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How does the DC bus technology change V2G to V2X to realize the friendly interaction between the source network and the load storage vehicle?

In 2020, the number of electric vehicles will exceed 5 million, and disorderly charging will require seven Three Gorges power stations to meet vehicle demand. Can our vehicles reduce the impact on the grid based on the existing distribution network? How to interact with the grid friendly and become a part of the smart grid? As a DC power supply and load at the same time, how to directly exchange energy with other DC loads through the application of DC bus, so as to improve energy utilization efficiency, save energy and reduce emissions?

In 2020, the number of electric vehicles will exceed 5 million, and disorderly charging will require seven Three Gorges power stations to meet vehicle demand. Can our vehicles reduce the impact on the grid based on the existing distribution network? How to interact with the grid friendly and become a part of the smart grid? As a DC power supply and load at the same time, how to directly exchange energy with other DC loads through the application of DC bus, so as to improve energy utilization efficiency, save energy and reduce emissions?

Energy Cloud and Big Data

In the application of microgrid, especially in the application of smart microgrid, load forecasting is a very important link. The models or quantitative algorithms made in the laboratory cannot take into account the complex real-world environment, resulting in a decrease in the accuracy of daily or weekly forecasts. In this case, we can collect data from existing projects. Do dynamic policy management.

The picture above is a screenshot of the special incoming energy monitoring system. On this platform, the daily energy flow, equipment operation, and customer basic data of projects across the country can be monitored in real time, and uploaded to the cloud platform through the real-time communication network.

The picture above shows the layout of the manufacturers in the country. We understand the site as a micro-grid system, and after all uploading to the cloud, a slightly larger micro-grid is formed, and then use these data to draw different curves for artificial intelligence optimization, such as controlling electrical losses, or understanding various places It is also possible to take into account factors such as the environment, and make hourly or day load forecasts.

The picture above shows the micro-grid technology system with the word “王”, from bottom to top: interaction layer, management and control layer, and platform layer. The energy management system can be considered from these three perspectives.

Interaction layer: the realization of self-distribution systems, such as electric vehicles, photovoltaics, energy storage, DC power consumption, and heat and cold, can all be concentrated in the interaction layer.

Management: used to do some things that interact with the power grid, such as shaving peaks and filling valleys, creating a green power grid, and realizing friendly interaction with the power grid.

Platform layer: the cloud layer, including the regulation cloud, energy cloud, charging and discharging cloud, equipment cloud, operation and maintenance cloud, payment cloud, electricity sales cloud, carbon trading cloud, etc. These are all in the future after the energy network and electric vehicle big data are opened up The resulting cloud platform.

Based on the existing automobile ecological charging network and the energy management to be done in the future, an ecological value system of “dual network integration” has been constructed, which integrates new energy microgrids, power transformation and distribution, smart energy storage, solar energy, and wind energy in the automobile charging network. It is integrated with systems such as energy big data. “Dual network integration” is the core, including the manufacture of intelligent equipment, intelligent operation and maintenance, and intelligent energy management, which are all realized with big data.

Microgrid Application Technology of Common DC Bus

DC microgrid refers to a microgrid system that flexibly integrates various elements such as DC power generation, energy storage, and DC load through a stable and fast control system with power Electronic conversion equipment as a link.

Why do DC microgrids? The loads around us, such as batteries in electric vehicles, energy storage batteries, distributed power sources, computers, LED lights, Inverter refrigerators, washing machines, air conditioners, etc. are all DC loads. If AC transmission is used and then converted into DC, there will be many Energy loss, so why not hang it directly on the DC bus, this is the original intention of the DC bus.

Taking the photovoltaic system as an example, the photovoltaic output is all direct current, which is converted by DC/DC voltage, and then connected to the AC bus as DC/AC. The energy storage is also connected to the network through DC to AC. When the photovoltaic power generation is transmitted to the vehicle, it is necessary not only to convert the DC into AC, but also to convert the AC into DC, so that there will be unnecessary loss of energy. The right side of the above figure is the architecture of the DC microgrid. The photovoltaic, energy storage and automobiles are directly connected to the DC side, and a super PDU is used for energy distribution to realize the direct mutual flow of energy on the DC side.

