Waqar A. Qureshi

Demand Side Management through innovative load control

Energy conservation is an important element of Demand Side Management (DSM) aimed at reducing energy consumption. Energy can be conserved by controlling consumption of certain discretionary load types such as Air Conditioning Load (ACL). In this paper a potential solution for partially addressing the energy crisis in Pakistan is proposed through efficient management of the ACL if it is implemented widely as a DSM option in distribution utilities. The proposed option is supported through results of experiments carried out on two identical buildings under same climatic conditions. These buildings are subjected to different temperatures settings which does not compromise comfort levels. The effect of temperature on the demand is studied and regression analysis is performed. The analysis are included illustrating the amount of energy conserved. Ripple control technique with modified priority circuit is also proposed which if implemented has the impact of potentially reducing load shedding periods.

Low-power area-efficient wide-range robust CMOS temperature sensors

This paper proposes six different CMOS-based temperature sensor topologies by exploiting temperature dependence of MOSFETs threshold voltage VT, the carriers mobility µ and the resistivity of n-well resistors. The proposed temperature sensors are designed for a wide temperature range of -100?C to +120?C and exhibit resolutions in the range of 0.04-0.448?C along with readout sensitivities in the range of 0.37-1.83mV/?C. For accuracy enhancement, automated single-point calibration is implemented for all topologies in conjunction with an off-chip reference temperature sensor. These calibrated temperature sensors exhibit measured inaccuracies between 0.2?C and 1?C for the proposed temperature range. These temperature sensors are designed in 0.25µm TSMC 1P/5M process and are embedded in a 5mmi?5mm imaging array readout IC to develop the thermal profile of the IC. The presented temperature sensors exhibit comparable performance metrics to state-of-the-art topologies in the literature with added advantage of a buffered output, which could be useful in case of a fast load drive and settling to implement faster control systems.

Systematic development of Low Voltage Ride-Through (LVRT) envelope for grids

Increased penetration of wind generation into high voltage transmission systems necessitates development of grid integration standards. One of them is Fault Ride-Through (FRT) or Low Voltage Ride-Through (LVRT) guidelines. Development of the voltage envelope depends on the transmission network characteristics along with considerations like contingency and protective relay settings. This paper outlines a systematic method for establishing LVRT criteria through a set of analysis involving contingency analysis, static and dynamic scenario based system simulations. Wind turbine technology is also discussed in context of development of LVRT criteria for large wind farms. The development of voltage envelope for LVRT criteria is shown through the case study for New Zealand transmission system.

Influence of DFIG models on fault current calculation and protection coordination

The increasing growth of doubly-fed induction generators (DFIG) in wind farms requires attention to understanding its short-circuit behaviour in order to meet grid code requirements. The DFIG model has been well known for years, but many application uncertainties still persist and their impact on short-circuit calculation has to be fully understood. This paper attempts to clarify the influence of different DFIG models on simulation results obtained from DIgSILENT PowerFactory. It further investigates the short-circuit model of DFIG under various operating conditions and its implication on protection relay settings.

Incorporating economic and demographic variablesfor forecasting electricity consumption in Pakistan

Precise electricity demand forecasting is necessary for power sector planning. Electricity consumption is typically governed by variation in severaleconomic and demographic variables including population, GDP and income per capita. In this study, relationship has been investigated between electrical power demand and the selected independent variables through correlation matrix. Univariate time series and econometric models have been developed to estimate electrical power demand for next fifteen years in Pakistan. Influence of chosen variables on electricity consumption has been employed for demand forecasting through multiple linear regression model. Validity of proposed model has been tested and results from both models are compared. This research would provide a quantitative analysis in order to support strategic planning and policy making for power sector from medium to long time frame.

