Controlled Voltage Source Research Articles

A Virtual Parallel Inductor Approach for Mitigating Reactive Power Sharing Error in a VSG Controlled Microgrid

Virtual synchronous generators (VSGs) deployed into an islanded microgrid emulates the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q-V</i> droop nature of a synchronous generator. Although the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q-V</i> droop control of VSGs enhances the voltage stability, the installed distant VSGs have unequal line impedances due to their random location and rated capacity. The unequal line impedance hinders the proportional reactive power-sharing between VSGs. The proposed study is focused on minimizing the reactive power sharing error by introducing a virtual parallel inductor (VPI) concept. A mathematical model is proposed to create and exploit the analogous relation between the exponential behavior of the VPI and the controllable voltage source to mitigate the reactive power sharing error and simultaneously strengthen the voltage control accuracy. In addition, a droop within a droop strategy is introduced to enhance the reactive power sharing capability of the VSGs. Furthermore, a detailed eigenvalue analysis is conducted to evaluate the limitations of the proposed model. Finally, to test the superiority of the proposed model over the state-of-the-art methods, simulation and hardware experimental results are presented.

-Synthesis-Based Generalized Robust Framework for Grid-Following and Grid-Forming Inverters

Grid-following and grid-forming inverters are integral components of microgrids and for integration of renewable energy sources with the grid. For grid following (GFL) inverters, which need to emulate controllable current sources, a significant challenge is to address the large uncertainty of the grid impedance. For grid forming (GFM) inverters, which need to emulate a controllable voltage source, large uncertainty due to varying loads has to be addressed. This article presents a generalized control framework by leveraging the voltage-current duality in the plant dynamic model of GFL and GFM inverters. The modeling of uncertainties is also generalized under the control framework by quantifying the uncertainties in grid impedance parameters and the uncertainties in equivalent loading parameters for GFL and GFM inverters, respectively. Based on the generalized control framework, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\mu}$</tex-math></inline-formula> -synthesis-based robust control design methodology is proposed for both GFL and GFM inverters. The control objectives, while designing the proposed optimal controllers, are reference tracking, disturbance rejection, and harmonic compensation capability with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${i})$</tex-math></inline-formula> sufficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${LCL}$</tex-math></inline-formula> resonance damping under large variations of grid impedance uncertainty for GFL inverters and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${ii})$</tex-math></inline-formula> with enhanced dynamic response under large variations of equivalent loading uncertainty for GFM inverters. A combined system-in-the-loop, controller hardware-in-the-loop, and power hardware-in-the-loop based experimental validation on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {10}$</tex-math></inline-formula> -kVA microgrid system with two physical inverter systems is conducted in order to evaluate the efficacy and viability of the proposed controllers.

Improved Multiphase Interleaved LLC Resonant Converter With Virtual Controllable Voltage Sources

In this article, a simplified virtual controllable voltage sources (SVCVSs) structure for multiphase ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n \ge3$ </tex-math></inline-formula> ) interleaved LLC resonant converter has been proposed. The SVCVS in each phase is constructed by single auxiliary winding of transformer of the nearby as the phase number is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\ge 3$ </tex-math></inline-formula> , hence printed circuit board (PCB) layout of the improved multiphase interleaved LLC resonant converter becomes much simpler. The feasibility of the multiphase interleaved LLC resonant converter with SVCVSs has been illustrated by vector diagrams, and a family of topologies has been derived. Finally, the 12-V/60-A three-phase interleaved LLC converter with VCVSs/SVCVSs has been tested based on a laboratory built-up prototype. Experimental results show that the three-phase converter with SVCVSs can achieve close output current ripple but higher efficiency than the converter with VCVSs.

Primary and Secondary Control of Grid Connected Micro Grids using ANFIS Controller

The microgrid has been defined to cope with the large penetration of distributed generations (DGs). The microgrid is capable of operating in grid-connected mode (GC) and islanded mode (IS). In microgrid, distributed generations (DGs) are always connected to power network via power inverters. In the Grid Connected mode, DGs commonly acts as current controlled sources to retain a high grid-current quality and a fast dynamic response in the photovoltaic and wind generation systems. However, this current controlled DGs cannot work alone without the voltage/frequency support from utility-grid. Islanding occurs when a portion of a micro-grid becomes electrically isolated, yet continues to be energized by DGs connected to the isolated subsystem. In islanding mode, the inverter-interfaced DGs work as voltage-controlled sources. As system voltage and frequency are not determined by utility-grid, DGs should take care of the voltage/frequency stability. Moreover, the power sharing should be guaranteed according to their individual ratings to avoid circulating currents among DGs. The operation and control of existing utility networks are becoming more and more complex due to the increased interconnection of a DG systems with diverse characteristics. So this paper intends to address the above problems and come out with a proper control strategy using ANFIS controller that could be implemented for the successful operation of a microgrid.

