30kW Three-Phase PFC for AI Power Shelves

Choose the AC-front-end contract before the switches #

A 30kW three-phase PFC stage is the boundary between the facility feed and the high-voltage DC link inside an AI power shelf. It must meet line-current quality, bus-regulation, protection and ride-through requirements while leaving a stable input for the isolated DC/DC stage. The topology decision comes first: a Vienna rectifier is a strong unidirectional choice, while a three-level active front end (AFE) is appropriate when power must flow back to the grid or the platform needs independent reactive-power control.

This guide is for power-shelf architects, power-electronics and firmware engineers, and BOM owners freezing that decision. It uses current official reference designs as evidence, not as production BOMs. The distinction is important now because ST's active 30kW Vienna reference design still names the SCTWA90N65G2V-4 SiC MOSFET, but ST currently marks that device obsolete and out of production. A reference platform can remain technically useful after a named semiconductor is no longer a valid new-build sourcing choice.

Use reference designs as measured boundaries #

ST's STDES-30KWVRECT is the closest public match to this power class. The official page and UM3011 user manual describe a digitally controlled, 70kHz Vienna rectifier for 400VAC three-phase input, an 800VDC output and up to 30kW. ST reports power factor above 0.99, current THD below 5%, efficiency above 98.5%, soft start and inrush-current limiting. Its current product page identifies STM32G474RET3 and STGAP2SICS among the core products. The board is an evaluation reference and is not offered as an ordinary purchasable production assembly.

Those numbers form one tested operating point; they are not universal guarantees for every line, load, cooling condition or replacement switch. Put the full test condition next to each requirement. At 30kW and 400V line-to-line, unity-power- factor current is about 43.3A RMS per phase before efficiency margin. A ±10% facility range, overload, phase imbalance and harmonic limits all move the real semiconductor, inductor, contactor and connector stress.

TI's TIDA-010257 provides a useful modular comparison: a 10kW, 40kHz Vienna design for 380/400V line-to-line and a 650V DC output, with published peak efficiency above 98% and less than 1.5% THD at full load. Three 10kW channels can be an architectural starting point for a 30kW shelf, but paralleling three reference designs is not itself a released solution. Current sharing, clock synchronization, input-filter interaction, neutral-point behavior and the fault that removes one channel must be engineered and retested at shelf level.

Select Vienna or AFE by required operating states #

A Vienna rectifier uses a diode path plus controlled switches to shape three- phase input current and regulate a split DC link. Its unidirectional power path, lower controlled-switch count and established efficiency make it attractive when the shelf only converts AC to DC. The release work is concentrated in boost- inductor design, midpoint balance, reverse-current assumptions, device stress, EMI and fault isolation.

A bidirectional AFE replaces that one-way boundary with a fully controlled bridge. STDES-PFCBIDIR is a current 15kW, 400VAC/800VDC three-level reference; its official material covers rectifier operation above 0.99 power factor plus inverter-mode active and reactive power control. TI's TIDA-010210 demonstrates an 11kW three- level ANPC implementation with 600V GaN devices on a DC link up to 1000V, C2000 control, isolated drive and programmable-logic-assisted overcurrent protection.

Choose the AFE only when those additional states have a system owner. Battery charging behind the DC link does not automatically require exporting energy to the grid. If the shelf never regenerates, the additional switches, gate supplies, current-control states, LCL/filter behavior and grid-relay logic increase the qualification surface without adding a required function. If export, grid support or DC-bus energy recovery is mandatory, document direction, power, ramp rate, anti-islanding/interconnection behavior and the safe state for lost control power.

The topology decision also fixes the DC-link contract. A three-level stage needs defined positive- and negative-rail capacitance, midpoint-voltage tolerance, discharge behavior and imbalance protection. The downstream isolated converter must specify whether it accepts the full bus range and imbalance transient or whether PFC firmware must inhibit it until both halves are valid.

Partition 30kW into explicit fault domains #

One 30kW power train can minimize duplicated magnetics and controls. Two 15kW or three 10kW channels can reduce the energy inside one fault domain and may preserve partial power after a channel is isolated. Neither approach is inherently N+1. Redundancy exists only when the remaining channels, input protection, cooling, DC-link path and downstream converter are rated for the required load after the fault.

For a modular design, freeze these shared-resource rules:

• whether each channel has its own input fuse/contactor, precharge path, inductors,

current sensors and DC-link isolation;

• how PWM clocks are interleaved and how conducted-emission filters are prevented

from forming an uncontrolled coupled network;

• which controller owns current sharing and what each local controller does when

the coordinator, communication link or auxiliary rail fails;

• how a shorted switch, open phase, midpoint imbalance or sensor bias is contained

without back-feeding a failed channel; and

• whether service replacement is permitted with the shared bus energized.

The OCP ORv3 rack-power guide starts after this front-end decision and freezes the shelf, 48V busbar, BBU and management interfaces. A 30kW PFC block does not by itself make an ORv3-compliant shelf, and the baseline six-by-3kW ORv3 shelf must not be silently relabeled as a single 30kW architecture.

Make startup and fault shutdown one state machine #

PFC firmware should not begin current control immediately after auxiliary power appears. The sequence must validate phase voltage and frequency, close or verify the intended input path, charge the DC-link capacitance through the controlled precharge path, prove both bus halves, then enable PWM and release the downstream converter. Each transition needs a timeout and a measured value; a time delay alone cannot distinguish a charged bus from a welded contactor or failed sensor.

