Amidaddin Shahriari

Impact of load modeling in distribution state estimation

System state monitoring is crucial in order to maintain the system security, reliability and quality of a power system. Considering the limitation of monitoring devices in distribution network, state estimation technique could be employed. State estimation is an action of appraising an unknown system variables based on limited number of real-time measurements. The main objective of this paper is to find the suitable state estimation that able to estimate the state of the islanded distribution network. In this paper, state estimation for a distribution network is developed and enhanced by incorporating composite load model. By incorporating this model, the calculated state variables of the network will be more accurate (to obtain the most practical value of the system state variables). Moreover, the proposed state estimation results are compared with backward-forward sweep load flow technique to justify the system state variables.

An intelligent under frequency load shedding scheme for islanded distribution network

In islanding mode, system frequency is severely disturbed due to imbalance between generation and load demand resulting in overloading or loss of generation cases. In order to cope with these events, under-frequency load shedding scheme (UFLS) is applied to stabilize the frequency. This paper presents an intelligent under frequency load shedding scheme implemented on mini-hydro operating in islanded mode. The proposed UFLS scheme consists of a fuzzy logic load shedding controller (FLLSC) with load shedding controller module (LSCM). The FLLSC by measuring frequency and rate of change of frequency estimates the amount of load to be shed. The LSCM sheds the load estimated by FLLSC. This scheme is tested for event based and response based cases. The results have shown that proposed load shedding scheme successfully estimates the amount of load to be shed and stabilizes the frequency for these cases.

Comparative studies on Non-Divergent Load flow methods in well, ill and unsolvable condition

This paper describes a critical evaluation of Non-Divergent Load flow methods in well, ill and unsolvable conditioned systems. The comparison studies deals Multiple Load Flow Solution (MLFS) based Second-Order Load-Flow (SOLF) in polar coordinate and Continuation Load Flow (CLF). The analytical bases, ability consideration of theses methods to return operation of power system from unsolvable to solvable region solution. Attention is given to the problems and techniques of to provide optimal recommendations of the parameters, that using in these Non-Divergent Load flow methods to lead to solvable region, based on inequality constraints of power system. A part of the survey, this paper also presents the comparison of numerical result using different type of aforesaid load flow methods for well and ill- conditioned systems. Accordingly, load flow simulation has been solved using the C++ programming.

A new under-frequency load shedding scheme for islanded distribution network

High penetration of distributed generation (DG) in distribution level has open an opportunity for islanding operation of distribution networks. Through proper islanding operation, the reliability of the system can be improved by continuously supplying power from DG. However, an effective protection schemes for an islanded network are still an issue to be solved. Specifically to balance DG generation and load demand in order to maintain system frequency. Hence, an effective underfrequency load shedding scheme is required for an islanded distribution network which is not as strong as the grid. This paper presents a new under-frequency load shedding scheme for an islanded distribution network. A combination of adaptive under-frequency load shedding and state estimation is proposed for efficient and precise load shedding scheme. In this proposed method, overload is anticipated by utilizing an adaptive underfrequency load shedding scheme. Meanwhile, State estimation is used to estimate the load value. Finally, the estimated value of overload will be shed according to the estimated value of each bus demand.

Critical Reviews of Load Flow Methods for Well, Ill and Unsolvable Condition

Critical Reviews of Load Flow Methods for Well, Ill and Unsolvable Condition This paper presents a critical review of Load flow methods in well, ill and unsolvable conditioned systems. The comparison studies deals with multiple load flow solution (MLFS), second-order load-flow (SOLF) and continuation load flow (CLF). The ability of theses method to return from unsolvable solution to a solvable solution in load flow analysis is analyzed and discuss thoroughly. Special attention is given to the problems and techniques to provide optimal recommendations of the parameters that are used in these load flow methods. A part of the reviews, this paper also presents the comparison of numerical result using different type of aforesaid load flow methods for well and ill-conditioned systems.

