Reactive Power Supply Research Articles

Achieving Optimal Reactive Power Compensation in Distribution Grids by Using Industrial Compensation Systems

This paper presents a method for integrating industrial consumers owning compensation systems as alternative reactive power sources into grid operating processes. In remuneration, they receive a market-based provision of reactive power. The aim is to analyze the potential of reactive power compensation systems of industrial companies connected to medium-voltage (10 kV–30 kV) AC grids in order to increase the reactive power ability of distribution grids. Measurement methods and reactive power potential results of six industrial companies are presented to characterize the amount and temporal availability of their reactive power potential. The presented approach for using the decentralized reactive power potential is a centralized reactive power control method and is based on optimal power flow (OPF) calculations. An optimization algorithm based on linear programming is used to coordinate a reactive power retrieval tuned to the actual demand. The influencing quantities are the current grid status (voltage and load flow capacity reserves at grid nodes and power lines) and the current reactive power potential of the reactive power sources. The compensation impact of six measured industrial companies on an exemplary medium-voltage grid is shown by an application example.

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>

Power supply reactive power factor control as a function of consumer power and losses in transformers

The system of automatic control of the reactive power factor of the enterprise's power supply system is considered, in which one part of the transformer substations is equipped with adjustable capacitor units, and the second is not. Its advantage in comparison with the power factor control system is shown, firstly, lower requirements for its error and, secondly, the calculation of the consumer with the supplier for electricity is made taking into account the ratio of reactive energy to active energy. An estimate of the error of regulation of the reactive power factor on the higher voltage side of the transformers of the main step-down substation, where settlement meters are installed, is given, with stabilization of the reactive power factor on the low voltage side of these transformers. The synthesis of the system of automatic control of the reactive power factor, built as a function of the power of consumers and power losses in transformers, and the estimation of its error are considered. The proposed control system is intended for power supply systems with a combined load, the use of which will allow the consumer to avoid penalty coefficients to the tariff for active electricity, and ultimately reduce losses in the transmission of electricity and increase the transmission capacity of the electrical network.

Analysis of Electric Vehicles Battery Ageing Associated to Smart Charging Controls

EVs smart charging controls emerge as a possibility to overcome voltage quality issues caused by the increasing penetration of EVs in LV networks. However, solving voltage issues implies that EV chargers must deal with reactive power provision, inducing an extra AC ripple in the battery that influences the EV battery lifespan. Four decentralized smart charging controls have been analyzed, modelled and implemented together with a commercial EV charger model and EV battery model that includes both runtime and ageing behavior. Results show that solving voltage issues with EV smart charging controls can lead to a temperature increment in the battery that influences the EV battery lifespan. Nevertheless, this situation can be effectively overcome by minor modifications in the EV charger or in the EV battery cooling system.

VOLTAGE REGULATION IN RURAL NETWORKS WITH DISTRIBUTED GENERATION

The increase in distributed generation (DG) interferes with the energy distribution system, which may present low voltages due to voltage drops and high voltages due to the insertion of distributed generation, resulting from renewable energy sources in rural areas. These voltage levels must be controlled to comply with the limits imposed by the distribution rules and procedures (PRODIST). This study aims to evaluate the voltage rise caused by DG, simulating three DG insertion scenarios, as well as simulate strategies to correct these voltage levels, such as the limitation of the active power supply, the reactive supply by the consumer and the utility, and the installation of on-load tap changers. The simulations were performed using the MATLAB® program, more specifically the PSAT toolbox. Correction techniques were simulated using the active power supply limitation method, the reactive power supply method by consumers, and the voltage regulator process once the voltage rise effect was identified. The first two proved to be ineffective in this case, while the last one meets the voltage levels required by the National Electric Energy Agency.

