Indirect Current Control Research Articles

Power Management Based Current Control Technique for Photovoltaic-Battery Assisted Wind–Hydro Hybrid System

Abstract This article proposes new power management based current control strategy for integrated wind–solar–hydro system equipped with battery storage mechanism. In this control technique, an indirect estimation of load current is done, through energy balance model, DC-link voltage control and droop control. This system features simpler energy management strategy and necessitates few power electronic converters, thereby minimizing the cost of the system. The generation–demand (G–D) management diagram is formulated based on the stochastic weather conditions and demand, which would likely moderate the gap between both. The features of management strategy deploying energy balance model include (1) regulating DC-link voltage within specified tolerances, (2) isolated operation without relying on external electric power transmission network, (3) indirect current control of hydro turbine driven induction generator and (4) seamless transition between grid-connected and off-grid operation modes. Furthermore, structuring of the hybrid system with appropriate selection of control variables enables power sharing among each energy conversion systems and battery storage mechanism. By addressing these intricacies, it is viable to regulate the frequency and voltage of the remote network at load end. The performance of the proposed composite scheme is demonstrated through time-domain simulation in MATLAB/Simulink environment.

The New Type of Reactive Power Compensation Device under Direct Current Control and Indirect Current Control

This Paper Briefly Describes the Basic Principle of Reactive Power Compensation and Introduces the Indirect Current Control and Direct Current Control Method Based on Instantaneous Reactive Power Theory. Compare the Two Control Theory and Use the MATABLE Simulink Environment to Analyzing the Difference between the Two Methods

Controller Design and Implementation of Indirect Current Control Based Utility-Interactive Inverter System

The utility-interactive inverter with critical load should be able to provide critical loads with a stable and seamless voltage. This letter proposes an indirect current controller which does not include any nonlinear factors in the control block, so that the classical control theory can be applied to the controller design. Also, a phase-locked loop algorithm is proposed to maintain the constant frequency across the critical load during the unintentional islanding since the magnitude is well regulated, but the frequency may vary with the proposed controller. Further, an islanding detection method is proposed for the controller, which does not cause a change in magnitude and frequency of critical load voltage.

Comparison of Three leg and Four Leg VSC DSTATCOM for Power Quality Assessment

A new three-phase four-wire DSTATCOM (distribution static compensator) based on three-leg VSC (voltage source converter) and a star/delta transformer is proposed for power quality improvement. The star/delta transformer connection mitigates the neutral current and the 3-leg VSC compensates harmonic current, reactive power and balances the load. Three single phase transformers are connected as star/delta transformer for interfacing to a three phase four-wire power distribution system and the required rating of the VSC is reduced. However, a 4-leg VSC (voltage source converter) based DSTATCOM (Distribution Static Compensator) is used for the load compensation and neutral current compensation in 3-phase 4-wire distribution system. For extracting the reference source currents, Instantaneous Symmetrical Component Theory (ISCT) based control algorithm is modified for voltage regulation and used with indirect current control technique for controlling the DSTATCOM currents. The DSTATCOM is controlled for power factor correction and voltage regulation at PCC (point of common coupling). Simulations are performed for various load conditions such as a reactive linear load, an unbalanced load and a non-linear load in Power Factor Correction (PFC) mode and in Zero Voltage Regulation (ZVR) mode in MATLAB environment using SIMULINK and Sim Power System (SPS) toolbox.

Research on Control Strategy for the Three-Phase Grid-Connected Inverter

This paper proposes a control strategy，based on the grid voltage oriented vector control (VOC), which makes three-phase inverter control the active and reactive power of grid-connected inverter under the premise of the direct current control. This paper analyzes the principle of three phase photovoltaic grid connected inverter and describes the control structure of the inverter. The control strategy can overcome the deficiencies of the indirect current control scheme. This paper designs the current closed-loop control system, which not only improve the system dynamic response speed and output current waveform quality, while also reduce its sensitivity to parameter changes to improve the robustness of the system. The simulation results show the validity of control strategy proposed.

