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Multi‐terminal high‐voltage direct current technology based on voltage‐source converter stations (VSC‐MTDC) is expected to be one of the most important contributors to the future of electric power systems. In fact, among other features, it has already been shown how this technology can contribute to improve transient stability in power systems by the use of supplementary controllers. Along this line, this paper will investigate in detail how these supplementary controllers affect electromechanical oscillations, by means of small‐signal stability analysis. The paper analyses two control strategies based on the modulation of active‐power injections (P‐WAF) and reactive‐power injections (Q‐WAF) in the VSC stations which were presented in previous work. Both control strategies use global signals of the frequencies of the VSC‐MTDC system and they presented significant improvements on transient stability. The paper will provide guidelines for the design of these type of controllers to improve both large‐ and small‐disturbance angle stability. Small‐signal stability analysis (in Matlab) has been compared with non‐linear time domain simulation (in PSS/E) to confirm the results using CIGRE Nordic32A benchmark test system with a VSC‐MTDC system. The paper analyses the impact of the controller gains and communication latency on electromechanical‐oscillation damping. The main conclusion of the paper is that transient‐stability‐tailored supplementary controllers in VSC‐MTDC systems can be tuned to damp inter‐area oscillations too, maintaining their effectiveness. [ABSTRACT FROM AUTHOR]

This paper presents a control system based on a repetitive controller to compensate for key power-quality disturbances, namely voltage sags, harmonic voltages, and voltage imbalances, using a dynamic voltage restorer (DVR). The control scheme deals with all three disturbances simultaneously within a bandwidth. The control structure is quite simple and yet very robust; it contains a feedforward term to improve the transient response and a feedback term to enable zero error in steady state. The well-developed graphical facilities available in PSCAD/EMTDC are used to carry out all modeling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation. Index Terms--Dynamic voltage restorer (DVR), harmonic distortion, power quality (PQ), repetitive control, voltage sag.

This paper presents the detailed design, analysis, and application of the controller for a shunt active power filter based on a pulsewidth modulation dc-to-ac voltage source converter. The controller is mainly tailored to compensate harmonic currents of nonlinear loads connected to the mains. However, it can also achieve reactive-power compensation and mains-current balancing when required. The controller has a two-layer structure. The outer layer generates the current references for the inner layer. The former uses a plug-in discrete-time repetitive algorithm for current-harmonic compensation, a proportional-integral algorithm to maintain the dc-capacitor voltage in spite of unmodeled losses and a reactive-power-reference generator. The inner layer uses state-feedback with integral action for current control. The repetitive controller is justified to improve the tracking of the periodic current references required by the active filters. The stability of the resulting closed-loop system is studied and some indication of the system robustness is given. The proposed controller has been tested in a prototype with balanced and unbalanced nonlinear loads. A discrete-time model of the filter has been used from the beginning. The microcomputer delay when calculating the controller output and the delay due to the anti-aliasing filters have been included in the inner system state-variable model. Index Terms--Active power filters (APFs), dc-to-ac electronic converters, power quality, repetitive control.

This paper proposes systematic procedures to estimate the circuit parameters of an inverter-fed vector-controlled interior permanent-magnet synchronous motor when torque measurement is not available. The methodology presented here does not neglect iron losses. New procedures have been developed and justified since international standard recommendations (International Electrotechnical Committee Standards) cannot be applied. Experimental results from a test rig will be presented in this paper to validate the most important contributions. Thanks to the procedures proposed, secondary effects on the motor parameters, e.g., saturation or frequency dependency, have been evaluated. Index Terms--Parameter determination, permanent magnet, synchronous motor.

The always-increasing switching frequency of modern solid-state power switches, together with the application of multi-converter topologies, make it possible to use Pulse Width Modulation (PWM) in high power applications of STATCOMs (STATic Synchronous COMpensators). This paper investigates the control system for a PWM-based STATCOM. First of all, a discrete-time model of the STATCOM is derived to take into account the discrete-time implementation of the controller. Secondly, the control algorithm is detailed. It ensures decoupled control of the real and reactive power exchanged between the power converter and the electric-energy system. This is necessary to control the d.c. capacitor voltage during transients of the exchanged reactive power. Finally, the control of the capacitor voltage is explained in detail. The controller is tailored to keep the capacitor voltage almost constant in spite of the fast control of the reactive power. This helps to reduce the capacitor size significantly. The main contributions will be illustrated using a 15 kVA laboratory prototype. Index Terms--Pulse width modulated power converters, reactive power control, static var vompensators.

The objective of this paper is to compare the performance of thyristor-controlled reactors (TCR) and shunt-connected PWM voltage source inverters (PWM-VSI) for compensation of flicker caused by arc furnaces. First of all, arc-furnace principles are presented in order to explain the main characteristics of the problem. Secondly, traditional TCR control are analyzed. An improved measuring procedure is suggested to enhance TCR performance showing that it achieves faster compensation than more traditional methods. Thirdly, PWM-VSI control for flicker compensation is described in detail using Park's transformation. The analysis shows how real and reactive power control can be decoupled. Continuous-time and discrete-time models are considered. Finally, a TCR control and a PWM-VSI control are compared by simulation using data and measurements from a real arc-furnace installation. The analysis considers three different periods of the production cycle: a) bore-down, b) fusion, and c) refining. It is clear from the results obtained that a shunt-connected PWM-VSI is better than a TCR for flicker compensation. This can be easily justified noting that the bandwidth of the PWM-VSI control system is far better than that of the TCR control. However, the control system for a PWM-VSI inverter is more complicated than that of a TCR. Besides, the latter uses a better-established technology than the former. Index Terms--Arc furnace, flicker mitigation, PWM, TCR control, voltage source inverter control.

This paper proposes a set of algorithms for stator parameter online estimation (stator resistance, stator inductance, and leakage inductance) of an induction motor using neither the rotor speed nor the rotor resistance. The estimation procedure is only based on stator current and voltage measurements. The algorithm performance is tested using simulation and experimental data from a commercial 15-kW induction motor. Index Terms--Induction motor, linear regression, parameter estimation.

This paper presents a generalized d-q loss model applicable to permanent-magnet synchronous motors, synchronous reluctance motors, induction motors, and dc motors. This model is used as the basis of a loss-minimization expression of easy implementation. Core saturation is taken into account. The paper reviews model-based loss-minimization schemes previously presented in the literature for specific types of motors. It shows how all these loss models can be derived from the general one proposed here. The results using the loss-minimization expression in specific motors are compared to those previously reported in the literature. Finally, experimental results for an interior permanent-magnet synchronous motor are presented to validate the applicability of the proposed expression. Index Terms--DC motor, induction, loss, minimization, permanent magnet, reluctance.