Voltage Reactive Power Research Articles

A Unified Power Flow Controller Using a Power Electronics Integrated Transformer

This paper presents a Unified Power Flow Controller (UPFC) application of the Custom Power Active Transformer (CPAT); a power electronics integrated transformer which provides services to the grid through its auxiliary windings. The CPAT structure integrates three single-phase transformers into one shunt-series combining transformer. This integration empowers a sub-station with the capability of dynamically regulating the terminal voltage and current of a transformer through isolated power electronics converters. This paper investigates the CPAT's capability to provide UPFC services which includes power flow control, reactive power compensation, voltage regulation, and harmonics elimination. Simulations of the CPAT-UPFC with a stiff grid and a 5-bus power system demonstrates its functionality as an inter-bus coupling transformer that provides the required grid services. Moreover, the impact of the CPAT-UPFC during load perturbations on the power system is investigated to further validate its transient and steady-state response. Furthermore, an experimental prototype reveals the operation of the three-phase CPAT-UPFC confirming its stable operation according to the theoretical expectations.

Distribution Electricity Pricing Under Uncertainty

Distribution locational marginal prices (DLMPs) facilitate the efficient operation of low-voltage electric power distribution systems. We propose an approach to internalize the stochasticity of renewable distributed energy resources (DERs) and risk tolerance of the distribution system operator in DLMP computations. This is achieved by means of applying conic duality to a chance-constrained AC optimal power flow. We show that the resulting DLMPs consist of the terms that allow to itemize the prices for the active and reactive power production, balancing regulation, and voltage support provided. Finally, we prove the proposed DLMPs constitute a competitive equilibrium, which can be leveraged for designing a distribution electricity market, and show that imposing chance constraints on voltage limits distorts the equilibrium.

Linear matrix inequality approach in stability improvement through reactive power control in hybrid distributed generation system

Stability of a standalone hybrid power system (HPS) in a smart grid is always a challenging task. Further, the operational stability of the power system depends on the associated communication infrastructure. Therefore, it is always crucial to pick up a controller that can assure system's stability along with performance, despite disturbances like (load and input wind variations) with communication delays. Present study focuses on reactive power management and voltage stability issues of an isolated HPS. The stability aspects of HPS are improved through reactive power compensation, by custom power devices like static var compensator. The control aspects of SVC as well as the whole hybrid system are taken care by H ∞ linear matrix inequalities approach. Further, H-infinity control, Lyapunov stability along with linear matrix inequalities techniques estimate the delay boundary of controllers. The iterative performance of the proportional–integral–derivative controllers, and robust H ∞ damping controller of the HPS, are designed through LMI approach. Later experimental study of the HPS is done, with a prototype model in dSPACE real-time control environment. In this case, dSPACE 1104 is added for data acquisition and control. Adaptability and robustness of the proposed controllers are verified under fluctuating loads and uncertain wind power input.

Conservation voltage reduction of networked microgrids

This study proposes a strategy for coordinated operation of networked microgrids (MGs), distributed energy resources (DERs), and volt-VAR control devices in the implementation of volt-VAR optimisation (VVO). The authors’ formulation is focused on implementing conservation voltage reduction, although it can be extended for any other VVO problems. They consider the voltage–power control modes of DERs contemplated in IEEE Std. 1547, namely, constant power factor, voltage–reactive power, active–reactive power, and constant reactive power. DERs are considered at the distribution network (DN) and within the MGs. The problem is formulated as a bi-level optimisation problem where the DN operator (DNO) is in the upper-level and each MG in the lower-level. The DNO and each MG are assumed to be players with their individual objective functions. Finally, they validate their formulation in two test systems: a 9-node system and a modified IEEE 33-node system. On average the proposed method can improve the efficiency of the grid by 4% compared to the economic operation scenario. The results of the study show that the different control modes of the DERs can have better performance depending on the objective of the VVO formulation. The findings of this study are compelling for the implementation of VVO in active distribution systems with networked MGs.

