Three-level Inverter Research Articles

Performance evaluation of multilevel multiphase inverters by piece-wised linearized simulation models

The paper deals with the design issue of the computer simulation models of the traction inverter reflecting request on the rapid investigation of the efficiency performance under various operational conditions. According to this, a piece-wised linearized simulation tool PLECS is selected for model development, which considers the relevant loss behaviour of the main power circuit semiconductor components. The topologies, for which the simulation models are created, are topologies, one of which is commonly used across the automotive industry as the heart of the traction drive (VSI – Voltage Source Inverter), and its perspective alternative three-level traction inverter topology T-NPC – T-type Neutral Point Clamped. The simulation models created in the given simulation tool are thus subjected to the analysis of power parameters, which also include the calculated power losses of the entire system of semiconductor devices for both topologies of the traction inverter. Based on the obtained power parameters, the efficiency performance under various operational conditions of both topologies is evaluated. The presented methodology enables rapid investigation of operational performance enabling fast optimization methods. Any design of linearized simulation models in the PLECS simulation tool, whose core consists of semiconductor elements, can be analyzed by the proposed methodology.

A Modified Discontinuous PWM Method for Three-Level Inverters With the Improved LCL Filter

A Modified Discontinuous PWM Method for Three-Level Inverters With the Improved <i>LCL</i> Filter

Asymmetric SVPWM and Error Suppression Method for Current Reconstruction of T-Type Three-Level Inverter

Asymmetric SVPWM and Error Suppression Method for Current Reconstruction of T-Type Three-Level Inverter

A Modified SVPWM Strategy for Reducing PWM Voltage Noise and Balancing Neutral Point Potential

PWM (pulse width modulation) is the most widely applied current conversion technology, but the high-frequency harmonics it causes have a significant negative impact on inverter system performance. This paper focuses on the three-phase T-type three-level inverter as the research object and addresses existing PWM voltage noise and midpoint potential imbalance issues by proposing an improved random SVPWM strategy, named Neutral Point Potential Balance Random Space Vector PWM (NPB–RSVPWM). The NPB–RSVPWM strategy includes three main steps: (1) introducing a midpoint potential balancing control loop to adjust the synthesis timing of the effective vectors to generate pulse signals, optimizing midpoint potential balance; (2) employing a randomly varying carrier frequency in place of the carrier used in the SVPWM strategy to generate the driving signals for switching devices; and (3) controlling the inverter through the driving pulse signals. This strategy optimizes the synthesis sequence of traditional SVPWM strategy vectors and incorporates random frequency modulation techniques. The mathematical model analyzes PWM harmonic expressions corresponding to fixed switching frequencies, and a random frequency carrier is chosen to suppress these PWM harmonics. The effective vector’s equivalent circuit is analyzed, proposing a technique for optimized vector synthesis timing. The simulation and experimental results verify that the NPB–RSVPWM technique can disperse PWM harmonic energy, reduce voltage noise, and optimize midpoint potential balance. Under the NPB–RSVPWM strategy, the line voltage spectrum becomes uniform, the maximum harmonic content is greatly reduced, and the fluctuation in the DC side midpoint potential is significantly improved. Compared with the traditional SVPWM strategy and random PWM strategy, the NPB–RSVPWM strategy has a lower voltage noise, smaller total harmonic distortion, and a more stable midpoint potential. The effectiveness and feasibility of the NPB–RSVPWM strategy are verified by simulation and experimental results.

