Voltage And Frequency Controller Research Articles

A Frequency and Voltage Coordinated Control Strategy of Island Microgrid including Electric Vehicles

Frequency and voltage deviation are important standards for measuring energy indicators. It is important for microgrids to maintain the stability of voltage and frequency (VF). Aiming at the VF regulation of microgrid caused by wind disturbance and load fluctuation, a comprehensive VF control strategy for an islanded microgrid with electric vehicles (EVs) based on Deep Deterministic Policy Gradient (DDPG) is proposed in this paper. First of all, the SOC constraints of EVs are added to construct a cluster-EV charging model, by considering the randomness of users’ travel demand and charging behavior. In addition, a four-quadrant two-way charger capacity model is introduced to build a microgrid VF control model including load, micro gas turbine (MT), EVs, and their random power increment constraints. Secondly, according to the two control goals of microgrid frequency and voltage, the structure of DDPG controller is designed. Then, the definition of space, the design of global and local reward functions, and the selection of optimal hyperparameters are completed. Finally, different scenarios are set up in an islanded microgrid with EVs, and the simulation results are compared with traditional PI control and R(λ) control. The simulation results show that the proposed DDPG controller can quickly and efficiently suppress the VF fluctuations caused by wind disturbance and load fluctuations at the same time.

Voltage and Frequency Controller for PMSG-Based Small-Hydro Power Generation

This paper deals with the implementation of voltage and frequency controller (VFC) of a small-hydro system using permanent magnet synchronous generator (PMSG) supplying power to isolated loads in remote areas. An improved second-order generalized integrator control technique is presented for controlling voltage source converter (VSC) of VFC. A circuitry for voltage and frequency regulation across a 230 V, 50 Hz, 3.7 kW PMSG feeding three-phase consumer loads is presented in this work. The VSC is used for regulating voltage constant at the generator terminals and also to ensure balanced stator currents, stabilized DC link voltage and current harmonics mitigation at linear/nonlinear and balanced/unbalanced loading conditions. The VFC is used for maintaining frequency intact by supplying excess power in the dump load. This system is modelled and simulated in MATLAB/Simulink environment. Simulated and experimental results demonstrate that the generated voltage and frequency are regulated under dynamic changes in consumer loads.

Impedance Modeling and Analysis of MMC-HVDC for Offshore Wind Farm Integration

The offshore ac side impedance model of the modular multilevel converter (MMC) based high voltage direct current (HVdc) system is essential for analyzing the interaction stability between MMC-HVdc and the offshore wind power plants. This paper develops the offshore ac side impedance model of an MMC-HVdc system for wind power integration taking the effects of offshore station, dc cable and onshore station into consideration. The dc impedance model of the onshore station is first derived which includes the effects of dual closed loop dc bus voltage control and circulating current control. Then, the dc impedance of the onshore station and dc cable impedance are used to derive the ac side impedance of the offshore station under open loop control. In addition, the influence of the dual closed loop based ac bus voltage and frequency (VF) control on the offshore ac impedance is analytically derived. As a result, the proposed model can be used to reveal the coupling between offshore offshore ac system and dc system as well as to investigate the influence of the dc system and VF controller in the offshore ac impedance of the MMC-HVdc system. Furthermore, the proposed model overcomes the deficiencies in harmonic resonance analysis of MMC-HVdc based offshore wind power integration system. The results of the simulation in PSCAD/EMTDC validate the proposed models and analyses.

Features of Power Quality in Single-Phase Distributed Power Generation Using Adaptive Nature Vectorial Filter

This paper presents the new controller for voltage and frequency control (VFC) of two-winding single-phase induction generator. It provides coordinated control of battery energy storage system (BESS) and dump load during the mismatch of power between loads and generator using VFC loop. It provides protection against overcharging of BESS. For this purpose adaptive vectorial filter (AVF) is implemented to operate single-phase induction generator in standalone mode of operation for power quality features. The unique feature of this filtering technique is its simplicity and no other analogy filters are required to produce the reconstructed signal of fundamental frequency. This procedure uses the vectorial natures of the single-phase input signal, which is decomposed by shifting property in the α–β orientation frame in order to get the diverse harmonic constituents. The design and analysis of AVFs for the proposed system is carried out in order to find the required performance. The proposed control method is evaluated by simulations in MATLAB/Simulink followed by experimental validation in laboratory for signifying its capability to execute different harmonic constituents under an extremely distorted generator current. Apart from control method, design of generator with finite-element method and its electromagnetic properties are also discussed.

