Key technologies of DC microgrid 1. Energy management system, which uses a set of software to strategically control and schedule system energy. 2. DC converter impedance matching technology. This impedance matching circuit can reduce the impact on the resonant frequency of the converter resonant circuit when the filter circuit and output load change, so that the resonant frequency of the converter resonant circuit is only within a wide range during operation. changes within a small frequency range to ensure high conversion efficiency of the converter and simplify the control circuit of the converter. 3. The distributed collaborative control technology of segmented buses ensures the stability of collaboration and the adaptability of the system.
(3) AC and DC hybrid microgrid
The AC and DC hybrid microgrid combines all the characteristics of the previous two microgrid types and is very powerful. The combination of the entire system requires very high equipment and technology. In aspects such as energy storage and PCS, if the coordination and control of distributed energy access to the entire system are not properly handled, the system will be paralyzed. AC and DC hybrid microgrids can be widely used in scenarios such as islands, areas without electricity, and industrial and commercial parks.
1MWh Container Energy Storage Technology Solution And Application
(1) Microgrid energy storage solution
Core components such as integrated batteries, BMS, converters, intelligent switching cabinets, and EMS are all placed in a container, which can be achieved with a 40-foot container. This integrated solution can be applied in peak shaving and frequency modulation of energy storage power stations, or the utilization of cascade batteries, emergency power supply situations, and some commercial applications for peak shaving and valley filling.
2. Power Station Energy Storage Solutions
The entire system of an energy storage power station is relatively large in scale. I personally recommend that the PCS and battery parts be separated and placed in a separate container. This will be more reasonable in terms of maintenance and ventilation and heat dissipation of the battery.
3. Cabinet Energy Storage Solution
All in one energy storage solution is suitable for small commercial energy storage applications. By placing the PCS and battery modules in a cabinet, the entire system occupies a relatively small space.
Design of 1MWh Energy Storage Container
The design of the 1MWh energy storage container is mainly divided into two parts:
1. Battery compartment: The battery compartment mainly includes 1MWh battery, battery rack, BMS control cabinet, heptafluoropropane fire extinguishing cabinet, cooling air conditioner, smoke sensing lighting, surveillance camera, etc. The battery needs to be equipped with a corresponding BMS management system. Battery types can be lithium iron batteries, lithium batteries, lead-carbon batteries and lead-acid batteries. Lead-acid batteries have low energy density and are large in size. A standard 40-foot container may not be able to accommodate them. The current mainstream standard design is a 1MWh lithium iron phosphate battery. The cooling air conditioner adjusts in real time according to the temperature in the warehouse. Surveillance cameras can remotely monitor the operating status of equipment in the warehouse. Finally, a remote client can be formed to monitor and manage the operating status and battery status of the equipment in the warehouse through the client or app.
2. Equipment warehouse: The equipment warehouse mainly includes PCS and EMS control cabinets. PCS can control the charging and discharging process, perform AC and DC conversion, and can directly power AC loads when there is no power grid. In the application of energy storage systems, the function and role of EMS are relatively important. In terms of distribution network, EMS mainly collects the real-time power status of the power grid through communication with smart meters and monitors changes in load power in real time. Control automatic power generation and evaluate the safety of power system status. In a 1MWh system, the ratio of PCS to battery can be 1:1 or 1:4 (energy storage PCS 250kWh, battery 1MWh).
The heat dissipation design of the 1MW container-type converter adopts a forward-distribution and rear-discharge design. This design is suitable for energy storage power stations that place all PCS in the same container.
The wiring, maintenance channels and heat dissipation design of the container’s internal power distribution system are integrated and optimized to facilitate long-distance transportation and reduce subsequent maintenance costs.
3. Composition of standard MW energy storage solution
The standard MW energy storage solution integrates batteries, BMS, PCS and EMS. Most systems use PCS as the core basic equipment and provide customized, one-stop energy storage solutions by integrating batteries, BMS and EMS.
Energy storage microgrid has become the key infrastructure of energy Internet
- The role of energy storage microgrid in the energy internet
There is a one-to-one correspondence between energy storage and the Internet. The energy in energy storage corresponds to the data in the Internet; the battery is the so-called energy storage, which corresponds to the cache in the Internet; the bidirectional conversion device of the energy storage converter corresponds to the role of the router in the Internet; the microgrid in energy storage It is equivalent to a local area network; all data and devices added together form the Energy Internet, which is equivalent to the structure of the Internet.
2. Application of energy storage
Power generation side: solve the problem of abandoning wind and light and stabilize fluctuations. At present, the wind abandonment rate in some areas reaches 10%-15%, and the light abandonment rate reaches 15%-20%. Equipped with energy storage on the power generation side, power generation can be stabilized and the impact on the power grid will be greatly reduced.
Grid side: Participate in the frequency regulation of the power grid to improve stability. At present, some places in the frequency regulation market use thermal power for frequency regulation, but the response time and cycle of thermal power frequency regulation are relatively long. Energy storage output power changes very quickly and can generally respond within 10 seconds. Energy storage frequency modulation has advantages in comparison.
User side: energy storage, peak shaving and valley filling, and earning the peak-valley electricity price difference.
