Active Power Supply Research Articles

Advanced Nonlinear Control of Shunt Active Power Filter Connected to PV System via DC/DC Converter

We address the challenge of controlling a single-phase shunt active power filter in the presence of nonlinear loads. The active power filter is linked to a photovoltaic (PV) system, which supplies active power to the load. The main control objectives are: (i) mitigation of harmonics current and reactive power induced by the non-linear load; (ii) regulation the PV generator output voltage to follow its reference provided by the Maximum Power Point Tracking (MPPT) block, (iii) regulation the DC bus voltage to a constant value that must be greater than the amplitude of the grid voltage in order to guarantee full power injection to the non-linear load. To solve this problem, we use a nonlinear multi-loop controller. The inner loop is designed using the Backstepping method to cope with compensation problems. The external loop is responsible for regulating the dc bus voltage. The DC-DC boost control loop is designed to achieve the MPPT objective. The efficiency of the proposed controller is validated by simulation in MATLAB/Simulink.

Improvement of Power Quality in Grid Connected Wind Energy System

Abstract: This research covers industrial plant-connected wind turbine system control. An algorithm permits a control structure that uses a four-leg inverter linked to the grid to inject energy and operate as an active power filter, reducing load current disturbances and improving power quality. Algorithms enable this control structure. A four-wire system considers linear and nonlinear three-phase and single-phase loads. The utility-side controller supplies active and reactive power and adjusts for reactive, nonlinear, and unbalanced single- and intra-phase demands during wind turbine connection. Besides providing power, this is done. If there is no wind power, the controller uses the DC-link capacitor and grid-connected power converter to improve power quality. The proposed control structure is based on conservative power theory decompositions, which distinguishes it from previous techniques. This option separates the inverter control power and current references, giving a broad variety of adaptable, selective, and powerful functions. Real-time software benchmarking has tested the recommended control technique for comprehensive real-time implementation. The real-time simulator "FACTS" and the DSP microcontroller test and implement the control strategy in hardware-in-the-loop. These results confirmed our power quality improvement control, allowing us to omit passive filters. This created an electronic smart grid-based control system that was more efficient, adaptive, and reliable.

Technical Assessment of the Key LVRT Techniques for Grid-Connected DFIG Wind Turbines

As a key portion of renewable energy resources (RESs), wind energy penetration is rapidly deployed. The effects of grid faults on grid-connected wind turbines (WTs) are causing problems for wind energy producers. To meet the necessary requirements, additional resources and technical interventions are needed. One of these requirements is low voltage ride-through (LVRT) of doubly fed induction generator (DFIG)-based WTs. This means that DFIG-WTs must stay connected to the grid during transient grid faults and supply active and reactive power after the fault is cleared. Many techniques for improving the LVRT capability of DFIG-WTs have been developed and this paper examines them. The paper also evaluates how well they align with grid codes, and offers case studies and simulations of the selected key techniques. Lastly, this paper provides guidelines and suggested designs for the LVRT techniques for DFIG-WTs to ensure they meet local grid codes.

Improved Operation and Stability of a Wind-Hydro Microgrid by Means of a Li-Ion Battery Energy Storage

This article presents an isolated microgrid which combines two renewable power generators: a Hydraulic-Turbine-Generator (HTG) and a Wind-Turbine-Generator (WTG) with a Li-ion battery-energy-storage (BES). Depending on the generator(s) which supply active power, the microgrid can operate in three modes: Hydro-Only (HO), Wind-Hydro (WH) and Wind-Only (WO). In WH mode, the HTG supplies the difference between the power demanded by the consumers and the power supplied by the WTG. This net demanded power can be negative when the WTG power is greater than the load and this situation can lead to a microgrid collapse. This article shows by means of simulations how the BES is controlled to consume the WTG power excess guaranteeing the microgrid stability. Additionally, when the negative net demanded load is persistent the microgrid must transition from WH mode to WO mode, where only the WTG supplies active power, and this WH-WO transition is also simulated. In the simulations in WO mode, the BES is controlled to regulate the microgrid frequency. The needed controls to command the BES in WH and WO modes and in the WH-WO transition are also explained. The simulations show the effectiveness of using the BES since the microgrid stability and reliability is improved.

