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This paper proposes a startup sequence for a modular multilevel converter (MMC) HVDC-connected offshore wind farm (OWF) and demonstrates how it can be simulated using an electromagnetic transient-type tool. The objective is to analyze inrush currents of transformers and cables (HVAC and HVDC). Modeling accuracies and computational performances are examined using three existing modeling methods for the MMCs. [ABSTRACT FROM PUBLISHER]

Different from the traditional converter transformer and ac passive filtering method, this paper presents a new converter transformer and a corresponding inductive filtering method for HVDC systems. Based on this, characteristic parameters of the new converter transformer are studied in detail by theoretical analysis, simulation, calculation, and experimental verification. By deducing voltage relation, the constraint condition of the turn ratio is obtained, which can satisfy the demand of a 12-pulse converter in HVDC systems. By deducing current relations, the characteristics of the fundamental and the harmonic currents in the winding are obtained. According to the established operation equations, the simple but practical calculation methods for the short-circuit impedance and the rated capacity are proposed. Then, the change characteristic of the short-circuit impedance is analyzed and calculated. The detailed simulation and test results verified the correctness of the aforementioned theoretical analysis and calculation. [ABSTRACT FROM AUTHOR]

This paper presents the control system based on the so-called repetitive control for a five-level flying-capacitor dynamic voltage restorer (DVR). This DVR multilevel topology is suitable for medium-voltage applications and operated by the control scheme developed in this paper. It is able to mitigate power-quality disturbances, such as voltage sags, harmonic voltages, and voltage imbalances simultaneously within a bandwidth. The control structure has been divided into three subsystems; the first one improves the transient response of the filter used to eliminate the modulation high-frequency harmonics, the second one deals with the load voltage; and the third is charged with maintaining balanced voltages in the flying capacitors. The well-developed graphical facilities available in PSCADIEMTDC are used to carry out all modelling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation. [ABSTRACT FROM AUTHOR]

This paper proposes a protection scheme which utilizes modern voltage-source converters as fast-acting current-limiting circuit breakers. This paper investigates the main challenges of detecting and localizing a fault, and interrupting it as quickly as possible in a multiterminal dc system. A system protection scheme consisting of smart relays associated with converters has been developed. The protection relays monitor local quantities to detect and isolate disturbances/faults. It is shown that overcurrent-based schemes can be adopted for these relays to meet the fast response requirements. The effectiveness of the proposed protection scheme is illustrated through simulations. [ABSTRACT FROM AUTHOR]

The feasibility of future multiterminal dc (MTDC) systems depends largely on the capability to withstand dc-side faults. Simulation models of MTDC systems play a very important role in investigating these faults. For such studies, the test system needs to be accurate and computationally efficient. This paper proposes a detailed equivalent model of the modular multilevel converter (MMC), which is used to develop the MTDC test system. The proposed model is capable of representing the blocked-mode operation of the MMC, and can be used to study the balancing control of the capacitor voltages. In addition, the operation of the MMC when redundant submodules are included in the arms can also be studied. A simplified model of a hybrid high-voltage dc breaker is also developed. Hence, the developed test system is capable of accurately describing the behavior of the MMC-based MTDC system employing hybrid HVDC breakers, during fault conditions. Using time-domain simulations, permanent dc-side faults are studied in the MTDC system. In addition, a scheme to control the fault current through the MMC using thyristors on the ac side of the converter is proposed. [ABSTRACT FROM AUTHOR]

This paper presents an improved algorithm for power hardware-in-loop (PHIL) simulation that takes the errors introduced by the interface equipment into account. Through modeling and analysis of a PHIL simulation circuit, which is composed of a voltage-source converter and a simple network, the impact of the bandwidth of the interface amplifier and equipment on the PHIL simulation is examined. Based on the analysis, an improved algorithm is proposed that uses additional interface filters (implemented in hardware and/or software) rather than the use of previously attempted compensation techniques. More stable and accurate results can be obtained by using the new algorithm. The validity of the proposed algorithm is verified through a software case study and hardware case studies. [ABSTRACT FROM AUTHOR]

Proper operation of a multilevel flying capacitor converter (FCC) necessitates a closed-loop voltage balancing strategy. This paper proposes a space vector modulation (SVM)-based approach that benefits from the switching state redundancy of an n-level FCC to implicitly carry out the voltage balancing task within the switching strategy. Based on the voltage deviations of the capacitor voltages, a cost function is defined and minimized to choose the proper redundant switching states among the available switching states. The performance of a grid-connected four-level FCC under the proposed SVM strategy for various operating conditions is studied and evaluated based on time-domain simulations in the PSCAD/EMTDC environment, and experimentally verified. The studies demonstrate the capability of the proposed SVM strategy to regulate the capacitor voltages at their nominal reference values. [ABSTRACT FROM AUTHOR]