A Voltage and Frequency Control Strategy for Stand-Alone Full Converter Wind Energy Conversion Systems

This paper addresses the design and analysis of a voltage and frequency control (VFC) strategy for full converter (FC)-based wind energy conversion systems (WECSs) and its applicability for the supply of an isolated load. When supplying an isolated load, the role of the back-to-back converters in the FC must change with respect to a grid-connected application. Voltage and frequency are established by the FC line side converter (LSC), while the generator side converter (GSC) is responsible for maintaining constant voltage in the DC link. Thus, the roles of the converters in the WECS are inverted. Under such control strategies, the LSC will automatically supply the load power and hence, in order to maintain a stable operation of the WECS, the wind turbine (WT) power must also be controlled in a load-following strategy. The proposed VFC is fully modelled and a stability analysis is performed. Then, the operation of the WECS under the proposed VFC is simulated and tested on a real-time test bench, demonstrating the performance of the VFC for the isolated operation of the WECS.

Modeling and Control of LCC Rectifiers for Offshore Wind Farms Connected by HVDC Links

This paper presents a voltage and frequency control (VFC) and an average-value model (AVM) of a line-commutated converter for a rectifier station in an offshore wind farm (OWF) connected by a high-voltage direct current link. A capacitor bank is placed at the AC terminals of the rectifier station to perform VFC within the OWF. The proposed model uses the active and reactive power generated by the OWF as inputs, while the state variables are the voltage magnitude and phase angle at the capacitor bank bus. The proposed VFC is based on the orientation of the voltage vector at the capacitor bank bus toward a synchronous reference axis. It is then demonstrated that frequency control is achieved by regulating the reactive power balance at the capacitor bank bus, while voltage control is carried out by regulating the active power balance. Moreover, it is demonstrated that in a diode rectifier, although voltage cannot be controlled as in a thyristor rectifier, it is bounded within acceptable limits. In addition, small-signal study is performed to facilitate controller design and system stability analysis. VFC and the accuracy of the proposed AVM are validated by simulation, using both the proposed AVM and a detailed switching model.

Back-Propagation Algorithm-Based Controller for Autonomous Wind–DG Microgrid

This paper deals with a wind–diesel generator hybrid configuration of the microgrid using a voltage source converter (VSC) as a voltage and frequency (VF) controller. The wind power generated by permanent magnet brushless dc generator, and the maximum power is captured by a maximum power point technique using a boost converter with an incremental conductance approach. This power is supplied to the consumer loads and surplus power is stored into battery system (BS). BS is attached at dc link of VSC, which provides load leveling during less or no wind conditions. With such combination of energy resources, a reduced rating, diesel engine-driven squirrel cage induction generator feeds loads, and VSC at point of common coupling (PCC) supports the system when the wind generation is unable to meet out the load demand. Back-propagation feed-forward control algorithm is used for VF control of VSC. This controller provides harmonics elimination, load leveling, and reactive power compensation, and also regulates the voltage at PCC. This microgrid is modeled in MATLAB Sim power tools, and simulation results are produced to verify the appropriate working of both the converters and the overall system. A prototype of the microgrid is also developed to validate the design and model through test results. A comparative study of simulated and experimental work is given in detail.

Soft Computing Technique-Based Voltage/Frequency Controller for a Self-Excited Induction Generator-Based Microgrid

Microgrids (MGs) are small scale energy unit networks that can offer an adequate energy supply to cover local demand by incorporating renewable energy and storage technologies. The system capacity is generally between several kW to several MW. They work in terms of low voltage (LV) level or medium voltage (MV) level. They can also be connected/disconnected from main grid whenever it is necessary. This paper presents a comparison of two soft computing (SC) techniques fuzzy logic (FL)/artificial neural network (ANN) over a conventional proportional integral (PI)-based voltage frequency controllers used for improving the performance of MG under islanding mode. Microgrid is formed by using three 7.5[Formula: see text]kW, four pole, 50[Formula: see text]Hz, self-excited induction generators (SEIGs) driven by small hydro turbine feeding three-phase four-wire consumer load. The proposed topology functions excellently in maintaining phase angle, voltage and frequency (VF) regulation of the micro sources (MSs) in islanded mode as well as in resynchronization when one of the MSs is turned off due to fault or unavailability of resources. The conventional PI controller is replaced by a controller based on SC techniques, as it has disadvantages like explicit description of mathematical model, affected by variations in consumer loads and sources, thus the proposed SC techniques enhance the performance of VF controller. A comparative analysis of PI/FL/ANN controller is also carried out to highlight the superiority of AI controller. The performance of controller with proposed configuration is verified for balanced/unbalanced non-linear load. Microgrid and control schemes are simulated in MATLAB Sim Power Systems environment.

