Vineeta Agarwal

FPGA Realization of Trapezoidal PWM for Generalized Frequency Converter

Combining concept of cyclo-converter and cyclo-inverter, a generalized frequency converter has been developed where undesirable harmonic components are minimized using nonsinusoidal carrier-based PWM, which is a trapezoidal pulsewidth modulation technique. The study begins by establishing a model of frequency converter to obtain the firing sequence for cyclo-converter and cyclo-inverter mode of operation. The converter is simulated using the well-known software Matlab and simulations results are presented for a single-phase ac supply. It has been found that, for cyclo-inverter operation, the minimum total harmonic distortion in the output voltage is found to be 4.8%, while during cyclo-converter operation it is only 2%. Simulation results are validated with the experimental results. A prototype of frequency converter is developed where a field-programmable gate array is used to generate the PWM trigger signal through Xilinx 9.2i. The results are also compared with other existing carrier-based modulation techniques.

Design of Delta-Modulated Generalized Frequency Converter

This paper proposes a novel power electronic application, which is an IGBT-based frequency converter that performs the function of both cycloconverter and cycloinverter by changing the 2-b input parameter. It finds its application in speed control of induction motor, induction heating, fluorescent lighting, ballast, high-frequency power supplies, and so many other applications. A methodology is developed to generate the trigger signals for various IGBTs used in frequency converters such that the circuit is not restricted to a particular value of output frequency but it can produce any output frequency that is an integer multiple of the input supply frequency. The output of the converter has been improved using delta-modulation technique. Hardware design is obtained using readily available ICs and other components. The trigger circuit has been tested qualitatively by observing waveforms on CRO. The operation of the proposed system has been found to be satisfactory.

A Comparative Study of PWM Schemes for Grid Connected PV Cell

A photovoltaic (PV) cell connected to the grid system has been modeled in MATLAB environment. Various characteristics have been plotted with changing atmospheric condition. An operating point at which photovoltaic cell exhibits maximum efficiency and generates maximum power is tracked by, a method called voltage Based Maximum Power Point tracking (VMPPT). To inject a sinusoidal current into the grid system, two modulations techniques namely; Sine PWM and State Vector PWM (SVPWM) have been implemented, and their performance is evaluated based on different parameters. Simulation results demonstrate the fast and effective response.

Delta modulated cyclo-inverter

Delta modulation (DM) is simple and has characteristics advantageous to the operation of cyclo-inverter. Analysis and implementation of delta modulated switching is presented in this paper both for cyclo-inverter as well as for cyclo-converter. Simulation results are shown for single-phase to single-phase centre tapped transformer configuration using SIMULINK software. This confirms a validity of the delta modulation technique for step up as well as step down operation. It has been found that total harmonic distortion (THD) is low for modulation index lying from 0.75 to 1.5. Any further increase or decrease in modulation index increases the harmonics in the converter. The output improves with increasing sampling frequency above 2 KHz where THD has been found to be as low as 4% for cyclo-inverter and 2% for cycloconverter.

Delta-Modulated AC–AC Converter for PM WECS

An ac-to-ac converter has been developed to convert the variable input frequency in wind energy conversion system (WECS) to a constant output frequency of 50 Hz for a distributed generation unit. The switching strategy and control mechanism for the converter is presented using time domain simulations in MATLAB environment. A specific triggering pattern has been generated for the switching devices in the converter to achieve desired polarity of the output voltage across the distributed load. The harmonics in the input supply side of the converter are mitigated by using delta modulation technique, whereas in the output of the converter, passive filtering has been used along with delta modulation technique. The design and implementation issues of the modulation technique and the switching scheme are discussed in detail with suitable simulation and experimental results. The analysis and properties of the proposed solution is compared with the known solutions. It has been concluded that an ac-ac converter is technically a viable option to interface a wind turbine to a utility grid.

