Two-level Inverter Research Articles

Polar Voltage Space Vectors of the Six-Phase Two-Level VSI

The paper recommends polar voltage space vectors of the six-phase and two-level inverter as a useful mathematical tool for vector control of the inverter. The inverter model is described using three mathematical tools: analytic expressions, voltage state, and space vectors. The analytic formulas allow for the determination of elementary physical inverter quantities: current and voltage. The state voltage vectors make it easy to define phase voltage distribution in every possible state of the inverter and voltage space vectors are the most important tool used for inverters’ control. The space vectors are defined using the standard voltage space vector transformation, while the state vectors are denoted by binary numbers and determine all voltage states of the inverter. The proposed notation system and vectors’ marking seem to be extremely useful in specifying the inverter states. This system certifies a deep correlation between the space and state vectors as they are described using the same digits. The properties of the system were confirmed during the simulation tests. Some examples of the inverter vector control based on polar voltage space vectors prove that the proposed solution is a useful mathematical tool and may be in fact suitable in designing inverter control algorithms. The simulation experiment described in this paper shows that the assumed control strategy allows for a significant reduction in the amount of switching compared to PWM. At the same time, the adopted vector strategy allows for the obtaining of a very favorable value of the current THD coefficient while maintaining the RMS values of the currents.

T-Type Multi-Inverter Application for Traction Motor Control

The structure and principle of the T-type 3-level reverse voltage source that will be fed to three-phase induction motors will be presented in this study. The implementation of Space Vector Pulse Width Modulation (SVPWM) and the math models of the induction motor, the stator currents, and the speed controller design of the electric traction drive system based on Field-Oriented Control (FOC) will be also shown. This three-level T-type inverter in the FOC structure decreases Total Harmonic Distortion (THD) more than the previous two-level inverters. By combining the FOC control structure with the T-type 3-level inverter, the speed and torque responses necessary for railway traction motor load were improved. Finally, Matlab/Simulink will be used to demonstrate the correctness of the T-Type multi-level inverter theory.

Execution of a 15-level multilevel inverter for hybrid energy storage system (HESS)-based Electric Vehicles

With non-linear loads laying a siege in almost every corner of our households, harmonics are hard to mitigate. The short pulses of current drawn by such loads distort the current waveform and deteriorate the health of the electric utility and appliances. The integral multiple of the fundamental waveform’s frequency i.e. the harmonics when summed up become total harmonic distortion (THD). Multilevel inverters (MLI) outshine the traditional two-level inverters because of their capability to produce reduced THD and electromagnetic interference (EMI). In this research article, an innovative 15-level inverter is realized for THD mitigation with 10 MOSFET switches to regulate high power values. The system is initially modelled on MATLAB/SIMULINK and then practically implemented which affirms a THD mitigation of 4% with swish waveform to fulfill the IEEE519.

Computationally Efficient Fixed Switching Frequency Direct Model Predictive Control

This article presents a direct model predictive control (MPC) method for drive systems with superior steady-state and dynamic performance. Specifically, the discussed MPC algorithm achieves a steady-state behavior that is similar or better than that of a linear controller with a dedicated modulator, and fast transient responses that characterize direct controllers. Moreover, it ensures a fixed switching frequency by allowing for one switching transition per phase and sampling interval. Furthermore, the controller utilizes the stator current gradient to predict the evolution of the drive system within the prediction horizon. To find the optimal switching time instants—and thus ensure favorable performance—the control and modulation problems are formulated in one computational stage as a constrained quadratic program (QP). To solve the latter within a few microseconds, a computationally efficient QP solver based on a gradient method is proposed that enables the real-time implementation of the presented algorithm. To further alleviate the computational demands of the proposed method, a mechanism that can identify suboptimal switching sequences at the very early stages of the optimization process is proposed. The effectiveness of the proposed control scheme is experimentally verified on a 3 kW drive system consisting of a two-level inverter and an induction machine.

