Reactive Power Balance Research Articles

FC-TCR based controller for SPV grid interconnected system

Abstract Renewable based energy generation system and its interconnection to the traditional grid system is always a good choice among the researchers to combat the energy crises. The interconnection of the solar PV system to the grid not only increases the power security problem but also decreases the grid reliability on the overall system performance. Nature-dependent source of energy such as Solar PV system always produces fluctuating energy and hence imbalances the reactive power, and thereby pollutes the power distribution system. Reactive power balancing remains a major challenge for obtaining power balance in the transmission line. Therefore, the present research focuses on expanding the uses of the Solar PV system in the traditional power system and also addresses the concerning issues arising in the power distribution system such as harmonic mitigation. The primary objective is to investigate the coordinated control of FC-TCR in an IEEE-5 Bus system connected by the PV system. To address this issues a MATLAB Simulink model has been developed with the IEEE-5 Bus system to check the performance of the system.

Optimal Placement and Sizing of Inverter-Based Distributed Generation Units and Shunt Capacitors in Distorted Distribution Systems Using a Hybrid Phasor Particle Swarm Optimization and Gravitational Search Algorithm

In this paper, a novel hybrid population-based meta-heuristic algorithm, called the hybrid Phasor Particle Swarm Optimization and Gravitational Search Algorithm (PPSOGSA), is proposed to solve the problem of optimal placement and sizing of inverter-based distributed generation (DG) units and shunt capacitors in radial distribution systems with linear and non-linear loads. The objective of the problem is reduction of active power losses considering constraints of the fundamental frequency active and reactive power balance, RMS voltage, and total harmonic distortion of voltage (THDV) at each bus of the network, as well as the branch flow constraints. The performance of the PPSOGSA-based approach is evaluated on the standard IEEE 33- and 69-bus test systems under sinusoidal and non-sinusoidal operating conditions. Compared to the original PPSO and GSA and other algorithms commonly used in the optimal sitting and sizing problem of DG units and shunt capacitors, it is found that the proposed algorithm has yielded better results.

Performance Improvement of DC Capacitor Voltage Balancing Control for Cascaded H-Bridge Multilevel Converters

In this article, an improved dc capacitor voltage balancing control is proposed for single-phase cascaded H-bridge (CHB) multilevel converters. Compared with conventional voltage balancing control methods, the proposed scheme has a comprehensive consideration of three aspects while balancing the capacitor voltages among H-bridges: coupling effect elimination, reactive power balancing, and dynamic performance improvement. First, the system mathematical model in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> reference frame is derived, and the relationship among duty cycle modifications of H-bridges is revealed to eliminate the coupling effect of voltage balancing control on the current control loop. Then, based on the H-bridge power model, a quantitative solution for reactive power balancing is presented to design the reactive duty cycle modifications. In order to enhance the dynamic performance of voltage balancing control, a dynamic references design method is adopted to evaluate the active duty cycle modifications. Finally, both simulation and experimental results are presented to validate the effectiveness of the proposed scheme.

Turbo-Expander Generators for Supplemental Power Generation in LNG Liquefaction Plants

Incentives to increase efficiency and reduce CO2 emissions have led to the development of many plant process designs incorporating turbo-expanders. Turbo-expanders provide the most efficient solution when it is required to reduce the pressure of a fluid stream. By expanding high pressure fluid, energy in the high-pressure fluid entering the turbo-expander can be efficiently used for electrical power generation. The energy recovered from the expansion is supplementary, thereby improving the thermal efficiency of the plant without leaving any noticeable trace of greenhouse gas emissions. This article focuses on both mechanical and electrical considerations for the implementation of turbo-expander generators. In an example of LNG liquefaction plant, the article discusses the plant thermal efficiency, turbo-expander performance curve, generator sizing, and the choice between the induction and the synchronous generator. The impact on the plant real and reactive power balance and the system stability is shown in an example. Furthermore, this article evaluates the options for the turbo-expander generator tie-in points within the electrical system.

