Five-level Diode-clamped Inverter Research Articles

Capacitor voltage unbalance minimization for three-phase five-level diode-clamped inverter using hexagonal hysteresis space vector modulation

Capacitor voltage unbalance minimization for three-phase five-level diode-clamped inverter using hexagonal hysteresis space vector modulation

DTC Based on Five-level SVM with Balancing Strategy of Sensorless DSSM

This paper presents a direct torque control based on multilevel space vector modulation of a double star synchronous machine operating without speed sensor. Each star of the machine is supplied by a five-level diodeclamped inverter. This topology of multilevel inverters represents one of the most interesting solutions to increase voltage and power levels and to achieve high quality voltage waveforms. However, a very important issue in using diode-clamped inverters is the ability to guarantee the stability of the DC-link capacitor voltages. To overcome this problem the multilevel space vector modulation equipped by a balancing strategy is proposed to suppress the unbalance of DC-link capacitor voltages. For achieving high performances control of the multiphase drive, the proposed control method needs accurate information about rotor position and rotor speed. To this end, they are estimated by using Luenberger observer.

Multirate Predictive Control for Diode Clamped Inverters with Data-Based Learning Implementation

Diode clamping is a widely used topology for power inverters due to the low number of components, low cost, and general efficiency of the circuit, but its main drawback is the difficulty in controlling a multilevel configuration. For that, finite-control-set model predictive control was chosen, as it is a multivariable optimal controller that takes into account constraints and deals with multiple objectives. However, it has high computational burden and its control solution is held constant during the sampling period if not using modulation. This work first proposes a multirate enhancement for this control technique to address the latter issue, and then uses a novel learning method to allow the online implementation and overcome the high computation time. This method is tested in simulation in a three-phase, five-level diode-clamped inverter. Comparisons and performance gains of the multirate technique are provided.

Five-level DTC-ANN with Balancing Strategy of DSIM

This paper presents an artificial neural networks controller devoted to improve the performance of direct torque control strategy of double star induction machine fed by two five-level diode-clamped inverters. The resulting control scheme presents enough degrees of freedom to control both torque and flux with very low ripple and high dynamics. Unfortunately, the diode-clamped inverter has an inherent problem of DC-link capacitors voltages variations. To overcome this problem, an artificial neural network based direct torque control with balancing strategy is proposed to suppress the unbalance of DC-link capacitor voltages. Simulations results are given to show the effectiveness and the robustness of the suggested control method.

Five-Level Inverter Fed DTFC-SVM of Permanent Magnet Synchronous Motor Drive

In this paper, a five-level diode clamped inverter fed DTFC-SVM of Permanent Magnet Synchronous Motor (PMSM) drive is proposed for high power industrial applications. In Direct Torque and Flux Control with Space Vector Modulation (DTFC-SVM) technique, the speed of PMSM drive is regulated by controlling stator flux and electromagnetic torque directly and independently such that it abandons the use of direct torque control for PMSM Drive. The proposed multilevel inverter fed DTFC-SVM based PMSM drive gives very less ripples in stator flux and electromagnetic torque and also gives very less total harmonic distortion (THD) in the stator winding voltages and currents which consequences excellent dynamic and steady-state performance of drive. The five-level inverter switching pulses are designed using five-level space vector modulation (SVM) based on two-level SVM, so that it reduces the complexity of the SVM and also gives very good performance under all environmental conditions. The proposed model is simulated in MATLAB/SIMULINK software under various conditions, such as, No-load, load, reversal speed, and change in speed. In order to show the feasibility and effectiveness of the proposed model, it is also implemented in the experimental setup under various conditions.

Five-level Direct Torque Control with Balancing Strategy of Double Star Induction Machine

This work relates to the study of direct torque control of the double star induction machine drive fed by two five-level diode-clamped inverters. The analysis of the three-phase direct torque control shows that this concept can be extended easily to double star induction machine even when it is fed by a multilevel inverter. Diode-clamped inverter, as one of the prominent multilevel inverters, has several advantages like high voltage and low current waveform distortion. However, it suffers from the problem of neutral point potential variation. The variation causes an unbalance in the DC-link voltage levels and increases consequently the current waveform distortion. This problem can be solved in satisfactory way by using multilevel direct torque control equipped by a balancing strategy. The simulation results, illustrating the steady state and dynamic performances, prove the effectiveness of the proposed control approach.

