Tareq Aziz

VAR Planning With Tuning of STATCOM in a DG Integrated Industrial System

Wide-scale penetration of distributed-generation (DG) units into a weakly meshed distribution system is one of the major concerns for power system engineers in recent years. As grid standards limit voltage control operation of small DG units, a lack of sufficient reactive power support brings the problem of slow voltage recovery and this leads to the usage of expensive flexible ac transmission system (FACTS) devices, such as a static synchronous compensator (STATCOM). In this paper, a systematic methodology has been developed for fast voltage recovery at the DG bus. This methodology reduces the number as well as the rating of STATCOMs through the tuning of control parameters. The STATCOM rating at selected locations has been tested and verified to be adequate at various dispatch levels of DG units. Additional benefits of STATCOM tuning on the damping of weak modes have also been studied. An IEEE industrial test system has been used for validating the methodology, providing grid compatible voltage recovery and satisfactory damping performance.

A grid compatible methodology for reactive power compensation in renewable based distribution system

The penetration level of renewable based distributed generation (DG) has increased rapidly in recent years. Grid standards demand small DG units to operate with constant power factor control mode and large DG units with voltage control mode. As a result, small DG units are exposed to the problem of slow voltage recovery due to contingencies like fault. This paper proposes a new sensitivity index based methodology for placement of shunt reactive power compensators to support voltage at load bus and generator bus under steady state and transient conditions. Two different test systems with diverse network and load configurations have been used to test and verify the proposed methodology.

Analysis and mitigation of transient overvoltage with integration of small scale power-electronic interfaced DG

As the amount of non-scheduled small scale distributed generation (DG) units are increasing, lack of fault ride through (FRT) capability of these generators may have an adverse affect on the overall power system. This study focuses on the basics of transient overvoltage issue arising under faulty condition with integration of power-electronic (PE) interface based DG units in a system. Reasons behind this overvoltage issue and its impact on DG integration with present grid standard have been investigated. A methodology has been utilized to overcome this overvoltage issue in a system, which has conventional generator as well as wide penetration of full-converter based solar and wind generation. An IEEE industrial test system with varieties of motor loads has been used to carry out the analysis and to verify the methodology.

An Index for STATCOM Placement to Facilitate Grid Integration of DER

In recent years, the penetration level of renewable-based distributed energy resource (DER) units has increased significantly. Consequently, standards have been developed and deployed demanding small DER units to operate in constant power factor mode and large DER units in voltage control mode. This results in exposing small DER units to the problem of slow voltage recovery for contingencies like faults. Hence, this paper proposes a methodology of static and dynamic reactive power compensation to avoid tripping of small DER units due to slow voltage recovery. A new sensitivity index has been developed for the placement of STATic synchronous COMpensator (STATCOM) to ensure fast voltage recovery at all the buses of interest. The case studies involving two IEEE test systems with varying size and load compositions validate the proposed methodology and index.

Distributed generators placement for loadability enhancement based on reactive power margin

This paper proposes a simple methodology for placing two principal types of DG units - synchronous machine and induction machine with an objective of enhancing loadability of distribution system. The proposed methodology is based on the concept of reactive power margin. Buses have been ranked based on the reactive power margin and grouped as “strong” and “weak” buses for finding suitable location of DG units. The effect of size of DG unit on loadability is also examined along with grid loss measure which leads to suitable size selection. The proposed methodology is successfully applied to a modified 16 bus primary distribution system using a commercially available analytical tool and the results are verified using a research analytical software tool.

Integration of wind energy system in microgrid considering static and dynamic issues

Microgrid is an integrated structure of distributed energy resources (DERs) which are connected together to deliver electrical power to a group of consumers under standalone mode and can also exchange power with the existing utility grid under grid connected mode. Integrated DERs in microgrid is getting importance over the last few years. As the integration of renewable based generation specially wind energy system has significant influence on various static and dynamic features of power system, wide scale penetration of wind turbines in microgrid system deserves a detailed investigation. This paper has investigated one of the major static issues - grid loss for the placement of wind turbine in a microgrid system. The level of penetration has finally been determined by examining the grid rule compatibility of post-fault voltage recovery feature of wind integrated system. Results show that maximum 30% wind energy penetration in test microgrid can ensure satisfactory static and dynamic operation.

