Voltage Reactive Power Research Articles

Voltage Instability Analysis for Electrical Power System Using Voltage Stabilty Margin and Modal Analysis

Voltage instability analysis in electric power system is one of the most important factors in order to maintain the equilibrium of the power system. A power system is said to be unstable if the system is not able to maintain the voltage at all buses in the system remain unchanged after the system is being subjected to a disturbance.The research work presented in this paper is about the analysis of voltage instability of electric power system by using voltage stability margin (VSM), load real power (P) margin, reactive power (Q) margin, reactive power-voltage (QV) and real power-voltage (PV) modal analysis. IEEE 30-bus system has been chosen as the power system. The load flow analysis are simulated by using Power World Simulator software version 16. Both QV and PV modal analysis were done by using MATLAB application software.

The Output Characteristic Analysis for Wind Turbine Based Two Control Strategies

For studied the rule of wind turbine output characteristic in condition of variable wind. The paper set up a wind model for a wind farm and a simulation model of 1.5MW wind turbine. Choose two control tactics which called voltage control and reactive power control to do the simulation and test. The result shows that took reactive power control at normal operation, the turbine get a well performance. If fault happened, choose voltage control was reasonable. So it provide reference for turbine operation.

New Generator and Shunt Reactive Power Control Based Secondary Voltage Control Approach

In Malaysian Transmission System (TNB), most of the voltage control and reactive power resources are manually controlled. For better and optimal voltage control of the TNB power system network, new secondary voltage control (SVC) system that coordinates the voltage and reactive power control of continuous and discrete control devices has been developed. The primary goal of new SVC system based control strategy is to control the bus voltage at the selected pilot buses to follow the optimal reference values as updated by TVC system, and the secondary goal is to provide a high-side voltage set-point for power plant control to equilibrate the reactive power distribution among all control generators in each control zone to enhance the security of the power system. In this approach, the coordinated SVC system is designed to control not only the generating units, but also the reactive power devices including transformer tap-changers as well as switched shunt capacitors and reactors. The selection of reactive power devices for control is implemented through substation voltage control (SSVC) system, which then will be the input to the SVC system. If the target voltage of the pilot buses is followed, the power plant voltage controller (PPVC) will be able to equilibrate VAR among the participating power generations to enhance the power system security by increasing the MVAr reserve for dynamic control. Simulation studies based on PSS/E load flow and closed-loop real-time power system simulator using TNB snapshots shows that the new coordinated SVC system approach is able to provide more consistent voltage control actions and has produced great control actions for flatter voltage profile, reducing transmission system loss and increasing VAr reserve margin as compared to the existing SVC approach that is only focused on generator control as the main source for the voltage control.

Hardware Implementation of Shunt APF Using Modified Fuzzy Control Algorithm with STM32F407VGT Microcontroller

This article presents a modified fuzzy controller (MFC) to generate a reference signal for the control algorithm to drive the shunt active power filter (SAPF) for improving the power quality of a microgrid at the distribution end. The proposed MFC, based on the alive-and-kicking behavior of the system, is used to regulate the DC-link voltage of the SAPF. The MFC is implemented through the general dynamic behavior of a process with introducing the new rules set. It is compared with the PI controller for evaluation of optimal steady-state, dynamic, and transient performance of SAPF, namely the reactive power and DC voltage control. The effectiveness of the proposed controller is tested on non-linear loads using a hardware prototype. The STM32F407VGT (ARM Ltd., San Jose, California, USA) processor is used to interface algorithm with the hardware setup. The results of the proposed controller scheme are promising and are compared with MATLAB (The MathWorks, Natick, Massachusetts, USA) simulation results. The system is capable for minimizing current harmonics, reactive power and improving the power factor. Also, the advantage of the STM32F407VGT over the Digital Signal Processor (Texas Instruments, USA) is introduced. The performance of the proposed controller is better in comparison with conventional controller.

