Control Strategy For Inverter Research Articles

Predicting the stability of smart grid for improving the sustainability using distributed generation technology

Distributed Generation balances the supply in the grid effectively. Numerous distributed power generation technologies need more efficiency, cost, and power output to meet the energy requirements. Hence, this paper has aimed to provide an efficient DG system by integrating a PV module with a smart grid through a 3-phase AC-DC converter. Numerous PV modules are combined through DC linking, and different inverter control strategies are used to control the network. The ANN algorithm is used to optimize the demand and supply in the network. PV modules are included in the network to boost up the renewable energy source for the network. The power generated from the PV module is converted to DC through 3 phase AC-DC converter. A DC-link modeling is carried out between various converters and PV modules. It helps balance the variation in the DC input from the PV modules converted by AC-DC converters. The input current is again sent into a closed-loop inverter system to control the input current appropriately based on the demand. The problems between demand and supply are sorted through an ANN algorithm that optimizes the whole model based on supply and demand. The whole is simulated, and the results obtained are discussed in detail. The results are compared with similar Distributed power generation technologies to compare their efficiency. The comparison clearly shows that the proposed model provides better environmental sustainability and expandability to the system.

Design and analysis of a new multi-level inverter topology with a reduced number of switches and controlled by PDPWM technique

With their many advantages, including low power dissipation in power switches, low harmonic content, and reduced electromagnetic interference (EMI) from the inverter, multilevel converter (MLI) topologies are becoming more and more in demand in high and medium power applications. This paper introduces a novel multi-level symmetric inverter topology with adopted control. The objectives of this article are to architecturally define the positions of the various switches, to choose the right switches and to propose an inverter control strategy that will eliminate harmonics while producing the ideal output voltage/current. By using fewer switching elements, fewer voltage sources, and switches with a total harmonic content (THD) which reduces losses and a drop in minimum voltage (Vstrssj), the proposed topology is more efficient than conventional inverters with the same number of levels. The new topology will be demonstrated using a seven-level single-phase inverter. For various modulation indices, MATLAB-SIMULINK is used to study and validate the topology.

A Universal Model Predictive Control Strategy for Dual Inverters Fed OW-PMSM Drives

This study proposed a universal model predictive control (MPC) strategy for dual inverters fed open-winding permanent magnet synchronous motor (OW-PMSM) drives where two isolated buses have arbitrary DC voltages. Diverse and unordered space vector distribution caused by different voltage ratios of DC buses that greatly increases the calculation burden for the conventional MPC algorithm is analyzed in detail. Based on this, a novel MPC strategy that is universally applicable to any voltage ratio is put forward, which could decrease the number of candidate vectors from 49 to less than 15 in every cycle. Although the computational burden is reduced, the output power quality is unaffected owing to the effective simplification of the vectors. Besides, an optimized switching algorithm is designed to adapt to the situation when the voltage ratio changes during the operation state. The experimental results are presented to verify the effectiveness of the proposed method.

Bang-Bang Funnel Control of Three-Phase Full-Bridge Inverter Under Dual-Buck Scheme

This paper proposes a bang-bang funnel control strategy for the three-phase full-bridge inverter under dual-buck scheme. By adopting the so-called dual-buck scheme, only two switches on the different phase legs are controlled at high frequency, precluding the dead-time utilization. Furthermore, the full-bridge topology can be physically decoupled into two parallel-connected buck units, which allows the inverter to be formulated and analysed by the dynamic model of buck chopper. The bang-bang funnel controller (BBFC) works with just two control values, and it is able to restrain the tracking error between the system's output and the reference within the pre-specified funnel boundaries. The nature of BBFC makes it simpler, faster and more robust, suitable for the inverter operating in dual-buck scheme. The proposed strategy not only guarantees accurate static output performance, but also promotes the inverter's dynamic response against rapid variations of the load, the reference and the input voltage, as well as its robustness to the unexpected parameter changes of the elements. Finally, the effectiveness of the proposed strategy is validated by the simulation and experimental results.