Fault-Tolerant Operation of a Six-Phase Permanent Magnet Synchronous Hub Motor Based on Model Predictive Current Control With Virtual Voltage Vectors

This paper proposes a model predictive current control (MPCC) compensation method based on virtual voltage vectors for single-phase open-circuit faults of an asymmetric six-phase permanent magnet synchronous hub motor (PMHSM). The proposed strategy adopts the normal vector space to decompose the transformation matrix without reconfiguring the controller topology. By analyzing the difference between the open-circuit phase voltage and the state of health, the disturbance term of the prediction vector in the α-β and x-y subspaces is obtained. 64 voltage vectors are obtained from the switching states of the 6-phase two-level inverter, and then these 64 voltage vectors are appropriately compensated and synthesized into 24 new virtual voltage vectors. The new virtual vectors avoid the adjustment of the MPCC weighting factors and the synthesized virtual vectors can suppress current harmonics. Finally, the experimental results show the effective performance of the method before and after the fault-tolerant operation.

Power system solution based on root matching method in FPGA environments

Digital electromagnetic transient simulation is an important means to analyze the operation, planning and control of power systems. Numerical integration algorithm is the core of electromagnetic transient simulation analysis. By analyzing the existing electromagnetic transient simulation methods of power systems, it is difficult to solve the numerical oscillation and decoupling problems, and the root matching method is proposed to solve such problems. From the perspectives of basic component modeling methods and basic simulation algorithms, the disadvantages of mainstream algorithms in solving electromagnetic oscillations are analyzed. Combining the calculation and simulation features in FPGA, the three-phase two-level inverter model of the power system built is verified.

A Review on Multilevel Inverter Topologies

In this paper, a brief review of the multilevel inverter (MLI) topologies is presented. The two-level Voltage Source Inverter (VSI) requires a suitable filter to produce sinusoidal output waveforms. The high-frequency switching and the PWM method are used to create output waveforms with the least amount of ripples. Due to the switching losses, the traditional two-level inverter has some restrictions when running at high frequencies. For addressing this problem, multilevel inverters (MLI) with lower switching frequencies and reduced total harmonic distortion (THD) are employed, eliminating the requirement for filters and bulky transformers. Furthermore, improved performance at the high switching frequency, higher power quality (near to pure sinusoidal), and fewer switching losses are just a few of the benefits of MLI inverters. However, each switch has to have its own gate driver for implementing MLI, which adds to the system's complexity. Therefore, reducing the number of switches of MLI is necessary. This paper presents a review of some of the different current topologies using a lower number of switches. Doi: 10.28991/ESJ-2022-06-01-014 Full Text: PDF

Compensation of Unbalanced Low-Voltage Grids Using a Photovoltaic Generation System with a Dual Four-Leg, Two-Level Inverter

In this paper, a grid-connected photovoltaic (PV) generation system is proposed with the purpose of providing support to low-voltage grids, namely through the elimination or attenuation of the grid imbalances. This compensation must consider the load types, which can be either linear or non-linear, and whether the reactive power and current harmonics generated by the non-linear loads need to be compensated in addition to the unbalanced active power. This must be well considered, since the compensation of all aspects requires oversized PV inverters. Thus, the different unbalanced compensation schemes are addressed. Several schemes for the generation of the inverter current references taking into consideration the compensation and load type are presented. For this PV generation system, a dual four-leg, two-level inverter is proposed. It provides full unbalanced compensation owing to the fourth leg of the inverter and also extends the AC voltage, which is important when this compensation is required. To control this inverter, a control scheme for the inverter that considers several compensation factors is proposed. A vector voltage modulator associated with the controller is another aspect that is addressed in the paper. This modulator considers the balance between the DC voltages of the inverters. Several compensation schemes are verified through computational tests. The results validate the effectiveness of the proposed PV generation system.

