Testing Solutions for AI Power Electronics

Introduction

Artificial Intelligence has rapidly evolved from experimental research into the backbone of modern innovation, driving breakthroughs in autonomous systems, aerospace, healthcare, and data-driven decision making. As AI models grow larger and more complex, the demand for computational performance has skyrocketed, pushing data centers and server architectures to their physical and electrical limits.

Behind every large-scale AI cluster lies an intricate power network supporting thousands of GPUs, CPUs, and accelerators operating at full capacity. These systems consume massive and rapidly fluctuating amounts of energy, generating electrical and thermal challenges that conventional test methods were never designed to handle. Ensuring that every component (from power supply units to distribution modules) performs reliably under extreme loads is now essential to maintaining uptime, safety, and computational accuracy.

At Rexgear, we are at the forefront of this transformation. Our expertise in high-power testing and automation enables engineers and manufacturers to validate next-generation AI servers and power systems with precision, repeatability, and confidence. By combining advanced instrumentation, automated test software, and real-world simulation capabilities, Rexgear helps leading organizations design and qualify the most demanding AI and high-performance computing infrastructures on the planet.

AI Server Power Architectures: Two Dominant Models in Modern Data Centers

As AI computing has scaled into the multi-megawatt range, two primary power architectures have emerged across modern data centers. Each architecture reflects a different strategy for delivering high current, minimizing losses, and simplifying large-scale deployment, each introducing unique testing requirements across the power delivery chain.

HVDC Rack Architecture (800 V DC Distribution)

Traditional AC-Fed Servers with Redundant Power Supplies

This article will take a deeper look at both power delivery models—examining how each architecture is structured and the unique testing considerations each one introduces. It will also outline the key test objectives across every stage of the power delivery chain and highlight the corresponding testing solutions available within Rexgear’s product lines.

HVDC Rack Architecture (800 V DC Distribution)

A recent, rapidly growing architecture (shown in the diagram) replaces the per-server AC PSUs with a centralized room-level AC/DC cabinet that distributes high-voltage DC (HVDC) across an entire rack (commonly 50V up to 800 V DC).

Inside the rack, compact power shelves convert the HVDC bus to 48 V or 50 V DC, which is then delivered to the AI servers, GPU trays, and NVLink switches. This model dramatically improves efficiency, power density, and thermal performance, reducing both copper losses and conversion stages.

However, the HVDC approach introduces new validation challenges: engineers must characterize high-voltage bus behavior, power shelf DC-DC conversion performance, HVDC fault response, transient loading at 48 V, and the interaction between shared power shelves and individual server VRMs.

AC-DC Converter Testing — Validation of 480 Vac to 800 VDC Conversion Performance

At the top of the HVDC rack architecture sits the room-level AC-DC converter, responsible for transforming the facility’s 480 Vac input into a stable high-voltage DC bus (typically 700–800 VDC). This converter powers multiple racks simultaneously, making its stability, efficiency, and fault performance fundamental to the reliability of the entire AI computer infrastructure. To accurately validate its behavior, the test setup uses a Regenerative Grid Simulator to emulate the utility-side AC input and a High-Speed DC Electronic Load to represent the downstream 800 VDC bus demand. This configuration enables engineers to test the converter under controlled, repeatable, and highly dynamic conditions that mirror real data-center operation.

Test Objectives

• Input Performance & Grid Compliance
Evaluate voltage, frequency, and phase behavior under programmable AC conditions including sags, swells, dips, and harmonics.

• Output Voltage Regulation (700–800 VDC) 
Verify DC bus stability under varying load levels and during transient load changes.

• Dynamic Load Response 
Measure converter response to fast load steps that simulate rapid changes in power shelf and rack-level consumption.

• Efficiency Characterization 
 Identify conversion efficiency across the full power range and quantify thermal performance under sustained loading.

• Protection & Fault Behavior
 Validate overcurrent, overvoltage, short-circuit, and brownout response, ensuring safe operation during unexpected grid events.