Full-Observable Three-Phase State Estimation Algorithm Applied to Electric Distribution Grids

This paper proposes the development of a three-phase state estimation algorithm, which ensures complete observability for the electric network and a low investment cost for application in typical electric power distribution systems, which usually exhibit low levels of supervision facilities and measurement redundancy. Using the customers´ energy bills to calculate average demands, a three-phase load flow algorithm is run to generate pseudo-measurements of voltage magnitudes, active and reactive power injections, as well as current injections which are used to ensure the electrical network is full-observable, even with measurements available at only one point, the substation-feeder coupling point. The estimation process begins with a load flow solution for the customers´ average demand and uses an adjustment mechanism to track the real-time operating state to calculate the pseudo-measurements successively. Besides estimating the real-time operation state the proposed methodology also generates nontechnical losses estimation for each operation state. The effectiveness of the state estimation procedure is demonstrated by simulation results obtained for the IEEE 13-bus test network and for a real urban feeder.

Coordinated Control for Operating Characteristics Improvement of UHVDC Transmission Systems under Hierarchical Connection Scheme with STATCOM

Ultra-high voltage direct current (UHVDC) systems under hierarchical connection schemes (HCSs) linked to AC grids with different voltage levels (500 and 1000 kV) have been a great concern for power utilities to transfer bulk power. They have some operating issues like cascaded commutation failures and longer fault recovery time under certain fault conditions. Since STATCOM has the ability to effectively regulate AC busbar voltages, thus it is considered in this paper to improve the operating characteristics of UHVDC-HCS systems. To further improve the operating characteristics, a coordinated control between an UHVDC-HCS system and STATCOM is presented. To validate the effectiveness of coordinated control, the comparison between different control modes such as reactive power control (Q-control) and voltage control (V-control) in the outer loop control of STATCOM are conducted in detail. Various indices like commutation failure immunity index (CFII) and commutation failure probability index (CFPI) are also comprehensively evaluated in order to investigate robustness of the adopted coordinated control. An UHVDC-HCS system with multiple STATCOMs on the inverter side (500 kV bus) is developed in PSCAD/EMTDC. The impact of coordinated control on commutation failure phenomena and fault recovery time during single and three phase AC faults is analyzed. The analysis shows that coordinated control with V-control mode of STATCOM exhibits better performance in enhancing the operating characteristics of UHVDC-HCS system by improving the CFII, effectively reducing the CFPI and fault recovery time under various AC faults.

Three-Phase Custom Power Active Transformer for Power Flow Control Applications

This paper presents the three-phase custom power active transformer (CPAT), characterized by the integration of power electronics in a transformer to facilitate grid services. Such integration enables step-up/step-down transformation between primary and secondary as well as shunt and series compensation services to the power system through a single transformer. The CPAT can empower the grid with flexible ac transmission system and power quality services such as power flow control, reactive power compensation, active filter, and voltage regulation through a single monolithic transformer. In this paper, designs of the three-phase CPAT are realized and analyzed based on their equivalent magnetic circuit as well as their structure requirements and constraints. Simulation analysis of the three-phase CPAT clarifies its capability to actively regulate power flow between the primary and secondary windings as well as achieve grid harmonic current compensation. Moreover, through real-time simulations and an experimental prototype, the merits and performance of the three-phase CPAT were further validated.

