Reference Current Components Research Articles

Simultaneous active and reactive power compensation using STATCOM with supercapacitor energy storage system

STATCOM is taking challenges skilfully in the field of power system to maintain the AC bus voltage constant and to compensate for reactive power. When the STATCOM is integrated with energy storage device through DC/DC buck-boost converter, it compensates the active power also. In this paper, the regulation of DC link voltage to its rated value has been done to compensate simultaneous active and reactive power demanded by the load. The circuit model, mathematical expressions and MATLAB/Simulation model based on the mathematical model has been analysed. The hysteresis current control (HCC) strategy is used to generate the pulses for the 6-pulse 2-level voltage source converter (VSC). The conventional PI controller is used to generate the reference current direct and quadrature axis components. The PI controller is also used to generate the modes, whether it works in buck mode or boost mode. These modes decide the charging and discharging of supercapacitor. Here total reactive power is taken by STATCOM and the grid reactive power is near to zero and hence the burden on the grid is drastically reduced.

Virtual-Torque-Based Control of Three-Phase Rectifier Under Grid Imbalance and Harmonics

The paper deals with a new control method of three-phase rectifier operating under simultaneous grid voltage imbalance and harmonics. The proposed method uses virtual electromagnetic torque, which is calculated on the basis of converter current and virtual flux of the power grid. Direct calculation of reference alpha/beta components of current vector does not require any synchronization procedure or grid voltage/virtual flux orientation of the reference frame. On the other hand, the proposed control is still as simple in implementation as other vector control methods such as voltage-oriented control or virtual-flux-oriented control. The introduced variable (virtual torque) allows us to calculate reference current vector components in alpha/beta frame without symmetrical components decomposition. The current vector obtained by using the proposed control method has the same asymmetry factor as unbalanced grid voltage. It means that the rectifier is seen by the grid as a resistive load with the same resistance in each phase. For the grid it is preferable target because the phase with the highest voltage is loaded most, while the other phases are less loaded. Converter power can be increased by progressive balancing of three-phase converter current keeping the phase current limit.

A control strategy for the stable operation of shunt active power filters in power grids

This paper introduces a control strategy for the assessment of SAPF (shunt active power filters) role in the electrical power networks. The proposed control scheme is based on the Lyapunov control theory and defines a stable operating region for the interfaced converter during the integration time with the utility grid. The compensation of instantaneous variations of reference current components in the control loop of SAPF in ac-side, and dc-link voltage oscillations in dc-side of the proposed model, is thoroughly considered in the stable operation of interfaced converter, which is the main contribution of this proposal in comparison with other potential control approaches. The proposed control scheme can guarantee the injection of all harmonic components of current and reactive power of grid-connected loads, with a fast dynamic response that results in a unity power factor between the grid currents and voltages during the integration of SAPF into the power grid. An extensive simulation study is performed, assessing the effectiveness of the proposed control strategy in the utilization of SAPF in power networks.

A control plan for the stable operation of microgrids during grid-connected and islanded modes

This paper presents a control technique that enhances microgrids stability during the grid-connected and islanded modes. The proposed technique is compared with several existing control strategies in the context of microgrids integration into smart grids. The Lyapunov control theory is utilized in this paper to investigate the operation stability of DG units operating along with the utility grid. As the main contribution, the proposed technique compensates for the instantaneous variations of the reference current components of DG units in the ac-side of the converters. The presented method also considers and properly addresses the dc-voltage variations in the dc-side of the interfacing system. Under the proposed control strategy, DG units are able to deliver active and reactive power to the local loads and/or the main grid in fundamental and harmonic frequencies, with a fast dynamic response and without any interruption. Several simulation scenarios are carried out to demonstrate effectiveness of the proposed control strategy in microgrids during the transient and steady-state operation.

