Pengju Kong

Analysis of Unified Output MPPT Control in Subpanel PV Converter System

Photovoltaic (PV) systems frequently suffer disproportionate impacts on energy production due to mismatch cases. To remedy this, academia proposed a distributed max power point tracking (MPPT) solution and has been implemented commercially. Taking the trend of the “distributed MPPT” concept a step further, this paper discusses and analyzes an MPPT converter that connects to each PV cell string, called a subpanel MPPT converter (SPMC), to better address the real-world mismatch issues. The SPMC system with a unified output MPPT control structure is also proposed in order to reduce the cost and simplify the distributed MPPT system. The proposal saves A/D units, current sensors, and MPPT controllers on the premise of guaranteeing that the SPMC is working on its optimal maximum power point regardless of the mismatch case. This is favorable for the further integration and makes the whole SPMC system less expensive and easier to realize. Finally, the effectiveness of the proposal is confirmed experimentally.

Power architecture design with improved system efficiency, EMI and power density

The optimized design of power architecture is discussed in this paper. The paper first discusses the asymmetrical interleaved multi-channel PFC technique and its benefits to system power density and the reduction of differential mode noise. A balance technique is then proposed to minimize the common mode noise of asymmetrical interleaved multi-channel PFC. Greatly reduced EMI leads to the size reduction of EMI filters. System power density is therefore improved. For DC/DC stage, a 1 MHz, LLC resonant converter with novel synchronous rectifier is proposed to reduce body diode conduction time. Both conduction loss and reverse recovery loss can be reduced. The whole systems efficiency, EMI and power density can be greatly improved by applying the techniques proposed in this paper.

Analysis and suppression of conducted EMI emissions for front-end LLC resonant DC/DC converters

LLC resonant DC/DC converters are becoming popular in computing applications, such as telecom, server systems. For these applications, it is required to meet the EMI standard. In this paper, novel EMI noise transferring path and EMI model for LLC resonant DC/DC converters are proposed. DM and CM noise of LLC resonant converter are analyzed. Several EMI noise reduction approaches are proposed. Shield layers are applied to reduce CM noise. By properly choosing the ground point of shield layer, significant noise reduction can be obtained. With extra EMI balance capacitor, CM noise can be reduced further. Two channel interleaving LLC resonant converters are proposed to cancel the CM current. Conceptually, when two channels operate with 180 degree phase shift, CM current can be canceled. Therefore, the significant EMI noise reduction can be achieved.

High-Frequency High-Efficiency

This paper proposes a CLL resonant dc-dc converter as an option for offline applications. This topology can achieve zero-voltage switching from zero load to a full load and zero-current switching for output rectifiers and makes the implementation of a secondary rectifier easy. This paper also presents a novel methodology for designing CLL resonant converters based on efficiency and holdup time requirements. An optimal transformer structure is proposed, which uses a current-type synchronous rectifier (SR) drive scheme. An 800-kHz 250-W CLL resonant converter prototype is built to verify the proposed circuit, design method, transformer structure, and SR drive scheme.

CLL

This paper investigates the effects of transformer structure and parasitic on common mode (CM) EMI noise of isolated power converters. Study on typical transformer winding structures indicates that the distribution of inter-winding capacitances and the distribution of voltage potentials on windings are the two critical factors that determine the CM noise levels of the converter in switching frequency ranges. CM noise reduction methods by improving the transformer structure and by compensation are proposed. At high frequencies, leakage inductances of the transformer resonate with the inter-winding capacitances or the junction capacitances of the secondary side switches. It may result in severe high frequency CM noise peaks. Methods of controlling such peaks are also discussed.

Resonant Converters With Synchronous Rectifiers

This paper proposes novel electromagnetic interference (EMI) suppression techniques for dc-dc converters. For low-voltage high-current applications, windings are paralleled and interleaved. Although low conduction loss and low leakage inductance can be achieved, the winding capacitances are considerably increased, thereby deteriorating the converters EMI and soft-switching performances. To solve these problems, a novel balanced choke concept is proposed, as well as other techniques. The advantages of the proposed concepts and strategies are verified and demonstrated on a 1-kW 1-MHz 400-V/12-V LLC resonant converter prototype. More than 52-dB noise attenuation and 75% equivalent winding capacitance reduction are achieved. Hence, EMI and soft-switching performances are significantly improved.

Transformer structure and its effects on common mode EMI noise in isolated power converters

This paper addresses the common-mode (CM) electromagnetic interference noise issues in the two-switch forward converter. The two-switch forward converter has low CM noise compared to other topologies because its symmetric primary-side circuit has two out-of-phase dv/dts that cancel each other. However, parasitic capacitances of the circuit significantly affect the symmetry and degrade the noise reduction. Moreover, the secondary-side circuit of the converter is not symmetric and still contributes to the CM noise. In this paper, the parasitic capacitances of the converter are first modeled. Different transformer structures and their parasitic capacitances are characterized. A general balance technique is introduced to further reduce the CM noise of the converter. For each transformer structure, balance can be achieved with proper connection of the windings terminals and control of the parasitic capacitances to minimize the CM noise of the converter. Experimental results validated the proposed techniques.

Novel Techniques to Suppress the Common-Mode EMI Noise Caused by Transformer Parasitic Capacitances in DC–DC Converters

Bridgeless boost PFC converter has high efficiency by eliminating the input diode bridge. However, Common Mode (CM) conducted EMI becomes a great issue. The goal of this paper is to study the possibility to minimize the CM noise in this converter. First the noise model is studied. Then a balance concept is introduced and applied to cancel the CM noise. Two approaches to minimize CM noise are introduced and compared. Experiments verify the effectiveness of both approaches.

Reducing Common-Mode Noise in Two-Switch Forward Converter

Critical conduction mode (CRM) power factor correction (PFC) converters are widely used in industries. For CRM PFC converters, high inductor current ripples generate high differential mode (DM) electromagnetic interference (EMI) noise, which calls for big EMI filters. On the other hand, the switching frequency varies during a half line cycle. The characteristics of the EMI in CRM PFC converters have not been carefully investigated and the worst case DM EMI noise has not been identified. The design of an EMI filter is difficult. In this paper, a mathematical model based on the principle of quasi-peak noise detection is proposed to predict the EMI noise in CRM PFC converters. The developed model is verified by experimental results. Based on this model, the worst case DM EMI noise can be predicted. This will greatly help in the design of EMI filters for CRM PFC converters.

Common mode EMI noise suppression in bridgeless boost PFC converter

This paper addresses the common mode (CM) electromagnetic interference (EMI) noise issues in the twoswitch forward converter. Two-switch forward converter has low CM noise with its symmetric primary side structure. However, the asymmetric parasitic capacitances and secondary side noise source have adverse effects on the symmetry and degrade the CM noise reduction. In order to solve the issues, CM noise model of the converter and transformer is first derived. Symmetry conditions are then summarized as the guideline for achieving CM noise reduction. Methods are proposed to minimize the CM noise by controlling the transformer termination, parasitic capacitances and structure. Experimental results validated the proposed techniques.