CONTROL STRATEGY OF PHOTOVOLTAIC GENERATION INVERTER GRID-CONNECTED OPERATING AND HARMONIC ELIMINATION HYBRID SYSTEM

This paper proposes a three-phase three-wire photovoltaic generation inverter grid-connected operating and harmonic elimination hybrid system. The hybrid system mainly consists of photovoltaic array battery, photovoltaic output filter, three-phase voltage-type inverter, inverter output filter and passive filters. Based on working principle and working characteristics of the proposed hybrid system, the composite control strategy about active power, reactive power and harmonic suppression is proposed. The composite control strategy mainly consists of a single closed-loop control slip of active power and reactive power, double closed-loop control slip of harmonics. Simulation results show the correctly of this paper’s contents, the hybrid system have an effective to improve power factor, supply active power for loads and suppress Key words - Micro grid; harmonic restraint; active power control; reactive power control; photovoltaic generation.

Reactive power control of grid-connected solar photovoltaic system

Solar Photo Voltaic (SPV) based distributed generation is providing a clean and green energy to meet human needs nowadays. In grid-connected mode, most of the capacity of converter circuit is under-utilized as peak power is available for a small duration in the daytime and no utilization during the night. The converter used for PV system may be modified to work as STATCOM, that is capable to convert DC to AC and can compensate reactive power simultaneously. Thus in daytime this modified PV-STATCOM system supply both active and reactive power and in the night it will supply only reactive power resulting in better utilization of Power Conditioning System (PCS). In this paper, modified PV-STATCOM is tested in the grid-connected mode through simulation in MATLAB/Simulink/SimPower under various operating conditions. The proposed system supply active and reactive power locally in the grid-connected load resulting in less burden on the grid.

Optimal Configuration of Photovoltaic-wind-storage Microgrid for Agricultural Irrigation in Mountainous Areas

Water and electricity supply for irrigation is difficult in remote mountainous areas. This paper explores agricultural irrigation systems’ integration mechanism, pumped storage power plants, and renewable power sources in mountainous areas to solve this problem. It establishes a microgrid power supply system with multiple complementary energy sources according to local conditions. By analyzing the load of agricultural irrigation in mountainous areas, the irrigation water consumption and electricity consumption are obtained. The capacity of pumped storage power stations, wind power, and photovoltaic power generation in the microgrid can be configured accordingly. They use the renewable power supply active power fluctuation rate index as a constraint and use the spectrum analysis method to calibrate the capacity configuration results. Finally, the scenic storage microgrid model is constructed and solved to minimize the microgrid’s grid connection cost. The algorithm shows that the proposed capacity allocation method can meet the irrigation load demand and realize the microgrid’s coordinated operation.

Smart Transformer-Enabled Meshed Hybrid Distribution Grid

Renewable energy sources (RES) induce problems such as voltage and current limit violations, absence of inertia and consequent stability problems, and poor power quality. Smart transformer (ST) is a promising solution for avoiding such a changing grid scenario leading to strong grid reinforcements. This article proposes an ST-enabled meshed hybrid distribution grid to achieve voltage and power flow control simultaneously with a centralized controller. In this configuration, a low-voltage dc (LVdc) line is proposed which connects the ST LVdc link with the dc bus of distributed generation (DG) converters. This introduces various active power flow paths to support the loads. The DG converters supply active power near the load points which ensures that line losses are reduced significantly while achieving improved voltage regulation as compared to conventional microgrid. Moreover, the DG converters can draw active power from ST LVdc link during absence of RES to support the load, resulting in improved utilization of these converters. The control complexity of the DG converters is reduced as the ST controls both the LVac and LVdc line voltages. Further, the newly developed power flow path allows reverse power flow from DG plants more efficiently. Performance of the proposed system is verified with simulation and experimental results.