Fast and accurate second order load flow method based on fixed Jacobian matrix

This paper presents the second order load flow method (SOLFM) based on the constant Jacobian matrix, with flat initial guesses (1.0Â?0Â?) in polar coordinates. The proposed SOLFM does not need to calculate the Jacobian and Hessian matrix separately; keeping the PV type buses. Accordingly, the solution sped up the proposed SOLFM to a level that is much faster than the classical Newton Raphson Load Flow Method (NRLFM). Moreover, the polar coordinate system can simplify the proposed methods load flow equation. The convergence characteristic of the proposed SOLFM is superior to the NRLFM due to the usage of the Hessian matrix. The validation of proposed SOLFM is proven by testing the Malaysian 664 bus system with respect to NRLFM and the Fast Decoupled Load Flow Method (FDLFM) in the context of computation time and convergence characteristic.

Distribution state estimation for smart distribution system

With the penetration of distributed generations into distribution network, more distribution automation will be required. Therefore, smart grid technologies become more important aspect in electric power system. Real-time monitoring of the network is a main step to achieve smart grid technologies. Hence, distribution state estimation becomes more essential for real-time monitoring of traditional distribution network. This paper addresses a distribution state estimation method to achieve smart grid technologies in a traditional distribution network. It will involve exploring distribution state estimation method with minimum number of real-time measurement devices. Therefore, pseudo measurements are applied to address the limitation of the number of real-time measurements. In addition, by incorporating load model, state estimation results are improved and enhanced. In this paper, dynamic aspect of distribution state estimation has been developed for smart grid purposes. The proposed distribution state estimation results are justified with PSCAD/EMTDC software to verify and validate the system state variables.

Optimal multiplier load flow method using concavity theory

Determine desirable low voltage solution for multi-LVS at maximum loading point.Compute the exact optimal multiplier for optimal multiplier load flow method.Calculating the maximum loading point (MLP).Using the polar coordinate system based on the second order load flow method. This paper utilises concavity properties in the optimal multiplier load flow method (OMLFM) to find the most suitable low voltage solution (LVS) for the systems having multiple LVS at the maximum loading point. In the previous method, the calculation of the optimal multiplier is based on only one remaining low voltage solution at the vicinity of voltage collapse point. However, this does not provide the best convergence for multi-low voltage solutions at the maximum loading point. Therefore, in this paper, concavity properties of the cost function in OMLFM are presented as the indicator to find the most suitable optimal multiplier in order to determine the most suitable low voltage solutions at the maximum loading point. The proposed method uses polar coordinate system instead of the rectangular coordinate system, which simplifies the task further and by keeping PV type buses. The polar coordinate in this method is based on the second order load flow equation in order to reduce the calculation time. The proposed method has been validated by the results obtained from the tests on the IEEE 57, 118 and 300-bus systems for well-conditioned systems and at the maximum loading point.

The calculation of low voltage solution based on state space search method in ill-conditioned system

This paper implements the State Space Search Method (SSSM) in polar coordinate form to calculate low voltage solution and Maximum Loading Point of system in ill conditioned system. SSSM modifies the direction of state variable (buses voltage and phase) by using optimal multiplier in order to converge load flow equations in ill conditioned system. The privilege of SSSM emerges in the keeping dimension of load flow jacobian matrix constant. While another method such as continuation and homotopy methods change the framework of jacobian matrix based on predictor and corrector in term of increasing load demand. Indeed, the calculation process of SSSM is based on standard Newton Raphson load flow method. The validation of SSSM is shown by the testing IEEE test systems of 14 and 30 in well and maximum loading point as ill-conditioned systems.

Combination of adaptive and intelligent load shedding techniques for distribution network

One of the challenge in islanding operation is to maintain frequency stability when generation is less than demand. This paper presents a new Under-Frequency Load shedding scheme for an islanded distribution network. The scheme is based on an adaptive and intelligent load shedding techniques. This proposed scheme is able to conserve power system collapse even for large disturbance and events in the system. The proposed scheme is evaluated through simulation in PSCAD/EMTDC software. A distribution network connected with mini-hydro generation in Malaysia is chosen for the test. Various test scenarios show the effectiveness of the proposed load shedding scheme to shed optimum load.