Kishore Chatterjee

An instantaneous reactive volt-ampere compensator and harmonic suppressor system

A novel control method for a reactive volt-ampere compensator and harmonic suppressor system is proposed. It operates without sensing the reactive volt-ampere demand and nonlinearities present in the load. The compensation process is instantaneous, which is achieved without employing any complicated and involved control logic. The compensator is operated in cycle-by-cycle reference-current-controlled mode to achieve the instantaneous compensating feature. A mathematical model of the scheme is developed. Detailed analysis and simulation results are presented. A laboratory prototype of the compensator is developed to validate the results.

One-Cycle-Controlled Single-Stage Single-Phase Voltage-Sensorless Grid-Connected PV System

Reforms in the electricity sector along with various renewable-energy-promotion policies have increased the importance of small grid-connected photovoltaic (PV) systems utilizing single-stage single-phase inverters. Ruggedness, reliability, and cost effectiveness are the desirable characteristics of such inverters used in distributed low-power applications. Schemes based on one-cycle control (OCC) which do not require the service of a phase-locked loop for interfacing the inverter to the grid are increasingly being employed for such applications. However, the OCC-based schemes reported earlier require sensing of the grid voltage which somewhat offsets one of the inherent strengths of OCC-based systems. In an effort to overcome the aforementioned limitation, an OCC-based grid-connected single-stage PV system is proposed in this paper which does not require to sense the grid voltage. Further, it requires less number of sensors (two) as compared to that required (four) in the earlier reported scheme for the implementation of the core controller comprising of OCC and maximum-power-point-tracking blocks. The viability of the proposed scheme is confirmed by performing simulation and experimental validation.

A simple maximum power point tracker for grid connected variable speed wind energy conversion system with reduced switch count power converters

In this paper, a simple control strategy for an optimal extraction of output power from grid connected variable speed wind energy conversion system (VSWECS) with reduced switch count power converters is presented. In order to improve the overall efficiency and to reduce the cost, B-4 PWM converters are used. The system consists of a variable speed wind turbine coupled to a permanent magnet synchronous generator (PMSG) through a gear box, two PWM B4-power converters. Output power from PMSG is first converted into DC and then it is fed to the grid. Both the power conversions are performed at unity power factor and the DC link voltage is maintained constant. The MPPT extracts optimum power from the wind turbine from cut-in to rated wind velocity by sensing only the turbine output power. The complete system has been simulated for various wind velocities. The control algorithm is implemented on TMS320F243 DSP and the simulated results are validated by experimental results.

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.

PLL-Less Active Power Filter Based on One-Cycle Control for Compensating Unbalanced Loads in Three-Phase Four-Wire System

In this paper, a shunt active power filter (APF) based on unified constant frequency integration or one-cycle control (Smedley et al., 2001) for compensating unbalanced loads in a three-phase four-wire system is explored. The APF provides compensation currents in such a way that the utility supplies only the balanced fundamental current at unity power factor, even if the load draws reactive and harmonic currents. The scheme neither requires the service of a phase-locked loop nor requires to sense the utility voltages. This makes the scheme insensitive to the distortions that are generally present in the utility voltages. First, the one-cycle control technique is applied to a topology involving a four-leg converter for the proof of concept. Then it is utilized to control a conventional three-leg converter having a split-capacitor dc link. The effectiveness and the viability of the schemes are demonstrated through detailed simulation and experimental verification.

Two-Stage Solar Photovoltaic-Based Stand-Alone Scheme Having Battery as Energy Storage Element for Rural Deployment

Solar photovoltaic (PV)-based stand-alone systems have evolved as a promising solution to the issue of electrification in areas where the grid is not available. The major challenges in designing such systems are as follows: 1) extraction of maximum power from the PV array; 2) protection of the battery from overcharge and overdischarge; 3) dc to ac conversion; and 4) provision for adequate voltage boosting. As multiple objectives are required to be satisfied, the existing schemes for stand-alone systems require a minimum of three converter stages, leading to considerable reduction in the reliability and efficiency of the system. In order to address this issue, a two-stage stand-alone scheme consisting of a novel transformer-coupled dual-input converter (TCDIC) followed by a conventional full-bridge inverter is proposed in this paper. The proposed TCDIC can realize maximum power point tracking and battery charge control while maintaining the proper voltage level at the load terminal. The small signal mathematical model of the TCDIC is derived. A suitable control strategy for the proposed TCDIC is devised. The operation of the scheme is verified by performing detailed simulation studies. A laboratory prototype of the scheme is developed. Detailed experimental validation of the scheme utilizing the laboratory prototype is carried out to confirm the viability of the scheme.

Monitoring torque and traverse force in friction stir welding from input electrical signatures of driving motors

Abstract Experimental measurements of torque, traverse force and thermal cycles in friction stir welding (FSW) are challenging due to the simultaneous rotational and linear motions of the tool and the deformation of workpiece material around the tool pin. We propose here a methodology to measure the torque and the traverse force by monitoring the current and power transients of the electrical motors that drive the rotational and linear motions of the FSW tool respectively. The measured values of torque and traverse force in FSW of AA 7075-T6 and AA 2524-T351 at different combinations of tool rotational speed and tool shoulder diameter are validated with the corresponding computed results from a well tested numerical model. The proposed method alleviates the need to use expensive torque and force dynamometers, and provides an economical and robust route for indirect measurement of real time torque and traverse force in FSW.

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.