Application and Verification of a Leg-Transfer Method for Three-Level Active Neutral-Point-Clamped Inverters for Railway Vehicles

In this paper, a two-leg-transfer switch structure method that can continuously supply three-phase power even when an accident occurs in a power semiconductor of a three-level active neutral-point-clamped (ANPC) inverter for railway vehicles is presented. The proposed method can minimize the ripple effect caused by power semiconductor faults by separating the faulty leg from the main circuit and connecting the load-side circuit to a neutral point. As a result of simulations, the average values of MAE and RMSE can be reduced by 1.53 [A] and 1.77 [A], respectively, when using the proposed leg-transfer switch structure compared to using the conventional structure. In the IGBT failure experiment, when the proposed method was applied to a three-level ANPC inverter, there was only a 0.21 [%] difference from the THD under normal conditions. As a result, the magnitude, phase, and total harmonic distortion of the three-phase current waveforms measured before and after the fault were identical. Thus, normal three-phase power could be effectively supplied to the load when the proposed leg-transfer switch method was applied after a power semiconductor fault occurred in the three-level ANPC inverter. If this leg-transfer switch method is applied in three-level ANPC inverterd for railway vehicles, track schedule errors can be minimized by continuously supplying three-phase power to the electric motor even when an accident occurs in a power semiconductor.

Hybrid varied virtual vector modulation method of parallel three-level inverter considering neutral point potential and phase current balance

Hybrid varied virtual vector modulation method of parallel three-level inverter considering neutral point potential and phase current balance

Non-Weighted Two-Stage Model Predictive Control Strategy Based on Three-Level NPC Inverter

This paper investigates the asynchronous motors driven by a Three-Level Neutral-Point-Clamped Voltage Source Inverter (3L-NPC-VSI) and aims to achieve control without weight factors and reduce torque ripple. It puts forward a non-weighted two-stage Finite-Control-Set Model Predictive Control (FCS-MPC) strategy. First, a hierarchical optimization method is adopted to address the difficulty of setting weight factors in traditional FCS-MPC applications. The method offers stratified designs of three performance indices, voltage jump, common-mode voltage, and current tracking, obviating the need for weight factor setting and reducing the calculation load of predictions. Secondly, to further mitigate torque ripple, an optimal vector or vector combination is implemented at the current control layer by adhering to the principle of minimal current tracking error. During the selection of the optimal vector combination, the first vector of the combination is chosen to be the vector at the end of the present cycle. This ensures that there is at most one switch within each control period, reducing the switching losses of the two-stage FCS-MPC. Lastly, detailed simulation and experimental analyses are conducted to verify the feasibility and effectiveness of the proposed strategy.

A Hybrid PWM Strategy for Switching Loss Reduction in Three-Level Inverters

The advanced bus-clamping PWM (ABCPWM) sequences are well known to reduce line current THD in a three-level neutral point-clamped inverter. This paper deals with ABCPWM sequences employed optimally to achieve minimum switching loss throughout the linear operating region in a three-level inverter. The work extensively analyzes the performance of these sequences in terms of inverter switching loss and compares them with centered space vector modulation PWM (CSVPWM). Based on the analysis, a hybrid PWM scheme termed as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">switching loss reduction</i> is proposed by optimally employing ABCPWM sequences in conjunction with variation in power factors. At a given average switching frequency, the proposed hybrid scheme reduces inverter switching loss compared to CSVPWM and the recently proposed discontinuous PWM-based optimization strategy at all power factors and modulation indices. With this scheme, switching loss reduces to 22% to 36% compared to CSVPWM and a maximum of 12% reduction than the existing optimization strategy. Furthermore, the scheme gives lower harmonic distortion compared to these two existing PWM schemes near high modulation indices and near unity power factor load. The theoretical, simulated, and real-time simulation results are presented with experimental results using TMS320F28335 DSP controller for validating the proposed work.

Optimization of the Symmetrical SVPWM for Three-Level T-Type Inverters With Unbalanced and Oscillated Neutral-Point Voltages

The symmetrical space-vector pulse-width-modulation (SVPWM) has been widely adopted in three-level (3L) T-type inverters due to its low current harmonics and high linear modulation index. However, when faced with unbalanced and oscillated neutral-point (NP) voltages, extra current harmonics will be generated. In this paper, a new solution is provided. Other than adopting the existing strategies for balancing the NP voltage, the symmetrical 3L SVPWM is optimized to work with unbalanced and oscillated NP voltages. Firstly, the vectors are idealized, based on which ideal dwell times are obtained by an analytical simplified symmetrical 3L SVPWM. Then, a dc-zero-sequence component is calculated and injected to maximize the linear modulation index, and the real dwell times are further derived after the adjustment according to the ‘volt-second balance’ principle. In addition, a control strategy is investigated to actively adjust the NP voltage. Finally, the optimized symmetrical 3L SVPWM is verified by comparative experiments, showing its low current harmonics with unbalanced and oscillated NP voltages.

