Inverter Output Voltage Research Articles

DC Component Suppression of Grid-Connected Z-Source Inverter Based on Disturbance Observer

Regarding the problems of resonance and direct current (DC) components when the Z-source inverter (ZSI) without an isolation transformer is connected to the grid through an LCL filter, this paper proposes a novel DC component suppression strategy for a grid-connected ZSI based on the split capacitor method of disturbance observer (DOB). The split capacitor method is utilized to convert a third-order LCL filter into a first-order one to eliminate the resonance problem. The DC component of the inverter output voltage is regarded as an external disturbance, and the employed DOB is used to observe it, which is fed forward to suppress the DC disturbance component. Various comparison results of the simulation and experiment show that the proposed control strategy can effectively reduce grid-connected DC components injected into the grid at less than 0.5%, which decreases the DC component from 1.8% to 0.1%.

Selective Pole Placement and Cancellation for Proportional–Resonant Control Design Used in Voltage Source Inverter

The proportional–integral (PI) control is usually applied in synchronous reference frame to regulate the output voltage of three-phase voltage source inverter (VSI). However, the PI controller is constrained by the capability of suppressing harmonic and negative sequence components; besides, its direct application in single-phase VSI is limited. While the proportional–resonant (PR) control can track ac reference and achieve harmonic suppression in stationary frame for both single-phase and three-phase VSI. Due to the high order of the resonant controller, lots of efforts are needed during the parameter design to get a satisfactory performance, such as trial-and-error. In this article, the way to approximately reduce the order of the resonant controller in the discrete time domain is presented, and then a method of selective pole placement and cancellation for the PR control design used in VSI is proposed. With the proposed method, the closed-loop pole-zero distribution of the PR control structure used in the VSI is well handled, and the parameters of the feedback controller and the reference feedforward controller are directly calculated by placing the selected poles and zeros in desired positions. The procedure of the parameter design is facilitated, and the performance of the VSI with PR control is improved.

Pulse Frequency Modulation for Parity-Time-Symmetric Wireless Power Transfer System

This article proposes and implements an advanced pulse frequency modulation (PFM) scheme to adjust the output power of the parity-time (PT) symmetric wireless power transfer (WPT) system. The key is to utilize PFM to adjust the duty ratio of the self-excited oscillating inverter for the PT-symmetric WPT system, hence transferring more power than that of the conventional forced oscillating inverter under the same input voltage and duty ratio. Besides, the transmission efficiency can maintain high when the coupling coefficient is larger than the critical value. With a proper signal processing circuit, the phase of the inverter output voltage can lead to that of the primary-side current, which can help reduce the switching loss. Therefore, the system efficiency of this self-excited oscillation scheme for WPT can keep high, while the output power can be larger than that of using the conventional forced oscillation scheme. Theoretical analysis and simulation results are given to verify the feasibility of the proposed scheme.

Model Predictive Voltage Control of Uninterruptible Power Supply Based on Extended-State Observer

Finite-set model predictive controls have been widely used in inverter control because of the flexible target control and no need of a modulation unit. However, the mismatching of prediction model parameters produces prediction errors, resulting in a significant decline in the performance of finite-set model predictive controls. Aiming at the problem of model parameter mismatch, an extended-state observer was proposed to accurately estimate the disturbance of the system in this paper, and the obtained disturbance value was added to a finite-set model predictive control controller to compensate for the prediction error and achieve parameter robustness. By constructing a prediction model of the inverter output voltage in αβ coordinates, all the possible output voltage values were predicted by using different voltage vectors and system measurement values. A set of voltage vectors that minimized the cost function was selected, and its corresponding switching state was applied to the inverter in the next sampling period to achieve control of the output voltage quality. Both the simulation and experimental results showed that the finite-set model predictive voltage control method based on the extended-state observer can estimate the total disturbance quickly and accurately, suppress the influence of capacitance parameter disturbance, and improve the control effect of an inverter.

Inverter and Ternary Content‐Addressable Memory Based on Carbon Nanotube Transistors Using Chemical Doping Strategy

AbstractCarbon nanotubes (CNTs) have attracted much attention in transistors because of their unique structure and electrical properties. However, the implementation of transistor polarity control and complementary logic functions remains a key challenge. In this work, the polarity of carbon nanotube transistors using chemical doping strategy is modulated. By triethyl oxonium hexachloro antimonate doping and polyethylene imine doping with chemically modified, p‐type CNTs and n‐type CNTs as the transistor channel of the bottom gate structure field effect transistors are prepared. An inverter is constructed by connecting p‐type transistor and n‐type transistor in series. The inverter has a voltage hysteresis window and gain over 20.5. A Schmitt trigger with operating frequency over 2 MHz is built based on high‐low conversion of inverter output voltage during dual‐scan has different threshold voltage characteristics. Two inverters are used to construct a ternary content‐addressable memory cell with four transistors, which has an on/off ratio up to 104, a data retention characteristic of 104 s, and a good stability of more than 1000 cycles, indicating the great potential of practical application in future computing‐in memory.

