A Classification of DC Node Voltage Control Methods for HVDC Grids

In a DC grid, contingencies such as converter outages give rise to a current imbalance that is reflected in the DC node voltages in the grid. This imbalance has to be accounted for by changing the currents flowing in and out of the DC system. These DC node voltages can be directly influenced by controlling the DC current of the HVDC converter at that node. Different control strategies can be applied to balance the currents in a DC grid after a contingency. In this paper, the different converter control strategies are introduced systematically, thereby aiming to provide a framework for classifying the different converter control strategies available in literature. It is discussed how all converter control strategies theoretically can be regarded as limiting cases of a voltage droop control. It is also explained how the different converter control concepts can be combined, leading to more advanced converter control schemes such as voltage margin control, dead-band droop control and undead-band droop control. Based on the introduced converter control strategies, different grid control strategies are introduced and classified. The application of the advanced converter control strategies results in advanced grid control strategies and the advantages of those are discussed.status: publishe

Operational Security Assessment - Planning and Control

publishedVersio

Flow-based forward capacity mechanism: an alternative to the regulated capacity remuneration mechanisms in electricity market with high RES penetration

The rapid adoption of variable renewable generation has created new challenges in the maintenance of power system adequacy. On one hand, its non-dispatchable nature increases the need for firm and flexible load-following peaking power generation. On the other hand, its significantly lower short-run marginal cost raises the missing-money issue, which increases the tendency of conventional generators in terminating their services because of the reduced economic incentives. Therefore, many regulators have begun to implement remedial measures called capacity remuneration mechanisms (CRMs) to curb the problem. Though effective in supporting the operation of these generators, the mechanisms affects the cross-border sharing of generation resources. The shortcomings are discussed in this paper. Afterwards, the paper proposes a mechanism called the flow-based forward capacity mechanism as an alternative for accommodating the involvement of both domestic and foreign capacity generators in the cross-border competition for the supply of capacity generation. The mechanism is able to recover the missing-money bear by the capacity generators in a fair manner. Additionally, it offers a concise method for gradually phasing-out the service of capacity generators as the market transforms into a full RES form

An approach for establishing a common grid model for flow-based market mechanism simulations

The discussions on the development of an electricity market model for accommodating cross-border cooperation remains active in Europe. The main interest is the establishment of market couplings without curtailing the fair use of the scarce transmission capacity. However, it is difficult to gain mutual consensus on this subject because of the absence of convincing simulation results for the entire region. To achieve that, researchers need a common grid model (CGM) which is a simplified representation of the detailed transmission model which comprises aggregated buses and transmission lines. A CGM should sufficiently represent the inter-area power flow characteristics. Generally, it is difficult to establish a standard CGM that represents the actual transmission network with a sufficient degree of exactness because it requires knowledge on the details of the transmission network, which are undisclosed. This paper addresses the issue and reviews the existing approaches in transmission network approximation, and their shortcomings. Then, it proposes a new approach called the adaptive CGM approximation (ACA) for serving the purpose. The ACA is a data-driven approach, developed based on the direct current power flow theory. It is able to construct a CGM based on the published power flow data between the inter-connected market areas. This is done by solving the issue as a non-linear model fitting problem. The method is validated using three case studies

Time-Frequency analysis for nonlinear and non-stationary signals using HHT: A mode mixing separation technique

Time and frequency localizations are of crucial importance in the analysis of nonlinear and non-stationary processes, especially in systems with high level of complexity where detection of information/events, estimation of parameters and classification of signals in classes is necessary to take decisions. The Hilbert Huang Transform (HHT) offers an adaptive approach to analyze no-linear and non-stationary processes. This paper exposes the HHT approach and its new methodologies for improvement of the analysis, such as the masking process. Two examples are given to show the techniques, first a synthetic signal, representing a typical behavior of an electrical signal immersed in a power electronic environment and second a brain signal to extend the acknowledgment to a biological process. Finally a mode mixing separation technique is presented