Photovoltaic inverters are core equipment of photovoltaic power generation systems, responsible for converting DC power generated by PV modules into AC power for grid connection. Their insulation performance and withstand voltage capability directly determine the operational safety and long-term reliability of PV power plants. Insulation and withstand voltage testing is a mandatory safety standard item throughout the R&D, mass production inspection, grid access certification, and maintenance of photovoltaic inverters, including power-frequency withstand voltage tests, impulse withstand voltage tests, insulation resistance tests, and PID endurance tests. As the key power component of insulation withstand voltage test systems, high‑voltage power supplies deliver stable, high-precision, wide-range high‑voltage output. Their adjustable voltage range, stability, ripple suppression, and long-term reliability directly affect the accuracy, compliance, and safety of test results. Current standards require test voltages covering AC 0–5 kV and DC 0–10 kV; high-voltage string and central inverters even require DC 0–15 kV, with voltage stability better than ±0.5%, peak-to-peak ripple ≤1%, and comprehensive protections such as short‑circuit, overcurrent, and arc detection. Traditional power-frequency withstand voltage transformers suffer from large size, heavy weight, narrow adjustment range, high ripple, and poor continuous precision regulation, failing to meet full-standard safety testing for various inverters. The design strictly complies with GB/T 18216.1, IEC 61730-2, GB/T 37409, GB 7251.12 and other national and international safety standards, while supporting automated testing, multi-scenario adaptation, and safety interlock functions. Targeting core demands and technical challenges, this methodology establishes a full-process framework covering wide-range topology design, high-precision regulation, low-ripple optimization, safety insulation engineering, scenario adaptation, and comprehensive protection. It supports full insulation withstand testing for string, central, and micro inverters, providing standardized guidelines for domestic PV test equipment upgrading. Adopting a main topology of front-end PFC voltage stabilization + high-frequency inversion + multi-stage modular voltage doubling rectification + fully digital closed-loop regulation, combined with linear post-regulation and graded insulation, the solution breaks traditional limitations, achieving continuously adjustable DC 0–15 kV and AC 0–5 kV with outstanding stability and low ripple to fully satisfy safety certification requirements. Five core principles are defined. First, the cascaded modular topology enables ultra-wide output while reducing single-stage voltage stress, simplifying insulation and improving precision. The front-end PFC stabilizes grid input with PF ≥ 0.99 and THD ≤ 5%. The intermediate full-bridge LLC resonant inverter realizes high-frequency soft-switching boosting with frequency-based coarse regulation. Rear multi-stage symmetric voltage doubling modules achieve scalable high DC output with evenly distributed voltage stress. An independent power-frequency sine-wave inverter provides 0–5 kV 50/60 Hz AC for conventional withstand tests, integrating AC and DC functions into one system. Second, dual-stage coarse/fine regulation with fully digital closed-loop control ensures high precision across the full range. Frequency tuning controls coarse output (10%–100% rated), while high-voltage linear fine adjustment achieves resolution below 1 V with excellent ripple rejection. A DSP+FPGA controller with 24-bit ADC implements high-speed PID closed-loop regulation, delivering accuracy within ±0.2%, long-term stability ≤±0.5%/8 h, line regulation ≤±0.1%, and load regulation ≤±0.2%. Third, graded insulation and safety engineering adopt equal-potential gradient design and finite-element electric field optimization. All high-voltage connections use rounded transitions to eliminate local discharge risks, maintaining maximum field strength below 30% of material breakdown limits with over threefold insulation margin. High-voltage transformers adopt multi-layer polyimide insulation, Faraday shielding, and epoxy vacuum potting. Fully isolated sealed enclosures and alumina ceramic bushings ensure reliable insulation and mechanical strength with insulation materials ≥20 kV/mm. Fourth, multi-level filtering achieves ultra-low ripple and full EMC compliance. Soft-switching LLC minimizes original switching noise; cascaded RC π filters suppress low/mid/high-frequency ripples, limiting DC ripple ≤0.5% and AC sine distortion ≤3%. Full metal shielding, independent high/low-voltage cavities, and three-stage EMI filtering comply with GB/T 17626 electromagnetic compatibility requirements. Fifth, scenario adaptation embeds standard test templates for power-frequency DC, insulation resistance, impulse, and PID tests, supporting automatic voltage ramping, dwell timing, and leakage alarm settings. High-precision nA-level leakage monitoring triggers cutoff within 1 μs upon over-limit current. Synchronous interfaces connect PLCs, data acquisition, and safety interlocks for automated mass production testing, with complete data logging and traceable certified reports. Wide-range output and precision optimization form the core of this methodology. Hybrid frequency-phase LLC control extends adjustable range to 0–100% while maintaining soft switching. Switched multi-stage voltage doubling optimizes low/high voltage performance respectively. Adaptive FPGA PID ensures fast non-overshoot regulation across all ranges with feedforward compensation for grid and load disturbances. Soft start/stop eliminates voltage surge risks. Full-load adaptive control supports operation from no-load high impedance to short-circuit breakdown, with automatic constant-voltage/constant-current switching for reliable protection. Differential sampling and full-range calibration guarantee consistent precision at both low and high output levels. Safety compliance and protection adopt strict alignment with IEC 61010-1, GB 4793.1, and GB/T 16927.1, implementing reinforced double insulation with isolation ≥ twice maximum voltage, low-resistance earthing ≤0.1 Ω, and standardized emergency stop/voltage warning devices. Ten-layer hardware-software redundant protection includes overvoltage, overcurrent, short circuit, leakage, overtemperature, arc detection, high-voltage interlock, safety door interlock, and emergency shutdown, with hardware response ≤1 μs. High-frequency arc detection prevents fire hazards; active residual voltage discharge reduces high voltage to safe levels within 50 ms. Over-derated long-life components, high-performance film capacitors, low-leakage high-voltage rectifiers, and optimized forced-air cooling ensure MTBF ≥30,000 hours for continuous production use. Rich communication protocols support remote automation and multi-user permission management to avoid unauthorized operation. In summary, this complete technical framework solves traditional weaknesses including narrow range, large volume, low precision, and high ripple. It realizes DC 0–15 kV / AC 0–5 kV fully adjustable output with ±0.2% accuracy and ripple below 0.5%, fully meeting international safety standards. Widely applicable to inverters, PV modules, energy storage equipment, and low-voltage electrical products, it provides core technical support for domestic substitution and performance improvement of China’s high-voltage test equipment.