Nested-Loop Control of DC/DC Converter Twins via a Novel Per-Unit and Time–Angular Transformation

The application of DC power electronics has expanded significantly across modern transmission and distribution systems, spanning medium-voltage direct current (MVDC) and high-voltage direct current (HVDC) networks, as well as low-power DC supplies for nanoscale applications, in which experimental validation remains indispensable for verifying system performance and control strategies. However, developing experimental platforms for high-power, high-voltage, or nanoscale DC systems is technically challenging and expensive and has not been adequately addressed in the existing literature. To overcome these limitations, this paper presents a per-unit-based experimental twin (Ex-Twin) framework for Buck converters implemented with a nested-loop control architecture. By transforming the converter dynamics from the time domain to an angular-domain representation, the proposed per-unit framework enables the development of dynamically equivalent experimental twins across a wide range of operating scales. The feasibility and effectiveness of the proposed Ex-Twin framework are validated through comprehensive electromagnetic (EMT) simulation studies and hardware experimental results, demonstrating its potential as a scalable and cost-effective platform for the development, testing, and validation of advanced DC power electronic systems. EMT simulations verify the cross-scale dynamic equivalence of the converter models over power ratings from 2 kW to 2 MW and voltage levels from 54 V to 54 kV, provided that the corresponding per-unit parameters and normalized disturbances are preserved. Under the investigated operating conditions, the systems achieved efficiencies of 95.3%, 96.7%, and 94.3% at 2 kW, 20 kW, and 2 MW, respectively, using both the real-scale and corresponding per-unit controllers. These results demonstrate consistent performance across the evaluated power scales. In addition, laboratory tests conducted on a 1 kW, 50 V Buck-converter platform validate the real-time implementation of both the real-scale and per-unit controllers under reference-voltage and load disturbances. An experimentally measured efficiency of 92.1% was achieved with both controllers, further demonstrating their consistent performance.