PV Charging Station with VSS-IMSAF and SOSMCC Disturbance Observer Based Controls to Enhance the Distribution Grid Capability

This paper present a three-phase grid-tied (GT) charging station (CS) based on photovoltaic (PV) arrays. The purpose of the proposed CS is to support the distribution grid under heavy electric vehicles (EVs) loads with improved power quality. The variable step size improved multiband adaptive structured filter (VSS-IMSAF) technique is used to control voltage source converter (VSC). Due to the variable step size, the control regulates the grid currents and subjects to the proper step size selection to improve the performance of CS. Moreover, the charge/discharge operations of the electric vehicle battery (EVB) are also incorporated. For regulation of the DC bus voltage, second-order sliding mode cascaded control (SOSMCC) is used, which also controls the charge/discharge operations. The SOSMCC is equipped with the linear observer (LINO), second-order sliding mode observer (SOSMO), linear extended state observer (LESO), and nonlinear extended state observer (NESO), which reduce the overshoot, undershoot, and uncertainties in the voltage at DC link and EV battery current quickly and accurately. This charging station is also capable to operate under load unbalancing, unavailability and reduced insolation, and sudden change of the mode of operation (charging/discharging). The presented controls improve the performance of the CS and feed the reduced harmonic current to the grid under nonlinear load. The test results are presented using the OPAL-RT real-time simulator under various scenarios.

Genetic Algorithm Based Smart Grid System for Distributed Renewable Energy Sources

This work presents the smart grid system for distributed Renewable Energy Sources (RES) with control methods. The hybrid MicroGrids (MG) are trending in small-scale power systems that involve distributed generations, power storage, and various loads. RES of solar are implemented with boost converter using Maximum Power Point Tracking (MPPT) with perturb and observe technique to track the maximum power. Also, the wind system is designed by permanent magnet synchronous generator that includes boost converter with MPPT technique. The battery is also employed with a Direct Current (DC)-DC bidirectional converter, and has a state of charge. The MATLAB/Simulink Simscape software is used to design the proposed model. The switching element of all converters is metal oxide semiconductor field effect transistor. The hybrid system is controlled by a voltage source controller using Proportional Integral Derivative (PID)-Genetic Algorithm (GA), and inductors-capacitors filter is used to reduce the system’s harmonics. Also, smart meters are used for monitoring purposes in residential loads. This paper analyses the performances of the MG against various scenarios.

Active Arc Suppression Algorithm for Generator Stator Winding Ground Fault in the Floating Nuclear Power Plant

Electrical equipment of the floating nuclear power plant operates in a long-term vibration environment. Ground faults occur frequently and are often accompanied by arc, a reliable arc suppression algorithm for the generator stator winding is necessary. In this paper, an active arc suppression method is proposed by connecting a controllable voltage source to the generator neutral point. Through regulating the neutral point voltage to be equal in amplitude and opposite in phase to the fault potential, the fault point voltage can be clamped to a low level to achieve arc suppression. Since the generator's phase potential contains certain harmonic components, the controllable voltage source includes fundamental and third-order harmonic components. To accurately calculate the output voltage, online calculation methods for the fault location, fault potential and grounding capacitance are proposed. The accuracy of the fault location method is verified by simulation and dynamic test. And simulation results based on PSCAD/EMTDC software show that the proposed method can achieve effective arc suppression at different ground fault conditions.

Research on Control Strategy of Grid-connected Brushless Doubly-fed Wind Power System Based on Virtual Synchronous Generator Control

The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid, which leads to the decline of grid stability. Therefore, a control strategy of brushless doubly-fed reluctance generator (BDFRG) based on virtual synchronous generator (VSG) control is proposed to solve the problem in this paper. The output characteristics of BDFRG based on VSG are similar to a synchronous generator (SG), which can support the grid frequency and increase the system ‘inertia’. According to the mathematical model of BDFRG, the inner loop voltage source control of BDFRG is derived. In addition, the specific structure and parameter selection principle of outer loop VSG control are expounded. The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy. Finally, the effectiveness and feasibility of the proposed strategy are verified in the simulation.

