Igor A. Pires

Increasing Ride-Through Capability of Control Panels Using Square-Wave Series Voltage Compensator

Voltage sag is the most important power quality problem. The classical solution to protect industrial processes against voltage sags is based on the use of a large series voltage compensator (SVC), such as the dynamic voltage restorer. Although the SVCs are a general solution, in most cases alternative measures should be checked before purchasing such an expensive piece of hardware. For instance, some adjustable speed drives (ASDs) have embedded protection functions to mitigate voltage sags. In addition, contactors and power line carriers could be protected by low-power single-phase square-wave SVCs, which have been shown to be cost effective. This paper shows that, using the “ride-through” function of ASDs combined with cost-effective square-wave SVCs, a significant improvement in the ride-through capability of the protected process is achieved. Extensive testing of a low-power ASD panel supports the proposed voltage sag mitigation alternative.

Central inverter topology issues in large-scale photovoltaic power plants: Shading and system losses

Most of the large-scale PV power plants are based on central inverters, in which the PV panels are concentrated in single or few MPPTs and connected to the grid through three-phase inverters. Although its high conversion efficiency, extracting the total available power from an association of a large number of PV panels represents an issue in these systems. The irregular shading effects added to the intrinsic limitations in series/parallel panel associations may result in severe limits on the power injected into the grid. This paper is focused on simulations and experimental results from a power plant subjected to controlled shading conditions. In addition of this work, an alternative multi-MPPT converter topology capable of dealing with such conditions is enunciated and proper references from it are also pointed out.

A new fault-tolerant realization of the active three-level NPC converter

The three-level (3L) neutral-point-clamped (NPC) voltage-source (VSC) converter has been the standard solution in medium-voltage range for industrial applications. Recently, the NPC converter structure was improved by adding two extra active switches per phase leg, thus overcoming one of its main drawbacks: the unequal power loss among the power semiconductors. The resulting structure became known as active NPC (ANPC) converter. The high availability of these power converters is mandatory, since their maintenance or replacement imply equipment downtimes incompatible with the requirements of the production processes. The fault-tolerant operation of such converters has been addressed in the technical literature, but the main proposed solutions result in more complexity and higher parts count. This work proposes a new fault-tolerant structure for the ANPC IGBT-based converter, using standard devices, with very low additional cost and small complexity. The main goal is to show that the ANPC converter can overcome different and successive failures in its power devices without loss of functionality, before its definitive downtime.

Low voltage PV power integration into medium voltage grid using high voltage SiC devices

High voltage high power semiconductor devices are being used for grid integration of renewable energy sources. 1200V, 100A SiC Mosfets, 10 kV SiC Mosfets and 10kV SiC JBS Diodes have proven to be beneficial for high voltage application. High Voltage SiC devices enable high switching frequency operation thus reducing size of passive elements. Scope of this paper focuses on an alternative approach for 0.9 MW PV power plant, which is currently being constructed in Brazil. Use of high power SiC devices for PV power plant for integration into 13.8 kV grid provides higher efficiency, reduction in size and volume.

Cost effective voltage sag mitigation using square-wave Series Compensators

Voltage Series Compensators typically insert a sinusoidal voltage to compensate voltage sags. In order to achieve a sinusoidal waveform, the output circuitry is formed by a PWM inverter with a sinusoidal filter. However, the sag disturbance is a phenomenon that typically occurs during hundreds of milliseconds. Instead of injecting a sinusoidal voltage, this paper proposes a series compensator that injects a square-wave voltage to protect the sensitive loads. The proposed compensator does not need the high switching frequency PWM inverter, thyristor by-pass switches and sinusoidal output filter, reducing the overall cost and volume of the final equipment. This paper presents the proposed series compensator topologies and control. Experimental results are also included to demonstrate the compensator performance when protecting microcomputer and PLC loads.

Protecting Control Panels Against Voltage Sags: Using a Square-Wave Series Voltage Compensator

Voltage sags are among the most important power quality problems affecting sensitive industrial equipment, including control panels. one or several units of programmable logic controllers (PlCs), contactors, and adjustable-speed drives (asDs) are present in an industrial control panel, and all of these are sensitive to voltage sags. When a voltage sag occurs, contactors may trip, and one or more PLCs may reset with the process still running. Eventually, the process protection trips, and an unplanned shutdown takes place. This article discusses the use of a square-wave series voltage compensator (SW-SVC) in control panels to create a sag-free, single-phase bus to supply PLCs, contactors, and other sensitive control hardware. The simulation results of control hardware equipment fed through a sag-free bus based on SW-SVC technology are presented. The experimental results obtained from a typical ac drive panel show the effectiveness of this proposition.

Protecting control panels against voltage sags using square-wave series voltage compensators

Voltage sag is one of the most important power quality problems affecting sensitive industrial equipment. Control panels consist of one or several units of Programmable Logic Controllers (PLC), Contactors and Adjustable Speed Drives. These devices are all sensitive to voltage sags. When a voltage sag occurs, a contactor could trip or a PLC could reset while the controlled process would still work, eventually tripping the process protection and leading to an unplanned process shutdown. This paper discusses the use of a square-wave series voltage compensator in the protection of control panels against voltage sags. PLCs and contactors are modeled. Simulation results of a protected control panel by the square-wave series voltage compensator are presented, showing the effectiveness of this proposition.

Design aspects of a square-wave Series Voltage Compensator

Among several solutions for the voltage sag problem, the Series Voltage Compensator (SVC) stands out. This device injects a compensating voltage at the moment the sag occurs, recovering the voltage supplied to the protected load. The injected voltage is usually produced by a PWM inverter in series with a LC filter, producing a sinusoidal compensating voltage (Sinusoidal SVC). Instead of using sinusoidal voltage waveforms, the authors claim that line frequency square-wave compensating voltages yield more cost effective solutions. For instance, in a square-wave SVC, the LC filters and high switching frequency losses are eliminated. This paper presents several square-wave SVC topologies, including a cost comparison between sinusoidal and square-wave solutions. It is demonstrated that the square-wave SVC is more cost effective than the sinusoidal one.

Increasing ride-through capability of control panels using square-wave series voltage compensator

Voltage sag is the most important power quality problem. The classical solution to protect industrial processes against voltage sags is based on the use of a large series voltage compensator (SVC), such as the dynamic voltage restorer. Although the SVCs are a general solution, in most cases alternative measures should be checked before purchasing such an expensive piece of hardware. For instance, some adjustable speed drives (ASDs) have embedded protection functions to mitigate voltage sags. In addition, contactors and power line carriers could be protected by low-power single-phase square-wave SVCs, which have been shown to be cost effective. This paper shows that, using the “ride-through” function of ASDs combined with cost-effective square-wave SVCs, a significant improvement in the ride-through capability of the protected process is achieved. Extensive testing of a low-power ASD panel supports the proposed voltage sag mitigation alternative.

On the Application of Single-Phase Voltage Sag Compensators in Three-Phase Systems

Voltage sag is one of the most frequent power quality problems found in industries and power system. Its effects can be numerous such as control equipment trips, process shutdown, and production losses. This paper reports three years of voltage sag measurements collected in a research lab. This site is located near many metal industries which lead to a correlation between the obtained results and possible voltage sags in these industries. From the resulting analysis, this paper proposes the usage of single-phase voltage sag compensators in three-phase systems aiming a cost-effective solution. This procedure would not wholly eliminate the voltage sag incidence but it would diminish voltage sag effects on electrical loads.