Three-level Voltage Source Inverter Research Articles

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

Power Loss Modelling and Performance Comparison of Three-Level GaN-Based Inverters Used for Electric Traction

The main aim of this work is to present a step-by-step procedure to model and analyze the power loss distribution of three-level Gallium Nitride (GaN) inverters. It has been applied to three distinct three-phase three-level voltage source inverters utilized in electric traction drives: Active Neutral Point Clamped, Neutral Point Clamped and T-Type Neutral Point Clamped. The proposed analytical power loss modelling, combined with an equivalent representation of the electrical machine proved to be a viable solution to achieve a time-saving and low computational burden simulation platform, leading to satisfying accurate results. This has been confirmed by comparing the results carried out from the simulations of a 110 kW permanent magnet synchronous motor drive and those determined by considering a simplified circuital representation based on the proposed analytical power loss modelling.

Discrete space vector modulation and optimized switching sequence model predictive control for three-level voltage source inverters

This paper proposes a discrete space vector modulation and optimized switching sequence model predictive controller for three-level neutral-point-clamped inverters in grid-connected applications. The proposed strategy is based on cascaded model predictive control (MPC) for controlling the grid current while maintaining the capacitor voltage balanced without weighting factor. To enhance the closed-loop performance, the external MPC evaluates 19 basic and 138 virtual vectors (VV) of the proposed space vector method. The optimal control voltage is then selected using an extended deadbeat method to reduce the execution time of the proposed control algorithm. By using the discrete space vector modulation principle, the VV are synthesized based on switching sequence (SS) and are divided into negative and positive SSs considering their impact on the neutral point (NP) potential. The inner MPC evaluates both types of SSs and selects the one that keeps the capacitor voltage balanced. Various controllers are evaluated and compared against the proposed control strategy. The results show that the proposed strategy improves performance without weighting factor, while maintaining a total harmonic distortion of current to be less than 2%. Compared to the modulated MPC which provides the same fixed switching frequency, the proposed controller reduces the computational burden by over 50% while also providing better NP voltage balance accuracy.

Three-level NPC voltage source converter based direct power control of the doubly fed induction generator at low constant switching frequency

This paper deals with an improvement of the direct power control ‘DPC’ for three-level voltage source inverter NPC-VSI feeds the rotor of the doubly fed induction generator ‘DFIG’ based wind power generation system. This converter allows controlling the rotor voltage in magnitude and phase angle with a high flexibility and can therefore be used for active and reactive power control of DFIG. The control is especially designed to reduce the harmonic distortion of the generated currents and active power ripples of the classical DPC control using switching table. In addition, it’s convenient for high power drive and variable speed generator applications with constant switching frequency. The detailed operation principle and simulation results of the proposed DPC-NPC strategy for 1.5 MW of DFIG are also discussed.

Influence of switching sequences on the neutral point voltage balance in a three-level voltage source invertor

BACKGROUND:Ensuring the voltage balance of the neutral point of the DC link within acceptable limits is one of the mandatory requirements during the operation of a three-level autonomous neutral point clamped voltage source inverter. It is known that neutral point voltage imbalance can adversely affect the operation of the inverter and the load at all, lead to the failure of both power switches and capacitors in the DC link. Neutral point voltage imbalance mostly often occurs due to the asymmetry of the nominal values of DC capacitors, inconsistent properties of switching devices, asymmetric three-phase load, and also due to the imperfection of the converter control algorithm.
 AIMS:Selection of the optimal switching sequence that ensures the smallest deviation of the neutral point voltage and the number of switching of power switches in a three-level voltage source inverter.
 METHODS:For an objective comparison of the considered switching sequences and their influence on the neutral point voltage balance, a simulation model of a three-level neutral point clamped voltage source inverter was developed in theMATLAB/Simulinksoftware. To control this inverter, a space vector modulation method was used with three different switching sequences: five-segment, seven-segment and standard.
 RESULTS:The topology of a three-level neutral point clamped voltage source inverter is presented. The experimental dependencies of the neutral point voltage deviation error was taken with a change in the modulation coefficient, the frequency of the fundamental harmonic at the inverter output, and load characteristics for three different switching sequences.
 CONCLUSIONS:In this paper, the influence of the basic vectors and the influence of switching sequences on the neutral point voltage balance are studied. Combinations of states of large and zero basic vectors do not affect the neutral point voltage. For the medium basic vectors, the neutral point voltage can increase or decrease depending on the operating conditions of the inverter. The small basic vectors significantly affect the neutral point voltage. Considering the abovementioned, the seven-segment sequence that ensures both the optimal balance of the neutral point voltage and the level of switching losses should be considered as the best switching sequence for a three-level inverter.