An equivalent circuit model of NBTI effect for short-channel P-MOSFET

An equivalent circuit model of the negative bias temperature instability (NBTI) effect in 65 nm P-MOSFET is presented in this paper. Based on an existing P-MOSFET model of a 65 nm CMOS foundry PDK (Process Design Kit) and several basic electrical components and arithmetic cells in the EDA (Electronics Design Automation) library, an equivalent circuit model for NBTI degradation has been achieved. The electrical components and arithmetic cells include voltage source, voltage-controlled voltage source, voltage-controlled current source, adder, and multiplier. The equivalent circuit model includes five tunable input parameters: gate width (W), gate length (L), temperature (temp), stress time (t), and process corner (typical/fast/slow). The model takes into account the effects of drain-source, drain-gate, and gate-source voltage stress states. The effect of process corner on NBTI is also considered. The simulation results show that the performance curve of this P-MOSFET equivalent circuit model is consistent with the measured data in some published literature. This equivalent circuit model can be utilized for long-term reliability IC design.

Excitation control of variable speed pumped storage unit for electromechanical transient modeling

In this paper, a new excitation control of variable speed pumped storage unit (VSPS) for electromechanical transient modeling is presented. Compared with the traditional VSPS excitation control based on current source, the inner loop control of rotor current is retained. The new VSPS excitation control model considers the rotor flux dynamics and represents it as a second-order system. The effectiveness of the proposed excitation control model is verified by the comparison between electromagnetic transient simulation and electromechanical transient simulation. The electromechanical transient simulation of VSPS based on current source and VSPS based on voltage source is compared to verify the necessity of considering rotor flux dynamics. The proposed VSPS excitation control model reflects the characteristics of controllable voltage source and can provide more accurate reactive power and voltage simulation results in transient stability analysis.

Research and Development of Adjustable Discontinuous Pulse Width Modulation Method for Three-Phase Voltage Source Inverter

Continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM) strategies are used to control voltage source inverter operation. CPWM strategies allow for the reduction of total harmonic distortion values, while DPWM strategies provide a more effective reduction in inverter switching losses. The paper is devoted to the problem of improving the three-phase voltage source inverter efficiency by a controlled transition from CPWM to DPWM. The article proposes an adjustable discontinuous pulse width modulation (ADPWM) method, which means a transition from space vector PWM (refers to CPWM strategies) to DPWM in all inverter phases when the switches’ temperatures exceed the allowable value in at least one of the inverter phases. The method flowchart is presented and an algorithm for modifying the envelope curve within one sector is given. In order to test the ADPWM method a Simulink-model of a three-phase voltage source inverter and its control system were developed. A study of the proposed ADPWM method’s efficiency in comparison with CPWM, PCDPWM and NCDPWM methods was carried out using a Simulink-model. It was established that the proposed ADPWM method provides dynamic losses reduction in the inverter switches by 2.86 times compared to CPWM and by 1.89 times compared to PCDPWM and NCDPWM methods. Power supply systems for medium and high-power AC motors provide a promising area for application of the proposed ADPWM method.

Performance Analysis of a Newly Designed DC to DC Buck-Boost Converter

Most of the electronic devices operate on the principle of the voltage-controlled voltage source. With the improved technology and an increase in circuit complexity, the necessity of controlling the output voltage level irrespective of the change in the load current or line voltage is increasing at a tremendous rate. Moreover, battery dominated electronic devices and gadgets demand a wide range of variation and control over DC voltage and power, which currently faces many challenges. This study proposes a design of a DC to DC Buck-Boost converter and analyzes the converter's performance by placing the Pulse Width Modulation of 40% and 48% duty cycles for buck-mode and 66% and 100% for boost-mode in the switching circuit. The result is simulated in the Proteus Suite software.

A Novel Iterative Technique for Interoperability of Real-Time Simulation and Finite Element Simulation Using Railgun Circuit

High-power railgun circuit design and construction is costly and time-consuming. Verifying the behavior and performance of the circuit using a circuit simulator before hardware implementation is faster and more cost-effective. In this brief, a rail type electromagnetic launcher is modeled as a controlled voltage source to the pulse forming circuit and a real-time simulation is performed on that circuit. To validate the developed real-time model of the railgun circuit, the current pulse generated is given as an input to the finite element model developed in LS-Dyna. Obtained results of finite element (FE) simulation and real-time (RT) simulator are compared from a mechanical viewpoint. An iterative procedure is utilized to exactly model the railgun in real-time simulation along with finite element simulation. In the iterative process, the result of the inductance gradient obtained in the finite element simulation is plugged back into the real-time simulator. The current obtained in the real-time simulator is given as an input to finite element simulation. Among the models, the linear fit model of inductance gradient has performed better. A tolerance condition of least approximate error in the muzzle velocity is selected for termination of iterations.

