Control Strategy For Inverter Research Articles

Accurate control of virtual oscillator-controlled islanded AC microgrids

Virtual oscillator control (VOC) is an emerging control strategy for grid-forming inverters. In contrast with the droop and virtual synchronous generator methods, VOC is a nonlinear and time-domain strategy that requires only the inverter output current measurement to control the inverter output. Hence, it is characterized by its good dynamic response and stable operation. To explore the VOC performance in islanded AC microgrids, this paper initially demonstrates for the first time the negative impacts of impedance mismatching of the interfacing feeders on power sharing among VOC-based inverters. Then, new control schemes to enhance the operation of VOC-based islanded AC microgrids are proposed. First, a fast and robust secondary control loop to restore voltage and frequency in the microgrid based on the adaptive tuning of the VOC voltage-scaling factor and the VOC inductance parameters is developed. Second, an optimal tuning approach of virdual complex impedance combines virtual inductance and resistance for each inverter is proposed to fully mitigate the impacts of impedance mismatch of the interfacing feeders. Consequently, accurate active and reactive power sharing among VOC-based inverters is achieved. Third, an online and non-invasive estimation technique for feeder impedance is embedded in the control loop of each inverter. Hence, prior knowledge of feeders’ impedances used to tune the virtual impedances of inverters is not required. Simulation and experimental results are presented to validate the efficacy of the proposed control scheme. • The negative impacts of impedance mismatch on power sharing are demonstrated. • A fast and robust secondary control loop for the VOC-based microgrid is developed. • An optimal tuning approach of the virtual impedance for each inverter is proposed. • The impacts of impedance mismatch of the interfacing feeders are fully mitigated. • An impedance estimation technique is embedded in the control loop of each inverter.

Indirect Vector Control of Linear Induction Motors Using Space Vector Pulse Width Modulation

Vector control schemes have recently been used to drive linear induction motors (LIM) in high-performance applications. This trend promotes the development of precise and efficient control schemes for individual motors. This research aims to present a novel framework for speed and thrust force control of LIM using space vector pulse width modulation (SVPWM) inverters. The framework under consideration is developed in four stages. To begin, MATLAB Simulink was used to develop a detailed mathematical and electromechanical dynamic model. The research presents a modified SVPWM inverter control scheme. By tuning the proportional-integral (PI) controller with a transfer function, optimized values for the PI controller are derived. All the subsystems mentioned above are integrated to create a robust simulation of the LIM’s precise speed and thrust force control scheme. The reference speed values were chosen to evaluate the performance of the respective system, and the developed system’s response was verified using various data sets. For the low-speed range, a reference value of 10 m/s is used, while a reference value of 100 m/s is used for the high-speed range. The speed output response indicates that the motor reached reference speed in a matter of seconds, as the delay time is between 8 and 10 s. The maximum amplitude of thrust achieved is less than 400 N, demonstrating the controller’s capability to control a high-speed LIM with minimal thrust ripple. Due to the controlled speed range, the developed system is highly recommended for low-speed and high-speed and heavy-duty traction applications.

Control strategy for grid-connected inverters based on STATCOM reactive power compensation Research

The problem of grid-connected inverter reactive power compensation becomes a decisive factor for grid-connected power quality. To ensure the system unit power factor operation, this paper designs a reactive power compensation control strategy for grid-connected inverters based on STATCOM. On the basis of detailed analysis of the working principle of STATCOM, the grid-connected inverter model is built with the help of MATLAB simulation environment. The experimental results show that the use of STATCOM for grid-connected inverter reactive power compensation ensures stable grid-side output voltage of the grid-connected inverter and can improve the power factor of the system at the same time, which has certain reference significance for upgrading the grid-connected inverter design.

