Investigations into the stability of large power systems with embedded power electronic subsystems using frequency impedance scanning
In this study, an advanced frequency scanning method is used to extract the frequency dependent network equivalent (FDNE) impedance characteristic of a power electronic subsystem such as an HVDC transmission system or FACTS device including its controls. This is achieved by simulating it in the time domain on an EMT program, and exposing it to an energy dispersed chirp disturbance which has a broad harmonic spectrum. The impedance (or admittance) of this subsystem at the given operating point can then be determined using a Discrete Fourier Transform. The impedance scan can be in the form of a frequency response plot or can be fitted with a rational transfer function. This method will be used to identify potentially unacceptable resonance or instability modes in the power network of Manitoba Hydro, thereby improving the security of power supply to its customers. Also, the scanning result, coupling with analytical study, will benefit the future planning and controller design in Manitoba Hydro system.