A Phase-Shifting DC-Link Voltage Control Strategy for Parallel Inverters to Suppress Interharmonics in PV Systems

The large-scale installation of PV systems leads to interharmonic problems, which greatly affect the power quality of power system. It has been revealed that the DC-link voltage oscillation caused by the perturbation maximum power point tracking (MPPT) algorithm is one of the main causes of interharmonics. To address this issue, a phase-shifting DC-link voltage control strategy for parallel inverters to suppress interharmonics in PV systems is proposed. In this method, the relationship between interharmonic characteristics and reference DC-link voltage is the basis for suppressing interharmonics. The proposed system contains two parallel inverters whose reference DC-link voltages are antiphase. Therefore, the interharmonic current can be eliminated with each other. Simulations and experiments have been constructed to verify the effectiveness of the proposed interharmonic suppression strategy.

Two-Stage Grid-Connected Frequency Regulation Control Strategy Based on Photovoltaic Power Prediction

The large number of photovoltaics connected to the distribution network via power electronic converters squeezes the functional space of traditional synchronous generators in the power system and reduces the inertia of the network itself. However, due to the random and fluctuating nature of PV power generation, different types of meteorological conditions can also affect the inertia support capability of PV output power. Therefore, this paper proposes a frequency regulation control strategy based on the dynamic characteristics of the grid-side DC capacitor. Firstly, the control strategy of the grid-side inverter is improved and the mechanism of the frequency dynamic response model under PV penetration is analysed. Secondly, data from different weather types are correlated and analysed to predict PV power, and wireless sensor technology is used to introduce the data signals into the control link. Finally, a simulation model of a two-stage PV power generation system is developed and the fast-response capability of the system under different control parameters when the load is increased or decreased is analysed. The results show that under the proposed frequency regulation strategy, the larger the regulation coefficient and virtual inertia time constant, the greater the virtual inertia provided by the PV power generation, which improves the stability of the distribution network.

Grid-Connected PV Inverter Control Strategy Based on the Sliding Mode

The Photovoltaic grid-connected inverter is an essential equipment of photovoltaic grid-connected system. Due to the disadvantages of the traditional PI control method for grid-connected photovoltaic inverters, this paper adopts the integral sliding mode variable structure to control grid-connected inverters. Grid inverter DC control mode was introduced in detail in the sliding mode variable structure control strategy. Using Matlab simulation platform to compare and analyze the traditional PI voltage compensation control strategy and sliding mode variable structure control strategy. From the waveform of the simulation output, the current harmonic at the output of the grid-connected inverter is reduced, and the power factor is increased, with the power factor is close to 1. The control precision, robustness and anti-interference ability of grid-connected system are improved. Which proved the feasibility and the superiority of the proposed control strategy.

An individual sequencing control strategy for three-phase four-leg inverter under unbalanced loads

Under the influence of the unbalanced load, the negative and zero sequence components in the output voltage of the three-phase four-leg voltage source inverter(TPFL-VSI) will cause asymmetry voltage. This paper designs an individual sequencing control for the three-phase four-leg inverter to address this problem. The second-order generalized integrator is adopted to extract the current’s positive and negative sequence components. The virtual oscillator control(VOC) controls the positive sequence component, and the negative sequence component is suppressed by designing the virtual impedance and the multiple proportional resonance controller. The proportional resonance control is used to control the zero-sequence voltage of the fourth bridge arm. Considering that voltage deviation is caused by the access of negative sequence virtual impedance and load step, the secondary voltage compensation strategy is further added in the individual sequencing control to improve the droop relationship in the VOC and effectively solve the problem of system voltage instability. Ultimately, a TPFL-VSI model is built in Matlab/Simulink, and simulation results verify the feasibility and effectiveness of the proposed control strategy under different conditions.