Three-Level T-Type qZ Source Inverter as Grid-Following Unit for Distributed Energy Resources

Distributed energy resources (DERs), such as solar photovoltaics (PVs), are required to achieve a high performance and an efficient use of generated renewable power in grid-integrated applications, both in normal and fault operating conditions. In this article, a grid-following (GFL) multifunctional control strategy for a three-phase three-level T-type quasi-impedance source inverter (3L-T-type qZSI) is studied through simulation and experimental tests. The GFL functionality is achieved by a proportional–integral (PI)-based dq current controller for the active and the reactive power tracking. A PI-based dc controller is used for the dc-link voltage control by taking advantage of the quasi-impedance source (qZS) network ability for input voltage boosting. The dc–ac power conversion is accomplished through a space vector pulsewidth modulation (SVPWM) with inner capacitors voltages balancing capability and minimum common-mode voltage (CMV) generation. Besides, a low-voltage ride-through (LVRT) strategy was implemented to fulfill the fault requirements imposed by the Spanish standard. The simulation and experimental results demonstrate the abovementioned functionalities and validate the stability and good dynamic response of the grid-connected 3L-T-type qZSI. Thus, this work supposes a novel contribution due to the few works previously reported in the literature concerning the performance of this relatively recent inverter topology in grid-tied applications.

Control Strategy for Resonant Inverter in High Frequency AC Power Distribution System with Harmonic Suppression and Transient Performance Improvement

In high frequency AC (HFAC) distribution system, the resonant inverter is used to improve power quality and keep the stability of the output AC voltage. Aiming at the problems of poor output power quality and slow transient performance caused by unreasonable filter parameter design and load change during inverter operation, a single-phase H-bridge LCLC resonant inverter based on analog circuit controller implement is introduced in this paper for HFAC power distribution system (PDS). In this study, to design harmonic compensator and analyze the responsiveness of the inverter, it is necessary to analyze the output voltage total harmonic distortion (THD) of LCLC resonant inverter and the performance of the open loop system in detail. On the one hand, a proportional-integral-resonant (PIR) controller is designed to maintain the zero static error of the voltage output and suppress the output voltage THD of LCLC resonant inverter. On the other hand, an integral controller combines with phase-shift modulation (PSM) method is presented to effectively improve the transient performance of resonant inverter and provide the fixed frequency of the output voltage. On the basis of the above, the experimental prototype is implemented with the output AC voltage root mean square of 28 V, and the output voltage frequency for resonant inverter is equal to switching frequency. A rated output power of 130 W experimental platform is built to verify the effectiveness of the theoretical analysis, control strategy, and modulation method.

Improved master-slave voltage and active power control strategy for multiple grid-connected inverters

In the microgrid with high penetration rate of renewable energy, multiple distributed generations operate in parallel. To ensure stable operation of the microgrid, research for multi-inverter coordination control is necessary. Master-slave control can realize various functions with the combination of different control strategies. Voltage and active power control strategy can provide voltage support for the grid and reduce the voltage fluctuation in the point of common coupling. Previous voltagesupporting methods are usually based on constant droop coefficient, where the control curve is linear. When the voltage fluctuation is too large, the change of the distributed generations power is too small to support the gird voltage. This paper presented an improved master-slave voltage and active power control strategy for multiple photovoltaic inverters. The master inverter operates under maximum power point tracking control strategy as the sample. The slave inverter adopts nonlinear voltage and active power control. When the voltage is too high, increase the droop coefficient to accelerate the power reduction. Conversely, when the voltage is much below the rated value, the distributed power supply will output its maximum power. Finally, the effectiveness of the proposed control strategy is verified by simulation.

Control Strategy for Inverter Based Micro Grid

Control Strategy for Inverter Based Micro Grid

Development of Voltage Control Algorithm for Improving System Stability in Korean Distribution Grids

Problems with overvoltage and reverse energy flow arise as the percentage of distribution energy resources (DERs) in distribution system rises. This paper implements a MATLAB/Simulink linked model that communicates with the OpenDSS engine. The point of common coupling (PCC) voltage typically mitigates using the inverter outputs control. However, case overvoltage issues occur in distribution networks and the influence of the volt–var control effect is insufficient to reduce PCC voltage to a stable range. To improve the reactive control effect, this paper proposes active power control and voltage error compensation methods that maximize the reactive power control effect. The DER management system (DERMS) platform was constructed to analyze the effect of changing DER output values. The DERMS data are organized based on real distribution line (D/L) system data where overvoltage occurred in Korea and the control effect of the real system is analyzed. This control method analysis can be used to develop an inverter control scheme for the over voltage issues described in this paper.