Improved Direct Current Control for Grid-Connected Multilevel Inverters

This article presents a sensorless voltage detection method for direct current control in grid-connected multilevel inverters. The direct current control is based on scalar hysteresis controller (SHC). The SHC is a simplified, and parametric direct current controller with the ability to work with an arbitrary level count on multilevel inverters. In combination with the sensorless voltage detection method, it is able to improve the switching behavior, and minimize the current error compared to existing direct current controllers. The proposed control concept is validated with experimental measurements using a three-, and five-level diode clamped inverter under steady-state conditions, and various grid disturbances. In comparison to the standard SHC method, it is verified that the proposed concept shows an improved switching behavior, and a reduced error current.

Novel Filters Based Operational Scheme for Five-Level Diode-Clamped Inverters in Microgrid

This paper introduces a new operational scheme for several multilevel (five-level diode-clamped) inverters in the microgrid. The presented operational scheme has a central structure (different from the distributed controllers for droop schemes) to alleviate the drawback of the conventional droop control for microgrid operation. The contribution of this paper is focused on the suggested operational scheme, which has two contributory components. The first component is the novel smooth variable structure filters (SVSF), which are formulated to estimate the disturbances of voltage harmonics and voltage unbalance. The second component is an efficient adaptive sliding mode controller to operate these inverters. This proposed operational achieves equal power sharing among working inverters, compensating for voltage unbalance at the point of common coupling (PCC) at loads, and mitigation for voltage harmonics at the PCC. More importantly, the propounded operational scheme efficiently stabilizes voltage with the variation of balance, unbalanced and nonlinear loads in addition to the seamless transient and steady-state performance for injected power by inverters. The performance of the suggested operational scheme is justified by simulation results.

A Generalized Carrier-Overlapped PWM Method for Neutral-Point-Clamped Multilevel Converters

The neutral-point voltage unbalance problem holds back the extensive application of neutral-point-clamped (NPC) multilevel converters with more than three voltage levels in industry. Traditional phase-disposition pulsewidth modulation (PDPWM) or nearest-three-vector (NTV) modulation cannot achieve the voltage balance over the full modulation indexes and load power factors when the voltage level is higher than three. To solve this problem, a novel generalized carrier-based PWM method, named carrier-overlapped PWM (COPWM), for NPC multilevel converters is proposed in this article, which is proven to satisfy the volt-second balance principle. With this modulation method, the average values of all the neutral-point currents are equal to zero in a fundamental period, and therefore, all the dc-link capacitor voltages can be naturally balanced in the ideal and steady-state conditions. In order to simplify its implementation, an equivalent multireference modulation method with only one triangular carrier is also derived. Simulation and experimental results on a five-level diode-clamped inverter are presented to verify the proposed modulation method.

A Novel Interval Type-2 Fuzzy-Based Direct Torque Control of Induction Motor Drive Using Five-Level Diode-Clamped Inverter

This article provides an interval type-2 fuzzy-based direct torque control (IT2FDTC) of the induction motor drive (IMD) in which the space vector modulation technique is used here to activate a five-level diode-clamped inverter (FDCI). Moreover, it is implemented with the help of the DSPACE-1103 controller in a real-time application using 2HP induction motor and its overall performance is compared with a conventional proportional-integral direct torque control (CPIDTC). In IT2FDTC, all four capacitor voltages of FDCI based on minimum energy principles are balanced well and settled back quickly with fewer peak overshoots than CPIDTC during various operational conditions. In addition, it can provide lesser torque and flux ripples with a fast dynamic performance of IMD over a CPIDTC. A 3-D Mamdani type-2 fuzzy controller along with the centroid method is used in IT2FDTC. Hence, the proposed method of study not only controls the gains of proportional integral effectively but also controls the duty ratios of a modulating wave to further improve the dynamic performance and current profile of IMD.

Design and software implementation of solid state transformer

The work presented in this paper concerned with the analysis, design and software implementation of the Solid State Transformer as an alternative to the conventional power transformer. The proposed transformer aims to perform the same task as the conventional one with additional facilities and advantages. Three stages are considered to configure the Solid State Transformer. The first stage which is known as input stage and implemented using Vienna rectifier which converts the AC voltage of the main supply to a DC voltage. The second stage (isolation stage) step down the DC voltage to a lower level DC voltage. This stage consists of a single – phase five-level diode clamped inverter, 1 KHz step – down transformer and fully controlled bridge rectifier. The output stage (third stage) is a three-phase three-level diode clamped inverter which converts the low level DC voltage to a three-phase, 50 Hz AC voltage. Model Predictive Current Control has been employed for driving transformer’s stages. The gating signal is produced directly when the given cost function is minimized, therefore there is no need of any modulator. Behavior of the proposed structure is achieved by simulation which shows high quality power conversion with low Total Harmonic Distortion.

