Madhuri A. Chaudhari

High Power Factor Operation of a Three-Phase Rectifier for an Adjustable-Speed Drive

This paper presents a novel approach to improve the power factor (PF) and reduce the harmonics generated by an adjustable-speed drive (ASD). A high-frequency (HF) current injection technique is used to improve the PF and harmonic performance. The HF current at the same switching frequency (33 kHz) is injected into the input of a front-end rectifier from the output of an HF inverter. The main feature of the circuit is that it does not require any additional active devices for current injection. The inverter driving the induction motor is operated using a sinusoidal pulsewidth-modulation technique. The circuit simulation and experimental prototype results are presented for 67-hp (50 kW) and 3-hp three-phase induction motors, respectively.

Simplified Space Vector Modulation Techniques for Multilevel Inverters

This paper presents simplified techniques for the space vector modulation (SVM) of any n-level multilevel inverter. Three techniques have been presented to simplify the identification of the nearest three vectors to the reference vector. The first two techniques are based on resolving the multilevel inverter space vector diagram into appropriate two-level hexagons. This results in simplification of the multilevel SVM problem into a two-level SVM problem. The third technique is an algorithm-based technique which makes use of a 60°-spaced gh coordinate system to perform the SVM of a multilevel inverter. Switching sequence design for all the three techniques is presented with the aim of minimization of the device switching frequency. Simulation and experimental results have been provided to verify the feasibility of the proposed techniques. Simulation results are provided for up to 21-level cascaded H-bridge (CHB) inverters, while the experimental verification is done on a five-level laboratory prototype. Although only the CHB inverter is considered in this study, the proposed techniques are perfectly general and can be applied to all types of multilevel inverters, and are extendable to any number of levels.

Optimized Space Vector Pulse-width Modulation Technique for a Five-level Cascaded H-Bridge Inverter

This paper presents an optimized space vector pulse-width modulation (OSVPWM) technique for a five-level cascaded H-bridge (CHB) inverter. The space vector diagram of the five-level CHB inverter is optimized by resolving it into inner and outer two-level space vector hexagons. Unlike conventional space vector topology, the proposed technique significantly reduces the involved computational time and efforts without compromising the performance of the five-level CHB inverter. A further optimized (FOSVPWM) technique is also presented in this paper, which significantly reduces the complexity and computational efforts. The developed techniques are verified through MATLAB/SIMULINK. Results are compared with sinusoidal pulse-width modulation (SPWM) to prove the validity of the proposed technique. The proposed simulation system is realized by using an XC3S400 field-programmable gate array from Xilinx, Inc. The experiment results are then presented for verification.

Digitally Implemented Novel Technique to Approach Natural Sampling SPWM

Abstract Digital signal processor (DSP) based sinusoidal pulse width modulation (SPWM) uses symmetrical and asymmetrical regular sampling. These samplings do not attain the performance of natural SPWM at low sampling. This paper presents a simple technique using digital sampling to approach naturally sampled SPWM. The proposed technique samples the modulating waveform at every peak of the triangular carrier signal and calculates precise magnitude of modulating signal for the instant of intersection. This signal has enough information to minimize the error in switching instant. The original modulating signal appears in the PWM output spectra unattenuated, without any distortion components, and without phase delay, regardless of the frequency or modulation depth of that signal. The presented technique is suitable for real time implementation using commercial DSP. This technique is also applicable to multilevel inverter and does not generate superfluous pulses like asymmetrical sampling in the output voltage of multilevel inverter. Simulation and experimental results are presented to demonstrate and confirm the validity of the proposed technique.

Three-phase Series Active Power Filter as Power Quality Conditioner

In this paper, a simplified control algorithm of a three-phase Series Active Power Filter (SAPF) as Power Quality Conditioner is presented. SAPF compensates supply voltage distortions/unbalance, supply voltage harmonics in a view as such they does not reach at the load end with very low THD in load voltage. The series APF is realized using a three-phase, three leg VSI. A dynamic model of the SAPF is developed in the MATLAB/SIMULINK environment and the simulation results demonstrating the power quality improvement in the system are presented in terms of constant RMS Voltage at load.

Grid Interfaced Distributed Generation System With Modified Current Control Loop Using Adaptive Synchronization Technique

This paper presents real-time implementation of a grid interfaced distributed generation (DG) system with modified current control loop using three phase amplitude adaptive notch filter (AANF) based synchronization tool. A grid current feedback based modified

Design of resonant converter for high power factor operation and optimum losses in magnetic components

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Synchronous vector control design of multilevel inverters for AC grid applications

-current control technique for interfacing inverter is developed in order to achieve constant loading on the grid, transient-free operation, and power factor improvement close to unity power factor (UPF) of the utility grid during sudden load variations. This technique does not require separate calculation of reference reactive component and harmonics component of currents hence reduces control circuit complexity. In addition, it requires only three voltage and three current sensors. Three phase AANF is developed and is used for online extraction of utility voltage phase angle to generate synchronized reference current signals for interfacing inverter. AANF is used because of its adjustable accuracy and amplitude adaptability even under unbalanced voltage sag and swell, frequency variation, and distorted grid conditions. Fast and accurate behavior of three phase AANF improves the dynamic response of entire DG system control performance for sudden load variations. The dynamic behavior of the proposed grid interfaced DG system is experimentally evaluated in maintaining constant loading on grid, transient-free operation, and power factor improvement close to UPF operation of the utility grid, by compensating total reactive power and harmonic current demanded by variable linear as well as nonlinear load.

Single-Phase Resonant Converter with Active Power Filter

This work presents a systematic design procedure of resonant converter for its operation in high input line power factor. Selection of quality factor of the resonant tank circuit influences instantaneous gain and power factor of the converter. The design calculations are done for AC to DC modified series-parallel resonant converter (MSPRC) delivering a peak power of 2P/sub o/ (P/sub o/ is output power), by choosing quality factor Q at the peak of AC line cycle for minimum AC input voltage. For high power factor operation the value of Q at peak of AC input should be chosen such that the instantaneous available gain of the converter is greater than the required gain. Design of magnetic components under cost and loss constraints is outlined. The optimal number and the diameter of the strands to minimize loss in magnetic components are given for particular design example. The sub-optimal stranding is also considered to arrive at best cost-loss compromised designs. A MATLAB program is used to arrive at cost-loss compromised design. To validate the design procedures simulation results of a typical MSPRC are presented. Finally results of an experimental prototype built in the laboratory are given to substantiate the outlined design procedure.

Modified Synchronous Vector Control Design of Multilevel Inverters for AC Grid Applications

This article presents advanced vector control technique for a five-level cascaded H-Bridge inverter for integration of distribution generation based on renewable energy to the power grid. The presented control strategy has designed with SRF PLL and the proposed control plan is completed by setting suitable reference current components for the d and q axis in the control loop of DG, which are given based on the objectives of projected method. The objectives of control technique of DG interface system are employed to enhance the standard of power grid by injection of active and reactive current elements through integration of DG resources to the grid. In this paper an Optimized Space vector pulse width modulation (OSVPWM) control technique of five-level H-Bridge VSI has been conferred support on analysis of voltage and current elements in abc-αβ and αβ-dq special reference frames. High performance of the projection technique indicates with injection of most accessible power from renewable energy resources to power grid, this increases power factor of the grid, and reduces total harmonic distortion (THD) of grid current. The proposed control design is verified with simulations results carried using Matlab/Simulink software to carry out the different operational conditions.