Design and real-time validation of PI and Fuzzy Logic tuned photovoltaic integrated DSTATCOM to improve power quality.

Power loss and malfunctioning of equipment due to current and voltage harmonics produced by nonlinear loads are major concerns for both power suppliers and consumers. This paper employs DSTATCOM to mitigate these harmonic distortions in distribution systems. DSTATCOM is a current controlled voltage source PWM converter with passive components. It supplies compensating current that eliminates current harmonics and provides reactive power compensation thereby providing a smooth source current. The performance of DSTATCOM is controlled using proportional integral and fuzzy logic-based control (FLC) schemes to improve power quality at dynamic loading. As the penetration of photovoltaic (PV) systems in energy production is significant, the power quality issues for PV-integrated systems have also been investigated. The maximum power point for a PV array is tracked using perturb and observe and FLC methods. The complete system is simulated in MATLAB and extensively investigated for a large range of balanced and unbalanced nonlinear load conditions. The simulation results are validated in real time through the hardware in loop (HIL) test bench using Opal-RT controller. The proposed PV-integrated DSTATCOM with FLC yields better performance in terms of DC link voltage settling time, total harmonics distortion, and smooth source current as compared to other schemes.

Gyrator-capacitor based modelling and simulation of forward converter

PurposeThis paper aims to propose an efficient model for analysis of power electronic circuits with integrated magnetic components.Design/methodology/approachThe inductance modeling technique is used as the traditional method for analyzing magnetic components. This model is simple and enough to generate for individual components, that is, an inductor and a transformer. However, it becomes difficult to realize this model for the integrated magnetic structures. This paper shows an appropriate model for individual magnetic components as well as integrated magnetic components and its application to magnetically coupled DC–DC converters. Gyrator–capacitor (G–C) modeling offers a unified, reasonable way of understanding the magnetic components commonly met with in power electronics and the other disciplines.FindingsG–C model allows any electrical and magnetic circuit to be simultaneously simulated with circuit simulators. In this regard, this paper gives a complete simulation model and analysis as an illustrative example. There is no limitation of this paper or future works. The proposed G–C model can be applied to all power electronic circuits having integrated magnetic components.Originality/valueIn the proposed model, the magnetic circuit is converted to a pure electric circuit with capacitors and controlled sources; every winding is replaced with a pair of current controlled voltage sources, namely, a gyrator.

Water Cycle Algorithm Based Parametric Tuning of Non-Negative LMMN Control of Grid Tied Renewable Energy Systems

ABSTRACT This work proposes a hydrological cycle-based optimisation technique for performance enhancement of a non-negative least mean mixed norm (NNLMMN) based voltage source control (VSC) for a three-phase grid integrated wind/photovoltaic (PV) system. Water cycle algorithm (WCA) is employed to tune the proportional–integral (PI) controller parameters of VSC to regulate voltage variations at DC link generated during dynamic load and wind conditions. This results in generation of a specific loss component (Iloss) of current to boost the performance of VSC. The NNLMMN control deals with system identification troubles with a non-negativity limitation in varied Gaussian noise conditions. It generates accurate Iloss to upgrade the ability of VSC to accurately extricate weight signals and the fundamental load current component in terms of improvement in DC link voltage (vdc) and total harmonic distortion. The proposed algorithm mitigates problems like voltage fluctuations besides performing operations like reactive power compensation, enhancement of power quality, load and power balancing at the point of coupling during steady-state and dynamic conditions. In conjunction with the NNLMMN algorithm, the proposed technique reduces the surplus mean square error iteratively, resulting in a compact expression of step size. The proposed topology stands out with an improved performance of vdc under wind gusts and the well-known bell-shaped irradiance curve. For relative evaluations, the performance of non-optimised PI and particle swarm optimised PI has been added to analyse the improved response of vdc and Iloss. Extensive simulation results obtained in MATLAB/Simulink are exhibited to corroborate the efficacy of the suggested system.