Study of power quality with changing customer loads in an urban distribution network

Power quality is one of the most significant current discussions in electric energy distribution systems. The issue of harmonics has been a controversial and much disputed subject within the field of power quality. Harmonic current originates from all types of nonlinear loads. This paper attempts to show the impacts of rapidly increasing share of nonlinear loads on harmonic distortion of urban distribution feeders. The recommendations of IEEE Std. 519-1992 and Bangladesh Grid Code are considered carefully. Simulations have been carried out to find out how far the existing distribution system can accommodate non-linear loads. Results show that though the connected load is not hampering power quality of test distribution at present, an increase of nonlinear load share above 30% would cause Total Harmonic Distortion (THD) go beyond tolerable limit and result in poor power quality.

Impact of supercapacitor placement in renewable integrated microgrid to minimize post-fault frequency fluctuation

Microgrid structure provides economically attractive electricity supply to customers with less impact on the environment. Microgrid losses frequency support when its operation switches from grid connected mode to islanded mode. Hence, controlling of frequency is of utmost importance in islanded mode. During post-fault condition, frequency gets deviated and hence, lack of necessary steps to minimize frequency deviation results in tripping of generators. This ultimately leads to disconnection of utility power at consumer ends. By using energy storage devices efficiently, frequency deviation can be minimized during post fault condition. Storage device can provide energy when grid connection is not available. Because of high power density and high charging/discharging rate, supercapacitor is used as a storage device for providing post fault condition power in microgrid. In this paper, impact of supercapacitor in microgrid to minimize the frequency deviation has been investigated through a number of case studies. Results show that placement or location of supercapacitor has significant impact on stabilizing frequency fluctuation under post-fault scenarios in microgrid.

A review of interconnection rules for large-scale renewable power generation

Around the world penetration levels of renewable-based power into power systems have been increasing rapidly over the last few years. In the year 2011, almost half of the estimated 208 GW of newly added electric capacity was reported from renewable-based generation. Wind and solar photovoltaic (PV) generators accounted for almost 40 % and 30 % of new renewable capacity, respectively, followed by hydropower. Besides rooftop and small-scale systems, the trend toward very large-scale wind farms and ground-mounted PV systems continued to play an important role. It is evident that renewable-based generation will be comparable to conventional power generation in the coming decades. Therefore, many transmission system operators (TSOs) and regulators around the world have come up with interconnection rules/codes to request these volatile renewable resource-based power plants to have more or less the same operating competence as conventional power plants. Depending on system characteristics and renewable penetration levels, the level of requirements imposed by these grid codes are getting more stringent over time to ensure the common aim of secured and reliable power system operation. This chapter presents a comprehensive study of the grid interconnection rules set by various TSOs and regulators for large renewable-based power plants. A brief discussion explaining the necessity of grid codes has been presented in the beginning, followed by a list of principal static and dynamic operation issues usually addressed in existing grid codes. A comparative study has then been carried out to compare various rules among grid codes around the globe. The study focuses on the primary concerns such as active and reactive power regulations under static operation, active and reactive power response during and after faults, and fault ride-through requirements imposed by the codes. A useful discussion on future trends for synchronizing diverse grid codes has also been presented. The contents of this chapter will be helpful for regulators as well as for renewable-based generator manufacturers to form better frameworks, which will ultimately result in secure system operation with increased penetration of large-scale renewable generation.

A study of fault ride through with widespread grid integration of distributed generation

Along with number of benefits, wide-scale penetration of distributed generation (DG) units in distribution system imposes some critical challenges for power engineers. The major issues with interconnection of small DG units are related to protection, voltage control and power quality. Furthermore, overall system stability can also be affected due to the lack of fault ride through (FRT) capability of these small generators. This paper presents challenges in integration of small DG units and shows how their integration is affected by various transmission and distribution faults. A 43-bus industrial system fed from nine bus transmission system has been utilized as test system to perform the simulations. An analysis of the results identifies local-voltage collapse in distribution feeder as the most critical problem with large integration of DG.