Reactive Current Components Research Articles

Currents’-Physical-Component-Based Reactive Power Compensation Optimization in Three-Phase, Four-Wire Systems

In this paper, we aim to address the limited capacity of compensation devices by enhancing their utilization rate by applying the currents’ physical component (CPC) theory for reactive power optimization in three-phase four-wire systems. When reactive currents cannot be fully compensated for, we propose using CPC theory to generate reference currents for the compensation devices. Weight coefficients associated with different reactive current components are introduced, enabling flexible combinations of these independent current components. The maximum output amplitude of the three-phase current from the compensation device serves as a constraint condition, allowing for the calculation of reference currents under various compensation targets. Additionally, a reactive current optimization compensation scheme focusing on loss reduction is selected. The simulated annealing–particle swarm optimization (SA-PSO) hybrid algorithm is employed to solve the optimization mathematical model. The discussed calculations, current waveforms, and voltage waveforms are generated using the constructed mathematical model and then used for a theoretical explanation. The simulation verifies the feasibility of the proposed method.

Power quality enhancement of dual stage three phase grid integrated SPV system using sequential neural network-based algorithm

In this paper, a single-layer sequential neural network (SNN) control algorithm has been proposed for managing the power quality (PQ) in the double-stage three-phase grid-integrated solar photovoltaic (SPV) system. The proposed algorithm efficiently extracts the active and reactive fundamental components of the load current, with a higher convergence rate. The extracted reference currents are matched with the sensed source currents to generate gating pulses for the voltage source converter (VSC). To handle power quality issues in distribution networks such as harmonic imbalances, voltage fluctuations (sags/swells), and the need for active and reactive power compensation, the VSC is controlled very precisely. The control algorithm consists of two-stage processes. In the initial stage, the incremental conductance (INC) based DC-DC converter has been incorporated to extract the peak power from the SPV system. In the later stage SNN-based algorithm is used to control the VSC. A 100 KW solar PV system connected to the utility grid has been designed by using a three-leg VSC in the MATLAB/Simulink environment. The system performance has been evaluated by comparing it to existing techniques. The simulation results comfortably meet the requirements of the IEEE-519–2014 and IEEE 1547–2003 standards for utility grid connection.

Smart meter for the estimation of power quality indices based on second-order generalized integrator.

With the increasing integration of renewable energy sources and nonlinear loads in the grid, it is necessary to compute energy and power quality parameters for monitoring as well as analyzing the power consumption indices (PCI) and power quality indices (PQI). Smart meters (SMs) can monitor the PCI and PQI at the consumer end. SM necessitates the measurement of voltage and current, which can be further processed by an algorithm for estimating different parameters through signal processing and arithmetic operations. This paper proposes the combined dual second-order generalized integrator (SOGI) and proportionate least mean square (PLMS) algorithm-based PCI and PQI estimation for smart metering. Dual SOGIs individually process voltage and current signals to extract the respective fundamental in-phase and quadrature components. To account the variations in grid frequency, the SOGI processing the voltage also incorporates a frequency locked loop. This prevents performance degradation on account of frequency variations. The PLMS algorithm then process the output of SOGI processing the current for extracting the fundamental active and reactive components of current. Moreover, the PLMS algorithm results in further attenuation of harmonics. Also, only two separate values of learning rate are required, which is easy to tune for better dynamic performance. With only two quantities to be determined, this results in largely reduced computation. These computations facilitate in PCI and PQI computations. The proposed smart meter calculates peak value, RMS value, and phase angle for the fundamental components of voltage and current for each phase. Additionally, it assesses fundamental power factor, total harmonic distortion (THD), distortion factor, true power factor, active power, reactive power, and apparent power for each phase. The performance validation of the proposed combined dual-SOGI-PLMS algorithm-based PCI and PQI estimation for smart metering is carried out in MATLAB/SIMULINK for fifteen different operating scenarios. Further, the real-time implementation of the proposed methodology is carried out on dSPACE MicroLab Box 1202. Comparative analysis is also presented, which reveals the computational simplicity and other merits of the proposed scheme over the earlier reported scheme.

