Packed U-cell Inverter Research Articles

Fault-Tolerant Analysis of 5-level Modified T-type and Packed U Cell MLI

ABSTRACT In this work, 5-level modified T-type and modified Packed-U-Cell (PUC) multilevel inverter (MLI) topologies are designed with reduced device count for the reliability analysis of the MLI under faulty conditions. This work aims to incorporate the fault either by loss of an individual switch or due to the loss of a single h-bridge leg. Also, the proposed T-type and PUC inverter have an inherent self-voltage balancing capability that reduces the complexity and enhances the circuit’s reliability. First, the proposed topologies are simulated using Matlab/Simulink environment, and the results obtained are then compared with the conventional MLI. Finally, both MLIs are experimentally tested on a laboratory prototype as a proof of concept to validate the analytical developments.

A Method for Suppressing DC-Link Ripples of Multilevel Packed U-Cell Inverter by Compensate-Control Combination

A Method for Suppressing DC-Link Ripples of Multilevel Packed U-Cell Inverter by Compensate-Control Combination

Average Model-Based Sliding Mode Control for Quality Improvement of a Grid-Connected PUC Inverter

This paper presents a new Sliding Mode Phase-Shift PWM (SM-PSPWM) based control strategy for a grid-connected Packed U-Cell (PUC) inverter. The proposed control strategy is based on the average model of the PUC inverter while using a multi-carriers phase-shift pulse width modulation (PS-PWM) technique. The use of the PWM strategy, based on the inverter average model, ensures high steady-state performance, low harmonic current, and enhanced thermal properties. In addition, the Sliding Mode Control (SMC) is applied to generate the input signals to achieve a fast dynamical response and high robustness against disturbances. To further improve the robustness under parameter mismatch and distorted grid voltage conditions, an integral term is added to the surface function for better accuracy and stability. To validate the performance of the proposed controller (fast dynamics, global stability, low current THD, ...) shown by the simulation results, a laboratory setup is used to validate the theoretical analysis.

Model predictive control of Packed U-Cell inverter for microgrid applications

In this paper, an outline of microgrid arrangements and control methods at various hierarchical levels of Packed U-Cell (PUC) converters are provided. The paper discusses the control of these topologies using various techniques. The goal of these control strategies is to maintain a small THD, superior steady-state, fast-dynamic response, and high-power factor while balancing capacitor voltages under different operating conditions. The PI current controller is modelled on five and seven-level PUC inverters. The PI voltage and current controllers have also been modelled on a seven-level PUC inverter. Thereafter, model predictive control of five, seven and fifteen level inverters are also formulated and then simulated using MATLAB/Simulink. Finally, HIL validation of different PUC inverters is performed.

Harmonics Minimization in PUC Type Solar Multilevel Converter with Multicarrier Switching Schemes

This paper presents the power quality investigation of a seven-level three-phase packed U-cell (PUC) converter with multicarrier switching schemes. This system is grid-connected, and each phase has two solar PV arrays of different voltages. Various modulation schemes are available for switching the multilevel converter, and level-shifted multicarrier pulse width modulation is widely used for easy implementation. A new modified carrier-based modulation technique is introduced for solar PV array fed PUC inverter. The main aim is to reduce the harmonic content in the seven-level output voltage. It also increases the magnitude of the fundamental component of the converter voltage. The comparison of the presented technique shows its advantages over other existing modulation schemes. Closed-loop control is implemented with the inclusion of a modified switching scheme for switching the three-phase PUC converter. The proportional resonant controller provides excellent dynamic performance to feed the power into the grid. Modeling and simulation of the system are done in MATLAB/Simulink. Furthermore, obtained simulation results verify the effectivity of the switching scheme towards minimizing total harmonic distortion. The overall system is validated in the real-time simulator for steady-state and dynamic environmental conditions.

