Massimo Bongiorno

Input-Admittance Calculation and Shaping for Controlled Voltage-Source Converters

A controlled power electronic converter can cause local instabilities when interacting with other dynamic subsystems in a power system. Oscillations at a certain frequency cannot, however, build up if the converter differential input admittance has a positive conductance (real part) at that frequency, since power is then dissipated. In this paper, input-admittance expressions for a voltage-source converter are derived. It is seen how the admittance can be shaped in order to get a positive real part in the desired frequency regions by adjusting the controller parameters.

Practical Implementation of Delayed Signal Cancellation Method for Phase-Sequence Separation

In this paper, the use of a method for online detection of positive- and negative-sequence components of three-phase quantities, named the delayed signal cancellation (DSC) method, is investigated. Problems that arise in practical implementation of the DSC method in computer-controlled systems are investigated. Expressions of the detection error due to nonideal discretization are derived and calculations are verified experimentally. Two methods for reducing the detection error are presented and verified. It is also shown that the given expressions and proposed methods for reducing the detection errors can also be applied to the case of grid frequency variations

On Control of Static Synchronous Series Compensator for SSR Mitigation

This paper deals with the analysis and simulation of the static series compensator (SSSC) for subsynchronous resonance (SSR) mitigation. The purpose of the paper is to derive and analyze a novel control strategy for SSSC dedicated for SSR mitigation. Objective of the proposed controller is to increase the network damping only at those frequencies that are critical for the turbine-generator shaft. By using frequency scanning analysis, the effectiveness of the proposed method for mitigation of SSR due to torsional interaction effect is presented and compared with the existing control strategy. Finally, simulation results show the performance of the proposed method in mitigating SSR due to torque amplification effect.

A Novel Control Strategy for Subsynchronous Resonance Mitigation Using SSSC

In this paper, a novel control strategy for subsynchronous resonance (SSR) mitigation using a static synchronous series compensator will be presented. SSR mitigation is obtained by increasing the network damping only at those frequencies that are critical for the turbine-generator shaft. This is achieved by controlling the subsynchronous component of the grid current to zero. Using the IEEE first benchmark model, the effectiveness of the proposed control algorithm when mitigating SSR due to torsional interaction and torque amplification effect will be shown.

Single-Phase VSC Based SSSC for Subsynchronous Resonance Damping

In this paper, a novel control strategy for subsynchronous resonance (SSR) mitigation using a static synchronous series compensator (SSSC) will be presented. The SSSC is constituted by three single-phase voltage source converters. SSR mitigation is obtained by increasing the network damping only at those frequencies that are critical for the turbine-generator shaft. This is achieved by controlling the subsynchronous component of the grid current to zero. Using the IEEE First benchmark model, the effectiveness of the proposed control algorithm when mitigating SSR due to torsional interaction and torque amplification effect will be shown.

Effect of Sampling Frequency and Harmonics on Delay-Based Phase-Sequence Estimation Method

This paper investigates issues related to practical implementation of the one-quarter of cycle-based estimation method [here called delayed signal cancellation (DSC)] for online detection of positive and negative sequence components of three-phase quantities. The detection error due to non-ideal sampling frequency is calculated. Furthermore, the effect of the DSC method on estimation when harmonic components are present in the input signal is analyzed. It is shown how harmonics transfer through the DSC and how a non-ideal sampling frequency affects the estimation of the harmonics. Experimental verification of the analytical results is presented.

An Adaptive Power Oscillation Damping Controller by STATCOM With Energy Storage

This paper deals with the design of an adaptive power oscillation damping (POD) controller for a static synchronous compensator (STATCOM) equipped with energy storage. This is achieved using a signal estimation technique based on a modified recursive least square (RLS) algorithm, which allows a fast, selective, and adaptive estimation of the low-frequency electromechanical oscillations from locally measured signals during power system disturbances. The proposed method is effective in increasing the damping of the system at the frequencies of interest, also in the case of system parameter uncertainties and at various connection points of the compensator. First, the analysis of the impact of active and reactive power injection into the power system will be carried out using a simple two-machine system model. A control strategy that optimizes active and reactive power injection at various connection points of the STATCOM will be derived using the simplified model. Small-signal analysis of the dynamic performance of the proposed control strategy will be carried out. The effectiveness of the proposed control method to provide power oscillation damping irrespective of the connection point of the device and in the presence of system parameter uncertainties will be verified through simulation and experimental results.

Input Admittance Expressions for Field-Oriented Controlled Salient PMSM Drives

This paper presents analytical expressions for the converter input admittance in field-oriented controlled permanent-magnet synchronous motor (PMSM) drives. The effect of rotor saliency is taken into consideration and the derived admittance expressions are valid for maximum-torque-per-ampere as well as high-speed (field weakening) operation. Experimental results illustrate the validity of the derived admittance expressions. The presented work can be used to predict dc-link voltage instabilities in PMSM drives in, e.g., railway traction, aerospace and automotive applications.

Online Estimation of Subsynchronous Voltage Components in Power Systems

In this paper, the problem of online estimation of subsynchronous frequency components in the measured grid voltage is treated. Two estimation methods, one based on the use of lowpass filters and a recursive least square algorithm, are investigated and compared. In particular, due to its higher degree of freedom in the design, the lowpass filters-based estimation method is found to be the most appropriate and accordingly further analyzed. The method is improved to cope with inaccurate knowledge of the subsynchronous frequency. The simulation results prove the effectiveness of the investigated method both for the ideal and the disturbed case.

Voltage Dip Mitigation Using Shunt-Connected Voltage Source Converter

In this paper, a voltage source converter (VSC) connected in shunt with the grid to mitigate voltage dips for sensitive processes is presented. The VSC maintains the magnitude of the grid voltage at the connection point constant by injecting reactive power to compensate for the voltage dip. This is achieved by using a cascade controller, constituted by an inner vector current-controller (VCC) and an outer voltage controller, which calculates the current references for the VCC. The paper shows that using an inductor/capacitor/inductor (LCL)-filter instead of the simpler L-filter in between the VSC and the grid yields high performance and robust controller. Furthermore, in order to compensate for unbalanced dips, both positive- and negative-sequence components of the grid voltage must be controlled separately. This is done by using two independent controllers for the two sequences, with the same cascaded structure described above. Simulation results under balanced and unbalanced dips are presented to show the performance. Also, stability analyses are done to determine the robustness of the system against grid parameter variation.