Energy storage technology can smooth the output of photovoltaic power and make new energy power stations merge them friendly. Therefore, the “photovoltaic+energy storage” mode will make it possible for us to truly enter the renewable energy era.
The function of the energy storage system is to store the photovoltaic energy into the battery timely, and then input the electric energy into the power grid timely. Compared with AC-side energy storage system, the DC-side energy storage system, for its higher efficiency, has more advantages in the application of photovoltaic power generation side. It is very important for DC-DC bidirectional converter, the most critical power conversion center for energy storage on DC-side, to adapt to the diversity of batteries and to own functional diversity.
Can DC-DC adapt to the diversity of batteries?
- Lithium battery
Currently, most electrochemical energy storage power stations are mainly dominated by lithium batteries, which have high power density and long cycle life. Due to the rapid development of electric vehicles, the cost of lithium batteries has been greatly reduced, and the cost per watt of ternary lithium-iron batteries is less than 0.15USD. Therefore, lithium batteries have been widely used in energy storage power stations.
However, the safety problem of lithium batteries is also very serious, and this asks strict requirements of power devices. DC-DC shall, thus, have adjustable bidirectional voltage with gradual onset, and need to communicate with BMS of batteries, so as to protect batteries.
- 2. Flow battery
The flow battery is now called the “best match” battery for energy storage in photovoltaic system. It is characterized by high reliability, long service life, high residual value and ease of maintenance, well-matched with photovoltaic power stations that can generate electricity for 25 years. However, there is no obvious breakthrough in the problems of low density and low conversion efficiency of flow battery, so most of the flow battery projects are still pilot demonstration projects.
However, DC-DC bidirectional energy storage converter is supposed to be compatible with flow battery. DC-DC has to run at low voltage and be able to limit current and precharge flow battery, since the voltage of flow battery is low and there is no voltage at its first use.
- 3. Echelon battery
The echelon battery, also known as the secondary battery, belongs to the battery of secondary utilization. Nowadays, with such a large scale of electric vehicles, a large number of echelon batteries will appear continuously. The consistency of the echelon battery is poor, which asks very high requirements for DC-DC and BMS. Therefore, in order to match the echelon battery, DC-DC is supposed to have two-stage topology to solve the consistency problem well.
Can DC-DC meet the requirements of different functions under different circumstances?
- Application of constant power mode
At present, the common application mode of DC-DC is mainly constant power mode, that is, DC-DC connects the battery with the DC bus, as shown in the following figure. In this application, DC-DC bidirectional converter is supposed to achieve remote control, accept the scheduling of EMS, and charge and discharge under certain circumstances.
- 2. Application of MPPT mode
In some areas with high demand for frequency modulation, DC-DC has an innovative application whose topology is shown in the following figure. This application requires DC-DC to have MPPT function, which can track the maximum power point of photovoltaic panels to generate electricity, so as to achieve the highest power generation. Besides, the application system can well assist the work of power grid.
Based on a deep understanding of the development trend of energy storage, Kehua has developed the DC-DC bidirectional converter product that can meet the needs of multiple conditions, and has been applied in southern India for two years. After these two years of continuous verification and upgrading, Kehua’s DC-DC bidirectional converter has been already equipped with various functions.
About Kehua
Deeply involved in power electronics core technology for 32 years, Kehua has become the world-leading energy solution provider. With combining artificial intelligence with cutting-edge technology applications of the Internet of Things, Kehua is committed to applying the “digital and situation-based intelligent energy integrated management system” in different scenes. In the three major fields of new energy, high-end power supply and cloud basic services, Kehua provides safe, reliable and efficient intelligent energy integrated management solutions for customers from various walks of life such as government, finance, industry, communications, transportation and Internet.
