TBEA Hao Xiang: AC/DC hybrid microgrid can save 22% of cost compared with traditional AC microgrid

The "Inverter Digital Technology Transformation Forum" was held in Beijing on December 6-7, 2017. The forum was hosted by the China Photovoltaic Industry Association and organized by Jianheng Certification. Leaders and experts from government departments, industry organizations, photovoltaic power station developers, equipment manufacturers, and domestic and foreign research and consulting institutions were invited to attend the forum. Nengjian App broadcast the entire conference live.

Hao Xiang, General Manager of Smart Microgrid Product Line of TBEA Xi'an Electric Technology Co., Ltd., attended the "Summit Forum 1: Smart Inverters and Smart Power Systems" and delivered a keynote speech.

The following is the transcript of the speech:

The report is divided into five parts. When mentioning microgrids, we will talk about the development background, because microgrids are still a relatively new field. We will talk about the work and solutions of campus-level microgrids. Routers. What are the characteristics and value of using campus-level microgrids. The prospects of microgrids.

The development background of microgrids. Everyone mentioned the energy internet. Why? The development of the energy internet is closely related to economic development, resource shortages and environmental pollution. The smog in Xi'an is very serious. In the past, we only knew that there was fog but not smog. Now, due to environmental impact, China's per capita energy consumption resources are less than half of the world level, but China's GDP energy consumption is 2.5 times the world average, which will inevitably cause resource shortages and environmental pollution. We are committed to improving the problem in the new energy industry, and the development of clean energy is bound to be a trend. There are many problems with clean energy, such as wind power generation, photovoltaic power generation and hydropower stations. Take photovoltaic power generation as an example. Because the earth is revolving and rotating, it will cause changes in the solar radiation of photovoltaic power at the exact location on the ground. Wind power also has similar problems. The time dimension is unevenly distributed.

Unbalanced spatial dimension. At present, the largest wind energy resource areas in my country are Inner Mongolia and northern Gansu. Areas with large energy loads may not be able to be supplied, and some ultra-high voltage DC and AC transmission channels are still needed. In order to solve the uneven distribution of energy and the imbalance in time and space dimensions, many experts have proposed the concept of energy Internet, which is to achieve widespread access to new energy. After this concept was proposed, there were many different concepts, but the organizational structure is consistent. State Grid proposed the concept of global energy Internet, advocating clean energy as the main body, and high-voltage and ultra-high voltage power grids as the grid. Foreign research centers and domestic companies have also proposed many concepts, mainly including clean energy and ultra-high voltage DC, AC and high-voltage DC and AC, as well as smart microgrids.

The technical system of the energy internet. It covers the entire process from energy production to energy transmission and distribution, to energy storage and energy consumption, from production to consumption. The technology is divided into three levels: equipment layer, information layer, and application layer. There are many technologies involved. We are engaged in efficient solar energy utilization technology, and now the technology is very mature. Advanced transmission technology and flexible direct current transmission technology. Smart microgrid technology and energy router technology. Smart microgrid technology covers all technologies of the entire chain from energy production to energy transmission and distribution to energy storage and consumption. Improving the energy internet can transition to smart microgrids. If the energy internet transformation is really achieved, the underlying energy internet is needed.

There are many concepts for the proposal of smart microgrids, mainly distributed power sources, energy storage devices, energy conversion devices, load monitoring and protection devices, which form a small power generation and distribution system according to a certain topological structure. The concept was proposed to promote the access of a high proportion of new energy and the development of energy Internet. Many energy storage policies have been issued abroad, and Japan is no exception. my country has also issued some policies. Since 2009, laws and policies have been issued to promote the construction and implementation of microgrids. The microgrid market environment is divided into two types: networked and independent microgrids. Networked microgrids can be divided into two entities: the main body of users of electricity, including industrial and commercial parks and data centers. The main body of electricity sales includes distributed energy investors, power sales companies and energy service providers such as electric vehicle charging stations. Independent microgrids are mainly used in the market where there is no electricity on islands and border outposts to solve local power supply problems. The technical development of microgrids, Wisconsin Madison in the United States proposed the concept of microgrids, and then companies such as GE and Oracle came in to do some microgrid demonstrations. There are many in the world, but these are just some typical ones.