Determining optimal location and size of PEV fast-charging stations in coupled transportation and power distribution networks considering power loss and traffic congestion

The placement and sizing of plug-in electric vehicle fast-charging stations (PEVF-CS) can significantly influence traffic flow in urban transportation networks. Consequently, suboptimal choices regarding the location and size of PEVF-CSs may lead to increasing travel time and traffic congestion in transportation networks and deterioration of the power quality indexes in power distribution networks. Also, each PEVF-CS is equipped with power electronic converters that can be used as power line conditioners and active filters to compensate for the reactive power and current harmonic components due to nonlinear loads and reduce the power loss. Thus, PEVF-CSs can improve the voltage profile, decrease voltage THD, and reduce the power loss in power distribution networks. Accordingly, this paper develops a mixed-integer linear programming model (MILP) to determine the optimal locations and sizes of PEVF-CSs. In addition, the proposed model considers traffic congestion and power quality in the coupled transportation and power distribution networks. The model considers various load profiles and origin-destination demands to address the different operational aspects of transportation and power distribution networks. The main features of the proposed model are 1- road congestion reduction, 2- traveling time reduction, 3- power loss reduction, and 4- power quality improvement. The proposed model is implemented using GAMS software and applied to different-scale test systems in different scenarios. The results show that the proposed method decreases traffic congestion and improves power quality.

CTF-based control technique for power quality enhancement in the SPV system tied to the grid

The solar photovoltaic (SPV) system tied to grid through distribution static compensator (DSTATCOM) is controlled by Character of triangular function (CTF)-based control technique. The reference currents are computed for synchronisation of SPV to the grid. The essential active and reactive components of load current are computed with above mentioned technique and firing pulses for the voltage source converter (VSC) are generated by comparing these currents with grid currents. It requires adders, multipliers and low pass filter blocks so it is a simple and fast technique. The proposed technique is used for harmonic suppression, load balancing and supply reactive power for local load demand. This technique has been tested for steady-state and dynamic conditions for the SPV system with varying nonlinear load in the power factor correction (PFC) mode of DSTATCOM operation. The proposed technique can reduce the grid current harmonics within IEEE standards which are observed in the simulation results.

IMPROVING THE EFFICIENCY OF 6–10 KV POWER GRIDS OF INDUSTRIAL ENTERPRISES THROUGH OPTIMAL REACTIVE POWER CONTROL

"The article deals with improving the efficiency of an industrial power system, which is determined by the level of power losses in its elements. One of the most important methods of increasing the efficiency of power supply systems and distribution networks that ensure the transmission and distribution of electricity is to reduce the amount of electrical energy that is expended in this process. Reducing power losses in electrical grids is achieved by reducing the reactive component of the electric current, i.e., by increasing the cos φ. The Electrical Installation Code recommends, first of all, using the synchronous motors available at the enterprise. It is reasonable to solve the problem of minimizing active power losses in the power grid using the method of mathematical modeling and mathematical programming. The article presents the main features of the criterion programming method for solving a class of problems with a positive degree of difficulty, which is quite well-known in the electric power industry for solving optimization problems. We propose the method of criterion programming to solve the problem of improving the efficiency of the power grid by optimal control of the operation of synchronous motors according to the reactive power mode. "

A variable step size robust normalized least mean absolute third‐based control scheme for a grid‐tied multifunctional photovoltaic system

