N. Sandeep

A new simplified multilevel inverter topology for grid-connected application

Multilevel inverter performance is high compared to the conventional two level inverters due to their reduced harmonic distortion, lower electromagnetic interference. However the main drawback of multilevel inverter is increased number of switches, complex pulse width modulation control and balancing of capacitor voltages. This paper proposes a single phase seven level inverter for grid connected system. The proposed inverter topology consists of fewer components with low complexity gate drives and control signals. An LC filter is used to limit the switching current ripple by providing high attenuation of harmonic and high dynamic performance. This paper also presents the most relevant control and modulation methods by a new reference/carrier based PWM scheme employing three similar reference signals with an offset of magnitude equal to the amplitude of the carrier signal. The entire system is numerically simulated using MATLAB/SIMULINK and the simulation results are presented.

A comparison of seven-level inverter topologies for multilevel DC-AC power conversion

Multilevel inverter (MLI) performance is high compared to the conventional two level inverters since they offer high power capability, associated with lower output harmonics and lower commutation losses. However the main drawback of MLI is their increased number of power devices, passive components, complex pulse width modulation control and balancing of capacitor voltages. In this paper the most popular topologies like diode-clamped inverter (neutral-point clamped), cascaded multicell with separate dc sources, and transistor clamped H-Bridge inverter are discussed. A simplified multilevel inverter (Switched Transistor MLI) is proposed and its performance is compared with the above said topologies. Component count and the % total harmonic distortion (THD) of the output voltage are considered as the indexes of the comparative performance. The operating principle of each topology, the most relevant modulation method of all the topologies and the detailed analysis of the proposed Switched Transistor MLI is included. The selection of topology and control techniques depends and varies according to power demands of inverter. Simulation study of all the topologies considered is carried out on MATLAB/SIMULINK platform and the performance of the proposed topology is verified experimentally by the tests performed on a scaled laboratory prototype.

Design and Implementation of a Sensorless Multilevel Inverter With Reduced Part Count

This letter proposes a single-phase nine-level (9L) inverter topology suitable for grid-connected renewable energy systems. The proposed inverter is realized using a T-type neutral-point-clamped inverter connected in cascade to a floating capacitor (FC) H-bridge. Additionally, two low-frequency switches are added across the dc-link enabling the inverter to generate a 9L waveform. A sensorless voltage control based on redundant switching state is developed and embedded with PWM controller, which is responsible for regulating the FC voltage at one-quarter of the dc source voltage. The proposed PWM technique employs the generation of 9L waveform without using any voltage sensor, thereby reducing the complexity of the overall control scheme. This, in turn, will make the overall system appealing for various industrial applications. In comparison to conventional and recent topologies, generation of the 9L waveform using a lower number of components is the notable contribution. Another important feature of the proposed inverter is that if FC H-bridge fails, it can be bypassed, and the inverter can still operate as a 5L inverter at its nominal power rating. Furthermore, a comprehensive comparison study is included which confirms the merits of the proposed inverter against those of other state-of-the-art topologies. Finally, simulation and experimental results are included for validating the feasibility of the proposed system.

Single-phase grid-connected photovoltaic system based on ripple correlation control maximum power point tracking

This work presents a comparison of ripple correlation control maximum power point tracking (MPPT) technique and the modified version of the same MPPT applied to single-phase, single-stage, grid-connected photovoltaic (PV) system, as the technique is fast and suitable for fast changing environmental conditions. Both the techniques are compared on the basis of the time taken to reach (track) the MPP, operating point oscillations about MPP and the dependence of the algorithms, if any, on array configuration and parameters. An LCL-Filter based grid connected inverter with proportional-resonant (PR) current controller is suggested to provide power to the line with unity power factor and the inverter offers much less total harmonic distortion. The focus is on presenting a systematic design procedure for AC current, DC voltage controllers for the VSI and low complexity grid synchronization method. The complete system is numerically simulated in MATLAB and the results are presented for rapidly changing irradiation levels.

A new nine-level single-DC source-based inverter topology for distributed generation

Multilevel inverter enables to completely remove the passive filtering requirement at the grid interfacing end, resulting in improved efficiency and reduced cost. These features have led to increasing attention towards their application to medium and high-power arena. In this paper, investigation of a hybrid 9-level inverter topology for grid integration of renewable energy sources is presented. The structural details, operating principle, capacitor voltage balancing control and the main features of the proposed inverter are presented. The proposed topology is compared with other similar 9-level converters to emphasize its superior characteristics and performance. Simulation results demonstrating the grid connected operation of the converter for two test cases are presented. The results affirm the effectiveness of the capacitor voltage balancing control in maintaining capacitor voltages at set values, under steady state and transient operation of the converter.