The development of microgrids in China. The earliest off-grid microgrid was built in Zhoushan, then the microgrid group of renewable energy in Inner Mongolia, and then the AC/DC hybrid microgrid built in Jiangsu and Guangdong. Where is the technology of microgrid applied? Industrial parks. Our own parks will also build distributed photovoltaic and decentralized wind power, and will also use some battery energy storage, and there will be some loads. It can earn the difference between peak and valley electricity prices. Its relatively stable load can realize the planned inspection, reduce the technical support of the park, and provide industrial reliability for the park. For industrial parks, the cost of using energy storage is very high, and the peak-valley price difference of electricity used in the park is relatively small. The advantage of commercial complexes is that the peak-valley electricity difference will be large, which provides a guarantee for the economic feasibility of microgrids after energy storage is connected. In islands and mountainous areas without electricity, small hydropower was used when there was water in the past, and large ones still used diesel power generation. An island in Thailand is a trend of diesel power generation, with a kilowatt-hour of electricity at 1.6 yuan. If microgrids are used now, the power supply cost can be reduced to 70 cents.

Analysis of the current status of energy consumption in industrial parks. There are four types of loads: loads that need to be guaranteed, interruptible loads, transferable loads, and later added loads. From these loads, it can be seen that there are many types of loads in the park, and they are also very complex. In Beijing, it can be seen that large-scale electricity consumption can reach more than one yuan during peak hours, and the valley value is about 37 cents. The difference between peak and valley electricity prices can be close to 80 cents, and the same is true in Shanghai. Beijing has peak electricity value. The general pricing method adopted by the park is two parts, one is the basic electricity price, and the other is the power grid price. The basic electricity price is charged according to the capacity of the transformer. If a park is 60 megawatts, it needs to pay a fixed fee of 60 megawatts every month. Take the two-step electricity price of a typical industrial park as an example, which is also the actual statistical data. From the perspective of industrial parks, the statistics of non-residential electricity consumption account for 6%, the basic capacity supporting fee accounts for 42%, and the kilowatt-hour fee accounts for 52%. The basic electricity fee accounts for a large proportion. The peak and valley electricity consumption time is 35% and the normal period is 37%, which has a lot of room for optimization. Today’s industrial parks face many problems, including high operating costs, and there is a lot of room for expansion in the future. We believe that building microgrids in industrial parks is an effective way to solve the energy supply problem in industrial parks.

The network architecture of the park-level microgrid provides data access and analysis on the cloud. The middle layer is the management system responsible for the system management of the microgrid. For AC/DC hybrid microgrids, if an energy router is used, it can replace the central controller and energy management system in the microgrid. We want to provide services, system solution services. The load conditions of microgrids are different, and the production conditions of parks are different. The built microgrid is a customized problem. It is necessary to analyze how to configure the capacity and analyze the design according to the load conditions. Solutions and energy consumption analysis need to be provided. Multi-time scale energy management, from the cloud layer to the management layer to achieve the corresponding functions. Remote operation and maintenance functions are performed through data and cloud platforms. At the primary device layer, what kind of device is the energy router? What is a router, and how is it different from a traditional Internet router? There are similarities. It is necessary to provide interfaces for all devices. There must be AC ​​and DC interfaces, high-voltage and low-voltage interfaces, and data control functions must be realized. Energy control must be realized when it is placed on energy. We believe that the energy router can be connected to photovoltaic and wind power equipment.