Power Quality Improvement using Solar Fed Multilevel Inverter Based STATCOM

The major goal about suggested technique is to use a PSO-based proportional-integral (PI) controller towards enhance power quality performance about three-phase grid-connected inverter system. An approach like aforementioned tries to stabilize output current & voltage, lower harmonics, & lessen DC link input voltage fluctuation. Through reducing error about voltage regulator & current controller schemes in inverter system, particle swarm optimization (PSO) technique was used towards adjust PI controller settings. When compared to conventional approach, simulation results show certain optimal parameters PI controller created among PSO produces better performance index results. According towards various research, reactive power supply can only modestly reduce voltage sags while totally mitigating harmonics using specialized power devices. Effective & dependable use about PV solar farm inverters as STATCOMs is required towards guarantee certain generating units stay connected towards grid during voltage sags & towards enhance system performance during abnormal circumstances.

Research on induction generators for isolated rural applications: State of art and experimental demonstration

-Asynchronous machines/Induction machines are one of the leading machines in the electrical sector and which are well suitable for the motoring and generating applications of a few kilowatts rating to megawatt ratings. Research on induction machines for generating applications is drawing attention among the researchers due to its low cost, rugged construction, brushless arrangement and all. The operation of induction generator (IG) is quite interesting and which is different for grid and off-grid mode of operation. The IG for the off-grid applications (so called self-excited induction generator, SEIG) requires an additional reactive power supply for the successful build-up of voltage and as well as for supplying the electric loads. On the other hand, load power balance is also one the challenges since off-grid systems are directly connected to the loads. In this context, many researches have been reported the different approaches and techniques for the successful and economical operation of IG for small scale off-grid power generation. In this paper, an exclusive analytical study is presented on the excitation requirement and load balance phenomena of self-excited induction generator (SEIG). Further, a basic experimental setup of renewable energy source driven SEIG system and its operation for the electric power generation is demonstrated and the same is simulated by using MATLAB/Simulink.

Impact of cyber‐attack on coordinated voltage control in low voltage grids

AbstractPower grid is facing several challenges such as voltage violation, power losses, and power quality issues due to the high integration of renewable energy sources such as solar and wind. One of the several strategies to overcome the voltage violation problem is the provision of reactive power from wind and solar power plants. Local controller of these plants coordinates with the controller to generate the reactive power. The coordinated controller performs its function based on the information obtained from the whole grid via communication network. Communication network infrastructure has high responsibility to ensure secure and stable services in order to provide reliable voltage control in distribution grids (DGs). Unstable or insecure communication networks can lead to several problems in the power system, such as increased power losses and in worse case blackouts. Therefore, this paper analyses the impact of cyber‐attacks on the voltage quality control supported by the reactive power generation of PV plants in DGs. Two cyber‐attack scenarios are demonstrated via a voltage coordination scenario based on a real distribution grid in Northern Denmark. Simulations are done in a Simulink model of Thy Mors Energi Grid, Denmark. A cyber control block is implemented within the coordinated controller in order to mitigate the effect of cyber‐attack. Experimental results show that it is possible to detect and mitigate a cyber‐attack such as denial of service and integrity attack before sending a control signal thus contributing towards a secure, stable, and resilient power grid.

Day-ahead local flexibility market for active and reactive power with linearized network constraints

This paper presents a Day-Ahead Local Flexibility Market in the Distribution Network cleared using a novel Successive Linear Programming algorithm for Optimal Power Flow in the Distribution Network. The proposed algorithm is shown to be robust and produce high quality, AC feasible solutions with satisfactory solution speed. The efficiency of the proposed algorithm is validated via its application in various distribution networks and under different loading scenarios. The proposed Flexibility Market encompasses flexibility products for upward and downward active energy as well as service products for the provision of reactive power. The efficiency of the proposed Flexibility Market in solving operational issues of the distribution network is demonstrated via a case-study.