Control technique for enhancing the stable operation of distributed generation units within a microgrid

This paper describes a control technique for enhancing the stable operation of distributed generation (DG) units based on renewable energy sources, during islanding and grid-connected modes. The Passivity-based control technique is considered to analyze the dynamic and steady-state behaviors of DG units during integration and power sharing with loads and/or power grid, which is an appropriate tool to analyze and define a stable operating condition for DG units in microgrid technology. The compensation of instantaneous variations in the reference current components of DG units in ac-side, and dc-link voltage variations in dc-side of interfaced converters, are considered properly in the control loop of DG units, which is the main contribution and novelty of this control technique over other control strategies. By using the proposed control technique, DG units can provide the continuous injection of active power from DG sources to the local loads and/or utility grid. Moreover, by setting appropriate reference current components in the control loop of DG units, reactive power and harmonic current components of loads can be supplied during the islanding and grid-connected modes with a fast dynamic response. Simulation results confirm the performance of the control scheme within the microgrid during dynamic and steady-state operating conditions.

A Multifunction Control Strategy for the Stable Operation of DG Units in Smart Grids

This paper describes the development of a multifunction control strategy for the stable operation of distributed generation (DG) units during the integration with the power grid. The proposed control model is based on direct Lyapunov control (DLC) theory and provides a stable region for the proper operation of DG units during the integration with the power grid. The compensation of instantaneous variations in the reference current components in ac-side and dc-voltage variations in the dc-side of the interfacing system are adequately considered in this control plan, which is the main contribution and novelty of this paper in comparison with previous control strategies. Utilization of the DLC technique in DG technology can confirm the continuous injection of maximum active power in fundamental frequency from the DG source to the power grid, compensating all the reactive power and harmonic current components of grid-connected loads through the integration of DG link into the grid. Application of this concept in smart grids system can guarantee to reduce the stress on the utility grid during the peak of energy demand. Simulation and experimental test results are presented to demonstrate the proficiency and performance of the proposed DLC technique in DG technology.

Direct Lyapunov Control Technique for the Stable Operation of Multilevel Converter-Based Distributed Generation in Power Grid

This paper deals with a control strategy of multilevel converter topologies for integration of distributed generation (DG) resources into the power grid. The proposed control plan is based on the direct Lyapunov control (DLC) technique, which is an appropriate tool for the analysis and definition of a stable operating condition for DG link in the power grid. The compensation of instantaneous variations in the reference current components in ac side and dc voltage variations of cascaded capacitors in dc side of the interfacing system is considered properly, which is the main contribution and novelty of this paper in comparison with other control methods. By utilization of the proposed control technique, DG can provide continuous injection of active power in fundamental frequency from the dispersed energy sources to the grid. In addition, reactive power and harmonic current components of nonlinear loads can be provided with fast dynamic response, by setting a multiobjective reference current component in the current loop of DLC-based model. Therefore, achieving sinusoidal grid currents in phase with load voltages are possible, while the required power from the load side is more than the maximum capacity of interfaced multilevel converter. Simulation results confirm the effectiveness of the proposed control strategy in DG technology during dynamic and steady-state operating conditions.

Passivity-based control technique for integration of DG resources into the power grid

This paper deals with a control method for integration of Distributed Generation (DG) sources to the power grid. The proposed control strategy has been designed based on passivity technique and provides compensation for the active, reactive, and harmonic current components of loads during the connection of DG link to the grid. The proper switching functions of interfaced converter have been defined based on the passivity method through the achieving space equations and suitable series damping injection. The proposed control plan is completed by setting suitable reference current components for the d and q axis in the control loop of DG, which are defined based on the objectives of proposed method. The effectiveness of the proposed control scheme is validated with injection of maximum available power from the DG resources to the power grid, correction of power factor between the grid current and load voltage, generates a fix voltage at the point of common coupling (PCC), and reduces total harmonic distortion (THD) of grid current, through the simulation results under steady-state and dynamic operating conditions.

High selectivity filter based reference current generation method for three-level shunt active power filters under adverse source voltage conditions

This paper presents comparison of four different control strategies to generate reference current components for shunt active power filter based on a three-level inverter. These strategies are instantaneous reactive power p–q method, modified p–q method, synchronous d–q reference frame method and I d –I q method. The performance of four methods has been evaluated under different source voltages conditions in steady state. For the same operating conditions, the performance of all control laws are analysed and compared in terms of the total harmonic distortion of source currents. Based on this comparative study, it is possible to select the best strategy to meet the required load compensation characteristics for available source voltages.

