Hani Vahedi

Crossover Switches Cell (CSC): A new multilevel inverter topology with maximum voltage levels and minimum DC sources

Renewable energy resources are widely used because of providing green and economic energy for the consumers. Multilevel inverters generates low harmonic waveforms at the output, therefore they are most suitable for energy conversion to deliver efficient power to the loads from renewable energy sources like photovoltaic systems. In this paper a new dc source less topology has been introduced for multilevel inverters. It uses crossover switches to generate the maximum output voltage levels. The Crossover Switches Cell (CSC) multilevel inverter can generate all possible voltage level among the DC supply and regulated DC voltage capacitor. A voltage controller has been proposed to keep the DC capacitor voltage regulated in case of load changes. The simulation results prove the capability of CSC in producing maximum voltage levels as well as the controller ability in balancing the capacitor voltage even if the DC supply voltage changes.

Sensor-Less Five-Level Packed U-Cell (PUC5) Inverter Operating in Stand-Alone and Grid-Connected Modes

In this paper, a new mode of operation has been introduced for packed U-cell (PUC) inverter. A sensor-less voltage control based on redundant switching states is designed for the five-level packed U-cell (PUC5) inverter, which is integrated into switching process. The sensor-less voltage control is in charge of fixing the dc capacitor voltage at half of the dc source value results in generating symmetric five-level voltage waveform at the output with low harmonic distortion. The sensor-less voltage regulator reduces the complexity of the control system, which makes the proposed converter appealing for industrial applications. An external current controller has been applied for grid-connected application of the introduced sensor-less PUC5 to inject active and reactive power from inverter to the grid with arbitrary power factor, while the PUC auxiliary dc bus is regulated only by sensor-less controller combined with new switching pattern. Experimental results obtained in stand-alone and grid-connected operating modes of proposed PUC5 inverter prove the fast response and good dynamic performance of the designed sensor-less voltage control in balancing the dc capacitor voltage at desired level.

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.

Pinned mid-points multilevel inverter (PMP): Three-phase topology with high voltage levels and one bidirectional switch

High power applications need high efficiency devices to produce lower power losses and harmonics while meeting the limitation of voltage and current. Multilevel inverters generate smoother and higher voltage at the output with lower harmonics. They can deliver high power while using medium-voltage switches. In this paper a Pinned Mid-Points (PMP) multilevel inverter topology is introduced and studied which is derived from a Bidirectional Neutral Point Clamped (BNPC) three-level inverter. The proposed PMP multilevel inverter has fewer switches and clamping diodes than the Cascaded H-bridge (CHB) and Neutral Point Clamped (NPC) inverters, moreover it has less bidirectional switches in comparison with the BNPC. Moreover, it can be extended to three-phase inverter same as a NPC only using three legs and common DC link. A five-level inverter using proposed topology is validated by Matlab/SimPowerSystems. It shows the appropriate results of voltage and current as well as their THD%.

Hybrid SHM–SHE Modulation Technique for a Four-Leg NPC Inverter With DC Capacitor Self-Voltage Balancing

In this paper, selective harmonic mitigation (SHM) and selective harmonic elimination (SHE) modulation techniques have been combined to produce appropriate pulses for a four-leg three-level neutral point clamped (NPC) inverter. In the proposed hybrid method, the SHM technique is applied to phase legs in order to mitigate non-triplen harmonics (fifth, seventh, . . .), and the fourth leg is controlled by the SHE principle to eliminate important low-order triplen harmonics (third, ninth, . . .) completely. In this context, it is demonstrated that using SHM instead of an SHE modulator for phase legs leads to a reduced vast range of harmonic orders in the NPC output voltage, significantly. Moreover, it is proved that the presented hybrid switching technique has the ability of dc-bus capacitor voltage balancing, inherently. Furthermore, analyses are performed to calculate the dc-bus capacitances accurately to show 5% voltage ripple acceptably. Simulation and experimental results validate a good dynamic performance of the proposed hybrid modulation technique in firing the NPC inverter switches to generate low-harmonic voltage waveforms supplying balanced and unbalanced loads while balancing the dc capacitor voltages in a four-wire network with small dc-link capacitors.