Performance of a Self-Excited Induction Generator With DSTATCOM-DTC Drive-Based Voltage and Frequency Controller

This paper presents the performance of a self-excited induction generator (SEIG) with a voltage and frequency controller (VFC) in a standalone microhydro power generating system. The VFC consists of a distribution static compensator (DSTATCOM) and a direct torque controlled variable frequency induction motor drive (VFIMD) operating as an electronic load controller (ELC). The DSTATCOM is an insulated-gate bipolar transistor-based three-leg voltage source inverter with a self-sustaining dc bus. The main objective of DSTATCOM is to regulate the system voltage through reactive power compensation. In addition to voltage regulation, the DSTATCOM compensates the harmonics generated by nonlinear loads as well as ELC. The ELC controls the system frequency through the active power balance. The VFIMD of the ELC drives a pump and it consumes the power in excess of consumer load power to maintain constant power generation at the SEIG terminals, which in turn regulates the system frequency. A prototype-proposed VFC is developed and tested with a variety of loads. Experimental results demonstrate that the proposed VFC can effectively control the system voltage and frequency.

Asynchronous Generator With Battery Storage for Standalone Wind Energy Conversion System

This paper deals with the implementation of a voltage and frequency controller (VFC) for an isolated asynchronous generator (IAG)-based stand-alone wind energy conversion system (SWECS) with a battery energy storage system (BESS) feeding three-phase four-wire loads. The control algorithm for VFC is based on a low-pass filter (LPF) for estimation of reference source currents. The VFC is realized using a voltage source converter (VSC) with a BESS at its dc bus and a nonisolated T-connected transformer to feed three-phase four-wire consumer loads. Test results are presented to demonstrate the performance of a proposed VFC for an IAG in the wind power generation.

Voltage and Frequency Controller for An Autonomous Asynchronous Generator

A battery Energy storage system (BESS) based voltage and frequency controller (VFC), for an Autonomous Asynchronous Generator (ASG) driven by an uncontrolled pico hydro turbine used in constant power mode, is presented in this paper. Excitation of the asynchronous generator with capacitor bank enables it to generate rated voltage at no load. The additional reactive power demand of the ASG on load and that for the load itself is provided by the VFC. The proposed controller has the capability of harmonic reduction, load balancing and load leveling along with voltage and frequency control. The VFC has been realized using an IGBT based current controlled voltage source converter (CC-VSC) having a battery at its DC link. A simple and effective linear control scheme using SPWM control has been used to control the CC-VSC. This control scheme is easier to implement on hardware than the other reported schemes, as it involves only linear PI controllers. The effectiveness of the proposed controller for an autonomous generator is demonstrated by simulation on MATLAB platform.

Doubly fed induction generator‐based off‐grid wind energy conversion systems feeding dynamic loads

This study deals with the operation and control of a doubly fed induction generator (DFIG)-based off-grid wind energy conversion system (WECS). Two back-to-back connected voltage source converters with intermediate DC-link supported with a battery energy storage system are used as a voltage and frequency controller (VFC). A field oriented control algorithm is used for VFC to perform as a load leveller, a load balancer, an active filter along with a VFC. Simulation results are verified on a developed prototype of VFC for DFIG-based off-grid WECS. The performance of WECS is demonstrated feeding non-linear and dynamic loads.

Design and Implementation of Four-Leg Voltage-Source-Converter-Based VFC for Autonomous Wind Energy Conversion System

This paper deals with the design and implementation of a voltage and frequency controller (VFC) for a three-phase four-wire autonomous wind energy conversion system (WECS). The VFC is realized using a four-leg voltage source converter and a battery energy storage system. The enhanced phase-locked loop-based control algorithm is used in the VFC. A prototype of a 3.7-kW isolated asynchronous generator-based WECS is developed to demonstrate the performance of the VFC. The obtained test results have shown that the proposed VFC functions as a load leveler, a load balancer, a neutral current compensator, and a harmonic eliminator.

Stand-Alone Single-Phase Power Generation Employing a Three-Phase Isolated Asynchronous Generator

This paper deals with a stand-alone single-phase power generation using a three-phase isolated asynchronous generator (IAG) coupled with a wind turbine or a pico-hydro turbine. The proposed voltage and frequency controller (VFC) for a stand-alone single-phase power generation is used as a phase balancer for a three-phase IAG, a load leveler, and an active filter. The VFC is realized using a three-leg voltage-source converter and a battery energy storage system. The VFC ensures optimum utilization of a three-phase IAG for feeding a variety of single-phase loads, improves conversion efficiency, and reduces noise and vibration in the IAG. The rating considerations of an IAG and VFCs are also discussed for a single-phase power generation. The performance of an IAG system is demonstrated under steady-state and dynamic conditions of feeding single-phase linear and nonlinear loads. Simulated results are validated with test results on a developed system.