Decoupled State-Feedback Based Control Scheme for the Distributed Generation System

This article presents a new development for the decoupled state-feedback control to operate the distribution generation unit (DGU) within an efficient distribution generation system (DGS). The developed decoupled state-feedback is better than the conventional voltage vector control and sliding mode control for dealing with active and reactive power. Therefore, it is embraced to form a new control scheme, which is employed to effectively decouple and precisely control the injected active and reactive power to the distribution system. A five-level diode-clamped inverter is adopted to build the DGU in order to minimize the injected harmonics, facilitate the operation of the proposed control scheme, and ease the design of its passive filter. The proposed control scheme enables the DGS to be functional in several operational modes such as grid-connected, intentional islanding, unintentional islanding, anti-islanding, and ride-through modes. The effectiveness of the proposed control scheme is proved through the simulation results for all foregoing modes. Experimental results are provided to show how the proposed concepts are practically implemented to control the voltage of the DGU so that the active power and reactive power are exchanged between the power grid and the DGS in the grid-connected mode.

Power Control in Grid-Connected Wind Energy System Using Diode-Clamped Multilevel Inverter

ABSTRACTThis paper presents dynamic modelling and control of real and reactive power in grid-connected variable speed wind energy conversion system using diode-clamped multilevel inverter (DCMLI). A modified five-level DCMLI is used for power control, which eliminates the requirement of transformer and improves the quality of controlled output voltage. It is shown that the system is dynamically stable and is able to control the real and reactive power independently, and provides harmonic compensation within standard limits. The voltage balancing across the capacitors of the five-level diode-clamped inverter is obtained using external balancing circuits. The performance of the proposed control method is tested under variable wind speed, sudden load changes, and under single-phase and three-phase faults. Simulation studies PSCAD/EMTDC verifies the proposed control method.

Design and Implementation of a Multilevel Inverter Fed by Photovoltaic Generators with MPPT

In this paper is presented an implementation of a fundamental frequency on a three-phase multilevel inverter supplied by a photovoltaic generator in a stand-alone system. The high cost of photovoltaic solar power makes it necessary to track the maximum power point (MPP) of the photovoltaic generator regardless the adopted scheme for the power converters. Several maximum power point tracking techniques for photovoltaic systems have been developed to maximize the produced energy and most of these techniques are well published. The topology adopted for this implementation consists of two main blocs. In the first one, a buck-boost-type converter is used to interface the photovoltaic generator (PVG) to the voltage bus of the inverter. The second bloc contains a five-level diode-clamped multilevel inverter (DCMLI), generating fundamental modulation staircase three-phase output voltages. A microcontroller is used to control both converters. Experimental tests were done using a set of two tanks, one for extracting water and the other for the storage. The pumping system is built around an induction motor coupled to a single centrifugal pump. The main idea of such a system is to improve the global efficiency by increasing the stored water in a day.

Five-Level Diode-Clamped Inverter With Three-Level Boost Converter

This paper proposes an active front-end solution to balance the dc-link capacitor voltage of the five-level diode-clamped inverter. Capacitor voltage balancing is performed by a three-level boost converter connected to the two inner capacitors of a five-level diode-clamped inverter and additional balancing circuits at the other two outer capacitors. The proposed configuration is tested through simulation and experiment for various load power factor conditions at a high modulation index. The result demonstrates the reliability of the proposed configuration to balance the dc-link capacitor voltage at the desired level.