Cascaded multilevel inverter with multicarrier PWM technique and voltage balancing feature

Multilevel inverters generate low harmonic waveforms at the output, which makes them suitable for high voltage energy conversion scheme to deliver efficient high power to the loads from renewable energy sources like photovoltaic systems which are penetrating to the electric grid nowadays, significantly. In this paper a single-phase hybrid multilevel inverter based on cascading full bridge and half bridge cells is introduced. Moreover the associated switching technique with multicarrier PWM is designed to generate five-level voltage at the output. As well, the designed switching technique allows the capacitors of the half bridge cell to have balanced voltage despite load changes. Furthermore, this study is extended to more cells using unequal DC sources to produce more voltage levels. Simulations have been performed on two and three cells to demonstrate the efficiency of the presented cascaded inverter with equal and unequal DC sources and switching technique.

Review and Simulation of Fixed and Adaptive Hysteresis Current Control Considering Switching Losses and High-Frequency Harmonics

Hysteresis Current Control (HCC) is widely used due to its simplicity in implementation, fast and accurate response. However, the main issue is its variable switching frequency which leads to extraswitching losses and injecting high-frequency harmonics into the system current. To solve this problem, adaptive hysteresis current control (AHCC) has been introduced which produces hysteresis bandwidth which instantaneously results in smoother and constant switching frequency. In this paper the instantaneous power theory is used to extract the harmonic components of system current. Then fixed-band hysteresis current control is explained. Because of fixed-band variable frequency disadvantages, the adaptive hysteresis current control is explained that leads to fixing the switching frequency and reducing the high-frequency components in source current waveform. Due to these advantages of AHCC, the switching frequency and switching losses will be diminished appropriately. Some simulations are done in MATLAB/Simulink. The Fourier Transform and THD results of source and load currents and the instantaneous switching frequency diagram are discussed to prove the efficiency of this method. The Fourier Transform and THD results of source and load currents are discussed to prove the validity of this method.

Sliding Mode Control of PMSG Wind Turbine Based on Enhanced Exponential Reaching Law

This paper proposes a sliding-mode control (SMC)-based scheme for the variable-speed direct-driven wind energy conversion systems (WECS) equipped with a permanent magnet synchronous generator connected to the grid. In this paper, diode rectifier, boost converter, neutral point clamped inverter, and L filter are used as the interface between the wind turbine and grid. This topology has abundant features such as simplicity for low- and medium-power wind turbine applications. It is also less costly than back-to-back two-level converters in medium-power applications. The SMC approach demonstrates great performance in complicated nonlinear systems control such as WECS. The proposed control strategy modifies reaching law (RL) of the sliding mode technique to reduce chattering issue and to improve total harmonic distortion property compared to conventional RL SMC. The effectiveness of the proposed control strategy is explored by simulation study on a 4-kW wind turbine, and then verified by experimental tests for a 2-kW setup.

A new voltage balancing controller applied on 7-level PUC inverter

In this paper a novel model of the packed U-cell (PUC) inverter is derived considering the concept of single-phase multilevel converters. Based on the proposed model, a voltage balancing controller is designed to apply on the 7-level PUC inverter. The applied controller is in charge of fixing the capacitor voltage in PUC structure at a desired value to have the seven levels of the voltages at the output. The 7-level pulse width modulation (PWM) technique is used to produce the associated pulses for firing the PUC switches. The performance of the introduced controller is investigated via simulations in various conditions including changes in the load and DC bus voltage variations. The results prove the ability of the good dynamic performance and fast response of the controller in stable and unstable conditions.

Design and Implementation of Space Vector Modulation-Based Sliding Mode Control for Grid-Connected 3L-NPC Inverter

This paper presents a closed-loop space vector modulation (SVM)-based sliding mode controller (SMC) for a three-level grid-connected neutral point clamped (3L-NPC) inverter. The nonlinear SMC based on Gaos reaching law has been designed to control the grid current and inject desired amount of active and reactive power into the network. Due to using single dc source at the NPC inverter dc bus, neutral point voltage is controlled through redundant switching states and instantaneous dc voltage feedback integrated into SVM technique. Meanwhile, there is no external voltage controller involved, thus no associated fine tuning issues are existed. The performance of the proposed hybrid controller to inject a desired active/reactive power to the grid is investigated through external perturbations such as change in the line current amplitude/phase shift, ac voltage fluctuation, as well as dc voltage variation. Full converter state-space model was developed and simulated. Experimental results are provided to verify the fast dynamic performance, low content of line current THD%, and good voltage balancing of dc bus capacitors of the NPC inverter.