VSC control strategy for HVDC compensating negative sequence and decaying DC components

This paper proposes a voltage source converter (VSC) control strategy for the high voltage direct current (HVDC) transmission systems compensating the negative sequence and decaying DC (DDC) components. The mathematical model of the grid fault current is established firstly, and the DDC component is extracted using the property that the integral of the periodic signal is 0. Secondly, the fundamental wave component of the grid fault current signal is separated in the rotating frame system to obtain the compensation current command of VSC-HVDC. Finally, the performance of the proposed control strategy is compared with the conventional inverter control strategy when compensation the negative sequence and decaying DC (DDC) components by the experimental platform, and the experimental results show that the flexible HVDC transmission system with the proposed control strategy has the desired ability of compensating the negative sequence and DDC components simultaneously.

A control strategy of microgrid voltage source inverter based on self‐learning sliding mode control

AbstractIn island mode, voltage source inverter (VSI) supports the frequency and voltage of microgrid. After the complex load is connected, the VSI control performance is degraded, and the output voltage has deviation, negative sequence, waveform distortion and other problems, which further deteriorate the power quality of the microgrid. Different from the traditional strategy that only focus on a single problem, the strategy proposed in this paper can deal with these three power quality problems simultaneously. In this paper, a self‐learning sliding mode control strategy is proposed. First, a nonlinear smooth function is used to design an expansion observer, which can estimate the expansion state of the internal uncertainties and external disturbances of the control system. Second, the extended observer is combined with the self‐learning synovial control technology to realize the self‐learning synovial disturbance rejection control of VSI control strategy. This strategy can improve the stability of voltage control under various working conditions without precise mathematical model. The simulation results show that, compared with the traditional control strategy, this strategy has good robustness under different working conditions.

Droop control strategy for microgrid inverters: A deep reinforcement learning enhanced approach

To better tap into the potential of distributed renewable energy generation, microgrid system has become an emerging technology. As the bridge of microgrids, the inverters can flexibly convert distributed DC power input into AC power output. It is verified that the traditional droop control strategy for microgrid inverters has inherent defects of uneven reactive power distribution. To this end, this paper proposes a droop control strategy as a multi-objective optimization problem while considering the deviations of bus voltage and reactive power distributions of microgrids. Then, the optimization problem is further formulated as a Markov decision process and solved by a deep reinforcement learning (DRL) algorithm called deep deterministic policy gradient to obtain a dynamic optimal droop coefficient control strategy. Simulation results demonstrated that our DRL-based strategy eliminates the uneven reactive power distribution without voltage drop.

Analysis of primary frequency regulation characteristics of PV power plant considering communication delay

With the large-scale development of photovoltaic power generation, photovoltaic power plants (PVPP) are required to participate in primary frequency regulation to maintain the stability of the power system. Existing researches seldom consider the influence of the data communication delay of PVPP on the primary frequency regulation ability of PVPP. From the perspective of the communication system structure and control strategy of PVPP, this paper firstly analyzes the composition of the communication delay involved in the process of primary frequency regulation. Through the simulation of the three-machine nine-bus power system, the frequency regulation performance of PVPP under different time delays are analyzed. Furthermore, the influence mechanism of time delays on the primary frequency regulation results is discussed. Finally, two optimization schemes are proposed, which can reduce the communication delay and improve the tolerance of PVPP to the communication delay, respectively. The research results show that there are mainly two types of delays in the primary frequency regulation process of traditional large-scale PVPP. The longer the delays, the weaker the PVPP’s ability to participate in primary frequency regulation. In addition, the optimization of PVPP communication system and control strategy of inverters can help improve the frequency regulation ability of the PVPP, thereby maintaining the frequency stability of the power system.