A Control Strategy of LCL-Type Grid-Connected Inverters for Improving the Stability and Harmonic Suppression Capability

The conventional inverter-side current single-loop feedback control scheme is weak in suppressing the grid-side current harmonics, posing a challenge for an inverter to inject high-quality current under distorted grid voltage. With capacitor current compensation added, the control scheme achieves controllability of the grid-side current harmonics so that it can effectively suppress some specific harmonic components. However, due to the stability requirements, only a few low-order harmonic resonance controllers can be applied, which limits the mitigation of high-order harmonics. To tackle this problem, the grid-side current feedback control with inductor–capacitor–inductor (LCL) resonance damping is proposed in this paper. In this case, a higher LCL resonance frequency can be set compared to the inverter-side current single-loop feedback control scheme. Thereby, more resonance controllers can be applied to suppress high-order grid-side current harmonics. The active damping method of capacitor current proportional feedback plus capacitor voltage proportional feedback is adopted because of its high robustness to grid impedance variations. Furthermore, this paper reveals that the applied active damping method has a limitation in that it only considers a single inverter under inductive grid impedance, which cannot eliminate the risk of resonance caused by the interaction of multiple inverters and the grid. To address this issue, a phase lead compensator (PLC) is proposed, eliminating the resonance risk by removing the non-passive region of the inverter output admittance. To retain the advantage of the inverter-side current single-loop feedback control scheme, i.e., only a few measuring devices are required, a digital differentiator is used to calculate the capacitor current from the capacitor voltage. The difference between the measured inverter-side current and the calculated capacitor current is taken to approximate the grid-side current for the feedback control. The control performance is comparable to using the grid-side current for feedback. Simulation and experimental results demonstrate that the proposed control scheme endows the inverter with good stability and current quality without extra measurement devices.

A simple and highly efficient flyback inverter control strategy for AC module application

A simple and efficient control structure of a flyback converter is proposed in this paper considering its intrinsic dynamic characteristics. The proposed control strategy makes use of a PI controller with a low pass filter to overcome the limitations on determining the gains of the feedback control system result from the right-half-plane (RHP) zero and LC filter dynamics. Therefore, the target output current is properly tracked and the disturbances are attenuated by the proposed control system. Furthermore, the stability requirements are satisfied and a zero steady-state error is obtained by appropriately regulating the control signal. This control method is very fast applying the minimum number of delays in its scheme which causes the computational burden to be significantly reduced. Finally, the theoretical claims are confirmed by simulation and experimental results on a 200-W laboratory prototype.

Genetic algorithm tuned adaptive discrete-time sliding mode controller for grid-connected inverter with an LCL filter

The development of a two-stage cascaded control strategy for a single-phase grid-connected inverter with an LCL filter based on inverter-side current is proposed. The main objective of the proposed controller is to minimize both the grid current tracking error and the current total harmonic distortion and to overcome the system resonance introduced because of the third-order LCL filter. In the first part, a feed-forward controller calculates the reference values for the system states at the steady-state operation with no external disturbance. In contrast, an adaptive discrete-time sliding mode controller is used for disturbance rejection caused by parameter uncertainties in the second stage. The proposed control approach also considers the nonlinear behavior of the pulsed nature of the inverter’s hard switching pulse width modulation modulator. The grid-side current is taken as in-phase to the grid voltage for the inverter-side reference values calculation. Numerical simulation and experimental tests were performed to validate the proposed control strategy’s faster dynamic response under external disturbances and parametric uncertainties. An improvement of approximately 18% in THD was recorded against the variation of grid-side impedance ranging from 50%–150% over the conventional discrete sliding mode control These results demonstrate the robustness and effectiveness of the proposed controller to integrate the solar photovoltaic energy sources seamlessly.