The figure above is a schematic diagram of a campus microgrid. The blue part of the picture above is the DC bus, which uses a 1250 double split transformer. The loads on each side are symmetrical. Each bus is connected to 500kw photovoltaic, 200kw energy storage, and 200kw electric power. The car charging and discharging system, and some DC loads are also mounted, so that an autonomous small DC micro-grid is formed, and then the energy is converted with the AC side through the bidirectional converter, so that a large part of the energy is realized. Autonomy, for example, the electricity generated by photovoltaics can be directly stored to charge electric vehicles during the day. When the electricity load is relatively large during the day, the vehicle is discharged. When the DC side needs energy or excess energy, it can pass the AC/DC bidirectional converter. It is also called a four-quadrant module, which is connected to the AC side distribution network, and sends electricity to the AC side or draws power from the AC side, reducing the power draw from the large power grid and realizing the autonomy of small areas.

In such a system, the role of the car has to be mentioned. Electric vehicles are the future development trend. The concept of V2G for electric vehicles proposed by the State Grid is quoted here. V2G means vehicle-to-grid discharge. After the introduction of the DC bus, there is no need to first V2G, and then G to the load, you can directly V2H Or V2L, which forms a new concept “V2X”, that is, through the interaction of the DC side, the friendly interaction of source-grid-load-storage-vehicle can be achieved, and the vehicle can directly charge and discharge various energy sources. Management.

Taking microgrids in other regions as an example, for example, in the left half of the above figure, a set of energy management software is used to manage and control relatively independent things such as power distribution, photovoltaics, charging, and energy storage. Use, but personally feel that this is not an optimal solution.

We highly integrate power electronic equipment such as power distribution, photovoltaics, energy storage, charging, etc. into a box transformer, connected to 10kv outside, with two AC and DC busbars, AC load on the AC bus, and DC load on the AC bus. On the DC bus, such a box transformer solves the problem of four box transformers. The investment of one box transformer is used to replace the investment of four box transformers. The comprehensive investment of the equipment, including the floor space and the degree of intensification, will have a great effect. Progress, it will form a highly integrated system.

The operation of the equipment can use the energy management mode, the power distribution of the park, the energy consumption, monitoring, and the operation of the equipment in the factory area can be centrally monitored and placed in the Display system, because this energy management is placed on the cloud, so The display, monitoring, scheduling, etc. of the far transmission can all be realized.

Park power distribution

Display and monitor real-time electrical parameters such as voltage, current, and power in the park, and visually display system operating conditions

Energy consumption overview

All internal frictions occurring in the park

PV monitoring

Monitor and count the rooftop photovoltaic power generation in the park

Micro cage change

Display the real-time operating conditions of the equipment in the form of configuration diagrams

The microgrid is realized based on multiple levels of control such as local control and cloud control. On-site control can realize millisecond-level control, such as large power grid outages, on-grid switching, or cloud blocking photovoltaics, photovoltaic output reduction, etc., can realize on-site switching of equipment, through the energy management system to do minute-level or Hour-level energy load prediction, charging and discharging, economical scheduling, and cloud control.

The picture above shows the initial electricity consumption of the park. The left is the electricity load, the middle is the electricity bill, the green column represents the pure load of the plant, plus the disordered charging after the introduction of electric vehicles, as can be seen from the picture on the right, the peak is very high in the morning, Basically no one uses the electricity at night, which is also the current electricity consumption of most parks.

According to the above situation, we introduced photovoltaics into the microgrid, and the electricity bill in the park was directly reduced to 8,730 yuan; after the orderly charging and discharging of the car and the introduction of energy storage batteries, the load situation on the right side can be seen from the load situation in the trough period. It is much higher than before, and the peak time is much lower than before. The load is relatively smooth throughout the day, and the electricity bill has reached about 50% of the energy-saving expenditure. It can be said that it has achieved certain success in the application of microgrid.

key equipment configuration

The four-quadrant module integrates the functions of power products such as inverter, rectification, SVG (reactive power compensation), APF (harmonic control), off-grid operation, PCS (energy storage converter), etc. Energy routing and interconnection.