A simplified model of Type‐4 wind turbine for short‐circuit currents simulation analysis

The electromagnetic transient (EMT) model of Type 4 wind turbine generator (WTG) requires a small simulation step, and cannot be simplified based on Thevenin-Norton theorem, which results in the low simulation efficiency of large-scale Type 4 WTG-based wind power plants (WPPs) widely connected to the power grid, bringing challenges to the short-circuit currents analysis in the research of protection. Therefore, in order to solve the problem of low simulation efficiency, a simplified model of Type 4 WTG is proposed based on the principle of internal active power balance of Type 4 WTG. The simplified model is represented by controlled voltage source, which eliminates the power electronic switch and DC-link, greatly simplifies the typical EMT model of Type 4 WTG, and does not require small simulation step. The simplified model has simple modelling process and high universality of modelling method. The simulation results show that the proposed model can accurately reflect the EMT characteristics of Type 4 WTG under fault. Compared with the typical EMT model, the simulation time of this simplified model is significantly reduced, and the EMT simulation efficiency of the power grid connecting with large-scale Type 4 WTG-based WPPs has been effectively improved.

Modelling and design of parameters for fast simulation of electromagnetic transient in AC / DC hybrid microgrid

AC/DC microgrids contain a large number of power electronic devices, and their frequent switching process will bring a huge amount of calculation to the electromagnetic transient simulation, thus reducing the simulation efficiency. The research on the external characteristics of the microgrid does not need to pay attention to the dynamic process inside the converter. Therefore, the equivalent simplification of mathematical model is used in this paper to reduce the amount of simulation calculation data of the electromagnetic transient model to achieve the purpose of improving simulation efficiency. This method is concise and efficient, which does not relay on the performance of computer or change the program algorithm of software. By simplifying the current loop with fast dynamic response in the control system, he time response capability of the model is improved, and the converter is replaced by a controlled voltage source, which reduces the dynamic process of frequent changes in the converter. Based on the mathematical equivalent simplified model of microgrid, an electromagnetic transient simulation model was established. Through simulation verification, the simulation efficiency can be significantly improved while the accuracy of the simulation results is guaranteed.

A Novel Flexible Fault Current Limiter for DC Distribution Applications

As an effective carrier of new energy collection, DC power grid has characteristics of low inertia and weak damping, which makes DC fault propagate extremely fast. However, the existing protection and DC circuit breaker (DCCB) technique still could not match its fault propagation speed. Therefore, to solve this problem, a novel of flexible fault current limiter (NFFCL) is presented in this paper. Under normal operation condition, NFFCL is connected to DC line in series without negative influence. When a fault occurs to DC line, NFFCL’s rectifier circuit, according to the protection criterion, provides cascade inductor, which is connected to DC line in series, with a set-slope linear current. In this case, the voltage drop between both ends of inductor can be clamped flexibly, which can even completely isolate the fault area. A controlled voltage source (CCVS) is applied to generate inverse flux to prevent the cascading inductor from magnetic saturation. When the fault disappears, the energy of current-limit inductor can be released and transferred to AC power grid through NFFCL’s converter. Finally, simulation cases are carried out to verify the working principles and practicability of proposed NFFCL.

An efficient multidisciplinary design research for the integrated low speed permanent magnet motor system based on analytical and numerical hybrid analysis

This paper proposed an efficient high-accuracy multidisciplinary design process for the integrated system of low speed permanent magnet synchronous motor (PMSM). The method combined the analytical models and numerical models together to get an efficient way to design the integrated motor. In the proposed method, a magnetic equivalent circuit (MEC) model of the motor is established first based on one modular structure of the motor, and the finite element analysis (FEA) numerical model is used to correct the results of the analytical model next. Then the iron loss, copper loss, and switching loss from the results of the electromagnetic model are loaded to a proposed simplified lumped parameter fluid-thermal model. This fluid-thermal coupled analytical model cuts the fluid flow into several parts depends on the parameters of the cooling path, each parts act as a current controlled voltage source coupled with these parameters. And because this coupled model has controlled sources, the conventional node voltage method is not suitable anymore, so a more universal list parameter calculation method is proposed for this coupled model. Finally, the computational fluid dynamics (CFD) model is used to correct the results of the analytical model as well. The aim of the above analytical models is to quickly get the suitable multidisciplinary pre-design or design trends, and this pre-work or trends will reduce the design process time of the high-accuracy numerical models.