623 research outputs found
Control of MTDC Transmission Systems under Local Information
High-voltage direct current (HVDC) is a commonly used technology for
long-distance electric power transmission, mainly due to its low resistive
losses. In this paper a distributed controller for multi-terminal high-voltage
direct current (MTDC) transmission systems is considered. Sufficient conditions
for when the proposed controller renders the closed-loop system asymptotically
stable are provided. Provided that the closed loop system is asymptotically
stable, it is shown that in steady-state a weighted average of the deviations
from the nominal voltages is zero. Furthermore, a quadratic cost of the current
injections is minimized asymptotically
Distributed Primary Frequency Control through Multi-Terminal HVDC Transmission Systems
This paper presents a decentralized controller for sharing primary AC
frequency control reserves through a multi-terminal HVDC grid. By using
Lyapunov arguments, the proposed controller is shown to stabilize the
equilibrium of the closed-loop system consisting of the interconnected AC and
HVDC grids, given any positive controller gains. The static control errors
resulting from the proportional controller are quantified and bounded by
analyzing the equilibrium of the closed-loop system. The proposed controller is
applied to a test grid consisting of three asynchronous AC areas interconnected
by an HVDC grid, and its effectiveness is validated through simulation
Dynamical Decentralized Voltage Control of Multi-Terminal HVDC Grids
High-voltage direct current (HVDC) is a commonly used technology for
long-distance electric power transmission, mainly due to its low resistive
losses. When connecting multiple HVDC lines into a multi-terminal HVDC (MTDC)
system, several challenges arise. To ensure safe and efficient operation of
MTDC systems, the voltage of all terminals need to be steered to within an
operational range. In this paper we study the commonly used decentralized
voltage droop controller, and show that it in general does not steer the
voltages to within the operational range. We propose a decentralized PI
controller with deadband, and show that it always steers the voltages to within
the operational range regardless of the loads. Additionally we show that the
proposed controller inherits the property of proportional power sharing from
the droop controller, provided that both the loads and the line resistances are
sufficiently low. The results are validated through simulation in MATLAB
Distributed Secondary Frequency Control through MTDC Transmission Systems
In this paper, we present distributed controllers for sharing primary and
secondary frequency control reserves for asynchronous AC transmission systems,
which are connected through a multi-terminal HVDC grid. By using Lyapunov
arguments, the equilibria of the closed-loop system are shown to be globally
asymptotically stable. We quantify the static errors of the voltages and
frequencies, and give upper bounds for these errors. It is also shown that the
controllers have the property of power sharing, i.e., primary and secondary
frequency control reserves are shared fairly amongst the AC systems. The
proposed controllers are applied to a high-order dynamic model of of a power
system consisting of asynchronous AC grids connected through a six-terminal
HVDC grid.Comment: arXiv admin note: text overlap with arXiv:1409.801
Control of multi-terminal HVDC networks towards wind power integration: A review
© 2015 Elsevier Ltd.
More interconnections among countries and synchronous areas are foreseen in order to fulfil the EU 2050 target on the renewable generation share. One proposal to accomplish this challenging objective is the development of the so-called European SuperGrid. Multi-terminal HVDC networks are emerging as the most promising technologies to develop such a concept. Moreover, multi-terminal HVDC grids are based on highly controllable devices, which may allow not only transmitting power, but also supporting the AC grids to ensure a secure and stable operation. This paper aims to present an overview of different control schemes for multi-terminal HVDC grids, including the control of the power converters and the controls for power sharing and the provision of ancillary services. This paper also analyses the proposed modifications of the existing control schemes to manage high participation shares of wind power generation in multi-terminal grids.Postprint (author's final draft
Optimal Control Design for Multiterminal HVDC
This thesis proposes an optimal-control based design for distributed frequency control in multi-terminal high voltage direct current (MTDC) systems. The current power grid has become overstressed by rapid growth in the demand for electric power and penetration of renewable energy. To address these challenges, MTDC technology has been developed, which has the potential to increase the flexibility and reliability of power transmission in the grid. Several control strategies have been proposed to regulate the MTDC system and its interaction with connected AC systems. However, all the existing control strategies are based on proportional and integral (PI) control with predetermined controller structures. The objective of the thesis is to first determine if existing control structures are optimal, and if improved controller structures can be developed.The thesis proposes a general framework to determine the optimal structure for the control system in MTDC transmission through optimal feedback control. The proposed method is validated and demonstrated using an example of frequency control in a MTDC system connecting five AC areas
Protection Testing for Multiterminal High-Voltage dc Grid:Procedures and Procedures and Assessment
eAssessment The application of multiterminal (MT), high-voltage dc (HVdc) (MTdc) grid technology requires test procedures for the operation and implementation of the protection solutions. The test procedures are usually derived from experience and from extensive measurement data, which, at present, are still not widely available. Based on a hardware-inthe- loop (HIL) method, advanced dc protection testing strategies, utilizing existing experience for ac grids and requirements for MTdc grids, may overcome this gap
Control and Protection of MMC-Based HVDC Systems: A Review
The voltage source converter (VSC) based HVDC (high voltage direct current system) offers the possibility to integrate other renewable energy sources (RES) into the electrical grid, and allows power flow reversal capability. These appealing features of VSC technology led to the further development of multi-terminal direct current (MTDC) systems. MTDC grids provide the possibility of interconnection between conventional power systems and other large-scale offshore sources like wind and solar systems. The modular multilevel converter (MMC) has become a popular technology in the development of the VSC-MTDC system due to its salient features such as modularity and scalability. Although, the employment of MMC converter in the MTDC system improves the overall system performance. However, there are some technical challenges related to its operation, control, modeling and protection that need to be addressed. This paper mainly provides a comprehensive review and investigation of the control and protection of the MMC-based MTDC system. In addition, the issues and challenges associated with the development of the MMC-MTDC system have been discussed in this paper. It majorly covers the control schemes that provide the AC system support and state-of-the-art relaying algorithm/ dc fault detection and location algorithms. Different types of dc fault detection and location algorithms presented in the literature have been reviewed, such as local measurement-based, communication-based, traveling wave-based and artificial intelligence-based. Characteristics of the protection techniques are compared and analyzed in terms of various scenarios such as implementation in CBs, system configuration, selectivity, and robustness. Finally, future challenges and issues regarding the development of the MTDC system have been discussed in detail
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