Test Equipment

• Regenerative Grid Simulator — Programmable AC Source
  The regenerative grid simulator emulates the 3-phase 480 Vac utility input with full programmability over voltage, frequency, phase imbalance, and harmonic distortion. This allows engineers to observe how the AC-DC converter reacts to real-world electrical challenges.
• High-Speed DC Electronic Load — HVDC Bus Load Emulator
  The high-speed DC e-load applies programmable loading to the 800 VDC output.This ensures accurate characterization of DC bus stability and converter robustness under fluctuating AI-rack demand.

DC Power Shelf Testing — Validation of 800 VDC to 50 VDC Conversion

In HVDC rack architectures, the DC Power Shelf converts the high-voltage DC bus (380–800 VDC) into the 48–50 VDC rail that feeds GPU trays, AI servers, and NVLink switches. Because the power shelf sits directly on the HVDC bus and delivers kilowatts of power per module, its stability, efficiency, and dynamic response are critical to the reliability of the entire rack. To replicate real operating conditions, the test setup uses a Bidirectional DC Power Supply to emulate the HVDC bus and a High-Speed DC Electronic Load to simulate the fast, high-current demand of the 50 V server rail. This configuration mirrors the rack architecture shown in the diagram and allows engineers to evaluate the full behavior of the conversion stage.

Test Objectives

• Voltage Regulation & Load Performance
 Validate 50 V output accuracy under light, nominal, and full load conditions.

• Transient Response
Measure overshoot, undershoot, and recovery during rapid current steps representative of GPU activity.

 • Efficiency & Thermal Behavior
Characterize efficiency across the HVDC input range (380–800 VDC) and observe thermal performance at sustained high power.

• Protection & Fault Handling
Verify proper operation of OCP, OVP, short-circuit response, and controlled shutdown during HVDC disturbances.

• Startup & Pre-Charge Behavior
Evaluate inrush current, soft-start timing, and coordination with upstream HVDC converters and rack BBU systems.

 Test Equipment

• Bidirectional DC Power Supply — HVDC Bus Emulator
  Provides a programmable 380–800 VDC source with the ability to source and sink power, enabling testing of steady-state, transient, and fault conditions on the high-voltage bus.
• High-Speed DC Electronic Load — 50 V Rail Emulator
  Simulates the fast dynamic behavior of GPU and AI server loads, supporting high-current operation, rapid load steps, and fine control for transient characterization.

Using this setup, engineers can validate conversion accuracy, dynamic response, efficiency, and fault robustness—ensuring that the DC power shelf delivers stable, reliable 50 V power for high-density AI compute racks under real-world operating conditions.

HVDC BBU Testing — Validating Rack-Level Energy Storage and Ride-Through

In HVDC rack architectures, the Battery Backup Unit (BBU) is directly tied to the high-voltage DC bus (typically 380–800 VDC) and acts as an energy buffer during grid disturbances, brownouts, or upstream converter faults. When the room-level AC/DC cabinet or utility feed is interrupted, the BBU must seamlessly take over, sustaining the HVDC bus long enough for a controlled shutdown or for backup generation to come online. Because the BBU interacts directly with the HVDC bus and high-power conversion stages, its behavior under charge, discharge, fault, and transient conditions must be thoroughly validated. Poorly tuned control loops, incorrect contactor sequencing, or insufficient capacity can result in bus sag, nuisance trips, or even damage to downstream AI servers.

Test Objectives

• Ride-Through & Backup Duration
Verify that the BBU can maintain the HVDC bus voltage within specified limits for the required backup time under realistic rack load profiles.

• Charge/Discharge Dynamics
Characterize current ramp rates, response times, and stability during transitions between charge, float, and discharge modes.

• Bus Voltage Stability & Protection
Confirm proper operation of overvoltage/undervoltage, overcurrent, and short-circuit protections during abnormal conditions and fault events.

• System Integration & Sequencing
Validate contactor/pre-charge sequences, isolation behavior, and coordination between the BBU, HVDC bus converter, and rack power shelves.

Test Equipment

• Bidirectional DC Power Supply — HVDC Bus Emulator & Charger
  A high-voltage, high-power bidirectional DC power supply is used to emulate the HVDC bus and/or act as a programmable charger/discharger for the BBU. It must support seamless transition between sourcing and sinking power while providing precise control of bus voltage and current limits.
• Battery Simulation Software — BSS2000
  For system-level validation where the physical battery pack is replaced by a virtual model, BSS2000 Battery Simulation Software allows engineers to emulate a wide range of pack behaviors directly through the bidirectional power supply.
• Battery Cycling System — ITS5300 for Pack and Module Testing
  To qualify the actual battery modules or packs that will be used in the BBU, an ITS5300 Battery Cycling Test System is employed.