TECHNIQUE DE CONTRÔLE INTÉGRÉE OPTIMISÉE POUR VAUTOUR AFRICAIN POUR APPLICATION DE POMPE À MOTEUR À INDUCTION À ENROULEMENT OUVERT À ALIMENTATION PV

Open-end winding induction motors (OEWIM) have gained much attention, and they are used for solar photovoltaic (PV) fed pumping applications as a compromise alternative to multi-level inverters. Solar irradiance conditions further exacerbate the nonlinear control problem, resulting in significant loss of power and low reliability, which affects motor operation. To overcome these issues, this paper presents an optimized integrated control technique-based PV integrated three-level dual inverter fed Open-end winding induction motors for pumping application. An integrated African vulture optimization algorithm and scalar coupled pulse width modulation (AVO-SCPWM) based control techniques are proposed to extract the maximum power from the solar PV source and control the induction motor pump. Here, the AVO-based maximum power point tracking (MPPT) technique adjusts the modulation index (ma) by insolation and temperature. The proposed technique balances the zero-sequence current, reduces THD, and reduces the switching losses over the inverter. The proposed work is evaluated in MATLAB/Simulink software and compared with the existing conventional induction motor (IM), Conventional OEWIM Drive, and scalar decoupled PWM-based IM techniques under two climatic conditions. Thus, the simulation results demonstrate that the proposed technique accomplishes better than the existing techniques.

A Small-Sized High-Precision Digital Closed-Loop Modulation Method for Dead-Time Compensation for Flying Capacitor Three-Level Inverters

A Small-Sized High-Precision Digital Closed-Loop Modulation Method for Dead-Time Compensation for Flying Capacitor Three-Level Inverters

Enhanced Carrier-Based Discontinuous PWM for Three-Level Inverters With Unbalanced Neutral-Point Voltage

Enhanced Carrier-Based Discontinuous PWM for Three-Level Inverters With Unbalanced Neutral-Point Voltage

Model Predictive Control Strategy Based on Loss Equalization for Three-Level ANPC Inverters

Targeting the issue of high losses of individual switching tubes in Neutral-Point Clamped (NPC) three-level inverters, an Active Neutral-Point Clamped (ANPC) three-level inverter is used, and a model predictive control strategy using the loss equalization of the inverter is proposed. This method organizes and analyzes multiple zero-state current pathway commutation modes and adds mode three under the original two commonly used zero-state commutation modes. On this basis, the three modes are flexibly switched by model predictive control, and the output is optimized according to the value function for the space vector in each operation, while the midpoint voltage control is added to the value function. The simulation results suggest that the recommended strategy in this study may effectively realize the loss equalization control and midpoint voltage control of the ANPC inverter, which improves the operation efficiency of the electromechanical actuator.

An Open-Circuit Fault Diagnosis Method for Three-Level Neutral Point Clamped Inverters Based on Multi-Scale Shuffled Convolutional Neural Network.

This study constructs a power switching device open-circuit fault diagnosis model for a three-level neutral point clamped inverter based on the multi-scale shuffled convolutional neural network (MSSCNN) and extracts and classifies the fault information contained in the output current of inverters. The model employs depthwise separable convolution and channel shuffle techniques to improve diagnostic accuracy and reduce model complexity. The experimental results show that the new model has lower model complexity, better noise resistance and higher average diagnostic accuracy compared with fault diagnosis models based on CNN, ResNet, ShuffleNet V2 and Mobilenet V3 networks.

