Inverter Output Research Articles

Harmonics Reduction in Virtual Synchronous Generator Using Fuzzy Logic controller

Harmonics are always present in the electrical networks in both no-load and load conditions. Harmonics reduces the power quality of the VSG in the presence of nonlinear loads and distorted grid. Completely removing the Harmonics from the network is impossible but we need to reduce them to a minimum value so that the system efficiency improves. A hybrid harmonic suppression scheme is proposed to enable the further improvement of the adaptability of VSG, which mainly consists of a voltage harmonic control loop and a grid current-controlled loop. The voltage harmonic control loop aims to scale down the inverter output impedance via a negative feedback loop, while the grid current-controlled compensator is intended to counteract the adverse effects from a weak grid via an additional voltage, which leads to substantially lower total harmonic distortion for both the load voltage and the grid current at the same time .By using a proper controller we can reduce the THD value of the grid to the minimum.

Internal Short-Circuit Fault Location of Rail Transit Auxiliary Inverter Based on Voltage Deviation

In order to improve the ability of locating and detecting the internal short-circuit fault of rail transit auxiliary inverter, a method of locating the internal short-circuit fault of rail transit auxiliary inverter based on voltage deviation is proposed. The fault sensing information acquisition module of rail transit auxiliary inverter is constructed by using the detection method of fundamental frequency characteristics of differential mode current of excitation winding, and the voltage deviation analysis of rail transit auxiliary inverter under internal short-circuit fault state is realized by using the methods of MVCR excitation winding control and output reactive power adjustment. Combined with the dynamic distribution characteristics of output harmonics and initial phase of rail transit auxiliary inverter, the equivalent compensation and capacity expansion methods of excitation winding circuit are adopted. The signal test model of fault location is established, and the spectral characteristics of the internal short-circuit fault signal of rail transit auxiliary inverter are extracted. A fault joint feature location and monitoring model is established by using the data clustering analysis method of fusion difference, and the internal short-circuit fault location detection of inverter is realized according to the voltage deviation distribution characteristics of inverter in short-circuit state. The test results show that the accuracy of short-circuit fault location in rail transit auxiliary inverter is high, and the dynamic estimation ability of inverter output voltage deviation is strong.

Minimizing Total Harmonic Distortion of 7-Level Packed U-Cell Multilevel Inverter Using Whale Optimization Algorithm

This paper presents an innovative study introducing a novel design for a single-phase, 7-level inverter. The design combines the modified pulse width modulation (MPWM) technique with the compact packed U-cell (PUC) topology. We evaluate this inverter's performance through comprehensive simulations in the MATLAB Simulink software. Multi-level inverter (MLI) technology is crucial for high-power, medium-voltage energy control. However, using numerous semiconductor switches in traditional MLI setups poses challenges at higher voltage levels, including increased size, costs, and losses. To address these issues, our study proposes a transformative approach, emphasizing reducing active switches within the multi-level inverter architecture. Consequently, we introduce an innovative 7-level PUC-MLI design. This configuration not only reduces harmonic distortion but also addresses cost concerns. Strategically manipulating semiconductor switch sequences significantly enhances the inverter's operational efficiency. A notable contribution is our inventive method to reduce total harmonic distortion (THD) in the inverter's output voltage, achieved through a whale optimization algorithm (WOA). Implementing this algorithm substantially lowers THD levels. Importantly, this approach's effectiveness extends to various inverter topologies and levels, offering a substantial THD reduction without additional expenses.

Improvement of grid injected currents in single-phase inverters rejecting DC link voltage oscillations based on multi-resonant filtering

The operation of grid-tied single-phase inverters generates oscillations in its DC link voltage. If only active/reactive power is controlled by the inverter, this oscillation is at twice the grid frequency. In situations where the inverter output current and/or the grid voltage also has harmonic components, the DC link voltage becomes also polluted by oscillating components at even multiple frequencies of the grid voltage. Such oscillations are propagated through the DC link voltage control loop, increasing the THD index of grid current reference signal. To solve this drawback, this article proposes the insertion of a multi-resonant filter into the DC link voltage control loop, ensuring a harmonic free grid current reference signal. With the proposed filter and without any increase in the power circuit, the use of smaller capacitances in the DC link is allowed, since the DC link voltage oscillation does not interfere in the power quality indexes of the controlled current. A filter tuning methodology is presented to ensure that the design of each filter and of the DC link voltage controller is independent, relating the filter settling time and the system stability. At the same time, the use of the proposed filter allows the voltage controller to be tuned at higher frequencies, improving the DC link voltage dynamic response. The proposal is experimentally validated through a single-phase grid-tied double-stage photovoltaic (PV) system, that can also operate only as a parallel active power filter (PAPF) or, simultaneously as a multifunctional PAPF + PV system.