Бесступенчатое управление индексом модуляции трехфазного преобразователя электропривода в режиме «flat-top»

The article discusses one of the ways of stepless overmodulation in a semiconductor three-phase voltage inverter implemented according to the B6 scheme. In the review part of the article, the features of the PWM and overmodulation (“flat-top”) modes are briefly considered. The formation of the maximum possible values of the output voltage of the converter is possible due to the maximum values of the modulation index and the voltage inverter coefficient. It is shown that a variable-modulation index in the "flat-top" mode has a number of significant advantages over a fixed one, formed, for example, by "mixing" the PWM reference signal with additional harmonic signals. The geometric interpretation of the positions of the inverter output voltage vectors on the plane and their connection with the PWM reference signal made it possible to synthesize a high-precision (basic) non-linear characteristic in the inverter reference voltage path and to form a linear stepless control law for the inverter output voltage when the “flat-top” of the specified voltage coefficient is activated. The results of comparison of the basic variant of converter output voltage control with a simpler one obtained by approximating the basic equations using numerical methods of mathematics and computer simulation are presented. The absolute error of the modulation index in the case of approximation is no more than one percent in the entire "flat-top" range. The hodographs of the output voltage of the inverter in the X-Y axes are given for three different coefficients of the converter during the transition from PWM to "flat-top". The advantages of the method include the simplicity of its implementation in a new or existing space-vector PWM, the implementation of which is carried out exclusively by a software product. This aspect makes this method particularly attractive in low budget drives.

Improved Sampled Average Modulation Technique for the Modular Multilevel Converters

In this article the improved sampled average modulation technique is proposed, this technique has 2N + 1 levels in the output voltage waveform of MMC and it is considered as of low complexity of implementation for any number of submodules per arm. For that, characteristics such as dynamic response, implementation complexity, inverter output voltage waveform levels, and switching frequency are considered to evaluate and validate the proposed modulation technique. The proposed technique is compared with other three previously proposed techniques, its considering parameters such as the THD and the fundamental value of the output voltage, and also the peak-to-peak variation of the submodule capacitor voltage. Several simulations were performed in the Matlab/Simulink software and with these results, it was validated the proposed modulation technique, and also it is verified that the proposed technique is computationally more efficient. This last one shows its potential for multiphase multilevel applications.

Structural and Algorithmic Synthesis of Three-Phase Traction Voltage Inverters

An approach to the structural and algorithmic synthesis of power electronic devices based on multichannel energy flow transformation is further developed. Previously, the obtaining of a high-current output with current-limited capabilities of the used semiconductor switches was considered [1]. In this paper, the approach is extended to the use of high-voltage switches with a limited operating voltage. A distinctive feature of the approach lies in using transfilters to equalize the instantaneous voltage values of the channels with the simultaneous rejecting action of higher harmonic components. The feasibility of the approach is shown using two options for generating the output voltage of a two-channel three-phase inverter: according to the algorithms of pulse-amplitude and pulse-width modulation. The adequacy of the structural-algorithmic synthesis results is confirmed by computer simulation in the OrCAD/PSpice environment [2]. The interrelations between the inverter input and output voltages necessary for its designing are determined. The operation principle of transfilters is considered, and their power-to-size ratio is estimated as a fraction of the load power (according to the fundamental harmonic). Recommendations for using a three-phase voltage inverter in a high-voltage traction frequency-controlled electric drive of railway rolling stock are given.

Performance analysis and multi-mode control of grid connected micro Wind–solar hybrid generator in Saudi Arabia

The objective of this paper was to study and analyze the performance of a micro Wind – Solar Hybrid Generator (WSHG) in the Kingdom of Saudi Arabia (KSA). The WSHG consists of a micro wind solar system connected to a secondary distribution grid. The system was tested in two locations in the KSA namely DAMMAM and HA`IL and used the wind speed and solar radiation of two periods of the year. Two operating modes were discussed for the system: the Normal Operating Mode (NOM) and the Default Operating Mode (DOM). The simulation results showed the best performance of the system during the two periods of the year, in the two locations of the KSA, and in the two operating modes. The experimental measurements of the WSHG have been carried out and showed the similarity between the measured and simulated values of the output inverter voltage and of the DC-link voltage.

