Jayashri Ravishankar

Fault ride-through of doubly-fed induction generators

The aim of this paper is to explore the various dynamic controllers to enhance the fault ride-through (FRT) of doubly-fed induction generators (DFIGs). A wind farm of total capacity 9 MW is considered for the study. The flexible AC transmission system (FACTS) controllers like Static Synchronous Compensators (STATCOM) and Unified Power Flow Controllers (UPFC) are modelled and analysed to study their effect on the voltage at the point of common coupling (PCC) and FRT capability. This is then compared with the FRT capability of existing crow bar controller added to the converters of DFIG. The simulation is carried out using MATLAB/Simulink. A new Simulink model is developed for DFIG, to make it versatile for any FRT control strategy. The results presented show the effectiveness of the model.

Using iPads/Tablets as a teaching tool: Strategies for an electrical engineering classroom

This paper explores the potential impact of the iPad/Tablet and its applications on teaching and learning, especially in the area of electrical engineering. The authors discuss the effective and innovative strategies introduced by the School of Electrical Engineering and Telecommunications, the University of New South Wales (UNSW). The unique apps developed for Electrical Engineering are elaborated. The on-going survey results that examine the iPad as a pedagogical tool are described along with the implications for further implementation. The results suggest that these devices may offer an exciting platform for creating content in a collaborative, interactive way.

A decentralized coordinated controller for load sharing in a microgrid with renewable generation

The aim of this paper is to introduce a control algorithm for load sharing in a microgrid with renewable generation mix. A decentralized coordinated power sharing control scheme is proposed considering both resistive and inductive line parameters, dynamics of the sources, weather condition, and multiple distributed energy resources (DERs). In this paper, a central power management unit is developed that specifies the reference real and reactive power generation for each distributed generator (DG) by considering the load demand and the generation availability. Local controllers are responsible for controlling the voltage and angle to inject the required amount of power into the grid. Simulation results show the viability of the proposed control scheme.

Modelling and control of modular multi-level converter based HVDC systems using symmetrical components

This paper studies the use of modular multi-level converter (MMC) in a HVDC transmission system. MMC, thanks to its robustness and high current quality and flexibility, has been widely used in HVDC transmission applications. However not many work is devoted to the area of MMC based HVDC system under unbalanced grid condition. This paper investigates a point to point MMC-HVDC system characteristics under unbalanced AC conditions. A model of a MMC converter is built under unbalanced conditions. Based on this model a control method, which controls positive- negative- and zero-sequence current components independently is proposed. A simulation case study is conducted to test the performance of the proposed controller.

Detection of partial discharge signals in high voltage XLPE cables using time domain features

Almost all cases of insulation degradation in high voltage cables are due to partial discharge (PD) activity. To date, wavelet based analysis has been widely used to extract PD pulses from noisy environments. This paper explores the use of time domain features, namely short-time energy and short-time zero-crossing counts, to detect the presence of partial discharge signals prior to de-noising the signal for further investigation. In order to demonstrate the effectiveness of short-time energy and zero-crossing counts to identify PD signals embedded in noise, these features are tested with laboratory data. To further verify these results, real data was collected from a substation and the overall results demonstrate that these two time domain features are very effective in identifying PD pulses and are computationally efficient such that they can be considered for use in online PD monitoring.

A review of demand response techniques in smart grids

The worldwide installation of renewable energy generators has rendered the conventional frequency regulation techniques insufficient. However, smart grid in the recent years has shown great potential in regulating frequency by changing end-user demand so as to match supply. A large and growing body of literature in the past has investigated load scheduling and frequency deviation as two separate problems and proposed centralized or decentralized control techniques for eliminating power mismatch, that result in complex computational tasks and huge economic burden. Much of the research thus far fails to account for factors such as random customer demand, storage devices and various load groups in a single control model. The paper reviews previously presented demand scheduling and frequency regulation techniques as well as gives future directions for introducing a new, improved demand control system.

The modeling of partial discharge waveforms in power systems equipment

This paper looks at the modeling of partial discharge (PD) waveforms to gain an understanding of the characteristics of PD signals. To accurately model the PD waveforms, a high sampling rate of 500 MHz was used in collecting the PD data with the use of a high-frequency current transformer. While characteristics such as rise time, fall time and pulse width have been used in the past to analyze PD waveforms, this paper uses Pronys method to fit a digital transfer function to the PD waveform, such that the impulse response of the digital filter approximately matches the waveform. Results show that this technique can be applied to internal, corona and surface partial discharge signals, and a model like this can be used for simulating and interpreting PD waveforms.

Taste of Electrical Engineering workshops for high school students

The School of Electrical Engineering and Telecommunications (EET) at The University of New South Wales (UNSW) initiated two workshops for Year 10 and Year 11 high school students, with a view to giving secondary school students a feel for electrical engineering, thereby encouraging them to consider tertiary study in this discipline. The workshops were run for three days each. Activities included introduction to EET laboratories, a design challenge, soldering, a competition and a field trip. This paper details the activities of these two workshops, the involvement of electrical engineering students and the impact of these workshops on the participating high school students. The results of the study indicate that the taste of electrical engineering workshops made the attitudes of high school students more favourable towards electrical engineering.

A flipped mode teaching approach for large and advanced electrical engineering courses

ABSTRACT A fully flipped mode teaching approach is challenging for students in advanced engineering courses, because of demanding pre-class preparation load, due to the complex and analytical nature of the topics. When this is applied to large classes, it brings an additional complexity in terms of promoting the intended active learning. This paper presents a novel selective flipped mode teaching approach designed for large and advanced courses that has two aspects: (i) it provides selective flipping of a few topics, while delivering others in traditional face-to-face teaching, to provide an effective trade-off between the two approaches according to the demands of individual topics and (ii) it introduces technology-enabled live in-class quizzes to obtain instant feedback and facilitate collaborative problem-solving exercises. The proposed approach was implemented for a large fourth year course in electrical power engineering over three successive years and the criteria for selecting between the flipped mode teaching and traditional teaching modes are outlined. Results confirmed that the proposed approach improved both students’ academic achievements and their engagement in the course, without overloading them during the teaching period.

Three-Stage Robust Inverter-Based Voltage/Var Control for Distribution Networks with High-Level PV

This paper proposes a novel three-stage robust inverter-based voltage/var control (TRI-VVC) approach for high photovoltaic (PV)-penetrated distribution networks. The approach aims at coordinating three different control stages from centralized to local VVC to reduce energy loss and mitigate voltage deviation. In the first stage, capacitor banks and an on-load tap changer are scheduled hourly in a rolling horizon. In the second stage, PV inverters are dispatched in a short time-window. In the third stage, the inverters respond to real-time voltage violation through local droop controllers. A new PV inverter model for voltage control is developed to support both the centralized var dispatch and the local var droop control. To address uncertain PV output and load demand, a robust optimization (RO) model is proposed to optimize the first two stages while taking into account the droop voltage control support from the third stage. A linearized distribution power flow model with power loss is developed and applied in the RO. The simulation results show high efficiency and robustness of the proposed TRI-VVC strategy.