Designing Parameters to Reshape the Inverter Output Impedance Based on the D-Split Method under Weak Grid Conditions

Novel energy generation technologies, such as high-permeability wind power and photovoltaic systems, exhibit inherent intermittency, randomness, and volatility. During periods of energy production from these sources, the impedance of the electrical grid frequently experiences significant fluctuations. Consequently, the grid manifests characteristics akin to a weak grid, highlighting the challenges associated with integrating renewable energy sources with variable output profiles. These fluctuations lead to a shift in resonance spikes of the LCL-type filter towards the lower frequency band, consequently impacting the stability of inverter grid connections. To mitigate this issue, the present study introduces a novel approach integrating the D-split method and a proportional–differential feedforward strategy. This combination aims to reshape the inverter’s output impedance, ensuring its consistent stability even amidst significant fluctuations in grid impedance. In this research, the optimal controller parameters for systems operating under robust grid conditions are initially determined. This selection process involves the application of the D-split method, supported by graphical visualization. Additionally, the amplitude and phase angle margin tester is employed while considering the system bandwidth as a limiting constraint. Moreover, accounting for the influence of grid impedance, the D-split method is reapplied to ascertain the most suitable values for the proportional–differential feedforward parameters. This adjustment aims to enhance the adaptability of the grid-connected inverter specifically in scenarios characterized by a weak grid. The hardware-in-the-loop (HIL) simulation results demonstrate that despite the presence of harmonics within the grid and a short circuit impedance ratio (SCR) of 3, the inverter maintains grid stability and effectively suppresses harmonics. Moreover, the total harmonic distortion factor (THD) of the grid-connected current remains below 5%.

Intelligent Approach for Control Techniques Based on Complex Converter Structures

Hybrid frequency control strategies are used to eliminate the problem of current inversion in multilevel cascaded asymmetrical H-bridge inverters. Unfortunately, this technique results in unbalanced power at the inverter output. The improved hybrid PWM modulation strategy helps to regulate power balances within a reasonable range at high and low voltages, by adjusting the conduction angle of the cells in high frequencies. However, as the conduction angle of a high-voltage cell increases, the fundamental amplitude of the inverter output voltage decreases, since waveforms with absolute values greater than 2 E cannot be perfectly modulated. Based on mathematical models of the conduction time for each level synthesis method, a new modulation strategy is proposed to solve the problems associated with the two strategies mentioned above. This new high-frequency modulation strategy adopts a combination of pulse-width modulation (PWM) and step modulation to combine control of the high-voltage and low-voltage units. At given intervals, the control voltage signals of the low-voltage unit are exchanged. Finally, the power of each unit is balanced and the basic amplitude of the inverter output voltage is not affected. Finally, the MATLAB/Simulink simulation model and experimental platform verify the feasibility of this strategy.

Adaptability enhancement of fractional‐order LLCL‐type grid‐connected inverter to weak grid based on grid voltage weighted feedforward scheme

SummaryGrid‐connected inverter with a novel fractional‐order LLCL filter has the advantage of high grid current tracking accuracy and low total harmonic distortion without passive or active dampers, and the grid voltage full feedforward scheme is an effective method to improve the quality of grid current. However, due to the digital control delay, the suppression of the grid current harmonics is weakened, and the inverter output impedance has an additional negative phase shift, which deteriorates the stability of grid‐connected systems under weak grid. In this paper, a weighted grid voltage fractional‐order feedforward control scheme is proposed based on a quasi‐proportional resonant (QPR) controller, which introduces two weighting factors in the full feedforward path of the grid voltage and compensates the phase lag of the output impedance by designing appropriate weighting factors. Then, an improved scheme combining the QPR controller with a phase compensator is presented. As a result, the suppression ability of grid current harmonics and the adaptability to grid impedance variations are enhanced. Simulation and experimental results verify the effectiveness of the proposed grid voltage fractional‐order weighted feedforward scheme.