The four-quadrant module in the above figure mainly converts the energy from AC to DC. When the energy on the DC side is insufficient, this module is used to convert the energy from the AC side to realize the bidirectional conversion of DC/AC. It also integrates functions such as rectification of the power grid, reactive power compensation, switching between on-grid and off-grid, and energy storage inverters, making a modular structure.

Smart energy storage unit:

For the first time, the high-power electric energy interaction between the DC microgrid and the energy storage unit has been realized

60kW DC/DC conversion module

Single cabinet rated up to 240kW conversion, 60kW can be increased step by step

High efficiency: peak efficiency 97.5%, rated above 96.5%

Wide operating voltage range: 50~780Vdc

Wide operating temperature range: -40 degrees to 65 degrees

The same shape and size as the four-quadrant conversion module

Core device: bidirectional DCDC energy storage module

The above picture is a car charging and discharging cabinet. The car’s charging and discharging module is installed in the cabinet. Unlike ordinary charging piles, the car’s discharge function is realized here. Each module is a 10kW bidirectional DC power conversion, which can directly convert the car’s electricity Put it on the DC bus, which is equivalent to the role of DC voltage regulation and voltage transformation.

Car charging and discharging unit:

For the first time, the charging and discharging function of the DC microgrid for electric vehicles has been realized

Modular 10kW Bidirectional DC Power Conversion

The rated operating power of a single cabinet is up to 100kW, which can be increased by 10kW step by step

Combined cabinets to achieve 100kW*n power conversion

Two-way PDU realizes intelligent distribution and flexible transformation of module and electric vehicle charging

Car charging and discharging module:

Based on the third generation semiconductor SIC technology

Unidirectional main power topology plus bidirectional contactor realizes bidirectional flow of electric energy

Two-stage structure topology creates high efficiency: peak efficiency 97.5%, rated above 96.5%

Wide operating voltage range: A/B port voltage 200-700Vdc

The two-way PDU unit can be docked with the car to charge the car when the car is out of power, and it can also discharge the power on the car:

Enables power flow between vehicle end and DCDC module

Internal integrated BMS controller and power module controller

Two-way PDU real-time monitoring of charging and discharging operation process

Ensure orderly and reliable charging and discharging operations

Application Scenarios & Value Reflection

1. High-tech Industrial Park

Conducive to the development of building photovoltaics

The scale of electric vehicles

Typical peak-to-valley difference

There is a large DC load

Guaranteed power supply for important loads

Multi-energy complementary comprehensive energy saving

A large number of photovoltaics can be laid in the park, and the value of charging, discharging and energy storage of electric vehicles can be deeply utilized to realize the benefits of peak-valley price difference, and it can also ensure the power supply of important loads, and achieve comprehensive energy saving in the form of multi-energy complementation. This industrial-type microgrid system is more suitable for high-tech industrial parks.

2. New Town

Building photovoltaic power generation

Household energy storage staggered power consumption

Electric vehicle energy storage

Smart home smart electricity

It is foreseeable that in the future, glass roofs will be installed on the roofs of residential areas, energy storage on the user side, off-peak power consumption, electric vehicles will participate in power interaction, mutual discharge between neighbors, and smart homes will all appear in new towns.

3. Light storage and charging parking lot

The above picture is a micro-grid parking lot integrating photovoltaic and energy storage. The equipment contained in each column forms a small micro-grid. This type of micro-grid can also be connected to the large power grid and support each other with the large power grid. It is a better concept of distributed micro-grid.

In addition to the above scenarios, microgrids can also be used in data centers, science and technology exhibition halls, islands and villages lacking electricity, etc., combining light, wind, diesel engines, cold, heat and power in the microgrid to form a microgrid cluster to achieve and The friendly interaction of the large power grid contributes to the power grid.

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