A synchronverter is an inverter that mimics synchronous generators, which offers a mechanism for power systems to control grid-connected renewable energy and facilitates smart grid integration. Similar to other grid-connected inverters, it needs a dedicated synchronization unit, e.g., a phase-locked loop (PLL), to provide the phase, frequency, and amplitude of the grid voltage as references. In this paper, a radical step is taken to improve the synchronverter as a self-synchronized synchronverter by removing the dedicated synchronization unit. It can automatically synchronize itself with the grid before connection and track the grid frequency after connection. This considerably improves the performance, reduces the complexity, and computational burden of the controller. All the functions of the original synchronverter, such as frequency and voltage regulation, real power, and reactive power control, are maintained. Both simulation and experimental results are presented to validate the control strategy. Experimental results have shown that the proposed control strategy can improve the performance of frequency tracking by more than 65%, the performance of real power control by 83%, and the performance of reactive power control by about 70%.

https://www.sheffield.ac.uk/polopoly_fs/1.323811!/file/IEEEPE_SelfSynch.pdf

Self-Synchronized Synchronverters: Inverters Without a Dedicated Synchronization Unit

Most motors are designed to operate at a constant speed and provide a constant output; however, modern technology requires different speeds in many applications where electric motors are used. A variable speed drive (VSD) is a device that regulates the speed and rotational force, or output torque of mechanical equipment. Effects of applying VSDs are in both productivity improvements and energy savings in pumps, fans, compressors and other equipment. Variable speed drive technology and the importance of controlling the speed of existing motors have fascinated many attentions in the last years with the advent of new power devices and magnetic materials. This paper is a comprehensive review on applications of VSD in electrical motors energy savings. The aim is to identify energy saving opportunities and incorporated costs of applying variable speed drives to the existing applications of electrical motors. Subsequently, economic analysis, payback period and the effect of current and voltage harmonics generated by VSDs are presented. Authors are hopeful to provide useful information for future variable speed drive applications like fans, pumps, chillers, ventilators and heaters.

Applications of variable speed drive (VSD) in electrical motors energy savings

Industry 4.0 implementation for multinationals

Previous research for detecting incipient wind turbine failures, using condition monitoring algorithms, concentrated on wind turbine Supervisory Control and Data Acquisition (SCADA) signals, such as power output, wind speed and bearing temperatures, using power-curve and temperature relationships. However, very little research effort has been made on wind turbine SCADA alarms. When wind turbines are operating in significantly sized wind farms, these alarm triggers are overwhelming for operators or maintainers alike because of large number occurring in a 10 min SCADA period. This paper considers these alarms originating in two large populations of modern onshore wind turbines over a period of 1–2 years. First, an analysis is made on where the alarms originate. Second, a methodology for prioritizing the alarms is adopted from an oil and gas industry standard to show the seriousness of the alarm data volume. Third, two methods of alarm analysis, time-sequence and probability-based, are proposed and demonstrated on the data from one of the wind turbine populations, considering pitch and converter systems with known faults. The results of this work show that alarm data require relatively little storage yet provide rich condition monitoring information. Both the time-sequence and probability-based analysis methods have the potential to rationalize and reduce alarm data, providing valuable fault detection, diagnosis and prognosis from the conditions under which the alarms are generated. These methods should be developed and integrated into an intelligent alarm handling system for wind farms, aimed at improving wind turbine reliability to reduce downtime, increase availability and leading to a well-organized maintenance schedule.

Wind turbine SCADA alarm analysis for improving reliability.

A novel technique for detecting stator interturn faults in a doubly fed induction generator (DFIG) is proposed by analyzing its rotor current and search-coil voltage. So far, fault-diagnostic techniques proposed for stator-interturn-fault detection in DFIGs are based on analysis of stator current or vibration of generator. Results from these methods are ambiguous because they either fail to account for condition when the DFIG is operating under imbalanced load or these methods are based on experimental results alone without any theoretical basis. Our recent observations suggested that harmonics induced in the rotor circuit are very promising in detecting stator interturn faults in DFIGs. Hence, in this paper, an in-depth investigation is conducted to determine the origin of various harmonic components in rotor currents and their feasibility to detect stator interturn faults unambiguously. Detailed analysis is presented, which explains the mechanism by which the stator-interturn-fault-related harmonics are induced in the rotor circuit. The theory is verified with simulation and extensive experimental results. To confirm the feasibility of the proposed technique for detecting stator interturn faults and obtain results on speed sensitivity of fault detection, a prototype of digital-signal-processor-based fault-diagnostic system has been developed, which is capable of producing very fast trip signal in about 2 s.

Stator Inter-Turn Fault Detection of Doubly-Fed Induction Generators Using Rotor Current and Search Coil Voltage Signature Analysis

FUNDAMENTALS. Units. Fundamentals of Electricity and Magnetism. Fundamentals of Mechanics and Heat. ELECTRICAL MACHINES AND TRANSFORMERS. Direct Current Generators. Direct Current Motors. Efficiency and Heating of Electrical Machines. Active, Reactive, and Apparent Power. Three-Phase Circuits. The Ideal Transformer. Practical Transformers. Special Transformers. Three-Phase Transformers. Three-Phase Induction Motors. Selection and Application of Three-Phase Induction Motors. Equivalent Circuit of the Induction Motor. Synchronous Generators. Synchronous Motors. Single-Phase Motors. Stepper Motors. ELECTRICAL AND ELECTRONIC DRIVES. Basics of Industrial Motor Control. Fundamental Elements of Power Electronics. Electronic Control of Direct Current Motors. Electronic Control of Alternating Current Motors. ELECTRIC UTILITY POWER SYSTEMS. Generation of Electrical Energy. Transmission of Electrical Energy. Distribution of Electrical Energy. The Cost of Electricity. Direct Current Transmission. Transmission and Distribution: Solid State Controllers. Answers to Problems.

Theodore Wildi

Papers

Electrical Machines, Drives, and Power Systems