Consensus-Based Decentralized Optimization for Distributed Generators Power Allocation Over Time-Varying Digraphs in Microgrids

In this article, a consensus-based decentralized optimization method for distributed generators (DGs) power allocation is proposed to ensure the economic and reliable operation of microgrids. According to the method, all parameters are designed in a fully distributed fashion, which does not depend on any centers or leaders. To further achieve decentralization and to meet the flexible requirement of DGs, the strategy is adaptable to time-varying communication topologies (time-varying digraphs) and is proved to be convergent. During the communication process, the stochastic noise is introduced to imitate a nonideal communication environment, and the convergence rate is accelerated via coupling designed gains of noise and feedback (mismatch). Meanwhile, the cost of reactive power generation and reactive power compensation are considered for a comprehensive optimization, which guarantees the locally reactive power balance and reduces the cost. Simulations based on a test microgrid are used to verify the effectiveness of the proposed method. Finally, the dynamic characteristics and robustness are evaluated and compared by numerical simulation results.

Technique for stability enhancement of microgrids during unsymmetrical disturbances using battery connected by single‐phase converters

This study proposes a technique for the enhancement of the stability of microgrids during unsymmetrical temporary faults in the distribution network. In order to enhance the transient stability and the quality of voltage in the microgrid during different disturbances caused by faults in the distribution network, this study proposes a concept with a centralised battery energy storage system. The battery is connected to the network through single-phase converter units which are to be implemented in every phase so that they can inject independently both the active and reactive power in certain phases. The proposed technique enhances the transient stability of microgrids and provides symmetrical operating conditions for consumers and generators in it during all temporary symmetrical and unsymmetrical faults in the distribution network. An innovative concept has been proposed for managing the balance of active and reactive power that uses, as control variables, magnitude and voltage phase angle at the point of connection of the microgrid to the distribution system. The proposed concept and technique have been tested on the IEEE 33 BUS system with additional sources. The dynamic simulations of disturbances and the verification of the proposed technique have been performed in DIgSILENT PowerFactory software.

Multi‐slack power flow for islanded microgrids with radial and meshed topologies

This study proposes a new power flow formulation for islanded microgrids. The proposed power flow is based on the effect of the superposition principle and the solution of a small non-linear subproblem to determine the frequency of the microgrid and the voltage magnitude in the angular reference node in each iteration. These variables are determined by considering the following equations in the non-linear subproblem: active and reactive power balance equations and specified phase at the angular reference node. The application of the superposition principle allowed to obtain two versions of the proposed technique: one for radial networks - based on the current summation method - and another for meshed networks - based on the Gauss-Zbus method. Therefore, the iterative framework prosed in this study expands in a simple and integrated way the two most commonly used power flow methods in conventional distribution networks for islanded microgrids. The tests in microgrids with 33, 310 and 1438 nodes showed that the proposed approach has the same accuracy as Newton-Raphson algorithm, but with significantly lower computational cost in large scale microgrids. In addition, the proposed method for island microgrid showed good accuracy and convergence for the most common load models applied in power flow studies of islanded microgrids.

Reactive power balancing transformers in control systems for electric drives of direct and alternating current

The features of the application of the balancing transformers with artificial switching as regulated power sources of the process plants are considered. The proposed approach makes it possible to convert AC to DC to supply the load and simultaneously generate reactive power of a capacitive nature, which is aimed at meeting the current Russian and foreign standards for electromagnetic compatibility of the consumer with the supply network. The characteristics obtained as a result of computer simulation in the MATLAB Simulink environment and its SimPowerSystems application confirmed the main positive features of compensation converters. It is shown that the main advantage of controlled compensation converters is the possibility of creating a frequency-controlled asynchronous electric drive with separate frequency and voltage control, which will significantly improve the energy characteristics of an asynchronous motor by reducing losses, increasing the service life of insulation, and significantly improving electromagnetic compatibility.