By combining a bidirectional source, BSS2000 battery simulation, and the ITS5300 battery cycling system, Rexgear delivers a complete ecosystem for HVDC BBU testing—from virtual pack emulation to full-power, real-battery qualification—ensuring that rack-level energy storage performs reliably under the most demanding AI data center conditions.

Traditional AC-Fed Servers with Redundant Power Supplies

In the first architecture, illustrated in the simplified AI server diagram, each server contains multiple redundant AC-to-DC power supplies (typically 200–240 Vac input). These PSUs generate 12 V, 12 V Standby (12 VSB), and sometimes 48 V DC rails that feed the OR-ing & PDB modules and ultimately the VRMs. This design prioritizes fault tolerance and modularity: if one PSU fails, the redundant units maintain uninterrupted operation. It remains widely used in enterprise environments and is still the standard for many OEM GPU servers. From a testing perspective, this architecture requires thorough validation of redundant PSU behavior, OR-ing circuits, standby rails, PSU failover, and multi-rail power sequencing, making AC-side grid simulation and PSU characterization essential.

Unlike traditional enterprise servers, AI servers are purpose-built for massively parallel computation. Their architecture is designed to move and process data at extraordinary speeds, but this performance comes with an equally extraordinary demand for power.

At the heart of an AI server lies a dense array of graphics processing units (GPUs) or AI accelerators — sometimes dozens per chassis — each capable of drawing hundreds of watts during peak workloads. Surrounding these compute elements is an intricate power delivery network (PDN). Multiple high-efficiency power supplies convert AC input into regulated DC rails that feed processors, memory, and interconnects. These supplies must respond to instantaneous load changes that can exceed several kilowatts per rack. In addition, cooling systems, VRMs (Voltage Regulator Modules), and redundant backup systems form a delicate balance between electrical performance, thermal management, and reliability.

From a testing perspective, this architecture creates an entirely new landscape of challenges: transient behavior, voltage droops, harmonic distortion, and energy efficiency must all be characterized under real operating conditions. Any instability in the power chain can lead to computation errors, reduced model accuracy, or even catastrophic hardware failure — outcomes that are unacceptable in mission-critical AI environments.

Inside the Power Delivery Network (PDN): From Wall Power to the Silicon

Power in an AI server travels through a carefully engineered hierarchy known as the Power Delivery Network (PDN) — a multilayer system that converts, regulates, and distributes energy from the facility’s AC mains all the way down to the millivolt levels used inside GPU and CPU cores.

The process begins with high-efficiency AC-DC power supplies that convert incoming power (typically 208 V or 277 V AC) into intermediate DC voltages such as 12 V or 48 V. These rails are then distributed across the server’s backplane and into the mainboard, where a network of copper planes, bus bars, and high-current connectors ensure low-resistance delivery to every subsystem.

Once the intermediate voltage reaches the processor area, Voltage Regulator Modules (VRMs) take over. Each VRM is a high-frequency DC-DC converter located physically close to the processor socket or accelerator package. Its role is to step down the 12 V or 48 V rail into the precise voltage required by the silicon — often as low as 0.8 V or less — while supplying hundreds of amperes of current with microsecond-level response time.

Modern GPUs and AI accelerators contain multiple power domains, meaning separate VRMs may feed distinct parts of the chip such as compute cores, memory controllers, and high-speed I/O interfaces. These VRMs use advanced topologies (multiphase buck converters, digital controllers, and adaptive compensation) to maintain voltage stability even during sudden current spikes that occur when thousands of cores switch simultaneously.

The final stage of the PDN consists of on-package and on-die decoupling capacitors, which smooth out transient noise and provide instantaneous charge to the transistors inside the chip. Together, this chain — from rack power supply to PCB traces to silicon — forms a dynamic ecosystem where every milliohm and nanohenry matter. Even small parasitic elements in the PDN can cause voltage droops, timing errors, or reduced efficiency, making power integrity testing and validation critical for AI-class hardware.