Control of Reduced Switches Count and Classical Multilevel Inverters: a Comparison

Multilevel inverter has appeared as one of the important topologies in the area of high power and medium voltage because it can efficiently realize lower harmonics with reduced switching frequency. These Multilevel inverters (MLI) improve the energy quality shaped by producing many voltage levels. However, improving the quality of the output voltage of a multilevel inverter requires many switches, which tend to weigh down the structure and make it complex to control. This work deals with a comparison in terms of the spectral content of two configurations of thirty-one-level inverters for injection into the electrical grid. The first configuration is a classical cascaded H-bridge and the second one is a reconfigured Packed U-Cell (PUC) multilevel inverter. The classical configuration requires sixteen switches while the second uses only ten ones. The control technique based on the half-height modulation was performed and the Total Harmonic Distortion (THD) is calculated for each topology. For the PUC, we got a THD equal to 2.61% while we got 2.72% for the cascaded H-bridge. These results obtained in the MATLAB/Simulink environment, show that the reconfigured structure of the PUC inverter is a good candidate for injection into the electrical network.

Seven-level grid-connected packed U-cells inverter using photovoltaic generators system

In this article, one of the most recent multilevel converter topologies named packed U-cells is developed for three-phase grid-connected inverter mode using photovoltaic input voltage sources. This topology makes a very important research subject in what concerns the adaptation of multilevel inverters with photovoltaic systems. According to the literature, it is well applicable with the string type and suitable for high-voltage applications because the number of switches is less than conventional topology and maximum blocking voltage is Udc and 2 Udc; however, it is not applicable for multistring type and unsuitable for the central type because it is based on isolated DC source. The packed U-cells topology is highly optimized from the point of view of the number of passive and active components. The output voltages of our converter are composed by seven levels obtained by the auxiliary buses voltages regulation. In order to obtain the DC input voltages of 120 V for the inverter, photovoltaic generators are connected to a boost converters. The maximum power point tracking method based on the Perturb and Observe was used to improve and optimize the performance of the photovoltaic system control in the simulation part. The grid-connected PUC7 inverter operates with a unit power factor and injects active power into the grid. The control is configured to make the current waveform in phase with the AC voltage waveform. Reference angle variations have been made to operate with different power factors to test the performance of the applied control and the influence of these variations on the auxiliary buses voltages regulation. The simulations were done under Matlab/Simulink platform and have been experimentally verified using dSpace 1104 controller board and three-phase packed U-cells inverter composed by nine half-bridge insulated-gate bipolar transistor modules.

Artificial Intelligence-Based Weighting Factor Autotuning for Model Predictive Control of Grid-Tied Packed U-Cell Inverter

The tuning of weighting factor has been considered as the most challenging task in the implementation of multi-objective model predictive control (MPC) techniques. Thus, this paper proposes an artificial intelligence (AI)-based weighting factor autotuning in the design of a finite control set MPC (FCS-MPC) applied to a grid-tied seven-level packed U-cell (PUC7) multilevel inverter (MLI). The studied topology is capable of producing a seven-level output voltage waveform and inject sinusoidal current to the grid with high power quality while using a reduced number of components. The proposed cost function optimization algorithm ensures auto-adjustment of the weighting factor to guarantee low injected grid current total harmonic distortion (THD) at different power ratings while balancing the capacitor voltage. The optimal weighting factor value is selected at each sampling time to guarantee a stable operation of the PUC inverter with high power quality. The weighting factor selection is performed using an artificial neural network (ANN) based on the measured injected grid current. Simulation and experimental results are presented to show the high performance of the proposed strategy in handling multi-objective control problems.

A novel control scheme for three-phase seven-level packed U-Cell based DSTATCOM

With the advent of SiC devices, the packed U-Cell converter has become a promising topology among the multilevel converters for medium voltage DSTATCOM application. It utilizes fewer components while achieving the maximum voltage levels with higher reliability. However, as a reactive power compensator, its dc-link consists of flying capacitors, whose voltages must be balanced which presents a challenging problem for a seven-level packed U-Cell inverter, as there are no-redundant switching states. This paper proposes a novel control scheme to keep these flying capacitors balanced under normal/abnormal grid conditions. It consists of a standard cascaded: inner and outer controllers. The inner current controller regulates both the active and reactive currents and the outer controller regulates the upper flying capacitor voltage. In parallel with the cascaded controllers, a novel model predictive voltage balancing controller is proposed to maintain the lower flying capacitor voltage at a given setpoint. To cope with the unbalance grid conditions, an additional zero-sequence injection regulator is also integrated into the designed control scheme. The proposed control scheme was simulated and real-time tested on the Hardware-In-the-Loop system. The results show that the proposed controller effectively balances the two flying capacitor voltages while controlling the reactive power.