Circuit analysis and modeling of a soft-switching pulse power supply based on full-bridge inverter for DBD application

PurposeHow to use a simple and classical topology to provide a high-efficiency excitation voltage for dielectric barrier discharge (DBD) loads is one of the primary problems to be solved for DBD application fields.Design/methodology/approachTo address the issue, a set of modes that can generate a high-efficiency pulse excitation voltage in a full-bridge inverter are adopted. With the set of modes, the unique equivalent circuit of DBD loads and the parasitic parameter of the step-up transformer can be fully used. Based on the set of modes, a control strategy for the full-bridge inverter is designed. To test the performance of the power supply, a simulation model is established and an experimental prototype is made with a DBD excimer lamp.FindingsThe simulation and experimental results show that not only a high-efficiency excitation voltage can be generated for the DBD load, but also the soft switching of all power switch is realized. Besides this, with the set of modes and the proposed control strategy, the inverter can operate in a high frequency. Compared with other types of power supplies, the power supply used in the paper can fully take advantage of the potential of the excimer lamp at the same input power.Originality/valueThis work considers that how to use a simple and classical topology to provide a high-efficiency excitation voltage for DBD loads is one of the primary problems to be solved for DBD application fields.

Design and Simulation of Grid-Connected Photovoltaic Single-Phase Inverters

This paper focuses on a new control strategy for single-phase photovoltaic inverters connected to the electrical power distribution network. The inverter studied is single-phase H bridge, equipped with a robust control strategy by sinusoidal duty cycle modulation. This new control strategy offers the advantage over the control strategy. Most used control in its first approximation (PWM control technique): A low Hardware complexity; a variable modulation frequency/period; a topology of modulation with feedback. This inverter structure is further composed of the robust PI controllers, a boost chopper and an LCL filter. The low voltage electrical network to which this inverter is connected is materialized and simulated by a voltage source of characteristics 230V-15A-50Hz and synchronized to the latter by a phase-locked loop (PLL). In this article, the main components of the grid-connected PV power plant are modeled and simulated under Matlab/Simulink as well as the simulation of the global behavior of the entire network+PV inverter and the results obtained are presented.

Modeling simulation and inverter control strategy research of microgrid in grid-connected and island mode

Under the “double carbon” goal, distributed generation (DG) with inverters will show an explosive growth trend. The microgrid can operate in different modes as a channel for DG to connect to the main grid. In the microgrid, the fast response characteristics of power electronics exacerbate the instability of the microgrid when switching between grid-connected and islanded modes. On the PSCAD/EMTDC simulation platform, a refined power generation model with wind–solar–load–storage microgrid is built to capture the behavior of the system, rather than using a highly simplified model. At the same time, a reasonable control strategy is necessary, which is the key to maintaining the stability of the system. Existing control strategies can only operate in a single mode or the control effect is not ideal. Based on this, on the basis of droop control, the virtual adaptive control loop is added in this study, and the virtual impedance value is adaptively changed according to different output conditions to achieve the purpose of precise control; In the active power control loop, the frequency signal is drawn from the phase-locked loop, and becomes a power feedback variable through the signal transformation process, thereby participating in the power control process and improving the accuracy of frequency control. A standard microgrid power generation model and an inverter control model suitable for grid-connected and off-grid microgrids are built, and the voltage and frequency fluctuations in the two modes are analyzed to verify the effectiveness of the strategy.

Combined feed-forward control strategy for LCL-type grid-connected inverters

LCL-type grid-connected filter circuits are widely used for line network transmission because of their high ability to suppress current harmonics. However, due to the presence of resonance points in this third-order circuit, the system can generate severe oscillations. In order to improve power quality, a combined feed-forward factor control strategy is proposed in this paper. The control system introduces a combined feed-forward factor and incorporates the idea of dual PI control to ensure that the order of the system is reduced while improving its stability, followed by a detailed derivation of the constraint equations for each link parameter. The simulation verifies that the control scheme can regulate the output voltage of the line network and effectively reduce the harmonic content of the line network, providing a reference for reducing the harmonic content of grid-connected currents in engineering.