Improved current droop control strategy of parallel inverters for microgrid based on negative feedback of current

In order to increase the current distribution accuracy of the system and restrain the system frequency fluctuation on the basis of reducing the control operation complexity, this paper proposes an improved current droop control strategy. The strategy can be described as follows: Firstly, a virtual negative inductance and a virtual resistance are introduced into the voltage and current double closed loop control to balance the output impedance of the inverter unit. Then an impedance ratio is introduced to solve the contradiction between the virtual complex impedance and potential drop. Finally, by introducing new current variables and using these current variables to form the negative feedback to the droop coefficient in the voltage equation in the droop control, the allocation of the active current and reactive current is implemented in terms of the inverter capacity, and the plug and play function of the inverter unit is realized in the low-voltage microgrid. A great number of simulation results show that by the strategy, the active and reactive currents output can be distributed in terms of the own capacities of the inverters in the system, the smooth operation of parallel inverters with the same or different capacities is ensured and the computational complexity is simplified.

Low voltage ride through control strategy for grid-tied solar photovoltaic inverter

Abstract This paper presents a low voltage ride through (LVRT) control strategy using an active power oscillations based reference current generation approach for grid tied solar photo voltaic (SPV) system under line-to-ground (LG) and double line-to-ground (LLG) faults. Proposed control strategy minimizes the harmonics injected into the grid, as well as oscillations in injected reactive power and DC-link voltage. Further this control strategy provides a dynamic control of active and reactive powers, the flow of sinusoidal currents into the grid, and avoids the disconnection between the utility grid and SPV system during faults. A proportional resonant (PR) current controller is developed in a stationary reference frame to achieve the power quality by fulfilling the grid codes. Simulation and experimental results are presented to highlight the merits of the proposed control scheme.

Integration of PV Sources in Prosumer Installations Eliminating Their Negative Impact on the Supplying Grid and Optimizing the Microgrid Operation

This paper concerns the mitigation of voltage disturbances deteriorating power quality and disrupting the operation of LV distribution grids due to the high penetration of PV energy sources in prosumer installations. A novel control strategy for 3-phase 4-wire PV inverters is proposed, which ensures the transmission of PV active power and simultaneous compensation of load unbalance and reactive power, making the prosumer installation balanced and purely active. It results in the balance of phase voltages and the mitigation of their variability. Unlike other methods used for voltage regulation in LV grids, the proposed solution contributes to the reduction in losses, is simple, and does not require additional costs. In the paper, a control algorithm for the PV inverter is described. Its effectiveness was tested by simulation using a model of the real LV distribution grid developed in the PSCAD/EMTDC program. The results of the simulations are presented and evaluated.

A sigmoid-based adaptive inertia control strategy for grid-forming inverter to enhance frequency stability

Introduction: This paper proposes a sigmoid-based adaptive inertia control strategy for grid-forming (GFM) inverter to enhance frequency stability.Methods: Firstly, the frequency response characteristics under different disturbances are analyzed theoretically. Then, to solve the problem that fixed inertia leads to a contradiction between the maximum frequency deviation and the setting time, a non-linear inertia regulator is investigated. This non-linear inertia regulator, which is based on an improved sigmoid function, is applied to achieve real-time inertia by the frequency deviation. Moreover, the full-order small-signal model of the system containing the nonlinear inertia regulator is established and thus the stability of the proposed strategy is analyzed.Result and Discussion: The proposed control strategy is implemented without derivative action, which may suffer from high-frequency noises. Finally, the hardware-inthe-loop (HIL) results verify the remarkable performance of the proposed control strategy.

High Frequency Resonance Analysis and Resonance Suppression of a Grid-Connected Inverter Coupled With a Long Feeder

With the development of distributed generation (DG) technologies, various inverter-interfaced DG systems have been connected to the grid, which can cause serious harmonic issues. For an inverter-interfaced DG source connected to the grid via a long feeder, multiple resonances may occur due to the non-negligible distributed capacitance of the long line. Multiple resonances can cause current distortions when the DG delivers power to the grid and the harmonic voltage may be amplified because of the resonances. Many inverter control strategies have been studied, but few can suppress harmonics. To solve this issue, this paper derives the voltage transmission equations to analyze the transmission characteristics of harmonic voltages along a long feeder and reveals the reasons for the multiple resonances in the current. Based on the transmission line theory, a new control strategy of inverter is proposed to suppress the multiple resonances in current and the amplification of harmonic voltages. Finally, the effectiveness of the proposed control strategy is verified by the simulation and experimental studies.