SummaryThis paper develops a variable step size robust normalized least mean absolute third (VSSRNLMAT)‐based control scheme for a three‐phase grid‐tied multifunctional photovoltaic system (GTMPVS). The GTMPVS delivers PV power to grid‐connected loads and feeds excess power to the grid through a voltage source converter (VSC) when PV power is available. It enhances power quality (PQ) by mitigating current harmonics and compensating for an unbalanced load and reactive power simultaneously. The proposed control scheme accurately extracts the fundamental active and reactive weight components of nonlinear load current. The power exchange at the grid side occurs with balanced and sinusoidal grid currents. During the absence of PV power, the VSC continues its operation as a distribution static compensator (DSTATCOM), thus increasing the effective utilization of the power electronic switches employed in the VSC. The GTMPVS model is created in MATLAB/Simulink. The response of GTMPVS is observed under steady‐state and dynamic operating conditions while feeding power to a nonlinear load. The dynamic operating conditions are created by a change in solar irradiation and an unbalanced nonlinear load. Further, the proposed VSSRNLMAT control scheme is compared with some of the other adaptive filtering‐based control schemes, including least mean square (LMS), least mean fourth (LMF), least mean absolute third (LMAT), and normalized LMAT (NLMAT) in terms of convergence, oscillations, mean square deviation (MSD), computational complexity, and grid current total harmonic distortion (THD). It is found that the VSSRNLMAT control scheme offers THD of grid current as per IEEE‐519 standard. The proposed control scheme is implemented to operate the laboratory‐developed GTMPVS to verify the simulation results.

Power Quality Improvement in Rural Grid Using Adaptive Control Algorithm to Enhance Wind Energy Penetration Levels

The intermittency associated with Wind Energy causes Power Quality (PQ) disturbances, which in turn can limit the penetration levels. These penetration levels are further restricted due to the non-linear (NL) loads and the weakness of the grid (especially in the rural grid). This paper proposes a methodology to enhance wind power penetration levels into the rural grid by mitigating PQ disturbances using a DSTATCOM controlled by Adaptive Least Mean Fourth (ALMF) control. The proposed algorithm computes the active and reactive load current components with the help of updated weights by continuously adapting the changes in grid voltages, wind speed and DC-link voltage to generate reference currents, which are used to generate switching signals for the DSTATCOM. Various case studies establish the effectiveness of the proposed algorithm in MATLAB simulation and experimentally to enhance the wind energy penetration level up to 25% into the rural grid with a short circuit ratio as low as 2.74 in the presence of NL loads.

RL 부하 연동 단상 태양광 발전 시스템의 부하 전류 센서리스 무효 전류 보상기법

The PV (photovoltaic) system can be used with RL loads on the grid side. However, when RL Load is connected, the phase of the grid current and voltage will not match due to the reactive current component. The reactive current generated at this time can be compensated by the inverter. In the case of such a single-phase PV system, a total of two current sensors are used to detect the inverter output current and the RL load current. This paper proposes a compensation technique using one current sensor without using two current sensors in a single-phase photovoltaic power generation system connected with an RL load.

A comprehensive review of control techniques for compensating the fault current in resonant grounded distribution networks: From the perspective of mitigating powerline bushfires

Powerline faults are responsible for major bushfires around the world where arcs provoked from ground faults are common causes for igniting such fires. The grounding techniques (mainly resonant grounding) used in distribution substations and arc suppression devices play a crucial role for compensating fault currents in order to extinguish arcs so that the likelihoods of powerline bushfires are significantly reduced. Though passive arc suppression devices (e.g. Petersen coils) are extensively used for compensating the reactive component of the fault current, the active component of this current is still large enough to ignite the fire in bushfire prone areas for which active arc suppression devices are recently used. These active arc suppression devices incorporate residual current compensation inverters and the full compensation of the fault current rely on the control scheme of these inverters. This paper comprehensively reviews different control schemes that are used for compensating the fault current in resonant grounded power distribution systems. The existing control schemes are discussed in terms of the model used during the controller design process, loop structures, control block diagrams, and performance analysis frameworks (i.e. the type of fault impedances). It is worth mentioning that faults on resonant grounded power distribution networks exhibit the characteristics of high impedance faults and it important to consider this aspect for performance analysis of the control scheme. This paper also covers a brief overview of different grounding techniques used for mitigating fault currents and finally, the challenges with the existing controllers are identified in terms of extinguishing powerline bushfires. The comprehensive review motivates and guides future research activities on developing more efficient fault compensation techniques.