Research on control system of new energy storage combined thermal power unit based on improved voltage droop control

The new energy station and its configured energy storage of a certain scale can be used as a stable power supply point to participate in the whole process of black start of the thermal motor unit on the opposite side of the power grid. In this paper, active frequency and reactive voltage droop control strategies are adopted in the whole process of new energy storage black start. In order to keep the voltage stable in the initial stage of black start, that is, in the process of energy storage zero start boost air charging line, a voltage control scheme of variable slope energy storage inverter is proposed in this paper. The variable slope transfer function module is introduced into the traditional reactive power voltage droop control to suppress the impulse current in the process of black start voltage building. The above strategy is verified by Matlab / Simulink simulation. The scheme proposed in this paper can meet the requirements of the whole process of new energy storage black start and ensure the stability of the control system of energy storage inverter device.

A voltage recovered control strategy for microgrid inverters based on Narendra-MRAC

Distributed generation (DG) needs to be connected to the microgrid (MG) through an inverter. The power quality of MG is impacted due to the characteristics of DGs and access to many types of loads. Traditionally, robust control or secondary regulation is used in MG inverters to solve power quality problems. However, there are issues in which the controller order is too high or the design is too complicated. A novel adaptive control strategy based on Narendra theory for voltage source inverter in MGs is proposed in this paper to solve the above problems. This strategy improves the control performance by designing an adaptive law. The MG inverter can adjust the parameters adaptively to change the output voltage quality under complex working conditions. The example shows that the inverter with the proposed adaptive control strategy can maintain good voltage control performance under complex conditions of MG, thus ensure the power quality in the MG.

MPC-based control strategy of PV grid connected inverter for damping power oscillations

With global warming and the depletion of fossil energy, the development of photovoltaic (PV) energy has attracted attention in many countries. However, when large-scale PV power stations are connected to the power grid through inverters, the inertia and damping capacity of the power system are greatly reduced, leading to frequent power oscillations in the power system. To solve this problem, this study proposes a control strategy for PV grid-connected inverters based on the model predictive control (MPC) algorithm. Based on the MPC algorithm and the establishment of a discrete-time predictive model, the PV grid-connected inverter dynamically adjusts its output current to suppress power oscillations. The simulation results demonstrated the effectiveness of the proposed control strategy in damping power oscillations in the power grid and enhancing the stability of the power system.

An H∞ filter based active damping control strategy for grid-connected inverters with LCL filter applied to wind power system

Since the LCL filter has good performance to attenuate high frequency harmonics, it is widely used in wind power inverters. But it can cause high-frequency oscillations and instability, which limits its application in wind power system. For an LCL-type grid-connected inverter, the conventional capacitor-current-feedback type active damping control strategy can retain the high-frequency characteristics of LCL filter while suppressing the resonant peak effectively, with the drawback of requiring additional current sensors. Therefore, an H∞ filter based active damping strategy of LCL grid-connected inverter is proposed. The state space model and the process noise model of the LCL inverter are built, and then the general model of the standard H∞ control problem is derived, which helps to solve the H∞ filter. The H∞ filter can estimate the filter capacitor current according to sample values of the injected current and the voltage of the point of common coupling, and the estimation accuracy can be guaranteed even if parameter perturbations exist in the LCL filter. The proportional resonant controller is adopted to track the grid current. Therefore, the proposed control strategy can effectively suppress the resonance peak of the LCL filter without additional current sensors and be insensitivity to system parameter perturbations. The simulation and experimental results verify the feasibility and superiority of the proposed method.

A new control strategy for harmonic reduction in photovoltaic inverters inspired by the autonomous nervous system

Abstract This paper proposes a new inverter control strategy whose main purpose is to reduce the current harmonic distortion resulting from unnecessary control actions without sacrificing the system’s dynamic response. The brain’s capabilities to learn and react to stress are mimicked to generate control actions based on emotional cues. The model is based on the brain emotional learning based intelligent controller, to which an autonomous nervous system was added. The modified controller aims at separating the strategy during transient states from the one during steady states. The proposed method was compared to the PI controller, the PR controller, and a neural network-based controller on Matlab Simulink. It shows major improvements in terms of harmonic distortion and a complete removal of the inter-harmonics. It provides a good dynamic response in transient states and an immunity to irrelevant signal variations during the steady state, which results in an improvement in the harmonic production.