N. Mithulananthan

Analytical Expressions for DG Allocation in Primary Distribution Networks

This paper proposes analytical expressions for finding optimal size and power factor of four types of distributed generation (DG) units. DG units are sized to achieve the highest loss reduction in distribution networks. The proposed analytical expressions are based on an improvement to the method that was limited to DG type, which is capable of delivering real power only. Three other types, e.g., DG capable of delivering both real and reactive power, DG capable of delivering real power and absorbing reactive power, and DG capable of delivering reactive power only, can also be identified with their optimal size and location using the proposed method. The method has been tested in three test distribution systems with varying size and complexity and validated using exhaustive method. Results show that the proposed method requires less computation, but can lead optimal solution as verified by the exhaustive load flow method.

Multiple Distributed Generator Placement in Primary Distribution Networks for Loss Reduction

This paper investigates the problem of multiple distributed generator (DG units) placement to achieve a high loss reduction in large-scale primary distribution networks. An improved analytical (IA) method is proposed in this paper. This method is based on IA expressions to calculate the optimal size of four different DG types and a methodology to identify the best location for DG allocation. A technique to get the optimal power factor is presented for DG capable of delivering real and reactive power. Moreover, loss sensitivity factor (LSF) and exhaustive load flow (ELF) methods are also introduced. IA method was tested and validated on three distribution test systems with varying sizes and complexity. Results show that IA method is effective as compared with LSF and ELF solutions. Some interesting results are also discussed in this paper.

Comparison of shunt capacitor, SVC and STATCOM in static voltage stability margin enhancement

This paper compares the shunt capacitor, SVC and STATCOM in static voltage stability improvement. Various performance measures are compared under different operating system conditions for the IEEE 14 bus test system. Important issues related to shunt compensation, namely sizing and installation location, for exclusive load margin improvement are addressed. A methodology is also proposed to alleviate voltage control problems due to shunt capacitor compensation during lightly and heavily loaded conditions.

A maximum loading margin method for static voltage stability in power systems

In this paper, the maximum loading margin (MLM) approach is proposed in finding generation directions to maximize the static voltage stability margin, where the MLM is evaluated at various possible generation directions in the generation direction space. An approximate and simple model representing the relationship between the generation direction and the LM is used to obtain the MLM point. The proposed method is validated in the modified IEEE 14-bus test system and applied to the Thailand power system. LMs of the system with the generation directions are compared for different generator combinations using the proposed technique.

Linear performance indices to predict oscillatory stability problems in power systems

Various indices are proposed and studied to detect and predict oscillatory instabilities associated with Hopf bifurcations (HBs) in power systems. A methodology is also presented to produce a linear profile for these indices. They are based on eigenvalue and singular values of the state and extended system matrices. Their application to several test power systems is presented to demonstrate their usefulness, particularly for online applications.

Static Voltage Stability Margin Enhancement Using STATCOM, TCSC and SSSC

In this paper, voltage stability assessment with appropriate representations of STATCOM, TCSC and SSSC is investigated and compared in the modified IEEE 14-bus test system. AC and DC representations of STATCOM, TCSC and SSSC are used in the continuation power flow process in static voltage stability study. The appropriate representation provides more practical solutions in the DC parts of these devices. Static voltage stability margin enhancement using STATCOM, TCSC and SSSC is compared in the modified IEEE 14-bus test system

Determining PV Penetration for Distribution Systems With Time-Varying Load Models

A constant or voltage-dependent load model is usually assumed in most distributed generation (DG) planning studies. However, this paper proposes several different types of time-varying voltage-dependent load models to determine the penetration level of photovoltaic (PV) units in a distribution network. Here, a new analytical expression is first proposed to size a PV unit, which can supply active and reactive powers. This expression is based on the derivation of a multiobjective index (IMO) that is formulated as a combination of three indices, namely active power loss, reactive power loss and voltage deviation. The expression is then adapted to allocate PV units while considering the time-varying load models and probabilistic PV generation. The effectiveness of the proposed approach was validated on 69- and 33-bus test distribution systems. The results showed that PV allocation with different types of time-varying load models can produce dissimilar penetration levels.

Location and Sizing of Distributed Generation Units for Loadabilty Enhancement in Primary Feeder

Limitations of generation, transmission, and distribution of reactive power have significant impact on voltage stability of electric power systems. Moreover, the location and size of a distributed generation (DG) unit that alters reactive power flow and its path in a radial distribution network can also have a substantial influence on voltage stability. Therefore, this paper proposes an optimization methodology for identifying proper location and size of DG units in a primary distribution system to enhance the loadability of distribution system by improving static voltage stability. The optimization is implemented with the help of a particle swam optimization technique for four types of DG units. The proposed methodology is tested in two standard radial distribution test systems and one practical radial distribution of Lào Cai province, Vietnam. Results show the importance of selecting the location and sizes of DG units for enhancing the loadability of the primary distribution feeder.

Control Strategies for Augmenting LVRT Capability of DFIGs in Interconnected Power Systems

This paper presents a new control scheme for the enhancement of the low-voltage ride-through (LVRT) capability of doubly fed induction generators. The LVRT capability is provided by extending the range of operation of the controlled system to include typical postfault conditions. Controllers are designed simultaneously for both the rotor- and grid-side converters using a linear quadratic output-feedback decentralized control strategy. The nonlinear terms in the power system model are represented in this paper by an uncertain term derived from the Cauchy remainder of the Taylor series expansion. A genetic algorithm is used to calculate the bound on the uncertainty. The robust controller resulting from this design provides acceptable performances to enhance voltage and transient stability margins and thereby to limit the oscillations, the peak value of the rotor current, and the dc-link voltage fluctuations. The performance of the designed controller is demonstrated under different operating conditions by large-disturbance simulations on a test system.

A Comprehensive Comparison of FACTS Devices for Enhancing Static Voltage Stability

This paper presents a comparison of FACTS devices for static voltage stability study. Various performance measures including PV curves, voltage profiles, and power losses are compared under normal and contingency conditions. Placement and sizing techniques of series FACTS devices and UPFC are proposed for loading margin enhancement. The paper provides a guide for utilities to have an appropriate choice of FACTS device for enhancing loading margin and static voltage stability.