Duty-Cycle Correction-Based Model Predictive Current Control for PMSM Drives Fed by a Three-Level Inverter With Low Switching Frequency

In this paper, a duty-cycle correction-based model predictive current control (DC-MPCC) is proposed for permanent magnet synchronous motor (PMSM) supplied by a neutral-point clamped three-level voltage source inverter (NPC-3LVSI). Unlike the conventional MPCC, which evaluates the impact of basic voltage vectors on the concerned state variables, the proposed DC-MPCC modifies the output voltage levels with optimized duty-cycle corrections. Firstly, the last three-phase voltage levels are assumed to be kept during the next control period. Then, the current tracking error and neutral-point potential are predicted. After that, the voltage levels are modified with zero, one, or two state changes, which formulate seven candidate solutions. Subsequently, the duty-cycle corrections of the modified voltage levels are computed based on the principle of minimizing current tracking error and neutral-point voltage drift. Finally, the optimal switch sequence is generated by evaluating and sorting a cost function with a penalty on switch actions. The proposed DC-MPCC features variable switching instants, relatively lower sampling frequency, and satisfactory performance under low switching frequency. Experimental tests carried out on a NPC-3LVSI fed PMSM drive, with 100 Hz fundamental frequency and 400 Hz switching frequency, accompanied by a video demonstration, validate the effectiveness of the proposed method.

A Novel Continuous Control Set Model Predictive Control for LC-Filtered Three-Phase Four-Wire Three-Level Voltage-Source Inverter

In this article, a novel continuous control set model predictive control (CCS–MPC) is proposed for an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -filtered three-phase three-level four-wire voltage-source inverter (3P-4W-3L-VSI). The proposed MPC algorithm provides independent control of each phase of the 3P-4W-3L-VSI under various unbalanced load conditions, which shows superior performance under unbalanced loads. Furthermore, different from conventional MPC methods, the CCS–MPC achieves fixed switching frequency, hence simplifying the design of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filters. In addition, dc offsets are introduced to the proposed modulation to effectively balance the neutral-point voltage of the 3P-4W-3L-VSI. Experimental results are presented to verify the effectiveness of the proposed MPC algorithm.

A high degree of direct torque control applied to a grid-connected wind energy system based on a DFIG

This paper presents the performances improvement of a doubly fed induction generator (DFIG) driven by a wind turbine (WT) using direct torque control (DTC). However, the major drawbacks related to DTC are high torque/flux ripples that produce mechanical vibration and disagreeable noise. The use of multilevel inverters seems to be an interesting solution. A three-level voltage source (inverter) converter (3LVSI) connected to the rotor side of the DFIG is considered in this paper. The high freedom degree of the voltage vectors selection in the 3LVSI allows a control with minimal torque and flux ripples. In addition, a fuzzy logic approach is introduced, to ensure an intelligent extraction of the energy sweeping the WT blades. A variable adjustment step enables an optimal extraction in a minimum tracking time with significant reduction of oscillations in the steady state. Simulation results obtained using MATLAB/SIMULINK demonstrate the effectiveness of the 3LVSI-DTC control based on Fuzzy MPPT in the wind energy conversion system (WECS).

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.

Space vector PWM ‐based current error boundary investigations for three‐level VSI fed induction motor drive

Field oriented control (FOC) of induction motor (IM) powered by a three-level voltage source inverter (3L -VSI) with space vector (SV) based continuous and dis -continuous pulse width modulation (PWM) is presented in this paper. The current error variations in each sector with above-mentioned PWM techniques are monitored and analyzed mathematically. These boundary investigations play a great role in the implementation of Current Error Space Phasor (CESP) based hysteresis current controller (HCC) which incorporates the advantages of a constant switching frequency PWM fed three-level inverter (3LI) into highly dynamic current controlled – voltage source inverter. As a preliminary step, FOC of IM with the conventional space vector PWM and bus clamping PWM (BC30 and BC60) fed 3LI have been simulated using SIMULINK toolbox of MATLAB. Transient analysis of the drive with acceleration, deceleration, and load change studies with different switching schemes are analyzed with d SPACE RTI1103 experimentation on a 2.2 kW three-phase IM drive in detail.

Robust model predictive control for three-level voltage source inverters

To solve the problem of parameter mismatch in model predictive control (MPC), this paper presents a robust model predictive control method based on a fixed window optimization (FWO) algorithm for a three-level voltage source inverter that only needs to sample the current value. When compared with the traditional observer-based model predictive control (such as the Luenberger observer, sliding mode observer (SMO) and Kalman filter (KMF)), the proposed method does not require an observer with a complicated design, and its algorithm is simple and easy to understand. Meanwhile, high current sampling accuracy is not needed in the proposed method. However, it is necessary in some types of model-free predictive control. In addition, low switching frequency operation and delay compensation are also considered in this paper. In general, the proposed method is simple to implement and does not have high requirements in terms of the accuracy of its current sensor. Experimental results show that the proposed method can accurately estimate parameter values and improve the parameter robustness of MPC.

