U-cell Inverter Research Articles

VOLTAGE SENSORLESS CONTROL OF FIVE-LEVEL PACKED U-CELL INVERTER BASED ON LYAPUNOV APPROACH FOR GRID-CONNECTED PHOTOVOLTAIC SYSTEM

This paper deals with the nonlinear control of a five-level packed U-Cell (PUC5) inverter used in a grid-on photovoltaic (PV) system. The sensorless modulation strategy is adopted to control the switching of the six power switches. This topology generates a five-level output voltage with fewer active and passive components than traditional multilevel inverters. A nonlinear controller was designed to control the grid current using the Lyapunov theorem to ensure the asymptotic stability of the overall system. The proposed control scheme addresses two key challenges: minimizing the injected grid current's total harmonic distortion (THD) while balancing the capacitor voltage at their reference under various operating conditions. The efficiency of the proposed approach was comprehensively evaluated using theoretical analysis, mathematical modeling, and simulation results obtained using MATLAB/Simulink software.

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.

DE SHM Based Harmonic Minimization for Modified PUC 15 Level Inverter

A 15-level Modified Packed U-cell (MPUC) Inverter is investigated in this study, and a Selective Harmonic Mitigation (SHM) method is used to reduce and eliminate several harmonic components on the output voltage, resulting in a lower Total Harmonic Distortion (THD) factor. The proposed MPUC-15 inverter can provide a 15-level output with only eight switches, making it the most compact inverter to date. In order to achieve the 15-level output, the inverter's dc link voltage is kept in the ratio of 1/4:3/4:1. A detailed explanation of the PMUC15 inverter's operation with various switching states is provided. The MPUC15 inverter allows for the elimination of more harmonics. However, the equation of the harmonic becomes more complex as additional switching angles emerge in the harmonic equations, which are difficult to solve using typical linear optimization methods. The SHE-PWM equations for a 15-level inverter are created and solved using Deferential Evaluation (DE) with a variable modulation index, a current optimization method. The reported output THD has been less than 5%, and angles for various modulation indexes have been compiled and provided in tabular format. The inverter prototype is built in MATLAB®/Simulink, with a Typhoon HIL SCADA setup for testing the results of the DE algorithm.

Output voltage and conducted EMI-based open-circuit fault detection signatures in a single-phase packed U-cell inverter

Output voltage and conducted EMI-based open-circuit fault detection signatures in a single-phase packed U-cell inverter

A New ANN-Based Controller with Variable Frequency for a 12-Switches Cascaded Modified Packed U-Cell Inverter

This study describes the results of combining two Modified Packed Ucell (MPUC) inverters to construct a cascaded MPUC network. With only 12 switching combinations, this topology can create up to 49 levels of voltages. The voltages of two MPUCs are adjusted such that each auxiliary source has one-third of the voltage level of the primary source and the primary source voltage level of the MPUC is one-seventh of the value of the DC voltage of the cascaded unit. The formation of different voltage levels by cascading is presented in detailed manner. An Artificial Neural Network (ANN) trained for harmonic removal in the output voltage waveform is used to control this converter. ANN is trained on two different frequency switching schemes. The cascaded unit with high voltage stress (14VDC) is switched at low frequency, low switching frequency operation of the MPUC, results in decreased power dissipation and higher system efficiency, and the multilayer output voltage waveform is virtually sinusoidal with negligible Total Harmonic Distortion (THD) content (less than 2%). The presented inverter and its ANN based control method result in a design trade-off between filter size and switching frequency (efficiency). This is predominantly helpful for high power applications, such as HVDC transmission system. The simulation realized for converter and its control in MATLAB®/Simulink environment show good agreement with theoretical values.

A Simple SVM Technique on Three-Phase MPUC7 Inverter for Solar Photovoltaic System

In This paper, a simple single-dimension Space Vector Modulation (SVM) technique is introduced to implement on three-phase thirteen-level Modified Packed U-Cell (MPUC) inverter for photovoltaic system in which many DC sources are available. The three-phase thirteen-level converter consists of three single-phase seven-level MPUCs that each phase has six switches and two isolated DC sources. One major advantage of proposed method is to produce an output voltage with nearly constant amplitude in desired range in case of input DC voltage fluctuations, which is common in renewable sources like Photovoltaic Systems (PV). On the other hand, the conventional Pulse Width Modulation (PWM) strategies do not have such capability. Thus, the converter behavior is investigated for the proposed control method and Level Shift PWM (LS-PWM) and it is shown that the LS-PWM method does not function properly when the DC voltage varies. In order to produce an output voltage with seven equal levels, which results in reduction of the switching losses and Total Harmonic Distortion (THD), it is necessary to trigger switches in proper way. Consequently, two switching patterns are introduced and the significant decrease in power loss due to the second switching pattern is shown. Furthermore, it is investigated that in three-phase mode, the 3rd order line-voltage harmonics are eliminated well and the voltage and current THD are further improved by the proposed method. To validate the proposed SVM technique, MATLAB Simulink simulation results are presented and a comparative analysis is done between the proposed method and LS-PWM.