중요부하를 갖는 계통연계형 인버터의 고조파주입에 의한 단독운전방지 기법

The utility-interactive inverter with critical loads should supply continuous and stable voltage to critical loads even during the grid fault. The conventional control method which performs current control for grid-connected mode and voltage control for stand-alone mode undergoes the critical load voltage variation during grid fault. The critical load voltage may have large transient when the inverter performs mode transfer after the islanding detection. Recently, the indirect current control method which does not have the transient state during not only islanding detection but also the mode transfer has been proposed. However, since the voltage control is maintained even during the grid-connected mode it is difficult to detect the islanding. This paper proposes an active anti-islanding method suitable for the indirect current control method which does not have NDZ(Non-Detection Zone).

Improvement of Power Factor and Harmonic Elimination in Distribution Line using PI with Hysteresis Current Controller

Power quality improvement is a major research area in current context. Though much work has been done by many researchers still scope is there to work on this area. In this paper an attempt is made to eliminate the harmonics as well as for the improvement of power factor. Here distribution static synchronous compensator (DSTATCOM) is used to improve power factor in distribution line & mitigate harmonics with an optional feature of voltage regulation. Further the frequency analysis of the distribution line is analyzed both before & after compensation. A relay based hysteresis current regulator is used for DSTATCOM controller in indirect current control technique. Simulation is carried out in standard MATLAB environment. Results of simulations are presented for linear & nonlinear load.

Digital Signal Processor based Performance Investigation of Indirect Current Controlled Active Power Filter for Power Quality Improvement

Abstract This paper presents a novel Digital Signal Processor (DSP) based control algorithm for 3-phase shunt active power filter (APF) using neural network and indirect current control strategy to eliminate current harmonics and reactive power compensation under ideal and distorted supply voltage. The compensation process is based on sensing of source current instead of filter current, and thus differs from conventional techniques for elimination of switching ripples. Fundamental frequency signal extraction is done using adaptive linear neuron (ADALINE) network from distorted voltage signal without using low-pass filter or phase-locked-loop block. ADALINE gives simple, robust and accurate design for selected frequency extraction. Instead of calculating oscillating and reactive power, the reference generation is used to calculate average active power component. Various simulation results are presented to study the performance of proposed design during steady-state and transient conditions of non-linear loads using MATLAB/ Simulink tool under sinusoidal and distorted supply voltage conditions. Simulated response has been validated with a laboratory prototype using a Texas make floating-point TMS320F28335 DSP. Based on the simulated and experimental results it can be concluded that the spectral performance of the input current are in compliance with the harmonic limits imposed by IEEE-519 standard.

Indirect Current Control for Seamless Transfer of Three-Phase Utility Interactive Inverters

This paper proposes an indirect current control algorithm for seamless transfer of three-phase utility-interactive voltage source inverters. With the proposed method the inverter is able to provide critical loads with a stable and seamless voltage during the whole transition period including both clearing time and control mode change. The LCL filter design which is suitable for the indirect current control is also proposed to meet the harmonic limits. The proposed control method is validated through simulation and experiment.

Improvement in Dynamic Performance of Indirect Current Control Strategy on Three Phase PWM Rectifier

Three phase voltage source PWM rectifier (VSR)’s indirect current control (ICC) strategy has good static performance, simple control steps and low cost. But bad dynamic performance is its inherent drawback. If this weakness is overcome, it is still valued. In this article normal ICC is deeply studied beginning with its mathematical model under synchronous rotating coordinate. It is indicated that its bad dynamic performance originates from bad current response. So an improving scheme adding compensation in series is brought out. Additionally a differential negative feedback loop of DC output voltage is added to limit the voltage overshoot. Lastly the control system’s computer simulation model is established by MATLAB and the simulating results prove that improved ICC makes great process in dynamic performance and has advantages of both indirect and direct current control (DCC).

Performance of Voltage and Frequency Controller in Isolated Wind Power Generation for a Three-Phase Four-Wire System

This paper deals with a new control algorithm for a voltage and frequency controller (VFC) of an isolated wind energy conversion system (IWECS) using an isolated asynchronous generator to feed three-phase four-wire consumer loads. The reference source currents are estimated for the indirect current control of a voltage source converter (VSC) using the single-phase PQ theory to control the voltage and frequency of IWECS. A three-leg VSC with a battery energy storage system is used as a VFC for an IWECS. A nonisolated star-polygon transformer is used to provide a neutral terminal for four-wire loads and to compensate the neutral current resulting in reduction in rating of VSC. The proposed VFC is implemented using a DSP. Experimental results are presented to demonstrate the additional capabilities of VFC as a load leveler, a load balancer, a harmonic eliminator, and a neutral current compensator.

