Steady-state Voltage Stability Analysis Research Articles

Voltage Stability Analysis of IEEE118 Bus System with Wind Penetration

The increased penetration of renewable energy sources affects the voltage stability of the system. This article provides steady state voltage stability analysis with wind penetration. The standard IEEE 118 bus system is used for the analysis. The system is modelled in PSSE software and NR-Power flow method is used to perform the power flow studies with various levels of wind penetration. From the load flow studies voltage profile at load buses is analysed through PV curves. System is further studied with reactive power compensation provided at wind generator terminals. All cases are analysed for voltage stability with respect to increase in loading of the system.

On Steady-State Voltage Stability Analysis Performance in MATLAB Environment

Nowadays, electric power systems have been often operated close to their limits due to increased electric power consumptions, vast installments of renewable power sources and deliberated power market policies. This poses a serious threat to stable network operation and control. Therefore, voltage stability is currently one of key topics worldwide for preventing related black-out and islanding scenarios. In this paper, modelling and simulations of steady-state voltage stability problems in MATLAB environment are performed using author-developed computational tool implementing both conventional and more advanced numerical approaches. Their performance is compared with Simulink-based library Power System Analysis Toolbox (PSAT) in terms of solution accuracy, CPU time, and possible limitations. Their use for both real-time and off-line monitoring and assessment of system's voltage stability are also discussed.

A General Steady-State Voltage Stability Analysis for Hybrid Multi-Infeed HVDC Systems

As large-scale offshore wind farms are integrated into the power grid, a hybrid multi-infeed HVDC (HMIDC) system including both LCC-HVDC and VSC-HVDC links is facing a critical steady-state voltage stability problem which mainly stems from a weak AC system under high-level DC power injections. To overcome this challenge, this paper proposes a general steady-state voltage stability analysis to accurately measure the critical voltage stability point of HMIDC systems. In this paper, a typical HMIDC system is firstly modeled as a general dual-infeed system composed of an LCC-HVDC, a VSC-HVDC, and a virtual equivalent voltage source behind a virtual equivalent impedance at the AC side. Then a hybrid power sensitive factor (HPSF) is established to indicate the critical voltage stability point with the consideration of dynamic power-voltage characteristics of HVDC links, as well as operational changes in AC system (e.g. dynamics of excitation voltage control in generator and network topology change). Finally, a general voltage stability index, called hybrid generalized short circuit ratio (HGSCR), is further derived to effectively explain the critical voltage stability point of HMIDC systems. Moreover, multiple comparative studies with existing voltage stability indices are conducted in this paper to verify the effectiveness of the proposed general steady-state voltage stability analysis by using both PSCAD/EMTDC™ power flow and time-domain simulations.

The new steady state voltage stability analysis methods with computation loads separation technique in DC power systems

The steady state voltage stability analysis is extremely important to the security of power systems. The continuation power flow (CPF) is one of the important tools for the steady state voltage stability analysis. However, its computation load is very large. To improve the analysis performance in DC power systems, a basic technique is used to explore the exact relationships between injected currents, buses voltages, lines currents and lines voltages. Based on the basic technique, the computation loads can be separated and some repeated computation can be avoided. In this paper, two new methods to calculate critical point are proposed. One is by combining the basic technique and a correctness method for CPF. The method improves the calculation speed by avoiding the repeated computation of same topology and buses types analysis. Another method is a direct method. The direct method is based on the novel view to understand power systems and the physical (and mathematical) essence of critical point and voltage collapse. Most CPF is discussed in AC system. The corresponding CPF in DC system will be studied to get standard results for comparison. Compared with CPF in DC systems, the numerical verification shows that the proposed methods can reduce most computation loads of CPF method in DC systems.

Generic Demand Model Considering the Impact of Prosumers for Future Grid Scenario Analysis

The increasing uptake of residential PV-battery systems is bound to significantly change demand patterns of future power systems and, consequently, their dynamic performance. In this paper, we propose a generic demand model that captures the aggregated effect of a large population of price-responsive users equipped with small-scale PV-battery systems, called prosumers , for market simulation in future grid scenario analysis. The model is formulated as a bi-level program in which the upper-level unit commitment problem minimizes the total generation cost, and the lower-level problem maximizes prosumers’ aggregate self-consumption. Unlike in the existing bi-level optimization frameworks that focus on the interaction between the wholesale market and an aggregator, the coupling is through the prosumers’ demand, not through the electricity price. That renders the proposed model market structure agnostic, making it suitable for future grid studies where the market structure is potentially unknown. As a case study, we perform steady-state voltage stability analysis of a simplified model of the Australian National Electricity Market with a significant penetration of renewable generation. The simulation results show that a high prosumer penetration changes the demand profile in ways that significantly improve the system loadability, which confirms the suitability of the proposed model for future grid studies.