Method for determining the power of squirrel-cage induction motors

Squirrel-cage induction motors are the main type of electric motors used for the electric motor drive of the working mechanism of industrial processes. The task of the electrical service of the enterprise is to control the engine power during operation and to prevent overloads or inefficient operations. In order to do that a non-contact method for determining the power of squirrel-cage induction motors is proposed. The method is based on the property of the mechanical characteristics of an induction motor, when with increasing the moment of resistance on the drive shaft, the rotor speed decreases in proportion to the load. Therefore, by measuring the rotor speed of the engine, it is possible to judge the degree of its load. To confirm this, experimental studies of axial fans were carried out. Linear supply voltage, winding current, active power, power factor and engine speed were used as the analyzed parameters of the motors. For more information about the state of the motor, in addition to analyzing the stator current, an analysis of the frequency of the supply voltage, as well as the input power, which is directly related to the current and supply voltage, was made. In the course of the experiments, a number of functional dependences of engine performance on its speed were obtained. It was established that tests are necessary for not only repaired engines, but also new ones to determine the optimal modes of its operation and identify production defects.

Optimal Integration of Distributed Generation in Primary Distribution System and its Economics

The paper analyses four types of DG (distributed generators) for their optimal placement in primary distribution system. They are sited and sized optimally to obtain maximum loss reduction. The ultimate objective of the adopted work in this paper is to identify the size and location of distributed generators for their placement in primary distribution network and to justify the economics of these placements. To serve the purpose, an analytical method is used in this paper for determination of sizes and sites for four DG types. The analytical method is considered suitable for the analysis purpose in proposed work. The paper presented a comprehensive analysis for four types of DGs for their placement in primary distribution system. The type 1 DG is capable of delivering real power only whereas type 3 DG is capable of providing real as well as reactive power to the distribution network. Out of other two types, type 2 can deliver only the reactive power whereas type 4 supplies active power but at the same time it consumes reactive power. The paper compares the economic feasibility of placement of four DG types in primary distribution system.

SPV-Based UPQC with Modified Power Angle Control Scheme for the Enhancement of Power Quality

Unified Power Quality Conditioner (UPQC) with a modified Power Angle Control (PAC) scheme is presented for effective interconnection of renewable energy system into the grid. The UPQC consists of both shunt and series Active Power Filters (APFs). The shunt and series APF is one of the most effective custom power devices, which provides compensation for current and voltage-based disturbances, respectively. The shunt APF supplies active power to the load from the Distributed Generation (DG) in addition to reactive power demand supplied by it. Because of this functionality, the Volt–Ampere (VA) burden increases along with the rating of the shunt inverter. The PAC scheme aims to effective utilization of series and shunt APFs through sharing of reactive power to reduce VA burden on shunt APF. The PAC scheme is based on Synchronous Reference Frame (SRF) theory, which has simple computations, is robust and uses existing measurements of Solar Photovoltaic (SPV)-integrated UPQC. The performance of the proposed SPV-integrated UPQC is verified with the manifestation of nonlinear loads and reactive burdens with the SPV power generating system. The dynamic performance of the PV-UPQC is verified under the grid disturbances such as voltage sag, swell, varying load and change in solar irradiation. The effectiveness of the proposed control scheme is evaluated through the digital simulation and hardware experimental prototype model.

Optimized Hierarchical Control for an AC Microgrid Under Attack

Context: An inverter-based microgrid working in islanded mode can suffer cyber- attacks, these can be done against either the local controller or the communication links among the inverters. Secondary control is able to reject those attacks, however, a tertiary control action is necessary in order to stabilize the power flow among the microgrid.
 Method: Confidence factor technique allows to reject attacks in a microgrid acting directly over the secondary control, however, this technique omits other factor related to the power available. In this case, secondary control was complemented with a tertiary control that includes optimization criteria.
 Results: An inverter-based microgrid is simulated in Matlab for different scenarios and under cyberattack, this allows checking the correct response of the controller under attacks and the effective powersharing among inverters.
 Conclusions: The tertiary control allows stabilizing the active power of the system after the rejection of a cyber-attack by the secondary control. Each inverter supplies active power according to its máximum power rating without affecting the stability of the whole system.

