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Interactions between three-phase grid-connected voltage source converter (VSC) and ac network have been analyzed using the VSC ac-side impedance models in the dq-domain, and more recently, in the sequence domain. Both dq and sequence domain approaches ignore the effects of a network at the VSC dc-side terminals. Interactions between VSC and dc network have been similarly analyzed by ignoring the effects...
This paper presents a control strategy based on Model Predictive Control for Energy Storage Systems. The mathematical formulation of this controller is outlined, and the procedure for applying this controller to a Generalized Energy Storage model is then documented. The dynamic performance of the control strategy presented is compared with that of a PI-based control technique. A comprehensive case...
During the last decade there has been an increasing interest in the High Voltage DC grids amongst researchers and policy makers. Protection has been identified as a critical component in the realization of these multi-terminal direct current (MTDC) systems. The fault currents in the DC systems are limited by the circuit resistance and inductance and thus are likely to reach very high values. This...
This paper studies the inclusion of averaged VSC-based grid interfaces and HVDC networks into stability type simulations, and compares the accuracy and speed of three multi-terminal DC dynamic models: 1) a state-space based model, 2) a multi-rate improved model, and 3) a reduced-order model. The accuracy comparison is conducted by qualitative time-domain analysis taking the state-space model as a...
Solar storms can affect the terrestrial power grid by inducing potential differences between points on the earth. These can couple into the power system through earthed structures such as transformer earths, which in turn can result in transformer saturation through geomagnetically induced current (GIC). For systems such as voltage-source converter (VSC) HVDC, this causes a variety of problems. This...
This article is focused on the droop-based DC voltage control design for multi-terminal VSC-HVDC grid systems, considering the AC and the DC system dynamics. The droop control design relies on detailed linearized models of the complete multi-terminal grid, including the different system dynamics, such as the DC grid, the AC grid, the AC connection filters and the converter inner controllers. Based...
Point-to-point VSC-HVDC Wind power plant (WPP) links connected offshore by AC cables can be called an AC integrated VSC-HVDC scheme or virtual multi-terminal DC (MTDC) grid. Since, the AC integrated VSC-HVDC scheme forms an offshore AC grid, parallel operation of offshore VSC-HVDC converters is required. This paper compares three offshore converter control topologies: (i) feedforward control of AC...
Voltage problems are challenging in modern power systems with a high penetration of renewables integrated via power electronics. This paper extends the transient time-scale classification to identify voltage dynamics in modern power systems. Voltage dynamics in the current control time-scale is firstly proposed and then the mechanism of terminal voltage change is elaborated. After that the significant...
High-voltage, high-power dc transmission based on Modular Multilevel Voltage-Sourced Converters represents currently the best solution when system resilience, flexibility of control, reliability and availability are of essence. In Europe, such systems are currently being installed or considered as interconnectors between several synchronous zones or embedded into a synchronous zone. New concepts and...
Two decades ago, a renewed interest in the development of power flow control technology resulted in the creation of unified power flow controller (UPFC) with the use of voltage-sourced converters due to the availability of high power semiconductor switches, such as 4500 V, 4000 A-rated Gate Turn-Off thyristors. Lessons learned from this experience continue to reinforce the true needs of a power flow...
The Hybrid Power Flow Controller (HPFC) is a Flexible AC Transmission System (FACTS) controller recently proposed to replace the Unified Power Flow Controller (UPFC) at lower capital costs, while providing similar regulation capabilities to address congestion problems. In this paper, an overview of the HPFC and its controls is presented, and its application to the Ontario-Canada grid is discussed...
This paper discusses a novel application of the SSSC which is a VSC-based FACTS device connected in series with the transmission line. An unloaded transmission line experiences Ferranti effect, i.e. the unloaded end of the transmission line experiences a voltage rise, which increases in magnitude as the length of the line increases. The SSSC can inject a controllable voltage in quadrature with the...
This paper presents a novel voltage-based controller for frequency control in inverter-based isolated microgrids through load voltage regulation. The proposed controller, described here in detail, makes use of the load sensitivity to operating voltage to regulate load consumption. The performance of the controller is evaluated and validated through simulation studies on PSCAD/EMTDC based on medium...
The voltage source converters (VSC) are the key power interfaces between the individual ac grids and dc grids in the hybrid power system. When the ac grid is unbalanced, the grid currents are distorted and the harmonic is induced. Meanwhile, the oscillations in the active and reactive power are also increased,which may damage these interfaces. In order to ensure the safety of the converters and the...
The impact of phase locked loop (PLL) parameters on the dynamic and steady-state behavior of a Voltage Sourced Converter (VSC) in an HVdc transmission system is determined as a function of the system strength (parameterized by the short circuit ratio -SCR). This is achieved by using a linearized small signal model of the converter system and its controls. The model is validated via electromagnetic...
The increase of renewable energy sources and HVDC links lead to power systems composed of a large number of interconnected Voltage Source Converters, involving predominant nonlinear oscillations. The strong coupling effect in the severely stressed system obscures the characteristics of the nonlinear dynamics. To tackle this problem, a proposed Nonlinear Mode method based on Normal Form theory makes...
This paper demonstrates the stabilization of large power systems using voltage source converter based high voltage direct current (VSC-HVDC) links. Based on global power system measurements, a model predictive controller (MPC) manipulates the power injections of the HVDC links to keep the AC system in synchronism. The grid controller explicitly accounts for constraints and the future behavior of the...
This paper addresses an advanced vector current control for a voltage source converter (VSC) connected to a weak grid. The proposed control methodology permits high-performance regulation of the active power and the voltage for the feasible VSC range of operation. First, the steady state characteristics for a power converter connected to a very weak system with a short circuit ratio (SCR) of 1 are...
Frequency control of AC systems using Voltage Source Converter (VSC) HVDC links is of growing importance as interconnectors and links to offshore generation replace conventional synchronous generators in many countries. This paper investigates the use of local system feedback and advanced droop control to achieve frequency stabilization for a two-area test system.
Synchronous instability may also occur to the P-f droop-controlled voltage source converter as well as virtual synchronous machine during large disturbance, similar to the synchronous generator's synchronous instability in conventional power systems. Moreover, the current limiting link will result in a more complicated instability process and a greatly decreased stability margin of the converter....
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