Investigation of SVPWM Based Sliding Mode Control Application on Dual-Star Induction Motor and Dual Open-End Winding Induction Motor

The present paper deals with a comparative study of the Sliding Mode Control (SMC) technique application on three-phase Dual Star Induction Motor (DSIM) topology and the Dual Open-End Winding Induction Motor (DOEWIM). Where, in these two topologies the Space Vector Pulse Width Modulation (SVPWM) has been used for the control of the two two-level inverters and the four two-level inverters, which have been used to power the two motors under application respectively. The main objective of this study is to demonstrate the higher performances of the DOEWIM under the application of SMC combined with SVPWWM, which aims to overcome the main drawbacks faced when using the conventional topology DSIM in industrial applications. Especially in terms of decreasing the harmonics content in the stator current, reducing the overall ripples of the developed electromagnetic torque, the elimination of the common mode voltage and increasing the robustness against the load torque variation and speed reverse. The obtained simulation results show clearly the main advantages of using the topology of DOEWIM compared to the DSIM topology which present a very promising application especially in heavy industrial requiring high power motors.

Fixed switching frequency and three level inverter to improve the performance of sensorless PMSM

The vector control drive system is a very important method to get high dynamic performance. To increase the reliability and decrease the cost of this system, the sensorless speed control is used. Here sensorless speed control conventional model reference adaptive system was studied. It was studied due to have many advantages. Although it has many advantages, but also, it has some drawbacks. These drawbacks an increase in the torque ripples, an increase in distortion of the stator currents, fluxes and motor speed. The aim of this paper is beating the drawbacks of the chosen system through simulation only. Three level inverter with space vector modulation constant switching frequency is used to overcome these drawbacks. To show the effect of the proposed system, it was compared to the conventional system. The conventional system here uses the two-level inverter with space vector modulation. To show the advantages of the constant switching frequency, the three-level inverter was used without keeping the constant switching frequency. The comparison held among the conventional model, the improved model which using the three-level inverter only and proposal model (the three-level inverter which using constant switching frequency). In the conventional model, the reference currents and the estimating currents compared to generate the reference voltage of the space vector modulation. In proposal model, the stator fluxes were estimated and compared to the reference stator fluxes to generate the same voltage of the space vector modulation through keeping the switching time constant. The simulation results proved that importance of the proposed model to improve the drawbacks of the conventional model reference adaptive system.

Modelling and analysis of space vector pulse width modulated inverter drives system using MatLab/Simulink

This paper presents high frequency cable modelling and analysis of cable. Advantages of dodecagonal space vector switching and two-level inverters are achieved with a constant input DC supply. An improved high-frequency power cable is connected between the drive and induction motor to measure the harmonic distortion and reflected overshoot voltage at the motor terminal. The results have confirmed that the present method has very high frequency and time domain. This model is used to predict the effect of long cables for any space vector pulse width modulation technique (SWPWM), the six-step two-level voltage inverter fed induction machines. The harmonic distortion from low to high frequency switching from this SVPWM technique is estimated and results are compared. For different range of frequencies, the cable equivalent circuits are developed and the same has been implemented and the results are shown in MatLab/Simulink.

Implementation of Integer Factor based Space Vector PWM through Digital approach for Grid Connected Multilevel Inverters

Space vector pulse width modulation control for grid connected multilevel inverters are very popular. However, it gets exceedingly tough with the increase in the number of output voltage levels. The total number of possible switching states will increase with the output voltage level of the inverter. Due to increase in the number of switching states, the sub triangles in the various sectors of the hexagon will also increase, that result in increased complexity and storage requirements for implementation using conventional space vector methods. The objective of the paper is to simplify and generalize the space vector algorithm for an n-level inverter. The proposed algorithm uses integer factor approach to find the exact location of the reference vector, synthesize switching times and generate the nearby switching states. It is a generalized algorithm applicable to any sequence and can be applied to any level judiciously. In this article description of the algorithm is given for a three–level inverter and validated by implementing experimentally using dspace control desk. The PWM signals generated by three level Space Vector algorithm with conventional switching sequence of 0127 is used to control an open end winding induction motor fed with two two-level inverters. The performance factor of motor voltage and line current THD at different modulation index is measured and compared with simulation result.