Design and evaluation of a multi-level reactive power market

The shift from conventional power plants on transmission level to distributed energy resources in the distribution grids requires procedures to enable efficient and economic reactive power exchange across different voltage levels. In this paper, we propose a multi-level reactive power market that enables reactive power provision from distributed energy resources to higher voltage levels. Each grid operator operates a local reactive power market and offers local reactive power potential, as an intermediary, to superordinate grid operators by passing on its aggregated cost curve and flexibility range. As a result, there is a low requirement of communication between the market participants and each grid operator is free to choose its local market rules as well as the optimization algorithm used. First results from a case study show that our decentralized market approach can realize an economically efficient multi-level reactive power provision that is close to a centrally computed optimal solution, without violating local grid constraints.

Distributed secondary controller to ensure proportional sharing of reactive power in AC microgrid

In an ac microgrid, reactive power sharing accuracy is affected due to unequal values of interconnecting cable impedances. To resolve this issue, secondary controllers are used to compensate the effect of cable impedances. Various types of secondary controllers are suggested in the literature which includes linear proportional plus integral (PI) controllers to minimize the difference in reactive power sharing created by conventional E−Q droop law. The reference value of the PI controller is the average value of reactive powers supplied by the sources. When the PI controller is used to minimize the difference between the actual and reference value of reactive power, the difference between the algebraic sum of reactive powers supplied by the sources and the reactive powers demanded by the loads has a nonzero value. Therefore, the performance of these controllers becomes poor in the case of ac microgrid having sources of unequal ratings. To resolve this issue, a proportional reactive power-sharing (PRPS) controller-based distributed secondary controller is proposed in this paper. The PRPS controller modifies the droop gain of the E−Q droop control loop of each source in such a way that each source supplies reactive power equal to its proportional value of reactive power. The proportional value of reactive power supplied by each source is the power when the equivalent output impedance of all sources as seen by the loads are identical. The key advantage offered by the proposed controller is the accurate reactive power-sharing in the case of ac microgrid having sources of unequal ratings. The proposed controller ensures zero value of the difference between the algebraic sum of reactive powers supplied by the sources and the reactive powers demanded by the loads. This ensures accurate sharing of reactive power among the sources. The validation of the proposed controller is carried out for islanded mode of operation of ac microgrid. Further, the proposed controller requires of low bandwidth communication for its implementation. The effect of the proposed controller on the stability of the system is demonstrated using reduced order small-signal model. The effect of communication delay on the performance of the system is analyzed with the help of roots locus plots. To validate the efficacy of the proposed controller, detailed simulation studies are carried out in Matlab/Simulink.

Over-Voltage Regulation of Distribution Networks by Coordinated Operation of PV Inverters and Demand Side Management Program

The increase of Photovoltaics (PV) units’ penetration factor in the power grids might create overvoltage over the network buses. The active power curtailment (APC) and the reactive power provision methods use inverters to regulate their output active and reactive powers for high PV-penetrated grids. However, the mentioned solutions would reduce the maximum injectable active solar power to the grid, not financially acceptable. Continuous employment of the maximum apparent power capacity of the inverters will practically decrease the inverters’ lifetime, require special design considerations, and make the control system complex. To overcome those issues, a feasible solution would be increasing the load consumption within the time intervals in which the grid faces the over-voltage problem. In this research, the demand response (DR) program is employed. Load shifting techniques are exerted to move a portion of loads from the peak hours to when further power consumption is expected for voltage level reduction purposes. A new long-term strategy based on the coordinated operation of the PV inverters and load shifting techniques is proposed to resolve the over-voltage issue in the network. Consequently, the PV inverter’s contribution to voltage control is reduced; a new sight of DR potential is implemented, and also the under-voltage level in peak times is decreased significantly.

