This paper addresses the problem of damping interarea oscillations via power modulation of a VSC-HVDC link integrated in a power AC grid. Motivated by the fact that interarea modes may be at higher frequencies, close to other modes of the system, and classic tuning methods of standard (IEEE) power oscillations damping controller structures may not give satisfactory results. A reduced order model of a meshed AC grid with a HVDC link is proposed for control design. Based on this model which carefully integrates the dynamics of interest, a robust controller for the HVDC link is designed to damp interarea oscillations and enhance the damping of the other modes. Investigations with both linearized and nonlinear model of the system are carried out to settle and validate the approach. The efficiency and robustness of the proposed controller are tested and compared with standard controller structures.
This paper proposes a mixed sensitivity H∞ controller to deal with damping of inter-area oscillations with a HVDC inserted in a meshed AC grid. In this case, inter-area modes may be at higher frequencies, close to other modes of the system. The classic tuning methods of standard (IEEE) power oscillations damping controller may not give satisfactory results for dynamics. A robust controller which is effective under different operating conditions is required. The controller design has been carried out based on the H∞ mixed-sensitivity formulation in a LMI framework with pole-placement constraints. Investigations with nonlinear model of the system were done to settle and validate the approach. The efficiency and robustness of the proposed controller are tested and compared with a standard IEEE controller and a Linear Quadratic Gaussian one.
In this article, we consider the particular situation of a HVDC link inserted in a meshed AC grid, which has interarea modes at upper frequencies than the usual ones. In this case, the standard IEEE (lead-lag plus gain) controllers may not be efficient. As a matter of fact, in this grid situation, the control is challenged by unstable zeros and system uncertainties, systematically put into evidence. Two original robust strategies based on matching a reference model using LMI optimization approach are designed to provide coordinated active and reactive power modulation for the HVDC link. They are based on a reduced order control model of the HVDC and the neighboring AC zone, which integrates the dynamics of interest. Besides increased damping and diminished impact of the unstable zeros, this new control achieves robustness against grid variations. Investigations with both linearized and nonlinear model of the system are carried out to settle and validate the approach. The efficiency and robustness of the proposed controllers are tested and compared with the ones of several standard controllers on a realistic benchmark of 19 generators interconnected by a meshed AC grid.damping controller, HVDC, interarea modes, power system oscillations, robustness | INTRODUCTIONElectromechanical oscillations are a major concern of today power grids. This is a problem of power system oscillatory stability, as shown, for example, in Europe in December 2016 when low damping oscillations related to the most spread interarea mode (at 0.15 Hz) have been experienced. 1 When provided with supplementary damping control, the HVDCs have a good damping effect, which can be used to solve the problem of low-frequency oscillations between regions. Especially, voltage source converters (VSC)-HVDC transmission systems have the advantage to control both active and reactive power. This provides the opportunity to maintain system stability through supplementary power oscillations damping (POD) loops of control for both active and/or reactive power modulations. 2 The most analyzed and controlled in the past were the most spread interarea modes of the interconnected system, which are the ones in which are involved a large number of generators. They are at low frequencies, for example, around 0.2 Hz in Europe. Recent HVDC reinforcements in Europe (like France-Italy interconnection) are in the oscillation path of interarea modes of higher frequencies, around 1 Hz. There are also other dynamics of the grid in this frequency range (see References 3,4). These different dynamics should be taken into account more directly than in classic POD controllers (IEEE structures) and methodologies for gain computation (like, eg, Reference 5).
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This paper addresses the problem of a particular case of high-voltage direct current transmission inserted into a meshed AC grid, which has an inter-area oscillation mode with a higher frequency than the normal mode. The classic Power Oscillation Damping (POD) controller failure to deal with this situation and the other changing operation point cases . Moreover, Non-Minimum Phase Zeros (NMPZs) were systematically put into evidence. Combined with the system uncertainties, they present a serious challange for the control. A same reducedorder model of High-Voltage Direct Current line (HVDC) and adjacent AC area as former research is used for control design in this paper. Based on the reference model, using the LMI optimization method, a Dynamic Output Feedback Controller (DOFC) is proposed to provide modulation of active and reactive power to damp the inter-area oscillations, enhance the damping of the other modes, eliminate some impacts of NMPZs in the system and achieve robustness against variation of the operation point. The linearization and nonlinear models of the system are studied to establish and verify the method. The efficiency and robustness of the proposed controller were tested on the same actual benchmark of 19 generators connected through the mesh AC grid.
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