No abstract

The virtual synchronous control is regarded as an effective solution for grid-tied converters to operate under weak grid conditions and provide inertia support. However, for those grid-tied converters which control the DC voltage, e.g., the receiving end converter (REC) in modular multilevel converter based high-voltage direct-current (MMC-HVDC) transmission systems with wind farm integration, the application of virtual synchronous control is difficult due to the cascade control loops. The dynamic performance of DC voltage control may also be degraded. To address these issues, a novel grid-forming control strategy with real-time inertia support and fast DC voltage control is proposed for the REC. The cascade control loops of the virtual synchronous control are simplified by utilizing the internal energy stored in sub-module capacitors to emulate synchronous generator rotors. Moreover, the DC voltage is decoupled with the submodule capacitors voltage, thus being robust to sudden power change. Simulation results in PSCAD/EMTDC show that the proposed control realizes fast inertia support and desired dynamic control of the DC voltage, especially in weak grid operation.

No abstract

<p>The chirp sweep is a go-to wide-band impedance measurement technique when speed and simplicity are of main concern. Additionally, the time-frequency trait of chirp scans provide unique benefits for systems exhibiting frequency couplings - a phenomenon often encountered in single-phase VSCs. Unfortunately, time domain interpretation of chirp responses are inaccurate if the VSC-based system exhibits weak damping, as the free response induced by the chirp cannot be safely neglected. We quantify this error for linear(ised) time-invariant and time-periodic systems, with impedance representations of scalar transfer functions and harmonic transfer functions, respectively. An observer termed the Multiple Chirp Reference Frame Filter is proposed which enables real-time estimation of the harmonic transfer functions and their corresponding chirp errors. By controlling the relative errors to negligible values, the chirp exhibits low rate around resonances and high rate elsewhere. An experimental admittance sweep of a single-phase STATCOM operated by dispatchable Virtual Oscillator Control, consolidates the proposed approach as a simple frequency scan technique for weakly damped and frequency coupled systems. </p>

<p>The chirp sweep is a go-to wide-band impedance measurement technique when speed and simplicity are of main concern. Additionally, the time-frequency trait of chirp scans provide unique benefits for systems exhibiting frequency couplings - a phenomenon often encountered in single-phase VSCs. Unfortunately, time domain interpretation of chirp responses are inaccurate if the VSC-based system exhibits weak damping, as the free response induced by the chirp cannot be safely neglected. We quantify this error for linear(ised) time-invariant and time-periodic systems, with impedance representations of scalar transfer functions and harmonic transfer functions, respectively. An observer termed the Multiple Chirp Reference Frame Filter is proposed which enables real-time estimation of the harmonic transfer functions and their corresponding chirp errors. By controlling the relative errors to negligible values, the chirp exhibits low rate around resonances and high rate elsewhere. An experimental admittance sweep of a single-phase STATCOM operated by dispatchable Virtual Oscillator Control, consolidates the proposed approach as a simple frequency scan technique for weakly damped and frequency coupled systems. </p>