Current and power quality multi-objective control of virtual synchronous generators under unbalanced grid conditions

In recent years, with the large-scale application of distributed power sources in the power grid, the power grid is moving toward low inertia and low damping. The virtual synchronous generator (VSG) has become a hot topic for scholars since it can simulate the moment of inertia, damping and frequency modulation of synchronous generators. Due to its unbalanced load distribution and the random variation of power loads, grid voltage is asymmetrical. Under grid voltage asymmetry, a VSG experiences output current imbalance and power oscillation. The grid current imbalance further reduces the transformer’s three-phase voltage, which makes it unequal, cyclic, and very easy to cause electricity accidents. Aiming at this problem, this paper proposes three modes of current balance, reactive power balance and active power balance without changing the characteristics of VSGs. The output current balance and power are constant when the grid voltage is asymmetrical. The effectiveness and feasibility of the control strategy are verified by simulation and experimental results, which provides an effective scheme for balanced and stable operation of the grid.

Power factor correction and power quality improvement of supply grid with self-supported transformer-less DSTATCOM for different control strategies

This paper investigates the performance of transformer-less distribution static compensator (DSTATCOM) integrated at the side of the utility distribution system for four different control strategies, viz., unit template (UT) theory, synchronous reference frame (SRF) theory, instantaneous reactive power theory (IRPT) and power balance theory (PBT). The simulation models for the three-phase three-wire power system have been designed to achieve unity power factor with different loading conditions (balanced and unbalanced linear and nonlinear loads). The DC-link is self-supported, i.e., no energy storage element is used but a DC-link capacitor is used only. DSTATCOM fulfils almost all the objectives related to the current related power quality problems created by different types of load. Here, it eliminates the harmonics, compensates reactive power which reduces the burden on the grid, makes the grid power factor unity and eliminates the load unbalances. Here, steady-state and dynamic state analysis has been discussed and comparative results have been presented.

Power factor correction and power quality improvement of supply grid with self-supported transformer-less DSTATCOM for different control strategies

This paper investigates the performance of transformer-less distribution static compensator (DSTATCOM) integrated at the side of the utility distribution system for four different control strategies, viz., unit template (UT) theory, synchronous reference frame (SRF) theory, instantaneous reactive power theory (IRPT) and power balance theory (PBT). The simulation models for the three-phase three-wire power system have been designed to achieve unity power factor with different loading conditions (balanced and unbalanced linear and nonlinear loads). The DC-link is self-supported, i.e., no energy storage element is used but a DC-link capacitor is used only. DSTATCOM fulfils almost all the objectives related to the current related power quality problems created by different types of load. Here, it eliminates the harmonics, compensates reactive power which reduces the burden on the grid, makes the grid power factor unity and eliminates the load unbalances. Here, steady-state and dynamic state analysis has been discussed and comparative results have been presented.

Research on Source-Network Coordination Voltage Control Strategy of Photovoltaic Power Plant Considering the Stability of Inverter Port Voltage

At present, the reactive power distribution method considering the reactive power adjustment capacity of the inverter in the photovoltaic (PV) power plant will lead to the output voltage of the inverter exceeding the limit. In particular, the PV inverter adopts the constant reactive power control to support the voltage at point of common coupling (PCC), which has a good effect in the steady-state operation. However, when the system is subject to transient disturbance, the PV inverter cannot flexibly support the voltage level of the system by changing the reactive power output. Therefore, this paper proposes a source-network coordination control strategy aiming at the stability of bus voltage at PCC and inverter port voltage. Firstly, the paper introduced the advantages of constant voltage control of PV inverter. Then, the voltage and reactive power control objectives of the PV Inverter in the PV power plant were calculated by considering the PCC voltage, tie lines, power collection lines, the power of transformers and the voltage loss to realize the voltage and reactive power balance control between the inverters. Finally, an actual PV power plant simulation model was built to analyse the PCC voltage under the two conditions of PV output fluctuation and system fault to verify the effectiveness of the control strategy proposed in this paper. The proposed strategy has engineering application value for the realization of closed-loop voltage control between the power grid and PV power plant and the improvement of the active response ability to the PCC voltage.