Closed loop control of voltage source converters during faults in high voltage DC transmission system

High voltage DC transmission is very cost effective alternate solution for high voltage AC transmission. High voltage DC transmission towers occupy less space and poles carry more current compared to high voltage AC system. High voltage DC transmission lines are emerging as an alternate solution for flexible AC transmissions (FACTS) technology. Earlier either thyristor valves or mercury valves were used in converters. Voltage source converter has replaced conventional converter in high voltage DC system because of their flexible control, black start capability, and they can work with weak AC system. Switching at higher frequency is also an added advantage. In voltage source converter-based high voltage DC transmission, both real and reactive power transmitted can be controlled whereas in conventional line commutated converter-based high voltage DC transmission system, only the real power transmitted was controlled. There may be chances of grid faults in sending end and receiving end stations. The typical faults are single line fault, double line to ground fault and three phase fault. The faults in one high voltage DC station should not affect the other end station. Necessary control should be initiated to take care of AC faults on both the sides that are before rectification in the sending end station and after inversion in the receiving end station. To handle such faults, the voltage source converters should be controlled to regulate the power transmitted through the line in such a way that the fault in one grid will not affect the parameters of the other grid. This paper presents closed loop control of both voltage source converters to take care of line to ground fault. The controller uses PQ theory. The behavior of high voltage DC system during fault without and with controller is presented in this paper. This simulation study is used to educate electrical transmission and faults detection to the trainees, they can easily understand.

Energy Routing Control Strategy for Integrated Microgrids Including Photovoltaic, Battery-Energy Storage and Electric Vehicles

The Energy Internet is an inevitable trend of the development of electric power system in the future. With the development of microgrids and distributed generation (DG), the structure and operation mode of power systems are gradually changing. Energy routers are considered as key technology equipment for the development of the Energy Internet. This paper mainly studies the control of the LAN-level energy router, and discusses the structure and components of the energy router. For better control of the power transmission of an energy router, the energy routing control strategy for an integrated microgrid, including photovoltaic (PV) energy, battery-energy storage and electric vehicles (EVs) is studied. The front stage DC/DC converter of the PV system uses maximum power point tracking (MPPT) control. The constant current control is used by the bidirectional DC/DC converter of the battery-energy storage system and the EV system when they discharge. The DC/AC inverters adopt constant reactive power and constant DC voltage control. Constant current constant voltage control is adopted when an EV is charged. The control strategy model is simulated by Simulink, and the simulation results verify the feasibility and effectiveness of the proposed control strategy. The DG could generate reactive power according to the system instructions and ensure the stable output of the DC voltage of the energy router.

Coordination of generation, transmission and reactive power sources expansion planning with high penetration of wind power

High penetration of renewable energy is one of the important feature of future power systems. However, the randomness and intermittence of renewable energy have brought new challenges to planners. To accommodate the uncertainty and variability of wind power, an innovative scenario-based stochastic model that incorporates generation, transmission, and reactive power planning is presented, considering spinning reserve, unit ramp rate, and current output of units. To consider reactive power flow and voltage, a second-order cone programming model based on relaxed AC optimal power flow is introduced. Moreover, unit status and optimal transmission switching are implemented to promote wind consumption, reduce congestion, and attain a more flexible topology. The proposed methodology organically combines operational constraints with planning issues. Finally, two modified test systems with high wind power integration are utilized to illustrate the effectiveness of the presented model.

Measurement-Based Characteristic Curves for Voltage Stability and Control at the Point of Interconnection of Wind Power Plants

In this paper, the measurement-based characteristic curves, reactive power-voltage ( Q-V) curve and reactive power-active power-voltage (Q-P-V) curve, are developed for voltage stability and control at the point of interconnection (POI) between a wind power plant (WPP) and a utility grid. The procedure to obtain an effective Q-V curve using the supervisory control and data acquisition (SCADA) measurement data is proposed. The SCADA data used in this paper were recorded in 2016 at the POI of a 27-MW WPP currently in operation in Newfoundland and Labrador (NL), Canada. Each Q-V curve is created for a particular month using the SCADA data corresponding to a very narrowly defined active power range, so the active power is considered constant as the conventional Q-V curve concept. The MATLAB curve fitting toolbox is used to realize the most fit mathematical equations for Q-V and Q-P-V curves. The developed Q-V and Q-P-V curves can be used for the data-driven voltage control for WPPs; and the Q-V curves can also be used for the voltage stability evaluation.

