Asymmetric Cascaded H-bridge Multilevel Inverter Research Articles

Multifunctional Control Strategy for Asymmetrical Cascaded H-Bridge Inverter in Microgrid Applications

A multifunctional control strategy for a single-phase asymmetrical cascaded H-bridge multilevel inverter (ACHMI), suitable for microgrid systems with nonlinear loads, is presented. The primary advantage of ACHMI is to produce a staircase output voltage with low harmonic content utilizing unequal dc voltages on the individual H-bridge cells. In a grid-connected mode of operation, the control strategy of the ACHMI is based on the conservative power theory, providing selective disturbing current compensation besides injecting its available energy. In autonomous mode of operation, two different control methods along with a damping resistor in the filter circuit are developed for regulation of the ACHMI instantaneous output voltage in a variety of load conditions. The first method is a single-loop voltage control scheme without the need of any current measurement. The second one is a multiloop voltage control scheme with a load current feedforward compensation strategy and preservation of the grid-connected current control scheme. The steady-state response and stability of both voltage control schemes are analyzed, and based on the application requirement, the control schemes are implemented individually. The effectiveness of each control strategy is experimentally verified using a hardware-in-the-loop setup with the control algorithm implemented in the TMSF28335 DSP microcontroller.

Modelling and Simulation of Photovoltaic System Fed Two Input Two Output DC-DC Boost Converter Interfaced with Asymmetric Cascaded H-Bridge Multilevel Inverter

Objectives: Multiple Input Multiple Output dc-dc boost converters is used to interface diversified renewable energy sources to Asymmetric Cascaded H-Bridge Multilevel Inverter whose output voltages can be connected to the grid system. The compensators and/or controllers are required to provide the constant output voltages of the boost converter against disturbances along with desired time domain specifications. In this paper, two input two output dc-dc boost converter is developed to interface with seven level multilevel inverter. Methods/Statistical Analysis: One of the input sources is replaced by Photovoltaic panel and Incremental Conductance based Maximum Power Point Tracking Algorithm is developed to improve the efficiency of the system. Compensators are designed to maintain the constant output voltages of the converter against disturbances using transfer function model obtained from developed small signal model of the converter. The developed system is simulated using MATLAB /Simulink and the total harmonic distortion in the output voltage of the inverter is observed .The simulated closed loop output voltages of the dc-dc converter are validated by developing prototype model of the converter using AT 89C51 microcontroller. Findings: It is found that the two input two output dc-dc converter provides constant dc voltages to the asymmetric multilevel inverter from the diversified energy sources with improved time domain specifications using compensators. Application/Improvements: The designed system is having the applications in renewable power system, aerospace power systems and hybrid energy vehicle.

A New Photovoltaic System Architecture of Module-Integrated Converter with a Single-sourced Asymmetric Multilevel Inverter Using a Cost-effective Single-ended Pre-regulator

In this paper, a new architecture for a cost-effective power conditioning systems (PCS) using a single-sourced asymmetric cascaded H-bridge multilevel inverter (MLI) for photovoltaic (PV) applications is proposed. The asymmetric MLI topology has a reduced number of parts compared to the symmetrical type for the same number of voltage level. However, the modulation index threshold related to the drop in the number of levels of the inverter output is higher than that of the symmetrical MLI. This problem results in a modulation index limitation which is relatively higher than that of the symmetrical MLI. Hence, an extra voltage pre-regulator becomes a necessary component in the PCS under a wide operating bias variation. In addition to pre-stage voltage regulation for the constant MLI dc-links, another auxiliary pre-regulator should provide isolation and voltage balance among the multiple H-bridge cells in the asymmetrical MLI as well as the symmetrical ones. The proposed PCS uses a single-ended DC-DC converter topology with a coupled inductor and charge-pump circuit to satisfy all of the aforementioned requirements. Since the proposed integrated-type voltage pre-regulator circuit uses only a single MOSFET switch and a single magnetic component, the size and cost of the PCS is an optimal trade-off. In addition, the voltage balance between the separate H-bridge cells is automatically maintained by the number of turns in the coupled inductor transformer regardless of the duty cycle, which eliminates the need for an extra voltage regulator for the auxiliary H-bridge in MLIs. The voltage balance is also maintained under the discontinuous conduction mode (DCM). Thus, the PCS is also operational during light load conditions. The proposed architecture can apply the module-integrated converter (MIC) concept to perform distributed MPPT. The proposed architecture is analyzed and verified for a 7-level asymmetric MLI, using simulation results and a hardware implementation.

