Einar Vaughn Larsen

Concepts for design of FACTS controllers to damp power swings

The design of controllers sited in the transmission network for damping interarea power oscillations requires several types of analytical tools and field verification methods. Probably the most important aspect of such control design is the selection of proper feedback measurements from the network. This paper describes concepts which provide design engineers with the insight to control performance and the understanding needed to ensure the secure operation of the bulk transmission system. Specific attention is directed to procedures for selecting feedback signals. >

Subsynchronous interactions with static VAR compensators-concepts and practical implications

In 1987, planning for the installation of a static VAr compensator (SVC) in Chester, Maine, was initiated. Project participants were concerned that the SVC might have an impact on torsional modes of vibration of nearby turbine-generators. A study was conducted to gain understanding of the phenomenon and to quantify the potential impact of the SVC on torsional damping. This work describes the analytical techniques used in the study and summarizes the key results. >

Damping control design based on time-domain identified models

This paper presents an integrated approach for designing damping controllers for large power systems. First, a low-order model is identified from a time simulation of the nonlinear power system model. Then an exact multi-modal decomposition is used to develop design indices for selecting on appropriate input signal to the controller. The method is illustrated with the design of thyristor-controlled series compensator damping controllers in two test systems.

A Refined Frequency Scan Approach to Sub-Synchronous Control Interaction (SSCI) Study of Wind Farms

Frequency-scan approaches for conducting Sub-Synchronous Control Interaction (SSCI) studies of wind farms is becoming a normal practice in the industry. Modern power electronics control used in many wind generators has a characteristic that couples two frequency components, similar to saliency effects of conventional generators. As a consequence, treating both wind farm and grid as single-dimension impedances could generate an inaccurate result. This paper describes a two-dimension transfer function approach that can be practically applied to ensure accuracy when evaluating SSCI aspects of power-electronic equipment such as renewable generation.

Torsional Mode Damping For Electrically Driven Gas Compression Trains In Extended Variable Speed Operation.

The oil and gas industry has a growing demand for electrically driven trains operated at variable speeds. Variable frequency electrical drives enable increased operational flexibility and energy efficiency. This is of great importance in applications requiring high power, such as gas compression. Load commutated inverters (LCIs) are one of the most widespread technologies for driving large gas compression trains because of excellent reliability records. One drawback of power electronics driven systems is the generation of nonfundamental air-gap torque ripple components due to electrical harmonics. The air-gap torque ripple can interact with the mechanical system at torsional natural frequencies of the drive train. Torsional vibration is an oscillatory angular motion that causes alternating twisting in shaft sections and machinery couplings. A consequence of uncontrolled excited torsional vibration may be a protective trip of the motor, to prevent mechanical damage, such as a failed coupling or a broken shaft. This paper discusses illustrative design details of applying a torsional mode damping control system to LCI driven multi-Megawatt centrifugal gas compressors. The coincidence of electrical drive harmonics and torsional natural frequencies of the mechanical system is sometimes unavoidable due to the large variable speed range of the compressor such as for process requirements. For these types of applications, a power electronic damping system technology can be applied to new units or as a retrofit solution to existing variable speed trains. The so-called integrated torsional mode damping (ITMD) unit is based on a torsional vibration measurement in the mechanical system and an interface to the existing inverter control of the drive system. The dc-link inductor of the LCI is partially used as an integrated energy storage unit and is combined with a smart damping controller, which reacts to a torsional vibration by modulating a small amount of the stored energy and sending it to the motor without impacting the normal operation of the system. As a result, the active power modulation at a torsional natural frequency of the mechanical system has a strong damping effect for torsional vibrations. Intensive simulations and several tests were performed on large LCIs (up to 50 MW) over the last three years. Selected experimental results will be presented and discussed to validate the suggested

Subsynchronous torsional interactions with static VAR compensators-influence of HVDC

Planning for the installation of a static VAR compensator (SVC) in Chester, Maine, was initiated in 1987. The prespecification subsynchronous torsional interaction (SSTI) studies showed that the SVC might have a negative influence on the stability of torsional modes of vibration of the nearby turbine generators. The parameters influencing the level of SSTI have previously been identified by the authors by using a simple system (1989). This work is extended to power systems containing an HVDC transmission system. The combined effect of SVC and HVDC on turbine-generator SSTI is investigated with the use of a hypothetical system. Simulation plots for the large machines of New Brunswick and Maine are included to quantify the level of interaction with the Chester SVC. Filtering as a mitigation measure is proposed to eliminate the small level of SSTI attributed to the Chester SVC. >

Wind generators and series-compensated AC transmission lines

This paper describes basic technical aspects to consider when applying wind generation to transmission grids that include series-compensated transmission lines, and some thoughts on how the industry can manage this combination in the future.

Potential benefits of STATCOM application to improve generation station performance

This paper describes the potential performance benefits that can be realized by the application of a STATCOM in conjunction with a conventional generator, by allowing the generator to increase its power output beyond its rated power.