Victor Anunciada

Power factor correction in single phase AC-DC conversion: control circuits for performance optimization

AC-DC conversion with power factor correction may use several well known power circuits (boost, half-bridge and full-bridge), or some single stage converters, in the case of switch mode power supplies. All of them present the same control problem: an accurate control of the input current and the simultaneous control of the voltage across the energy storage capacitor. The control of the voltage at the storage capacitor presents a high response time or a reduced gain, in order to avoid a significant distortion of the input current, with a dominant harmonic at the double of line frequency. In the case of switch mode power supplies, the storage capacitor is designed to perform a required stand-on time and, consequently, is bulky and expensive. This paper presents a survey of the more recent pulse width modulators used in the PFC circuits, namely UCI modulators and the design objectives of those control circuits and their main limitations. It is also presented a new technique for capacitor voltage sampling that permit an important reduction of the response time of the voltage regulators. The stability conditions for PI regulators with sampled feedback are presented. Experimental results obtained with a full-bridge single stage converter are also presented.

EMI reduction by optimizing the output voltage rise time and fail time in high-frequency soft-switching converters

In order to ensure the compatibility between devices, several electromagnetic compatibility (EMC) standards specify the maximum permitted levels of radiated noise. To comply with these standards, hard switching power converters need to use expensive solutions, namely shielding, Filtering techniques and snubbers, because the voltages have low values of rise and fall times. This fact leads into significant harmonic content at high frequencies. In this case, the most cost effective way to deal with radiated noise is to reduce it at the source. A way to achieve this goal is to impose moderate values of output voltage rise and fall times. This paper theoretically and experimentally explains, that the harmonic content at high frequencies can be significantly reduced with a selection of a suitable value of voltage rise time and fall time. Based on the study of a generic trapezoidal waveform, simple but precise equations, that permit to easily evaluate the envelope of the frequency spectrum, are derived. These equations also permit to analyze the importance and the influence of the rise and fall times in the spectrum envelope. Finally, with this simple analysis, the influence of the values of rise time and fall time in more complex waveforms are shown, as the output voltage waveform of a high frequency cycloconverter. The validity of the theoretical analysis is confirmed by experimental results.

1 kW/250 kHz full bridge zero voltage switched phase shift DC-DC converter with improved efficiency

This paper presents the analysis, design, simulation and experimental results of a full bridge zero voltage switched phase shift DC-DC converter, working with an internal frequency of 250 kHz, with an output power of 1 kW. The converter uses a two windings inductor with the secondary connected to the output by means of two clamping rectifier diodes, to allow resonant commutation of the passive to active leg of the converter. With this process it is possible to improve the efficiency of the converter.

Supra resonant fixed frequency full bridge DC-DC resonant converter with reduced switching losses

This paper presents the theoretical analysis and simulation results of a new topology of a full bridge DC-DC resonant converter that works with fixed frequency above resonance, providing nearly zero switching losses. The converter is basically a full bridge series parallel resonant converter that is connected to the input voltage source via two capacitors and an additional switch. The new idea presented in this paper consists in the proper control of the additional switch that connects and disconnects the two input capacitors, forcing zero voltage supply during the commutations of the bridge switches. This way, zero switching turn-on and, turn-off losses are obtained for the bridge switches, and ZVS for the auxiliary switch. This process allows the efficiency of the converter to be strongly improved, while maintaining fixed frequency operation. The converter is intended to be used in telecommunications equipment and is designed for 600 W output power with an internal frequency of 250 kHz, with PWM control.

A new single phase power factor corrector converter

This paper presents the basic principles of operation, the analysis, simulation and experimental results of a new single-phase power factor corrector circuit for AC-DC power supplies. This converter consists basically in a three diodes and capacitor arrangement connected at the output terminals of the input rectifier. The charge of these capacitors is forced by operating an electronic switch that controls the power flow from the AC line through an inductor with a secondary winding, the same way as in a flyback converter topology. This process enables input current shaping and with adequate control, sinusoidal input current is obtained. In order to validate the theoretical and simulation results, a 50 W lab prototype has been developed.