A combined reinforcement learning and sliding mode control scheme for grid integration of a PV System

The paper presents development of a reinforcement learning (RL) and sliding mode control (SMC) algorithm for a 3-phase PV system integrated to a grid. The PV system is integrated to grid through a voltage source inverter (VSI), in which PV-VSI combination supplies active power and compensates reactive power of the local non-linear load connected to the point of common coupling (PCC). For extraction of maximum power from the PV panel, we develop a RL based maximum power point tracking (MPPT) algorithm. The instantaneous power theory (IPT) is adopted for generation reference inverter current (RIC). An SMC algorithm has been developed for injecting current to the local non-linear load at a reference value. The RL-SMC scheme is implemented in both simulation using MATLAB/SIMULINK software and on a prototype PV experimental. The performance of the proposed RL-SMC scheme is compared with that of fuzzy logic-sliding mode control (FL-SMC) and incremental conductance-sliding mode control (IC-SMC) algorithms. From the obtained results, it is observed that the proposed RL-SMC scheme provides better maximum power extraction and active power control than the FL-SMC and IC-SMC schemes.

An ANFIS based improved control action for single phase utility or micro-grid connected battery energy storage system

This paper presents an improved performance of coordinated control scheme for exchanging power between a single phase electrical grid and battery energy storage system (BESS) using adaptive neuro-fuzzy inference system (ANFIS). The grid connected BESS has several practical applications in respect of storage of excess energy, reduction of maximum demand and reduction of power fluctuation on local grid/micro-grid. In these scenarios, the coordinated closed loop control strategy facilitates charging and discharging operation of the battery via dc-ac bidirectional converter. During charging mode of operation, the grid supplies active power to the battery for restoring back its energy. On the other hand, the closed loop action is also capable to control active and reactive power in decoupled way by discharging battery and the required electrical powers can be injected into the nearby grid conveniently. At first, the required closed loop control schemes are implemented using proportional-integral (PI) controller and the performance of the BESS using PI based control schemes is investigated. Then, the ANFIS based control strategy is used for improving overall control capability and it provides superior dynamic performance in comparison to the PI based control scheme under charging and discharging operation cycle of the battery. Various simulation studies are performed on 230 V, 50 Hz single phase ac grid connected 100 Ah, 120 V battery using MATLAB-SIMULINK 2014b software to validate the improved control concept.

Single‐phase solar grid‐interfaced system with active filtering using adaptive linear combiner filter‐based control scheme

This study deals with a control scheme for single-stage solar photovoltaic (SPV) grid-interfaced system. The voltage-source inverter (VSI) is a power electronic interface between SPV array and the grid. The VSI provides power quality features, i.e. harmonics mitigation, power factor correction and perturb and observe maximum power point tracking for single-stage SPV grid-interfaced system. The SPV array supplies active power to the non-linear load and grid through VSI, during daytime only or when SPV generation is more than the load power. To increase the utilisation of VSI, it is used as an active power filter at night, to mitigate harmonics and to provide active power to the load from the utility grid. The proposed adaptive linear combiner filter has the capability to extract harmonics and enhances the power quality in SPV grid-interfaced system. It has also satisfied an IEEE-519 standard of harmonics by improving the quality of power of SPV grid-integrated system. Simulation results of the SPV system are presented, which are simulated using MATLAB and response of system under non-linear load and varying environmental condition are also studied experimentally on a developed prototype in the laboratory.

Coordinated Control Strategy for a Hybrid Wind Farm with DFIG and PMSG under Symmetrical Grid Faults

This paper presents a coordinated control strategy for a hybrid wind farm with doubly-fed induction generator (DFIG)- and direct-driven permanent-magnet synchronous generator (PMSG)-based wind turbines under symmetrical grid faults. The proposed low-voltage ride-through (LVRT) strategy is based on a novel current allocation principle and is implemented for individual DFIG- or PMSG-based wind turbines. No communication equipment between different wind power generators is required. By monitoring the local voltages and active power outputs of the corresponding wind generators, the proposed control strategy can control the hybrid wind farm to provide the maximum reactive power to support the grid voltage during a symmetrical grid fault. As a result, the reduction in the active power output from the hybrid wind farm can be decreased, which also helps avoid generator over-speed issues and supply active power support for the power grid. In addition, the reactive current upper limits of DFIG- and PMSG-based sub-wind farms are investigated by considering different active power outputs and different grid voltage dip depths, and the feasible regions of the two types of sub-wind farms for meeting the LVRT requirements are further studied. Finally, the effectiveness of the proposed coordinated LVRT control strategy for the hybrid wind farm is validated by simulation and experimental results.