Design and Modeling of Solar Photovoltaic System Using Seven-Level Packed U-Cell (PUC) Multilevel Inverter and Zeta Converter for Off-Grid Application in India

DOI : 10.26650/electrica.2019.18053 In the present study, standalone operation of the solar photovoltaic system with storage is evaluated with the recently introduced seven-level packed U-cell (PUC) multilevel inverter. Zeta converter is used to regulate the output voltage of the photovoltaic (PV) array with the help of the MPPT algorithm. Level-shifted modulation scheme is applied for the PUC inverter. The standalone operation is taken into consideration keeping in view the application/penetration of the solar PV system in remote areas. The Ministry of New and Renewable Energy (MNRE), Government of India has set up the plan to establish the standalone solar PV system for off-grid application in the regions to meet the power requirement of those communities and regions that are difficult to connect with the grid. The climatic condition in the central and western parts of India is conductive for solar PV generation. In contrast to the other well-known inverter topologies, such as neutral point clamped, flying level capacitors, and cascaded H-bridge, among others, PUC inverter requires the least number of switches and capacitors for the same output levels. The system is modeled in the MATLAB®/Simulink using the Waaree Energies WSM-315 modules to supply a load of 2 kW. To optimize the solar PV-based system, incremental conductance optimization technique is used. Cite this article as : Azeem A, Ansari MK, Tariq M, Sarwar A, Ashraf I. Design and Modeling of Solar Photovoltaic System Using Seven-Level Packed U-Cell (PUC) Multilevel Inverter and Zeta Converter for Off-Grid Application in India. Electrica, 2019; 19(2): 101-112.

Comprehensive analysis of three- and five-phase PUC inverters with harmonic injection modulation techniques

Multiphase power electronic converters are gaining more popularity nowadays. Three-phase system is not enough to produce smooth torque in industrial application. So systems that have more than three phases are gaining popularity due to their smooth torque and more power than the three-phase systems for the same phase voltage and current. Selection of even number of phases is generally avoided because it degrades motor performance due to the coincidence of motor poles with each other. This paper deals with carrier-based pulse width modulation techniques with the third-harmonic and fifth-harmonic injections in three-phase and five-phase five-level packed U-cell (PUC) inverter. Harmonic injection gives improvement in DC bus utilization without going into the overmodulation region. The viability of this concept is verified by MATLAB/Simulink by taking the three-phase and five-phase VSI as an example. The relation between the three-phase and five-phase voltage and power is analyzed and verified mathematically. The PUC inverter comprises the least number of device count, so it can be a good option for multiphase application in industrial drives.

Evaluation of Level-Shifted and Phase-Shifted PWM Schemes for Seven Level Single-Phase Packed U Cell Inverter

An evaluation of level shifted and phase shifted triangular and sawtooth carrier modulation schemes for a seven level packed U cell (PUC) inverter is presented in this paper. The investigated PUC is the recently introduced topology for multilevel inverter having reduced switch count in comparison to the conventional topologies of multilevel inverters. The PUC inverter has six switches for 7 level inverter which is very less in comparison to the conventional topologies. In this paper, the level-shifted pulse width modulation (LS-PWM) and phase-shifted PWM (PS-PWM) for triangular and sawtooth carrier are presented and compared. A comparative harmonic analysis for all the cases is performed and results are presented in the paper. The difference in harmonics of the two modulation methods given by the theoretical approach for both the carrier is validated by the experimental results. DC voltage controller and load current controller of the PUC inverter are also designed and presented. The investigated PUC topology is tested in dynamic and steady state conditions and results obtained are presented. The analysis is done and validated using simulation in MATLAB Simulink environment and experimental approaches using FPGA platform.

