Gianpaolo Lisi

Distributed Maximum Power Point Tracking of Photovoltaic Arrays: Novel Approach and System Analysis

One of the major drawbacks of photovoltaic (PV) systems is represented by the effect of module mismatching and of partial shading of the PV field. Distributed maximum power point tracking (DMPPT) is a very promising technique that allows the increase of efficiency and reliability of such systems. Modeling and designing a PV system with DMPPT is remarkably more complex than implementing a standard MPPT technique. In this paper, a DMPPT system for PV arrays is proposed and analyzed. A dc and small-signal ac model is derived to analyze steady-state behavior, as well as dynamics and stability, of the whole system. Finally, simulation results are reported and discussed.

High-efficiency inverter with H6-type configuration for photovoltaic non-isolated ac module applications

A novel, high-efficiency inverter using MOSFETs for all active switches is presented for photovoltaic, non-isolated, ac module applications. The proposed H6-type configuration features high efficiency over a wide load range, low ground leakage current, no need for split capacitors, and low output ac-current distortion. The detailed power stage operating principles, PWM scheme, and novel bootstrap power supply for the proposed inverter are described. Experimental results of a 300 W hardware prototype show that not only are MOSFET body diode reverse-recovery and ground leakage current issues alleviated in the proposed inverter, but also that 98.3% maximum efficiency and 98.1% European Union efficiency are achieved.

High efficiency converter with charge pump and coupled inductor for wide input photovoltaic AC module applications

Existing photovoltaic (PV) panels have widely varying input voltages based on the panel configuration and size. In this paper, a novel topology with a single active switch — combining boost, flyback, and charge-pump circuits — is proposed in order to achieve wide input range, high voltage gain, high efficiency, and low cost simultaneously. It meets the input-voltage and power-level needs of the majority of modern PV panels while still being suitable for connection with a highvoltage dc bus. The circuit has been designed, simulated, and implemented with the 20 to 70 V input, 200±20 V output, and 220 W output power as a part of a PV ac module. Experimental results verify the validity of the novel circuit and show 97.4% peak efficiency and greater than 96.3% for 50 to 220 W.

High-Efficiency Contactless Power Transfer System for Electric Vehicle Battery Charging Application

In this paper, a contactless charging system for an electric vehicle (EV) battery is proposed. The system consists of three parts: 1) a high-frequency power supply from a full-bridge inverter with frequency modulation; 2) a loosely coupled transformer that utilizes series resonant capacitors for both the primary and secondary windings; and 3) a rectification output circuit that uses a full-bridge diode rectifier. With carefully selected compensation network parameters, zero-voltage switching can be ensured for all the primary switches within the full range of an EV battery charging procedure, which allows the use of low ON-state resistance power MOSFETs to achieve high-frequency operation and system efficiency. The design of loosely coupled transformer is simulated and verified by finite element analysis software. For a 4-kW hardware prototype, the peak dc-dc efficiency reaches 98% and 96.6% under 4- and 8-cm air gap conditions, respectively. The prototype was tested with an electronic load and a home-modified EV to verify the performance of constant current and constant voltage control and their transitions.

Modeling and Control of Series–Series Compensated Inductive Power Transfer System

In this paper, a T-equivalent circuit for loosely coupled transformer, which does not involve magnetic coupling, is presented. A detailed dynamic analysis based on extended describing function technique is presented for a series-series compensated inductive power transfer system. The continuous-time large-signal model, the steady-state operating point, and the small-signal model are derived in an analytical closed-form. This model includes both the frequency and the phase-shift control. Simulation and experimental verification results of the derived models are presented to validate the presented analysis.

High efficiency DC-DC converter with twin-bus for dimmable LED lighting

A novel twin-bus converter using n + 1 active switches is proposed for the n-string LEDs to be dimmable from true zero to the rated current level. With the proposed twin-bus structure, the n-switches that perform the current-loop regulation can operate at very high frequency because of significantly reduced voltage stresses, while achieving high efficiency over a wide load range. With operating frequency exceeding 1 MHz in the test case, the proposed LED driver demonstrates ultra compact size inductor and fast slew rates of the LED current. The dimming controlled switch, however, can operate at a low frequency to ensure high-efficiency operation without light flicker. The detailed power stage operating principle and control scheme of the individual string current for the presented converter are described. Experimental results of a 3-string 50-W LED driver hardware prototype show that the independent string current can be regulated from zero to the desired 350 mA for dimming control. A peak efficiency of 98.3% was achieved with 1.08 MHz switching frequency.

