Offshore wind power is a core component of clean energy in the new power system. Compared with onshore wind power, it features higher wind speed, stable wind conditions, high generation hours, and no occupation of land resources, making it the mainstream direction of global wind power development. The full-power converter is a key component of offshore wind turbines, responsible for rectifying variable-frequency AC power generated by wind turbines into DC power and then inverting it into grid-compliant power-frequency AC for grid integration. Its electrical performance, environmental adaptability, and long-term reliability directly determine the power generation efficiency and service life of offshore wind turbines. The high-voltage power supply acts as the core power unit of the offshore wind converter test system, simulating turbine output and grid operating conditions and providing high-voltage high-power power for converter testing. Its wide-temperature adaptability, three-proof performance, long-term operational reliability, and high-power output capability directly affect the environmental adaptability, test accuracy, and long-term stability of the converter test system. Offshore wind converter tests include onshore laboratory testing and offshore on-site testing. The offshore environment features extreme conditions such as high salt spray, high humidity, high temperature, mold, strong vibration, and severe electromagnetic interference. The test power supply must operate stably from -30℃ to +60℃ with IP65 or higher protection grade and excellent salt spray, moisture, and mold resistance, while withstanding strong vibration and impact on offshore platforms. Traditional industrial test power supplies suffer from poor wide-temperature adaptability, insufficient three-proof performance, and inability to operate long-term in harsh offshore environments, failing to meet on-site and long-term testing requirements. The design strictly complies with national and industry standards including GB/T 25386 Wind Turbines — Full-Power Converters, GB/T 30556 Offshore Wind Farms — Electrical Systems, IEC 61400 Wind Turbines, GB/T 7000.1 Luminaires — Part 1: General Requirements and Tests, and GB/T 4208 Degrees of Protection Provided by Enclosures (IP Code), while meeting high-power, high-reliability, and strong environmental adaptability requirements for offshore wind testing. Targeting core application demands and technical challenges, this methodology establishes a full-process general framework covering high-power topology design, wide-temperature environmental adaptability optimization, full-link three-proof protection, vibration-resistant structure design, offshore scenario adaptation, and safety protection. It supports R&D testing, factory inspection, and on-site maintenance testing for onshore and offshore full-power wind converters, providing standardized design guidelines for the localization and performance improvement of domestic offshore wind test equipment. Addressing key challenges such as wide-temperature operation, high-grade three-proof protection, high-power output, and strong vibration/anti-interference capability, the solution adopts a main topology of "front-end three-phase multi-level PFC rectifier + rear-end three-level NPC inverter + fully digital wide-temperature adaptive control", combined with liquid cooling, fully sealed three-proof structure, and wide-temperature component selection. It overcomes traditional limitations in environmental adaptability and three-proof performance, achieving stable operation from -30℃ to +60℃, IP65 or higher protection, and excellent corrosion/vibration resistance to fully satisfy onshore and offshore testing needs. Five core principles are defined. First, the high-power three-level back-to-back bidirectional converter realizes high-power output and bidirectional energy flow for full-condition testing. The front-end three-phase Vienna PFC rectifier achieves high-power unity power factor rectification and energy feedback with PF ≥ 0.99 and THD ≤ 3%, maintaining a stable high-voltage DC bus and feeding regenerative energy back to the grid to reduce power consumption. The three-level topology lowers device voltage stress and enhances reliability for 690V/1140V offshore converter testing. The rear-end three-phase three-level NPC inverter outputs more voltage levels with lower harmonic distortion and dv/dt, simulating variable-frequency turbine output and various grid conditions with AC 0–1200V and 0–100Hz adjustable range, supporting four-quadrant operation for low/high voltage ride-through and grid adaptability testing. Modular parallel expansion with master-slave fiber synchronization achieves current sharing accuracy within ±1%, flexibly covering hundreds of kilowatts to over ten megawatts. Second, wide-temperature design ensures stable full-range operation through component selection, topology optimization, and advanced thermal management. All core components adopt -40℃~+85℃ industrial/automotive-grade specifications; wide-temperature IGBT and SiC MOSFET modules support junction temperatures up to 175℃ with stable low-temperature switching performance. Wide-temperature film and solid capacitors cover -55℃~+105℃ to avoid capacity attenuation and aging issues of ordinary electrolytic capacitors. Precision wide-temperature resistors feature temperature coefficients ≤25ppm/℃, and auxiliary ICs, sensors, and relays all adopt wide-temperature models to guarantee performance from -30℃ to +60℃. Three-level soft-switching topology reduces heat generation; adaptive control adjusts drive parameters and switching frequency at low temperatures for reliable cold startup. An efficient liquid cooling system maintains junction temperatures below 80% of rated values under high temperatures, while intelligent preheating activates below 0℃ to raise internal temperature to the normal operating range. Third, the full-link three-proof protection system adopts a three-tier mechanism of material protection, structural sealing, and process reinforcement to achieve IP65+ performance against salt spray, humidity, and mold. All PCBs are coated with 50–100μm salt/mold/moisture-resistant polyurethane or acrylic conformal coating. Heat sinks use nickel-plated aluminum or oxygen-free copper with passivation; structural parts adopt 316L stainless steel or marine aluminum with anodization, powder coating, or fluorocarbon painting. Fasteners are 316L stainless steel; seals