Testing AC-fed Servers Architecture for AI Servers

As AI servers evolve to support increasingly dense GPU and CPU clusters, their power delivery networks (PDNs) face extreme demands for stability, efficiency, and redundancy. Validating these systems requires precise control, measurement, and monitoring at every stage — from the power supply units (PSUs) up to the voltage regulator modules (VRMs) and the load consumed by the processors.

This diagram summarizes how Rexgear’s integrated test solutions enable engineers to evaluate the full power path of an AI server. Each subsystem — including redundant PSUs, OR-ing and Power Distribution Boards (PDBs), and VRMs — can be tested individually or as part of a complete system-level validation. By using programmable power supplies, electronic loads, and high-performance power analyzers, our setup ensures accurate simulation of real-world operating conditions, from startup transients to dynamic load switching.

Through this approach, engineers can:

       • Characterize PSU performance under redundant and parallel configurations.

       • Verify OR-ing and PDB efficiency and fault protection.

       • Validate VRM regulation and transient response under realistic GPU/CPU activity.

       • Measure overall system power efficiency and dynamic behavior with precision instruments.

Together, these tools provide a complete ecosystem for AI server power testing, helping manufacturers ensure reliability, safety, and performance before deployment in high-density data centers.

VRM Testing — Precision Validation of Power Regulation Performance

The Voltage Regulator Module (VRM) is a critical stage in the AI server’s power delivery path, converting intermediate bus voltages (typically 12 V or 48 V) down to the ultra-low core voltages required by GPUs and CPUs — often below 1 V, at hundreds of amperes. Ensuring its accuracy, stability, and transient response is essential for overall system reliability and energy efficiency.

In this test configuration, a programmable DC power supply emulates the upstream bus (PSU output or PDB line), while a programmable High Speed DC E-Load Change the picture to the IT8100 series load replicates the dynamic current demand of the processor rails. This setup allows engineers to precisely characterize how the VRM performs under a wide range of real-world conditions.

Test Objectives

• Voltage Regulation Accuracy
Verify output voltage precision under static and dynamic load conditions.

• Transient Response 
Measure overshoot, undershoot, and recovery time during fast load steps.

• Efficiency and Thermal Characterization
Quantify conversion efficiency across load levels and monitor thermal behavior.

• Protection and Fault Tests 
Validate OVP, OCP, and OTP protections according to design specifications.

Test Equipment

• Programmable DC Power Supply 
  Provides a stable and adjustable input source for the VRM under test, supporting wide voltage and current ranges. A standard linear DC power supply is typically sufficient for this application, as the VRM input stage primarily requires steady and well-regulated power. However, if the same setup is expected to be used for more advanced or bidirectional test scenarios within the AI power system — such as OR-ing, PDB, or PSU testing — a bidirectional DC power supply can offer additional flexibility by allowing both sourcing and sinking operations.
• Programmable DC Electronic Load (Low-Voltage, High-Current)
  Simulates the rapid, variable current consumption behavior of GPUs and CPUs, enabling dynamic step loading and transient response analysis. Depending on the test objectives, this load can be linear or regenerative. A linear electronic load is ideal for precision transient characterization and high-bandwidth measurements, while a regenerative load allows energy recovery back to the grid during long-duration or high-power tests. The choice depends on the type of GPU behavior being emulated and whether the goal is to analyze short transient responses, continuous current draw, or system-level power cycling under realistic operating conditions. Linear loads Regenerative loads

Through Rexgear’s integrated VRM testing solution, engineers can replicate realistic load transients, capture millisecond-scale regulation events, and validate the stability of the entire power delivery network before system integration.

Busbar Testing

In high-density AI servers, bus bars serve as the main arteries of power distribution, carrying hundreds or even thousands of amperes from the power supply units (PSUs) to the voltage regulator modules (VRMs) and GPU boards. As AI workloads increase, so do the instantaneous current surges these conductors must sustain. Any resistance, imbalance, or thermal rise in the bus bar assembly can lead to voltage drops, localized heating, or even long-term reliability issues.

Bus bar testing ensures that these high-current pathways can deliver power efficiently and safely under real operating conditions. Using programmable DC power supplies and high-current electronic loads, engineers can replicate full-load and transient current events.