Research on optimization strategy of harmonic suppression and reactive power compensation of photovoltaic multifunctional grid connected inverter

In this paper, a new harmonic suppression and reactive power compensation strategy based on photovoltaic multi-functional grid connected inverter (PVMFGCI) and a three-layer optimization model based on adaptive ant colony algorithm are proposed for optimal control of power quality of grid connected photovoltaic (PV) power generation system. Here, an improved CPT (Conservative Power Theory) current detection method is used to extract harmonic and reactive current components from the load current, and a new PVMFGCI hierarchical optimization model is developed to optimize the power quality at the common connection point (CCP). The proposed three-layer optimization model is an improved form of the two-layer optimization model, which successfully solves the contradiction between the active power grid connection of the PV grid connected inverter and the power quality control. The main objective of the proposed three-layer optimization model is to meet the requirements of active power output of PV power generation, and at the same time, to utilize the remaining capacity of the inverter to control harmonics and compensate reactive power. However, when the remaining capacity of PVMFGCI is sufficient, PVMFGCI can reasonably allocate the remaining capacity through the three-layer optimization model to meet the optimal power quality at the CCP. In this process, the power quality of the microgrid is improved. PVMFGCI provides reactive power compensation, harmonic control and other power quality problems. In addition, when the remaining capacity of PVMFGCI is insufficient, it only needs to maximize the active power and make the harmonic distortion rate and power factor meet the grid connection requirements, which improves the utilization rate of PVMFGCI. The proposed techniques are modeled and the IEEE 33 bus systems are analyzed and their performances are verified experimentally on a developed prototype, in PV output active power variation condition, imbalance loading condition for linear/nonlinear loads, where it has shown a very good performance. The effect of harmonic control and reactive power compensation at each node of the system is obvious.

Coordinated Control of DFIG Converters to Comply with Reactive Current Requirements in Emerging Grid Codes

The doubly-fed induction generator (DFIG) is considered to provide a low-reactance path in the negative-sequence system and naturally comply with requirements on the negative-sequence reactive current in emerging grid codes. This paper shows otherwise and how the control strategy of converters plays a key role in the formation of the active and reactive current components. After investigating the existing control strategies from the perspective of grid code compliance and showing how they fail in addressing emerging requirements on the negative-sequence reactive current, we propose a new coordinated control strategy that complies with reactive current requirements in grid codes in the positive- and negative-sequence systems. The proposed method fully takes advantage of the current and voltage capacities of both the rotor-side converter (RSC) and grid-side converter (GSC), which enables the grid code compliance of the DFIG under unbalanced three-phase voltages due to asymmetrical faults. The mathematical investigations and proposed strategy are validated with detailed simulation models using the Electric Power Research Institute (EPRI) benchmark system. The derived mathematical expressions provide analytical clarifications on the response of the DFIG in the negative-sequence system from the grid perspective.

A Comparison of Inverter Control Modes for Maintaining Voltage Stability During System Contingencies

Inverter-based power sources are increasingly being connected to the power system due to the global drive towards renewable generation. This paper investigates the voltage stability of a power system where a load center is supplied by the grid through a transmission system along with an inverter-based generation located close to the load center. It is also assumed that there is no additional reactive power compensation at the load center and voltage control at Point of Common Coupling (PCC) is done by the inverter. This is challenging as the inverter has an added duty. If the inverter controllers are not designed properly, the inverter could reach its current limit following to contingencies rendering it unable to support the voltage at the PCC. This is due to the fact that once the current limit is reached, the inverter ceases to function as a voltage source. When the voltage at the PCC is not supported, the active power transfer capability of both the inverter and the grid will be reduced. An effective control method is required under such circumstances to handle the active and reactive components of the inverter current. Various strategies exist for controlling the active and reactive components of the inverter current while preserving the current magnitude at the rated value. The necessity of an adequate control strategy to sustain long-term voltage stability following a system contingency is emphasized in this research. This paper further discusses three candidate control strategies and the effectiveness of the reactive current prioritizing approach as a solution for operation upon system contingencies.

