Anderson Vagner Rocha

Motor drive systems reliability: Impact of the environment conditions on the electronic component failure rates

This article discusses the actual failure rate of electronic components when these are exposed to harsh environments, which can include vibration, dust, humidity, high temperature and others. It presents a compilation on the physico-chemical effects that can take place when electronic components are stressed and how such effects can reduce the component life. It is also presented a compilation of the results of a thorough and comprehensive research on different standards for reliability prediction, along with a critical and comparative analysis between the methodologies and applications related to each one of them. Furthermore, to provide the reader a broader understanding of the methodology used in these standards, an example employing a typical SV-PWM converter used in motor drive systems, submitted to different environmental stresses, is used as a case study.

A Thermal Management Approach to Fault-Resilient Design of Three-Level IGCT-Based NPC Converters

The three-level converter with neutral point clamped (NPC), introduced by Nabae in 1981, has become the most popular converter topology for high and medium-voltage industrial drives, being widely commercialized by major manufacturers worldwide. Responsible for driving key processes in various industries, high availability of these converters is mandatory, since their maintenance or replacement imply downtimes incompatible with the requirements of the production processes. Considering the possibility of failures in the protection schemes, this paper discusses a fault-resilient design for IGCT-based NPC converters based on proper thermal management of the power semiconductors. The main goal is show that the thermal stress caused by the short-circuit currents can be managed, improving the selectivity and tracing of the damaged components, thus reducing the overall converter downtime and the maintenance costs.

Thermal degradation management in a Fault-tolerant active NPC converter

Fault-tolerant operation of power converters has been a challenge for engineers and designers. Although several schemes have been proposed in recent years, they are typically restricted in terms of their capability to recover from successive failure events. The recently proposed Fault-tolerant ANPC converter has been shown to be able to deal with multiple failure events due to its flexible and reversible reconfiguration capability. In this paper, it is introduced a new thermal degradation management strategy, based on the FT-ANPC reconfiguration capabilities. Through an analytical lifetime estimation model, it is shown that the FT-ANPC converter can be available more than twice as much as an ordinary NPC converter. A metro-system application is studied to demonstrate the efficacy of the thermal degradation management of the FT-ANPC for mission-critical profiles.

Rectifier-to-Inverter Connection Through Long DC Cable—Part II: The Complete Copper Economy Characterization

High-frequency problems involving long cable PWM motor drive systems are well documented in the literature. Solutions based on passive filters are conventionally used to suppress these undesired phenomena that take place in such systems, but, in turn, bring up new considerations concerning filter size, weight, cost, and electrical losses. In this context, a concept of an alternative motor drive system that overcomes all these problems was outlined by the authors in a previous paper, where the long cable was used to connect the rectifier to the inverter, thus establishing a dc power transmission link. In addition, other important issues concerning the proposed system have also been adressed, along with a comprehensive analysis of the power losses in the (long) dc or ac cable and a preliminary estimation of the copper amount reduction in favor of dc transmission. In the present paper, the results from a more recent and general study for the complete copper economy characterization are presented, demonstrating that the proposed drive system configuration, aside from eliminating the whole high-frequency problem, is always advantageous also from the copper economy point of view.

Premature wear and recurring bearing failures in an inverter driven induction motor— Part II: The proposed solution

In a previous work, a real case of recurring bearing failures in an induction motor had been extensively studied. As a result, the cause of the problem was revealed to be the circulation of electric current through the bearings. In this way, the present paper deals with the high-frequency leakage currents in ac motors fed by pulsewidth-modulation inverters, contextualized in the analysis of an actual case. From the parameters of an equivalent circuit representing the connecting cable, motor, and inverter return path, a filter, characterized by a common-mode transformer, is designed to mitigate the common-mode quantities and the correlated problems. Both simulated and experimental results show that the proposed solution represents an advantageous alternative in comparison to the traditional RC and RLC filters, since, in addition to its effect on the common-mode quantities, it dissipates a negligible amount of power.

