Hydrogen fuel cell stack test systems serve as core equipment for fuel cell R&D, mass production offline inspection, and operational life verification, supporting comprehensive testing functions such as volt‑ampere characteristic testing, polarization curve testing, dynamic condition simulation, durability cycle testing, and cold-start testing. The high‑voltage bidirectional power supply acts as the key power unit of the test system. It provides precise high‑voltage power for stack startup and preheating, while absorbing electric energy generated by the stack during power generation to realize bidirectional energy flow and four‑quadrant operation. Its voltage/current control accuracy, smoothness during bidirectional switching, dynamic response speed, and long‑term operational stability directly determine the accuracy, repeatability, and reliability of test data. Current mainstream automotive fuel cell stack test systems require the high‑voltage bidirectional power supply to offer continuously adjustable output from 0 to 1000 V, current control accuracy better than ±0.1% FS, voltage control accuracy better than ±0.2% FS, voltage/current surge ≤0.5% of rated value during mode transition, dynamic response ≤200 μs, and grid energy feedback efficiency ≥93%. Traditional solutions combining unidirectional power supplies with electronic loads suffer from low efficiency, high energy consumption, slow dynamics, large switching surges, and inability to simulate continuous operating conditions, failing to meet full‑condition dynamic testing requirements. The design complies with national and industry standards including GB/T 20042, GB/T 33979, and GB/T 29830, while supporting automatic testing, programmable multi‑condition operation, and safety interlock functions required by fuel cell test platforms. Addressing core application demands and technical challenges, this methodology establishes a full‑process framework covering bidirectional topology design, high‑precision closed‑loop control, seamless mode transition, energy feedback optimization, test scenario adaptation, and safety protection. It applies to automotive, marine, and stationary fuel cell stack test systems of various power levels, providing standardized design guidelines for domestic equipment development and performance improvement. Targeting bidirectional energy flow, high precision, surge‑free switching, and wide load adaptability, the solution adopts a two‑stage topology: front‑end bidirectional PFC rectifier plus rear‑end interleaved parallel bidirectional Buck‑Boost with fully digital dual closed‑loop control, combined with multi‑point feedforward compensation and adaptive condition algorithms. This overcomes traditional limitations in efficiency, dynamic response, and switching impact, achieving high‑precision four‑quadrant operation and smooth bidirectional transition for comprehensive fuel cell testing. Five core principles are defined. First, the two‑stage reversible structure uses a three‑phase bidirectional Vienna PFC rectifier on the grid side to achieve unity power factor (≥0.99) and low THD (≤3%), supporting both rectified high‑voltage DC output and grid‑tied energy feedback with enhanced isolation and noise immunity. The rear multi‑phase interleaved parallel bidirectional Buck‑Boost minimizes current ripple, improves regulation precision, and enables wide voltage adjustment across stack specifications. Seamless transition between Buck step‑down (power supply) and Boost step‑up (energy recovery) eliminates bridge shoot‑through risks and ensures stable operation. Second, a high‑precision fully digital dual closed‑loop control architecture integrates current inner loop, voltage outer loop, load feedforward, and grid feedforward based on DSP+FPGA hardware acceleration. Control update frequency reaches ≥200 kHz for high bandwidth and fast response. Deadbeat predictive current control achieves bandwidth ≥50 kHz with rapid current tracking and fluctuation suppression. Adaptive PID voltage regulation balances fast response and overshoot‑free stability, while real‑time load and grid feedforward compensates transient disturbances within 1 μs, ensuring overall precision within ±0.1% FS, line regulation ≤±0.05%, and load regulation ≤±0.1%. Third, seamless bidirectional switching adopts condition recognition algorithms to automatically identify stack operating states and pre‑adjust duty cycles with adaptive dead‑time compensation. Output fluctuation during transition is controlled ≤0.5% with switching time ≤100 μs, fully supporting dynamic cycle testing. Interlock protection