Анализ качества электроэнергии при стабилизации активной мощности дуговой сталеплавильной печи с помощью статического тиристорного компенсатора

The paper presents the key findings of studying the quality of electricity at the buses of an electric steel-making complex as affected by a static var compensator (SVC) running a novel control algorithm designed to improve the electric performance of an electric arc furnace (EAF) by stabilizing its active power at an optimal value. Analysis of how an SVC runs this algorithm reveals a considerable degradation of voltage quality compared to experiments with conventional algorithms. For detailed evaluation of SVC effects on the quality of electricity (QE), the research team ran an SVC in active-power mode and computed the QE values characterizing slow voltage deviations, non-sinusoidality, imbalance, and fluctuation; the values were compared against those attained by the reactive power- or voltage-controlled compensator. Experimentation used the mathematical model of an existing EAF-120-SVC unit, which was developed and run in MATLAB Simulink. To enable the SVC to sustain a constant active EAF power while also keeping the QE values sufficiently high, the paper proposes a structure of additional voltage and reactive power coefficient constraints, voltage balancing, and flicker suppression.

Analysis on the Impact of Geomagnetic Storm on Reactive Power and Voltage in Extrahigh Voltage Power Grid

With the growing scale of the power grid and the improvement of the voltage level, the geomagnetically induced currents (GICs) generated by geomagnetic storms has become one of the leading factors that cause large-scale power outages in power grid. Considering the global simultaneity characteristic of geomagnetic storms, this paper presents the concept of mass reactive power disturbance for the first time, analyzes the mechanism of GIC reactive power loss of transformer and reveals the mechanism of mass reactive power disturbance’s influence on voltage. Finally, combined with the practical situation of 750kV EHV power grid in China, the reactive power loss and voltage distribution under the geomagnetic storms at various intensities are calculated, with the grid operating in two typical modes, and the impact of the geomagnetic storm on voltage is illustrated, which provides the theoretical basis for the study of voltage stability.

Smart Home Energy Management in Unbalanced Active Distribution Networks Considering Reactive Power Dispatch and Voltage Control

This paper presents a new optimization algorithm for home energy management systems (HEMSs) in three-phase unbalanced low-voltage (LV) distribution networks. Compared with conventional HEMS optimization methods, which consider only the active power consumption scheduling for smart home appliances and distributed energy resources (DERs) (e.g., solar photovoltaic (PV) systems and energy storage systems (ESSs)), the novelty of the proposed approach is to consider: i) both active and reactive power consumption schedulings of home appliances and DERs, ii) realistic three-phase unbalanced LV distribution networks with voltage-dependent load models, and iii) voltage control using an on-load tap changer transformer and smart inverters of PV system and ESS at the households. The proposed HEMS optimization algorithm, which is formulated using mixed-integer linear programming, is tested in the modified CIGRE LV distribution network. Numerical examples demonstrate the performance of the proposed algorithm in terms of active/reactive power consumption, three-phase voltage magnitudes, and the total cost of electricity.

Comparative Analysis on Small-Signal Stability of Multi-Infeed VSC HVDC System With Different Reactive Power Control Strategies

Voltage Source Converter based High Voltage Direct Current (VSC HVDC) technology is used more and more in modern power systems. Consequently, in the ac network, an increasing number of converters are appearing in mutual electrical proximity, thus forming Multi-Infeed (MI)-HVDC systems. For VSC technology, several aspects of MI-HVDC system operation are less well understood compared to Line Commutated Converter (LCC) HVDC systems. This paper studies an MI system which consists of two VSC HVDC schemes based on Modular Multilevel Converters (MMC) interconnected with an ac line and connected to an external grid. The aim of the study is to identify the small-signal stability properties of such a system, thereby focusing on the impact of different outer control loops for reactive power and ac voltage regulation.

