Dual-Mode Adaptive Control Strategy for Modulation Frequency Drift Compensation in Field Mill Sensors

Accurate monitoring of ground-level synthetic electric fields beneath ultra-high voltage (UHV) dc transmission lines is critical for assessing the electromagnetic environment. As the primary instruments for this task, field mill sensors deployed in outdoor environments are susceptible to ambient temperature fluctuations, particularly in regions with significant diurnal temperature variations. This sensitivity induces substantial measurement drift, which severely constrains the reliability of longterm electric field monitoring under complex operating conditions. This article investigates the mechanism of measurement errors caused by temperature-induced modulation frequency drift, and proposes a dual-mode adaptive control strategy based on a novel circuit topology to achieve automatic regulation of the modulation frequency. Experimental results demonstrate that, compared with conventional methods, the proposed strategy effectively compensates for measurement errors of the field mill sensor across a temperature range from -30 °C to 70 °C. Specifically, the coefficient of variation (CV) of sensitivity was reduced to 0.64%, and the maximum linearity error was suppressed to 0.28%. This work provides a reliable solution for accurate ground-level synthetic electric field measurement in complex outdoor environments, offering promising potential for engineering applications.