Minimum Reactive Power Research Articles

Improving photovoltaic hosting capacity of distribution networks with coordinated inverter control: A case study of the EPRI J1 feeder

AbstractAdding photovoltaic (PV) systems in distribution networks, while desirable for reducing the carbon footprint, can lead to voltage violations under high solar‐low load conditions. The inability of traditional volt‐VAr control in eliminating all the violations is also well‐known. This article presents a novel coordinated inverter control methodology that leverages system‐wide situational awareness to significantly improve hosting capacity (HC). The methodology employs a real‐time voltage‐reactive power (VQ) sensitivity matrix in an iterative linear optimizer to calculate the minimum reactive power intervention from PV inverters needed for mitigating over‐voltage without resorting to active power curtailing or requiring step voltage regulator setting changes. The algorithm is validated using the EPRI J1 feeder under an extensive set of realistic use cases and is shown to provide 3x improvement in HC under all scenarios.

Novel technologies for optimization of hydroelectric power plants with hydrogen energy storage system

An analytical equation for limiting the minimum reactive power of a salient-pole generator according to the condition of ensuring static stability for a given safety factor, current active power and voltage is obtained. Overall, group reactive power controllers have proven to be a highly effective solution for controlling reactive power in power systems. They offer several advantages over traditional individual controllers, including increased system stability, reduced losses, and reduced costs. When designing and deploying these controllers, it is important to consider factors such as system topology, load characteristics, and more. Overall, group reactive power controllers represent a promising technology for improving the efficiency and reliability of power systems, and further research and development in this area is needed.

Distribution Grid Hosting Capacity Improvement using Reactive Power Control Optimization Algorithm of Inverter-based Photovoltaic Generation System

This paper uses a reactive power control optimization algorithm to present an inverter-based photovoltaic generation system for increasing the distribution grid host capacity. The main objective of this study is to regulate bus voltages by providing sufficient minimal reactive power consumption, which is obtained by a Particle Swarm Optimization-based optimization algorithm. A modeling study of the system network is developed using DIgSILENT PowerFactory, and the control algorithm is implemented in MATLAB. The proposed approach is efficient for various scenarios of the IEEE 13-bus test system and practical distribution network. The analysis results are compared with outcomes from other control methods, including technical and economic assessments. The performance of the proposed optimization-based power system has shown that the proposed algorithm method yielded significantly superior mitigated voltage rises and increased hosting capacity compared to those achieved by existing control methods of a specific distribution network.

The realization of power stabilization and reactive power minimization for wireless charging system under high coils misalignment

The realization of power stabilization and reactive power minimization for wireless charging system under high coils misalignment

Control laws of a salient pole synchronous machine in a mine electric locomotive

Relevance. The need to find effective control of a traction synchronous motor with permanent magnets in a mining electric locomotive under conditions of limitation of current and voltage supplied to its windings from an autonomous power source. Aim. To choose a control law that ensures an increase in a mine electric locomotive mileage on one battery charge with its speed growth. Object. Control laws of a salient pole synchronous motor with permanent magnets of a mining electric locomotive; laws of current control along the transverse axis; control by the current minimum and control by minimizing the reactive power of a salient pole synchronous machine. Methods. Analysis of the state of the electric machine with different formation of control of an electric drive in the mine electric locomotive. The main limiting indicators of an electric machine with voltage and current limitation were considered. For each control law, the results of mathematical modeling are shown in graphical and tabular form. Results. The analysis of the current control law along the transverse axis demonstrates a significant increase in reactive power with increasing load. In an hourly mode of operation, the reactive power exceeds the active power spent on the movement of the electric locomotive. When limiting the current and voltage, the minimum current control allows you to increase the electromagnetic torque by 12.7% in hourly operation. The maximum engine speed is increased by 13%. The maximum power spent on the electric locomotive movement increases by 33%. Reactive power is reduced by 29%. With reactive power minimization, despite the decrease in the electromagnetic torque in the hourly mode of operation by 4.8%, the maximum possible engine speed increases by 53%, the power spent on the electric locomotive movement increases by 50%.