Constrained Modulated Model Predictive Control for a Three-Phase Three-Level Voltage Source Inverter

In the last decade, model predictive control (MPC) has been widely studied in power converters, such as voltage source inverters (VSIs). Unfortunately, MPC often presents a high computational burden that limits their applicability, especially when driving multilevel inverters (MLIs) because of their higher number of switching combinations than two-level inverters. As a result, some strategies have been developed to reduce the computational complexity of MPC. One of the most relevant is the use of artificial neural networks (ANNs) to approximate the behavior of an MPC. However, ANNs require to be evaluated at bounded inputs. Otherwise, their response cannot be guaranteed to be a good approximation of the controller they learned from. Furthermore, when driving an LC-filtered VSI, the inductor current can present high peaks due to the cross-coupling effect between the inductor and the capacitor. These current peaks can cause physical damages and loss of performance of an ANN-emulated MPC. This paper presents a new constrained modulated MPC (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PC), better suited for ANN emulation, to overcome these issues. The proposed strategy evaluates the cost function once per switching region, allowing easy and intuitive constraint inclusion. Additionally, an overmodulation stage is used to handle negative duty cycles and enhance disturbance rejection. Finally, the proposal is validated through simulations, using MATLAB-Simulink, taking into account different load conditions. Simulations show that the constrained M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PC keeps the inductor current below its desired limit while having a good performance (low harmonic distortions and fast dynamics) even when the inverter operates near its boundaries.

Comparison between two levels and multi-level (NPC and Cascad) inverters

Due to many advantages, the application of multilevel inverters is growing day by day. Compared with the conventional two-level inverter, the multi-level inverter is more efficient because it can eliminate the low-order harmonics in the output waveform without increasing the high-order harmonics. Therefore, the harmonic fluctuation of the inverter output voltage is reduced, and the waveform level is high.In this paper, a comparative study of multilevel inverters is carried out.Different topologies of inverters have been studied: two-level inverters, Neutral-Point clamped inverter types and cascaded inverter types (for both 3 and 5 configuration levels for the two types of inverts: Neutral-Point clamped and cascaded).All of these circuit configurations have been modeled using Matlab Simulink and the analysis results have been presented: Conclusions have been drawn on the efficiency of each configuration.

Modelling and analysis of space vector pulse width modulated inverter drives system using MatLab/Simulink

This paper presents high frequency cable modelling and analysis of cable. Advantages of dodecagonal space vector switching and two-level inverters are achieved with a constant input DC supply. An improved high-frequency power cable is connected between the drive and induction motor to measure the harmonic distortion and reflected overshoot voltage at the motor terminal. The results have confirmed that the present method has very high frequency and time domain. This model is used to predict the effect of long cables for any space vector pulse width modulation technique (SWPWM), the six-step two-level voltage inverter fed induction machines. The harmonic distortion from low to high frequency switching from this SVPWM technique is estimated and results are compared. For different range of frequencies, the cable equivalent circuits are developed and the same has been implemented and the results are shown in MatLab/Simulink.

Evaluation and Minimization of Total Harmonic Distortion in Three-Phase Two-Level Voltage Source Inverter with Low Switching Frequency

Evaluation and Minimization of Total Harmonic Distortion in Three-Phase Two-Level Voltage Source Inverter with Low Switching Frequency

Simple FCS-MPC Method for Reducing Common-Mode Voltage in a Three-Phase Two-Level Voltage Source Inverter