Tip Speed Ratio Based MPPT Algorithm and Improved Field Oriented Control for Extracting Optimal Real power and Independent Reactive Power Control for Grid Connected Doubly Fed Induction Generator

<p>Doubly Fed Induction Generator (DFIG) needs to get adopted to change in wind speeds with sudden change in reactive power or grid terminal voltage as it is required for maintaining synchronism and stability as per modern grid rules. This paper proposes a controller for DFIG converters and optimal tip speed ratio based maximum power point tracking (MPPT) for turbine to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages and also to meet desired reference real power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The performance of DFIG is compared when there is change in wind speed only, changes in reactive power and variation in grid voltage along with variation in wind speed.</p>

Tip Speed Ratio Based MPPT Algorithm and Improved Field Oriented Control for Extracting Optimal Real power and Independent Reactive Power Control for Grid Connected Doubly Fed Induction Generator

<p>Doubly Fed Induction Generator (DFIG) needs to get adopted to change in wind speeds with sudden change in reactive power or grid terminal voltage as it is required for maintaining synchronism and stability as per modern grid rules. This paper proposes a controller for DFIG converters and optimal tip speed ratio based maximum power point tracking (MPPT) for turbine to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages and also to meet desired reference real power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The performance of DFIG is compared when there is change in wind speed only, changes in reactive power and variation in grid voltage along with variation in wind speed.</p>

Fast discrimination of stable power swing with synchronous generator loss of excitation

Fast and accurate discrimination between stable power swing (SPS) and synchronous generator loss of excitation (LOE) has been a great concern for power engineers. Since there is no unbalance during SPS condition, detecting this phenomenon is still a challenge. LOE detection methods are prone to interpret an SPS as a LOE event. Over the last decade, several techniques have been developed for LOE protection that most of them are based on the impedance trajectory as it enters into the protective zone. Such methods may not be able to discriminate between SPS and LOE. Therefore, assigning a time delay is usually utilised to overcome the possible maloperation of the LOE relay. However, merely providing the intentional time delay to avoid maloperation in this condition is not a perfect solution. This study presents a fast detection approach for this condition. The combined proposed method is based on the derivatives of the machine's external variables (i.e. output reactive power and terminal voltage) and the variation of the fast Fourier transform coefficient of the three-phase active power available at the location of the relay. The main advantage of this method is its speed, security and sensitivity to distinguish between SPS and LOE.

Reactive power control in decentralized hybrid power system with STATCOM using GA, ANN and ANFIS methods

In this paper, STATCOM performance for voltage–reactive power control is investigated by comparing different tuning methods, used to evaluate gain parameters of STATCOM controller in presence of high probabilistic uncertainty in input wind power and reactive power load demand. To control voltage transient response in least time, reactive power demand is managed by STATCOM. The conventional methods for tuning gain parameters of STATCOM controller do not satisfactorily operate in case of random disturbances and therefore, advanced controllers such as Genetic Algorithm (GA), Artificial Neural Network (ANN) and Adaptive Neuro Fuzzy Inference System (ANFIS) are required. The main contribution of the paper is: (i) Investigation of STATCOM performance in presence of high probabilistic uncertainty with step changes in input wind power and reactive power load demand, (ii) system studies during dynamic conditions with composite load model in lieu of static load model in the system, (iii) comparison of voltage control and STATCOM reactive power using various tuning methods. Results comparison through all tuning methods show that advanced tuning methods are able to preserve optimal performances over wide range of disturbances using Integral of Square of Errors (ISE) criterion.