An intelligent capacity management system for interface converter in AC-DC hybrid microgrids

An interface converter (IC) is used in an AC-DC hybrid microgrid (HMG) and its main tasks are frequency regulation in the AC side, adjusting the DC voltage, and controlling the power flow between AC/DC sides based on the droop control method. The IC should be capable of providing ancillary services such as reactive power supply and compensation of unbalanced and harmonic components in the AC side. However, the use of the IC to provide ancillary services occupies its capacity, which may interfere with the main tasks of the IC. In addition, it is shown in this paper that in unbalanced conditions, the effective power capacity of the IC is reduced by considering the current limit of the converter. In this case, the converter may not be able to perform the main task and provide all the necessary ancillary services at the same time, otherwise, it may be exposed to an overcurrent condition. Therefore, an efficient strategy is needed to manage the IC converter capacity to facilitate optimal use of the entire IC capacity even in unbalanced conditions. Given this challenge, this paper proposes an intelligent strategy for managing the IC capacity, which prioritizes the realization of the main task and the provision of ancillary services. The proposed strategy is evaluated, and its effectiveness is proven by simulation results in Matlab/Simulink.

Research on Weak Node Power Flow Calculation and Voltage and Reactive Power Compensation of Off Grid Microgrid

The voltage stability control of off grid microgrid is the key and core issue of power grid stability. Aiming at the problem of voltage stability control of off grid microgrid with unbalanced nodes, the Newton Raphson homotopy algorithm is proposed to calculate the power flow, estimate the reactive power margin of each load node, and adopt reactive power supply droop compensation control for weak nodes to improve the voltage stability level. The simulation verifies the effectiveness of this method.

Grid-connected photovoltaic system to mitigate momentary voltage dip based on the balance between the active and reactive powers

With a great potential yet to be explored in Brazil, the grid-connected photovoltaic system, besides supplying the active power, can also contribute to improve the voltage level grid providing reactive power. Therefore, this work proposes to use a Grid-Connected Photovoltaic System (GCPVS) equipped with a control that uses the automatic voltage regulator (AVR) to balance the injection of the active and reactive powers, thus softening the short-duration voltage variation, more specifically the momentary voltage dip. For this purpose, the GCPVS was connected in part of a real distribution grid that attend the block 1106 South of Palmas city, state of Tocantins, northern region of Brazil. It is shown that the active and reactive power delivered to the grid can be controlled to help the power quality of the main grid during a disturbance. During a short-circuit situation, the active power is reduced, freeing up space from the inverter capacity for maximum supply of reactive power, in this way, helping the main grid to return to an adequate voltage level. The simulation results show that such voltage profile improvement is possible. Therefore, they confirm that photovoltaic systems, even though considered small, can also provide ancillary services to the low voltage distribution grid during abnormal conditions, adding to the actions normally performed by conventional power plants

Fault-Current Injection Strategies of Inverter-Based Generation for Fast Voltage Recovery

As the inverter-based generation replaces the conventional synchronous generators, it may also need to fill in the missing ancillary service support. One of these ancillary services is dynamic reactive power provision and voltage control. This paper analyzes optimal strategy of reactive and active fault-current support of the inverter-based generation leading to fast voltage recovery of the system. For the purpose of the analysis, new ramping active current controller able to emulate different behavior of active current injection is proposed. By optimizing its parameters for different case studies of the system, the conclusions about optimal behavior of the inverter based generation with respect to system parameters and operating conditions are drawn. It is observed that the optimal combination of active and reactive fault-current is the most sensitive to the dynamic load component penetration levels in the system. With the increasing penetration levels, the significance of active fault-current injection increases. The results show that with higher penetration levels of dynamic load component in the heavy load areas, the ramping down of the inverter-based generation active fault-current results in slower voltage recovery of the system. Following this conclusion, a recommendation on update of current European grid codes is proposed.