THD Analysis of Cascaded H-Bridge Inverter with Fuzzy Logic Controller

In recent days, the multilevel inverter technology is widely applied to domestic and industrial applications for medium voltage conversion. But, the power quality issues of the multilevel inverter limit the usage of much sensitive equipment like medical instruments. The lower distortion level of the output voltage and current can generate a quality sinusoidal output voltage in inverters and they can be used for many applications. The harmonics can cause major problems in equipments due to the nonlinear loads connected with the power system. So, it is necessary to minimize the losses to raise its overall efficiency. In this paper, a new topology of seven level asymmetrical cascaded H-bridge multilevel inverter with a Fuzzy logic controller had been implemented to reduce the Total Harmonic Distortion (THD) and to improve the overall performance of the inverter. The proposed model is well suited for use with a solar PV application. In this topology, only six IGBT switches are used with three different voltage ratings of PV modules (1:2:4). The lower number of semiconductor switches leads to minimizing overall di/dt ratings and voltage stress on each switches and switching losses. The gate pulses generated by Sinusoidal Pulse Width Modulation (SPWM) technique with a Fuzzy logic controller are also introduced. A buck-boost converter is used to maintain the constant PV voltage level integrated by an MPPT technique followed by Perturb and Observer algorithm is also implemented. The MPPT is used to harness the maximum power of solar radiations under its various climatic conditions. The new topology is evaluated by a Matlab/Simulink model and compared with a hardware model. The results proved that the THD achieved by this topology is 1.66% and realized that it meets the IEEE harmonic standards.

Interactive smart battery storage for a PV and wind hybrid energy management control based on conservative power theory

ABSTRACTThis paper presents interactive smart battery-based storage (BBS) for wind generator (WG) and photovoltaic (PV) systems. The BBS is composed of an asymmetric cascaded H-bridge multilevel inverter (ACMI) with staircase modulation. The structure is parallel to the WG and PV systems, allowing the ACMI to have a reduction in power losses compared to the usual solution for storage connected at the DC-link of the converter for WG or PV systems. Moreover, the BBS is embedded with a decision algorithm running real-time energy costs, plus a battery state-of-charge manager and power quality capabilities, making the described system in this paper very interactive, smart and multifunctional. The paper describes how BBS interacts with the WG and PV and how its performance is improved. Experimental results are presented showing the efficacy of this BBS for renewable energy applications.

A Modified Multiband Hysteresis Controlled DTC of Induction Machine with 27-level asymmetrical CHB-MLI with NVC modulation

Abstract The influence of Direct Torque Controlled Induction Motor Drive in the area of industrial application is very high; it presents foremost area of controllability of load at different states of operation. The major snags to the controller are maintaining Constant Switching Frequency and Infeasibility state. This paper concentrates on rectifying these problems with Modified Multiband Hysteresis Controller and Nearest Vector Control Modulated Asymmetrical Cascaded H-Bridge Multilevel Inverter for the better drive operation. In this case proper modification in MHC gives the optimal utilizations of each control vector to avoid the infeasibility states with a Lookup-Table and Multilevel Inverter gives more number of control voltage vectors with constant switching frequency for flexible operation of drive with low disturbances. Direct Torque Control equipped with these two modules achieves better operating conditions with low Torque ripples, low distorted flux and speed with different loads, and all other satisfactory load operating parameters.

