OEM & Lieferant Ausgabe 1/2022

90 Products and Markets Magnetic Components that Meet 1500 V Battery Energy Storage Requirements By Cathal Sheehan, Senior Technical Magnetics Marketing Manager at Bourns and Suker Zeng, Signal Magnetics Product Manager at Bourns The demand for renewable energy continues to grow and has led to the development of flexible energy systems to allow renewable sources to be reliably and safely connected to the energy grid. These next-generation systems need the support of equally advanced magnetic component technologies that provide power protection, switching and conversion. One of the potential solutions seen to help support system flexibility is in the use of energy storage systems, which have the unique capability to quickly absorb, hold and then reinject electricity. Over the last few years, DC voltages in energy storage systems have continued to increase leveraging higher lithium-ion battery voltages where today, 250 VDC, 600 VDC, 1000 VDC and now even 1500 VDC are employed. One of the key drivers of these higher-voltage systems is the availability of advanced solar inverters and power converters. Considering that most utility-scale battery energy storage systems are now being deployed alongside utility scale solar installations, it makes sense that the battery systems match the input DC voltages of the inverters and converters. Most utility-scale solar inverters and converters now use 1500 VDC input from solar panels. Magnetic Components Rated to 1500 VDC There are several ways energy sources can be connected to the grid such as with breakers, disconnect switches, insulation monitors, fuses and ground fault devices. Because these systems have evolved to support higher DC voltages, designers are increasingly challenged to find components rated at higher voltages and ones that also provide embedded protection features. Meeting the needs of these new systems, Bourns has developed insulated magnetics products rated at 1500 VDC. For example, Bourns’ new Model SM91527L single channel signal transformer with integrated common mode choke is designed to meet the demanding isolation and EMI filter requirements on isoSPI™ communication buses in a Battery Energy Storage System (BESS). Bourns® Model SM91527L features a creepage of 15 mm between primary and secondary so it is an ideal solution for use in environments requiring reinforced isolation with working voltages of 1500 V. In addition, Bourns’ new signal transformer has UL approval, which gives designers higher safety confidence. The Bourns 1500 V signal transformer isolates and protects the battery management system (BMS) board isoSPI™ interface (shown in Figure 1). Of importance in this application is that the BMS interface operates in a nonhazardous environment separate from the battery pack voltage, and at the same time, provides the necessary matching and common mode noise removal. This design is so that the communications between the monitoring ICs and the central management board are also secure and uninterrupted. In addition, the features of the Model SM91527L transformer allow it to still meet isoSPI™ driver recommendations in terms of insertion loss (Max. 1.2 dB at 4 MHz) and EMI (-50 dB 1-100 MHz CMRR). Transformer Testing Requirements Transformers with reinforced insulation up to 1500 V are required to meet test specifications as defined by IEC 60664. The standard was developed to prove the insulation supplied will survive sudden surges, which are possible from the electricity grid or from the battery pack itself. A key consideration for designers is that the application determines the level of surge testing that is required during qualification. That’s because consumer equipment has a particular overvoltage category requirement while industrial equipment may need to be rated to a different category. Surge tests are used to primarily check for adequate clearance, so that if an event such as a lightning strike were to occur, the gap between the windings on the transformer would not break down and ionize causing a crossover. To be rated at 1500 V for an overvoltage category 2 up to a 5000-meter altitude, a reinforced transformer must be able to withstand an impulse test of 12 kV peak. Graphics: © Bourns Figure 1: Block Diagram Showing the Connection of the IsoSPI™ Bus between Primary and Secondary

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