MPPT FOR HYBRID WIND, SOLAR AND THERMOELECTRIC POWER GENERATION SYSTEMS FOR OFF-GRID APPLICATIONS

Renewable energy resources for electrical generation are normally free but are not continuously available due to their sporadic availability. Thus, hybrid connections of various kinds of energy are made to increase utilization of renew-able energy. This paper involves a design of a hybrid renewable energy system employing maximum power point tracking (MPPT) techniques. The hybrid system consists of solar PV panels, a small-scale wind turbine, and a thermoelec-tric generator (TEG) module. Four MPPT techniques are examined in this research. They are the incremental conductance (IC) algorithm, fuzzy logic controllers (FLC) using 25 and 35 rules, and an interval type 2 fuzzy logic con-troller (IT2FLC). Each MPPT technique is tested in the system to determine which has the best maximum power tracking, stable operation, and efficiency. All of the studied energy resources are connected to a DC linked bus. The voltage of this bus is supplied to a three-phase inverter. Inverter output voltage is regulated for balanced and unba¬lanced loads. The generating capacity of the designed hybrid system is 5 kW and the system is simulated using MATLAB Simulink R2017a.

Conducted emission study in space vector modulated voltage source inverter

<p>To comply with electromagnetic interference (EMI) standards, the electromagnetic noise generated by power electronic converters must be analyzed and suppressed since the switching frequency of the converter affects EMI noise. Conducted emission occurs in drive systems due to inverter parasitic capacitances and rapidly switching inverter output voltages. The EMI noise produced space vector pulse width modulation (SVPWM) inverter is calculated using MATLAB/Simulink simulation data. The unwanted common mode and differential mode signals produced by the inverter are captured using a spectrum analyzer and examined using short time Fourier transform (STFT). To mitigate the effect of EMI in the circuit and to comply with the standards filters are developed. The passive filter components are defined by the EMI standards attenuation requirements. The MATLAB simulation findings are confirmed and verified by hardware implementation.</p>

Modeling & implementation of DRLA based partially shaded solar system integration with 3-ϕ conventional grid using constant current controller

Renewable Energy Resources (RERs) are widely used on the concern of global environment protection. Solar energy systems play an important role in the generation of electrical energy, remarkably minimize the utilization of nonrenewable fuel sources. Solar energy can be extracted and transformed into electrical energy via solar photovoltaic process. Several traditional, soft computing, heuristic, and meta-heuristic maximum power point tracking (MPPT) techniques have been developed to extract Maximum Energy Point (MEP) from the solar photovoltaic modules under different atmospheric conditions. In this manuscript, the combination of reinforcement learning algorithm (RLA) and deep learning algorithm (DLA) called deep Reinforcement Learning Algorithm based MPPT (DRLAMPPT) is proposed under partial shading conditions (PSC) of the solar system. DRLAMPPT can deal with continuous state spaces, in contrast to RL it can be operated only with discrete action state spaces. In this proposed DRLAMPPT, deep deterministic policy gradient (DDPG) solves the problem of continuous state spaces are involved to reach the GMEP in photovoltaic systems especially under PSC. In DRLAMPPT, the representative's strategy is parameterized by an artificial neural network (ANN), which uses sensory information as input and directly sends out control signals. This work develops a 2 kW solar photovoltaic power plant comprises of a photovoltaic array, DC/DC step-up converter, 3-Φ Pulse Width Modulated Voltage Source Inverter (PWM-VSI) integrated with conventional power grid using Constant Current Controller (CCC Effectiveness of the proposed DRLAMPPT with CCC can be validated through an experimental setup and with MATLAB. Simulation and tested at different input conditions of solar irradiance. Experimental results prove that, in comparison to existing MPPTs, suggested DRLAMPPT not only attains the best efficiency and also adopts the change in environmental conditions of the photovoltaic system at a much faster rate and able to reach the GMEP within 0.8 s under PSC. Experimental and simulation results also prove that suggested CCC with LC filter makes the inverter output voltage and the grid voltage are in phase at the lower value of THD i.e. 1.1% and 0.98% respectively.