Analytical voltage sensitivity-based distributed Volt/Var control for mitigating voltage-violations in low-voltage distribution networks

Integrating solar photovoltaic system in low-voltage distribution networks leads to significant voltage violations. This issue can be alleviated using the cutting-edge control techniques (Volt/Var control, Volt/Watt control, etc.) of smart inverters. Moreover, the smart inverters absorb/inject the necessary amount of reactive power from/into the substation to alleviate the over/under voltages. This increases the reactive power burden on the substation and deteriorates its power factor. Therefore, this paper proposes a novel distributed Volt/Var control technique to reduce the dependency on substations for reactive power support and improve its power factor. The proposed technique is based on analytical voltage sensitivity analysis. By developing suitable relations, the feeder nodes are categorized into two groups, one operating in lagging mode, while the other in leading mode. This ensures proper utilization of reactive power capability of the inverters. An IEEE 13-node low voltage distribution network with the solar photovoltaic system at different load conditions is used to test the proposed and other existing Volt/Var control techniques. Compared to other distributed Volt/Var control techniques, the proposed method requires a minimum reactive power support to regulate the feeder voltage. Additionally, the obtained results by the proposed method are closer to those by the optimal reactive power support approach using GAMS software and are validated on a real-time digital simulator platform.

Predictive Current Control for Three-Level Four-Leg Indirect Matrix Converter Under Unbalanced Input Voltage

In this paper, a robustness evaluation of model predictive current control with instantaneous reactive power minimization for a three-level four-leg indirect matrix converter is presented. Unbalanced voltages can be extremely dangerous, especially for motors and other inductive equipment. Unbalanced voltages can have a detrimental effect on equipment and the power system, which is exacerbated by the fact that a small phase voltage imbalance can result in a disproportionately large phase current imbalance. The robustness test is carried out by considering balance and unbalanced input voltages. The proposed control predicts the behavior of the load current and the instantaneous reactive power for every possible 96 switching states. Subsequently, it selects the optimum switching state which fulfils the objectives of the control without the need of modulators. The cost function has been adequately modified to consider the asymmetrical aspect of the input voltage. Experimental validation using a laboratory prototype was conducted by using FPGA under a wide range of input voltage unbalance. The experimental results show high fidelity load current reference tracking while maintaining relatively low instantaneous reactive power during the transient and steady-state condition. The percentage of reactive power after setting the optimal weighting factor, the average reactive power was found to reduce to approximately 10-20%.

Reactive power planning with the help of multi-objective genetic algorithm and flexible AC transmission systems devices

In this paper power quality of 3-bus solar-based hybrid system has been presented (where one or more than one distribution generator unit is connected to the grid). The injection of solar power into grid-connected systems creates power quality problems such as current consistency, electrical fluctuations, and inefficient power demand. A power quality control strategy based on a real-time self-regulation method for autonomous microgrid operation has been presented. In this paper solar farm design and satisfactory performance tests such as PV-static synchronous compensator (STATCOM) to improve the power quality of grid-based systems have been presented using the MATLAB/Simulink environment. Pulse width modulator (PWM) with proportional-integral derivative (PID) controller used for frequency control, reactive var compensation is used to control voltage profile. Multi-objective genetic algorithm (MOGA) for reactive power planning (RPP) with the objective of reactive power minimization is introduced. The optimization variables are generator voltage, transformer tap changer, and various operational constraints.

Reactive power planning with the help of multi-objective genetic algorithm and flexible AC transmission systems devices

In this paper power quality of 3-bus solar-based hybrid system has been presented (where one or more than one distribution generator unit is connected to the grid). The injection of solar power into grid-connected systems creates power quality problems such as current consistency, electrical fluctuations, and inefficient power demand. A power quality control strategy based on a real-time self-regulation method for autonomous microgrid operation has been presented. In this paper solar farm design and satisfactory performance tests such as PV-static synchronous compensator (STATCOM) to improve the power quality of grid-based systems have been presented using the MATLAB/Simulink environment. Pulse width modulator (PWM) with proportional-integral derivative (PID) controller used for frequency control, reactive var compensation is used to control voltage profile. Multi-objective genetic algorithm (MOGA) for reactive power planning (RPP) with the objective of reactive power minimization is introduced. The optimization variables are generator voltage, transformer tap changer, and various operational constraints.

