Yannick Phulpin

Communication-Free Inertia and Frequency Control for Wind Generators Connected by an HVDC-Link

This letter introduces a communication-free control scheme that allows wind generators connected by an HVDC-link providing inertia and primary frequency control services to the mainland system. The scheme consists of making the offshore and onshore frequency deviations proportional. It relies on frequency regulation at the offshore converter and dc voltage control with power and frequency droops at the onshore converter. This letter provides a mathematical formulation of the system and a discussion on application challenges related to the control scheme.

Cooperative frequency control with a multi-terminal high-voltage DC network

We consider frequency control in power systems made of several non-synchronous AC areas connected by a multi-terminal high-voltage direct current (HVDC) grid. We propose two HVDC control schemes to make the areas collectively react to power imbalances, so that individual areas can schedule smaller power reserves. The first scheme modifies the power injected by each area into the DC grid as a function of frequency deviations of neighboring AC areas. The second scheme changes the DC voltage of each converter as a function of its own areas frequency only, relying on the physical network to obtain a collective reaction. For both schemes, we prove convergence of the closed-loop system with heterogeneous AC areas.

HVDC control strategies to improve transient stability in interconnected power systems

This paper presents three HVDC modulation strategies to improve transient stability in an interconnected power system. AC variables such as rotor speeds, voltage phasors, and tie-line power flows are used as input to the controller that modifies the power flow settings through the HVDC-links. The proposed techniques are tested on the IEEE 24-Bus reliability test system and critical clearing times obtained for several contingencies are analyzed. The paper shows that HVDC modulation can lead to substantial improvement in transient stability.

Network coding in Smart Grids

Seeking to meet the resilience, efficiency and security challenges of smart grid communications, we present a set of strategies that leverage the benefits of network coding. The key idea is for intermediate nodes in the electrical power grid to store and send linear combinations of data packets they receive or overhear, thus ensuring that critical data can be shared reliably with the grid control system even when some of the connections break down. The impact of network coding on the reliability of multicast channels for control messages is also addressed. Our preliminary analysis of the achievable connectivity with different topologies and communication technologies (power-line and wireless) indicates that network coding techniques are well suited for smart grid communications.

Model predictive control of HVDC power flow to improve transient stability in power systems

This paper addresses the problem of HVDC control using real-time information to avoid loss of synchronism phenomena in power systems. It proposes a discrete-time control strategy based on model predictive control, which solves at every time step an open-loop optimal-control problem using an A* event-tree search. Different optimisation criteria based on transient stability indices are compared. The paper presents simulations results for two benchmark systems with 9 and 24 buses, respectively, and an embedded HVDC-link. The results show that the control strategy leads to a modulation of the HVDC power flow that improves significantly the systems ability to maintain synchronism in the aftermath of a large disturbance.

Coordination of voltage control in a power system operated by multiple transmission utilities

This paper addresses the problem of coordinating voltage control in a large-scale power system partitioned into control areas operated by independent utilities. Two types of coordination modes are considered to obtain settings for tap changers, generator voltages, and reactive power injections from compensation devices. First, it is supposed that a supervisor entity, with full knowledge and control of the system, makes decisions with respect to long-term settings of individual utilities. Second, the system is operated according to a decentralized coordination scheme that involves no information exchange between utilities. Those methods are compared with current practices on a 4141 bus system with 7 transmission system operators, where the generation dispatch and load demand models vary in discrete steps. Such a discrete-time model is sufficient to model any event of relevance with respect to long-term system dynamics. Simulations show that centrally coordinated voltage control yields a significant improvement in terms of both operation costs and reserves for emergency control actions. This paper also emphasizes that, although it involves few changes with respect to current practices, the decentralized coordination scheme improves the operation of multi-utility power systems.

Improved control strategy to mitigate electromechanical wave propagation using PSS

This paper addresses the problem of electromechanical wave propagation in power systems. To mitigate this type of disturbance, this paper proposes a remote control strategy that could be applied to power system stabilizers. This strategy is based on wide-area measurements, and exploits the disturbance propagation speed to introduce an extra damping torque simul-taneously with the disturbance arrival. Simulation results show that the application of such strategy improves the power system dynamics.

Decentralized reactive power dispatch for a time-varying multi-TSO system

This paper addresses the problem of reactive power dispatch in a power system partitioned into several areas controlled by different transmission system operators. Previous research has shown that nearly optimal performance could be achieved in a time-invariant system by using a specific iterative decentralized control scheme with no information exchange. At each iteration of this scheme, every transmission system operator concurrently schedules its own control settings for the next iteration while representing the neighboring areas with external network equivalents. This paper focuses on some parameter tracking techniques to extend the range of application of the decentralized control scheme to time-varying systems, where the time-varying nature of the system is modeled as a succession of steady-state operating conditions with variation of the load demand. Those new techniques are evaluated in the context of IEEE 118 bus system partitioned into three control areas.

Approaching generation variable costs from publicly available data

Generation variable costs are key parameters in economic studies of real power systems focusing on redispatch costs and power flows between regions, such as the ENTSO-E bidding zone review. These costs are commercial sensitive information unlikely to be disclosed, that depend on multiple time-varying factors that are difficult to determinate. This paper addresses the problem of estimating the variable costs of generation at national, regional and unit-scale using publicly available data. Different methods are tested to find the best correlation between spot prices and generation. Results are presented for France and Germany and demonstrate the usefulness of this approach providing a realistic estimation of the merit order between countries and technologies.

How compatible is perfect competition with transmission loss allocation methods

This paper addresses the problem of transmission loss allocation in a power system where the generators, the demands and the system operator are independent. We suppose that the transmission losses are exclusively charged to the generators, which are willing to adopt a perfectly competitive behavior. In this context, their offers must reflect their production costs and their transmission loss costs, the latter being unknown beforehand and having to be predicted. We assume in this paper that the generators predict their loss costs from the past observations by using a weighted average of their past allocated costs. Under those assumptions, we simulate the market dynamics for different types of transmission loss allocation methods. The results show that the transmission loss allocation scheme can lead to a poorly efficient market in terms of social welfare.