prevents simultaneous activation of Buck and Boost modes to avoid device damage. Fourth, energy feedback optimization enhances grid‑tied performance with phase‑locked synchronization, ensuring current phase error ≤1° and feedback THD ≤3%. Islanding, overvoltage, overcurrent, and grid anomaly protections ensure safe disconnection during faults. Adaptive energy distribution prioritizes power supply to auxiliary test equipment before feeding surplus energy to the grid, improving overall efficiency. Fifth, comprehensive test scenario adaptation integrates programmable templates for polarization testing, constant current/voltage operation, dynamic cycling, cold‑start simulation, and overload durability modes. High‑speed synchronous triggering interfaces enable microsecond coordination with electronic loads, cooling systems, gas supply, and data acquisition platforms for fully automated testing. Full‑parameter monitoring and traceable data recording support quality audits, while multi‑level redundant safety interlocks provide overvoltage, overcurrent, short‑circuit, overtemperature, reverse connection, insulation monitoring, hydrogen leakage protection, and emergency stop functions with dual hardware/software redundancy and fault response ≤1 μs, protecting stacks and test equipment from high‑voltage damage. High‑precision control and full‑condition optimization further enhance performance through expanded bandwidth, minimized latency, ripple suppression, nonlinear load adaptation, and multi‑unit parallel scalability. FPGA‑based hardware control reduces latency below 1 μs, while combined repetitive and deadbeat current control maintains steady accuracy and dynamic agility. Multi‑variable feedforward compensates temperature, parameter drift, and mode switching effects, reducing load transient voltage deviation by over 80% with dynamic response ≤200 μs. Interleaved parallel topology lowers current ripple below 0.1% of rated value, while multi‑stage LC filtering and differential sampling ensure ultra‑low noise and stable precision. Adaptive algorithms dynamically accommodate the strong nonlinearity and variable internal resistance of fuel cell stacks across current, temperature, humidity, and gas pressure changes, supporting seamless switching between constant voltage, current, power, and resistance modes for different test items. Master‑slave parallel control realizes high‑power scalability with fiber synchronization accuracy ≤1 μs and current sharing precision ≤±1%, covering applications from kilowatt to megawatt levels with independent fault isolation for enhanced system reliability. Reliability and compliance design ensure long‑term continuous operation under strict safety standards. All key power components adopt Class I derating with voltage stress ≤70%, current stress ≤60%, and temperature stress ≤80% to slow aging and extend service life. High‑efficiency SiC MOSFETs and diodes reduce switching losses and improve high‑temperature stability. Fanless liquid cooling maintains uniform temperature distribution with maximum deviation ≤5 ℃, achieving an MTBF ≥50,000 hours to support thousands of hours of durability testing. EMC design complies with GB/T 18268.1 and GB/T 17626 using three‑stage EMI filtering, fully sealed double shielding, optical isolation for drive signals, and complete physical separation between power and control circuits to eliminate interference with high‑precision measurement systems. Comprehensive twelve‑level redundant safety protection implemented via independent hardware circuits ensures rapid fault shutdown within 1 μs and active residual voltage discharge below safe levels within 100 ms. High‑voltage interlock and real‑time insulation monitoring prevent electric hazards. The design fully conforms to fuel cell testing standards, supporting standard data formats and multi‑protocol communication including CANopen, Modbus, TCP/IP, and GPIB for seamless integration with mainstream automated test platforms. In summary, this complete technical framework addresses traditional weaknesses in efficiency, dynamics, switching stability, and control accuracy. Fully digital composite control achieves current precision within ±0.1% FS and dynamic response ≤200 μs; seamless mode transition ensures surge‑free bidirectional operation; interleaved topology delivers ultra‑low ripple for reliable high‑accuracy testing. Widely applicable to automotive, marine, and stationary fuel cell test equipment, it provides core technical support for the localization and performance upgrading of China’s hydrogen energy testing industry.