By utilizing multiline voltage-source (VSC)-based flexible ac transmission system (FACTS) controllers, independent controllability over each compensated line of a multiline system can be achieved. While VSC-based multiline FACTS controllers emerged as a new opportunity to control two independent ac systems, the main constraints and limitations that are presented to the conventional transmission-line protection systems need to be investigated. In this paper, the impacts of VSC-based FACTS controllers on distance relays while controlling the power flow of compensated lines are evaluated analytically and by detailed simulations for different fault types and locations. [ABSTRACT FROM PUBLISHER]

This paper describes a new approach to the design of current-source converter (CSC)-based shunt active power filters (APFs) to reduce the converter kilovolt-ampere rating considerably. This design approach is called the selective harmonic amplification method (SHAM), and is based on the amplification of some selected harmonic current components of CSC by the ac-side filter, and the CSC control system specifically designed for this purpose. The proposed SHAM has been implemented on a CSC-based APF for the elimination of 11th and 13th current harmonics of 12-pulse rectifier loads supplied from a medium-voltage underground cable. Simulation and field test results have shown that SHAM can successfully be applied to a CSC-based APF for reduction of the converter kilovolt-ampere rating, thus making it a cost-competitive alternative to voltage-source-converter-based APFs traditionally used in industry applications. [ABSTRACT FROM AUTHOR]

This paper presents a new control strategy for islanded (autonomous) operation of an electronically coupled distributed generation (DG) unit and its local load. The DG unit utilizes a voltage-sourced converter (VSC) as the coupling medium. In a grid-connected mode, based on the conventional dq-current control strategy, the VSC controls real- and reactive-power components of the DG unit. Subsequent to an islanding detection and confirmation, the dq-current controller is disabled and the proposed controller is activated. The proposed controller utilizes 1) an internal oscillator for frequency control and 2) a voltage feedback signal to regulate the island voltage. Despite uncertainty of load parameters, the proposed controller guarantees robust stability and prespecified performance criteria (e.g., fast transient response and zero steady-state error). The performance of the proposed controller, based on time-domain simulation studies in the PSCAD/EMTDC software environment, is also presented. [ABSTRACT FROM AUTHOR]

In this paper, a new controller for single-phase PWM converter without the ac voltage sensor is described. The proposed controller requires only the dc voltage sensor and the ac current sensor to compensate the power factor and harmonics. Detail simulation model including power circuit and controller was developed to verify the operation of proposed controller. The ape plication feasibility of the proposed controller was verified through experimental works with a prototype. The proposed controller has a simple structure in the point of hardware implementation, and shows excellent performance in normal operation as well as in sudden load change. [ABSTRACT FROM AUTHOR]

Three configurations of voltage source converter multi-terminal HVDC transmission for large offshore wind farms are studied. The voltage-current characteristics of the converters are shown and the operation of the converters with different power output from the wind farms is discussed. The control system is designed to achieve automatic coordination between the converters without the need of fast communication between them. The operation of the multi-terminal HVDC transmission with the control system is tested through simulations using PSCAD/EMTDC and through experiments on a three-terminal test rig. The simulation and experimental results show good agreement. [ABSTRACT FROM AUTHOR]

A back to back (BTB) HVdc interconnector consisting of multilevel current reinjection (MLCR) converters is described, based on the parallel converter configuration. Since the MLCR creates a zero current region during the commutations, the proposed BTB configuration permits the continued use of thyristor valves, without loosing the control flexibility of the self-commutating process. Extensive EMTDC simulation is used to demonstrate the satisfactory response of the proposed BTB HVdc inter-connector control structure to varying active and reactive power operating conditions. [ABSTRACT FROM AUTHOR]

As power electronics are increasingly used in power-electric networks, there is an interest in the creation of time-domain simulation techniques that can model the diversity of the integrative power-electric and electronic system while achieving high accuracy and computational speed. In the proposed method, generation of electric network equivalents (GENE), this is supported through the nested structure of the overall simulation process. One or multiple parent simulations, in which the unknown voltages are calculated using nodal analysis, launch multiple child simulations concerned with diakoptic subdivisions of the system under study. The interfaces for information exchange between parent and child levels are designed to provide encapsulation. This makes the subdivisions appearing from outside in the form of network branches compatible with the nodal analysis approach. It also facilitates the use of diverse solution methods for different child simulations, as it is shown for the simultaneous solution of equations formulated with nodal analysis and state space methods. Computational efficiency is obtained through the coordinated application of sparse-matrix methods, piecewise linear approximation of nonlinear characteristics, and precalculation of operations pertaining to recurring power-electronic switch statuses. The resulting overall solution process is simultaneous, distributed, and suitable for real-time simulation. The devised methodology is validated through simulation of the CIGRE HVdc benchmark model, comprising ac networks, twelve-pulse power-electronic converter stations, harmonic filters, and dc transmission. [ABSTRACT FROM AUTHOR]