Improved Active Power Filter Performance Based on an Indirect Current Control Technique

This paper presents a method for the performance improvement of a shunt active power filter (SAPF) using the indirect current control (ICC) scheme. Compared to the conventional direct current control (DCC) scheme, the ICC gives better performance with a lower number of sensors. A simplified and efficient control algorithm using a low cost Intel 80C196KC microcontroller is implemented using only two current sensors for the source current and one voltage sensor for the DC-link voltage of the SAPF circuit. The objective is to eliminate harmonics and to compensate the reactive power produced by non-linear loads such as an uncontrolled rectifier feeding an inductive load. The APF is realized using a three phase voltage source inverter (VSI) with a dc bus capacitor. Experimental results are presented to prove the better performance of the ICC method over the DCC one.

Three-level Cascaded Inverter Based D-STATCOM Using Decoupled Indirect Current Control

In this paper, experimental setup of three-level cascaded inverter based 380V/±25kVAR D-STATCOM using decoupled indirect current control method (DICC) is realized. AC and DC side of D- STATCOM is modelled in dq-axis on account of D-STATCOM’s controlling. DICC is used for control of D-STATCOM’s dq-axis currents independently. Gate pulses for inverter are generated with multilevel sinusoidal pulse width modulation (SPWM) technique. In this study, controller card used for signal processing is dSPACEs DS1103. The control algorithm is prepared by the help of MATLAB/ Simulink® software. This algorithm is converted to C language by using Matlab/Real-Time Workshop and downloaded to DS1103’s program memory by dSPACE/Real-Time Interface. Implemented experimental setup is tested by changing reference reactive current (iqref) +20A to −20A and obtained results from this test are given.

New control approach for capacitor supported DSTATCOM in three-phase four wire distribution system under non-ideal supply voltage conditions based on synchronous reference frame theory

A large number of single-phase linear and non-linear loads may be supplied from three phase ac mains with neutral conductor. They cause excessive neutral current, harmonics and reactive power burden and unbalance. A four wire DSTATCOM (distribution static compensator) is used for neutral current compensation along with reactive power compensation, harmonics elimination and load balancing. A novel control approach is proposed for the control of four wire DSTATCOM under non-ideal supply voltage conditions. A four-leg voltage–source converter (VSC) with a dc capacitor is used as a four wire DSTATCOM. The proposed control approach is based on synchronous reference frame (SRF) theory and an indirect current control technique. The switching signals for the voltage–source converter (VSC) of the DSTATCOM are derived from the estimated reference supply currents. The load balancing, harmonics elimination and the neutral current compensation are demonstrated along with unity power factor (UPF) and zero voltage regulation (ZVR) modes of operation. Simulation results based on MATLAB software with its Simulink and power system blockset (PSB) toolboxes are presented to validate the control strategy. The DSTATCOM is able to maintain the self-supported dc bus under various disturbances.

A Three-Phase Rectifier for Wecs With Indirect Current Control

This paper presents a novel Wind Energy Conversion System (WECS) capable of processing the energy from a Permanent Magnetic Synchronous Generator (PMSG) coupled to a three-blade wind turbine and injecting it into the utility power grid. This WECS is composed by two stages: a three-phase rectifier and a single-phase inverter. The ac-dc stage consists of three single-phase bridgeless rectifiers processing the power of each phase of the PMSG separately. The dc-ac stage is composed of a full-bridge inverter with controlled output current. Besides, indirect current control for High Power Factor (HPF) operation is employed, allowing the unification of two important techniques currently available, that are one cycle control (OCC) and selfcontrol (SC). Additionally, a third technique, that comprises the optimum characteristics of both OCC and SC, is proposed and applied to the rectifier stage of the proposed WECS. The proposed WECS and control technique are both validated by experimental results from a 5kW prototype.