Test Objectives

• Conduction Losses & Voltage Drop 
Measuring millivolt-level voltage differentials across the bus bar under high current to verify low-resistance performance.

• Thermal Rise & Distribution
Monitoring surface and joint temperature increases to ensure adequate cooling and connector integrity.

• Mechanical & Contact Reliability 
Assessing joint resistance, connector alignment, and structural stability under continuous load cycles.

• Dynamic Load Response 
Observing how the bus bar and associated connections behave during rapid load transitions typical of GPU ramp-up events.

Through this testing, engineers gain confidence that the internal power backbone of the AI server maintains both electrical efficiency and thermal stability, ensuring reliable energy delivery to every computing module — even under extreme data center conditions.

Test Equipment

• Bidirectional DC Power Supply (Low Voltage, High Current — CC Priority)
Bus bar testing relies on the ability to drive extremely high currents with tight control and fast response. Because the main objective is to evaluate conduction losses, voltage drop, thermal rise, and dynamic behavior under heavy GPU-class loading, the test instrument must maintain stable and precise current regulation across a wide operating range.

For this application, the ideal tool is a low-voltage, high-current bidirectional DC power supply with current-priority (CC priority) control. This ensures that the current delivered into the bus bar remains accurate even during rapid load steps or transient transitions — exactly the type of behavior seen when GPUs ramp from idle to full compute workload in microseconds.

Through this testing, engineers gain confidence that the internal power backbone of the AI server maintains both electrical efficiency and thermal stability, ensuring reliable energy delivery to every computing module — even under extreme data center conditions.

• Recommended Instruments:
  IT-M3900C Series — Bidirectional DC Power Supply (Low Voltage / High Current, CC Priority)

OR-ing & PDB Testing — Validation of Redundant Power Distribution Paths

The OR-ing and Power Distribution Board (PDB) stage manages the transition between multiple redundant power supply units (PSUs) and the downstream voltage regulation modules (VRMs). It ensures that power is delivered continuously even if one or more supplies fail, using OR-ing controllers, diodes, or ideal MOSFETs to isolate and balance current flow between channels.

In this setup, the programmable DC power supplies emulate the redundant PSU outputs of the server. Each output channel represents a different voltage rail — for example 12 V, 12 V Standby (12 VSB), and 48 V — all feeding into the OR-ing & PDB module.

At the output side, DC load emulates the behavior of the VRM, allowing the engineer to draw controlled current and replicate downstream system behavior. This bidirectional capability enables both sourcing and sinking current, making it ideal for characterizing voltage transitions, backfeed protection, and fault recovery scenarios.

Test Objectives

• Redundancy and OR-ing Validation
Confirm proper current sharing and isolation between PSU channels.

 •Voltage Drop & Reverse Current Tests
Measure diode or MOSFET voltage drop and verify that no backfeed occurs during channel switching.

• Efficiency & Thermal Evaluation
Assess conduction losses and thermal behavior across OR-ing stages.

• Fault Tolerance Testing
Simulate PSU failure or disconnection and verify uninterrupted output delivery.

Test Equipment

• Bidirectional DC Power Supplies – Simulate multiple PSU outputs with precise voltage and current control (12 V / 12 VSB / 48 V).
• DC Load or Bidirectional DC Power Supply – Operates as a controllable load or VRM simulator, capable of both sourcing and sinking current for dynamic transition testing.

This configuration enables comprehensive OR-ing and PDB validation, ensuring reliable power redundancy, seamless failover behavior, and efficient current management across high-density AI server power architectures.

Cabinet-Level Testing — Full 400 kVA AC/DC Cabinet Validation

The room-level AC/DC cabinet is the heart of the HVDC rack architecture, converting facility power (480 Vac) into a high-voltage DC bus that feeds multiple AI racks simultaneously. Rated at hundreds of kilowatts, this cabinet must deliver stable, high-power DC output while maintaining grid compliance, high efficiency, and robust fault response under extreme and rapidly changing load profiles.

To validate the entire cabinet as a system, the test configuration uses a 400 kVA Regenerative Grid Simulator (or high-power AC power supply) to emulate the 3-phase utility input and a High-Speed DC Electronic Load to stress the cabinet’s full HVDC output. This allows engineers to verify real-world behavior at scale, ensuring the entire cabinet operates safely and efficiently before deployment in a data center.

