J. A. Laghari

A New Under-Frequency Load Shedding Technique Based on Combination of Fixed and Random Priority of Loads for Smart Grid Applications

This paper presents a new under-frequency load shedding technique based on the combination of random and fixed priority of loads. It has been observed that placing all of the loads in the distribution system with fixed priority results in un-optimum load shedding. On the other hand, designing the load priority with a combination of random and fixed priority provides the technique with some sort of flexibility in achieving the optimal load shedding. The validation of the proposed scheme on different scenarios proves that the proposed technique is capable of achieving the optimal load shedding and recovering frequency to nominal value without any overshoot.

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.

A fuzzy based load frequency control for distribution network connected with mini hydro power plant

Mini hydro power plants MHPP are gaining attraction as a cost effective source for rural electrification in developing countries due to its environmental friendly operation. These MHPP plants suffer from the speed control problem due to continuous load variation. PID controllers fail to provide optimum speed control due to its limitation of parameter tuning. Alternatively, Fuzzy logic control is commonly used for implementing intelligent control for the nonlinear system. This paper presents a new fuzzy logic based governor for frequency/speed regulation of MHPP for implementation in distribution network. For verification, the response of load frequency control using fuzzy based governor and PID based governor is compared. The simulation results show that fuzzy based governor ensures robust control by improving the frequency response as well as dynamic response in comparison to PID based governor. Furthermore, fuzzy based governor enables the generator to continuously supply power even at 25% load variation whereas generator with PID based governor fails to supply power even at 20% load variation.

A Sensitivity Analysis of Different Power System Parameters on Islanding Detection

This work analyzes the sensitivity of 16 power system parameters that can be used in passive techniques to detect islanding and nonislanding events. It is observed that the rate of change of frequency over reactive power (df/dq) can effectively detect minute disturbances in power supply. It is also shown that active and reactive power mismatch has an opposing effect on the variation of frequency (df) in real time environment. As a result of this, a new passive technique based on df/dq is proposed. The simulation results indicate that the proposed technique is able to distinguish islanding from other events of similar signatures, such as load variation, capacitor switching, faults, and induction motor starting.

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.

A new technique for islanding operation of distribution network connected with mini hydro

An islanding operation of a distribution network is a topic of interest due to the significant penetration of distributed generation (DG) in a power system network. However, controlling the frequency of an islanded distribution system remains an unresolved issue, especially when the load exceeds the generation. This paper presents a new technique for a successful islanding operation of a distribution network connected with multiple mini hydro based DGs. The proposed technique is based on three main parts. The first part uses an islanding detection technique to detect the islanding event correctly. The second part consists of a power imbalance estimation module (PIEM), which determines the power imbalance between the generation and load demand. The third part consists of a load shedding controller, which receives the power imbalance value and performs load shedding according to load priority. The proposed technique is validated on an 11 kV existing Malaysia distribution network. The simulation results show that the proposed technique is effective in performing a successful islanding operation by shedding a significant number of loads.

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.

Comparative studies on load frequency control for islanded distribution network connected with mini hydro

IEEE working group on prime movers recommended different governors for hydro power plants. This paper presents the comparative studies on all of these governors for mini hydro power plants (MHPP) operating in parallel and supplying power to distribution network. The purpose of this study is to find their suitability in controlling the frequency of the system for large load variations in an islanded distribution network. The mini hydro power plant with its distribution network is modeled in PSCAD software. The mechanical hydraulic governor, electro hydraulic PID governor, electro-hydraulic PI governor and Enhanced governor are evaluated one by one to find the best response in controlling frequency when disturbance occurs. The load variations from 10% to 50% both addition and reduction are tested for every governor. This study will assists in selecting a particular governor for isolated mode, interconnected mode as well as for islanding mode of operation in distributed generation.

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.