A DC-Offset Reduced Grid-Voltage Sensorless Model Predictive Control Strategy for Grid-Tied Inverters With a Two-Stage Optimal Voltage Vector Searching Method

Grid voltage sensorless model predictive control (MPC) strategies for grid-tied inverters (GTIs) have been studied frequently in recent years. However, the effects of DC-offset are not well addressed, and the current ripples are quite large as only one voltage vector (VV) is applied per control period. To solve these problems, a DC-offset reduced grid voltage sensorless MPC strategy for GTIs with a two-stage optimal VV searching method is proposed. First, a new grid voltage observer is proposed to reduce the effects of DC-offset. Second, by analyzing the proposed observer, it is found that the introduced intermediate variable can be used to estimate the DC-offset contained in the sampled grid current. Thus, the effects of DC-offset on the current control can be compensated accordingly. Third, to reduce the current ripples, a new two-stage optimal VV searching method is proposed on the basis of a detailed theoretical analysis. The novelty of this method is that it searches the phase and amplitude of the optimal VV in two independent stages, which reduces the number of VV that required to be evaluated online obviously. Finally, comparative experimental studies verify the effectiveness of the proposed methods in this paper.

Grid-connected photovoltaics prosumers to support smart city development in Rwanda: A case study for Ayabaraya Village

Access to electricity is among the important targets in Rwanda as in other regions. The grid-connected photovoltaic (PV) prosumers market segment can contribute to the rate of access to electricity in Rwanda. Grid connected PV prosumers contribute in not only increasing electricity generation capacity but also producing affordable and reliable electrical energy. Therefore, the current research analyzes the possibilities of interconnection of small-scale prosumers with a national grid. In addition, the bidirectional flow of electricity either from prosumer grid and vice versa, aiming at monitoring the continuous power supply of the load is analyzed. The study is conducted in Ayabaraya village in Rwanda and the load profile for residential, commercial and industrial prosumers are analyzed. In this research, meteorological data from Photovoltaic Geographical Information System (PVGIS) up to 2016 is used to give global horizontal irradiation and ambient temperature. The amount of energy imported from and exported to the grid is determined by the connected appliances, the capacity of the PV system, and the amount of available irradiance at the time. The Home Energy Management System (HEMS), inverter control strategies, and prosumer load types are considered. The simulation reveals that available irradiance less than 30W/m2 at a time is below the grid-tie inverter's threshold power thus, the prosumer imports electricity from the grid. At irradiance larger than 30W/m2, the prosumer may optimize self-consumption and injects the surplus into grid.

Hybrid Multi-Vector Modulated Model Predictive Control Strategy for Voltage Source Inverters Based on a New Visualization Analysis Method

Conventional model predictive control (MPC) strategy for voltage source inverters has large current ripple since only one voltage vector is applied in each control cycle. Although the multi-vector modulated MPC strategy can reduce the current ripple, its lack of theoretical basis makes its optimality questionable. To solve this problem, a new visualization analysis method is proposed in this article to evaluate the effectiveness of the conventional multi-vector modulated MPC strategy, based on which a new hybrid multi-vector modulated MPC strategy is further presented to improve the current control performance. First, the principle of the proposed visualization analysis method is introduced, based on which it is verified that the conventional multi-vector modulated MPC has better control performance than the single-vector MPC. Second, based on the proposed visualization analysis method, it is also found that both the conventional double-vector and triple-vector modulated MPC strategies cannot achieve optimal control. Thus, a new hybrid multi-vector modulated MPC strategy is further proposed. By selecting an optimal voltage vector from 18 alternative voltage vector combinations, the current control performance is improved. Detailed comparative experimental results based on experimental platform and StarSim hardware-in-the-loop platform validate the effectiveness of the proposed hybrid multi-vector modulated MPC strategy.