Long term electricity demand forecasting in residential sector of Pakistan

Pakistan is experiencing electrical power supply and demand challenge. Countrys demand is rising immensely, especially in domestic sector and it is imperative to decide the new power policies in order to control the situation. One of the primary requirements for power policy design is to construct a detailed electricity demand forecasting model. This study predicts electricity consumption for domestic sector by incorporating economic and demographic activity through Longrange Energy Alternative Planning System (LEAP). The forecasting would be performed up to 2030 when 2005 has been selected as the base year. An extensive data has been collected and structured for the essential factors including growth of enduse appliances, domestic consumption trends and the changes in urban rural ratio. Electrical demand has been predicted under the reference scenario of expected economic growth without any implication of new policies and the results have been compared with official government predictions. Moreover, four different scenarios have also been analyzed to investigate economic and technical aspects of complete electrification with high rate of urbanization, penetration of energy efficient devices, population growth control plan and high economic growth. This research would develop awareness in power system planners and policy makers to congregate the expected increment in demand.

Modeling diversified electricity generation scenarios for Pakistan

Long term power system planning is required to meet fast growing electricity demand in Pakistan. Policy makers need to consider both environmental and economic concerns to make timely decisions about electrical power generation mix. In this paper, energy demand is predicted for the country from 2005 to 2030. In order to meet this demand; energy supply modeling is performed through software Long-range Alternative Energy Planning System (LEAP) for the same period. A baseline or Business As Usual (BAU) scenario is developed according to official government policies. However, three scenarios are assumed considering new strategies. This study simulates the electrical power supply model in order to find out economically viable fuel mix with limited impact on environment. In this regard, the policies discussed are chosen with respect to comparative cost benefit analysis and CO2 emissions related to the selected fuel mix.

Fault Ride-Through Criteria Development

Wind energy integration into transmission systems has been accelerated by establishing robust grid codes relevant to the network. Fault Ride-Through (FRT) criteria is one of them, which requires generation to stay connected to transmission system under certain operational voltage envelope. Development of the criterion is a specialized task which will take into account existing grid characteristics, network history and generation response towards voltage and frequency disturbances. This chapter will outline a detailed systematic methodology for achieving FRT criteria through a set of analysis involving contingency analysis, static and dynamic scenario based system assessment. The uniqueness of this chapter is to present a case study for a grid having a high percentage of the generation through renewable energy and has HVDC connected island based transmission grid. Each island sub-system separated by HVDC link is pre-dominant with non-uniform distribution of generation units and load centres. Therefore, two different FRT criteria are found to be effective for this power systems network. None of the reported criteria in prevailing networks have introduced similar approach before. New Zealand power system has similar characteristics and has been utilized for this case study. FRT criteria development has been in practice but the current context has not been published in articles or books and hence the motivation for this book chapter.

Developing transmission fault ride-through criteria for New Zealand wind farms

Wind energy currently constitutes about 8% of the total energy generation in New Zealand. The penetration of wind generation into high voltage transmission systems necessitates development of grid integration standards. One of the requirements is the development of a voltage envelope as part of a generator Fault Ride-Through (FRT) criteria. The specialized development of FRT criteria for a country requires taking into account load and transmission network characteristics, selection of appropriate contingencies, and consideration of protective relay settings. This paper outlines the experience of the New Zealand (NZ) Transmission System Operator (TSO) development of the proposed FRT criteria through dynamic system studies. Wind turbine technology is also reviewed in context of development of FRT criteria for large wind farms connected to the NZ Grid. The final proposed FRT criteria for the New Zealand transmission system is also presented.

Assessment of Low Voltage Ride-Through behaviour of several wind farms with crowbar protection

Recently, as wind farms have increasingly been built on the same wind belt to make good use of wind resources, the interactions between wind farms and the grid have become more complicated. Requirements like Low Voltage Ride-Through (LVRT) capability and its impact on neighboring wind farms, therefore, pose higher challenges, particularly in case of several wind farms on the same wind. This paper focuses on the performance of several wind farms when in severe transmission disturbances. Equations are derived to estimate the stator and rotor peak current of wind generator and the IEEE 39 Bus System is applied to analyze the LVRT capability of several wind farms by using DIgSILENT/PowerFactory. The results indicate that the LVRT capability is affected by increased wind farms in the vicinity and different fault locations. The capability can be improved by applying proper crowbar switching strategies as illustrated through simulations.