Research on Emergency Control Strategy of Synchronous Condenser for Inhibiting HVDC Commutation Failure

As multi-infeed HVDC systems are integrated into power grid, the operation characteristics of power grid have changed significantly. The problems of the shortage of dynamic reactive power reserve and voltage support need the allocation of dynamic reactive compensation device such as synchronous condenser urgently. This paper researches the influence of installing synchronous condenser on system performance in multi-infeed HVDC power grid. Based on the analysis of the defects of synchronous condenser on HVDC commutation failure under existing conventional control mode, this paper presents the emergency control strategy and system architecture with synchronous condenser. In the end, the effectiveness of the proposed control strategy is verified based on the actual grid simulation.

Prediction of the electrical load of the power system using neural networks

Prediction of the electrical load schedule of an electrical system is an important aspect for determining electrical loads, which ensures the correct selection and cost-effective operation of reactive power compensation devices and voltage control devices, as well as relay protection and automation. This article discusses methods for predicting electrical load using an artificial neural network. The problems of choosing the optimal architecture and algorithm of neural network training are considered. The methods of the best forecast accuracy are determined. A genetic algorithm based on the group method of data handling was chosen as the main calculation.

Distributed generation integration optimization using fuzzy logic controller

Distributed generators (DGs) are connected near load centers and integrated to grid for optimum power system operations. The challenging task for integration of DGs is the proper size and location, due to random character of generation and energy consumption. The objective of the research is to provide the proper size and location of DGs to optimize the voltage profile and reduction in active and reactive power losses. Optimization of distributed generators is performed through fuzzy logic controllers at Ramchandrapura 33/11 kV, 69 bus radial distribution substation, Kota, India. Fuzzy logic controller provides possible solution on selection of distributed generators on the basis of voltage profile of the bus and the impedance of the branch connected DGs at consumer’s end. Forward or backward sweep methodology is used to optimize the load flow analysis for calculation of real and reactive power losses and voltage profile with and without implementation of distributed generators. Proposed approach provides a possible solution for efficient integration of DGs.

Performance Enhancement of DFIG Based Grid Connected SHPP Using ANN Controller

In the current span of time, Small Hydro Power Plant(SHPP) is gaining more attention due to its numerous pros among all the various renewable energy sources. The prime objective of this paper to present the comparative analysis of Proportional Integral (PI)control and Artificial neural network (ANN) control strategy which is used in doubly fed induction generator-based SHPP. Traditionally presented PI control scheme has numerous limitations due to nonlinear model of DFIG, as well as PI control scheme, needs plentiful mathematical equations. To significantly improve the transient response of the DFIG system as well as reduce the computational time of the system, ANN control scheme is implemented in the rotor side and grid side of the small hydropower plant system. The proposed ANN scheme significantly improves the transient behavior of active and reactive power in the rotor side and reactive power and dc bus voltage in the grid side as compared to the PI control scheme. MATLAB/SIMULINK is used for testing, analyzing and comparison of dynamic and steady-state realization of the proposed controller scheme. The stability of the system is constant under various load circumstances and it is scrutinized with the help of model and simulated results.

Placement of shunt reactors in high-voltage network using fuzzy constraints

In recent years, controlled shunt reactors (CSR) relevant to the class of FACTS facilities have been widely used to control voltage modes and reactive power flows in the high-voltage electrical network. The selection of location, as well as the definition of the law of CSR control in the conditions of stochastic variability of the operation mode of high-voltage power transmission, are associated with numerous technical and economic factors. At the same time, such constraint conditions as ease of use, performance efficiency, purpose and location in the system, as well as the period of commissioning should be taken into account. In the proposed procedure these factors are considered as fuzzy constraints. The procedure of CSR placement in the 330 kV electrical network of Azerenergy system for control of reactive power flows taking into account the mentioned fuzzy constraints is proposed. The obtained simulation results confirm the advantage of the proposed procedure.