Dharmraj V. Ghodke

Modified One-Cycle Controlled Bidirectional High-Power-Factor AC-to-DC Converter

AC-to-DC converters based on one-cycle control exhibit instability in current control at light load conditions as well as when they are operating in the inverting mode. In this paper, a modified one-cycle controller for bidirectional AC-to-DC converter is proposed. A fictitious current component in phase with the utility voltage is synthesized. The sum of this current component and the actual load current is compared with the sawtooth waveform to generate the gating pulses for the switches. This modification not only renders stability to the converter at light load conditions and the inverting mode of operations but also enables the converter to seamlessly transfer its operation from the rectifying mode to the inverting mode and vice versa. Detailed simulation studies are carried out to verify the effectiveness of the proposed scheme. To validate the viability of the scheme, detailed experimental studies are carried out on a 2-kW laboratory prototype.

Three-Phase Three Level, Soft Switched, Phase Shifted PWM DC–DC Converter for High Power Applications

A new three-phase, three-level dc to dc phase shifted pulsewidth modulation (PWM) converter is proposed for high power and high input voltage applications. Output voltage is controlled by incorporating phase shift PWM. Clocked gate signals of each leg are phase shifted by 2pi/3 from each other. Major features of the converter include: (1) outer two switches of each leg are turned on and off as zero voltage switching, (2) inner two switches of each leg are turned on and off as zero current switching, and (3) this is achieved without involving any extra passive or active components. The secondary side of the converter is of center tapped full-wave current tripler type. This results in an increase of ripple frequency by a factor of six, leading to a significant reduction in size of the output filter. In order to obtain behavioral and performance characteristics of the proposed converter topology, detailed analytical and simulation studies are carried out. Finally the viability of the scheme is confirmed through detailed experimental studies on a laboratory prototype developed for the purpose.

One-Cycle-Controlled Bidirectional AC-to-DC Converter With Constant Power Factor

Grid-connected unity-power-factor converters based on one-cycle control (OCC) do not require the service of phase-locked loop or any other synchronization circuits for interfacing with the utility. As a result, these schemes are becoming increasingly popular. However, as the power handled by the converter increases, the power factor deteriorates. To understand quantitatively the cause of poor power factor while negotiating high power loads, large signal models for these schemes are developed. Having understood the cause for poor power factor operation, a modified-OCC-based converter is proposed. This scheme has high power factor while supplying high power loads. Detailed simulation studies are carried out to verify the efficacy of the scheme. In order to confirm the viability of the scheme, detailed experimental studies are carried out on a 3-kW laboratory prototype.

Modified Soft-Switched Three-Phase Three-Level DC–DC Converter for High-Power Applications Having Extended Duty Cycle Range

A three-phase three-level dc-to-dc phase-shifted pulsewidth-modulation (PSPWM) converter which is reported in the literature for high-power and high-input-voltage applications is based on a three-phase three-wire configuration. However, the controllable duty cycle range of the aforementioned converter is 0-2π/3. Therefore, to obtain the rated voltage, the converter needs to be overrated by 33%. In order to overcome this problem, a modified topology of the three-level dc-to-dc PSPWM converter based on a three-phase four-wire configuration is proposed. The soft switching of devices is achieved by using a tapped filter inductor. The output voltage is controlled by incorporating PSPWM. The clocked gate signals of each leg are phase shifted by 2π/3 from each other. Major features of the converter include the following: 1) The outer two switches of each leg are operating as zero-voltage switch; 2) the inner two switches of each leg are operating as zero-current switch; and 3) this is achieved without involving any extra passive or active components. Realization of the secondary output filter by having a tapped inductor leads to considerable reduction in circulating current flow during a freewheeling period and results in appreciable mitigation in conduction losses. In order to obtain the behavioral and performance characteristics of the converter topology, analytical and simulation studies are carried out, and the viability of the scheme is ascertained through detailed experimental studies.

ZVZCS, dual, two-transistor forward DC-DC converter with peak voltage of Vin/2, high input and high power application

This paper presents a zero voltage and zero current switching (ZVZCS), dual, two-transistor forward converter (DTTFC) for high input voltage and high power application. Two identical two-transistor forward converters (TTFC) are connected in series and coupled through a single transformer using two primary windings, because of which it operates like a full bridge and makes it suitable for high power application. It imposes only half the input voltage across each of the four switches. This DTTFC has advantage of high reliability as compared to the full or half bridge converters. A modified pulse width modulation (PWM) controller is proposed for DTTFC to minimize the circulating RMS current flowing through the transformer and switching devices. This is without any extra hardware in series with primary of the transformer or in secondary. Conduction losses, being proportional to the square of the conducting current in a transformer and MOSFET, are important in high power converters operating at high currents. Since switching losses are also important in high frequency switching application, in DTTFC two switches, out of four switches, are turned-on and off at zero voltage condition due to the current in leakage inductance of a transformer. The remaining two switches are turned-off at zero voltage and turned-on at zero current condition due to transformer leakage inductance and minimized circulating current, over a wide range of load current. The advantages of this simple circuit topology is high efficiency, high reliability, low component count, and low cost, makes the new converter attractive for high input voltage, high power applications. In this paper we discuss the operating states, switching transitions, method of control, experimental results and associated waveforms of a MOSFET based practical 60 V, 50 A, 100 kHz, dual, two-transistor forward DC-DC converter operating at 750 V input bus. The measured efficiency was 95.07% at full load with maximum efficiency of 96.6% at 70% load.