A Steady State Voltage Stability Analysis of Wind Power Centralized System

It is significant to research the voltage stability of the wind power centralized system (WPCS) for the effective development of the large scale clustering wind energy resources. A steady state voltage stability analysis of the WPCS by employing the PV curve and model analysis is proposed to reveal the voltage stability influence from different aspects. The PV curve is utilized to trace and indicate the voltage collapse point of the WPCS when the small disturbance of wind power is increased gradually. Then the steady state voltage instability modes of the WPCS are analyzed by calculating the bus participation factors of the minimum eigenvalue model at the collapse point. The simulation results of an actual WPCS in North China show that the static state voltage instability mode of the WPCS is closely related to the operating features and control strategies of different reactive power sources. In addition, the implementation of the doubly-fed induction generator wind turbine generator voltage control is beneficial to improve the WPCS voltage stability.

Matpower CPF Program Improvement and Steady-State Voltage Stability Analysis

In steady-state voltage stability analysis, Continuation power flow (CPF) method is widely used for it can track power flow solution at the critical voltage point. The existing matpower CPF program can only simulate PV curve of a single bus when load increases at one certain bus. In this paper, original CPF program will be modified to be more flexible and in line with the actual situation. Several indices will be proposed to discuss how to determine the first crash bus (namely the system vulnerabilities) when load increases at multiple buses. Simulation results of a regional power grid in northern China verify the validity and practicability of the proposed method.

A Power Flow Method Using a New Bus Type for Computing Steady-State Voltage Stability Margins

In steady-state voltage stability analysis, it is well-known that as the load is increased toward the maximum loading condition, the conventional Newton-Raphson power flow Jacobian matrix becomes increasingly ill-conditioned. As a result, the power flow fails to converge before reaching the maximum loading condition. To circumvent this singularity problem, continuation power flow methods have been developed. In these methods, the size of the Jacobian matrix is increased by one, and the Jacobian matrix becomes non-singular with a suitable choice of the continuation parameter. In this paper, we propose a new method to directly eliminate the singularity by reformulating the power flow problem. The central idea is to introduce an AQ bus in which the bus angle and the reactive power consumption of a load bus are specified. For steady-state voltage stability analysis, the voltage angle at the load bus can be varied to control power transfer to the load, rather than specifying the load power itself. For an AQ bus, the power flow formulation consists of only the reactive power equation, thus reducing the size of the Jacobian matrix by one. This reduced Jacobian matrix is nonsingular at the critical voltage point. We illustrate the method and its application to steady-state voltage stability using two example systems.

Configuration of Jacobian Matrix in Steady-State Voltage Stability Analysis Based on Rotor Flux Dynamics of Rotating Machines

Abstract In the existing literatures, modal analysis for steady-state voltage stability is based on the reduced Jacobian matrix, i.e. active power equations are eliminated, and reactive power equations of the constant power/voltage buses (PV buses) are ignored in the polar coordinate expression, which is actually designed for voltage controllability, but questionable for voltage stability.In this article, power outputs of the rotating machines are newly decomposed to the steady-state and dynamic components, with the latter proportional to derivative of the rotor flux. Therefore, neither the active nor the reactive power equations of the rotating machines may be eliminated or ignored in the Jacobian matrix. Only the static buses with constant load impedance should be eliminated. Numerical results show that elimination of active power equations or ignorance of reactive power equations of the rotating machines will yield optimistic stability margins, while including power equations of static load buses yields pessimistic stability margin. It is also find that more static load component yields larger stability margin.

An investigation about the impact of the optimal reactive power dispatch solved by DE

With the advent of new technology based on power electronics, power systems may attain better voltage profile. This implies the proposition of careful strategies to dispatch reactive power in order to take advantage of all reactive sources, depending on size, location, and availability. This paper proposes an optimal reactive power dispatch strategy taking care of the steady state voltage stability implications. Two power systems of the open publications are studied. Power flow analysis has been carried out, which are the initial conditions for Transient Stability (TS), Small Disturbance (SD), and Continuation Power Flow (CPF) studies. Steady state voltage stability analysis is used to verify the impact of the optimization strategy. To demonstrate the proposal, PV curves, eigenvalue analyses, and time domain simulations, are utilized.

