Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Variable-Angle Phase-Shifted PWM for Multilevel Three-Cell Cascaded H-bridge Converters

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method

A Seven-level defined selective harmonic elimination PWM strategy

Selective harmonic elimination pulse-width modulation (SHE-PWM) techniques offer an optimized control approach for a given converter and are therefore suitable for the low switching frequency high-power applications. Optimization techniques can be successfully used to obtain the solutions of the equations defining the SHE-PWM waveform. In this paper, a seven-level multilevel strategy (MSHE-PWM) defined on the line-to-neutral basis and based on a ratio of a variable number of angles distributed over three levels to be able to calculate the transition points is reported. The technique provides eighteen switching transitions for every quarter period in the standard modulation index range. In the overmodulation region, this can be changed in order to increase the gain of the modulator which in turn results in a compromised bandwidth. The switching angles as a function of the modulation index are reported for the standard as well as the overmodulation range. Selected simulation results are presented to verify the effectiveness and feasibility of the proposed method

Optimization study of high power static inverters and converters Final report

Optimization study and basic performance characteristics for conceptual designs for high power static inverter

Study of state-of-the-art static inverter design Final report, 6 Jan. - 6 Jun. 1966

Multiple purpose inverter design based on phase demodulated inverter circuit selected from state-of-the-art assessment of ten inverter circuit

New Modulation Technique to Mitigate Common Mode Voltage Effects in Star-Connected Five-Phase AC Drives

Star-connected multiphase AC drives are being considered for electromovility applications such as electromechanical actuators (EMA), where high power density and fault tolerance is demanded. As for three-phase systems, common-mode voltage (CMV) is an issue for multiphase drives. CMV leads to shaft voltages between rotor and stator windings, generating bearing currents which accelerate bearing degradation and produce high electromagnetic interferences (EMI). CMV effects can be mitigated by using appropriate modulation techniques. Thus, this work proposes a new Hybrid PWM algorithm that effectively reduces CMV in five-phase AC electric drives, improving their reliability. All the mathematical background required to understand the proposal, i.e., vector transformations, vector sequences and calculation of analytical expressions for duty cycle determination are detailed. Additionally, practical details that simplify the implementation of the proposal in an FPGA are also included. This technique, HAZSL5M5-PWM, extends the linear range of the AZSL5M5-PWM modulation, providing a full linear range. Simulation results obtained in an accurate multiphase EMA model are provided, showing the validity of the proposed modulation approach.This work has been supported in part by the Government of the Basque Country within the fund for research groups of the Basque University system IT978-16 and in part by the Government of the Basque Country within the research program ELKARTEK as the project ENSOL (KK-2018/00040)

Analytical evaluation of output current ripple amplitude in three-phase three-level inverters

Nowadays, three-phase multilevel inverters are widely employed in medium and high-power applications, increasing the power ratings, improving the output voltage quality and reducing the conducted electromagnetic interferences. Despite of numerous pulse-width modulation (PWM) techniques have been developed for multilevel inverters, a detailed analysis of the output current ripple amplitude has not been reported yet. In this study, the peak-to-peak current ripple distribution over a fundamental period is analysed in details specifically for three-level three-phase voltage source inverters for both motor-load and grid-connected applications. In particular, the peak-to-peak amplitude of the current ripple is determined analytically as a function of the modulation index. The centred PWM strategy is considered in all the developments, implemented either by carrier-based or space vector (SV) PWM methods. With this modulation, the dc bus utilisation is maximised in a simple and effective way, and a nearly-optimal behaviour is obtained to minimise the current ripple rms. The results obtained in different cases and sub-cases identified in the proposed analytical approach are verified by experimental tests with reference to three-phase three-level neutral-point clamped configuration

A Comprehensive AC Current Ripple Analysis and Performance Enhancement via Discontinuous PWM in Three-Phase Four-Leg Grid-Connected Inverters

open5siA complete analysis of the ac output current ripple in four-leg voltage source inverters considering multiple modulation schemes is provided. In detail, current ripple envelopes and peak-to-peak profiles have been determined in the whole fundamental period and a comprehensive method providing the current ripple rms has been achieved, all of them as a function of the modulation index. These characteristics have been determined for both phase and neutral currents, considering the most popular common-mode injection schemes. Particular attention has been paid to the performance of discontinuous pulse width modulation (DPWM) methods, including DPWMMAX and DPWMMIN, and their four most popular combinations DPWM0, DPWM1, DPWM2, and DPWM3. Furthermore, a comparison with a few continuous techniques (sinusoidal, centered pulse width modulations, and third harmonic injection) has been provided as well. Moreover, the average switching frequency and switching losses are analyzed, determining which PWM technique ensures minimum output current ripple within the linear modulation range at different assumptions. Numerical simulations and laboratory tests have been conducted to extensively verify all the analytical claims for all the considered PWM injections.openMandrioli, Riccardo; Viatkin, Aleksandr, Hammami, Manel; Ricco, Mattia; Grandi, GabrieleMandrioli, Riccardo; Viatkin, Aleksandr, Hammami, Manel; Ricco, Mattia; Grandi, Gabriel

An Investigation on The Impacts of Inverter Modulation Techniques on The Performance of The Dual Inverter Drive

This work presents a comprehensive overview about the dual inverter drives in applications related to the electric vehicle industry. The requirement of efficient and integrated power electronic converter circuits has become an essential requirement to the vehicle function. Major research and progress have been made to achieve dual and bidirectional operation of power flow, while minimizing losses, volume and costs. This thesis surveys the single, three phase, and dual inverter structure and operation. The dual structures are earning growing attention due to their capability to provide multiple output voltages to the stator of the electric machine associated with the electric vehicle. The contribution of this work is to study the impact of the major modulation techniques on the regulated, dual inverter drive performance. The selected methods for evaluation include sinusoidal pulse width modulation, third harmonic injection pulse width modulation, and space vector modulation in terms of the drive’s output voltage, fundamental voltage and total harmonic distortion. The second investigation involves the manipulation of phase angle relationships between the gates of the two adjacent inverters, allowing the drive to achieve equal phase voltage and power between both inverters at varying loads