Reactive Power Minimization for Modular Multi-Active-Bridge Converter With Whole Operating Range

Multi-port power electronic transformers (PET) are widely used in modern power systems to facilitate flexible interconnection between various AC or DC buses, power sources, and loads. However, due to the wide range of “source-load-storage” operating points, achieving efficient operation of the isolated DC-DC converter in the PET can be challenging. This paper focuses on the modular multi-active bridge (MMAB) converter in the PET, and proposes an optimization modulation scheme based on reactive power minimization (RPM) to improve efficiency. The RPM scheme utilizes a simple reactive power open-loop and active power closed-loop control structure that can be modulated online without the use of look-up tables. Importantly, this generalized method not only significantly improves efficiency, but can also be extended to any number of ports. Finally, experimental results are presented to validate the theoretical analysis and effectiveness of the RPM scheme.

Non‐linear multivariable permanent magnet synchronous machine control: A robust non‐linear generalized predictive controller approach

AbstractPermanent magnet synchronous motors (PMSM) have become prevalent in industry and play an essential role in managing industrial processes, automation systems, and renewable energy sources due to their superior efficiency, torque, and power density. However, because it operates like a non‐linear system with quick dynamics, variable parameters during operation, and unknown disturbances, PMSM presents challenges for machine control. Non‐linear controls are required to account for the non‐linearities of the permanent magnet synchronous machine. Recently, predictive control techniques for non‐linear multi‐variable systems have gained popularity. In this work, a novel approach to robust non‐linear generalized predictive control (RNGPC) has been developed for PMSM, with the aim of tracking the reference speed while maintaining minimum reactive power, robustness to external disturbances, and parameter uncertainties. A new finite horizon cost function is integrated, with an integral action introduced in the control law. The main advantage of this technique is that it does not require the measurement and observation of external disturbance as well as parametric uncertainties. The control strategy method has been tested in the MATLAB/Simulink environment with various operating conditions. The results showed good robustness against parameter changes and ensured fast convergence.

Dual-Phase-Shift Control Strategy With Switch-Controlled Capacitor for Overall Efficiency Optimization in Wireless Power Transfer System

In this paper, a dual-phase-shift control strategy combining with a switch-controlled capacitor (SCC) is proposed to realize efficiency maximization while realizing zero voltage switching (ZVS) for a LCC-LCC compensated wireless power transfer (WPT) system. The dual-phase-shift control is employed with a semi-active rectifier (SAR) to reduce the current stress in the resonant network. To realize accurate ZVS operation, both the SCC control angle and the SAR phase-shift angle are used as the control variables. First, the conditions of ZVS operation and circulating reactive power minimization are derived based on the time-domain model. Then, the power losses in the resonant network, inverter and semi-active rectifier are analyzed and optimized under the constant voltage output. An optimal control strategy is further proposed to maintain the constant voltage output while maximizing overall system efficiency. It is worth mentioning that the proposed control strategy allows the decoupling of the ZVS control and the power regulation. Finally, the performance of the proposed control strategy is examined based on a 6.6-kW WPT prototype. The results show that all switches realize ZVS operation within the entire power range with a peak system efficiency of 95.1%, which exhibits a good agreement with the theoretical analysis.

Provision of reactive power services by energy communities in MV distribution networks

The paper presents a procedure for the optimal operation of a community of prosumers connected to a medium voltage distribution network equipped with generation and storage units that considers the penalization for low power factor operation, the exploitation of direct exchanges of both active and reactive power between the prosumers and the provision of reactive power services by the community to the local distribution system operator and the transmission system operator. The proposed procedure calculates the maximum and minimum reactive power deviations that each community participant can provide with respect to the reference profile. A deterministic day-ahead scheduling problem is considered assuming the forecast of load and photovoltaic production known without uncertainties. The formulation of the optimization problems and the solution computational requirements are suitable for the inclusion in a stochastic approach. The effectiveness of the approach is supported by numerical simulations of the daily scheduling for different test cases.

