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The multiport LCL dc hub is a high power electronic dc substation used to interconnect multiple dc systems in the future dc transmission grids. This paper proposes a distributed power balance controller for high power multiport LCL DC hub. The hub controller follows dispatcher demands for required power trading between the hub ports. In the proposed control method, each hub port (connected to local...
This paper provides an overview of the development and technology challenges of the world's first multi-terminal VSC-HVDC link that was successfully commissioned on 25th of December 2013. The link consists of three converter stations at three different geographic locations, connected by a combination of subsea DC cable, land DC cable and overhead DC line. A selection of the physical test results are...
A double-circuit line using commercially available 400 kV-50 Hz three-core XLPE-insulated submarine cables is considered for the evacuation of up to 1 GW offshore wind generation. Three transmission distances are studied, namely 80 km, 100 km and 160 km, evaluating conventional (line-end) as well as mid-line shunt compensation. Operating envelopes and transmission losses are assessed, showing the...
DC voltage droop control is suggested by a number of authors for multi-terminal VSC-HVDC systems, due to its power sharing capability and distributed control characteristics. However, the stability and robustness of such a closed-loop droop controlled system have not been addressed in detail. In this paper, analytical models capturing the key dynamics of the droop dc voltage loop are presented. Transient...
This paper focuses on the behaviour of the cell capacitor discharge currents during DC faults in half-bridge modular multilevel converters. Active switches, not designed for fault conditions, are tripped to minimize discharge currents effect on the semiconductor switches. Two levels of device protection are commonly in place; driver level protection monitoring collector-emitter voltage and overcurrent...
During the last years, more and more renewable power generation units have been connected to the European power grid, creating demands for higher transport capacity as well as longer transport distances. Plans for the construction of HVDC and hybrid HVAC/HVDC corridors in Europe lead to an increased interest in the corona behaviour of direct current overhead lines. Within the scope of this paper,...
At a short circuit in an HVDC system modular multi-level converters with half-bridge submodules contribute to the short-circuit current even after blocking of the submodules. DC circuit breakers are therefore necessary for the interruption of the short-circuit current especially for the reliable operation of multi-terminal HVDC systems. In this paper a calculation method of important parameters of...
The connection point of a VSC-HVDC for the transmission of RES electricity, can be located far from the large generation plants, leading to a weak grid connection. This paper analyses the limitations on the power flow transfer through a VSC-HVDC system connected to a weak grid. First, the impact of the angle and voltage stability limits and the VSC rating are examined. Then, the power transfer capability...
This paper focuses on comparison studies of the CIGRE DC grid test systems on the real time platform RTDS and the offline simulation program PSCAD. The real time MMC valve models employ a surrogate network topology to reduce the computational burden on the hardware to simulate MMC HVDC in real time at a time step of 2 to 4 usec. The main purpose of the paper is to further validate the real time MMC...
The Commutation Failure Immunity Index (CFII) is a good predictor which quantifies the susceptibility of an HVDC system to commutation failure. However, this index is based on many electromagnetic simulations and requires extensive computational time. In this paper, a faster calculation method for CFII is proposed and verified. This method significantly reduces the simulation effort and is applicable...
With increasing utilization of high power-electronic converters, power-system modeling and stability analysis become ever more challenging. This paper introduces a transfer-matrix-based modeling method for power-system stability analysis. The method has previously been applied for studying the dynamic interaction between voltage-source converters and ac systems. In this paper, the modeling method...
A modular, hybrid HVDC transformer, located in the turbine nacelle has been proposed for the offshore wind industry to improve efficiency and redundancy while reducing costs. The injection of harmonics by the transformer power electronics however, complicates the core loss calculations of such a transformer. The standard Steinmetz Equation is no longer valid and the alternative loss equations proposed...
When an HVDC system is subjected to AC side short circuit faults, the transformer core might be driven to saturation at fault recovery due to flux offset. The saturation will therefore cause the flow of inrush currents. In this paper, dynamic models of a MMC based VSC-HVDC system incorporating transformer magnetisation characteristics are derived and verified. Using disturbance sensitivity functions,...
The use of three-phase voltage inverters (DC to AC converters) is frequently met in the electric power system, such as in the connection of photovoltaics with the rest of the grid. The paper proposes a nonlinear feedback control method for three-phase inverters, which is based on differential flatness theory and a new nonlinear filtering method under the name Derivative-free nonlinear Kalman Filter...
Utilization of VSC converter technologies for power injection and transmission requires a solid understanding of their effect and capabilities. This work investigates the effect of VSC based battery storage devices on transient stability. The combination of various DC power control functions permits to adapt the power injection to the AC grid strength and to keep the power system transiently robust...
The demand of reactive power in the last mile of the networks is increasing by the time due to the change of loading types by time, beside increasing the total demand itself where new technologies are being introduced depend mainly on different types of electrical support such as electrical cars and more electronic devices in consumption process [1]. This expected situation would lead to take into...
This study presents a tool for solving the Optimal Power Flow (OPF) problem in mixed Direct Current (DC) and Alternating Current (AC) systems. It allows to analyse the optimal operation of multiple independent systems, DC connected and linked to the AC system, from a steady state point of view and for several objective functions. The tool, implemented through implemented through MATLAB® Optimization...
High voltage direct current (HVDC) systems have been used as an effective solution to transmit power over long distances. Performance of HVDC systems has significantly improved with the emergence of voltage source converter based HVDC (VSC-HVDC). Increased controllability provides independent control of active and reactive power which facilitates controlling of voltage and frequency. This paper investigates...
In this paper a communication-less method for obtaining inertial response from a VSC-HVDC connected wind farm is proposed and verified experimentally in a scaled laboratory model with ratings in the range of 20 kVA. A two-terminal HVDC grid, connecting a wind farm with variable speed wind turbines and a weak AC grid, is used to analyse the possibility of inertial support during load imbalances. The...
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