Performance Evaluation of Induction Motor Behaviour on Conventional and PV System Power Sources

The present study explores the integration of photovoltaic (PV) systems for enhancement of power system quality and reliability, particularly when PV system is deployed to power inductive loads which have wide applications in commercial and industrial settings. A mixed approach is deployed using MATLAB/Simulink for the modelling and simulation process. The study investigates the impact of inductive loads on PV system, comparing its performance with a conventional power source of same power willing capacity. The PV system was modelled by connecting PV arrays in series and parallel combinations. The output of the PV arrays was fed into a three phase PWM inverter, the harmonics present at the inverter output were eliminated using properly sized Inductor- capacitor (L-C) filter circuit. Also, a three-phase conventional source of same output capacity was modelled. Comparative analysis of the impacts inductive loads has on both sources were carried out and this was accomplished by integrating three-phase asynchronous motor rated at 15kW(20HP). The induction motors were independently powered by two distinct sources and further subjected to intermittent loading conditions. The major parameters investigated includes the rotor speed, rotor current, and electromagnetic torque of the asynchronous motor. The outcome of the study showed that the conventional source outperforms the PV system. These necessitates the studies on adoption of advance strategies on how the negative impacts and challenges encountered in the course of integrating PV system to power inductive loads will be address.

Frequency stabilization and synchronization between grid and AC microgrid

A 63-level inverter with fewer switches is proposed to reduce harmonics in the multi-microgrid scenario. Since the multi-microgrid is connected with varying loads, synchronizing the output of the multi-level inverter and controller is developed, which works by having a data testing phase. The weighted mean of vector optimization acquires the multi-microgrid data to feed the control variable to the controller. Multi-microgrid issues are managed by two degrees of freedom based on a fractional order proportional resonant controller. As a result, the proposed inverter scheme has yielded a very low THD when subjected to a renewable based DC supply. This improves the performance of the 63-level inverter by 20.1 % compared to the asymmetric 63-level inverter.

Analysis Of Voltage and Current Performance of 100 WP Solar Panel Using Matlab Simulink R2021a

The growing population increases the need for electrical energy. Development of renewable energy that is environmentally friendly and sustainable to replace fossil energy sources that are almost depleted and have an impact on global warming. Indonesia is on the equator where there is potential for the application of photovoltaic technology. However, the high cost of implementing a solar power system must be considered, as the energy supply is intermittent and highly dependent on environmental factors such as solar radiation and temperature. Therefore, it is necessary to design a solar power generation system using MATLAB Simulink 2021a software simulation method to avoid the implementation error rate and determine the success, especially the system performance. The MATLAB Simulink 2021a simulation method uses a 10 Wp monocrystalline Photovoltaic (PV) and a 12 V 20 Ah Lead-Acid battery. PV array design, PV Array, Buck Converter, Inverter, PV Controller, Battery Controller and Metering. To find out the value of the output voltage and current from solar panels, batteries, and the results of the DC to AC conversion by the inverter and using a load of 17 watts. The simulation results of a 100 Wp solar panel at MATLAB Simulink in the South Jakarta area with an intensity of 131W/m2 and a temperature of 27.99 °C produce a PV array output voltage and current of 17.6 V and 5.8 A, respectively. The battery voltage and current show the highest values are 12.58 V and 4.8 A. The actual voltage and current are close to the values of Vmp 17.8 V and Imp 5.2 A, so that the results of this system design can be stated to have maximum performance. Meanwhile, the inverter output has the highest voltage and current values of 218 V and 0.085 A.

Heat dissipation design of the mine-used inverter output filtering device

During long-distance transmission, pulse width modulation (PWM) signals are subject to voltage reflection. This results in spike voltages and high du/dt values at the motor end. Suppression is carried out by utilizing a series reactor at the output of the inverter. And the filtering parameters are optimally designed. Then, the EMF characteristics of the output reactor are analyzed and power losses are calculated. On this basis, an integrated heat dissipation scheme is proposed to design the output reactor for forced cooling. It is verified by ANSYS/Icepak simulation, which shows that the filter has good heat dissipation performance.