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.

Open-Circuit Fault Detection and Isolation Method for Five-Level PUC Inverter Based on the Wavelet Packet Transform of the Radiated Magnetic Field

This article proposes a noninvasive open-switch fault detection method based on the analysis of the high-frequency signals. The faulty power switch is detected by metering the emitted near-field above a new topology using the wavelet packet transform and considering a complex control algorithm. The proposed method is tested on a single-phase five-level packed U-cell (PUC5) inverter. The latter is controlled using the finite-control set model predictive control (FCS-MPC) technique that generates the gate signals with a variable switching frequency. Moreover, unlike the conventional pulsewidth modulation strategy, the switching pattern provided by the FCS-MPC technique is not known in advance. Despite these complexities, the proposed fault detection method proves its high performance and effectiveness. Experimental studies are carried out on a single-phase PUC5 inverter using the real-time controller (OP4510) from OPAL-RT and prove the capability of this method to properly identify the faulty switch in this multilevel topology.

Simulation and analysis of T-PUC9 inverter fed single phase induction motor application

This paper presents the simulation and analysis of a Nine-Level T-Type Packed U-Cell (T-PUC9) Inverter fed single phase Induction Motor. This inverter includes a T-type neutral point clamped (NPC) pole, two identical DC voltage sources and a one half-bridge module. It employs a Multiple pulse width modulation (PWM) scheme for generating the pulses for all the eight switches to synthesis the desired nine level voltages namely 2Vdc, 1.5Vdc, Vdc, 0.5Vdc, 0, -0.5Vdc, -Vdc, -1.5Vdc and -2Vdcwhich resembles a nearly sinusoidal wave owing to the rise in the number of steps. Due to its low-level harmonic distortion in the output it is used in industrial applications. The simulation model of the presented inverter has been developed for a single-phase induction motor application for a two identical DC voltage sources of 110V each using the MATLAB Simulink platform. The theoretical predictions and the performance of the Nine-Level T-Type Packed U-Cell (T-PUC9) Inverter fed single phase induction motor have been successfully validated with the help of simulation results.

Electric Spring Using MPUC5 Inverter for Mitigating Harmonics and Voltage Fluctuations

This article introduces a novel configuration of electric spring (ES) based on the modified five-level packed u-cell (MPUC5) inverter for mitigating harmonics and voltage fluctuations at various points of a grid with unstable generated power from distributed renewable energy sources. Immanent merits of the proposed configuration include, but are not limited to, halved dc-links voltages, boost mode operation, the possibility of higher power applications, smooth five-level voltage waveform with low total harmonic distortion (THD) index, the smaller size of output low-pass filter, and low switching frequency. The operation principles, design procedure, and configuration of the MPUC5-based ES (MPUC5-ES) are also presented. Besides, a simple and yet efficient controller without any extra control loop for regulating dc bus voltages has been proposed. Finally, the introduced multilevel ES is tested through extensive simulation and experimental studies to confirm its dynamic and steady-state performances in various operation modes in a weak grid fed by both conventional and intermittent renewable energy sources.

Seven-Level Packed U-Cell (PUC) Converter With Natural Balancing of Capacitor Voltages

A seven-level packed U-cell inverter is presented in this article. The converter uses a single dc source and two floating capacitors, whose voltages are balanced in open loop, to produce multilevel output voltage. Peak magnitude of the output phase voltage is equal to the magnitude of dc source. Voltages across floating capacitors add intermediate voltage-levels by establishing an asymmetric ratio (with respect to the available dc voltage in the circuit). The average energy exchange (when the network is in steady state) of the capacitors with the rest of the inverter circuit will be zero. This helps the capacitors to maintain desired voltages and thus create intermediate levels of steady dc voltages. Performance of the converter is validated in simulation by MATLAB/Simulink and testing of the converter is done for resistive as well as inductive loads. Experimental verification of the converter is carried out on a laboratory prototype and the obtained results match well with the simulation.

