Four design considerations when adding energy storage battery equipment to a photovoltaic grid

  While the number of photovoltaic (PV) facilities continues to grow, the imbalance between the supply and demand sides of the solar grid has become a major constraint. There is plenty of solar energy available during the day, but the demand is not very much. That means customers will pay a higher price per watt in the morning and evening during peak usage hours.

  Energy storage systems (ESS) for solar devices in residential, commercial, and public utilities use inverters to store electricity or the grid during the day when demand is lowest and to store when demand is huge, releasing the energy that has been generated. Adding ESS to a grid-connected solar system allows users to save money on the use of a technology called "peak shaving."

  Bidirectional Power Conversion

  Traditional PV equipment consists of unidirectional DC/AC and DC/DC power stages, but the unidirectional conversion method is a major obstacle to the incorporation of ESSs. More components, modules and subsystems are required, all of which significantly increase the cost of adding an ESS to an existing solar installation.

  To add a battery to an existing PV device, the two paths of battery charging and discharging must be combined into a single path consisting of power factor correction (PFC) and inverter power levels. . But how do you build a bidirectional power converter instead of two unidirectional power converters?

  Hybrid inverters can effectively improve the efficiency of the conversion stage, but this efficiency improvement is more important for ESS-equipped microgrids that perform multiple power conversions. The power converter system manages the DC/DC conversion to charge and discharge the battery. It also manages DC/AC and AC/DC conversion, which converts direct current stored in batteries to alternating current for both inflow and outflow from the grid.

  High voltage battery

  In a microgrid system with storage battery, the main function of the battery is to store photovoltaic energy and supply power to the grid on demand. Lithium-ion batteries have significantly higher storage capacity per unit than lead-acid batteries.

  While 400V batteries are gaining popularity in electric vehicles (EVs), solar grid devices are also increasing the battery voltage from 48V. But how do you manage the power conversion of a 400V battery pack?

  In addition to microcomputers with system control and communication capabilities that incorporate ESS into larger systems, low-loss and efficient power switches also improve the safety and reliability of energy storage systems. Compact power switches and real-time microcomputers based on silicon carbide (SiC) and gallium nitride (GaN) materials allow modification of two-way converters to accommodate a variety of DC energy storage units.

  Dual Active Bridge DC/DC Converter Design

  Wide-band gap semiconductors such as SiC and GaN play an important role in solving power conversion systems that can handle the rising battery voltage range as converters increase power density and reduce switching losses. . The power conversion system also allows the battery pack to better manage power fluctuations in the distributed generation system, resulting in smart and resilient grid operation at higher and wider voltages.

  Eventually, solar devices could mimic the battery packs used in electric cars. The idea of recycling battery packs currently used in electric vehicles as grid-connected ESS is becoming common.

  Wide Bandgap Materials Required for Efficiency and Natural Convection

  In order to build an intelligent wall-mounted storage system, it is necessary to design an inverter that optimizes heat dissipation using minimal natural convective cooling. Distributed power architectures allow heat to be centrally distributed throughout the system. This architecture ensures that the required energy storage inverters can handle high current levels at different voltages and reliably respond to rapidly changing load transients.

  Such systems require gate drivers that support high-speed switching and provide protection at switching frequencies of 100kHz to 400kHz. If the switching speed is not fast enough, you will find that the power conversion phase is significantly inefficient.

  This is where wideband gap materials with fast switching and high power densities, such as SiC and GaN, come in. These semiconductor devices facilitate the design of systems that do not require fan cooling. The LMG3425R030 GaN device with built-in driver and protection features features compact profile, high power density and fast switching.

  The gate driver converts the controller's digital PWM signal into the current required by the SiC or GaN field-effect transistor (FET). The PWM based controller allows accurate sampling of voltage and current across multiple power conversion stages.

  Current and Voltage Detection

  The design of high frequency switching power supply is faced with the challenge of accurate current and voltage sensing. Current measurements with a shunt not only improve accuracy but also speed up reaction times, allowing you to react quickly to any changes in the grid, so you can shut down system connections if the grid is short-circuited or disconnected. Increased.

  Current measurements are essential for inverter-centric designs, as the control algorithm requires electrofluometric measurements for control. Some design solutions are available for isolated current measurements using amplifiers/modulators and power supplies isolated from external shunts.

  Power converters need to measure the current in the grid to see if the current is in phase with the voltage. By measuring the current and voltage, in addition to controlling the charging current of the battery, the inverter operation and overload protection function are also controlled.

  Conclusion

  Hybrid inverters, which perform bidirectional power conversion between AC/DC and DC/DC, are expected to replace traditional solar inverters in the coming years. Solar inverter designers will be able to achieve power conversion with a wide output power and voltage range by using hybrid inverters.

  Increasing the battery voltage and expanding the voltage range are important issues for energy storage compatible solar inverters. With essential components like microcomputer control and wide bandgap semiconductors with built-in gate drivers and protection, these higher and wider cell voltages can be supported in addition to the need for high efficiency and natural convection.