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Abstract:Due to increasing level of power converter-based component and consequently the lack of inertia, automatic generation control (AGC) of interconnected systems is experiencing different challenges. To cope with this challenging issue, a derivative control-based virtual inertia for simulating the dynamic effects of inertia emulations by HVDC (highvoltage direct current) interconnected systems is introduced and reflected in the multi-area AGC system. Derivative control technique is used for higher level applications of inertia emulation. The virtual inertia will add an additional degree of freedom to the system dynamics which makes a considerable improvement on first overshoot responses in addition to damping characteristics of HVDC links. Complete trajectory sensitivities are used to analyse the effects of virtual inertia and derivative control gains on the system stability. The effectiveness of the proposed concept on dynamic improvements is tested through Matlab simulation of two-area test system for different contingencies.

The utilization of renewable sources brings many benefits to electric power systems, but also some challenges like the impact that renewable power plants employing power electronics have on the grid, which is gaining importance as the penetration of this type of generating stations increases, driven by the construction of large wind or solar photovoltaic power plants. This paper analyses the impact of large-scale photovoltaic power plants on a transmission grid for different penetration levels. The analysis considers power plants formed by a number of power converters employing synchronous power controllers, that allow them to have a harmonious interaction with the grid, and compares their performance with that of conventional power converter controllers, assuming in both cases that the power plants participate in frequency and voltage regulation. The study addresses both the small-signal stability of the system and its response to large disturbances that alter the active power balance and frequency stability. The results of the analysis show that photovoltaic power plants using synchronous power controllers are able to limit frequency deviations, improve the oscillation damping, and reduce the stress of other generating units, thus having a beneficial impact on the power system.

Grid-interactive converters with primary frequency control and inertia emulation have emerged and are promising for future renewable generation plants because of the contribution in power system stabilisation. This study gives a synchronous active power control solution for grid-interactive converters, as a way to emulate synchronous generators for inerita characteristics and load sharing. As design considerations, the virtual angle stability and transient response are both analysed, and the detailed implementation structure is also given without entailing any difficulty in practice. The analytical and experimental validation of frequency support characteristics differentiates the work from other publications on generator emulation control. The 10 kW simulation and experimental frequency sweep tests on a regenerative source test bed present good performance of the proposed control in showing inertia and droop characteristics, as well as the controllable transient response.

The impact that renewable energy sources interfaced by power electronics have on power systems becomes more important as their share in the generation mix increases, thus requiring detailed analyses that take into account their dynamics and controllers. In this paper, the impact of photovoltaic (PV) power plants on the power system of northern Chile is analysed. The studied plants employ a controller that allows power converters to interact with the grid like virtual synchronous generators, and their model includes the dynamics of the plant and converter controllers, as well as the dc and PV system. The presented analysis, which comprises modal analysis and time-domain simulations of large disturbances, evaluates the impact of these plants with respect to PV plants based on a conventional converter controller. Tests and validations of the proposed models and controllers are carried out for an actual PV plant connected to the power system of northern Chile, and for a higher PV penetration case. The results show the ability of PV plants formed by virtually synchronous power converters to limit frequency excursions induced by large power imbalances, and to mitigate power oscillations of the synchronous machines in the system.

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