Swarna Kotaiah

Analysis and design of an LCL-T resonant converter as a constant-current power supply

An LCL-T resonant converter (LCL-T RC) is shown to behave as a current source when operated at resonant frequency. A detailed analysis of the LCL-T RC for this property is presented. Closed-form expressions for converter gain, component stresses, and the condition for converter design optimized for minimum size of resonant network is derived. A design procedure is illustrated with a prototype 200-W 20-A current-source power supply and experimental results are presented. The LCL-T RC as a current source offers many advantages such as easy parallel operation and low circulating currents at light load. Additionally, with appropriate phase shift in paralleled modules, the peak-peak ripple in output current is reduced and the ripple frequency is increased, reducing filtering requirements. The leakage inductance of a transformer can be advantageously integrated into the resonant network. These merits make the topology applicable in various applications such as magnet power supply, capacitor charging power supply, laser diode drivers, etc.

A Full-Bridge DC–DC Converter WithZero-Voltage-Switching Overthe Entire Conversion Range

A new topology of full-bridge dc-dc converter is proposed featuring zero-voltage-switching (ZVS) of active switches over the entire conversion range. In contrast to conventional techniques, the stored energy in the auxiliary inductor of the proposed converter is minimal under full-load condition and it progressively increases as the load current decreases. Therefore, the ZVS operation over the entire conversion range is achieved without significantly increasing full-load conduction loss making the converter particularly suitable in applications where the output is required to be adjustable over a wide range and load resistance is fixed (e.g., an electromagnet power supply). The principle of operation is described and the considerations in the design of converter are discussed. Performance of the proposed converter is verified with experimental results on a 500-W, 100-kHz prototype.

LCL-T Resonant Converter With Clamp Diodes: A Novel Constant-Current Power Supply With Inherent Constant-Voltage Limit

The LCL-T resonant converter behaves as a constant-current (CC) source when operated at the resonant frequency. The output voltage of a CC power supply increases linearly with the load resistance. Therefore, a constant-voltage (CV) limit must be incorporated in the converter for its use in practical applications wherein the open-load condition is commonly experienced by a CC power supply, such as in an arc welding power supply. A novel LCL-T resonant converter with clamp diodes is proposed in this paper, which has built-in CC-CV characteristics. Since the CC-CV characteristics are inherent to the converter, and complex feedback control is not required, the proposed converter is rugged and reliable. The principle of operation of the converter is explained. Experimental results on a 500-W prototype are presented to demonstrate the inherent CC-CV behavior of the converter. Simple extensions of the topology featuring variable CV limits are described

A passive auxiliary circuit achieves zero-voltage-switching in full-bridge converter over entire conversion range

A passive auxiliary circuit is proposed to achieve zero-voltage-switching (ZVS) over the entire conversion range in a full-bridge (FB) pulse-width modulated (PWM) converter (FBZVS converter) with minimum conduction loss penalty. The stored energy in the auxiliary circuit is minimal under the full-load condition. It increases progressively as the load current decreases. The proposed auxiliary circuit is passive, simple and can be viewed as an add-on to the conventional FBZVS converter. The principle of operation is described and the performance is demonstrated on a 100 kHz, 500 W prototype.

Common-mode noise source and its passive cancellation in full-bridge resonant converter

In this paper the results of systematic investigation into identification of dominant source of CM noise generation in a full bridge resonant converter are presented. It is shown that a small mismatch in an apparently symmetrical circuit can result in large CM injection. Mathematical analysis to predict the CM current injection is presented and is validated using SPICE simulation. For cancellation of dominant CM injection simple passive techniques are suggested. Experimental results on 18 kW LCC resonant magnet power supply for INDUS-2 are presented to demonstrate the effectiveness of proposed passive techniques.

Performance of a DSP based phase-shifted PWM controlled, zero-voltage-switching direct-current regulated magnet power supply

In this paper, a power supply being used for powering quadrupole magnets of a 2.5 GeV synchrotron machine is discussed. Main focus is on the implementation of a digital control of the power supply using a digital signal processor (DSP), TMS320F2812 from TI. The control system is designed to regulate the magnet current against the variations of line-voltage, load-impedance and other parameters. The power circuit consists of an AC-DC converter followed by a DC-DC converter based on zero-voltage-switched (ZVS) high frequency inverter driven by phase-shifted pulses. The paper describes the power circuit, digital implementation of various control-loops, computer simulation and design of control loops, and finally, the simulation results along with the results achieved from the actual system

Passive techniques for compliance of single-phase rectifiers with IEC 1000-3-2 norms

A single-phase rectifier is often a front-end power stage for many power electronic circuits. The single-phase rectifier with capacitor filter generates high harmonic currents in the ac line that is unacceptable by the IEC 1000-3-2 harmonic-current-limit specifications. Passive circuits can achieve requisite compliance at low cost, with simplicity and reliability. Various techniques of the passive input-current-shaping are reviewed in this paper. Their design for compliance is presented.

COMPONENT TOLERANCE ANALYSIS OF A PARALLEL RESONANT MAGNET EXCITATION SCHEME FOR RAPID CYCLING SYNCHROTRON USING PSpice

The parallel resonant scheme used to excite the magnets is characterized with high quality factor. The characteristic steep slope of the network gain near the resonant frequency makes the performance susceptible to the changes in component values. To accommodate the effect of varying component values, appropriate amplitude and phase over-drive capabilities in the ac source are required to maintain the magnet current of desired amplitude and in desired phase. A method of analysis of component tolerances using general purpose circuit simulation software, PSpice, is proposed in this letter. Using proposed normalized circuit description of the parallel resonant scheme, worst-case combination of component tolerances is determined. The evaluation of the effect of component tolerances in terms of required magnitude and phase over-drive of the ac source is presented under illustrative circuit conditions. Effect of various parameters on the over-drive is examined.