Solid-state controller for an IAG-based stand-alone wind energy conversion system

This paper deals with an implementation of voltage and frequency controller (VFC) for isolated asynchronous generator-based three-phase autonomous wind energy conversion system. The focus of the proposed work is to provide a feasible solution for rural communities to serve their electricity needs. The least mean square algorithm is used for the extraction of active and reactive power components of the load currents. A three-leg voltage-sourced converter with a battery energy storage system is used as a VFC. The control algorithm is implemented using a digital signal processor. The steady-state and dynamic performances of VFC are demonstrated through test results under static and dynamic loads.

A New Voltage and Frequency Controller for Standalone Parallel Operated Self Excited Induction Generators

This work proposes a new voltage and frequency controller (VFC) for standalone parallel operated self excited induction generators driven by uncontrolled micro hydro turbines. This VFC consists of a current controlled static compensator (STATCOM) for regulating the voltage during different load conditions and a variable frequency induction motor drive driving a water pump operating as an electronic load controller (ELC) for balancing the generated power, which in turn regulates the system frequency. The STATCOM functions as a reactive power compensator for regulating the system voltage and an active filter for harmonics elimination. The control algorithm of STATCOM is based on the synchronous reference frame (SRF) theory.

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.

Neural Network Based Voltage and Frequency Controller for Isolated Wind Power Generation

This paper deals with an artificial neural network based control of the voltage and frequency (VF) of autonomous wind power generation using an isolated asynchronous generator (IAG) feeding three-phase four-wire loads. The reference generator currents are estimated using the adaptive linear neuron and its training through least mean square (LMS) algorithm to control the VF of an IAG system. Three-leg voltage source converter (VSC) with an isolated T-connected transformer is used as an integrated VSC. The integrated VSC with a battery energy storage system is used to control the active power of the wind energy conversion system (WECS). Bi-directional power flow capabilities of the proposed VF controller in WECS are demonstrated through simulation results. The proposed controller functions as a VF regulator, a load leveler, a load balancer and a harmonic eliminator in the WECS. The WECS is modeled and simulated in the MATLAB using the Simulink and the sim power system toolboxes.

Voltage and frequency control of asynchronous generator for stand-alone wind power generation

A synchronous detection-based control algorithm for voltage and frequency control (VFC) of an isolated asynchronous generator (IAG) is proposed for a stand-alone wind energy conversion system (SWECS). A three-legged voltage source converter (VSC) with an isolated star/polygon transformer is used as an integrated VSC. The integrated VSC with a battery energy storage system is used to control the active and reactive powers of the SWECS. The SWECS is modelled and simulated in the MATLAB using the Simulink and the sim power system toolboxes. Test results on the developed prototype of SWECS are also presented to validate the control algorithm. The proposed VFC functions as a voltage and frequency regulator, a load leveller, a load balancer and a harmonics filter in the SWECS.

Isolated Wind–Hydro Hybrid System Using Cage Generators and Battery Storage

This paper deals with a new isolated wind-hydro hybrid generation system employing one squirrel-cage induction generator (SCIG) driven by a variable-speed wind turbine and another SCIG driven by a constant-power hydro turbine feeding three-phase four-wire local loads. The proposed system utilizes two back-to-back-connected pulsewidth modulationcontrolled insulated-gate-bipolar-transistor-based voltage-source converters (VSCs) with a battery energy storage system at their dc link. The main objectives of the control algorithm for the VSCs are to achieve maximum power tracking (MPT) through rotor speed control of a wind-turbine-driven SCIG under varying wind speeds and control of the magnitude and the frequency of the load voltage. The proposed wind-hydro hybrid system has a capability of bidirectional active- and reactive-power flow, by which it controls the magnitude and the frequency of the load voltage. The proposed electromechanical system using SCIGs, an MPT controller, and a voltage and frequency controller are modeled and simulated in MATLAB using Simulink and Sim Power System set toolboxes, and different aspects of the proposed system are studied for various types of linear, nonlinear, and dynamic loads, and under varying wind-speed conditions. The performance of the proposed system is presented to demonstrate its capability of MPT, voltage and frequency control (VFC), harmonic elimination, and load balancing.