Sensorless Saliency-Based Control of Dual Induction Machines Under Dynamic Load Imbalances Using Three Current Sensors

To perform vector control of single-inverter dual induction motors, drives are standardly equipped with current and position sensors. In medium-power railway applications, a shaft encoder is usually mounted on each motor, and the inverter output current is measured using two current sensors. Yet, this configuration features some disadvantages. First, torque-sharing cannot be computed because stator current of each motor is unknown. Similarly, saliency extraction of each motor is not achievable since individual current drawn by each motor is not measured. An option that achieves torque-sharing calculation is to attach two current sensors to each motor, provided that both rotor positions are known. However, industrial inverter/control platforms considered offer a maximum of three input channels for current sensors. Besides, some industry fields tend towards encoderless speed control. Therefore, this paper proposes to use three current sensors in total and no shaft encoders. Thanks to a special current sensor arrangement and a voltage step excitation method, saliency-based encoderless control is achieved. In addition, a method is presented to estimate torque-sharing. Experimental measurements, taken on a dual induction motor test bench, will show the capability of the proposed methodology to identify individual loading as well as excellent encoderless control performance.

A Reconstructed Singular Return Ratio Matrix for Optimizing Design of the PLL in Grid-Connected Inverters

Phase-locked loop (PLL) is essential for the grid-connected inverter to ensure grid synchronization. Since the PLL introduces an negative-resistive admittance to be in parallel with the original inverter output admittance, it poses an instability risk for the grid-connected inverter under weak grid. The system stability can be evaluated by the return ratio matrix, which is the ratio of the inverter output admittance to the grid admittance. Due to the non-singular and non-diagonal properties of this matrix, its eigenvalues are irrational functions, leading to inconvenience of stability analysis and PLL parameters design. To address this issue, this paper reconstructs the return ratio matrix to make it singular. Thus, the eigenvalues become simpler, including a zero eigenvalue and a non-zero eigenvalue. Based on the non-zero eigenvalue, the relation between the gain margin and the PLL parameters is established, and an optimizing design method of the PLL parameters is proposed to achieve system stability and satisfactory PLL dynamic response. Finally, experimental results from a 10-kVA prototype of three-phase grid-connected inverter are provided to verify the validity of the proposed design method.

IoT Monitoring for PV System Optimization in Hospital Environment Application

Purpose: The objective of this study is to implement IoT monitoring to remotely monitor PV system output and efficiency to ensure the continuous supply to ventilators and monitors in the ICU Room of RSI Siti Khadijah Palembang.
 Methodology/approach: The approach implemented in this study is by installing IoT Monitoring as an automatic transfer switch to ensure the continuous supply for the load.
 Results/findings: The IoT monitoring shows the real-time production of PV panels, battery capacity, and inverter output. Hence, the operator can monitor the PV system output and decide whether to keep using sources from PV panels or switch to grid utilities during cloudy/rainy days.
 Limitations: The IoT monitoring system has supervised the system's reliability, but it is necessary to improve the output and efficiency of the PV system by adding artificial intelligence algorithms and installing active cooling to prevent overheating.
 Contribution: This study shows the effectiveness of implementing IoT monitoring for the On-Grid PV system installed on the rooftop of RSI Siti Khadijah Palembang.

A new generalized predictive current control algorithm with integration of fractional part function based modulation technique: Single phase self‐balanced type multilevel inverter topologies

SummaryIt is generally impossible to control the inverter output current (IOC) based on operator needs if only pulse width modulation (PWM) techniques are used. Conventionally, authors have reported the finite control set‐based predictive current control algorithm (FCS‐PCCA) to control the IOC with a fast dynamic response. However, this type of algorithm without a PWM stage generates a variable switching frequency (VSF) of operation, and it leads to filter design problems, inequitable thermal stress, and more current distortions that have been presented. To alleviate all these issues, a new generalized PCCA with the integration of a fractional part function‐based single carrier modulation technique (G‐PCCA‐FPF‐SCMT) has been proposed, and it provides constant switching frequency (CSF) of operation. In this technique, the normalized optimum inverter output voltage (N‐O‐IOV) has been fed with FPF‐SCMT. The particular modulation stage implementation is straightforward since even inverter level number increases, the number of references and triangular carrier signals is always only one. The complete control implementation process of the proposed technique is extremely low compared with all traditional CSF‐based PCCAs. To verify the proposed technique experimentally in both steady and transient state operations, one of the conventional five‐level switched capacitor‐based inverter topologies has been considered and elucidated vividly in both open‐loop and closed‐loop operations.

Can Locational Disparity of Prosumer Energy Optimization Due to Inverter Rules Be Limited?