Comparison of DTC between two-level and three-level inverters for LV propulsion electric motor in ship

Comparison of DTC between two-level and three-level inverters for LV propulsion electric motor in ship

COMPARATIVE STUDY OF TRADITIONAL PWM INVERTERS AND MULTILEVELS INVERTERS

The need of higher powers in electrical drives has forced the researchers to develop new power source possibilities. Multilevel inverters have been presented as a cost effective solution for various high voltage and high power applications including power quality and motor drive problems. The traditional pulse width modulated (PWM) Inverter does not completely eliminate the unwanted harmonics in the output waveform. Using the multilevel inverter as an alternative to traditional PWM inverters for electric motor drive applications is investigated. The concept of the Optimized Harmonic Elimination Stepped-Waveform (OHESW) technique for a multilevel inverter is presented. The effectiveness of this technique in minimizing the inverter switching losses and its output voltage harmonic content which cause reducing harmonic losses and torque pulsations of an induction motor fed form is investigated analytically. Comparison between the Selective Harmonic Eliminated PWM (SHEPWM) as a traditional PWM technique for three-level inverter and the OHESW technique for multilevel inverter with regard to the switching losses, harmonic distortion, additional harmonic losses in the motor and the pulsating torques is also presented.

The Design and Dynamic Control of a Unified Power Flow Controller with a Novel Algorithm for Obtaining the Least Harmonic Distortion

This study investigates the control and dynamic operation of the Unified Power Flow Controller made of shunt and series converters, a Static Synchronous Compensator, and a Static Synchronous Series Compensator, respectively, connected back-to-back through a common DC-link capacitor. The model of a 48-pulse Voltage Source Converter is constructed from a three-level Neutral Point Clamped converter, which allows the total harmonic distortion to be reduced. An optimal conduction angle tracking system of the three-level inverter is designed to minimize distortion by detecting proper harmonic component elimination. Starting from the six-step modulation strategy, the dq decoupled control schemes of both compensators in open and closed loops are presented. Finally, the MATLAB-Simulink model of the power flow controller is implemented and analyzed. The results show that the controller can track the power changes and apply a suitable voltage to the power system so that the power flow can be controlled. This way, the power flow controller dynamically improves the voltage and power quality across the power network while simultaneously improving the transient stability of the system. It can eliminate all system disturbances resulting from oscillations and harmonics in voltage and current within a very short time. The procedural approach used to model and simulate the Unified Power Flow Controller, as well as the new algorithm used to obtain the harmonic number that minimizes the total harmonic distortion, can be applied to any AC power system.

Self-Identification Strategy for an Inverter Nonlinearity Compensation of Three-Level Inverter

Self-Identification Strategy for an Inverter Nonlinearity Compensation of Three-Level Inverter

Minimization of DC-Link Ripple Current for Enhancing Reliability in Three-Level Voltage Source Inverters

Minimization of DC-Link Ripple Current for Enhancing Reliability in Three-Level Voltage Source Inverters

Open-Circuit Fault Diagnosis of T-Type Three-Level Inverter Based on Knowledge Reduction

Compared with traditional two-level inverters, multilevel inverters have many solid-state switches and complex composition methods. Therefore, diagnosing and treating inverter faults is a prerequisite for the reliable and efficient operation of the inverter. Based on the idea of intelligent complementary fusion, this paper combines the genetic algorithm–binary granulation matrix knowledge-reduction method with the extreme learning machine network to propose a fault-diagnosis method for multi-tube open-circuit faults in T-type three-level inverters. First, the fault characteristics of power devices at different locations of T-type three-level inverters are analyzed, and the inverter output power and its harmonic components are extracted as the basis for power device fault diagnosis. Second, the genetic algorithm–binary granularity matrix knowledge-reduction method is used for optimization to obtain the minimum attribute set required to distinguish the state transitions in various fault cases. Finally, the kernel attribute set is utilized to construct extreme learning machine subclassifiers with corresponding granularity. The experimental results show that the classification accuracy after attribute reduction is higher than that of all subclassifiers under different attribute sets, reflecting the advantages of attribute reduction and the complementarity of different intelligent diagnosis methods, which have stronger fault-diagnosis accuracy and generalization ability compared with the existing methods and provides a new way for hybrid intelligent diagnosis.