Staircase modulated AC to AC converter

Stair-case modulation technique, generally applied in multilevel inverter is now applied in AC to AC converter for reducing harmonics in the output for both cyclo-inverters as well as for cyclo-converter mode. Simulation results are shown for single-phase to single-phase matrix converter configuration using SIMULINK software. A relation has been obtained between the carrier frequency and output frequency for a given number of levels in staircase to obtain high fundamental output voltage and low distortion factor. The minimum total harmonic distortion factor (THD) obtained is 4.8 % for cyclo-inverter operation while for cyclo-converter operation it is only 3.12 %.

SPICE model development for SiC power MOSFET

SiC Power MOSFETs show a tremendous potential for high voltage, high temperature, high-power and high-frequency power electronic applications. A simplified SPICE model is proposed for the SiC Power MOSFET, CMF20120D, based on the understanding of the power MOSFET discrete devices terminal behavior. The aim of the model development is to reuse the available built-in MOSFET models of the regular lateral MOS devices in the commercial SPICE simulators and propose a new model to depict the same behavior as expected by SiC device. The advantage of such model is the limited number of required parameters, which can readily be extracted from simple external terminal measurements or from standard datasheets. The results of simulation and comparison with real device measurement show appreciable closeness with the datasheet.

A Novel Soft Switched Cycloinverter

A novel soft switched insulated-gate bipolar transistor (IGBT)-based cycloinverter, which is capable of converting voltage at the main frequency to voltage at high frequency, is proposed to improve the previously proposed pulse width modulation cycloinverter. An auxiliary switch, along with an inductor, is used to have simultaneous zero-current switching and zero-voltage switching for turn-on transitions of the IGBT in order to mitigate the internal losses and total harmonic distortion factor in the inverter. The principle of operation and design consideration are presented. The proposed cycloinverter is compared with a conventional hard switched cycloinverter, and it has been demonstrated that the losses have been reduced approximately 50% by this new switching technique and the efficiency of the inverter is increased significantly. A prototype of the cycloinverter is developed in the laboratory for verification of the simulation results. Experimental results are found in good agreement to the simulated results.

A study of conventional and fuzzy PI controller CSI fed induction motor

A comparative study has been made for closed loop performance of CSI fed induction motor using fuzzy logic PI controller with conventional PI controller. A slip control scheme has been used for the induction motor. The evaluation of the controllers behavior is made through computer simulation with MATLAB coding. The starting transients of the motor are investigated for different operating speeds. It has been shown that for fuzzy controller, once the parameters are selected for a specified load and speed, it works for all other speed whereas for conventional PI controller, the parameters have to change for each load and speed setting. The fuzzy controller reduces the over shoot value of speed approximately 2 to 5 % for the selected load. The peak value of input DC link current of the CSI is also less in fuzzy PI controller as compared to conventional PI controller. This reduces the rating of the semiconductor switches used in inverter and thus overall cost of the system.

A New Random SPWM Technique for AC-AC Converter-Based WECS

A single-stage AC-AC converter has been designed for a wind energy conversion system (WECS) that eliminates multistage operation and DC-link filter elements, thus resolving size, weight, and reliability issues. A simple switching strategy is used to control the switches that changes the variable-frequency AC output of an electrical generator to a constant-frequency supply to feed into a distributed electrical load/grid. In addition, a modified random sinusoidal pulse width modulation (RSPWM) technique has been developed for the designed converter to make the overall system more efficient by increasing generating power capacity and reducing the effects of inter-harmonics and sub-harmonics generated in the WECS. The technique uses carrier and reference waves of variable switching frequency to calculate the firing angles of the switches of the converter so that the three-phase output voltage of the converter is very close to a sine wave with reduced THD. A comparison of the performance of the proposed RSPWM technique with the conventional SPWM demonstrated that the power generated by a turbine in the proposed approximately increased by 5% to 10% and THD reduces by 40% both in voltage and current with respect to conventional SPWM.