Finite Control Set–Model Predictive Control of H8 Inverter Considering Dead-Time Effect for PMSM Drive Systems With Reduced Conducted Common-Mode EMI and Current Distortions

To reduce the conducted common-mode (CM) electromagnetic interference (EMI) and current total harmonic distortion (THD) in permanent magnet synchronous motor drive systems, this article proposes a finite control set–model predictive control (FCS–MPC) method for an H8 inverter considering the dead-time (DT) effect. In a real system, the DT causes unexpected peak common-mode voltages (CMVs) and distortion of the inverter output voltage, which deteriorates both the CM EMI and current THD. The conventional double active voltage vector (VV) based MPC methods with an H6 inverter may not be a good solution because of the numerous CMV variations and the limit of the VV transitions. In contrast, the proposed FCS–MPC method allows all VV transitions possible without the peak CMVs by instantly operating the series-connected switch of the H8 inverter based on the previous VV, predicted current sector, and next optimal VV. Furthermore, the nonlinearity of the inverter output voltage due to the DT is compensated in a discrete-time model used for the current prediction, considering the calculation delay of the digital controller. Consequently, the current THD as well as the CM EMI can be improved. The simulation and experimental results are presented to verify the effectiveness of the proposed method.

Complex Power Sharing Is Not Complex

This paper presents a distributed complex power sharing approach that solves the problem of active and reactive power sharing in inverter-based islanded microgrids. Previous state-of-the-art strategies based on droop controls with possibly virtual impedance methods and supplemented with hierarchical schemes may provide poor power sharing due to the R/X ratio and mismatched line impedances, even compromising microgrids stability if droop control parameters are not properly set. The novel control approach, that uses a communication network to exchange data among all inverters to fairly inject power, provides a set of appealing properties. First, it achieves accurate active and reactive power sharing for both resistive and inductive power lines with no additional control cost (avoiding unnecessary power injections), and regardless of load changes and connections and disconnections of inverters. Moreover, it ensures an exponential convergence rate, and the tuning of the control parameters can not compromise microgrid stability. The theoretical development relies on a change of variables that linearizes the complex power dynamics, thus easing the control law design task and providing the means for computing the appropriate amplitude and phase for each inverter output voltage. Selected experimental results on a laboratory microgrid certify the applicability and performance of the proposed control scheme.

Extensive investigation of symmetrical and asymmetrical cascaded multilevel inverters for electric vehicle applications

To optimize the conventional power electronics in electric vehicles, many researchers investigate the application of multilevel inverters (MLIs). Thereby, cascaded MLIs are of particular importance. One crucial design parameter of cascaded MLIs is the construction of the individual MLI modules. For example, the selection of the DC source voltage in each module affects the magnitude of any MLI step and as a consequence the symmetry characteristics of the inverter output voltage. Therefore, this paper mathematically highlights symmetrical and asymmetrical cascaded MLIs (SMLIs, AMLIs) in detail. The findings show that for a fixed number of modules, SMLIs typically show a significantly higher redundancy of voltage levels compared to AMLIs. In contrast, an increase of the number of different levels is achieved applying AMLIs. With a special design rule of AMLIs, an identical resolution of the output voltage is produced as with SMLIs while keeping the number of modules low. However, the asymmetric nature of the modules can have a negative impact on the power balance of the inverter. A final comparison regarding the total harmonic distortion demonstrates that lowest distortion is achieved by MLI configurations that provide a high number of voltage levels combined with symmetrical output voltage patterns.

A Novel Microgrid Islanding Detection Algorithm Based on a Multi-Feature Improved LSTM

Islanding detection is one of the conditions necessary for the safe operation of the microgrid. The detection technology should provide the ability to differentiate islanded operations from power grid disturbances effectively. Given that it is difficult to set the fault threshold using the passive detection method, and because the traditional active detection method affects the output power quality, a microgrid islanding detection method based on the Sliding Window Discrete Fourier Transform (SDFT)-Empirical Mode Decomposition (EMD) and Long Short-Term Memory (LSTM) network optimized by an attention mechanism is proposed. In this paper, the inverter output current and voltage at the point of common coupling (PCC) are transformed by the SDFT. The positive sequence, zero sequence, and negative sequence components of voltage and current harmonics are calculated and reconstructed by adopting the symmetrical component method (SCM). Meanwhile, the current and voltage are decomposed into a mono intrinsic mode function (IMF). The symmetric components of voltage, current, and IMFs are used as inputs to the deep learning algorithm. An LSTM with the features extracted to classify islanding and grid disturbance is proposed. By using the attention mechanism to set the weight values of the features of hidden states obtained by the LSTM network, the proportion of important features increases, which improves the classification effect. MATLAB/Simulink simulation results indicate that the proposed method can effectively classify the islanding state under different working conditions with an accuracy level of 98.4% and a loss value of 0.0725 with a maximal detection time of 66.94 ms. It can also reduce the non-detection zone (NDZ) and detection time and has a certain level of noise resistance. Meanwhile, the problem whereby the active method affects the microgrid power quality is avoided without disturbing the current or power of the microgrid.

