M. Aredes

Instantaneous p–q power theory for control of compensators in micro-grids

The main objective of this tutorial is to present the basic concepts on the instantaneous p–q Theory and then show its applicability for controlling switching converters connected in a micro-grid. These converters can be used for connecting renewable energy sources (solar, wind, and others) to the micro-grids or for harmonic, reactive power or unbalance compensation, and even for voltage regulation. The emphasis is given on the compensation characteristics derived from the p–q Theory, and simulation results of test cases are shown. Special attention is put on the oscillating component of the instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. This oscillating component, as defined in the p–q Theory, gives the amount of oscillating energy between the source and the load, and its compensation through a switching compensator must have an energy storage element to exchange it with the load. With the p–q Theory this energy storage element can be easily calculated as a function of the average component of the instantaneous real power, which depends on the observation period.

Compensation algorithms based on the p-q and CPC theories for switching compensators in micro-grids

The main objective of this paper is to compare the applicability and performance of a switching compensator when it is controlled by algorithms derived from the pq-Theory and from the Currents Physical Components Power Theory (CPC-Theory) considering a micro-grid application. Compensation characteristics derived from each one of these set of power definitions are highlighted, and simulation results of test cases are shown. Special attention is put on the oscillating instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. The oscillating instantaneous real power, as defined in the pq-Theory, gives the amount of energy oscillating between the source and the load, and its compensation using a switching compensator must have an energy storage element to exchange it with the load. The energy storage element can be easily calculated with the pq-Theory.

An Improved iUPQC Controller to Provide Additional Grid-Voltage Regulation as a STATCOM

This paper presents an improved controller for the dual topology of the unified power quality conditioner (iUPQC) extending its applicability in power-quality compensation, as well as in microgrid applications. By using this controller, beyond the conventional UPQC power quality features, including voltage sag/swell compensation, the iUPQC will also provide reactive power support to regulate not only the load-bus voltage but also the voltage at the grid-side bus. In other words, the iUPQC will work as a static synchronous compensator (STATCOM) at the grid side, while providing also the conventional UPQC compensations at the load or microgrid side. Experimental results are provided to verify the new functionality of the equipment.

Hardware-in-the-loop evaluation of DSP-controlled converters

Translation of power electronic circuit designs from simulations into actual hardware can give rise to difficulties, regarding the implementation of control functions with embedded controllers. This task is even more difficult when the power converter must operate connected to the grid. A design framework is described in this paper, which is suitable for testing and debugging software implementations of control algorithms for such applications, under nearly ¿real¿ conditions, while avoiding risks of damage to actual hardware. An example of application is given, along with experimental results.

A synchronverter to damp electromechanical oscillations in the Brazilian transmission grid

Nowadays a SVC at the Bom Jesus da Lapa (BJL) substation (250 MVAr) is utilized to control voltage at the Southeast/Northeast interconnection. This paper has two purposes. One is to show the technical possibility to substitute the Static VAR Compensator (SVC) by a synchronverter. Secondly, that the synchronverter mitigates electromechanical oscillations. A control strategy is utilized to damp the North/South mode in the same way as a Power System Stabilizer (PSS), based on the power flow on a transmission line at a distance of more than 1000 km.

Three-wire investigation of a hybrid power filter with four-switch structure applied to the attenuation of 5 th and 7 th harmonics with reduced inverter power rating

This paper studies a hybrid filter formed by a single tuned LC filter per phase and a small-rated three-phase active filter, which are directly connected in series without any matching transformer. The required rating of the active filter is much smaller than that of a conventional standalone active filter would be and it comprises a four-switch H-bridge inverter connected to the three-wire system. The analytical procedure is verified by simulation results to confirm the effectiveness of the proposed control scheme.

Attenuation of harmonics utilizing new control strategies for the SVC in Brazilian power system

Due to the high level of compensation with parallel reactors and series capacitors at the 500 kV transmission lines that interconnect the South and North regions of Brazil (from Serra da Mesa to Imperatriz substation), and the long distance compensation with parallel reactors at the South-East/North-East interconnection, harmonic resonances around 120 Hz and others occur in this region. This concerns directly to the SVC of Bom Jesus da Lapa (BJL), since this Power Electronic Compensator is capable of responding in this frequency range. This paper shows the capability of the SVC to attenuate harmonic resonances.

P&O method controls applied to grid connected PV systems

This paper proposes a fuzzy adaptive P&O controller for photovoltaic generation in AC systems. The goal of this controller is to overcome the MPPT accuracy of the classic P&O, which is impaired by the fixed step-size of the duty-cycle variation. Therefore, the fuzzy adaptive P&O controller varies the duty-cycle step-size to achieve fast dynamic response and accurate MPPT with reduced oscillation in steady state. Here, proposed algorithm as well as the classic P&O algorithm is assessed through a hardware-in-the-loop simulation in PSCAD/EMTDC environment. The controllers are compared in terms of performance, implementation availability and complexity.

Frequency analysis behavior of Hysteresis Current Control in VSI

This paper presents an analysis procedure for switching frequency in single and three-phase Voltage Sources Inverters (VSI), using Hysteresis Current Control (HCC). The instantaneous frequency profile, for synthesizing sinusoidal signals, and its behavior with several load variations, is presented. The analysis is performing with constant and proportional hysteresis bands, in single-phase VSI (with and without frequency limiters). Three-phase VSI, with independent HCC, and, Space Vector based hysteresis current controller are also shown.