Three-Phase Asymmetric Multilevel Inverter Topologies with Better Charge Balancing

Cascaded H-bridge multilevel inverter is among the most preferred topology in solar systems. While traditional asymmetric cascaded H-bridge multilevel inverter is easy to achieve higher number of output voltage levels compared to traditional symmetric cascaded H-bridge multilevel inverter, charge balancing between the voltage sources remains a challenge for asymmetric cascaded H-bridge multilevel inverter. This drawback results in unsteady DC voltage levels due to unbalanced power drawn from each voltage sources. Besides that, in battery powered applications, unbalanced power drawn results in unequal discharged in the batteries. In this paper, two three-phase asymmetric cascaded H-bridge multilevel inverter topologies are proposed which offer easier in terms of modularity while maintaining the ease in charge balancing control. The performance of these two proposed topologies with charge balance control has been evaluated using PSIM software.

Charge Balancing Control for an Asymmetric Multilevel Inverter with Multiple Paired-H-Bridges

Cascaded H-Bridge (CHB) multilevel inverter (MLI) is among the most preferred topology in solar PV systems. While traditional asymmetric CHB MLI is easy to achieve higher number of output voltage levels compared to traditional symmetric CHB MLI, charge balancing between the voltage sources remains a challenge for asymmetric CHB MLI. This drawback results in unsteady DC voltage levels due to unbalanced power drawn from each voltage sources. Besides that, in battery powered applications, unbalanced power drawn results in unequal discharged in the batteries. In this paper, an asymmetric CHB MLI topology is proposed which is easier to modularize as for symmetric CHB MLI while maintaining the ease in charge balancing control. The performance of this proposed asymmetric CHB MLI with charge balance control has been evaluated using PSIM software.

Asymmetric Cascaded DC Sources Multilevel Inverter with Less Active Switches and Simpler Control Strategy

Cascaded H-Bridge (CHB) multilevel inverter (MLI) is among the most preferred topology in solar PV systems. While traditional asymmetric CHB MLI is easy to achieve higher number of output voltage levels compared to traditional symmetric CHB MLI, charge balancing between the voltage sources remains a challenge for asymmetric CHB MLI. This drawback results in unsteady DC voltage levels due to unbalanced power drawn from each voltage sources. Besides that, in battery powered applications, unbalanced power drawn results in unequal discharged among the batteries. In this paper, an asymmetric half H-bridge (HHB) MLI topology is presented which is easy to modularize as for symmetric CHB MLI while maintaining the ease in charge balancing control. The performance of this proposed asymmetric HHB MLI with charge balance control has been evaluated using PSIM software.

English

3 ABSTRACT:A power electronic converters are becoming more and more popular for medium voltage & high power applications. To overcome the limitation of semiconductors current and voltage ratings in high power applications, multilevel inverter is often considered an effective solution. In addition, stepped waveform in the output of multilevel inverter has better harmonic spectrum than 2-level inverter in low switching frequencies. So, in recent years multilevel inverters have gained great interest in industry. Among the different solutions available for multilevel converters, the cascaded H-Bridge multilevel inverter are modular in nature and its asymmetric topologies allow to generate more voltage levels with less number of semiconductors and thus increase of output performance and system reliability. For these reasons, this kind of topology has attracted a lot of attention both from the customers and manufacturers view.This paper presents an asymmetrical cascaded H-Bridge multilevel inverter in three phase configuration using fixed frequency level shifted carrier based pulse width modulation technique feeding a three phase squirrel cage induction motor. This new control scheme is applied to 7, 9, 15 and 27 level asymmetrical cascaded H-Bridge multilevel inverter. Simulation using MATLAB/SIMULINK is done to verify the performance of all levels of an asymmetrical cascaded H-Bridge multilevel inverter.

Cascaded H-bridge inverter motor drives for hybrid electric vehicle applications

This paper presents the asymmetric cascaded H-bridge multilevel inverter for electric vehicles (EV) and hybrid electric vehicles (HEV) applications. Currently available power inverter systems for HEVs use a DC-DC boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. Asymmetric cascaded H-bridge multilevel inverter design for EV and HEV applications without the use of inductors to output a boosted AC voltage is proposed in this paper. Traditionally, each H-bridge needs a DC power supply having equal values of DC power sources. The proposed design uses the asymmetric cascaded multilevel inverter using non-equal DC power sources based on specified ratios. A fundamental switching scheme is used to do modulation control and to produce a seven-level phase voltage.