Low-level drive design and digital retrofitting of an electronic driver controller based on a dual-decoupled architecture

To address contact ablation, mechanical wear and maintenance challenges in conventional mechanical driver controllers used in freight diesel locomotives, this study develops a digital-retrofitting scheme that replaces the mechanical control structure while retaining the original drive-system architecture. A host–slave dual-decoupled architecture based on an isolated RS-485 bus and the Modbus-RTU protocol is implemented. The STM32F429-based host unit integrates a human-machine interface (HMI) and software interlocking, while the STM32F103-based slave unit drives a ULN2003ADR array and a 19-channel industrial relay array to reproduce the coding logic of conventional cam contacts at the ADLC-4 interface. Bench-scale validation on an integrated test platform demonstrated a driver-circuit voltage margin of 0.4 V and a current margin of 484.9 mA. The system responded correctly to directional and 33-level speed-regulation commands, and the software interlock rejected the tested invalid input sequences. These results provide bench-scale evidence supporting the feasibility of digital retrofitting for legacy freight-locomotive driver controllers. Field-test performance, long-term reliability, life-cycle cost, and environmental robustness require further validation.