Performance evaluation of different line current shaping controllers of shunt active power filters

This paper deals with the performance evaluation of three different control methods for line current shaping in single-phase system using shunt active power filter (APF). The first two methods are indirect current control based on source current sensing and the last one is a direct current control based on load current sensing. The method I is investigated with an aim to compensate only customer generated harmonics and reactive power to attribute the responsibilities of the utility and customer at the point of common coupling (PCC). The inventing feature of method I is its realisation without the use of source voltage signal. The methods II and III are presented with an objective to compensate customer as well as utility generated harmonics and reactive power. The detailed mathematical modelling of all three controllers is presented. The performance of these controllers is investigated for rapidly varying load under sinusoidal and non-sinusoidal source voltage conditions. The total harmonic distortion (TH...

Power Conditioner for Variable-Frequency Drives in Offshore Oil Fields

The proliferation of variable-frequency ac motor drives (VFDs) as submersible pumps in oil exploration has aggravated many power-quality problems on the distribution network, for which VFDs are themselves susceptible to maloperation. The distortion in the input voltage waveform is a major issue, since the offshore power system cannot be regarded as a stiff source, and thus, distortions in the voltage waveform become more severe, which disturbs other loads connected at the point of common coupling (PCC). The oil fields require the operation of many parallel-connected VFDs on the same bus. Such a system significantly increases the power-quality problems on the distribution network. In this paper, an active power conditioner which is connected in series between the source and the PCC, and its dc bus shared with one of the VFDs connected to the bus, is proposed to mitigate a majority of power-quality problems for the whole bus. The proposed single power conditioner is sufficient to block the harmonic currents flowing toward the source, balance the currents from the source side, protect the VFDs on the bus against sag/swell at PCC, protect preinstalled passive filters connected with VFDs against series and parallel resonances, and maintain regulated balanced voltages at PCC. Investigations are carried out to validate the use of the proposed topology of a power conditioner to safeguard the distribution system and a set of VFDs against major power-quality problems. The proposed power conditioner employs a new control scheme based on an indirect current control for its effective operation under varying load conditions on different VFDs connected to the same bus.

Design and Implementation of a Current-Controlled Parallel Hybrid Power Filter

This paper deals with the implementation of an indirect current control of a parallel hybrid filter (PHF) system with rectifier load to eliminate generated harmonics. The compensation principle, design, and PHF implementation are discussed in detail. The proposed control enhances the performance of the passive filters (PFs) under unbalanced situations that are existing in the PFs under fault conditions. Moreover, due to a limited capacity of voltage source inverter, an upper limit for such compensation may be imposed by the proposed indirect current control based on synchronous reference frame employing decomposition of current in synchronously rotating reference frame that is used to control PHF. The PHF is controlled using decomposition of load and source currents. The implementation of the control scheme is carried out on dSpace with digital signal processor for developed prototype of the PHF. PFs are developed keeping in view its operation with the PHF, so that the total harmonic distortion in the source current gets minimized along with minimized fundamental-frequency current sinking through the filter section. The design has been carried out by genetic algorithm, which optimizes the solution for multiple constraints. The operation of the PHF under dynamic change of load is also investigated through simulations under MATLAB and through experimentation.

Generalised single-phase p-q theory for active power filtering: simulation and DSP-based experimental investigation

The single-phase p-q theory for the purpose of active power filtering in the case of single-phase loads is dealt with here. A simple modification is proposed to develop a generalised single-phase p-q theory that can be utilised under the condition of distorted utility voltage. A systematic study is presented by realising both direct and indirect current control techniques. The simulation as well as the digital signal processor (DSP) (DS1104 of dSPACE) based experimental results are discussed. The developed single-phase shunt active power filter (APF) prototype is tested under different operating conditions with different loads to evaluate the full capabilities of the proposed generalised theory for practical uses. The shunt APF reduces the source current total harmonics distortion (THD) from 27.2 to 3.4% under a distorted supply voltage with a THD of 16.2%.

Indirect Current Control Algorithm for Utility Interactive Inverters in Distributed Generation Systems

Distributed generation (DG) systems should go into intentional islanding operation to back up private emergency loads when the main grid is out of electric power. Conventional utility interactive inverters which are normally operated in current mode must change their operation into voltage mode to ensure stable supply voltage for emergency loads when intentional islanding operation occurs in DG systems. During the transition between current mode and voltage mode, a serious transient problem may occur on the output terminal voltage of utility interactive inverters. This paper proposes a new inverter system and its control algorithm for seamless transfer during intentional islanding operation in DG systems. Filter design guidelines and data for LCL filters that is appropriate for the proposed control algorithm are also presented.