A European utility-scale energy storage developer faced a critical project milestone: their 50 MW / 200 MWh battery energy storage system had to achieve bidirectional power conversion efficiency above 97% while maintaining galvanic isolation between the 1500V DC battery bus and the medium-voltage AC grid. Standard off-the-shelf transformers could not meet the combined requirements of high efficiency, bidirectional operation, and grid code compliance. The project schedule left no room for multiple design iterations.
TPS Elektronik’s custom transformer solutions for energy storage applications were engaged to design, manufacture, and deliver a purpose-built isolation transformer that enabled the PCS to achieve bidirectional power conversion with minimal losses—from concept to grid-connected operation in under 16 weeks.
1. The Challenge: Bidirectional Power Conversion at Utility Scale
Utility-scale battery energy storage systems (BESS) are the backbone of grid modernization and renewable energy integration. These systems must efficiently convert power in both directions: from AC grid to DC battery storage during charging, and from DC battery to AC grid during discharging. At the heart of this bidirectional power flow is the power conversion system (PCS), which relies on a transformer to provide galvanic isolation, voltage transformation, and grid interface.
The customer—a European renewable energy developer—was planning a 50 MW / 200 MWh BESS installation to support grid stabilization and renewable integration. The project required:
- Bidirectional power conversion with efficiency above 97% in both directions
- Galvanic isolation between the 1500V DC battery bus and the medium-voltage AC grid
- Grid code compliance with European grid connection requirements
- Containerized footprint for rapid deployment and scalability
- Thermal management for continuous operation in outdoor environments
The previous supplier was unable to deliver a transformer that met the combined requirements of high efficiency, bidirectional operation, and the physical constraints of containerized deployment. Standard off-the-shelf transformers either lacked the efficiency required for the project’s ROI targets or could not provide the galvanic isolation needed for the 1500V DC bus.
TPS Elektronik was engaged to develop a custom energy storage transformer solution that would enable the PCS to achieve bidirectional power conversion with minimal losses while meeting all grid code requirements.
2. The TPS Solution: Custom Energy Storage Transformer Design
TPS Elektronik’s approach combined deep expertise in power electronics with a comprehensive understanding of grid-tied energy storage requirements. The solution encompassed custom transformer design, manufacturing, and integration support.
Custom Design & Engineering:
- Custom transformer design optimized for bidirectional power conversion
- Core and winding design for minimal losses at 50 Hz / 60 Hz operation
- Insulation system rated for 1500V DC bus voltage with appropriate creepage and clearance
- Thermal design for forced-air cooling in containerized deployment
Manufacturing & Quality:
- Precision winding and core assembly per IEC 60076 standards
- In-process quality control and testing at every manufacturing stage
- Factory Acceptance Testing (FAT) per customer specifications
- Full documentation package including test reports and material certificates
Integration Support:
- Mechanical integration guidance for containerized deployment
- Electrical interface coordination with PCS and grid connection equipment
- Commissioning support and on-site testing
TPS Elektronik’s custom transformer solutions service is built on a foundation of extensive EMS capabilities. TPS is a power electronics EMS service provider specializing in industrial power supplies, energy storage for renewable energies, and customized OEM and ODM production services. This vertical integration—from component sourcing to final assembly—enabled faster prototyping and reduced supply chain complexity for the customer.
3. Technical Approach: 1500V DC Isolation and Grid-Tied Compliance
The technical foundation of the TPS solution was a custom-designed isolation transformer that addressed the specific requirements of 1500V DC battery systems and grid-tied bidirectional operation.
Isolation Transformer Design:
- Voltage rating: Custom winding configuration to match the 1500V DC battery bus and medium-voltage AC grid
- Power rating: Scaled to match the 50 MW PCS capacity with appropriate overload margins
- Insulation system: Reinforced insulation with creepage and clearance per IEC 60076 and applicable grid codes
- Core material: Grain-oriented silicon steel with low losses for high efficiency
- Winding configuration: Optimized for bidirectional power flow with minimal impedance variation
Bidirectional Power Conversion Optimization:
Bidirectional operation presents unique challenges for transformer design. Unlike unidirectional transformers, where power flow is constant in one direction, bidirectional transformers must maintain efficiency and voltage regulation regardless of power flow direction. TPS addressed this through:
- Symmetric winding design that maintains consistent leakage inductance in both directions
- Low-loss core materials that minimize hysteresis and eddy current losses under varying load conditions
- Optimized turn ratios that support both charging and discharging voltage requirements
Grid Code Compliance:
- Harmonic distortion mitigation through optimized transformer design
- Voltage regulation to meet grid connection requirements
- Protection coordination with PCS and grid protection systems
For grid-tied BESS transformer applications, the isolation transformer serves as the critical interface between the battery system and the grid. It provides galvanic isolation for safety, voltage transformation to match grid levels, and impedance for fault current limitation. TPS’s design ensured that all three functions were optimized for the customer’s specific application.
4. Results: 98.2% Efficiency and Grid Code Compliance
The custom energy storage transformer delivered by TPS Elektronik exceeded the customer’s performance targets while meeting all grid code requirements.
Key Results:
- Bidirectional efficiency: 98.2% measured efficiency in both charging and discharging modes, exceeding the 97% target
- Galvanic isolation: Reinforced insulation rated for 1500V DC bus voltage with safety margins
- Grid code compliance: Full compliance with European grid connection requirements, including harmonic limits and voltage regulation
- Containerized deployment: Transformer footprint optimized for 20-ft ISO container installation
- Delivery timeline: Design, manufacturing, and FAT completed in under 16 weeks
Operational Benefits:
- Reduced energy losses: The 98.2% efficiency translates to approximately 1.8% losses in the power conversion chain, improving overall system ROI
- Simplified integration: The custom design eliminated the need for additional interface components, reducing installation time
- Future scalability: The modular design supports future expansion of the BESS installation
This case study demonstrates how TPS Elektronik combines expertise in power electronics, custom transformer design, and energy storage architectures to deliver end-to-end solutions for utility-scale BESS projects. By integrating custom transformer design with broader EMS capabilities, TPS ensured not only technical excellence but also regulatory compliance and long-term reliability.
5. TPS Custom Transformer Solutions for Energy Storage
TPS Elektronik’s custom transformer solutions for energy storage applications combine engineering expertise, manufacturing capability, and comprehensive quality assurance in a single integrated service.
Engineering & Design:
- Custom transformer design for BESS, PCS, and renewable energy applications
- Bidirectional power conversion optimization
- 1500V DC isolation system design per IEC 60076
- Thermal management and mechanical integration
- Grid code compliance and certification support
Manufacturing Capabilities:
- Precision winding and core assembly
- Reinforced insulation systems for high-voltage DC applications
- Forced-air and liquid-cooled designs
- Containerized and skid-mounted configurations
- Power ratings from kW to MW scale
Quality & Compliance:
- IEC 60076 transformer standards compliance
- UL 9540 and NFPA 855 for BESS applications
- Factory Acceptance Testing (FAT) per customer specifications
- Full documentation and material traceability
Integration Support:
- Mechanical and electrical interface coordination with PCS
- Grid connection support and protection coordination
- Commissioning and on-site testing
TPS supports energy storage projects of any scale, from small commercial systems to utility-scale installations exceeding 100 MW. TPS’s custom transformer solutions service is integrated with broader EMS capabilities—including power supply design, battery testing, and energy storage architectures—reducing supply chain complexity for system integrators and procurement teams.