Improving the energy efficiency of electric drives for auxiliary units of traction rolling stock

The review of technical solutions and schematic characteristics of auxiliary drives for traction vehicles has shown that the most rational variant is an electric drive with an induction machine. Given the operating modes of the auxiliary drives and the share of their power consumption in the total locomotive power, the task of using scalar control systems for induction machines becomes relevant. Based on a mathematical model describing the dynamic energy conversion processes in the T-shape substitution circuit of an induction motor, taking into account stator steel losses and current displacement effects in the rotor winding and saturation along the main magnetic path, possibilities for reducing stator current have been investigated. In order to improve the energy efficiency of electric drives two variants of control system have been proposed. One based on search method of self-tuning to the stator current minimum and the other - on maintaining the power factor of induction motor at the level that ensures equality of active and reactive components of stator current. The hardware and software requirements for implementing control systems have been analysed. Modelling using Matlab has shown that both control systems work - power loss reduction can be as low as 50% and as high as 60% in certain modes.

Determining the Electrical Losses in the Electrical Supply Line of a Sprinkler Using Autonomous Asynchronous Generator

The use of an asynchronous generator to power the electrical equipment of the sprinkler is a comprehensive solution that allows you to reduce electrical losses in the supply line. The problem of reactive power compensation for sprinkler machines can be solved by dividing capacitor units into main and additional, the main one is to create the required excitation current in the asynchronous generator, and the additional one is to compensate for the reactive component of the electric motor current. Moreover, an additional unit is installed directly at the outputs of the booster pump to unload the line, and the main capacitor unit is installed near the asynchronous generator.

Modified repetitive control design for two stage off board Electric Vehicle charger

In this paper, a three-phase, two stage, bidirectional off board plug-in Electric Vehicle (PEV) charger controller has been designed and implemented in real time. The proposed PEV charger is able to work in all four quadrants in active–reactivepower plane. Generally, power electronics converters are controlled by PI regulators in d-q reference frame, where the signals to be regulated are inherently DC in nature. These controllers are implemented in two loops i.e., Slow (outer) control loop and fast (inner) control loop. Setting the gains of outer loops are little bit easier in comparison to fast acting inner loops besides the involvement of decoupling terms to have independent operation of active and reactive current components. Therefore, a repetitive controller (RC) is designed to regulate the inner sinusoidal reference current having both active–reactive​ components as per the control requirement without involving any decoupling terms. The RC is well known for their ability to track periodic signal and inherently based on internal model control theory. However, the major problem with RC is its sensitivity due to which it provides high gains at all frequencies levels. Therefore, in proposed controller the sensitivity of RC is modified by squaring it. This results the deep notches at higher frequency levels This approach is found to be very much suitable for the compensation of reactive power and load current harmonics. This also helps to exclude unwanted frequencies which results reduction in THD level. Therefore, the main contribution of this paper is adapting such robust EV charger controller for harmonic compensation. Moreover, from the implementation, it is found that the conventional RC is capable to compensate load current harmonic to some extent but it takes around 140 μs computational time. However, the proposed RC takes around 100 μs computational time, this results the grid current purely sinusoidal. The MATLAB/Simulink environment has been used to simulate proposed PEV charger controller, further it has been verified on scaled down experimental prototype.

Affine projection sign algorithm based control for mitigation of distribution side power quality problems

AbstractThis paper proposes the implementation of Affine Projection Sign Algorithm (APSA) based control for DSTATCOM to mitigate distribution side power quality issues like harmonic elimination, reactive power compensation, load balancing, power factor compensation, voltage regulation, etc. Affine projection algorithms have already finds application in power quality mitigation, but they suffer from high complexity and degraded performance due to impulsive interference. Whereas, sign algorithms are known to be robust against the impulsive noise and converges faster. Hence, sign algorithm with affine projection is proposed for mitigation of power quality problems in this work. APSA is used to estimate the reference active and reactive power component of polluted load current, which is further used to generate the reference signal for DSTATCOM. The performance of the algorithm is investigated for some real operating conditions of power system network in MATLAB/SIMULINK environment. The algorithm is tested in real‐time simulator for validation. The result shows that the control algorithm is able to resolve distribution side power quality problems with fast convergence.