Novel asymmetrical multilevel inverter topology with reduced number of switches for photovoltaic applications

The performance of multilevel inverter is high compared to the classical two level inverters owing to their reduced total harmonic distortion, and lower electromagnetic interference. However the setbacks of multilevel inverter are increased number of power devices, complex PWM and gating circuitry. In this paper, a new multilevel inverter topology, capable of generating large number of levels with fewer number of power switches, gating circuits and power diodes is proposed. In contrast to classical multilevel topologies, the presented topology consequences in reduction of the number of power devices and conduction losses. The proposed topology is asymmetrical, employing isolated dc sources of voltage ratio 4:2:1 (Binary fashion). Staircase control PWM at fundamental frequency is employed for the gating of power switches makes it suitable in applications like flexible alternative current transmission systems (FACTS), renewable energy sources, drives control and vehicle propulsion system. The structure of the proposed inverter is modular and thus best suited for PV applications. Detailed simulation is carried out using MATLAB/SIMULINK platform and simulation results are presented.

Analysis and design of ZVS-PWM active clamping DC-to-DC Cuk converter based PV generation system

This paper presents the application of the “ripple correlation control (RCC)” maximum power point tracking (MPPT) algorithm for Stand-Alone photovoltaic (PV) system employing dc-dc Cuk converter to maximize the output power of PV module. The combination of auxiliary switch, clamp capacitor and resonant inductor is used to exploit the advantage of minimum voltage stress across the semiconductors at switching transitions due to clamping action. RCC technique uses the high frequency signal ripple, which is inherent in power converters to converge asymptotically to the maximum power point independent of module configuration and parameters. The operating modes of converter for different switching time intervals are analyzed and design considerations are presented. To evaluate the feasibility of ZVS Cuk converter with MPPT, simulation is carried out using MATLAB/SIMULINK platform for an 87 Wp solar PV system and the simulated performance results are presented.

Single-phase modular multilevel inverter based grid-connected photovoltaic system

This paper presents a control scheme for single-phase grid-connected modular five-level inverter applied to photovoltaic (PV) system. The five-level topology considered consists of two series connected H-bridge cells popularly known as cascaded H-bridge inverter. The reason that it requires an isolated dc sources makes it very attractive and its inherent modularity, easy scalability makes the system more reliable. One of the main challenges associated with multilevel converter is to control the drift in dc-link voltage caused by the power imbalance of the cells. A two loop control scheme is proposed to combat this issue; it consists of an asynchronous frame or proportional resonant (PR) for regulating the grid current and a proportional integral (PI) controller for regulating dc-link voltage. The proposed scheme regulates the dc-link voltage independently, in accordance with the reference value generated by the maximum power point tracking (MPPT) algorithm enabling the extraction of maximum power from each module. The inverter injects current which is in phase with the grid voltage ensures the unitary power factor operation with zero reactive power and less total harmonic distortion. The proposed control scheme can be extended to any number of cells connected in series for increasing the number of level in output voltage. Simulation results are presented to validate the analytical expectations and the control scheme developed.

Architectural framework of on-board integrator: An interface for grid connected EV

Vehicle to Grid (V2G) is the concept of connecting a group of electric vehicles (EV) to the grid for power transaction. EVs can be connected to the grid through the home interface or through the chargers available at charging stations. In this paper, a single phase on-board charger with low complexity control scheme is proposed for EV power transaction. The power flow from and to the grid is processed using two stage cascaded converters consisting of a bidirectional DC-DC and DC-AC converters. The LCL filter is used as an interface between DC-AC converter and the grid to attenuate the grid current harmonics. A proportional resonant (PR) controller is employed for the control of grid current and to enable the unity power factor operation of the DC-AC converter. The setbacks associated with the conventional proportional-integral (PI) controller for single phase system is elevated by employing PR controller. Filter design guidelines and the control strategy developed for the proposed system is numerically simulated and verified with extensive simulation carried using MATLAB/SIMULINK. The results demonstrating the feasibility and viability of the proposed system are presented.

Asymmetric H-Bridge Single-Phase Seven-Level Inverter Topology with Proportional Resonant Controller

ABSTRACT This paper presents an asymmetrical H-bridge single-phase seven-level inverter topology with modified gating scheme for reducing the number of high-frequency switches. Due to shortcomings like steady-state error and problems in removing low-order harmonics associated with proportional integral controller, proportional resonant controller is used for grid-connected converter current control. A practical application of proportional resonant current controller is developed using a low-cost dsPIC33EP256MC202 microcontroller to keep the current injected in to the grid. The validity of proposed inverter and control scheme is verified through simulation and implemented for low-voltage laboratory prototype.