Fast protection must remain below the supervisory loop. Cycle-by-cycle current limit, desaturation or short-circuit response, gate-driver UVLO and a hardware PWM trip should not wait for an MCU interrupt. Firmware owns attribution, retry policy, discharge and event logging after the switching state is already safe. Record the first initiating event before line loss, DC-link collapse and communication errors create secondary flags.

Qualification should capture all three phase currents, line-to-line voltages, both DC-link halves, precharge and main-contactor commands, gate-driver fault, hardware trip and downstream enable on the same timebase. Test minimum and maximum line, light and full load, phase loss/reversal, sensor offset, midpoint imbalance, auxiliary brownout, contactor failure, fan/coolant loss and a commanded downstream load step. The public efficiency and THD numbers matter only after the abnormal paths reach a deterministic safe state.

Treat the reference BOM as a lifecycle input #

The ST 30kW reference page names SCTWA90N65G2V-4 switches and the STPSC40H12C SiC Schottky-diode family; its core-product table resolves the board item as STPSC40H12CWL. The diode remains a current 1200V dual 2×20A TO-247 long-lead device on ST's product material. The 650V, four-lead SCTWA90N65G2V-4, however, is currently obsolete/out of production. Procurement therefore cannot release the reference BOM unchanged.

Current devices can seed an engineering search, not a paper substitution. ST's active SCT027W65G3-4AG is a 650V, 29mΩ-typical, four-lead HiP247 automotive- qualified SiC MOSFET. Infineon's active IMZA65R020M2HXKSA1 is a 650V, 20mΩ-typical, TO-247-4 industrial SiC MOSFET. Neither vendor describes these as drop-in replacements for STDES-30KWVRECT. Their current rating, on-resistance, transfer behavior, capacitances, short-circuit margin, gate-voltage needs and thermal characteristics differ from the obsolete 18mΩ reference device.

Changing the MOSFET reopens switching loss, dead time, gate resistance, driver UVLO, common-source inductance, heatsink/interface, current sharing, dv/dt, common- mode current and input-filter results. Preserve the four-lead Kelvin-source function in the layout rather than matching only the TO-247 outline. Re-run the full operating and fault matrix with production-intent magnetics, cooling and firmware.

Release measurements, firmware and mechanics with the BOM #

The MCU order code alone is not the controller deliverable. ST's reference uses an STM32G474RE-family device, while TI's current Vienna and ANPC examples use C2000 control. In either case, release source/binary version, compiler/toolchain, calibration constants, current/voltage polarity, sampling instant, PWM frequency, dead time, trip routing, startup thresholds, midpoint controller, checksum and programming owner. A blank replacement MCU does not restore a power shelf.

The RFQ should group the electrical assembly rather than quote semiconductors in isolation:

• topology and directionality; continuous/peak power; nominal and allowed AC

phase voltage, frequency, grounding and prospective fault-current assumptions;

• regulated DC-link range, split-bus capacitance/tolerance, ripple, discharge time,

precharge energy and downstream-enable contract;

• power factor, THD and efficiency limits with line/load/cooling test points, plus

the applicable EMC, safety and grid-interconnection evidence;

• exact switch, diode, driver, controller, sensor, contactor, fuse, capacitor and

magnetic OPNs, carrier suffixes, grades and lifecycle status;

• allowed substitutions and the requalification evidence required for each class;
• control firmware, configuration checksum, programming flow, calibration report

and first-fault log format; and

• cold plate or airflow boundary, interface material, torque, coolant/air limits,

hotspot sensors, derating curve and module-level repair policy.

Do not copy a reference efficiency into a quote without its measurement boundary. Request the loss breakdown at minimum/nominal/maximum line and several load points, including auxiliary, fan or pump power if the shelf-level metric includes them. For modular channels, also request current-share error and full-shelf THD when all channels operate and when one channel is disabled.

Conclusion #

A 30kW AI power-shelf front end should be released as a topology, control, protection and lifecycle contract. Use a Vienna rectifier when energy flow is strictly AC-to-DC; accept the qualification cost of a three-level AFE only when regeneration or grid-control states are required. Then partition the power into fault domains, prove precharge and midpoint balance before downstream release, and let hardware remove PWM before firmware records and manages the fault.

The current ST reference demonstrates that the 30kW operating point is practical, but its obsolete named MOSFET also demonstrates why reference-design status is not production-BOM status. Freeze complete order codes, firmware, magnetics, cooling and substitution evidence in the RFQ. That lets engineering qualify a real assembly and prevents purchasing from treating a package-compatible SiC device as an untested replacement.

Official references #

• STDES-30KWVRECT active 30kW Vienna PFC reference-design page
• ST UM3011: Getting started with the STDES-30KWVRECT 30kW Vienna PFC reference design
• STDES-PFCBIDIR active 15kW three-phase bidirectional AFE reference design
• TI TIDA-010257 10kW three-phase Vienna rectifier reference design
• TI TIDA-010210 11kW bidirectional three-level ANPC GaN reference design
• ST SCTWA90N65G2V-4 official lifecycle and device page
• ST SCT027W65G3-4AG active 650V four-lead SiC MOSFET product page
• Infineon IMZA65R020M2H active 650V TO-247-4 SiC MOSFET product and ordering page
• ST STPSC40H12C 1200V dual SiC Schottky diode data sheet
• ST STM32G474RE active MCU product and ordering page
• ST STGAP2SICS active isolated SiC gate-driver product and ordering page