A Novel Zero Dead-Time PWM Method to Improve the Current Distortion of a Three-Level NPC Inverter

This paper proposes a novel pulse width modulation (PWM) for a three-level neutral point clamped (NPC) voltage source inverter (VSI). When the conventional PWM method is used in three-level NPC VSI, dead time is required to prevent a short circuit caused by the operation of complementary devices on the upper and lower arms. However, current distortion is increased because of the dead time and it can also cause a voltage unbalance in the dc-link. To solve this problem, we propose a zero dead-time width modulation (ZDPWM) which does not require dead time used in complementary operation. The proposed technique applies the offset voltage to the space vector pulse width modulation (SVPWM) reference voltage for the same modulation index (MI) as the conventional SVPWM, but any complementary switching operation needs dead time. In addition, the proposed method is divided into four operation sections using the reference voltage and phase current to operate switching devices which flow the current depending on the section. This ZDPWM method is simply implemented by carrier and reference voltage that reduce the current distortion, because complementary operation that needs dead time is not implemented. However, the operation section is delayed due to the sampling delay that occurs during the experiment. Therefore, in this paper, we conduct a modeling of sampling delay to improve the delay of operation section. To verify the principle and feasibility of the proposed ZDPWM method, a simulation and experiment are implemented.

Voltage profile and power quality improvement in photovoltaic farms integrated medium voltage grid using dynamic voltage restorer

&lt;p class="Abstract"&gt;In this paper, we have presented a simulation study to analyze the power quality of three phases medium voltage grid connected with distribution generation (DG) such as photovoltaic (PV) farms and its control schemes. The system uses two-stage energy conversion topology composed of a DC to DC boost converter for the extraction of maximum power available from the solar PV system based on incremental inductance technique and a three-level voltage source inverter (VSI) to connect PV farm to the power grid. To maintain the grid voltage and frequency within tolerance following disturbances such as voltage swells and sags, a fuzzy logic-based Dynamic Voltage Restorer is proposed. The role of the DVR is to protect critical loads from disturbances coming from the network. Different fault conditions scenarios are tested and the results such as voltage stability, real and reactive powers, current and power factor at the point of common coupling (PCC) are compared with and without the DVR system.&lt;/p&gt;

Sensorless DTSMC of a three‐level VSI fed PMSM drive

This study proposes a novel sliding mode control (SMC) structure for a three-level voltage source inverter (VSI). The proposed controller is implemented in discrete time and is applied for the closed-loop speed control of permanent magnet synchronous motor (PMSM) drive powered from a three-level cascaded H-bridge VSI. The proposed discrete time SMC (DTSMC) has the distinct advantages of control over maximum switching frequency and relatively lower total harmonic distortion compared to that of a conventional hysteresis modulation (HM) control. Unlike HM, the proposed DTSMC relates the maximum switching frequency to sampling time, resulting in better utilisation of the bandwidth of the VSI. Additionally, a procedure to combine the DTSMC with a sliding mode observer to achieve sensor-less operation of the PMSM drive is presented. Verification of the proposed DTSMC is conducted using simulation and experimental tests. The simulation and experimental results are presented.

PWM control techniques for three phase three level inverter drives

In this paper two very efficient pulse width modulation techniques were discussed named Sin pulse width modulation and space vector pulse width modulation. The basic structure of the three-level inverter neutral-point clamped is introduced and the basic idea about space vector pulse width modulation for three-level voltage source inverter has been discussed in detail. Nearest three vectors space vector pulse width modulation control algorithm is adopted as the control strategy for the three phase three level NPC inverter in order to compensate the neutral-point shifting. Mathematical formulation for calculating switching sequence has determined. Comparative analysis proving superiority of the space vector pulse width modulation technique over the conventional pulse width modulation, and the results of the simulations of inverter confirm the feasibility and advantage of the space vector pulse width modulation strategy over sin pulse width modulation in terms of good utilization of dc-bus voltage, low current ripple and reduced switching frequency. Space vector pulse width modulation provides advantages better fundamental output voltage and useful in improving harmonic performance and reducing total harmonic distortion.