Common mode voltage (CMV) causes various issues, including a negative impact on the performance of a hybrid electric vehicle’s power system (HEV). Many papers have published methods that mitigate CMV, almost all of which attempt to avoid zero vectors, but this increases total harmonic distortion (THD). This work describes a simple and efficient method for reducing CMV in a two-level three-phase voltage source inverter (VSI) with an RL load. This method uses only active vectors. It replace the zero vector with the two opposite vectors V2 and V5. for T1 and T2 respectively in a one sampling period Ts. A numerical simulation, using Matlab-Simulink. is achieved to assess the effectiveness of the proposed control technique. The obtained results show a reduction in THD value (17% improvement) and a decrease in the peak value of CMV from (${{ + {V_{dc}}} \over 2}$ and ${{ - {V_{dc}}} \over 6}$) to $\pm {{{V_{dc}}} \over 6}$. These results are compared to those obtained by using the traditional predictive control model MPC.

Performance Enhancement of Induction Motor Based on Three-Level T-Type Inverter Using DTC-SVM

Induction motors (IM) that are driven using the conventional direct torque control algorithm (DTC) suffer from vital drawbacks which are high ripples in the torque and flux. These ripples result due to the use of a look-up table and hysteresis comparators which causes variable switching frequency. Moreover, the use of a traditional two-level inverter leads to the production of low-quality voltage and current. The work presented in this paper proposed a modified control system to overcome these drawbacks. The proposed control system is based on the use of the space vector modulation-based DTC algorithm (DTC-SVM) for driving three-phase IM via a three-level T-Type inverter. The conventional DTC-SVM algorithm has been modified to match the work of the proposed inverter. The modification process was based on the mapping of the standard DTC-SVM algorithm in the space vector of the three-level inverter. The conventional and the modified control systems are implemented using MATLAB/Simulink package. The comparison of the standard and the modified DTC-SVM has been performed by simulation. Simulation results showed the superiority of the proposed algorithm in terms of reducing ripple in torque and flux and improving the quality of current and voltage supplied to the motor.

A novel 7-Level symmetric inverter module with less circuit components

Multilevel Power Converters (MPCs) have vast potential in power electronics research and development of DC-AC electrical energy conversion system. MLIs have become an inescapable power electronics device in various power conversion applications due to the incompatibility of traditional two-level inverters. MLIs are extremely popular for medium power and high AC voltage applications, and thus predicted to gather incessant attention in future. This article suggests a novel single-phase symmetric 7-level inverter suitable for a renewable energy application with an effort to lower the count of switching components and conducting devices in the path for the flow of current. The proposed symmetric type inverter circuit could produce 7-level output voltage by using three DC sources and seven power electronic switches. The suggested inverter structure can be used to generate any number of voltage levels, and it can produce all output voltage levels (i.e.,+ve,-ve and zero), which significantly reduces the inverter's total standing voltage. The performance of the suggested 7-level inverter topology was confirmed by simulation results obtained in MATLAB/Simulink.

Improving Power Density of a Three-Level ANPC Structure Using the Electro-Thermal Model of Inverter and a Modified SPWM Technique

Multilevel inverter structures have become an interesting substitute for the well-known two-level inverters in a variety of applications due to their exceptional characteristics when compared to conventional inverters. One major issue regarding multilevel structures is the unequal junction temperature of the switches which deteriorates the power density and increase the cost of the inverter by reducing the maximum achievable output power with a given thermal model and cooling system. Hence, on account of the aggressive goals of power density and cost in a majority of power electronic applications, this article proposes a new technique for reducing the maximum junction temperature of switches in a three-level active neutral-point clamped (ANPC) inverter based on a junction temperature estimation method and a modified SPWM control scheme. This technique can ensure up to a 12% rise in the power density value when compared to basic SPWM techniques with no loss distribution algorithm. Moreover, the suggested approach can be used as a protection stage in the inverter which protects the inverter in transient loads, while allowing for reaching the maximum power capability of the inverter. Finally, the simulations of the proposed technique are validated with experimental results of a 400 V, 20 kW three-level ANPC inverter, controlled by the conventional and proposed techniques.