Optimal design and analysis of hybrid photovoltaic-fuel cell power generation system for an advanced converter technologies

Nowadays, the entire world is concentrated on alternative energy sources (AES) or renewable energy sources (RES) for developing the power in economical cost and the sources like tidal power, solar energy, geothermal energy, wind energy, biomass, fuel cells etc. Among all those sources solar energy and fuel cells are chosen for developing the hybrid power generation (HPG) system. The photovoltaic (PV) module is designed with an efficient maximum power point tracking (MPPT) technique of neuro-fuzzy (NF) tracking controller is developed to extract the maximum power and fed to boost DC-DC converter. In the meanwhile, air breathe fuel cell (ABFC) is designed and fed to the high step-up DC-DC converter with lesser duty cycle. The main concentration of this paper is to design the efficient HPG system for a competitive multilevel inverter (MLI) topology with less device count is the merit of this topology which is called packed U cell (PUC). In addition, this paper describes the mathematical analysis, design and operation of PV module, neuro-fuzzy (NF) MPPT controller based boost converter, ABFC, high step-up converter and PUC inverter. The P-V, I-V characteristics of PV module and ABFC stack effects on hydrogen pressure changes and temperature is examined. And also, the performance of HPG based PV-FC fed MLI is sifted for different load conditions. The overall performance is checked in terms of total harmonic distortion (THD) for phase voltages (Vph) and phase currents (Iph) which are accomplished through FFT analysis for each load case. The whole simulations are carried out in MATLAB/Simulink environment.

An original observer design for reduced sensor control of Packed U Cells based renewable energy system

This paper presents an original Switched Observer (SO) for reduced-sensor control of a grid-connected Packed U Cells (PUC) multilevel inverter. The proposed SO performance is evaluated using a single-phase 7-level PUC inverter connected to the grid through filtering inductor. Based on the actual grid current, the proposed SO estimates accurately the PUC capacitor voltage, which is fed to the Model Predictive Control (MPC) algorithm while making use of a hybrid model considering both discrete and continuous variables. For real-time application, necessary conditions are given to guarantee the practical stability of the proposed SO under system parameters and input voltage variations according to the selected switching pattern. Theoretical analysis and simulation investigations are conducted to prove that the proposed SO-MPC scheme is stable in closed-loop for all system configurations and has good performances even during various disturbances (load change, parameters mismatch, and input voltage variation).

Finite-Control-Set Model Predictive Control for Grid-Connected Packed-U-Cells Multilevel Inverter

This paper presents a finite-control-set model predictive control (FCS-MPC) for grid-tied packed U cells (PUC) multilevel inverter (MLI). The system under study consists of a single-phase 3-cells PUC inverter connected to the grid through filtering inductor. The proposed competitive topology allows the generation of 7-level output voltage with reduction of passive and active components compared to the conventional MLIs. The aim of the proposed FCS-MPC technique is to achieve, under various operating conditions, grid-tied current injection with unity power factor and low total harmonic distortion while balancing the capacitor voltage. Parameters’ sensitivity analysis was also conducted. The study is conducted on a low-power case study single-phase 3-cells PUC inverter and with possible extension to higher number of cells. Theoretical analysis, simulation, and experimental results are presented and compared.

Real-Time Implementation of a Seven-Level Packed U-Cell Inverter with a Low-Switching-Frequency Voltage Regulator

In this paper, a new cascaded nonlinear controller has been designed and implemented on the packed U-cell (PUC) seven-level inverter. The proposed controller has been designed based on a simplified model of PUC inverter and consists of a voltage controller as an outer loop and a current controller as an inner loop. The outer loop regulates the PUC inverter capacitor voltage as the second dc bus. The inner loop is in charge of controlling the flowing current, which is also used to charge and discharge that capacitor. The main goal of the whole system is to keep the dc capacitor voltage at a certain level results in generating a smooth and quasi-sine-wave seven-level voltage waveform at the output of the inverter with low switching frequency. The proposed controller performance is verified through experimental tests. Practical results prove the good dynamic performance of the controller in fixing the PUC capacitor voltage for various and variable load conditions and yet generating low-harmonic seven-level voltage waveform to deliver power to the loads. Operation as an uninterruptible power supply (UPS) or ac loads interface for photovoltaic energy conversion applications is targeted.