Remya Krishna

Direct predictive current control of grid connected neutral point clamped inverter for wave power extraction

In consequence of the generic irregularity of wave energy, it is difficult to envisage the performance of a grid connected wave energy converter without simulations. This paper details a study on directly driven, linear, permanent magnet generator based, wave energy extraction scheme provided with grid-connected three phase neutral point-clamped three level inverter. The linear permanent magnet generator is driven by a magnetic translator undergoing reciprocating motion with the floating buoy according to wave movement. It converts the mechanical power to three phase AC power. The converter-inverter system provides a fast, dynamic power balancing from generator to grid. The predictive current controller is used to control the three phase neutral point clamped inverter which calculates the inverter voltage required to force the load current to follow the reference. Simulation model of the system is implemented in Matlab/Simulink. The DC-link voltage is regulated by the converter. Neutral point voltage balancing is achieved through proper selection of inverter switching states. Three phase balanced current injection to the grid at unity power factor has been attained. The results obtained validate effectiveness of the predictive method of current control.

Contour-Based Dead-Time Harmonic Analysis in a Three-Level Neutral-Point-Clamped Inverter

The term dead time refers to a prime safety factor for most power electronic converter topologies, and it is included either in the control software or in the gate/base driver hardware, depending on the application as well as the control requirements. In this paper, the authors present a comprehensive numerical analysis of dead-time effects on the output voltage of a three-level neutral-point-clamped (NPC) inverter. To incorporate the dead-time effect in the output voltage, 3-D models of three-level carrier pulse width modulation (PWM) methods are modified for two dead-time implementations. Closed-form expressions of inverter phase voltage harmonics for phase opposition disposition (POD) PWM are derived based on the double Fourier series approach and modified contour plots. The harmonic spectra from numerical evaluations, simulations, and experiments for natural sampling (NS), symmetrical regular sampling (SRS), and asymmetrical regular sampling (ARS) are compared to validate the mathematical models. In addition, the fundamental voltage with respect to the dead time and the load phase angle is presented based on analytical results and simulation.

Control and implementation of three level boost converter for load voltage regulation

The multilevel converters offer significant advantages for high power applications. The use of multilevel DC/DC converters provides improved efficiency for power conversion and transmission at high voltage. This paper investigates the control and implementation of a three level boost converter for regulating the load voltages. A PI controller based switch signal phase delay control (SSPDC) method is used for adjusting the load voltages at equal turn on and turn off time of the converter switches. The circuit simulation is done in Matlab/Simulink. The controller is realized by using the FPGA in Labview/Compact-Rio module. Software waiting loop length control technique is used for implementing the switch signal delay control. The hardware circuit is implemented and tested. The results show a validation of the controller for regulating the voltages. This method can easily be applied for voltage balancing in a three level neutral point clamped inverter where neutral voltage imbalance is always an issue.

Analysis of three-level buck-boost converter operation for improved renewable energy conversion and smart grid integration

The increased smart grid integration of renewable energy sources demands high power handling and wide controllability for the enabling power conversion technologies. The conventional energy conversion techniques are inadequate to efficiently handle the highly varying nature of renewable energy sources like wave, solar, tidal and wind. The present work examines the advantages of using a three-level buck-boost DC-DC converter to aid three-level neutral-point-clamped inverter based grid integration. There are two main reasons for using this converter. It can provide the conventional buck-boost capability at higher power levels for absorbing and conditioning the renewable source output. Besides, it can be used as a voltage balancing device to satisfy the input requirement for the three-level neutral-point-clamped inverter. The work includes complete operating range analysis of the converter for the combined buck-boost action and voltage balancing effects to understand its suitability for various applications. The converter switching modes of operation are also presented in detail along with essential example waveforms. The final results show good controllability bandwidth for the converter which makes it an attractive solution for smart grid integration of renewable energy sources.

Predictive current controller for a grid connected three level inverter with reactive power control

This paper presents a predictive method of current control for grid connected three level neutral point clamped inverter in synchronous rotating frame. The predictive current controller calculates the inverter voltage required to force the load current to follow the reference. To validate the performance the computational time has been compared with DSP processor TMS320C240 and the maximum permissible sampling frequency is calculated. Transient performance of the controller is analyzed. The proposed controller also validates the neutral voltage balancing and reactive power control. Three phase balanced current injection to the grid with reactive power control has been attained. The decoupled control over active and reactive power has been achieved through the variation of synchronously rotating two axis currents.

Discontinuous conduction mode of a three-level boost DC-DC converter and its merits and limits for voltage cross regulation applications

Distributed generation and smart grid integration of renewable energy sources introduce a lot of challenges for the enabling power electronic converter technology. Some of these challenges include wide controllability range, high power handling and good reliability. Three-level boost converter is one of the attractive solution for applications requiring voltage cross regulation such as three-level neutral point clamped inverter based grid integration of renewable sources. The present work shows the advantages and disadvantages of using discontinuous conduction mode of a Three-level boost converter for voltage cross regulation. The converter working principle, modes of operation and operating cases are listed briefly. The simulation results compare the DCM and CCM cross regulation effects. Based on these results, the controllability range of the converter is analyzed to understand the suitability of the converter for various applications.

Synchronous Current Compensator for a Self-Balanced Three-Level Neutral Point Clamped Inverter

This paper presents a synchronous current control method for a three-level neutral point clamped inverter. Synchronous reference frame control based on two decoupled proportional-integral (PI) cont ...