Bertil Berggren

DC Grid Control Through the Pilot Voltage Droop Concept—Methodology for Establishing Droop Constants

Converter control is an important aspect of voltage-source-converter high-voltage dc (VSC-HVDC) based multi-terminal dc grids. Variants of power drooped against dc voltage control have previously been proposed for this purpose. However, there is at this time no clear methodology available on how to select the size of the droop constants for distributing a power mismatch, following, e.g., a converter trip, on several converters. This paper proposes a methodology for establishing droop constants for a variant of power drooped against dc voltage called pilot voltage droop control. The methodology is derived from the basic control laws in a straight forward fashion and the accuracy is exemplified by time domain simulations in Digsilents Powerfactory platform.

Simulation of synchronous machines in phase coordinates including magnetic saturation

Abstract This paper describes a novel way to account for magnetic saturation for simulation of synchronous machines in phase coordinate for power system studies. A synchronous machine model in phase coordinates is presented and the effect of saturation along direct and quadrature axes are taken into account by identifying the flux linkages of individual phases in terms of the flux linkages of direct and quadrature axes. The proposed model was simulated using the high-level dynamic simulation language (DSL) and its performance was compared with the standard dqo model in SIMPOW™ for a sample round rotor machine.

A research project to investigate the impact of electricity system requirements on the design and optimal application of the Powerformer/sup TM/

This paper describes the aims and the methodology of a major collaborative research project between the University of Queensland and Australian and Swedish industry partners, including ABB Corporate Research (Sweden), Alstom Power (Sweden and Australia), PowerLink Queensland, Stanwell Corporation, C S Energy and Tarong Energy. The project investigates the likely benefits of significance to the Queensland system, which will arise from the optimisation of the new Powerformer technology for the generation of electricity at transmission or sub-transmission voltages, i.e. without step-up transformers.

DC grid control through the pilot voltage droop concept - Methods for establishing set-point tracking

Control of voltage-source-converter high-voltage dc (VSC-HVDC) transmission systems embedded in ac systems is a central issue requiring attention in the context of multi-terminal dc grids. A number of power drooped against dc voltage control concepts have been proposed in the literature for this purpose. The main advantage of droop control in this context is that it facilitates for several converters to share a sudden mismatch in power, e.g., due to a converter trip. However, it is usually less clear how to re-establish set-point tracking in, e.g., power once it has been lost. This paper proposes two different methods that in conjunction can resolve this issue for both small and large disturbances for a variant of power drooped against dc voltage called pilot voltage droop control. The methods are derived from the basic control laws in a straight forward fashion and the accuracy is exemplified by time domain simulations in Digsilents Powerfactory platform.

An Alternative Method to Build DC Switchyard With Hybrid DC Breaker for DC Grid

In this paper, a new dc switchyard structure for a multiterminal dc (MTDC) grid is proposed. Fast fault current breaking capability, which is essential for a dc grid, can be achieved with available HVDC breaker solutions (e.g., ABBs hybrid HVDC breaker). However, the hybrid HVDC breaker concept also opens up possibilities for unconventional (relative to ac) switchyard solutions which may be more cost effective. The main aim of this paper is to expound how the proposed dc switchyard can be built with hybrid HVDC breakers in a configuration where the number of components is much less compared to a conventional switchyard structure. After that, the switchyard operation, fault current handling flexibility, and actions against component failure are described conceptually. Finally, the performance of the proposed switchyard is validated and compared with that of a conventional double breaker double busbar switchyard structure for selected cases through time-domain simulations

Development and comparison of DC grid model in powerfactory and Dymola for controller design

Dealing with large AC systems interfaced with DC grids through converters poses new challenges on simulation platforms. A linearized model is essential for many common control design procedures while various converter control mode implementations are required to emulate different operating conditions in the DC grid. Currently many of the domain specific tools are unable to provide such linearized model when the model contains DC Grid components. To overcome this limitation of the domain specific simulation platforms, it is proposed to use the general purpose modeling language Modelica and the tool Dymola to generate linear models to develop extensions for controller design while PowerFactory Digsilent is used for time domain simulations. In this way it is possible to validate the actual system performance of the controller which is designed based on the linearized model. In this paper VSC HVDC is considered for the DC grid.

Distributed power flow analysis for hybrid AC/HVDC grids by network decomposition

This paper proposes a distributed method for solving power flow problems for hybrid AC/HVDC grids using network decomposition. The hybrid system is decomposed at the AC side point of common coupling (PCC) buses. The power flows of the resulting subsystems are solved separately with fixed boundary conditions. The solutions are iterated with updated boundary conditions and coordinated by a master program until convergence. The method described here has a few advantages compared to previous decomposition methods: 1) all grid specific features are encapsulated and handled in self-contained power flow modules, which allows the re-use of existing AC grid PF program with no modification; 2) all equations in a DC grid are solved simultaneously and it requires no additional DC slack bus iterations, which enables the handling of various DC grid modeling features and easy maintenance and upgrade. The proposed method is illustrated by using a test hybrid AC/DC grid consisting of two asynchronous AC systems, one interconnecting multi-terminal DC grid and one embedded multi-terminal DC grid, involving both monopolar and bipolar DC grid designs.