Fundamentals of a Multi-Phase, Neutral-Point Clamped Multilevel Inverter

The conventional five-level diode-clamped inverter suffers from the problem of many active power switches when extended to multiphase system. As a consequence, increasing number of gate drive circuits are required; resulting in complex system circuitry. This paper presents the fundamentals of a multiphase, neutral point clamped multilevel inverter configuration capable of reducing the number of active power switches in the conventional topology for multiphase system. The proposed multilevel inverter configuration generates five line-to-line voltage levels for multiphase systems. From the generalized model, an exemplary 5-phase, 5-level line-line NPC inverter supplying an RL load is considered. The operational and modulation principles and the switching patterns are outlined. The THD, as a performance index, of the line voltage output waveform of the proposed 5-phase, 5-level line-line NPC inverter is similar to that of the corresponding well-known conventional 5-phase, NPC diode-clamped inverter. The proposed inverter achieves this with fewer power circuit components and simplicity. The validity of the proposed multilevel inverter is verified through simulations and experimental results.

Wavelet Modulus Maxima for Single Switch Open Fault in Multi-level Inverter

The multi-level inverter is widely used in high-power and high-voltage applications. Multi-level inverters use a large number of switches for high power conversion, resulting in increased system's fault probability. To ensure stable operation of the system, several fault diagnosis methods have been carried out by researchers. In this article, a fault diagnostic system in a multi-level inverter using wavelet modulus maxima is developed. The working situation of the power devices of a five-level diode-clamped multi-level inverter drive system under an open-circuit fault is analyzed through MATLAB (The MathWorks, Natick, Massachusetts, USA) simulation. The wavelet modulus maxima of output phase voltages are used to detect faulty phase (leg), and wavelet modulus maxima of DC bus currents are used to detect fault type and fault switch. Wavelet analysis is used for feature extraction, which can be used as input to the expert system to develop a fault identifier. The open-circuit fault on the five-level diode-clamped multi-level inverter of power devices is carried out experimentally. The experimental prototype is developed to validate the fault analysis with simulation results.

Simulation of DTC-CBSVPWM fed SPMSM Drive with Five-level Diode Clamped Inverter

this paper a simulation analysis of DTC-CBSVPWM of SPMSM drive using five-level diode clamped inverter is analyzed. It has simple structure and provides dynamic behavior comparable with classical DTC. Direct Torque Control (DTC) is an accurate controller for permanent magnet synchronous motor (PMSM) due to its robust and fast torque response in steady-state and transient operating condition. However, the main disadvantage of DTC is high ripples in stator current, flux linkage and torque due to the application of same active voltage vector during the whole sample period and possibly several consecutive sample intervals. This can be overcome by using proper modulation technique. Space Vector Modulation (SVM) which synthesizes any voltage vector lying inside the sextant gives good performance, but however the complexity involved is more in calculating angle and sector. To reduce the complexity involved in SVPWM, a novel modulation technique named Unified voltage modulation or carrier based space vector pulse width modulation (CBSVPWM) is described using the concept of effective time. By using this method the inverter output voltage is directly synthesized by the effective times and the voltage modulation task can be greatly simplified. The actual gating signals for each inverter arm can be easily deduced as a simple form using the effective time relocation algorithm. Keywords-CBSVPWM, SPMSM, Five-Level Diode Clamped Inverter.

Backstepping controller of five-level three-phase inverter

Multilevel converters are becoming increasingly used in many industrial applications due to the many advantages that they offer. The improvements in the output signal quality, lower Total Harmonic Distortion (THD) and many other properties make multilevel converters very attractive for connecting photovoltaic generators to medium voltage grid directly or to be used in a local power supply. In this paper, we focus on the implementation of a three-phase five-level diode clamped inverter and design of a performing nonlinear controller using the Backstepping approach. The control objective is to generate, at the system output, sinusoidal three-phase voltages with amplitude and frequency fixed by the reference signal independently of load variations. The performance study of the multilevel inverter and the designed controller are made by simulations in Matlab/Simulink environment.

Modified Combined DTC and FOC Based Control for Medium Voltage Induction Motor Drive in SVM Controlled DCMLI

Modified combined direct torque control (DTC) and field oriented control (FOC) based method is proposed in this paper to improve the performance of induction motor (IM) drive. The proposed method includes combined advantages of DTC and FOC schemes. An algorithm is developed for closed-loop control of the proposed control method and the scheme is implemented in space vector controlled five-level diode-clamped inverter. For this, an experimental prototype is developed to control three-phase, 3-hp IM drive. The comparative performance of proposed control method, DTC and FOC with experimental results in SVM controlled five-level inverter is presented to validate the effectiveness of the proposed control scheme. Also, the switching states are selected so as to control the inverter output voltage as well as reduce the common mode voltage (CMV) of the drive.