Steady-State and transient assessments of integral back-stepping current controllers in high-voltage direct current transmission systems

•Explains the synthesis of integral back-stepping inner current controllers for an illustrative voltage source converter based HVDC transmission system, and main theoretical bases that underpin the control design and gains’ selections.•Theoretical analysis and quantitative simulations are used to conduct one-to-one comparisons, which aim to assess the steady-state and transient performances of integral back-stepping inner current controllers against the proportional-integral counterparts.•For the same control targets, it has been established that the back-stepping current controllers exhibit different characteristics in time and frequency-domains compared to that of the equivalent proportional-integral current controllers, i.e., closed loop poles and bandwidths and time domain trajectories.•Simulation corroboration of the theoretical analysis reveals that the back-stepping current controllers are promising and exhibit excellent performances during normal operation as active and reactive powers set-points being varied, and operation at current limits during AC faults. In the last five decades, proportional-integral (PI) controller remains dominant in control of high-power converters in industrial and utility power systems despite its bandwidth, hence, the performance is coupled to power circuit parameters and degrades in parts of operating range. Consequently, further mitigation measures such as fine-tuning or loop reshaping might be needed. In contrast, integral back-stepping (IBS) decouples controller bandwidth and performance from the system parameters; hence, leads to consistent performance throughout the operating range and simplifies tuning of controllers with complex structures with multiple loops. Therefore, this paper investigates the suitability of IBS for implementation of inner current controllers of the voltage source converter (VSC)-based high-voltage direct current (HVDC) transmission systems. The paper presents step-by-step synthesis of back-stepping current controller and supporting theoretical bases, and assesses its performance against the conventional PI current controller. Theoretical analysis and discussions and comparative simulations reveal that the characteristics of IBS technique enjoys unique characteristics: decouples the controller gains from the converter parameters; restricts closed loop poles to real axis; and exhibits larger closed loop bandwidth than the PI counterpart. It has been shown that the gains of IBS current contro