Phase Balancing and Reactive Power Support Services for Microgrids

Alternating current (AC) microgrids are expected to operate as active components within smart distribution grids in the near future. The high penetration of intermittent renewable energy sources and the rapid electrification of the thermal and transportation sectors pose serious challenges that must be addressed by modern distribution system operators. Hence, new solutions should be developed to overcome these issues. Microgrids can be considered as a great candidate for the provision of ancillary services since they are more flexible to coordinate their distributed generation sources and their loads. This paper proposes a method for compensating microgrid power factor and loads asymmetries by utilizing advanced functionalities enabled by grid tied inverters of photovoltaics and energy storage systems. Further, a central controller has been developed for adaptively regulating the provision of both reactive power and phase balancing services according to the measured loading conditions at the microgrid’s point of common coupling. An experimental validation with a laboratory scale inverter and a real time hardware in the loop investigation demonstrates that the provision of such ancillary services by the microgrid can significantly improve the operation of distribution grids in terms of power quality, energy losses and utilization of available capacity.

Frequency Control of Offshore Wind Farm With Diode-Rectifier-based HVdc Connection

This paper presents a direct frequency control for offshore wind farms (OWFs) connected to the diode-rectifier-based (DR-based) high voltage direct current (HVDC) link. The frequency control is guaranteed through reactive power balance at the DR station without a capacitor bank placed at the DR station; while AC-voltage magnitude is clamped by the DR, provided that the HVDC link voltage is imposed by the onshore inverter. The control system is implemented by a voltage source converter (VSC) connected to the DR station. The VSC is also used to compensate harmonic currents, leading to passive AC-filters being also removed from the DR station. The proposed control system provides comparative advantages in terms of DR station volume and OWF installation cost with other centralized controls where besides a VSC, a high-voltage large capacitor bank is needed to be placed at the DR station. A new average-value model (AVM) of the DR system is derived to test the proposed frequency control, while the stability of the system is evaluated through a small-signal analysis. The proposed control system performance and the accuracy of the proposed AVM are verified through a detailed switching model of the system using operation of a cascaded H-bridge VSC.

Optimal Power Flow Incorporating Frequency Security Constraint

Optimal power flow (OPF) minimizes the production cost, while satisfying the constraints on the system, such as real and reactive power balance, equipment capability constraints, and voltage limits. This article presents a method of incorporating a frequency security constraint within the framework of the OPF problem. Increasing displacement of conventional generation by renewable resources that contribute little or no frequency regulation capability may necessitate the enforcement of such a constraint to meet frequency security requirements. The system frequency is required to be maintained within a safe limit, thus indicating the balance between generation and consumption. Hence, the solution for optimization of power flow should not only present a minimum cost of generation within the operating conditions, but also ensure frequency stability. In order to obtain this solution, the requirement of frequency stability is introduced as a new constraint of the power dispatch problem and is represented by the maximum frequency deviation limit. This new constraint is constructed as a nonlinear function of system inertia and the frequency regulation constant, since frequency deviation is highly sensitive to these factors. It is shown that the inclusion of this constraint causes the OPF to preferentially select higher inertia generators as necessary, to satisfy the frequency security requirement. A genetic algorithm is utilized as the optimization tool in this article. The IEEE RTS-79 test system is used to demonstrate efficacy of the proposed method.

Modeling and Investigation of Self-Excited Reluctance Generators for Wind Applications

In the last few years, wind energy conversion systems have been increasingly installed worldwide. The self-excited reluctance generators (SERGs) are found to be potential candidates as isolated wind turbine generators, especially for low- and medium-power applications. This article focuses on the characteristics of SERG for wind turbine generation system. A simplified dynamic model of the generation system is developed, discretized by backward Euler formula, and simulated. With this model, the process of self-excitation and operation characteristic of SERG are investigated. Considering the varying generated voltage at different speeds, variable capacitances allow suitable regulation of the voltage. The variation of capacitance with speed is obtained by the active and reactive power (PQ) balances method. Combining the power speed characteristics of wind turbine and SERG, the PQ balances method is also used to determine the “optimal capacitor and resistor combination” that achieves the highest usage of wind power. This article exhibits the performance of SERG for wind applications, and most importantly, makes the prediction of the highest energy conversion efficiency of the system.

