Anwendungen von bidirektionalen Stromversorgungen: Vom EV-Laden bis zur Netzstabilisierung
Aug 9, 2024
As the world moves away from fossil fuels toward renewable energy, the electrical grid is evolving to keep pace. The traditional model — large coal, gas, or nuclear power plants supplying electricity to consumers in a largely monopolistic structure — is giving way to a smart grid that combines conventional generation with renewable energy sources from both public and private suppliers. Alongside this shift is a growing need for bidirectional power supplies to enable efficient power conversion and energy flow between different smart grid elements. In this blog, we examine bidirectional power supplies, their applications, and how RECOM is helping customers address these emerging requirements.
Table of Contents
- The Power Grid is Evolving: From One-Way to Smart Grid Architecture
- Energy Storage: The Key to Grid Stability and Renewable Integration
- Battery-Based Energy Storage and Renewable Energy Sources
- EV Charging: Bidirectional Power Supplies Enable V2G and V2H
- Unidirectional vs Bidirectional Power Architectures
- RECOM’s Solutions for High-Reliability Bidirectional Power Supplies
- Conclusion
The Power Grid is Evolving: From One-Way to Smart Grid Architecture
The foundation of the traditional power grid dates back to 1935 and is defined by a one-way power flow, from generating stations through the distribution network to consumers. Generating capacity is relatively static, with minimal excess capacity available to accommodate sudden spikes in demand.
As a result, the conventional grid is prone to instability, as it struggles to respond to rapid load changes. Its reliance on legacy electromechanical control technologies offers limited control capability and little real-time insight into usage patterns. This one-directional architecture also makes it difficult to efficiently integrate renewable energy sources such as wind or solar.
Utility companies are actively modernizing grid infrastructure. The smart grid is designed to deliver real-time monitoring and control, integrate wind and solar generation, support grid stabilization, and dynamically balance energy supply with load demand.
As a result, the conventional grid is prone to instability, as it struggles to respond to rapid load changes. Its reliance on legacy electromechanical control technologies offers limited control capability and little real-time insight into usage patterns. This one-directional architecture also makes it difficult to efficiently integrate renewable energy sources such as wind or solar.
Utility companies are actively modernizing grid infrastructure. The smart grid is designed to deliver real-time monitoring and control, integrate wind and solar generation, support grid stabilization, and dynamically balance energy supply with load demand.
Energy Storage: The Key to Grid Stability and Renewable Integration
Increasing the share of electricity generated from wind and solar introduces greater uncertainty in generation capacity. The availability of energy from wind and sunlight varies unpredictably, making renewable power inherently more variable than fossil fuel or nuclear generation. A typical solar installation delivers less than 25% of its theoretical maximum output over a year, known as the capacity factor (CF), while wind turbines achieve less than 40%. By comparison, nuclear power plants commonly exceed a 90% CF. In addition, renewable generation capacity cannot be ramped quickly to match minute-by-minute fluctuations in electricity demand.
Energy storage provides a critical mechanism to balance supply and demand. When demand exceeds supply, stored energy can be discharged to stabilize the grid and prevent brownouts or outages. Conversely, when generation exceeds demand, surplus power is used to recharge energy storage systems.
Energy storage provides a critical mechanism to balance supply and demand. When demand exceeds supply, stored energy can be discharged to stabilize the grid and prevent brownouts or outages. Conversely, when generation exceeds demand, surplus power is used to recharge energy storage systems.
Battery-Based Energy Storage and Renewable Energy Sources
Pumped-storage hydropower remains the most widely deployed energy storage technology, but battery-based energy storage systems are the most scalable and are experiencing the fastest growth.
Fig. 2: ESS functional blocks (Source: SAFT batteries)
Figure 2 illustrates the main functional blocks of a grid-scale battery-based energy storage system. Bidirectional power supplies enable energy transfer between the grid and the storage system. AC power from the grid is converted to DC to charge the batteries, while stored DC energy is converted back to AC and returned to the grid during grid stabilization events. In many installations, the ESS is paired with renewable energy sources. Green energy from wind turbines, which produce AC power, or photovoltaic arrays, which generate DC power, can be routed either to the battery system or directly to the grid as required. Solar panels on commercial or residential buildings can likewise supply energy to an ESS or export it to the grid.
All of these energy flows must be carefully controlled, coordinated, and monitored. RECOM supplies a wide range of low-power, high-isolation DC/DC converters, offering isolation voltages of up to 20kVDC, for battery management systems, communication networks, and the voltage, current, temperature, fire, and pressure sensors required to build reliable and safe battery energy storage installations.
