Stability Monitoring Using Voltage Perturbation for DC Distributed Power Systems

Abstract

The stability issues in nonlinear systems such as multi-module power electronics systems, especially DC distributed power systems, are often dealt with by employing the impedance criterion. However, for on-line system stability monitoring, to direct measure the impedance of the source and load subsystems and then making comparisons is complicated and difficult. This paper proposes a practical and simple method, which involves utilizing voltage perturbation, to monitor the stability margin of DC distributed power systems. A voltage perturbation source is applied to the DC side of the system and only the amplitude of two voltages needs to be measured, therefore this method can be easily used for on-line stability monitoring. An implementation approach of this method, which does not employ additional voltage perturbation source but utilizes the front-end subsystem, is also presented. Theoretical analysis and computer simulations are given to verify the effectiveness of both the monitoring method and the implementation approach. A comparative evaluation of the voltage perturbation method versus the current perturbation method for stability monitoring is provided.

Stability evaluation of a DC micro-grid and future interconnection to an AC system

“…Their Fourier transform is computed. Finally the values at the perturbation frequency determine the input impedance of the inverter for small signal stability analysis or output impedance of the grid [2,8,9]. The current or voltage injection to obtain the impedance for the VSC is presented in Fig.…”

“…The source v gen is the perturbation signal with variable frequency produced by a signal generator (1). This is isolated by a small power transformer and connected to a linear amplifier (2), hence the perturbation is applied to the DC grid by the secondary of the Fig. 7.…”

Impedance-Based Stability and Transient-Performance Assessment Applying Maximum Peak Criteria

“…The minor-loop gains in (2) and (4) form similar sensitivity functions as the voltage loop but based on the impedance ratios. Therefore, low margins in the minor-loop gain would cause peaking in the corresponding sensitivity function according to (7) and consequently, in the corresponding transfer functions in (2) and (4) [26]. It should be noted that the full effect of the described peaking affects only the internal or unterminated transfer functions of the corresponding converter, which is also the basic assumptions behind the MPC theory in [26] …”