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.

Modified U Cell Inverter using Advanced Process Controller for Photovoltaic Applications

This paper proposes a single phase modified seven level U-Cell inverter configurations in which the advanced process controller has been implemented. By using the boost operation the output of the inverter will produce higher output voltage when compared to the maximum DC source value used. To obtain maximum power the designed inverter is implemented with the photovoltaic system where the power is produced from two different PV panels which is connected to DC link by using DC-DC converters. The semiconductor switches and DC links are used to generate the inverter AC output voltages with seven levels. Two PV panels with different voltages are used in which two panels voltages are combined and their powers are injected to the grid. To validate the dynamic performance of the proposed U-Cell inverter the advanced process controller is used in the inverter connected to the grid. The controller is designed and processed to maintain the capacitor voltage to obtain the desired AC output with desired magnitude. The dynamic performance during changes in the supply current and DC voltage of capacitor for the process controller has been obtained.

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.

Average Model-Based Feedforward and Feedback Control for PUC5 Inverter

This paper proposes new average model based control strategies for a 5-level Packed U-cell (PUC5) inverter in both standalone and grid-connected modes of operation. First, a simple feedforward controller (FFC) is designed, using only two pulse width modulation (PWM) carrier signals, for the PUC5 inverter operating in standalone mode. This proposed control technique ensures self-balanced operation with high steady-state performance. Moreover, the employment of the proposed FFC leads to a decrease in the capacitor’s value as well as the minimization of the Total Harmonic Distortion (THD). Then, a feedback linearizing control technique is designed to improve the transient and steady-state performances. In grid-connected mode, a reduced-sensor technique based on the FFC and the state feedback (FC) techniques was applied. Simulations and experimental results are presented to prove the high performance of the proposed solutions for standalone and grid-connected operating modes.

A Nine-Level T-Type Packed U-Cell Inverter

This letter proposes a novel nine-level T-type packed U-cell inverter, which consists of one T-type neutral point clamped leg, one half-bridge, two switches, and two identical dc sources. The single-carrier modulation scheme can easily produce the corresponding switching sequences, which makes the T-type leg switching under high frequency and other switches operating under low frequency. To further improve the operational efficiency, the T-type leg can be constructed by using silicon carbide (SiC) devices for withstanding the necessary high-frequency switching. The experimental results verified the performance of the proposed topology.

Comparative study of multi‐objective finite set predictive control methods with new max–min strategy applied on a seven‐level packedU‐cell inverter

This article studies the design and implementation of multi-objective predictive control (MO-PC) of a grid-connected seven-level packed U-cell (PUC7) inverter for minimising the line current total harmonic distortion (THD) and capacitor voltage error simultaneously. The weighting factor method is usually used as a simple method for solving the control problem in the literature. However, there are some difficulties and shortcomings in the calculation of weighting factors. Here, max–min selection strategy with together priority is adopted to reduce these deficiencies and improves the system performance. The switch model of the PUC inverter is derived and then applied in designing the MO-PC for grid-connected applications, where a controlled active or reactive power is injected into the utility. A comparative study among three strategies of weighting factor, fuzzy decision-making and max–min selection is performed to distinguish the proposed method superiority. Experimental results are given to validate the practicality of the applied controller in regulating the line current and capacitor voltage of the grid-connected PUC7 inverter.

An Effective Sliding Mode Control Design for a Grid-Connected PUC7 Multilevel Inverter

This paper proposes an effective sliding mode controller (SMC) for a grid-connected 7-level packed U-cell (PUC7) inverter. The aim is to design a simple controller that deals effectively with the complex control problem of the PUC7 inverter (multiobjective control problem). The selection of the control actions is achieved according to the system state error at every sampling time, regardless of the previous values, which makes the control technique model-independent. The control algorithm evaluates online two cost functions (one for each state error), which are derived on the basis of sliding mode theory, and it selects the optimal control input in order to satisfy the reaching conditions of the two cost functions. Compared with the existing solutions, the proposed SMC technique ensures lower average switching frequency by tuning the hysteresis bandwidth of the capacitor-voltage error. The fast implementation, needless of gains tuning, and simple design procedure are the main features of the proposed algorithm. Simulation and experimental results are presented to prove the effectiveness of the proposed technique in controlling the PUC7 inverter with high dynamic performance and robustness against disturbances and parameters mismatch.

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.