Large Scale Proactive Power-Quality Monitoring: An Example from Australia

In Australia and many other countries, distribution network service providers (DNSPs) have an obligation to their customers to provide electrical power that is reliable and of high quality. Failure to do so may have significant implications ranging from financial penalties theoretically through to the loss of a license to distribute electricity. In order to ensure the reliability and quality of supply are met, DNSPs engage in monitoring and reporting practice. This paper provides an overview of a large long-running power-quality monitoring project that has involved most of Australia\u27s DNSPs at one time or another. This paper describes the challenges associated with conducting the project as well as some of the important outcomes and lessons learned. A number of novel reporting techniques that have been developed as part of the monitoring project are also presented. A discussion about large-volume data management, and issues related to reporting requirements in future distribution networks is included

Rectifier capacitor filter stress analysis when subject to regular voltage fluctuations

Lamp flicker levels which arise as a result of voltage fluctuations can exceed limits set by appropriate standards. New lamp types such as compact fluorescent lights (CFLs) are less sensitive to voltage fluctuations as their flicker characteristics are considerably different compared to those of the traditional incandescent lamp. These differences could support the moderation of the present voltage fluctuation and flicker standards and hence the associated limits. The potential detrimental effects on electrical equipment which may be caused by relaxation of these limits should be investigated before any changes to the present standards take place. The impact of voltage fluctuations on a fullbridge rectifier with a capacitor filter is considered as a case study in this paper. Such a circuit is found at the front end of many different types of equipment that are connected to the public AC supply network. The capacitor ripple current characteristic is of particular interest. The research reported in this paper indicates that the filter capacitor will accumulate and dissipate increased amount of charge when the rectifier is subjected to AC source voltage fluctuations. The consequence is that the RMS value of the capacitor current will increase where the magnitude of this increase is related to the modulation frequency and magnitude of the fluctuating voltage. Therefore, an AC supply with a voltage fluctuation component will cause a full-bridge rectifier with capacitor filter to sustain increased stress. This stress may accelerate the capacitor ageing process, eventually resulting in premature equipment failure. The research indicates that there is a need for indices other that the short-term and long-term flicker indices required for equipment compatibility levels

Secondary control of voltage & current unbalance in a multi-bus microgrid using cooperative adjustment of Q− droop gains

This paper describes a combined current and voltage unbalance compensation scheme for static power converters on a multi-bus microgrid utilizing cooperative regulation on a sparse ad-hoc communication network. The proposed control scheme is both robust to changing network conditions and corrects for sub-optimal gain settings at each distributed generation unit. The scheme is based on local voltage and current measurements by each distributed generation unit on the network, and utilizes a primary and secondary control hierarchy. The scheme is then simulated using Matlab SimPowerSystem to demonstrate operation of the compensation scheme and evaluate its performance

Deadband control of doubly-fed induction generator around synchronous speed

Semiconductor devices in power electronic converters of the doubly-fed induction generator (DFIG) are susceptible to significant junction temperature variations when operating around synchronous speed, thereby reducing the lifetime of the converters. This is due to the fact that the frequency of the rotor current in a DFIG is determined by the stator flux frequency and rotor speed, and hence will lead to low rotor current frequency when operating closer to the synchronous speed, and ultimately result in significant thermal stress on semiconductor devices. In this paper, a multimode operation control strategy is proposed for the DFIG to prevent operating around the synchronous speed (within a predefined deadband); thus, the proposed control strategy can avoid the thermal stress problem. The proposed strategy engages the existing crowbar scheme for DFIG-based wind energy conversion system to intentionally alter the operating mode of the generator between DFIG and induction generator (IG). Smooth transition between the two operating modes can be achieved with the supplementary control strategies. Unity power factor can also be maintained in both operating modes by using the grid side converter as a static synchronous compensator (STATCOM) to fulfill the reactive power requirement of the DFIG in IG mode

Voltage-based storage control for distributed photovoltaic generation with battery systems

Recent advances and continued research in energy storage systems suggest that storage management in grid-connected applications is an area of increasing importance. Hence, this paper proposes a novel voltage-based storage control scheme which reduces network stress and is capable of increasing customer remuneration where variable energy pricing schedules are implemented. The scheme charges the battery during instances of low load and discharges during peak load using only locally available data. The scheme is also capable of adapting to changes in load behaviour throughout the year and is capable of identifying whether local load is dependent on the working week. The scheme is verified both in the small-signal environment and in the steady-state load flow environment using MATLAB. Two case studies covering a typical residential and commercial load profile are conducted to investigate the performance of the proposed scheme

Analysis of Harmonic Levels from PWM Rectifiers due to Background Voltage Distortion

© 2020 IEEE. PWM rectifiers receive significant attention due to their flexible control and perceived low harmonic currents, and as a consequence are replacing controlled and uncontrolled rectifiers as the preferred technology in industrial applications. However, low harmonic currents from PWM rectifiers are generally limited to applications where supply voltages have very low background distortion. An investigation using derived mathematical equations, simulation and laboratory measurement is presented to assess the influence of higher levels of background voltage distortion on the harmonic current distortion of PWM rectifiers. The mathematical expression for the harmonic current is derived using the Double Fourier Integral method. A simulation model is developed to quantity the effect of increased supply voltage distortion on harmonic currents from PWM rectifiers. Simulation results and laboratory measurements are presented for the simple case of a PWM rectifier to validate the methodology, which will ultimately be used for future work to quantity the influence of supply voltage distortion. As expected the increase in harmonic current of a PWM rectifier is heavily impacted by the severity of the voltage distortion appearing at the PWM rectifier terminals