use fluororubber or silicone rubber. The whole machine adopts fully welded sealed construction with no gaps; external interfaces use IP67 marine waterproof connectors and cable glands. Closed liquid cooling eliminates ventilation openings to prevent corrosive air ingress; liquid pipelines use 316L stainless steel with sealed joints. Double-door sealing with fluororubber gaskets, drainage holes, and waterproof breathable valves balance internal pressure while blocking moisture and salt spray. Strict manufacturing processes including lead-free soldering, thorough PCB cleaning, standardized coating curing, surface blasting, phosphating, and full environmental testing (salt spray, humidity, mold) ensure reliable three-proof performance. Fourth, vibration-resistant structural design enhances shock resistance through reinforced framing, secure component mounting, and professional vibration isolation. Thickened 316L stainless steel frames with reinforcing ribs increase structural stiffness and avoid resonance with offshore platform vibration frequencies. Heavy components such as power modules, capacitors, and reactors use reinforced multi-point fixing; thickened ≥2mm FR-4 PCBs with supporting columns prevent deformation and solder detachment under vibration. Large components are potted; SMD parts are reinforced with underfill; cables are fixed with reserved buffer length. High-efficiency wire-rope or rubber vibration isolators with ≥80% isolation efficiency reduce external shock; flexible connections protect sensitive components while limit structures prevent excessive displacement during impact, complying with GB/T 25386 and IEC 61400 vibration standards. Fifth, offshore test scenario adaptation integrates standard offshore converter test templates including turbine characteristic simulation, grid adaptability, voltage ride-through, frequency response, harmonic immunity, three-phase unbalance, efficiency, power factor, and durability cycling, fully compliant with GB/T 25386, GB/T 19963, and GB/T 36994. One-click automatic testing, ≥95% efficient bidirectional energy feedback, multi-module parallel expansion, multi-channel independent output, synchronous triggering interfaces, full data black-box recording, and remote monitoring support unmanned offshore operation. Wide-temperature adaptability and thermal management optimization form the core of this methodology. Full-temperature component parameter modeling characterizes device behavior across -40℃~+85℃ to guide adaptive control and thermal design. Preferring high junction-temperature SiC/IGBT modules, long-life film capacitors, low-temperature-stable magnetic materials, and wide-temperature auxiliary power supplies ensures reliable performance in extreme temperatures. Real-time temperature compensation dynamically adjusts dead time, switching frequency, and loop parameters to counteract thermal drift. Closed liquid cooling delivers uniform heat distribution with ≤5℃ temperature difference and ≤30℃ junction-to-coolant temperature margin; low-temperature antifreeze coolant adapts to harsh climates. Intelligent cooling regulation optimizes energy consumption, while comprehensive liquid system monitoring prevents leakage and overheating. Independent temperature-stabilized cavities protect sensitive low-voltage circuits. Low-temperature preheating enables safe cold startup; high-temperature power derating and hysteresis temperature protection ensure stable and secure extreme-condition operation. Three-proof and environmental optimization adopts corrosion-resistant materials, fully sealed structures, and standardized processes. External metal parts use 316L stainless steel; internal components adopt marine aluminum with hard anodization; conductive parts apply nickel/gold plating. High-performance conformal coatings, EPDM/FKM seals, and high-temperature insulation materials resist aging and chemical erosion. Fluorocarbon exterior painting withstands ≥3000 hours of salt spray; internal epoxy anti-corrosion coatings enhance durability. Fully welded sealed enclosures, double-door gaskets, bottom waterproof interfaces, closed cooling loops, and waterproof breathable valves isolate corrosive environments; internal desiccants suppress mold growth. Strict PCB cleaning, vacuum coating, component potting, professional metal surface treatment, dust-free assembly, and full environmental validation guarantee consistent three-proof quality. Reliability and safety protection provide fundamental safeguards for long-term unmanned offshore operation. All key components implement Class I derating with voltage stress ≤70%, current stress ≤60%, and temperature stress ≤80% of rated values; junction temperatures are limited to 70% of maximum ratings. Fanless full-liquid cooling eliminates wearing parts, achieving MTBF ≥50,000 hours. Built-in self-diagnostics and health monitoring predict aging and potential faults; redundant control circuits and sensors enhance operational continuity. EMC design complies with GB/T 17626 standards; three-level soft-switching reduces electromagnetic interference; full metal shielding, three-stage EMI filtering, optical isolation, and optimized multilayer PCB layout ensure immunity to severe offshore electromagnetic noise. A 15-level dual hardware/software protection mechanism covers overvoltage, overcurrent, short circuit, overtemperature, phase unbalance, liquid cooling faults, leakage, humidity abnormality, safety interlock, and emergency stop with ≤1μs hardware response speed. Dual current limiting protects against overload and short circuit; hardwired emergency stop and high-voltage interlock ensure absolute safety, while active residual voltage discharge reduces DC bus voltage to safe levels within 100ms. In summary, this complete technical framework resolves traditional weaknesses in environmental adaptability, three-proof performance, and offshore long-term stability. The three-level bidirectional topology delivers high-power output and efficient energy feedback; wide-temperature components and intelligent thermal management enable reliable operation from -30℃ to +60℃; the three-tier three-proof system achieves IP65+ corrosion resistance; reinforced vibration-resistant structures meet offshore mechanical requirements. Fully applicable to R&D, factory, and on-site maintenance testing of offshore wind converters, it provides core technical support for the localization upgrading of China’s offshore wind power test equipment.