An Enhanced Power Sharing Scheme for Voltage Unbalance and Harmonics Compensation in an Islanded AC Microgrid

In this paper, an enhanced hierarchical control structure with multiple current loop damping schemes for voltage unbalance and harmonics compensation (UHC) in ac islanded microgrid is proposed to address unequal power sharing problems. The distributed generation (DG) is properly controlled to autonomously compensate voltage unbalance and harmonics while sharing the compensation effort for the real power, reactive power, and unbalance and harmonic powers. The proposed control system of the microgrid mainly consists of the positive sequence real and reactive power droop controllers, voltage and current controllers, the selective virtual impedance loop, the unbalance and harmonics compensators, the secondary control for voltage amplitude and frequency restoration, and the auxiliary control to achieve a high-voltage quality at the point of common coupling. By using the proposed unbalance and harmonics compensation, the auxiliary control, and the virtual positive/negative-sequence impedance loops at fundamental frequency, and the virtual variable harmonic impedance loop at harmonic frequencies, an accurate power sharing is achieved. Moreover, the low bandwidth communication (LBC) technique is adopted to send the compensation command of the secondary control and auxiliary control from the microgrid control center to the local controllers of DG unit. Finally, the hardware-in-the-loop results using dSPACE 1006 platform are presented to demonstrate the effectiveness of the proposed approach.

Photovoltaic Solar Farms Operating in VAR Mode: A Review

The PV solar inverter plays a vital role in solar farms for electrical power generation at distribution end. By generating active power, such at lower distributed end results like voltage rise issues and voltage fluctuations which affect power quality standards. Increasing penetration level of distributed generation sources connected to the power system cause increasing reverse power flow when demand is not adequate, which raises the voltage level at point of common coupling at grid connection. For regulation of voltage at such PCC, FACTs devices based on power electronic converter are in practice. During night time or some cloudy days, when PV system is unable to generate active power, photovoltaic inverters are utilized for reactive power support to the grid. Here, various control techniques for utilization of PV inverter operating in VAR mode are reviewed. When active power is not available by PV inverter, various methodologies for reactive power control, voltage regulation and control of load reactive power have been mentioned by useful literature survey. The role of inverter as FACTs device for reactive power compensation is elaborated comprehensively. Keywords: PV solar farms, FACTs, PV-STATCOM, PCC voltage regulation, VAR compensation

Integrated volt/Var control in modern distribution power systems based on support vector machines

Summary Integrated volt/Var control (IVVC) is an important tool to optimize voltage and VAR resources and improve energy efficiency and, therefore, plays an important role to support the smart grid vision. This paper investigates the application of support vector machines (SVMs) to control switched capacitor banks and voltage regulators of distribution systems in order to minimize system losses and maintain acceptable voltage profile. The objective is to develop an approach that can use voltage/current measurements provided by active and reactive monitors to IVVC control without the need to perform retraining or repeat optimization simulations. The performance of the SVM scheme for different input selection (i.e., active and reactive power and node voltage) is discussed. Moreover, the generality of the proposed SVM scheme is investigated under noisy environment as well as under network reconfiguration. Studies on a typical distribution system show that the proposed approach has been able to achieve satisfactory results. Copyright © 2016 John Wiley & Sons, Ltd.

The Application and Practice of the Voltage Reactive Power Optimization Automatic Control System (AVC)in the Power Grid of Wuhu Region

In the paper, the influence of harmonic was taken into consideration during the realization of the AVC system in the power grid of Wuhu region, relevant study and development were conducted from the perspective of application and practice, and concrete proposal of practicable reactive voltage power optimization was put forward. The system adopted two-layer control plan: whole-network coordination layer and execution layer within transformer substation. Optimization algorithm adopted the reactive power optimization method with relaxed constraints so as to improve the convergence and computation speed of reactive power optimization. To control the impact of harmonic, a hybrid active power filter scheme which was made up of passive power filter and active power filter was adopted, thus improving the cost performance of the AVC system. The result of applying the AVC system in the power grid of Wuhu region shows that the system is stable and reliable, obviously decreasing the operation times of equipment and improving the voltage qualified rate and power factor of panel point.

