Juan Antonio Sabate

Design considerations for high-voltage high-power full-bridge zero-voltage-switched PWM converter

A steady-state analysis is presented with complete characterization of the converter operation. A small-signal model of the converter is established. The design procedures based on the analysis are presented and the various losses in the circuit assessed. Critical design considerations for a high-power, high-voltage application are analyzed. The results of the analysis are verified using a high-voltage. 2 kW prototype.<<ETX>>

Zero-voltage and zero-current-switching full bridge PWM converter for high power applications

A novel zero-voltage and zero-current-switching (ZVZCS) full bridge (FB) PWM converter is proposed. The new converter overcomes the limitations of the ZVS-FB-PWM converter such as high circulating energy, severe parasitic ringing on the rectifier diodes, and limited ZVS load range for lagging leg switches. By utilizing the DC blocking capacitor and adding a saturable inductor, the primary current during the freewheeling period is reduced to zero, allowing the lagging leg switches to be operated with ZCS. Meanwhile, the leading leg switches are still operated with ZVS. The new converter is attractive for high voltage, high power applications where IGBTs are predominantly used as the power switches. The principle of operation, and DC characteristics of the new converter are analyzed and verified on a 2 kW, 83 KHz experimental circuit.<<ETX>>

High-voltage, high-power, ZVS, full-bridge PWM converter employing an active snubber

The authors present the analysis, design, and applications of a high-voltage, high-power, zero-voltage switched (ZVS), full-bridge (FB) pulse-width-modulated (PWM) converter with an active snubber in the secondary circuit. The nondissipative snubber completely eliminates the voltage overshoot and ringing across the rectifiers. The ringing of the parasitic capacitance of the rectifiers and the leakage inductance of the transformer are eliminated in a nondissipative manner, thus increasing the overall efficiency of the circuit. The active snubber employs only a high-voltage low-power MOSFET and a high-voltage capacitor. The control of the snubber switch is simple and utilizes the PWM signal to control the primary switches with a time delay. The authors also present the complete steady-state analysis of the ZVS-FB-PWM converter employing the active snubber. The analysis shows that the transformer secondary voltage is a function of the steady-state duty cycle and gives the equation to calculate the steady-state secondary voltage. The results of the analysis are in good agreement with the experimental results.<<ETX>>

Small-signal analysis of the phase-shifted PWM converter

The specific circuit effects in the phase-shifted PWM (PS-PWM) converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control and the utilization of transformer leakage inductance and power FET junction capacitances to achieve zero-voltage resonant switching. The differences in the dynamic characteristics of the PS-PWM converter and its PWM counterpart are explained. Model predictions are confirmed by experimental measurements. >

Novel full bridge zero-voltage-transition PWM DC/DC converter for high power applications

A novel full-bridge (FB) zero-voltage-transition (ZVT) PWM DC/DC converter for high power applications is proposed. An auxiliary network which consists of two small switches and one small inductor provides zero-voltage-switching (ZVS) for entire line and load ranges without increasing device voltage and current stresses. Since the ZVS range is independent of the switch capacitance, IGBTs can be used instead of MOSFETs by adding external capacitors to the switches without increasing switching losses, which allows the proposed converter to handle higher power. Operation, analysis, and features are described and verified experimentally. A 1.8 kW ZVT PWM converter prototype is compared with a ZVS PWM converter prototype of the same power rating.<<ETX>>

A comparative study of central and distributed MPPT architectures for megawatt utility and large scale commercial photovoltaic plants

In this paper different distributed PV architectures are studied from an energy yield perspective. These distributed architectures are applied to massively paralleled thin film plants employing high voltage PV modules, mc-Si plants with long series strings of low voltage modules and plants with medium voltage thin film modules in order to evaluate the effectiveness of the distributed architecture in each case. The effects of partial shading, module mismatch and cable losses are quantified in order to obtain the energy yield for each of the architectures under study. The results of this trade-off study are used to quantify the benefits of a distributed architecture as well as determine the optimal location of the dc/dc converters that perform the MPPT function.

Ripple current cancellation circuit

A ripple current cancellation technique injects AC current into the output voltage bus of a converter that is equal and opposite to the normal converter ripple current. The output current ripple is ideally zero, leading to ultra-low noise converter output voltages. The circuit requires few additional components, no active circuits are required. Only an additional filter inductor winding, an auxiliary inductor, and small capacitor are required. The circuit utilizes leakage inductance of the modified filter inductor as all or part of the required auxiliary inductance. Ripple cancellation is independent of switching frequency, duty cycle, and other converter parameters. The circuit eliminates ripple current in both continuous conduction mode and discontinuous conduction mode. Experimental results provide better than an 80/spl times/ ripple current reduction.

An Efficient Partial Power Processing DC/DC Converter for Distributed PV Architectures

In this paper, a dc/dc power converter for distributed photovoltaic (PV) plant architectures is presented. The proposed converter has the advantages of simplicity, high efficiency, and low cost. High efficiency is achieved by having a portion of the input PV power directly fed forward to the output without being processed by the converter. The operation of this converter allows for a simplified maximum power point tracker design using fewer measurements. The stability analysis of the distributed PV system comprised of the proposed dc/dc converters confirms the stable operation even with a large number of deployed converters. The experimental results show a composite weighted efficiency of 98.22% with very high maximum power point tracking efficiency.

Dc-dc converter topology assessment for large scale distributed photovoltaic plant architectures

Distributed photovoltaic (PV) plant architectures are emerging as a replacement for the classical central inverter based systems. However, power converters of smaller ratings may have a negative impact on system efficiency, reliability and cost. Therefore, it is necessary to design converters with very high efficiency and simpler topologies in order not to offset the benefits gained by using distributed PV systems. In this paper an evaluation of the selection criteria for dc-dc converters for distributed PV systems is performed; this evaluation includes efficiency, simplicity of design, reliability and cost. Based on this evaluation, recommendations can be made as to which class of converters is best fit for this application.

Constant-frequency, zero-voltage-switched, clamped-mode parallel-resonant converter

The DC behavior of a constant-frequency, clamped-mode parallel-resonant converter operating above resonant frequency is characterized. The converter is shown to be able to operate with zero-voltage turn-on for all the switches from no load to full load over a wide input range. Various circuit operating modes are identified and their corresponding operating regions defined. DC characteristics for the converter design are derived. A 5 V, 50 W prototype converter operating at 104 kHz is breadboarded to show the feasibility of constant-frequency, zero-voltage-switching operation and to substantiate the analytical results. The converter is operated with zero-voltage switching from no load to full load over the entire input voltage range without any external antiparallel diodes and snubbers. The experimental results are in good agreement with the analytical predictions. An efficiency of 85% is achieved.<<ETX>>