Improved modified a multi-level inverter with a minimum total harmonic distortion

Renewable energy sources are developed as a result of the increased demand for electrical power. The nature of the solar energy source is DC. The DC source for many applications needs to be converted to AC. The inverter is used to convert the power from DC to AC. Total harmonic distortion (THD) is a significant concern with inverters. Multi-level inverters are used to reduce the THD. The stair output voltage of the multi-level inverter not only reduces the THD but also reduces the switches' stresses, so a low voltage rating can be used for the switches. In this paper, a modified inverter topology is introduced in which the number of switches is reduced for the same number of output voltage levels, which leads to reducing the losses and the cost. To reduce the THD, different amplitudes for the carrier signals that control the switches in each level are suggested. Another method to reduce the THD by using different capacitor values across the input DC source is presented. The MATLAB/Simulink is used to show the validity of the suggested modified topology and the modifications.

Research on Input-Parallel Single-Switch Wireless Power Transfer System With Constant-Current and Constant-Voltage Output

The full-bridge can further improve the output power through parallel inverters. The inverter output voltage of single-switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -resonant circuit is a combination of trapezoidal wave and half-sine wave; there is no relevant research on parallel connection of single-switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -resonant circuit. Therefore, this article presents a novel input-parallel single-switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -resonant circuit; this topology adopts switchable secondary networks for constant-current (CC) and constant-voltage (CV) output, and prevents shoot-through of power switches. The decoupling between transmitters simplifies the analysis and calculation. The input-parallel structure avoids the unbalanced input voltage of each inverter and improves the stability of the wireless power transfer system. CC and CV output modes can be achieved by controlling one relay without adding dc–dc converters or changing the switching frequency. This article includes decoupling equivalent analysis of coils, topologies analysis of CC mode and CV mode, calculation of equivalent input ac voltage source, design of magnetic coupler, and circuit parameters. Finally, a 1-kW experimental prototype is built to verify the theoretical analysis; the maximum efficiency can reach up to 92.5%.

Multiplexed Optical Link for Gating Pulse Transmission in Multilevel Converters

Multilevel power converters play an increasingly important role in energy transmission, high-power electric drives and renewable energy systems. The transmission of control signals for the semiconductor switches in power converters is critical for the operation of the system, and therefore optical communications links are employed to minimize electromagnetic interference. However, conventional parallel communication topologies have the drawback of requiring a high number of independent optical fibers and transmitter-receiver pairs as the number of transmitted signals increase, which limits the flexibility and scalability of the link. In this paper we propose the design of an optical link with wavelength division multiplexing (WDM) based on a digital micromirror device (DMD) and a linear detector array as receiver. The main advantages of the proposed system are the high flexibility and scalability of the communications link. Simulation results are obtained from a mathematical modeling of the transmitter, the link and the receiver. The communication is established by means of an asynchronous protocol in order to ensure the correct decoding of the transmitted gating signals. A feasibility analysis of the optical link is carried out in terms of the waveform quality of the multilevel inverter output voltage, measured by its total harmonic distortion (THD). The simulation results obtained in MATLAB/Simulink environment validate the methodology to enable a future implementation of the proposed optical communication link.

Robust Optimal Control Design for Performance Enhancement of PWM Voltage Source Inverter.

PWM (pulse-width modulation) voltage source inverters are used in a wide range of AC power systems where the output voltage must be controlled to follow a sinusoidal reference waveform. In order to achieve precision and fast-tracking control, restrictive sliding mode control (RSMC) provides a fast system state convergence time. However, the RSMC still suffers from the chattering problem, which leads to high harmonic distortion and slow response of the inverter output state. Furthermore, the load of the inverter may be severe load changing and the control parameters become difficult to adjust, worsening the adaptability to achieve the desired control of the inverter output. In this paper, a robust optimal control design comprised of an enhanced restrictive sliding mode control (ERSMC) and density particle swarm optimization (DPSO) algorithm is proposed, and then applied to PWM voltage source inverters. The ERSMC not only has finite time convergence but also provides chatter elimination. The DPSO is highly adaptable for acquiring the control parameters of the ERSMC and finding the best solution in the global domain. The proposed controller is realized for the actual PWM voltage source inverter controlled by a TI DSP-based development platform, so that the inverter output voltage has fast dynamic response and satisfactory steady-state behavior despite high load changing and non-linear disturbances.