Analysis and parameters optimization of a contactless IPT system for EV charger

This paper discusses the characteristics of a series-series compensated inductive power transfer system (IPT) with theoretical analysis and experimental results. To maximize system efficiency, two-stage structure, which includes a PFC stage and a resonant DC-DC stage operating in ZVS region, is proposed. One of the major design challenges in implementation of a practical contactless EV charger is the variation of the coupling condition of the loosely coupled transformer. This combined with the battery chargers wide range load variation makes parameters design of the resonant DC-DC stage more complex. To optimize the parameter design for all coupling and load conditions, a parameter sweeping method is proposed. The design procedure searches parameters set to minimize the averaged primary current while keeping the voltage stress across the primary capacitor below the preset limit; both the high coupling and low coupling conditions are considered. To validate the analysis, a 4 kW resonant DC-DC prototype was built and tested. At 4 cm gap distance with 0.526 coupling coefficient, an efficiency of 97% for the DC-DC stage was achieved with output power range from 0.8 kW to 4 kW.

Hybrid serial-output converter for integrated LED lighting applications

This paper introduces a high power density step-up converter for LED applications, based on a hybrid serial-output (HSO) architecture [1], which is suitable for on-chip implementation. In this system, the output voltage is formed by stacking the output of a switched-capacitor (SC) converter on top of a boost converter output. The high power density SC converter processes around a half of the power of the system and is left unregulated. The boost converter processes the remainder of the power and regulates the output voltage. In comparison with conventional boost-based solutions, the introduced boost-SC HSO drastically reduces the passive component volume and decreases peak voltage stress of switches. Experimental results obtained with a 3.7 V to 13 V, 2.6 W, 1080 kHz prototype show that the introduced SC-boost HSO converter has about three times smaller reactive component area than a conventional boost having the same power processing efficiency.

Power vs efficiency analysis in high-frequency wireless power transfer systems — Part II: Applications

This paper presents examples of application of the model for High-Frequency Wireless Power Transfer Systems (WPTSs) introduced and discussed in the companion paper Part I. The impact of MOSFETs losses and mismatches of resonant elements and coupling factor is discussed in this paper. Results of the analysis realized on a 2W@6.78MHz WPTS are presented and valldated by means of experimental measurements.

Watt-level wireless power transfer based on stacked flex circuit technology

This paper presents the design, simulation, fabrication, and experimental characterization of a multi-layer spiral inductor that acts as the receiver coil for watt-level wireless power transfer. The inductor was designed with multiple vertical laminations where 88-μm-thick copper coils were separated by 25-μm-thick Kapton films using a flexible PCB fabrication technique. This Cu-Kapton approach has the potential for lower-cost coil fabrication than relatively expensive Litz-wire winding techniques. Varying turn widths were implemented to account for proximity effects and maximize the coil current distribution uniformity inside the coil windings at a given frequency, as validated by two-dimensional electromagnetic simulations. The multi-layer design incorporating lamination of four layers together with width variation exhibited a Q-factor improvement of 150% in comparison to the single-layer inductor. It was measured to have an inductance of 17 μH and a Q-factor of 50 at 300 kHz with an outer diameter of 5 cm. With a Litz-wire inductor as the transmitter coil for wireless power transfer, a load power of 7 Watts was transferred at 300 kHz over a distance of 5 cm and 5 Watts over 10 cm, two times the coil diameter, achieving an overall efficiency (defined as the ratio of the received load power to the total input power to the driving circuitry) of 46% and 23% respectively. In comparison, a manually-wound Litz-wire receiver coil with same characteristics under similar conditions demonstrated an overall efficiency of 58% and 39% at one and two-diameter distances, respectively.