Online Reactive Power Minimization and Soft Switching Algorithm for Triple-Phase-Shift Modulated Dual Active Bridge Converter

In a dc microgrid, a bidirectional dc–dc converter is an essential link between voltage bus and energy storage system (ESS). When galvanic isolation and high efficiency are required, dual active bridge (DAB) converter is preferred. Due to the instability of renewable energy sources, the DAB converter may transmit high or low power to ESS. To improve the efficiency across wide power range, this article proposes a reactive power minimization and soft switching optimization algorithm that combines the augmented Lagrangian method and triple-phase-shift (TPS) modulation. Unlike an offline algorithm with look-up table, the proposed algorithm can compute phase-shift-angle online, avoiding a large database for various working conditions. A prototype with an 800 W rated power is built, and the efficiency test results validate the efficiency improvement over other TPS-based algorithms. Furthermore, a current regulation experiment demonstrates that the proposed algorithm is suitable for ESS charging, which must deal with varying output voltage and power demand.

Voltage stability assessment using PMUs and STATCOM

<p class="Abstract">Since the previous few decades, researchers and utilities have been extremely concerned about voltage instability because to the numerous instances of system blackouts caused by voltage instability that have been recorded in various regions of the world. With the development of synchro phasor technology, it appears conceivable to track and manage the system's voltage stability in real time. This study suggests using phasor measuring units (PMUs) placed strategically to monitor voltage stability margin online and to regulate it using a static synchronous compensator (STATCOM). According to the minimum reactive and real power loanability for the most of the line outages, STATCOM has been installed at the critical bus. Based on the difference between the bus voltage and its reference value, STATCOM supplies reactive power into the bus. PMU measurements are used to determine bus voltages at regular intervals, and reactive power is then added to the bus online as necessary. The increased voltage stability margin brought on by STATCOM injecting reactive power is continuously checked. Based on simulations performed on the IEEE 14-bus system and the New England 39-bus system, the effectiveness of the suggested approach for online monitoring and management of voltage stability margin (VSM) has been proven.</p>

Influence of power oscillation damping assets reactive power capacity on damping low-frequency power system oscillations

Over the past ten years, the paradigm has shifted from conventional power generation to renewable generation. Large integration of these renewable energy sources (RES) into the power system poses challenges to system operators, leading them to put stringent requirements for their grid connection. Displacement of synchronous generators by RES reduces system inertia and consequently decreases the system damping capability of electromechanical oscillations. Poorly damped interarea oscillations reduce the transmission line's capacities and may damage power system components. Hence, future grid codes will require wind and solar power plants to provide damping to the system. Several papers have proposed adding an auxiliary damping controller to the wind turbine control algorithm to damp the low-frequency oscillations (LFOs) by modulating active or reactive power. However, these studies have not mentioned if small power plants can damp LFOs in a multimachine system. Therefore, this paper investigates the influence of reactive power capacity on the damping of LFOs and its effects on optimal controller parameters using a simplified SVC model connected at the midpoint of the tie line of a two-area test system. A local feedback signal is selected as the input signal to the SVC damping controller. Controller parameters are optimized using the particle swarm optimization algorithm. Time-domain simulations performed in PowerFactory software demonstrate the damping behavior of the controller at different SVC ratings. The results show a minimum reactive power capacity is required for effective damping of power system oscillations.

Optimal reactive power control for dual‐active‐bridge converter using improved dual‐phase‐shift modulation strategy for electric vehicle application

AbstractDual active bridge (DAB) based DC‐DC converters are in high demand for offering quick charging capacity to Electric vehicles (EVs). The conventional technique for DAB is based on single‐phase‐shift (SPS), though it provides simple control but suffers from high peaking in the inductor current under varying charging rates for EV and dc‐link voltage ratio. In this paper, initially the expression for optimal reactive power flow into DAB converter under SPS and dual phase‐shift (DPS) control techniques are thoroughly examined. Based on the analytical analysis, an improved dual‐phase‐shift modulation (IDPSM) method for real and reactive power control through a DAB converter is proposed for varying charging rates of an EV and dc‐link voltage ratio. The proposed IDPSM control technique is implemented using the inverse perturb and observe (IPO) method that provides optimum inner phase‐shift between the legs of the H‐bridge to track minimum reactive power or back power flow into the system. This method automatically adjusts the inner and outer phase shift ratios under different loading conditions. Further, the proposed IDPSM scheme enhances the range of ZVS operation even under light load conditions, which is lacking with the conventional control techniques. The Lyapunov theory used to determine the stability of the DAB DC/DC converter. To validate the proposed control scheme, a detailed simulation is carried out using MATLAB/Simulink with a 2 kW system under varying charging rates of an EV. Further, to support the effectiveness of the proposed scheme, a comparison with different phase shift modulation schemes is also presented. Finally, an experimental prototype for DAB is developed to confirm the feasibility of the control technique.