Fig. 2: ESS functional blocks (Source: SAFT batteries)
Figure 2 illustrates the main functional blocks of a grid-scale battery-based energy storage system. Bidirectional power supplies enable energy transfer between the grid and the storage system. AC power from the grid is converted to DC to charge the batteries, while stored DC energy is converted back to AC and returned to the grid during grid stabilization events. In many installations, the ESS is paired with renewable energy sources. Green energy from wind turbines, which produce AC power, or photovoltaic arrays, which generate DC power, can be routed either to the battery system or directly to the grid as required. Solar panels on commercial or residential buildings can likewise supply energy to an ESS or export it to the grid.
All of these energy flows must be carefully controlled, coordinated, and monitored. RECOM supplies a wide range of low-power, high-isolation DC/DC converters, offering isolation voltages of up to 20kVDC, for battery management systems, communication networks, and the voltage, current, temperature, fire, and pressure sensors required to build reliable and safe battery energy storage installations.
EV Charging: Bidirectional Power Supplies Enable V2G and V2H
Electric vehicles represent another rapidly expanding application for bidirectional power supplies. As battery-electric vehicles continue to gain market share, the installed battery capacity per vehicle is increasing. At the same time, consumers expect shorter EV charging times for these higher-capacity batteries. This demand is driving a shift in battery operating voltages from 400V to 800V, starting with high-performance models. An EV with sufficient battery capacity can effectively function as a mobile energy storage system, enabling use cases such as vehicle-to-home power supply, vehicle-to-grid operation, vehicle-to-vehicle charging, or jumpstarting another EV. Today’s EV charging infrastructure and onboard chargers are largely unidirectional, but these emerging vehicle to grid and V2G scenarios are accelerating the transition toward bidirectional architectures.
Scenarios that require bidirectional power supplies in EVs and EV charging systems include:
Scenarios that require bidirectional power supplies in EVs and EV charging systems include:
- EV supplying power back to the grid or to a residential microgrid.
- EV charging stations delivering power to vehicles either directly from the grid or from stored energy, depending on electricity pricing.
- EV charging stations recharging an onsite battery storage system.
Unidirectional vs Bidirectional Power Architectures
Designing a bidirectional power supply requires a fundamentally different approach than designing an equivalent unidirectional system. High-efficiency unidirectional AC/DC converters typically use wide-bandgap SiC or GaN devices with a totem-pole power factor correction stage feeding a DC/DC topology such as an LLC resonant converter.
While the totem-pole PFC stage is inherently bidirectional, the LLC resonant converter is not. For bidirectional power conversion, a CLLC resonant converter is preferred in the DC/DC stage, as it delivers high efficiency and supports a wide output voltage range in both charging and discharging modes. The CLLC topology employs soft-switching techniques to maximize efficiency, achieving zero-voltage switching on the primary side and a combination of zero-voltage and zero-current switching on the secondary side. SiC devices are increasingly becoming the dominant technology for these high-power applications.
Figure 3 shows an example of a bidirectional power stage designed for three-phase EV charging. The architecture requires 14 power transistors and uses an isolated topology, with the power devices supported by isolated gate drivers and isolated DC/DC power supplies.
While the totem-pole PFC stage is inherently bidirectional, the LLC resonant converter is not. For bidirectional power conversion, a CLLC resonant converter is preferred in the DC/DC stage, as it delivers high efficiency and supports a wide output voltage range in both charging and discharging modes. The CLLC topology employs soft-switching techniques to maximize efficiency, achieving zero-voltage switching on the primary side and a combination of zero-voltage and zero-current switching on the secondary side. SiC devices are increasingly becoming the dominant technology for these high-power applications.
Figure 3 shows an example of a bidirectional power stage designed for three-phase EV charging. The architecture requires 14 power transistors and uses an isolated topology, with the power devices supported by isolated gate drivers and isolated DC/DC power supplies.
RECOM’s Solutions for High-Reliability Bidirectional Power Supplies
RECOM offers high-reliability custom battery chargers, power conditioners, and bidirectional inverters based on proven platform designs for three-phase AC supplies, with power ratings up to 30kW and even higher when multiple units are connected in parallel. RECOM also maintains an extensive library of platform designs through RECOM Power Systems, which specializes in fast-turnaround, high-power, and full-custom solutions. These established designs can often be adapted for new applications without incurring significant additional development or certification costs.
Conclusion
The emergence of the smart grid and the continued expansion of renewable energy are driving increased demand for bidirectional power supplies capable of transferring AC or DC power between energy sources, energy consumers, and energy storage systems. RECOM supports every layer of the smart grid, from low-power DC/DC converters used to isolate battery management systems and wind turbine controllers, to low standby-power AC/DC converters for smart meters, EV charging equipment, and photovoltaic inverters, and up to kilowatt-scale power conversion solutions for off-grid systems, energy storage installations, and related applications
Ready to get started on your next design? Contact us today.
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