A least square support vector machine-based approach for contingency classification and ranking in a large power system

AbstractThis paper proposes an effective supervised learning approach for static security assessment of a large power system. Supervised learning approach employs least square support vector machine (LS-SVM) to rank the contingencies and predict the system severity level. The severity of the contingency is measured by two scalar performance indices (PIs): line MVA performance index (PIMVA) and Voltage-reactive power performance index (PIVQ). SVM works in two steps. Step I is the estimation of both standard indices (PIMVA and PIVQ) that is carried out under different operating scenarios and Step II contingency ranking is carried out based on the values of PIs. The effectiveness of the proposed methodology is demonstrated on IEEE 39-bus (New England system). The approach can be beneficial tool which is less time consuming and accurate security assessment and contingency analysis at energy management center.

Performance investigation of a Q-V-based Lyapunov finite time VSC control for grid interactive photovoltaic system

A photovoltaic (PV)-based voltage source converter (VSC) system, integrated with local load and utility grid is presented in this paper. The PV-VSC control hence considered on the reactive power (Qpv) and DC side VSC voltage (V2) errors, obtained from the measured parameters at point of common coupling (PCC) and DC side VSC capacitor respectively. The unmodelled dynamics of the phase-locked loop system (PLL) is averted for the proposed control approach as it is designed directly from instantaneous reactive power and DC voltage. A Lyapunov function-based finite time nonlinear Q-V controller is proposed to provide robustness with efficient error convergence during various micro grid operation disturbances. The performance evaluation of the proposed control during utility grid fault has been studied in MATLAB/m-file script. Validation of the proposed control is further obtained in MATLAB/Simulink environment. A conclusion is being carried out from simulation studies where the Lyapunov-based control is found efficient and robust compared with conventional PI control and feedback linearisation-based control (FLC).

Performance Analysis of Multi Functional VSC Based FACTS Devices in Power Flow Management

This paper illustrates the application of Voltage Source Converter (VSC) based Flexible AC Transmission systems (FACTS) controllers such as Static shunt Compensator (STATCOM) and Unified Power Flow Controller (UPFC) for power flow control. A unique modelling framework incorporating these FACTS controllers in Newton Raphson load flow solution is discussed. The effectiveness of both the devices for real power flows, power loss, reactive power injection and voltage profile improvement are analysed. The modes of operation of each device with respect to specified voltage are analysed. The performance of these devices under single line contingency is also discussed. Test results on standard 5 bus system and IEEE 30 bus test system are analysed which justifies the potency of these devices for the above said applications.

风电场无功电压模糊多目标决策方法

针对风电场并网运行难以有效兼顾稳定性与经济性的问题，提出了风电场运行经济性和稳定性目标，其中经济性目标考虑风电场有功损耗指标，稳定性目标考虑风电场无功源无功裕度和风电场电压偏差两个指标。在此基础上，建立了风电场无功电压多目标优化控制模型。该模型以SVC与双馈风电机组的无功功率为控制对象，运用模糊多目标决策方法将风电场无功电压优化转换为一个多目标、多约束的非线性规划问题，并采用粒子群算法进行求解。仿真算例结果表明，所提出的优化决策方法能够实现风电场运行经济性和稳定性的双重目标，在提高风电场电压稳定性的同时，合理降低了风电场损耗。 To solve stability and economy coordinated problem caused by wind farm integration, the targets of stability and economy are put forward, in which economy target considers active power loss, and stability target includes reactive power reserve capacity and voltage deviation of wind farm. Based on this, an optimization control model of reactive power and voltage fuzzy multi-objective decision making method of wind farm is established, in which the reactive power of SVC and DFIG are taken as control objectives, and the fuzzy multi-objective decision making method is used to convert the optimization of reactive power and voltage into a multi-objective and multi-constrained nonlinear programming problem. The particle swarm algorithm (PSO) is adopted to solve the built model. The simulation example results show that the proposed method can achieve the dual targets of economy and stability of wind farms, and can improve the voltage stability of wind farms, and reasonably re-duce the power loss of wind farms.