A Probe into Reactive Power Management in Renewable Energy System using Facts Devices

In the modern era, most of the utility grid is connected with Renewable Energy resources (RERs). In addition to this, many power electronic converters and reactive power compensating devices are also incorporated into the existing grid. This makes the system complicated. Penetration of renewable energy resources affect many power system parameters like grid stability, quality of power, reactive power balance and Sufficient energy utilization. However, the Distributed Generation (DG) towards the power electronic interface creates some critical power quality events such as reactive power management, harmonics and voltage profile which makes the distributed system become a polluted one. This paper depicts the review of modelling and incorporation of various reactive power compensating devices like TCSC, SVC and STATCOM into RES. Power generation model of solar, wind and fuel farm is discussed in this paper. Reactive power compensating devices and its location and sizing are important for the stable and secure operation of the electric grid. Consequently, power quality issues, real-time interconnection issues and policies related to reactive power management are in this paper.

A Framework for $$H_{2} /H_\infty$$ Synthesis in Damping Power Network Oscillations with STATCOM

The escalating in load demand prioritized the incorporation of additional renewable energy generation plants to the existing grid. In parallel, the necessity of reactive power balance and damping characteristics has advised the incorporation of flexible AC transmission system controllers to the existing power network. Hereby, the modern power system has been driven towards the much more composite system which in turn necessitates a healthy controller technique. The objective of this paper is to contribute recommendations to incorporate robust controller technique in the field of the electrical power system. Detailed design considerations for the $$H\infty$$ controller design of a modern power network have been specified, and the same has been demonstrated with mathematical modelling of power network with static synchronous compensator (STATCOM) connected in the middle of the transmission line and in a multi-machine power system. To comment on the suitability of the controller design, a deep stability analysis has been presented and compared with the traditional power system stabilizer, power system stabilizer optimized using particle swarm optimization with time-varying acceleration coefficients algorithm and whale optimization algorithm under adverse system operating conditions. The proposed controller framework has been presented by considering the case studies of single machine infinite bus system, two-machine system model and the benchmark two-area four-generator multi-machine systems connected with STATCOM. The controller performance analysis has been verified by considering eigenvalues analysis, singular value analysis and dynamic response of system states during perturbations for the first two case studies, and system analysis under faulty condition has been investigated for the multi-machine system.

Hierarchical control system for a flexible microgrid with dynamic boundary: design, implementation and testing

The design, implementation, and testing of a control system for a flexible microgrid (MG) is presented in this study. The MG controllers can be implemented in a real-world MG with multiple smart switches, photovoltaic panel system, and battery energy storage systems (BESSs). With the benefits from smart switches, the MG has unique characteristics such as dynamic boundary and flexible point of interconnection (POI) concepts. To control such a unique MG and realise the dynamic boundary, an MG central controller and two types of local controllers are implemented. Compared to the MG with fixed boundary, the MG with dynamic boundary can have smaller BESS capacity, better utilisation of renewable energy, and multiple POI options. Also, compared with IEEE Std 2030.7–2017, the topology identification and active and reactive power balance functions are newly designed to realise the dynamic boundary concept. The planned islanding and reconnection functions are modified to realise the flexible POI concept. These functions are introduced including the software architecture, cooperation, and interaction among them. Finally, a hardware-in-the-loop testing platform based on the Opal-RT real-time simulator is set up to verify the performance, realisation of the dynamic boundary, and flexible POI concepts with four comprehensive test scenarios.

Active and Reactive Power Joint Balancing for Analyzing Short-Term Voltage Instability Caused by Induction Motor

Short-term voltage instability has a sensational effect once it occurs with massive loss of load, possibly area instability, and voltage collapse. This paper analyzes the short-term voltage instability caused by induction motor from the viewpoint of active and reactive power joint balancing. The analysis method is based on (1) the reactive power balancing between system supply and induction motor demand, and (2) the active power balancing between air-gap power and mechanical power, which is expressed by the region of rotor acceleration and deceleration in the Q-V plane. With the region of rotor acceleration and deceleration in the Q-V plane and the reactive power balancing, the movement direction of the operating point can be visually observed in the Q-V plane, thereby achieving a clear comprehension of physical properties behind the short-term voltage instability phenomenon. Furthermore, the instability mechanisms of two kinds of grid-connected induction motor operation conditions after a large disturbance are discussed to explain the basic theory of the analysis method and to provide examples of its application. Time-domain simulations are presented for a single-load infinite-bus system to validate the analyses.