KINETICS OF EXCITATION OF A MAGNETIC FIELD IN ASYNCHRONOUS VALVE CASCADE

The essence of the physical processes of vector control of an asynchronous valve cascade (AVC), in particular the processes of excitation of a rotating magnetic flux, becomes clearer if this field is considered as an independent object. The nonlinearity of the system of differential equations of AVC prevents the separation and consideration of a rotating magnetic field as an independent physical object. For AVC, when the stator of asynchronous machine (AM) is powered from the network, and the rotor circuit – from the frequency converter, the problem of studying the process of creating a magnetic field was not considered. It is possible to substantiate the possibility of considering the dynamics of the magnetic flux isolated from the reaction of the active power channel, provided that the rotor is held stationary by the control system and the reactive current of the rotor is stabilized by its regulator at a certain level.
 The process of magnetization of AM in the circuit AVC is mainly due to the voltage of the supply network, which significantly limits the possibility of actively influencing the formation of the reference vector of the stator flux linkage with the help of the regulator of the reactive component of the rotor current. It becomes impossible to qualitatively control the electromagnetic torque AM at the initial stage of start-up, when the stator flux linkage takes on a steady-state value after prolonged oscillations. This phenomenon leads to the need to supply a reference signal to the speed control channel when the stator flux linkage vector reaches a steady-state value when the rotor is stationary and there is no load torque on the shaft. In the article, the task is to investigate the process of excitation of the magnetic field of the AVC and the influence of the current regulator on this process at its different structures in the reactive power channel. An original method of studying the statics and dynamics of excitation of the magnetic field of the AVC is applied, the results of which allow us to conclude that to increase the stability margin of the reactive power circuit of the AVC, it is necessary to regulate the magnetizing current in the control system of this circuit instead of the reactive component of the rotor current.

Predictive current control of FL-shunt active power filter for dynamic and heterogeneous load compensation

In this paper, a predictive current control technique is utilized to generate switching pulses for four-leg-shunt active power filter (FL-shunt active power filter). The d-q theory technique is executed for removing the reactive and harmonic components of load current. MATLAB-based simulation and FPGA-controlled experimentation have been carried out to evaluate the behavior of predictive current control technique under dynamic and heterogeneous loading conditions. The 3-phase induction machine is considered as a dynamic load, and the capability of FL-shunt active power filter is assessed for compensating the reactive power. The compensation behavior of FL-shunt active power filter is observed with heterogeneous load, which is an amalgamation of dynamic and unstable static loads. Under steady-state and transient conditions, the simulation and experimentation results demonstrate that the proposed technique makes the supply current sinusoidal as well as balanced; compensates the reactive power; maintains near to unity power factor at the point of common coupling (PCC); and annuls the current flow in neutral conductor.

Upgradation of grid-connected water pumping system integrating multifunction PV inverter with reduced sensor

This article presents upgradation of existing grid-connected direct online-start water pumping system by integration of multifunction photovoltaic inverter. The multifunction photovoltaic inverter is operated using a voltage-oriented control such that it delivers the reactive power in addition to the real solar photovoltaic power to deal with practical issues like steady-state grid voltage variation and poor power factor on irrigation feeder. In the implemented voltage-oriented control, the adaptive modified second-order generalized integrator-based estimators are used to derive the grid voltage angle and the reactive component of the load current, which considerably reduces the requirement of the sensors. The methods to derive the different control system tuning parameters, i.e., second-order generalized integrator gains and proportional integral controller gains, are also described. A prototype is developed to investigate the performance of designed system. In the prototype, the control algorithm is implemented using a generic ARM Cortex-M4 microcontroller. Extensive experiments are performed, and the test results are presented to validate the system operations.