Proactive fault-tolerant IGBT-based power converters for mission critical applications in MW range

Mission Critical Application is a general term for any system whose loss could cause downtime in crucial operations for a company. Given the importance assumed by power converters in many critical systems, this research is conducted in the framework of the reliability engineering applied to a well-established medium voltage power converter in the industry environment. Condition monitoring techniques are used to detect changes in parameters of the IGBT power modules aiming to detect die and package degradation during operation. The main goal is anticipate degradation failures in power modules in such a way that the power converter can be reconfigured before a fatal fault. This fully proactive approach prevents the uncertainty related to different failure modes of power semiconductor devices. The premature detection of failure event allows a better equipment availability management.

Thermal Stress and High Temperature Effects on Power Devices in a Fault-Resilient NPC IGCT-Based Converter

The integrated gate-commutated thyristor and presspack power diodes have been successfully applied in medium-voltage neutral point-clamped converters in the power range from hundreds of kilowatt to tenths of megawatt. Responsible for driving key processes in the industry, high reliability and availability are crucial for these converters, since their repair or replacement after failure events may take too long. Given the vital importance of such equipment for the drive systems, they are equipped with protection schemes that are usually reliable, but not infallible. If the protection scheme of the converter does not work properly in a short-circuit situation, serious damages may be expected on its power semiconductor devices. In this paper, the power semiconductors thermal behavior is investigated using finite-element models in the COMSOL Multiphysics software. Three-dimensional thermal models of the power devices were raised by industrial radiography techniques, aiming to expand the information provided by the manufacturers. The authors show how these results can be used in a real equipment to attenuate the catastrophic effects of the protection scheme malfunction, so limiting the damage pattern within the converter to their least complex power devices.

Premature Wear and Recurring Bearing Failures in an Inverter-Driven Induction Motor—Part I: Investigation of the Problem

This paper provides an analysis about early incipient and recurring failures in three-phase induction motor bearings when driven by pulsewidth modulation (PWM) inverters, focusing on a real industrial process. The potential problems preliminarily defined were first discussed on a theoretical basis and afterward experimentally assessed by means of vibration, stator current, and common-mode current data acquisition and analysis. Over the investigation, it was concluded that the presence of common-mode currents at the verified levels could cause damages to the motor bearings, which was confirmed when the machine stopped working due to another bearing failure.

Driving AC motors through long distances with DC transmission: Experimental results

Driving induction motors with PWM inverters through long distances result in several undesired high frequency phenomena, such as transient overvoltages at the motor terminals, common-mode currents flowing through the system and the presence of a cable charging current, among others. Instead of filters, which represent the traditional method for the mitigation of these problems, in a previous work the authors proposed an alternative solution, where the rectifier and inverter bridges are separated and connected by the long cable, being the latter located right besides the motor. This alternative configuration, based on DC transmission, aside from solving the aforementioned problems, provides the additional benefits of reducing the voltage drop in the cable and providing copper economy for the power transmission. In this context, in the present work a prototype of a long cable motor drive system was built in both configurations (conventional and with DC transmission). Several results involving the transient overvoltages, cable charging and common-mode currents were obtained from each system and compared, in order to demonstrate the effectiveness of the proposed drive system topology in reducing these undesirable phenomena.

Fault-tolerant medium-voltage power converters for high-capacity belt conveyor systems

The bulk materials transportation from the mines to their destination is an important activity that often represents the major part of the total mining costs. More and more frequently, high-capacity belt conveyors in mining are efficiently driven employing medium-voltage power converters connected with large induction motors. Unfortunately, medium-voltage power converters use a high number of power semiconductors which are ranked as the most fragile components of a drive system and the failure of any of these devices often causes a total collapse of the converter, resulting in the conveyor system downtime with large financial losses for companies. In this work the authors will present new design alternatives for the most used power converter technologies aiming its fault-tolerant and fault-resilient operation. As the total tolerance to any kind of failure is still a practical impossibility, in the cases where catastrophic failures cause the converter breakdown and the conveyor downtime, it will be shown how to limit the damage pattern in the equipment, minimizing the maintenance costs and time-to-repair.