To mitigate issues related to the growth of variable smart loads and distributed generation, distribution system operators (DSO) now make it binding for prosumers with inverters to operate under pre-set rules. In particular, the maximum active and reactive power set points for prosumers are based on local voltage measurements to ensure that inverter output does not cause voltage violations. However, such actions, as observed in this work, restrict the range available for local energy management, with more adverse losses on arbitrage profits for prosumers located farther away from the substation. The goal of the paper is three-fold: (a) to develop an optimal local energy optimization algorithm for activation of load flexibility and inverter-interfaced solar PV and energy storage under time-varying electricity prices; (b) to quantify the locational impact on prosumer arbitrage gains due to inverter injection rules prevalent in different energy markets; (c) to propose a computationally efficient hybrid inverter control policy which provides voltage regulation while substantially reducing locational disparity. Using numerical simulations on three identical prosumers located at different parts of a radial feeder, we show that our control policy is able to minimize locational disparity in arbitrage gains between customers at the beginning and end of the feeder to 1.4%, while PV curtailment is reduced by 91.7% compared to the base case with restrictive volt-Var and volt-watt policy.

Design and analysis of single-phase five-level inverter based on integrated energy system

New energy power generation, mainly photovoltaic power generation and wind power generation, is one of the key research topics today. It is found that the grid-connected phase of power transmission is very important in the transmission process after power generation through these two ways. This paper introduces in detail the various stages of power transmission under the background of integrated energy system, mainly photovoltaic power generation and wind power generation as the research object. This paper presents a new grid-connected symmetrical cascade half-bridge multilevel inverter (SCHB) under the background of comprehensive energy and presents a Pulse Width Modulation (PWM) control scheme which can make the inverter output stable multilevel voltage. By this scheme, the voltage of the shunt capacitor is basically unchanged and the multistage voltage output of SCHB inverter is guaranteed. The advantages of the designed inverter are that the whole inverter can be powered by a single power supply and a single inductance, and the number of voltage levels can be controlled because of the use of a small amount of reactive power components. This paper describes the topological results of the inverter and the PWM control scheme of stable output multistage voltage.

MULTILEVEL INVERTER SIMULATION 9 LEVEL H-BRIDGE TOPOLOGY WITH HYSTERESIS CONTROL

Inverter is an electronic circuit to convert DC power source into AC. In general, the inverter will produce a relatively large Total Harmonic Distortion (THD) value so that it will result in damage to electronic devices, to minimize this, a multilevel inverter is made which can reduce the THD value by increasing the level using the switching method. In this research a 9-level cascaded H-Bridge topology cascaded H-Bridge topology simulation is designed to identify the output of this multilevel inverter. The addition of R, RL, RC, RLC, and induction motor loads affects the THD value. To calculate THD, we use Fast Fourier Transfer (FFT) on MATLAB Simulink. The no-load test results produced a THDv of 13.90%. In the R load test the resulting THDv and THDi values were 13.91%. In the RL load test it produces a THDv value of 13.91%, and a THDi of 0.2% to 0.12%. In the RC load test it produces a THDv value of 13.91% to 13.85%, and a THDi of 15.55% to 70.53%. The RLC load test produced a THDv value of 13.91% and the lowest THDi was 0.06%. In the load test, the induction motor produces a THDv value of 13.91% to 13.92%, and a THDi of 0.88% to 0.25%.

A Novel Backstepping Controller Based on Saturations Gains for Power Converters

The following paper presents the modeling and design of a backstepping controller based on saturation functions for a single-phase off-grid inverter system. The proposed controller consists of an algorithm that modifies the controller gains as a function of the error, which is intended to avoid the windup effect and to adapt to changes in system parameters, such as inverter load. The objective of the bakstepping controller acting on the system is to reduce the tracking error and improve the voltage quality at the inverter output by reducing the total harmonic distortion. The results of the backstepping controller with saturated gains are compared against backstepping with constant gains in order to test its performance improvement.

New method of current control for LCL-interfaced grid-connected three phase voltage source inverter

This paper presents an approach for the connection of a photovoltaic generator to the utility grid. A theoretical analysis, modelling, controlling and a simulation of a grid connected photovoltaic system using an output LCL filter are described in detail. In order to reduce the complexity of the system, a linear voltage and current controllers have been developed for a three phase grid connected inverter. Those controllers simultaneously regulate the dc link voltage (the photovoltaic power is delivered to the grid) and the current injected to the grid (to operate at unity power factor). The simulation results show the proposed methods work properly. Moreover they show that the control performance and dynamic behaviour of the inverter-LCL-grid combination. Simulation results show that the output LCL filter installed at the inverter output offer high harmonic attenuation.