A Steady-State Voltage Stability Analysis of Power Systems With High Penetrations of Wind

As wind generation begins to contribute significantly to power systems, the need arises to assess the impact of this new source of variable generation on the stability of the system. This work provides a detailed methodology to assess the impact of wind generation on the voltage stability of a power system. It will also demonstrate the value of using time-series ac power flow analysis techniques in assessing the behavior of a power system. Traditional methods are insufficient in describing the nature of wind for steady-state analyses, and as such, a new methodology is presented to address this issue. Using this methodology, this paper will show how the voltage stability margin of the power system can be increased through the proper implementation of voltage control strategies in wind turbines.

Voltage Stability Assessment of Multi-Machine Power Systems Using Energy Function and Neural Networks Techniques

Voltage stability problems have been one of the major concerns for electric utilities as a result of heavy loading of power system. Steady state voltage stability analysis is effectively used to determine a stability margin that shows how close the current operating point of a power system to the voltage collapse point. This article presents a generalized energy function for voltage stability assessment of multi-machine power systems. The formulated energy function provides an excellent indicator of the system vulnerability to voltage collapse. It is, also, used to rank the system buses according to their contributions to voltage collapse. The proposed technique is applied to a test system and Ontario-Hydro real power system. Also, an investigation on the application of artificial neural networks (ANN) in voltage stability assessment has been developed. A multi-layer feed-forward ANN with error back-propagation learning algorithm is proposed for calculation of voltage stability margins (VSM). Extensive testing of the proposed ANN-based approach indicates its validity for determination of power system voltage collapse.

A novel fuzzy index for steady state voltage stability analysis and identification of critical busbars

Abstract In this paper, a novel fuzzy index is proposed for the prediction of steady state voltage stability conditions in transmission networks. The uncertainties in the input parameters are efficiently modeled in terms of fuzzy sets by assigning trapezoidal and triangular membership functions. The results include fuzzy load flow solutions for the base case and critical conditions with and without contingencies. The proposed fuzzy voltage stability index clearly indicates the location and status of critical busbars. Case studies have been conducted on standard test systems (IEEE 14-bus, 30-bus, and 57-bus) with proper validation of the results.

Reactive Security Study of a Large Power System

This paper presents results of a reactive security study of the New South Wales main grid. System modeling is focused on the effect of load dynamics. A composite dynamic load model is used. The reactive security study reported here is based on a steady-state approach. A general method for steady-state voltage stability analysis is used to compute the saddle-node bifurcation point and the relevant security margin. The reactive security in the studied area is evaluated for the system under various scenarios. The impact of load models on the security margin is studied in detail.

Corrective Schemes for Voltage Stability Using Two Different Indicators

This paper discusses the steady state voltage stability analysis of two power systems: Wale and Hale 6-bus system and the IEEE 30-bus system by using four different correction schemes: transmission path, reactive compensation, generation voltage and reactive path, and load shedding. These correction schemes can improve voltage stability with the help of two indicator techniques: L-index value and V-Q sensitivity value. Results of tests carried on the above-mentioned systems are provided and discussed.

EFFECT OF LOAD MODELING ON STEADY STATE VOLTAGE STABILITY

ABSTRACT This paper discusses the importance of load modeling in power systems for voltage stability studies. The steady-state voltage stability analysis is carried out using the available continuation power flow. Different types of load models - constant power; constant current; constant impedance; and composite load, which is a combination of the first three models, are considered. The composite load model is obtained using the LOADSYN software, where the load dependency on voltage is considered. The concept of load connectivity is defined and the confusion about the critical point with respect to PV curves is clarified. It is shown that for nonlinear loads, the critical point is not at the tip of the PV curve.

The continuation power flow: a tool for steady state voltage stability analysis

The authors present a method of finding a continuum of power flow solutions starting at some base load and leading to the steady-state voltage stability limit (critical point) of the system. A salient feature of the so-called continuation power flow is that it remains well-conditioned at and around the critical point. As a consequence, divergence due to ill-conditioning is not encountered at the critical point, even when single-precision computation is used. Intermediate results of the process are used to develop a voltage stability index and identify areas of the system most prone to voltage collapse. Examples are given where the voltage stability of a system is analyzed using several different scenarios of load increase.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>