One cycle controlled bi-directional Ac to Dc converter with constant power factor

Grid connected unity power factor converters based on one cycle control (OCC) do not require the service of PLL or any other synchronization circuits for interfacing with the utility. As a result, these schemes are becoming increasingly popular. However, as the power handled by the converter increases, the power factor deteriorates. To understand quantitatively the cause of poor power factor while negotiating high power loads, large signal models for these schemes are developed. Having understood the cause for poor power factor operation, a constant power factor OCC based converter is proposed. This scheme has high power factor, while supplying high power loads. Detailed simulation studies are carried out to verify the efficacy of the scheme. In order to confirm the viability of the scheme, detailed experimental studies are carried out on a 3 kW laboratory prototype.

PLL-less one cycle controlled bi-directional high power factor ac to dc converter

Ac to dc converters based on one cycle control (OCC) exhibits instability in current control at light load conditions as well as when it is operating in the inverting mode. In this paper a modified OCC for a bi-directional ac to dc converter is proposed. The proposed technique neither requires the knowledge of the 60° angular sectors of input voltage nor it requires the service of additional multiplexers or any other complicated circuitry. A fictitious current component in phase with the utility voltage is synthesized. The sum of this current component and the actual load current is compared with the triangular waveform to generate the gating pulses for the switches. This modification not only renders stability to the converter at light load conditions and inverting mode of operations, but also enable the converter to transfer its operation seamlessly from rectifying mode to inverting mode and vice versa. Detailed simulation studies are carried out to verify the effectiveness of the proposed scheme. In order to validate the viability of the scheme, detailed experimental studies are carried out on a scaled down 2 kW laboratory prototype developed for the purpose.

Three-Phase/Level, Zero Voltage and Zero Current, Phase Shift PWM DC-DC Converter for High Power Application

A new three-phase, three-level (TPTL) DC-DC phase shift PWM converter is proposed for high power and high input voltage applications. Output voltage is controlled by incorporating phase shift PWM. Clocked gate signals of each leg are phase shifted by 2pi/3 from each other. Major features of the converter include: 1) in each leg the outer two switches are turned on and off as ZVS. 2) inner two switches of each leg are turned on and off as ZCS 3) This is achieved without involving any extra passive or active components. The secondary of rectifier is of center tapped full-wave current tripler type. This results in an increase of ripple frequency by a factor of six, leading to a significant reduction in size of the output filter. In order to obtain behavioral and performance characteristics of converter topology detailed simulation studies are carried out, finally the viability of the scheme is confirmed through detailed experimental studies on a laboratory prototype developed for the purpose

Development of cold cathode arc discharge filament based multi-cusp H− ion source

A cold cathode arc discharge filament based multicusp H- ion source (HNIS) has been developed using an innovative low power igniter system working in a glow discharge regime to achieve a longer lifetime of the filament. This HNIS is cesium-free and its experimental prototype generates a maximum H- ion beam (HNIB) current of 12 mA at 50 keV beam energy in pulse mode with a peak arc power of 27 kW using the triode extraction system. This article presents the results of initial commissioning of the HNIS and steering magnetic field used to separate out the co-extracted electrons from HNIB, verified through experiments and 3-D ion beam simulations.

Simulation & design of maximum current point tracking controller for 2 MHz RF H − source

This paper presents a Maximum Current Point Tracking (MCPT) Controller for SIC MOSFET based high power solid state 2 MHz RF inverter for RF driven H- ion source. This RF Inverter is based on a class-D, half-bridge with series resonance LC topology, operating slightly above the resonance frequency (near to 2 MHz). Since plasma systems have a dynamic behavior which affects the RF antenna impedance, hence the RF antenna voltage and current changes, according to change in plasma parameters. In order to continuously yield maximum current through an antenna, it has to operate at its maximum current point, despite the inevitable changes in the antenna impedance due to changes in plasma properties. An MCPT controller simulated using LT-spice, wherein the antenna current sensed, tracked to maximum point current in a close loop by varying frequency of the voltage controlled oscillator. Thus, impedance matching network redundancy is established for maximum RF power coupling to the antenna.