Challenges and Obstacles in the Development of Energy Storage Microgrids
At present, the entire energy storage market is in a tepid state, mainly for two reasons: First, policy and cost. The state’s policy subsidies for electric vehicles are very large. Therefore, after subsidies are provided for energy storage systems or batteries, the cost of the entire system will be reduced, the initial investment will be reduced, and the revenue of the system will increase. The second is the technical level. First of all, there are still constraints and technical difficulties in the development of active distribution networks; the exploration of energy management technology still needs to be explored; the coordinated and optimized operation technology of microgrids and large power grids needs to be improved; the grid adaptability of energy storage converters In terms of supporting technology for the power grid, there are technical requirements and thresholds for energy storage PCS manufacturers. People think that policy and cost are the main issues at present.
Opportunities and Prospects in the Development of Energy Storage Microgrids
(1) The high penetration rate of photovoltaic and wind power poses challenges to the stability of the power grid. Studies have found that the maximum penetration rate of photovoltaic power generation generally does not exceed 25%-50%. Otherwise, the power grid may experience voltage rise, voltage fluctuations caused by cloud changes, and large-scale disconnections caused by low voltage and frequency fluctuations.
(2) Electricity reform has activated the user-side energy storage market. With the further decline of energy storage costs, the improvement of the peak and valley electricity price system, the establishment of compensation mechanisms such as peak electricity prices and demand-side management, and the development of various value-added services on the user side of the power market, the energy storage market on the user side will appear. It has become one of the main areas for commercial application of energy storage in my country.
(3) With the rapid explosion of the electric vehicle market, the effective recycling of power batteries and the realization of sequential utilization of batteries have become one of the important issues in the development of new energy vehicles, and have been put on the agenda. The market for future automotive batteries Very big.
(4) The optical storage and charging microgrid system has investment value. It is an energy management and allocation scheme that comprehensively utilizes green energy and has high economic and environmental benefits.
Advantages of multi-branch energy storage technology in echelon battery utilization
Key technologies for echelon utilization
For the echelon utilization of retired power batteries of electric vehicles, the following processes generally need to go through: recycling of retired batteries, disassembly of battery PACK into single cells, battery screening and performance classification, and regrouping of batteries into echelon use battery modules or PACK. Pool balancing maintenance testing
When the power battery is retired, the entire pack is disassembled from the car. Different models have different battery pack designs, and their internal and external structural designs, module connection methods, and process technologies are different, which means that it is impossible to use one disassembly assembly line to fit all battery packs and internal modules. Then, in terms of battery disassembly, it is necessary to carry out flexible configuration and refine the disassembly assembly line into sections. When formulating the disassembly operation process for different battery packs, it is necessary to reuse the existing assembly line sections as much as possible. and processes to improve operating efficiency and reduce repeated investment.
For step-by-step utilization, it is most reasonable to disassemble it to the module level rather than the cell level, because the connections between cells are usually laser welding or other rigid connection processes, making it extremely difficult to disassemble without damage. Considering the costs and benefits, the gain outweighs the loss.
Key technologies for echelon utilization
PCS adopts a modular multi-branch solution, which can better reduce the number of parallel connections of battery packs. The charging and discharging of each battery does not affect each other.
Pain points solved by multi-branch technology: 1. Eliminate circulation problems caused by parallel connection of different battery packs. 2. Reduce the complex screening process after battery cascade utilization, reduce the cost of reusing cascade batteries, and improve the recycling efficiency and utilization value of cascade batteries. 3. Batteries from different battery manufacturers can be connected to improve system flexibility. 4. BMS adopts active balancing technology solution, which can maximize the balanced protection of the battery.
Technical advantages
1. The modular design of energy storage PCS has high stability. Single-mode failure does not affect the work of other modules. Module production is convenient, fast and efficient.
2. In terms of user value, the system can be powered on for module addition, removal, replacement and maintenance, and a single module can be replaced within 10 minutes; modular redundant parallel connection avoids waste of resources; it supports multiple energy access, making it convenient and flexible.
3. Using efficient three-level topology technology and adding zero-level conversion, the IGBT withstand voltage is half of the two-level and the switching loss is small; the three-level has a higher switching frequency and the output filter inductance is reduced; the three-level has one more layer ladder voltage, the output current waveform is closer to a sine wave, the harmonic content is small, and the power factor is 0.99. In terms of power factor, it can be adjusted at will from -1 to 1.
4. Independent heat dissipation design. The module adopts a layered structure to isolate the main control center and main heating components; an independent air duct is used to ensure that the air cavity has sufficient air pressure. Compared with a mixed air duct, the thermal design is better.
Discussion on the application of integrated optical storage and charging technology
The typical application mode of optical storage and charging is the AC microgrid mode. Its main architecture includes AC bus, photovoltaics, charging piles, energy storage and batteries, etc. The system can be operated on-grid or off-grid. The system can also be equipped with off-grid switching equipment for seamless switching.
The application of optical storage and charging will develop into a multi-energy complementary state in the future. In the later period, not only photovoltaics and energy storage, but also thermal loads, heat pumps, distributed energy sources, etc. will be connected to this system, gradually evolving into a huge microgrid system.
