Fluxgate Sensors in SST: Precision & Protection

What is SST?

SST stands for Solid-State Transformer, also known as Power Electronic Transformer (PET). From the perspective of power transmission, a typical SST connects to a 10 kV AC grid on the primary side and outputs approximately 800 V DC on the secondary side. The power conversion process generally involves two stages: AC-to-DC and DC-to-DC (step-down). When the output is used for individual equipment or integrated into servers, an additional stage to step down from 800 V to 48 V is required.

SSTs retain the basic functions of traditional transformers while integrating advanced capabilities such as reactive power compensation, harmonic mitigation, and bidirectional power flow control. They are primarily used in high-power applications such as renewable energy grid integration, EV charging stations, and computing centers (e.g., AIDC).

SST: The Optimal Solution for the High-Power AIDC Era

SST represents the third-generation high-voltage DC power distribution solution.

• First-generation HVDC retains the conventional power-frequency transformer structure, upgrading only the Uninterruptible Power Supply (UPS) side.

• Second-generation solutions, such as the Panama power supply, replace the power-frequency transformer with a phase-shifting transformer, improving integration.

• Third-generation SST replaces the power-frequency transformer with a high-frequency transformer, achieving the highest level of integration.

The core of SST lies in abandoning the iron-core and winding structure of traditional transformers, instead using semiconductor devices such as IGBTs and SiC. SST offers further advantages in:

• Conversion efficiency (end-to-end efficiency improved by over 3 percentage points),

• Construction time (only 30% of traditional UPS solutions),

• Footprint (reduced by more than 50% compared to traditional UPS),

• Renewable energy integration (direct green power supply without additional conversion modules).

Theoretically, by reducing the number of voltage and current conversions, SST minimizes power transmission losses, precisely addressing the pain points of power distribution in high-power data centers.

Application of High-Precision Fluxgate On-Board Current Sensors in SST

Precise Current Sensing for Power Conversion and Control

SST’s AC/DC and DC/DC converters rely on advanced modulation algorithms and closed-loop control. The upper limit of control accuracy is determined by sensor precision. The near-"absolute truth" current signal provided by fluxgate sensors forms the foundation for accurate controller calculations (e.g., generating compensation signals, computing active and reactive power). Low temperature drift ensures this accuracy is maintained not just under lab conditions, but across the full operating temperature range. As SST power modules generate significant heat during operation, environmental temperatures fluctuate dramatically. The low-drift characteristic ensures consistent control references from startup to full load, preventing efficiency degradation or control instability due to sensor drift.

Accurate Overcurrent and Short-Circuit Protection

Power semiconductor devices (e.g., SiC MOSFETs) inside SSTs operate at high switching frequencies but have limited tolerance to overcurrent. Fault currents must be interrupted within microseconds. The fast response of fluxgate sensors acts like a high-speed camera, instantly capturing current spikes, providing critical reaction time for drive and protection circuits to prevent cascading device failures. This not only ensures safety but also enhances system dynamic performance. Rapid current feedback allows the controller to quickly suppress disturbances caused by load transients, maintaining stable bus voltage.

Strong Noise Immunity for Data Accuracy and Reliability

SST itself is a powerful source of high-frequency electromagnetic interference. Traditional current sensors (e.g., Hall-effect sensors) are susceptible to such noise, resulting in signal spikes that can cause control malfunctions or distorted monitoring data. Fluxgate technology, based on magnetic core saturation principles, inherently suppresses out-of-band noise. It can clearly extract the desired fundamental or specific-band current signals from complex electromagnetic environments, providing reliable data for condition monitoring and health management systems.

Additionally, the on-board design of fluxgate sensors allows direct integration onto control PCBs, reducing system volume and optimizing layout. This is ideal for SST’s pursuit of high power density and miniaturization.