The essence of energy routers is power electronic devices, which used to be power electronic transformers. Power electronic transformers were proposed by GE R&D Center in the United States in 1970. They were mainly intended to replace traditional transformers with power electronic conversion technology plus high-frequency technology. There was AC at first, but why was AC finally adopted? The technical route shows that it is very difficult to change DC. The use of copper and iron as transformers can achieve electrical isolation and insulation. So far, AC is also the main architecture of the current power grid. In 1970, GE proposed that there were problems with power transformers and the cost was very high. The technology of devices is developing very fast. Now when making power electronic transformers, the performance technical indicators can be matched with the transformer level, so some people have started to make electronic transformers again. The functions achieved are the same. The ultimate goal is to achieve the lake-like interaction of electric energy and information and realize a user-friendly interface. The weight will be lighter, the volume will be smaller, there will be no pollution, and the changes and structural matching of multiple power sources can be realized, the matching of AC and DC and the matching of high and low voltage can be realized, and the two-way control of power flow can be realized.

Alstom, GE, and Bombardier all have applications, and the technical principles and topology are exactly the same. Initially, we wanted to use it for new energy and microgrids. After three years of development, we made a product that uses a 6-meter container standard design. The input power is one megawatt, the output high-voltage AC voltage level is 10 kilovolts, and the low voltage is 800 volts DC. The maximum efficiency is 98.2%, while the efficiency of traditional inverters will reach 98.5%, and the efficiency of box transformers is also about 98%. If an energy router is used to replace the inverter, the efficiency of the whole machine can be increased by more than one point. The research and development of electronic transformers and routers is a world-leading technology. We also encountered many problems when doing our work. When designing, we adopted a modular low-voltage side parallel and high-voltage side series architecture. The whole machine is composed of a certain unit. If one of them fails, it can be directly replaced. There are also benefits after using modularization. We will ensure that the system is online and running continuously. When maintenance is required, we will replace the module as soon as the maintenance time is reached to ensure the operation of key equipment at the microgrid interface.

Everyone mentioned the 98.2% efficiency. How can we achieve it? The engineering application technology of silicon carbide power devices, the soft switching technology of dual active bridge circuits, and the high-frequency isolation and high power density design technology can achieve an overall maximum efficiency of 98.2%. As a switching device, it needs to have excellent commonality, adopt a hierarchical control architecture and an integrated processor, and ultimately achieve excellent dynamics. We provide centralized high-voltage direct grid-connected solutions, as well as DC return type string type high-voltage direct grid-connected solutions. The second solution is provided for complex terrain conditions. In traditional string-type power generation, photovoltaic panels can only be connected to the AC power grid through inverters and AC cables. The use of integrated products can truly achieve simplicity through electronic routers. Photovoltaic grid connection is high voltage replacing low voltage, and DC replacing AC. We have carried out demonstration applications in the Xi'an Park. Data measurements for more than a year can achieve more than 98%, and the night standby loss is 20W.

AC microgrids can earn the difference between peak and valley electricity prices, improve power supply reliability, reduce energy consumption, and ensure environmental pollution. Taking the microgrid in Xi'an Park as an example, the photovoltaic capacity is 2 MWh, equipped with a 1 MWh energy storage system, and the investment payback period is about 6.1 years. Technically, the basic capacity needs to be reduced by 15%, and the photovoltaic self-generated and self-used electricity needs to be increased by an additional 10%.

The development of electric vehicles is charging with direct current, and photovoltaic power generation is also direct current, and the access to energy storage batteries is also direct current. The AC microgrid converts all DC loads from DC to AC, which wastes a lot of losses and increases costs. The equipment is highly integrated and can adapt to various adaptation cycles. Compared with traditional AC microgrids, the efficiency of AC/DC hybrid microgrids can be improved by 6.5% and the cost can be saved by 22%.

Microgrid market prospects. The market size of microgrids will grow steadily in the next three years. There are more than 400 microgrid demonstration projects under construction and put into use, radiating to Europe, America, Europe, and East Asia. Microgrids will participate in the power market in a new way. If our DC load accounts for a very high proportion, then AC/DC hybrid microgrids are very valuable. Energy routers will end the AC/DC dispute.