並列PSOによる電圧無効電力制御に対するディペンダビリティの評価

Various evolutionary computation techniques have been applied to reactive power and voltage control. High penetration of renewable energies and deregulation of power systems require to shorten an interval of the control. One of the practical solutions for this problem is applications of parallel and distributed computing with dependability, which is an ability to keep sustainable control against various accidents. This paper presents evaluations of dependability for parallel particle swarm optimization based voltage reactive power control. Simulation results with IEEE 14, 30, 57, and 118 bus systems indicate high dependability of the method.

Benefits analysis of Soft Open Points for electrical distribution network operation

Soft Open Points (SOPs) are power electronic devices installed in place of normally-open points in electrical power distribution networks. They are able to provide active power flow control, reactive power compensation and voltage regulation under normal network operating conditions, as well as fast fault isolation and supply restoration under abnormal conditions. A steady state analysis framework was developed to quantify the operational benefits of a distribution network with SOPs under normal network operating conditions. A generic power injection model was developed and used to determine the optimal SOP operation using an improved Powell’s Direct Set method. Physical limits and power losses of the SOP device (based on back to back voltage-source converters) were considered in the model. Distribution network reconfiguration algorithms, with and without SOPs, were developed and used to identify the benefits of using SOPs. Test results on a 33-bus distribution network compared the benefits of using SOPs, traditional network reconfiguration and the combination of both. The results showed that using only one SOP achieved a similar improvement in network operation compared to the case of using network reconfiguration with all branches equipped with remotely controlled switches. A combination of SOP control and network reconfiguration provided the optimal network operation.

Operating principle of Soft Open Points for electrical distribution network operation

Soft Open Points (SOPs) are power electronic devices installed in place of normally-open points in electrical power distribution networks. They are able to provide active power flow control, reactive power compensation and voltage regulation under normal network operating conditions, as well as fast fault isolation and supply restoration under abnormal conditions. Two control modes were developed for the operation of an SOP, using back-to-back voltage-source converters (VSCs). A power flow control mode with current control provides independent control of real and reactive power. A supply restoration mode with a voltage controller enables power supply to isolated loads due to network faults. The operating principle of the back-to-back VSCs based SOP was investigated under both normal and abnormal network operating conditions. Studies on a two-feeder medium-voltage distribution network showed the performance of the SOP under different network-operating conditions: normal, during a fault and post-fault supply restoration. During the change of network operating conditions, a mode switch method based on the phase locked loop controller was used to achieve the transitions between the two control modes. Hard transitions by a direct mode switching were noticed unfavourable, but seamless transitions were obtained by deploying a soft cold load pickup and voltage synchronization process.

DC-Bus Voltage Range Extension in 1500 V Photovoltaic Inverters

Solar plants based on single-stage conversion photovoltaic (PV) inverters (no dc–dc boost stage) have gained popularity due to their simplicity, high efficiency, and cost effectiveness. Existing PV plants mostly operate under 1000 V and are subject to wide dc-bus voltage variations due to the effect of PV cell temperature and the voltage of the maximum power point (well below the open-circuit voltage). In particular, attractive locations, such as U.S.–Canada mountain and central regions, are subject to extreme PV surface temperatures, making the dc-bus voltage variation a challenge for single-stage solar inverters. This paper investigates 1500 V solar inverters with a focus on dc-bus voltage range extension capabilities through novel modulation and power devices utilization. A comparative analysis with the existing 1000 V solar inverters is presented to illustrate the significant advantages of the wide dc-bus range in 1500 V systems. A lower voltage limit in the dc-bus is achieved by employing a novel voltage reactive power dc-bus control strategy and modified modulation. A higher dc-bus peak voltage is obtained by maximizing the use of power switches. As a result, the 1500 V inverter dc-bus voltage is significantly extended to capture energy under extreme PV surface temperatures, greatly improving the limited range of traditional 1000 V inverters. Simulations and experimental results using a three-phase three-level neutral point-clamped inverter level are presented to validate the proposed dc-bus extension range, control strategy, and modulation scheme.