Collaborative Management of Multi-Type Energy for Optimal Control of Voltage and Loss of Distribution Systems with DGs and SVCs

Aiming at the deficiencies and shortcomings of traditional reactive power compensation devices in controlling and improving voltage quality, a bilevel programming model for the coordinated optimal allocation of active and reactive power capacity of photovoltaic power generation systems, wind-driven generators, shunt capacitors and static var compensators is established based on chance-constrained programming. In the optimization model, the randomness and intermittence of the output power of the distributed generation and the reactive power regulation ability of the distributed generation are considered. The correlation of illumination, wind speed and load fluctuation is considered and affected by seasonal variation. Latin hypercube sampling method is used to deal with the correlation of random variables. Monte Carlo probabilistic power flow method is used to calculate the power flow of distribution network with intermittent distributed generation systems. The location and capacity of active and reactive power sources in outer programming are optimized by adaptive artificial fish swarm algorithm, and the allocation scheme of active and reactive power sources determined by outer programming is optimized by inner adaptive artificial fish swarm algorithm. The two-layer nested adaptive artificial fish swarm algorithm is used to solve the optimal allocation problem constructed in this paper, and the optimal allocation scheme of active and reactive power supply capacity is determined. Taking IEEE33 distribution system as an example, the feasibility and applicability of the proposed model and algorithm are verified.

Extension of the Output Speed Range of an Open-End Winding IPMSM Using an Induced Voltage-Limiting Ellipse

This study proposes a control method for a dual inverter to extend the output speed range of an interior permanent magnet synchronous motor with open-ended windings. The secondary inverter with a floating capacitor for the dual inverter supplies reactive power to the motor. In the proposed method, the reactive power required to drive the motor is calculated using an inductive voltage-limiting ellipse, and the d-axis current reference value and output voltage of the secondary inverter are determined. In the proposed control method, the primary inverter of the dual inverter supplies the effective power to the motor to expand the output speed range. The experimental results indicate that the output speed range is significantly improved and the constant torque region is expanded by approximately 41% compared with that in the conventional method.

A new configuration of grid‐connected photovoltaic‐based multifunctional power converter for single‐phase system

SummaryThe paper presents a new configuration of a grid‐connected converter centering on the needs of voltage‐sensitive nonlinear loads with source current compensation and photovoltaic (PV) power injection capability. The presented system consists of a six‐switch converter, which gives dual single‐phase output. The first output is connected in shunt near the source end to inject PV‐generated power along with the supply of load current harmonics and reactive power. The second output forms a series connection near the load end to protect the voltage‐sensitive nonlinear load from supply‐side voltage variations such as sags and harmonics. The system operation is validated through MATLAB simulation and real‐time simulation using Opal‐RT (OP4510) under different dynamic conditions such as variations in supply voltage, variation in solar irradiance, and load variation which is typically encountered in a modern distribution network. The performance of the proposed multifunctional converter is found to be satisfactory in all operating conditions by meeting the desired PV power injections along with the compensation of sensitive nonlinear load terminal voltage and source current harmonic issues within the standard allowable limit specified by IEEE.

Modeling of Photovoltaic Inverter Losses for Reactive Power Provision

In addition to their main functionality of converting DC input power to AC output power, today’s photovoltaic inverters are generally required to be capable of providing reactive power. While there are well-established mathematical models that use the correlation between inverter losses and the transmitted active power to estimate inverter efficiency for any given active power operating point, the additional losses in the inverter due to the supply of reactive power are less well studied. In this work, the conversion efficiencies of three different photovoltaic inverters were measured for various active power and reactive power setpoints. Based on these measurements, two mathematical models are proposed to represent the conversion losses as a function of active and reactive output power. One model is of empirical nature and expands preexisting models to include terms that take the reactive power into consideration. The other model takes the dominant loss mechanisms in the conversion stage of inverters into account and considers the effect of reactive power provision on them. Both models were compared with a model variant proposed in literature. They are shown to perform with high accuracy over the entire operating range, while requiring only a small number of known efficiency values for parametrization. There are several fields of application for these new models: They allow photovoltaic park operators to precisely estimate the individual losses of a solar power plant that feeds reactive power into the grid. For grid operators, they enable a comparative loss analysis for different reactive power sources.