Application of a battery energy storage for frequency regulation and peak shaving in a wind diesel power system

This study presents the modelling and dynamic simulation of a high penetration wind diesel power system (WDPS) consisting of a diesel generator (DG), a wind turbine generator (WTG), consumer load, dump load and a battery energy storage system (BESS). First the WDPS architecture and the models of the WDPS components are described. The WDPS is simulated in wind-only (WO) mode where the DG is not running and the WTG supply active power and in wind-diesel (WD) mode where both DG and WTG supply power. The simulation results are given showing graphs of the main electric variables in the WDPS (system frequency and voltage and active power in each component) and main battery variables (current, voltage and state of charge). The results in the WO mode show how the BESS, under the command of a proportional-integral-derivative (PID) controller, supplies/stores active power to regulate the isolated system frequency. The WD control enables the BESS to smooth the load and wind power variations, so that the isolated system power quality is improved. Also it is shown in the WD mode a peak shaving application where the control orders the BESS to supply active power temporarily to support system frequency in a DG overload situation.

Injection Impact of Photovoltaic Distributed Generations (PVDG) on Power Distribution System Stability

Utilization of photovoltaic power plants on distribution system has been widely used in many countries. Commonly, the photovoltaic system has been injected to the distribution system and called as photovoltaic distributed generations (PVDG) through medium or low voltage levels. The injection of the PVDG on the distribution system has been claimed to improve the voltage profile and reduce power losses. However, the good performance of the distribution system in term of the steady-state point of view, cannot directly guarantee to give a good response during the system disturbed. Therefore, to show the impact of the PVDG injection on power system stability is concerned in this paper. The size of the power injection and location of the injection site that have been determined by using the optimization technique, are then analyzed based on three scenarios, each of which represents the PVDG injection of 2x0.5MW, 4x0.5MW, and 6x0.5MW respectively at different bus locations. The voltage-, frequency-, and rotor angle-stabilities are analyzed to show the dynamic impact of the PVDG during three-phase fault condition. The analysis results indicate that the second scenario gives the best response in term of the rotor angle-, frequency-, and voltage-responses during dynamic conditions which supplies active power around 28.78% of the total load. The PVDG injection power in the first scenario (14.39% of total load) and also in the third scenario (43.18% of total load) would result in rotor angle and frequency responses with more oscillations being compared to the second scenario. However, the system dynamic responses for all scenarios show damped oscillations to reach the steady-state conditions.

IJIREEICE - Electrical, Electronics, Instrumentation and Control

Photovoltaic (PV) cell characteristics are highly nonlinear that gives single Maximum Power Point (MPP) on P-V curve under uniform insolation condition. The characteristics and hence MPP point changes with the variation in insolation and temperature. In order to extract a maximum power from PV array, a fuzzy based MPP tracking algorithm is proposed. The algorithm accepts single input that is slope of P-V curve and generates the duty ratio as an output that operates the boost converter to track MPP. The algorithm gives faster convergence by applying variable step in duty ratio and gives accurate MPP. The two stage grid interactive PV system described in this paper supplies active power as well as provides harmonic and reactive power compensation. This additional feature increases the effective utilization of PV inverter and increases the overall efficiency of the system. The simulation results validate the performance and stability of the grid interactive PV system using the proposed algorithm for active current injection as well as harmonics and reactive power compensation.

Per-phase vector control strategy for a four-leg voltage source inverter operating with highly unbalanced loads in stand-alone hybrid systems

This paper proposes a new per-phase vector (dq) control scheme for a four-leg grid-forming inverter operating in a three-phase four-wire hybrid stand-alone power system (mini-grid). The challenge is to provide balanced output voltages to highly unbalanced loads, very common in such systems, with a fast dynamic response. By using dq control in a per-phase basis one avoids the use of slow filter-based symmetrical components calculators (SCCs) while achieving zero error, i.e. voltage balancing, in steady-state. Further improvement in the dynamic response is achieved by using fictive axis emulation for obtaining the orthogonal current components required for the per-phase dq control. Simulation and experimental results are provided, to demonstrate the good performance of the system. It works very well, even when the grid-forming inverter supplies active power in two phases and absorbs in the other one, due to the presence of a single-phase PV inverter in the hybrid mini-grid.