Test Objectives

• Grid Input Performance
 Validate cabinet behavior under programmable grid conditions: voltage imbalance, sags, swells, harmonics, and frequency variations. Confirm power factor, THD, and startup inrush performance at full cabinet load. Verify compliance with utility and data center power standards.

•HVDC Bus Output (Rack-Level)
Validation Measure output voltage stability across the full load range (idle → rated kW). Evaluate dynamic load response using fast load steps representative of multiple AI racks activating simultaneously

• Efficiency & Thermal Characterization
Map efficiency at low, mid, and full power operation. Characterize thermal rise, cooling performance, and derating behavior during sustained high-load operation.

• Protection & Fault Response
Validate OCP, OVP, short-circuit, and brownout protection across all phases. Test controlled shutdown, restart, and recovery sequences at cabinet level. Verify safe coordination with downstream BBU, power shelves, and rack controllers.

•System-Level Coordination
Confirm load sharing stability when feeding multiple racks. Evaluate interaction between the cabinet’s internal AC/DC modules, HVDC filters, and distribution stages. Validate performance during simultaneous peak demand events from multiple AI clusters.

Testing equipment

• 400 kVA Regenerative Grid Simulator / High-Power AC Power Supply
  Used to emulate the 3-phase 480 Vac utility feed. This enables comprehensive line-side testing at real-world power levels.

PSU Testing — Input Grid Simulation and Efficiency Characterization

The Power Supply Unit (PSU) is the foundation of any AI server’s power delivery system. It converts AC grid input into multiple regulated DC rails such as 12 V, 12 V Standby, and 48 V, feeding downstream stages like the OR-ing board and VRM modules. Validating PSU performance ensures that the system can deliver consistent power, maintain high efficiency, and meet safety and redundancy standards under real-world operating conditions.

In this configuration, a regenerative grid simulator emulates the AC mains input of the server. It provides a fully programmable, single-phase power source capable of simulating voltage sags, frequency variations, and transient events to evaluate PSU robustness and compliance with grid standards.

On the DC side, three bidirectional power supplies or DC Electronic loads emulate the server’s internal power rails, drawing programmable current to simulate real operational load profiles across 12 V, 12 VSB, and 48 V outputs. A high-precision power analyzer is connected between the input and output to measure voltage, current, power factor, harmonics, and efficiency in real time.

Test Objectives

• Input Performance & Power Quality 
Evaluate PSU response to AC line variations, dips, and phase distortions.

• Output Regulation & Stability 
Verify voltage accuracy and current capability across all DC rails.

• Efficiency & Power Loss Analysis
Measure input vs. output power to calculate conversion efficiency and identify thermal losses.

• Protection Testing 
Validate PSU behavior under overcurrent, short-circuit, and brownout conditions.

Test Equipment

• Regenerative Grid Simulator or AC Power supply – Provides controlled AC input with programmable voltage, frequency, and harmonic distortion to simulate real-world grid behavior.
• Bidirectional Power Supply – Simulate multiple server DC rails (12 V / 12 VSB / 48 V) with adjustable current, enabling steady-state and dynamic load tests.
• Power Analyzer – Captures high-accuracy measurements of input/output power, PF, THD, and efficiency for comprehensive PSU characterization.

This setup allows engineers to perform complete PSU validation, from AC input compliance to DC output performance and overall efficiency, ensuring that each unit meets the stringent power integrity demands of modern AI servers.

Power Efficiency & 80 PLUS Validation

Beyond functional validation, this configuration also supports compliance testing for energy-efficiency standards such as 80 PLUS and Energy Star. By combining a grid simulator, bidirectional power supply, and a precision power analyzer, engineers can accurately measure input and output power under various load levels (20%, 50%, 80%, and 100%).These measurements determine the PSU’s conversion efficiency, power factor, and total harmonic distortion—key metrics required to certify high-efficiency power supplies. Through this setup, Rexgear’s test solutions enable manufacturers to validate compliance, optimize power conversion stages, and ensure that each PSU meets the demanding performance and sustainability goals of modern AI data centers.

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