Comparison of control strategies for DSTATCOM in three-phase, four-wire distribution system for power quality improvement under various source voltage and load conditions

This paper presents comparison of three different control strategies to generate reference current components for Distribution Static Compensator (DSTATCOM). Reference currents are tracked by a three-phase voltage source converter in a hysteresis band control scheme. These methods are instantaneous reactive power (IRP) theory, symmetrical component (SC) theory and an improved instantaneous active and reactive current component (IARCC) theory. The performance of three methods has been evaluated under various source voltage and load conditions with new IEEE Standard 1459 power definitions. A comparative study of their performance in terms of rms value of source current, Total Harmonic Distortion (THD), supply power factor and compensator ratings is also presented. A three-phase, four-wire distribution system supplying linear as well as non-linear load is considered for simulation study which is carried out using MATLAB/SIMULINK software. Under balanced and sinusoidal source voltage conditions, all three control strategies similar performance while an improved IARCC theory outperforms, particularly, under unbalanced and distorted source voltage conditions.

Improved Flux Pattern With Third Harmonic Injection for Multiphase Induction Machines

This paper presents an indirect vector control scheme with an improved flux pattern using third harmonic injection. The control objective is to independently control both flux and torque and to generate a nearly rectangular air-gap flux, resulting in improved machine power density. If there is a proportional relation between the third harmonic and fundamental plane currents, variable misalignment between fundamental and third air-gap flux components occurs with varying mechanical loading. Due to this misalignment, saturation may take place. Accordingly, the total flux is saturated and iron loss increases. Hence, coupling results between different sequence planes. Instead of a proportional relation between the current components, direct and quadrature current components of the injected third harmonic current reference are a function of the fundamental direct and quadrature reference current components, respectively. These functions ensure that the air-gap flux is near rectangular with a maximum value of 1 p.u. from no load to full load. Moreover, this controller guarantees complete decoupling between the sequence planes. An eleven-phase induction machine is used to validate the proposed controller experimentally, while supporting simulation results and theoretical analysis use both MATLAB and finite element platforms.

Method of Parallel Active Power Filter Compensation on 3-Phase 3-Wire Nonlinear Unbalanced Load System

The parallel active power filter has been accepted by users because of its’ installing and removing without disturbing other users and so its’ detecting and controlling algorithms have been studied with large efforts .A method about direction of active power flow (DAPF ) was raised in present paper under condition of the 3-phase asymmetrical voltage and 3-wire nonlinear unbalanced load. It’s means that detected currents on the point of common coupling can be put into two parts according the active power flow direction ,one of which is called positive direction current and another is called negative direction current .then decompose the asymmetrical voltage and positive directional current with Symmetrical Component Method. We can obtain the reference current components with clear physical meaning for the paralleled active power filter .The method shows there are several harmful power components could not be eliminated with parallel active power filter.

Electric citybus with two induction motors -power electronics and motor control

After a short introduction into the project of an electrically driven citybus with two individual induction machines, this paper describes the power electronic hardware including IGBT-inverter and on-board supply system as well as the structure of the field-oriented motor control. The on-board power supply has been especially designed for this vehicle. It supplies electric loads such as board systems, measurement devices and control components. The induction machines are separately fed by two ICBT-inverters. They are operated at a high switching frequency due to the low leakage inductance of the machines. Fast switching leads to high dU/dt-values which may destroy the motor windings. In order to reduce the high dU/dt-stress on the machines, an appropriate circuit has been developed and is presented. The induction machines are controlled by a field oriented control. The choice of the reference current components and the control structure assure a good dynamic performance and low machine losses. Measurements obtained in a laboratory test-setup are presented.

Field-Oriented Control by Forced Motor Currents in a Voltage Fed Inverter Drive

The paper proposes an optimally pulsed voltage fed inverter drive with field oriented control, in which the standard pulsewidth modulator as well as the dynamic decoupling system are completely eliminated. Instead, the reference current components supplied by the field oriented control system are used to directly control the switching state of the inverter with the aim of forcing the actual stator current vector to trace the time-variant locus of the current reference. The inverter switching control includes an algorithm which ensures either minimum harmonic torque at minimum switching frequency or, in the case of large-signal transients, operation at steepest possible current gradient. The optimization is being performed at steady state and transient operation, including operation at zero stator frequency.