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With the rapid development of distributed energy, home energy storage systems have become increasingly important in improving energy utilization efficiency and enhancing power supply stability. As a core component of home energy storage systems, bidirectional DC-DC converters play a crucial role in achieving efficient and flexible bidirectional energy flow between batteries, the grid, or loads. Among the various components of bidirectional DC-DC converters, high-current power inductors play an extremely important role, and their performance directly affects the overall efficiency, stability, and reliability of the converters.
1- Overview of the Working Principle of Bidirectional DC-DC Converters in Home Energy Storage Systems
Bidirectional DC-DC converters can transfer energy between different DC voltage levels. In charging mode, they convert the higher voltage from the grid or photovoltaic sources into a lower voltage suitable for battery charging to store energy. In discharging mode, they boost the lower battery voltage to a higher voltage that meets load requirements or can be fed back to the grid. Taking the common Buck-Boost type bidirectional DC-DC converter as an example, in the Buck step-down mode, when the power switch (MOSFET) is on, the input power supply supplies power to the load through the inductor, increasing the inductor current and storing energy. When the switch is off, the inductor current continues to flow to the load through a freewheeling diode (or synchronous rectifier), releasing its stored energy, thus achieving continuous power supply to the load during switch-off periods. In the Boost step-up mode, when the switch is on, the input power supply charges the inductor, which stores energy. When the switch is off, the inductor and the input power supply work together to increase the output voltage.
Figure 1. Residential energy storage application scenario diagram
2- The Role of Power Inductors in Bidirectional DC-DC Converters
Power inductors play a crucial role in bidirectional DC-DC converters as key components for energy storage and transfer. During the switching on phase, the inductor current gradually increases, and electrical energy is stored in the inductor as magnetic energy. When the switch is turned off, the inductor current decreases, and the magnetic energy is converted back into electrical energy, ensuring the continuity of current in the circuit and achieving voltage step-up or step-down conversion. Since power inductors in bidirectional DC-DC converters primarily operate in high-ripple current environments, resulting in significant losses, reducing the DCR of the inductor and increasing the operating frequency can help control these losses under high-ripple current conditions.
3- The Impact of Power Inductors on Bidirectional DC-DC Converters
3.1 Inductance Value
The inductance value directly affects the voltage conversion ratio, current ripple, and dynamic response speed of the converter. When the inductance value is large, the current ripple is small, which can make the output voltage smoother, benefiting the improvement of the converter's efficiency and stability. However, it may cause the dynamic response of the converter to slow down, making it unable to quickly adjust the output voltage when the load changes. When the inductance value is too small, although the dynamic response is fast, the current ripple is large, increasing the power device losses and reducing the converter's efficiency, and it may even cause circuit oscillation, affecting the normal operation of the system. In practical design, it is necessary to comprehensively consider the operating mode of the converter, load characteristics, and performance requirements to accurately select the inductance value.
3.2 Saturation Current
When the current across the inductor is too large, the magnetic flux density of the core reaches the saturation value, the inductor enters a magnetic saturation state, and the inductance value drops sharply. In bidirectional DC-DC converters, magnetic saturation of the inductor can lead to the current out of control, a significant increase in ripple, and damage to power switching devices due to over current, severely affecting the normal operation of the converter. To avoid magnetic saturation, it is necessary to reasonably design the core material and size to ensure that the inductor does not saturate under the maximum operating current of the converter. At the same time, methods such as increasing the air gaps can be adopted to broaden the linear operating range of the inductor and improve the reliability of the converter. Codaca has independently developed multiple series of high-current magnetic powder core inductors, using patented-formulated magnetic powder cores to enhance the saturation characteristics of the inductors.
3.3 DC Resistance (DCR)
DC resistance refers to the internal resistance of the inductor's coil under DC conditions. The lower the DCR, the less power loss is generated when current flows, thereby improving overall efficiency.
When selecting, prioritize products with low DCR characteristics to reduce conduction losses and improve converter efficiency.
3.4 Operating Frequency
Increasing the switching frequency of bidirectional DC-DC converters can reduce the size of passive components such as inductors and capacitors, enhancing the converter's power density and dynamic response speed. However, when inductors operate at high frequencies, the impact of parasitic parameters intensifies, with skin effect and proximity effect leading to a significant increase in inductor losses. Traditional magnetic materials may not meet the requirements, exacerbating issues such as core loss-induced heating. Therefore, selecting inductor products for high-frequency applications is a crucial step in ensuring system stable operation.
3.5 Operating Temperature
Household energy storage systems operate in complex environments, requiring power inductors to possess excellent physical properties and environmental adaptability. The size and weight of the inductor must meet the compact design requirements of household energy storage equipment. In harsh environments such as high temperatures and humidity, the inductor should maintain stable performance, with core materials that are not easily affected by temperature and humidity, and exhibit good heat dissipation performance along with moisture, mold, and corrosion resistance. When selecting, it is preferable to choose high-temperature operating inductors with low temperature and DC bias characteristics, such as high-current ferrite core products.
4- Codaca's Solutions for Household Energy Storage Bidirectional DC-DC Converters
Codaca has provided multiple adapted inductor solutions for residential bidirectional DC-DC converters through independent R&D and technological innovation, contributing to green and low-carbon development. CODACA has launched multiple models of high current power inductors, offering various electrical characteristics and package designs to meet the high-performance requirements of the inductors for this application. Among them, Codaca's independently developed high current power inductor with a magnetic powder core features high saturation current, low loss, high conversion efficiency, and high operating temperature, meeting the demands of the residential bidirectional DC-DC converter system for high operating current, low loss, and high power density.
Figure 2.Codaca High-Current Inductor
As the core component of residential bidirectional DC-DC converters, power inductors play an irreplaceable role in energy storage and conversion, as well as in current ripple suppression. Their performance directly impacts the efficiency, stability, and reliability of the converters. With the continuous advancement of residential energy storage technology, the performance requirements for power inductors are becoming increasingly stringent, with high power density, high-frequency operation, and integration emerging as key development trends. In response to these challenges, Codaca Electronics conducts in-depth research in areas such as magnetic core material development and structural design optimization to continuously enhance the performance of power inductors, providing solid support for performance improvement and technological innovation in residential bidirectional DC-DC converters. This helps facilitate broader and more efficient applications of home energy storage systems in the field of distributed energy.