An Enhanced Model Predictive Control Using Virtual Space Vectors for Grid-Connected Three-Level Neutral-Point Clamped Inverters

Reliability of power systems can be improved by the use of voltage source inverters (VSIs) with fast dynamic control, which can handle uncertainties induced by renewable energy resources and nonlinear loads. To ensure fast-dynamic response and simplified controller design, various model predictive control (MPC) methods are investigated in this paper. In the conventional MPC design for three-level VSIs, the cost function requires an additional term to ensure the balance of the neutral-point voltage (NP-V), which however can considerably impact the main goal of the MPC. To address this issue, an enhanced MPC using virtual space vectors is proposed, which allows the use of a significantly reduced weighting factor for the term in the cost function for NP-V balancing, while retaining fast-dynamic response. Additionally, the proposed MPC leads to reduced harmonic distortion in the VSI output voltage and current. Both simulation and controller hardware-in-the-loop studies are performed to demonstrate the effectiveness of the proposed enhanced MPC in an operating microgrid under both steady-state and fast-transient conditions.

Fault Diagnosis and Fault-Tolerant Control of Megawatt Power Electronic Converter-Fed Large-Rated Asynchronous Hydrogenerator

In recent years, it has been difficult to achieve power converter redundancy in the multichannel voltage-source inverter (VSI)-fed large-rated doubly fed induction machines (DFIMs), and it has not yet been adopted in any commissioned variable-speed pumped storage power plants. Multichannel VSIs are a fundamental part of DFIMs, and they control the real and reactive powers of the machines. This paper presents the fault-tolerant operation of a large-rated DFIM hydrogenerating unit at open-switch faults in back-to-back VSIs. A technique for diagnosing the open-switch faults in grid-side and machineside converters is proposed. An open-switch fault is detected based on the variation in rotor currents and dc link voltage, which reduces the computational efforts during fault diagnosis. A 250-MW DFIM with five-channel three-level VSIs (each rated at 9 MVA) is simulated in the MATLAB/Simulink environment to observe the drive behavior. Finally, a 2.2-kW DFIM is tested in a laboratory environment to verify the experimental results.

Implementation of 3L DPWM Techniques for Parallel Interleaved 2L VSIs

Parallel interleaved two-level (2L) three-phase voltage source inverters (VSIs) are widely used due to their distinct advantages of high power delivery, modularity, low current rating devices, etc. Along with these advantages, the parallel interleaved 2L VSIs could also be analyzed as a single three-level (3L) VSI. Conventionally parallel interleaved 2L VSIs are modulated using the 2L pulsewidth modulation (PWM) techniques. However, implementation of parallel interleaved 2L VSIs using the 2L PWM techniques may generate a higher ac side current ripple as compared to implementing the parallel interleaved 2L VSIs using 3L PWM techniques. This paper proposes a carrier-based method for implementing different 3L discontinuous PWM (DPWM) techniques for parallel interleaved 2L three-phase VSIs. Comparison of different 2L switching sequences for implementing a 3L DPWM switching sequence based on circulating current, line current ripple, and switching loss is also carried out. Simulation and experimental results are also displayed to validate the proposal.

Simplified double switching SVPWM implementation for three‐level VSI

A generalised space vector pulse width modulation (SVPWM) framework for the realisation of all double switching states with a memory-optimised method is proposed to reduce the total harmonic distortion (THD) and to provide neutral point voltage balancing for three-level NPC voltage source inverter (VSI). The proposal provides an efficient SVPWM implementationwith reduced hardware requirement and zero increase in software complexity in comparison to the existing schemes. Microcontroller analogue-to-digital converter (ADC) hardware replaces multichannel ADC and associated Field programmable gate array hardware in this proposal. The proposed method follows digital control architecture and eliminates the need to sample phase voltages separately. The proposed algorithm samples rms voltage of one phase and generates eight bit modulation index command by a suitable compensation algorithm. The implemented SVPWM algorithm takes the modulation index command value and generates phase voltage values by multiplying with the stored sine angle values. Gate pulses are generated in the proposed implementation by the hardware pulse width modulation (PWM) block and there is no need for digital-to-analogue converter. The proposed strategy is validated with a fundamental frequency of 50 Hz on a 2 KVA three-phase three-level insulated gate bipolar transistor-based VSI using low-cost PIC microcontroller. The superiority of the proposed method lies in providing an efficient three-level SVPWM implementation with reduced THD, neutral point voltage balancing, reduced hardware requirement, small lookup table and zero increase in the software computing overhead.

Direct torque control of doubly fed induction motor using three-level NPC inverter

This article presents the direct torque control (DTC) strategy for the doubly fed induction motor (DFIM) connected to two three-level voltage source inverters (3LVSIs) with neutral point clamped (NPC) structure. This control method allows to reduce the torque and flux ripples as well as to optimize the total harmonic distortion (THD) of motor currents. The use of 3LVSI increases the number of generated voltage, which allows improving the quality of its waveform and thus improves the DTC strategy. The system modeling and control are implemented in Matlab/Simulink environment. The analysis of simulation results shows the better performances of this control, especially in terms of torque and flux behavior, compared to conventional DTC.