Design Methodology of Bidirectional Resonant CLLC Charger for Wide Voltage Range Based on Parameter Equivalent and Time Domain Model

The bidirectional CLLC resonant converter has distinguished potential in battery chargers and energy storage systems for its advantages in soft switching and bidirectional power flow capability. However, traditional CLLC converters generally adopt symmetrical design to maintain bidirectional symmetrical characteristics, which means the secondary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network is designed to be equal to the primary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network after reflection. The symmetrical design is only suitable for voltage grade matching scenarios where a wide voltage range is not required, such as CLLC-type dc transformers. Whereas in the field of bidirectional chargers, due to the wide voltage range of battery, there are significant differences in the characteristics required between charging and discharging mode, which makes symmetrical design no longer applicable. To cope with this issue, this paper proposes a novel design methodology of CLLC based on parameter equivalent and time domain model. With the parameter equivalent principle, the CLLC resonant tank with arbitrary parameters is investigated to satisfy the requirements of wide voltage range for bidirectional charger application. Compared with the symmetrical design, the proposed method can meet the requirements of bidirectional gain within preset frequency range and guarantee the achievement of zero-voltage switching under required load conditions with the minimum reactive power. In addition, the area product capacity of the magnetic part of the CLLC resonant tank is minimized based on the parameter equivalent principle. Finally, experiments have been performed on a 1 kW prototype to confirm the validity and feasibility of the proposed design methodology.

Collaborative Control Framework of Multiple Electric Springs for Frequency Stabilization and Distribution Loss Reduction in Microgrids

Electric springs with capacitive energy storage (ES-1) have been proposed as a continuous demand-side management (DSM) technology to address the intermittency of renewables in power systems. The enabled smart load technology distinguishes itself from other DSM technologies with the unique function of achieving active power manipulation via reactive power control. However, the embedded coupled relationship between the active and reactive powers of the smart load usually results in the contradiction between grid frequency regulation and economic power flow with the conventional control scheme. To address this issue, a centralized control framework is proposed in this paper to achieve the collaborative operation of multiple ES-1s for frequency stabilization and economic power flow in microgrids. The proposed control framework exploits the power variations of the deferrable loads and enables the minimum reactive power flows in the microgrids, which leads to reduced storage requirement and minimum distribution loss. It is the first control framework to address the active and reactive power coupling issue of the ES-1 based smart loads, leading to the independent control of system frequency and optimal reactive power reallocation. The generalized and practical steady-state model of the ES-1 based smart load is investigated. The formulation for achieving the dual-objective optimization is established. Case studies based on experiments and simulations of a 110 V AC microgrid are performed to verify the effectiveness of the proposed control framework.

Multi-Resonating-Compensation for Multi-Channel Multi-Pickup Wireless Power Transfer

This article proposes and implements a multi-resonating-compensation (MRC)-based multi-channel multi-pickup (MCMP) wireless power transfer (WPT) system. The proposed compensation topology holds triple or more resonating points, which can establish multiple transmission channels with minimum reactive power losses without utilizing multiple transmitters or multiple inverters. The calculation complexity for MRC is as simple as that for dual-resonating-compensation, which costs fewer computing resources and hence facilitates the realization. In addition, this article adopts the amplitude overlay modulation method to arbitrarily distribute the desired output power under different transmission channels. Theoretical analysis, design procedure, and verification results are given to verify the feasibility and flexibility of the proposed MRC-based MCMP WPT system.